%% @article{fds365642, Author = {Grass, D and Beasley, GM and Fischer, MC and Selim, MA and Zhou, Y and Warren, WS}, Title = {Contrast mechanisms in pump-probe microscopy of melanin.}, Journal = {Opt Express}, Volume = {30}, Number = {18}, Pages = {31852-31862}, Publisher = {Optica Publishing Group}, Year = {2022}, Month = {August}, url = {http://dx.doi.org/10.1364/OE.469506}, Abstract = {Pump-probe microscopy of melanin in tumors has been proposed to improve diagnosis of malignant melanoma, based on the hypothesis that aggressive cancers disaggregate melanin structure. However, measured signals of melanin are complex superpositions of multiple nonlinear processes, which makes interpretation challenging. Polarization control during measurement and data fitting are used to decompose signals of melanin into their underlying molecular mechanisms. We then identify the molecular mechanisms that are most susceptible to melanin disaggregation and derive false-coloring schemes to highlight these processes in biological tissue. We demonstrate that false-colored images of a small set of melanoma tumors correlate with clinical concern. More generally, our systematic approach of decomposing pump-probe signals can be applied to a multitude of different samples.}, Doi = {10.1364/OE.469506}, Key = {fds365642} } @article{fds358289, Author = {McKeown Wessler and GC and Wang, T and Sun, J-P and Liao, Y and Fischer, MC and Blum, V and Mitzi, DB}, Title = {Structural, Optical, and Electronic Properties of Two Quaternary Chalcogenide Semiconductors: Ag2SrSiS4 and Ag2SrGeS4.}, Journal = {Inorganic chemistry}, Volume = {60}, Number = {16}, Pages = {12206-12217}, Year = {2021}, Month = {August}, url = {http://dx.doi.org/10.1021/acs.inorgchem.1c01416}, Abstract = {Quaternary chalcogenide materials have long been a source of semiconductors for optoelectronic applications. Recent studies on I<sub>2</sub>-II-IV-X<sub>4</sub> (I = Ag, Cu, Li; II = Ba, Sr, Eu, Pb; IV = Si, Ge, Sn; X = S, Se) materials have shown particular versatility and promise among these compounds. These semiconductors take advantage of a diverse bonding scheme and chemical differences among cations to target a degree of antisite defect resistance. Within this set of compounds, the materials containing both Ag and Sr have not been experimentally studied and leave a gap in the full understanding of the family. Here, we have synthesized powders and single crystals of two Ag- and Sr-containing compounds, Ag<sub>2</sub>SrSiS<sub>4</sub> and Ag<sub>2</sub>SrGeS<sub>4</sub>, each found to form in the tetragonal <i>I</i>4̅2<i>m</i> structure of Ag<sub>2</sub>BaGeS<sub>4</sub>. During the synthesis targeting the title compounds, two additional materials, Ag<sub>2</sub>Sr<sub>3</sub>Si<sub>2</sub>S<sub>8</sub> and Ag<sub>2</sub>Sr<sub>3</sub>Ge<sub>2</sub>S<sub>8</sub>, have also been identified. These cubic compounds represent impurity phases during the synthesis of Ag<sub>2</sub>SrSiS<sub>4</sub> and Ag<sub>2</sub>SrGeS<sub>4</sub>. We show through hybrid density functional theory calculations that Ag<sub>2</sub>SrSiS<sub>4</sub> and Ag<sub>2</sub>SrGeS<sub>4</sub> have highly dispersive band-edge states and indirect band gaps, experimentally measured as 2.08(1) and 1.73(2) eV, respectively. Second-harmonic generation measurements on Ag<sub>2</sub>SrSiS<sub>4</sub> and Ag<sub>2</sub>SrGeS<sub>4</sub> powders show frequency-doubling capabilities in the near-infrared range.}, Doi = {10.1021/acs.inorgchem.1c01416}, Key = {fds358289} } @article{fds355544, Author = {Jiang, J and Grass, D and Zhou, Y and Warren, WS and Fischer, MC}, Title = {Beyond intensity modulation: new approaches to pump-probe microscopy.}, Journal = {Optics letters}, Volume = {46}, Number = {6}, Pages = {1474-1477}, Publisher = {The Optical Society}, Year = {2021}, Month = {March}, url = {http://dx.doi.org/10.1364/ol.417905}, Abstract = {Pump-probe microscopy is an emerging nonlinear imaging technique based on high repetition rate lasers and fast intensity modulation. Here, we present new methods for pump-probe microscopy that keep the beam intensity constant and instead modulate the inter-pulse time delay or the relative polarization. These techniques can improve image quality for samples that have poor heat dissipation or long-lived radiative states and can selectively address nonlinear interactions in the sample. We experimentally demonstrate this approach and point out the advantages over conventional intensity modulation.}, Doi = {10.1364/ol.417905}, Key = {fds355544} } @article{fds352217, Author = {Fischer, EP and Fischer, MC and Grass, D and Henrion, I and Warren, WS and Westman, E}, Title = {Low-cost measurement of face mask efficacy for filtering expelled droplets during speech.}, Journal = {Sci Adv}, Volume = {6}, Number = {36}, Pages = {eabd3083}, Publisher = {American Association for the Advancement of Science (AAAS)}, Year = {2020}, Month = {September}, url = {http://dx.doi.org/10.1126/sciadv.abd3083}, Abstract = {Mandates for mask use in public during the recent coronavirus disease 2019 (COVID-19) pandemic, worsened by global shortage of commercial supplies, have led to widespread use of homemade masks and mask alternatives. It is assumed that wearing such masks reduces the likelihood for an infected person to spread the disease, but many of these mask designs have not been tested in practice. We have demonstrated a simple optical measurement method to evaluate the efficacy of masks to reduce the transmission of respiratory droplets during regular speech. In proof-of-principle studies, we compared a variety of commonly available mask types and observed that some mask types approach the performance of standard surgical masks, while some mask alternatives, such as neck gaiters or bandanas, offer very little protection. Our measurement setup is inexpensive and can be built and operated by nonexperts, allowing for rapid evaluation of mask performance during speech, sneezing, or coughing.}, Doi = {10.1126/sciadv.abd3083}, Key = {fds352217} } @article{fds365993, Author = {Fischer, EP and Fischer, MC and Grass, D and Henrion, I and Warren, WS and Westman, E}, Title = {Low-cost measurement of facemask efficacy for filtering expelled droplets during speech}, Year = {2020}, Month = {June}, url = {http://dx.doi.org/10.1101/2020.06.19.20132969}, Abstract = {<jats:title>Abstract</jats:title><jats:p>Mandates for mask use in public during the recent COVID-19 pandemic, worsened by global shortage of commercial supplies, have led to widespread use of homemade masks and mask alternatives. It is assumed that wearing such masks reduces the likelihood for an infected person to spread the disease, but many of these mask designs have not been tested in practice. We have applied a simple optical measurement method to evaluate the efficacy of masks to reduce the transmission of respiratory droplets during regular speech. We compare a variety of commonly available mask types and observe that some mask types approach the performance of standard surgical masks, while some mask alternatives, such as neck fleece or bandanas, offer very little protection. Our measurement setup is inexpensive and can be built and operated by non-experts, allowing for rapid evaluation of mask performance during speech, sneezing, or coughing.</jats:p>}, Doi = {10.1101/2020.06.19.20132969}, Key = {fds365993} } @article{fds349071, Author = {Jiang, J and Warren, WS and Fischer, MC}, Title = {Crossed-beam pump-probe microscopy}, Journal = {Optics Express}, Volume = {28}, Number = {8}, Pages = {11259-11259}, Publisher = {Optica Publishing Group}, Year = {2020}, Month = {April}, url = {http://dx.doi.org/10.1364/oe.389004}, Abstract = {<jats:p>We present a new imaging method for pump-probe microscopy that explores non-collinear excitation. This method (crossed-beam pump-probe microscopy, or CBPM) can significantly improve the axial resolution when imaging through low-NA lenses, providing an alternative way for depth-resolved, large field-of-view imaging. We performed a proof-of-concept demonstration, characterized CBPM’s resolution using different imaging lenses, and measured an enhanced axial resolution for certain types of low-NA lenses.</jats:p>}, Doi = {10.1364/oe.389004}, Key = {fds349071} } @article{fds347623, Author = {Yu, J and Li, Z and Kolodziej, C and Kuyuldar, S and Warren, WS and Burda, C and Fischer, MC}, Title = {Visualizing the impact of chloride addition on the microscopic carrier dynamics of MAPbI3 thin films using femtosecond transient absorption microscopy}, Journal = {The Journal of Chemical Physics}, Volume = {151}, Number = {23}, Pages = {234710-234710}, Publisher = {AIP Publishing}, Year = {2019}, Month = {December}, url = {http://dx.doi.org/10.1063/1.5127875}, Abstract = {<jats:p>The spatial heterogeneity of carrier dynamics in mixed halide perovskite CH3NH3PbI3−xClx thin films with a range of different chloride additions is mapped using femtosecond transient absorption microscopy (TAM). The comparison of TAM images of fibrous and granular polycrystalline CH3NH3PbI3−xClx films indicates that the impact of chloride addition on the local heterogeneity of carrier dynamics is highly dependent on the film preparation method and the resulting morphology. In addition to signals of pristine CH3NH3PbI3, CH3NH3PbI3−xClx films with a fibrous structure show long-lived excited state absorption (ESA) signals in localized, microscopic regions. The ESA signal exhibits transient absorption with a rise time of about 5 ps after the excitation pulse, indicating that these distinct micrograins have preferential carrier trapping properties. The chemical composition of these micrograins does not differ detectably from their surroundings. In contrast, in CH3NH3PbI3−xClx films with a granular structure, Cl addition does not seem to affect the charge carrier dynamics. These results provide insight into the localized effects of halide mixing and on the resulting photophysical properties of mixed halide perovskite materials on the micrometer length scale.</jats:p>}, Doi = {10.1063/1.5127875}, Key = {fds347623} } @article{fds345861, Author = {Yu, J and Li, Z and Liao, Y and Kolodziej, C and Kuyuldar, S and Warren, WS and Burda, C and Fischer, MC}, Title = {Probing the Spatial Heterogeneity of Carrier Relaxation Dynamics in CH3NH3PbI3 Perovskite Thin Films with Femtosecond Time‐Resolved Nonlinear Optical Microscopy}, Journal = {Advanced Optical Materials}, Volume = {7}, Number = {22}, Pages = {1901185-1901185}, Publisher = {Wiley}, Year = {2019}, Month = {November}, url = {http://dx.doi.org/10.1002/adom.201901185}, Abstract = {<jats:title>Abstract</jats:title><jats:p>The spatial heterogeneity of carrier dynamics in polycrystalline metal halide perovskite (MHP) thin films has a strong influence on photovoltaic device performance; however, the underlying cause is not yet clearly understood. Here, the sub‐micrometer scale mapping of charge carrier dynamics in CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbI<jats:sub>3</jats:sub> thin films using time‐resolved nonlinear optical microscopy, specifically transient absorption microscopy (TAM) with sub‐picosecond (ps) and time‐resolved photoluminescence (PL) microscopy with nanosecond temporal resolution is reported. To study the influence of physical morphology on charge carrier dynamics, MHP thin films having granular‐ and fibrous structures are investigated. On both types of films, spatial regions with short‐lived transient gain signals (fast nonradiative relaxation within ≈1 ps) typically show slower charge recombination via radiative relaxation, which is attributed to the presence of additional energy states near the band edge. In addition, fibrous films show longer PL lifetimes. Interestingly, the functional contrast shown in TAM images exhibits fundamental differences from the structural contrast shown in scanning electron microscopy images, implying that the variation of trap density in the bulk contributes to the observed spatial heterogeneity in carrier dynamics.</jats:p>}, Doi = {10.1002/adom.201901185}, Key = {fds345861} } @article{fds344710, Author = {Yu, J and Warren, WS and Fischer, MC}, Title = {Visualization of vermilion degradation using pump-probe microscopy}, Journal = {Science Advances}, Volume = {5}, Number = {6}, Pages = {eaaw3136}, Publisher = {American Association for the Advancement of Science (AAAS)}, Year = {2019}, Month = {June}, url = {http://dx.doi.org/10.1126/sciadv.aaw3136}, Abstract = {<jats:p>Pump-probe microscopy identifies metacinnabar and metallic mercury as possible degradation product of vermilion (α-HgS).</jats:p>}, Doi = {10.1126/sciadv.aaw3136}, Key = {fds344710} } @article{fds343499, Author = {Yang, JKW and Mrongovius, M and Fischer, MC and Boltasseva, A}, Title = {Design, Manufacture, and Analysis of Photonic Materials for Historical and Modern Visual Art: feature issue introduction}, Journal = {Optical Materials Express}, Volume = {9}, Number = {5}, Pages = {2128-2128}, Publisher = {The Optical Society}, Year = {2019}, Month = {May}, url = {http://dx.doi.org/10.1364/ome.9.002128}, Abstract = {© 2019 Optical Society of America. History has seen many significant contributions by artists in science and vice versa, e.g. Leonardo Da Vinci's flying machines, and Isaac Newton's color theory. More recently, with the advent of nanofabrication techniques, lasers, and materials, photonics research has found exciting new applications in art. The 14 papers positioned at the boundary between art and science in this feature issue capture this breadth of topics. Creative art-scientists/science-artists create new art using the colorful properties of metallic nanostructures, birefringence of liquid crystals, interference in thin films, and coherence of lasers. A noteworthy new art form that is gaining interest uses metals as the "canvas", lasers and nanolithography as the "brush", and resonant nanostructures as the "paint". We hope the reader will enjoy the spectrum of topics here that illustrate the potential of cutting edge photonic research for art-related applications: from the generation of modern visual art to the preservation and tagging of precious historical art.}, Doi = {10.1364/ome.9.002128}, Key = {fds343499} } @article{fds342577, Author = {Ju, K-Y and Degan, S and Fischer, MC and Zhou, KC and Jia, X and Yu, J and Warren, WS}, Title = {Unraveling the molecular nature of melanin changes in metastatic cancer}, Journal = {Journal of Biomedical Optics}, Volume = {24}, Number = {05}, Pages = {1-1}, Publisher = {SPIE-Intl Soc Optical Eng}, Year = {2019}, Month = {April}, url = {http://dx.doi.org/10.1117/1.jbo.24.5.051414}, Abstract = {More people die from melanoma after a stage I diagnosis than after a stage IV diagnosis, because the tools available to clinicians do not readily identify which early-stage cancers will be aggressive. Near-infrared pump-probe microscopy detects fundamental differences in melanin structure between benign human moles and melanoma and also correlates with metastatic potential. However, the biological mechanisms of these changes have been difficult to quantify, as many different mechanisms can contribute to the pump-probe signal. We use model systems (sepia, squid, and synthetic eumelanin), cellular uptake studies, and a range of pump and probe wavelengths to demonstrate that the clinically observed effects come from alterations of the aggregated mode from "thick oligomer stacks" to "thin oligomer stacks" (due to changes in monomer composition) and (predominantly) deaggregation of the assembled melanin structure. This provides the opportunity to use pump-probe microscopy for the detection and study of melanin-associated diseases.}, Doi = {10.1117/1.jbo.24.5.051414}, Key = {fds342577} } @article{fds340751, Author = {Ju, K-Y and Fischer, MC and Warren, WS}, Title = {Understanding the Role of Aggregation in the Broad Absorption Bands of Eumelanin}, Journal = {ACS Nano}, Volume = {12}, Number = {12}, Pages = {12050-12061}, Publisher = {American Chemical Society (ACS)}, Year = {2018}, Month = {December}, url = {http://dx.doi.org/10.1021/acsnano.8b04905}, Abstract = {In this work, we investigate the relationship between the complex hierarchical assembly structure of eumelanin, its characteristic broad absorption band, and the highly unusual nonlinear dynamics revealed by pump-probe or transient absorption microscopy. Melanin-like nanoparticles (MelNPs), generated by spontaneous oxidation of dopamine, were created with uniform but adjustable size distributions, and kinetically controlled oxidation was probed with a wide range of characterization methods. This lets us explore the broad absorption bands of eumelanin models at different assembly levels, such as small subunit fractions (single monomeric and oligomeric units and small oligomer stacks), stacked oligomer fractions (protomolecules), and large-scale aggregates of protomolecules (parental particles). Both the absorption and pump-probe dynamics are very sensitive to these structural differences or to the size of intact particles (a surprising result for an organic polymer). We show that the geometric packing order of protomolecules in long-range aggregation is key secondary interactions to extend the absorption band of eumelanin to the low energy spectrum and produce drastic changes in the transient absorption spectrum.}, Doi = {10.1021/acsnano.8b04905}, Key = {fds340751} } @article{fds339932, Author = {Yu, J and Warren, WS and Fischer, MC}, Title = {Spectroscopic Differentiation and Microscopic Imaging of Red Organic Pigments Using Optical Pump–Probe Contrast}, Journal = {Analytical Chemistry}, Volume = {90}, Number = {21}, Pages = {12686-12691}, Publisher = {American Chemical Society (ACS)}, Year = {2018}, Month = {November}, url = {http://dx.doi.org/10.1021/acs.analchem.8b02949}, Abstract = {Analysis of red organic pigments in artworks (and in forensics applications) is challenging, because conventional nondestructive mapping techniques provide little contrast, and most chemical analyses with high specificity require sample removal. Here we demonstrate a new optical approach, pump-probe microscopy, for the analysis of red organic pigments. We investigate Carmine naccarat, Lac dye, purpurin, alizarin, madder lake, and eosin Y and show that their intrinsic photophysical properties produce distinctive pump-probe spectra. We utilize this contrast for high-resolution, three-dimensional imaging without the need for physical sample removal. Lastly, we highlight the potential of pump-probe microscopy as an analytical tool for forensics of other types of organic colorants by investigating a series of automotive paints.}, Doi = {10.1021/acs.analchem.8b02949}, Key = {fds339932} } @article{fds339394, Author = {Liu, X and Jia, X and Fischer, M and Huang, Z and Smith, DR}, Title = {Enhanced Two-Photon Photochromism in Metasurface Perfect Absorbers}, Journal = {Nano Letters}, Volume = {18}, Number = {10}, Pages = {6181-6187}, Publisher = {American Chemical Society (ACS)}, Year = {2018}, Month = {October}, url = {http://dx.doi.org/10.1021/acs.nanolett.8b02042}, Abstract = {Light switchable materials are essential to optoelectronic applications in photovoltaics, memories, sensors, and communications. Natural switchable materials suffer from weak absorption and slow response times, preventing their use in low-power, ultrafast applications. Integrating light switchable materials with metasurface perfect absorbers offers an innovative route to achieving desirable features for nanophotonic devices, such as directional emission, low-power and broadband operation, high radiative quantum efficiency, and large spontaneous emission rates. Here we show an enhanced two-photon photochromism based on a metasurface perfect absorber: film-coupled colloidal silver nanocubes. The photochromic molecules, spiropyrans, are sandwiched between the silver nanocubes and the gold substrate. With nearly 100% absorption and an accompanying large field enhancement in the molecular junction, the transformation of spiropyrans to merocyanines is observed under excitation with 792 nm laser light. Fluorescence lifetime measurements on the merocyanine form reveal that large Purcell enhancement in the film-coupled nanocubes leads to large enhancements of the spontaneous emission rate and a high quantum efficiency. An averaged incident power as low as 10 μW is enough to initiate the two-photon isomerization of spiropyran in the film-coupled nanocubes, and a power of 100nW is able to excite the merocyanines to emit fluorescence. The power consumption is orders of magnitude lower than bare spiropyran thin films on silicon and gold, which is highly desirable for the writing and reading processes relevant to optical data storage. By sweeping the plasmonic resonance of the film-coupled nanocubes, wavelength specificity is demonstrated, which opens up new possibilities for minimizing the cross talk between adjacent bits in nanophotonic devices.}, Doi = {10.1021/acs.nanolett.8b02042}, Key = {fds339394} } @article{fds332388, Author = {Stanton, IN and Ayres, JA and Stecher, JT and Fischer, MC and Scharpf, D and Scheuch, JD and Therien, MJ}, Title = {Power-Dependent Radiant Flux and Absolute Quantum Yields of Upconversion Nanocrystals under Continuous and Pulsed Excitation}, Journal = {The Journal of Physical Chemistry C}, Volume = {122}, Number = {1}, Pages = {252-259}, Publisher = {American Chemical Society (ACS)}, Year = {2018}, Month = {January}, url = {http://dx.doi.org/10.1021/acs.jpcc.7b11929}, Abstract = {Elucidating structure-function relationships that determine the photophysics of nanomaterials that upconvert high-power, near-infrared (NIR) excitation to shorter wavelength NIR, visible, and UV emission requires both compositional characterization and experimental designs that rigorously define laser excitation conditions and the manner in which emitted photons are collected. Presented herein are laser power-dependent, total-emitted radiant flux (watts), and absolute quantum yield measurements of homogeneous, solution-phase 28 nm [NaYF4; Yb (15%), Er (2%)] upconversion nanocrystals (UCNCs) determined using a multidetector integrating sphere spectroscopy system. These studies compare for the first time quantitative total radiant flux and absolute quantum yield measurements of UCNCs determined as a function of laser power density for both 970 nm continuous-wave (CW) and 976 nm pulsed Ti-sapphire (140 fs pulse width, 80 MHz) laser excitation. This study illustrates that at intensities in the range 35-225 W/cm2, the total radiant flux is higher under CW excitation by an average factor of 1.5, and for this range of laser powers the high peak intensities associated with femtosecond-pulsed excitation conditions do not drive further augmentation of the radiant flux magnitude. This study has important ramifications for the field as it establishes the total radiant flux as the most appropriate figure of merit relevant for quantifying the emissive output intensity of UCNCs. In contrast to an UCNC emission quantum yield measurement, the total radiant flux may be determined with a high degree of accuracy; this point is critical, as this parameter is more closely connected to UCNC performance metrics important for imaging, emission fingerprinting, tracking, and energy conversion applications.}, Doi = {10.1021/acs.jpcc.7b11929}, Key = {fds332388} } @article{fds328433, Author = {Wilson, JW and Robles, FE and Deb, S and Warren, WS and Fischer, MC}, Title = {Comparison of pump-probe and hyperspectral imaging in unstained histology sections of pigmented lesions}, Journal = {Biomedical Optics Express}, Volume = {8}, Number = {8}, Pages = {3882-3882}, Publisher = {The Optical Society}, Year = {2017}, Month = {August}, url = {http://dx.doi.org/10.1364/boe.8.003882}, Abstract = {Microscopic variations in melanin composition can be mapped through linear and nonlinear optical responses. Though instrumentation to measure linear attenuation is simple and inexpensive, the nonlinear response provides more degrees of freedom with which to spectroscopically resolve pigments. The objective of this study is to assess differences in imaging melanin contrast by comparing hyperspectral (linear) versus pump-probe (nonlinear) microscopy of unstained histology sections of pigmented lesions. The images and analysis we have presented here show that pump-probe uncovers a greater variation in pigment composition, compared with hyperspectral microscopy, and that the two methods yield complimentary biochemical information.}, Doi = {10.1364/boe.8.003882}, Key = {fds328433} } @article{fds325218, Author = {Robles, FE and Deb, S and Fischer, MC and Warren, WS and Selim, MA}, Title = {Label-Free Imaging of Female Genital Tract Melanocytic Lesions With Pump-Probe Microscopy: A Promising Diagnostic Tool.}, Journal = {J Low Genit Tract Dis}, Volume = {21}, Number = {2}, Pages = {137-144}, Year = {2017}, Month = {April}, url = {http://dx.doi.org/10.1097/LGT.0000000000000290}, Abstract = {OBJECTIVES: Melanomas of the female genital tract present a unique clinical challenge. Not only are these lesions in an anatomically sensitive area, but also they tend to be multifocal and have high recurrence rates. Furthermore, several benign melanocytic proliferations resemble early-stage melanoma clinically and/or histopathologically. Thus, there is a significant need for additional tools that can help correctly diagnose and stage these lesions. Here, we quantitatively and nondestructively analyze the chemical composition of melanin in excised pigmented lesions of the female genital tract using pump-probe microscopy, a high-resolution optical imaging technique that is sensitive to many biochemical properties of melanin. MATERIALS AND METHODS: Thirty-one thin (~5 μm) tissue sections previously excised from female genital tract melanocytic lesions were imaged with pump-probe microscopy and analyzed. RESULTS: We find significant quantitative differences in melanin type and structure between melanoma and nonmalignant melanocytic proliferations. Our analysis also suggests a link between the molecular signatures of melanins and lesion-specific genetic mutations. Finally, significant differences are found between metastatic and nonmetastatic melanomas. The limitations of this work include the fact that molecular information is restricted to melanin pigment and the sample size is relatively small. CONCLUSIONS: Pump-probe microscopy provides unique information regarding the biochemical composition of genital tract melanocytic lesions, which can be used to improve the diagnosis and staging of vulvar melanomas.}, Doi = {10.1097/LGT.0000000000000290}, Key = {fds325218} } @article{fds325217, Author = {Robles, FE and Zhou, KC and Fischer, MC and Warren, WS}, Title = {Stimulated Raman scattering spectroscopic optical coherence tomography}, Journal = {Optica}, Volume = {4}, Number = {2}, Pages = {243-243}, Publisher = {The Optical Society}, Year = {2017}, Month = {February}, url = {http://dx.doi.org/10.1364/optica.4.000243}, Abstract = {We integrate spectroscopic optical coherence tomography (SOCT) with stimulated Raman scattering (SRS) to enable simultaneously multiplexed spatial and spectral imaging with sensitivity to many endogenous biochemical species that play an important role in biology and medicine. The combined approach, termed SRS-SOCT, overcomes the limitations of each individual method. Ultimately, SRS-SOCT has the potential to achieve fast, volumetric, and highly sensitive label-free molecular imaging. We demonstrate the approach by imaging excised human adipose tissue and detecting the lipids' Raman signatures in the high-wavenumber region.}, Doi = {10.1364/optica.4.000243}, Key = {fds325217} } @article{fds323184, Author = {Villafana, TE and Delaney, JK and Warren, WS and Fischer, MC}, Title = {High-resolution, three-dimensional imaging of pigments and support in paper and textiles}, Journal = {Journal of Cultural Heritage}, Volume = {20}, Pages = {583-588}, Publisher = {Elsevier BV}, Year = {2016}, Month = {July}, url = {http://dx.doi.org/10.1016/j.culher.2016.02.003}, Abstract = {Historic works on paper, illuminated (painted) or unpainted manuscripts, and textiles are fragile and nearly impossible to sample. Non-invasive techniques such as visible microscopy, X-ray fluorescence, Raman, and reflectance spectroscopy are commonly used to determine the artist material present. Recently, nonlinear optical ultrafast pump-probe microscopy was shown to provide non-invasive, high-resolution mapping of pigments in historic paintings to investigate paint stratigraphy. In this paper, we combine our pump-probe contrast with nonlinear fluorescence and second-harmonic generation contrasts exhibited by fibrous supports composed of natural bio-materials (cellulose, collagen, or lignin). Hence, our multi-modal nonlinear microscope is able to simultaneously investigate pigments in conjunction with their support in three dimensions with micrometer-scale spatial resolution. Here we examine the utility of nonlinear pump-probe microscopy by studying a series of mock-up samples, including indigo-dyed cotton cloth, ultramarine blue painted on various types of paper, and papers painted with mixtures and layers of the two pigments. In each case we find that we can combine pump-probe pigment contrast with nonlinear optical fiber contrast to obtain spatial information that is otherwise unavailable to the conservator.}, Doi = {10.1016/j.culher.2016.02.003}, Key = {fds323184} } @article{fds326161, Author = {Robles, FE and Fischer, MC and Warren, WS}, Title = {Dispersion-based stimulated Raman scattering spectroscopy, holography, and optical coherence tomography (Conference Presentation)}, Journal = {Multiphoton Microscopy in the Biomedical Sciences XVI}, Volume = {9712}, Pages = {1 pages}, Publisher = {SPIE}, Editor = {Periasamy, A and So, PT and König, K}, Year = {2016}, Month = {April}, ISBN = {9781628419467}, url = {http://dx.doi.org/10.1117/12.2212875}, Doi = {10.1117/12.2212875}, Key = {fds326161} } @article{fds325815, Author = {Warren, WS and Robles, F and Fischer, M and Wilson, J and Deb, S and Ju, K and Degan, S}, Title = {Melanin-targeted nonlinear microscopy for label-free molecular diagnosis and staging}, Journal = {Optics InfoBase Conference Papers}, Volume = {Part F19-Translational 2016}, Publisher = {OSA}, Year = {2016}, Month = {April}, ISBN = {9781943580101}, url = {http://dx.doi.org/10.1364/TRANSLATIONAL.2016.TTh3B.3}, Abstract = {Nonlinear pump-probe microscopy differentiates cutaneous, vulvar and conjunctival melanomas from less dangerous lesions, and can be used to assess metastatic potential. Applications in vivo (knockout mouse models) and in human biopsy are presented.}, Doi = {10.1364/TRANSLATIONAL.2016.TTh3B.3}, Key = {fds325815} } @article{fds335295, Author = {Villafana, T and Brown, B and Delaney, J and Fischer, M and Warren, W and Stranick, S}, Title = {3D chemical imaging of historic artworks and cultural heritage materials}, Journal = {ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY}, Volume = {251}, Pages = {1 pages}, Publisher = {AMER CHEMICAL SOC}, Year = {2016}, Month = {March}, Key = {fds335295} } @article{fds323185, Author = {Fischer, MC and Wilson, JW and Robles, FE and Warren, WS}, Title = {Invited Review Article: Pump-probe microscopy}, Journal = {Review of Scientific Instruments}, Volume = {87}, Number = {3}, Pages = {031101-031101}, Publisher = {AIP Publishing}, Year = {2016}, Month = {March}, url = {http://dx.doi.org/10.1063/1.4943211}, Abstract = {<jats:p>Multiphoton microscopy has rapidly gained popularity in biomedical imaging and materials science because of its ability to provide three-dimensional images at high spatial and temporal resolution even in optically scattering environments. Currently the majority of commercial and home-built devices are based on two-photon fluorescence and harmonic generation contrast. These two contrast mechanisms are relatively easy to measure but can access only a limited range of endogenous targets. Recent developments in fast laser pulse generation, pulse shaping, and detection technology have made accessible a wide range of optical contrasts that utilize multiple pulses of different colors. Molecular excitation with multiple pulses offers a large number of adjustable parameters. For example, in two-pulse pump-probe microscopy, one can vary the wavelength of each excitation pulse, the detection wavelength, the timing between the excitation pulses, and the detection gating window after excitation. Such a large parameter space can provide much greater molecular specificity than existing single-color techniques and allow for structural and functional imaging without the need for exogenous dyes and labels, which might interfere with the system under study. In this review, we provide a tutorial overview, covering principles of pump-probe microscopy and experimental setup, challenges associated with signal detection and data processing, and an overview of applications.</jats:p>}, Doi = {10.1063/1.4943211}, Key = {fds323185} } @article{fds326160, Author = {Robles, FE and Fischer, MC and Warren, WS}, Title = {Dispersion-based stimulated Raman scattering spectroscopy, holography, and optical coherence tomography}, Journal = {Optics Express}, Volume = {24}, Number = {1}, Pages = {485-485}, Publisher = {The Optical Society}, Year = {2016}, Month = {January}, url = {http://dx.doi.org/10.1364/oe.24.000485}, Abstract = {Stimulated Raman scattering (SRS) enables fast, high resolution imaging of chemical constituents important to biological structures and functional processes, both in a label-free manner and using exogenous biomarkers. While this technology has shown remarkable potential, it is currently limited to point scanning and can only probe a few Raman bands at a time (most often, only one). In this work we take a fundamentally different approach to detecting the small nonlinear signals based on dispersion effects that accompany the loss/gain processes in SRS. In this proof of concept, we demonstrate that the dispersive measurements are more robust to noise compared to amplitude-based measurements, which then permit spectral or spatial multiplexing (potentially both, simultaneously). Finally, we illustrate how this method may enable different strategies for biochemical imaging using phase microscopy and optical coherence tomography.}, Doi = {10.1364/oe.24.000485}, Key = {fds326160} } @article{fds323186, Author = {Wilson, JW and Warren, WS and Fischer, MC}, Title = {Real-time digital signal processing in multiphoton and time-resolved microscopy}, Journal = {Progress in Biomedical Optics and Imaging - Proceedings of SPIE}, Volume = {9703}, Publisher = {SPIE}, Year = {2016}, Month = {January}, ISBN = {9781628419375}, url = {http://dx.doi.org/10.1117/12.2218102}, Abstract = {The use of multiphoton interactions in biological tissue for imaging contrast requires highly sensitive optical measurements. These often involve signal processing and filtering steps between the photodetector and the data acquisition device, such as photon counting and lock-in amplification. These steps can be implemented as real-time digital signal processing (DSP) elements on field-programmable gate array (FPGA) devices, an approach that affords much greater flexibility than commercial photon counting or lock-in devices. We will present progress toward developing two new FPGA-based DSP devices for multiphoton and time-resolved microscopy applications. The first is a high-speed multiharmonic lock-in amplifier for transient absorption microscopy, which is being developed for real-time analysis of the intensity-dependence of melanin, with applications in vivo and ex vivo (noninvasive histopathology of melanoma and pigmented lesions). The second device is a kHz lock-in amplifier running on a low cost ($50 - $200) development platform. It is our hope that these FPGA-based DSP devices will enable new, high-speed, low-cost applications in multiphoton and time-resolved microscopy.}, Doi = {10.1117/12.2218102}, Key = {fds323186} } @article{fds325989, Author = {Robles, FE and Deb, S and Wilson, JW and Gainey, CS and Selim, MA and Mosca, PJ and Tyler, DS and Fischer, MC and Warren, WS}, Title = {Pump-probe imaging of pigmented cutaneous melanoma primary lesions gives insight into metastatic potential.}, Journal = {Biomed Opt Express}, Volume = {6}, Number = {9}, Pages = {3631-3645}, Year = {2015}, Month = {September}, url = {http://dx.doi.org/10.1364/BOE.6.003631}, Abstract = {Metastatic melanoma is associated with a poor prognosis, but no method reliably predicts which melanomas of a given stage will ultimately metastasize and which will not. While sentinel lymph node biopsy (SLNB) has emerged as the most powerful predictor of metastatic disease, the majority of people dying from metastatic melanoma still have a negative SLNB. Here we analyze pump-probe microscopy images of thin biopsy slides of primary melanomas to assess their metastatic potential. Pump-probe microscopy reveals detailed chemical information of melanin with subcellular spatial resolution. Quantification of the molecular signatures without reference standards is achieved using a geometrical representation of principal component analysis. Melanin structure is analyzed in unison with the chemical information by applying principles of mathematical morphology. Results show that melanin in metastatic primary lesions has lower chemical diversity than non-metastatic primary lesions, and contains two distinct phenotypes that are indicative of aggressive disease. Further, the mathematical morphology analysis reveals melanin in metastatic primary lesions has a distinct "dusty" quality. Finally, a statistical analysis shows that the combination of the chemical information with spatial structures predicts metastatic potential with much better sensitivity than SLNB and high specificity, suggesting pump-probe microscopy can be an important tool to help predict the metastatic potential of melanomas.}, Doi = {10.1364/BOE.6.003631}, Key = {fds325989} } @article{fds232467, Author = {Wilson, JW and Park, JK and Warren, WS and Fischer, MC}, Title = {Flexible digital signal processing architecture for narrowband and spread-spectrum lock-in detection in multiphoton microscopy and time-resolved spectroscopy}, Journal = {Review of Scientific Instruments}, Volume = {86}, Number = {3}, Pages = {033707-033707}, Publisher = {AIP Publishing}, Year = {2015}, Month = {March}, ISSN = {0034-6748}, url = {http://dx.doi.org/10.1063/1.4916261}, Abstract = {<jats:p>The lock-in amplifier is a critical component in many different types of experiments, because of its ability to reduce spurious or environmental noise components by restricting detection to a single frequency and phase. One example application is pump-probe microscopy, a multiphoton technique that leverages excited-state dynamics for imaging contrast. With this application in mind, we present here the design and implementation of a high-speed lock-in amplifier on the field-programmable gate array (FPGA) coprocessor of a data acquisition board. The most important advantage is the inherent ability to filter signals based on more complex modulation patterns. As an example, we use the flexibility of the FPGA approach to enable a novel pump-probe detection scheme based on spread-spectrum communications techniques.</jats:p>}, Doi = {10.1063/1.4916261}, Key = {fds232467} } @article{fds323187, Author = {Villafana, TE and Brown, W and Warren, WS and Fischer, M}, Title = {Ultrafast pump-probe dynamics of iron oxide based earth pigments for applications to ancient pottery manufacture}, Journal = {Proceedings of SPIE - The International Society for Optical Engineering}, Volume = {9527}, Publisher = {SPIE}, Year = {2015}, Month = {January}, ISBN = {9781628416879}, url = {http://dx.doi.org/10.1117/12.2184758}, Abstract = {We demonstrate that ultrafast pump-probe microscopy provides unique dynamics for natural iron oxide and iron hydroxide earth pigments, despite their chemical similarity. First, we conducted a pump-probe spectroscopy study on heat-treated hematite (the pure red iron oxide mineral) and found the pump-probe dynamics to be temperature dependent. Second, we investigated pottery fired under known conditions and observed firing dependent pump-probe dynamics. Finally, we imaged a New World potshard from the North Carolina Museum of Art. Our results indicate that pump-probe microscopy could be a useful tool in elucidating pottery manufacture.}, Doi = {10.1117/12.2184758}, Key = {fds323187} } @article{fds323188, Author = {Wilson, JW and Anderson, M and Park, JK and Fischer, MC and Warren, WS}, Title = {Separating higher-order nonlinearities in transient absorption microscopy}, Journal = {Proceedings of SPIE - The International Society for Optical Engineering}, Volume = {9584}, Publisher = {SPIE}, Year = {2015}, Month = {January}, ISBN = {9781628417500}, url = {http://dx.doi.org/10.1117/12.2187133}, Abstract = {The transient absorption response of melanin is a promising optically-accessible biomarker for distinguishing malignant melanoma from benign pigmented lesions, as demonstrated by earlier experiments on thin sections from biopsied tissue. The technique has also been demonstrated in vivo, but the higher optical intensity required for detecting these signals from backscattered light introduces higher-order nonlinearities in the transient response of melanin. These components that are higher than linear with respect to the pump or the probe introduce intensity-dependent changes to the overall response that complicate data analysis. However, our data also suggest these nonlinearities might be advantageous to in vivo imaging, in that different types of melanins have different nonlinear responses. Therefore, methods to separate linear from nonlinear components in transient absorption measurements might provide additional information to aid in the diagnosis of melanoma. We will discuss numerical methods for analyzing the various nonlinear contributions to pump-probe signals, with the ultimate objective of real time analysis using digital signal processing techniques. To that end, we have replaced the lock in amplifier in our pump-probe microscope with a high-speed data acquisition board, and reprogrammed the coprocessor field-programmable gate array (FPGA) to perform lock-in detection. The FPGA lock-in offers better performance than the commercial instrument, in terms of both signal to noise ratio and speed. In addition, the flexibility of the digital signal processing approach enables demodulation of more complicated waveforms, such as spread-spectrum sequences, which has the potential to accelerate microscopy methods that rely on slow relaxation phenomena, such as photothermal and phosphorescence lifetime imaging.}, Doi = {10.1117/12.2187133}, Key = {fds323188} } @article{fds365770, Author = {Warren, WS and Fischer, M and Wilson, J and Robles, F and Deb, S}, Title = {Enhancing Pigmented or Transparent Tissue Imaging with Laser Pulse Shaping}, Journal = {Optics InfoBase Conference Papers}, Year = {2015}, Month = {January}, ISBN = {9781943580033}, Abstract = {Enhanced control over femtosecond lasers (pulse shaping or pulse train modulation) improves contrast in tissue imaging. Pump-probe applications to melanoma diagnosis and cross phase modulation measurement in transparent tissues will be presented.}, Key = {fds365770} } @article{fds365771, Author = {Fischer, MC and Villafana, TE and Brown, W and Delaney, J and Warren, WS}, Title = {Nonlinear Optical Imaging in Art Conservation and Heritage Science}, Journal = {Optics InfoBase Conference Papers}, Year = {2015}, Month = {January}, ISBN = {9781943580033}, Abstract = {Pump-probe microscopy can extract molecular and structural contrast with high spatial resolution even in thick, scattering samples. We will discuss the technique’s principle and applications for imaging historic paintings and other cultural heritage objects.}, Key = {fds365771} } @article{fds351259, Author = {Park, JK and Fischer, MC and Susumu, K and Therien, MJ and Warren, WS}, Title = {Femtosecond pulse train shaping for accurate two-photon excited fluorescence measurements}, Journal = {Optics InfoBase Conference Papers}, Year = {2014}, Month = {October}, ISBN = {1557522863}, url = {http://dx.doi.org/10.1364/ls.2014.lth4h.3}, Abstract = {We report a simple measurement method that exploits pulse train shaping to suppress linear contributions to the fluorescence, and allows for extraction of the two-photon absorption cross sections. © 2014 OSA.}, Doi = {10.1364/ls.2014.lth4h.3}, Key = {fds351259} } @article{fds232470, Author = {Park, JK and Fischer, MC and Susumu, K and Therien, MJ and Warren, WS}, Title = {Femtosecond pulse train shaping improves two-photon excited fluorescence measurements}, Journal = {Optics Letters}, Volume = {39}, Number = {19}, Pages = {5606-5606}, Publisher = {The Optical Society}, Year = {2014}, Month = {October}, ISSN = {0146-9592}, url = {http://dx.doi.org/10.1364/ol.39.005606}, Abstract = {Measurements of two-photon absorption (TPA) cross sections are greatly confounded by even very weak linear absorption, for example from hot bands. In this case, the experimental power dependence of fluorescence from amplified and mode-locked laser systems can differ drastically, even if the peak intensity is adjusted to be the same in both cases. A simple pulse train shaping method suppresses linear contributions and extracts the nonlinear absorption cross section, demonstrated here for a meso-to-meso ethyne-bridged bis[(porphinato)zinc(II)] fluorophore (DD) at 800 nm. This approach permits reliable TPA cross-section measurement, even with standard modelocked lasers under conditions identical to that used for multiphoton microscopy.}, Doi = {10.1364/ol.39.005606}, Key = {fds232470} } @article{fds232471, Author = {Robles, FE and Fischer, MC and Warren, WS}, Title = {Femtosecond pulse shaping enables detection of optical Kerr-effect (OKE) dynamics for molecular imaging}, Journal = {Optics Letters}, Volume = {39}, Number = {16}, Pages = {4788-4788}, Publisher = {The Optical Society}, Year = {2014}, Month = {August}, ISSN = {0146-9592}, url = {http://dx.doi.org/10.1364/ol.39.004788}, Abstract = {We apply femtosecond pulse shaping to generate optical pulse trains that directly access a material's nonlinear refractive index (n2) and can thus determine time-resolved optical Kerr-effect (OKE) dynamics. Two types of static pulse trains are discussed: The first uses two identical fields delayed in time, plus a pump field at a different wavelength. Time-resolved OKE dynamics are retrieved by monitoring the phase of the interference pattern produced by the two identical fields in the Fourier-domain (FD) as a function of pump-probe-time-delay (where the probe is one of the two identical fields). The second pulse train uses three fields with equal time delays, but with the center field phase shifted by π/2. In this pulse scheme, changes on a sample's nonlinear refractive index produce a new frequency in the FD signal, which in turn yields background-free intensity changes in the conjugate (time) domain and provides superior signal-to-noise ratios. The demonstrated sensitivity improvements enable, for the first time to our knowledge, molecular imaging based on OKE dynamics.}, Doi = {10.1364/ol.39.004788}, Key = {fds232471} } @article{fds232493, Author = {Villafana, TE and Brown, WP and Delaney, JK and Palmer, M and Warren, WS and Fischer, MC}, Title = {Femtosecond pump-probe microscopy generates virtual cross-sections in historic artwork}, Journal = {Proceedings of the National Academy of Sciences}, Volume = {111}, Number = {5}, Pages = {1708-1713}, Publisher = {Proceedings of the National Academy of Sciences}, Year = {2014}, Month = {February}, ISSN = {0027-8424}, url = {http://dx.doi.org/10.1073/pnas.1317230111}, Abstract = {<jats:title>Significance</jats:title> <jats:p>We show that a nonlinear microscopy technique (femtosecond pump-probe microscopy) allows for nondestructive 3D imaging of paintings with molecular and structural contrast. Until now, studying the layering structure of a painting has generally required the physical removal of a cross-section sample. Pump-probe imaging has previously been shown on biological tissue, but applications to cultural heritage are more challenging: the variety of pigments in the artist’s palate is enormous compared with the biological pigments present in skin. Nonetheless, we show virtual cross-sectioning capabilities in mockup paintings and nondestructive imaging on an intact 14th century painting. This work represents a comprehensive collaborative effort between laser and biomedical imaging experts and scientists and conservators in national museums.</jats:p>}, Doi = {10.1073/pnas.1317230111}, Key = {fds232493} } @article{fds232468, Author = {Park, JK and Fischer, MC and Susumu, K and Therien, MJ and Warren, WS}, Title = {Femtosecond pulse train shaping for accurate two-photon excited fluorescence measurements}, Journal = {Laser Science, LS 2014}, Year = {2014}, Month = {January}, ISBN = {1557522863}, Abstract = {We report a simple measurement method that exploits pulse train shaping to suppress linear contributions to the fluorescence, and allows for extraction of the two-photon absorption cross sections. © 2014 OSA.}, Key = {fds232468} } @article{fds232498, Author = {Wilson, JW and Degan, S and Fischer, MC and Warren, WS}, Title = {Optical clearing and multiphoton imaging of paraffin-embedded specimens}, Journal = {Progress in Biomedical Optics and Imaging - Proceedings of SPIE}, Volume = {8588}, Publisher = {SPIE}, Year = {2013}, Month = {June}, ISBN = {9780819493576}, ISSN = {1605-7422}, url = {http://dx.doi.org/10.1117/12.2003155}, Abstract = {New labeling, imaging, or analysis tools could provide new retrospective insights when applied to archived, paraffinembedded samples. Deep-tissue multiphoton microscopy of paraffin-embedded specimens is achieved using optical clearing with mineral oil. We tested a variety of murine tissue specimens including skin, lung, spleen, kidney, and heart, acquiring multiphoton autofluorescence and second-harmonic generation, and pump-probe images This technique introduces the capability for non-destructive 3-dimensional microscopic imaging of existing archived pathology specimens, enabling retrospective studies. © 2013 SPIE.}, Doi = {10.1117/12.2003155}, Key = {fds232498} } @article{fds232499, Author = {Robles, FE and Wilson, JW and Fischer, MC and Warren, WS}, Title = {Adapting phasor analysis for nonlinear pump-probe microscopy}, Journal = {Progress in Biomedical Optics and Imaging - Proceedings of SPIE}, Volume = {8589}, Publisher = {SPIE}, Year = {2013}, Month = {May}, ISBN = {9780819493583}, ISSN = {1605-7422}, url = {http://dx.doi.org/10.1117/12.2002600}, Abstract = {Phasor analysis has become a powerful tool for examining signals in fluorescence life-time microscopy (FLIM), where the analysis provides a fast, robust and intuitive means of separating different fluorescent species and mixtures thereof. In this work we adapt this analysis for pump-probe microscopy, a method that provides molecular contrast of pigmented samples by probing their excited state dynamic properties. The bipolar nature of the pump-probe signals presents important differences in the resulting phasors compared to FLIM - here, we discuss these differences and describe the behavior of bipolar signals in phasor analysis. Results show that this method is indeed able to separate multiple molecular species of interests and allows facile assessment of pigment chemistry and its distribution in samples. © 2013 Copyright SPIE.}, Doi = {10.1117/12.2002600}, Key = {fds232499} } @article{fds323578, Author = {Wilson, JW and Degan, S and Warren, WS and Fischer, MC}, Title = {Optical clearing of archive-compatible paraffin embedded tissue for multiphoton microscopy: erratum}, Journal = {Biomedical Optics Express}, Volume = {4}, Number = {2}, Pages = {219-219}, Publisher = {The Optical Society}, Year = {2013}, Month = {February}, url = {http://dx.doi.org/10.1364/boe.4.000219}, Doi = {10.1364/boe.4.000219}, Key = {fds323578} } @article{fds326162, Author = {Fischer, M}, Title = {Shedding new light on old art}, Journal = {Physics World}, Volume = {26}, Number = {12}, Pages = {19-23}, Publisher = {IOP Publishing}, Year = {2013}, Month = {January}, url = {http://dx.doi.org/10.1088/2058-7058/26/12/30}, Doi = {10.1088/2058-7058/26/12/30}, Key = {fds326162} } @article{fds232516, Author = {Samineni, P and De Cruz and A and Villafana, T and Fischer, MC and Warren, WS}, Title = {Pump-probe microscopy of pigments used in historical art}, Journal = {2012 Conference on Lasers and Electro-Optics, CLEO 2012}, Year = {2012}, Month = {December}, ISBN = {9781467318396}, Abstract = {We have developed a nonlinear microscopy technique that uses sensitive modulation transfer to extract excited state dynamics with high spatial resolution. Here, we use this technique to characterize several pigments used in historical artwork. © 2012 OSA.}, Key = {fds232516} } @article{fds232517, Author = {Wilson, JW and Samineni, P and Fischer, MC and Warren, WS}, Title = {Nonlinear cross-phase modulation microscopy using spectral shifting}, Journal = {2012 Conference on Lasers and Electro-Optics, CLEO 2012}, Year = {2012}, Month = {December}, ISBN = {9781467318396}, Abstract = {Nonlinear phase contrast may be acquired by measuring spectral shifting of an ultrafast pulse due to cross phase modulation. This technique is used to obtain structural details in a pigmented cell from a melanoma biopsy. © 2012 OSA.}, Key = {fds232517} } @article{fds232525, Author = {Li, B and Yi, C and Brown, A and Fischer, MC and Warren, WS}, Title = {Homodyne near-degenerate four-wave-mixing microscopy for graphene imaging and biomedical applications}, Journal = {2012 Conference on Lasers and Electro-Optics, CLEO 2012}, Year = {2012}, Month = {December}, ISBN = {9781467318396}, Abstract = {Homodyne detection of near-degenerate four-wave-mixing with a single laser pulse is used to imaging graphene in biological samples. © 2012 OSA.}, Key = {fds232525} } @article{fds232491, Author = {Villafaña, TE and Samineni, P and Warren, WS and Fischer, MC}, Title = {Historical pigments revealed by pump-probe microscopy}, Journal = {Laser Science, LS 2012}, Year = {2012}, Month = {December}, ISBN = {9781557529565}, Abstract = {Nonlinear optical pump-probe microscopy is able to sensitively extract excited state dynamics from historical art pigments. This technique allows three-dimensional imaging and characterization of different pigments, with far reaching applications for conservation science. © OSA 2012.}, Key = {fds232491} } @article{fds232526, Author = {Li, B and Cheng, Y and Liu, J and Yi, C and Brown, AS and Yuan, H and Vo-Dinh, T and Fischer, MC and Warren, WS}, Title = {Direct Optical Imaging of Graphene In Vitro by Nonlinear Femtosecond Laser Spectral Reshaping}, Journal = {Nano Letters}, Volume = {12}, Number = {11}, Pages = {5936-5940}, Publisher = {American Chemical Society (ACS)}, Year = {2012}, Month = {November}, url = {http://www.ncbi.nlm.nih.gov/pubmed/23101475}, Abstract = {Nonlinear optical microscopy, based on femtosecond laser spectral reshaping, characterized and imaged graphene samples made from different methods, both on slides and in a biological environment. This technique clearly discriminates between graphene flakes with different numbers of layers and reveals the distinct nonlinear optical properties of reduced graphene oxide as compared to mechanically exfoliated or chemical vapor deposition grown graphene. The nonlinearity makes it applicable to scattering samples (such as tissue) as opposed to previous methods, such as transmission. This was demonstrated by high-resolution imaging of breast cancer cells incubated with graphene flakes.}, Doi = {10.1021/nl303358p}, Key = {fds232526} } @article{fds232523, Author = {Wilson, JW and Degan, S and Warren, WS and Fischer, MC}, Title = {Optical clearing of archive-compatible paraffin embedded tissue for multiphoton microscopy}, Journal = {Biomedical Optics Express}, Volume = {3}, Number = {11}, Pages = {2752-2752}, Publisher = {The Optical Society}, Year = {2012}, Month = {November}, url = {http://www.ncbi.nlm.nih.gov/pubmed/23162713}, Abstract = {Standard histopathology techniques (including paraffin embedding) are incompatible with thick tissue multiphoton imaging, and standard clearing techniques on those specimens destroy some molecular information. We demonstrate multiphoton imaging in specimens prepared according to standard histopathology techniques. This permits unlabeled 3-dimensional histology on archival tissue banks, which is of great value in evaluating prognostic indicators.}, Doi = {10.1364/boe.3.002752}, Key = {fds232523} } @article{fds232522, Author = {Robles, FE and Wilson, JW and Fischer, MC and Warren, WS}, Title = {Phasor analysis for nonlinear pump-probe microscopy}, Journal = {Optics Express}, Volume = {20}, Number = {15}, Pages = {17082-17082}, Publisher = {The Optical Society}, Year = {2012}, Month = {July}, ISSN = {1094-4087}, url = {http://dx.doi.org/10.1364/oe.20.017082}, Abstract = {Pump-probe microscopy provides molecular information by probing transient, excited state dynamic properties of pigmented samples. Analysis of the transient response is typically conducted using principal component analysis or multi-exponential fitting, however these methods are not always practical or feasible. Here, we show an adaptation of phasor analysis to provide an intuitive, robust, and efficient method for analyzing and displaying pump-probe images, thereby alleviating some of the challenges associated with differentiating multiple pigments. A theoretical treatment is given to understand how the complex transient signals map onto the phasor plot. Analyses of cutaneous and ocular pigmented tissue samples, as well as historical pigments in art demonstrate the utility of this approach. ©2012 Optical Society of America.}, Doi = {10.1364/oe.20.017082}, Key = {fds232522} } @article{fds232521, Author = {Li, B and Claytor, KE and Yuan, H and Vo-Dinh, T and Warren, WS and Fischer, MC}, Title = {Multicontrast nonlinear optical microscopy with a compact and rapid pulse shaper}, Journal = {Optics Letters}, Volume = {37}, Number = {13}, Pages = {2763-2763}, Publisher = {The Optical Society}, Year = {2012}, Month = {July}, url = {http://www.ncbi.nlm.nih.gov/pubmed/22743521}, Abstract = {Homodyne detection can dramatically enhance measurement sensitivity for weak signals. In nonlinear optical microscopy it can make accessible a range of novel, intrinsic, contrast like nonlinear absorption and nonlinear phase contrast. Here a compact and rapid pulse shaper is developed, implemented, and demonstrated for homodyne detection in nonlinear microscopy with high-repetition rate mode-locked femtosecond lasers. With this method we generate two-photon absorption (TPA) and self-phase modulation images of gold nanostars in biological samples. Simultaneous imaging of two-photon luminescence and TPA also enables us to produce two-photon quantum yield images.}, Doi = {10.1364/ol.37.002763}, Key = {fds232521} } @article{fds232520, Author = {Wilson, JW and Samineni, P and Warren, WS and Fischer, MC}, Title = {Cross-phase modulation spectral shifting: nonlinear phase contrast in a pump-probe microscope}, Journal = {Biomedical Optics Express}, Volume = {3}, Number = {5}, Pages = {854-854}, Publisher = {The Optical Society}, Year = {2012}, Month = {May}, ISSN = {2156-7085}, url = {http://dx.doi.org/10.1364/boe.3.000854}, Abstract = {Microscopy with nonlinear phase contrast is achieved by a simple modification to a nonlinear pump-probe microscope. The technique measures cross-phase modulation by detecting a pump-induced spectral shift in the probe pulse. Images with nonlinear phase contrast are acquired both in transparent and absorptive media. In paraffin-embedded biopsy sections, cross-phase modulation complements the chemically-specific pump-probe images with structural context.}, Doi = {10.1364/boe.3.000854}, Key = {fds232520} } @article{fds232519, Author = {Samineni, P and deCruz, A and Villafaña, TE and Warren, WS and Fischer, MC}, Title = {Pump-probe imaging of historical pigments used in paintings}, Journal = {Optics Letters}, Volume = {37}, Number = {8}, Pages = {1310-1310}, Publisher = {The Optical Society}, Year = {2012}, Month = {April}, url = {http://www.ncbi.nlm.nih.gov/pubmed/22513669}, Abstract = {A recently developed nonlinear optical pump-probe microscopy technique uses modulation transfer to sensitively extract excited-state dynamics of endogenous biological pigments, such as eumelanin and pheomelanin. In this work, we use this method to image and characterize several inorganic and organic pigments used in historical art. We show substantial differences in the near-IR pump-probe signatures from nominally similar pigments and suggest extensions to art restoration.}, Doi = {10.1364/ol.37.001310}, Key = {fds232519} } @article{fds232518, Author = {Samineni, P and Li, B and Wilson, JW and Warren, WS and Fischer, MC}, Title = {Cross-phase modulation imaging}, Journal = {Optics Letters}, Volume = {37}, Number = {5}, Pages = {800-800}, Publisher = {The Optical Society}, Year = {2012}, Month = {March}, url = {http://www.ncbi.nlm.nih.gov/pubmed/22378398}, Abstract = {We demonstrate a cross-phase modulation measurement technique based on the sensitive detection of modulation transfer in a pump-probe setup. By modulating the amplitude of the pump beam and spectrally analyzing the probe beam, we achieve a rapid, background-free measurement of nonlinear phase modulation using power levels acceptable in biological imaging. This measurement technique would allow the extension of widely employed phase microscopy methods to the nonlinear regime, providing intrinsic and universal nonlinear contrast for biological imaging.}, Doi = {10.1364/ol.37.000800}, Key = {fds232518} } @article{fds232486, Author = {Claytor, K and Li, B and Samineni, P and Warren, W and Fischer, M}, Title = {Femtosecond pulse shaping enables nonlinear imaging in highly scattering materials}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, Month = {December}, ISBN = {9781557529176}, Abstract = {Spectral re-shaping of pulses from a mode-locked femtosecond laser allows detection of two photon absorption and self phase modulation in highly scattering materials, which permits nonlinear tissue imaging with this intrinsic contrast. © 2011 OSA.}, Key = {fds232486} } @article{fds232487, Author = {Samineni, P and Fischer, MC and Warren, WS}, Title = {Cross-phase modulation microscopy}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, Month = {December}, ISBN = {9781557529176}, Abstract = {We report our recently developed spectral re-shaping technique for cross-phase modulation imaging, which extends widely employed phase microscopy to the nonlinear regime. © 2011 OSA.}, Key = {fds232487} } @article{fds232490, Author = {Li, B and Claytor, K and Warren, WS and Fischer, MC}, Title = {Optimizing shape of femtosecond laser pulses for homodyne detection of nonlinear optical signals}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, Month = {December}, ISBN = {9781557529176}, Abstract = {Based on homodyne detection of weak nonlinear signals with our spectral reshaping technique, pulse shapes are optimized for fast nonlinear imaging using femtosecond mode-locked lasers. © 2011 OSA.}, Key = {fds232490} } @article{fds232529, Author = {Fischer, MC and Samineni, P and Li, B and Claytor, K and Warren, WS}, Title = {Accessing nonlinear phase contrast in biological tissue using femtosecond laser pulse shaping}, Journal = {Progress in Biomedical Optics and Imaging - Proceedings of SPIE}, Volume = {8086}, Number = {8086}, Pages = {80860O}, Publisher = {SPIE}, Year = {2011}, Month = {July}, ISBN = {9780819486837}, ISSN = {1605-7422}, url = {http://dx.doi.org/10.1117/12.889668}, Abstract = {Nonlinear imaging takes advantage of the localized nature of the interaction to achieve high spatial resolution, optical sectioning, and deeper penetration in tissue. However, nonlinear contrast (other than fluorescence or harmonic generation) is generally difficult to measure because it is overwhelmed by the large background of detected illumination light. Especially challenging to measure is the nonlinear refractive index - accessing this quantity would allow the extension of widely employed phase microscopy methods to the nonlinear regime. We have developed a technique to suppress the background in these types of measurements by using femtosecond pulse shaping to encode nonlinear interactions in background-free regions of the frequency spectrum. Using this individual pulse shaping based technique we have been able to measure self-phase modulation (SPM) in highly scattering environments, such as biological tissue, with very modest power levels. Using our measurement technique we have demonstrated strong intrinsic SPM signatures of glutamate-induced neuronal activity in hippocampal brain slices. We have also extended this measurement method to cross-phase modulation, the two-color analogue to SPM. The two-color approach dramatically improves the measurement sensitivity by reducing undesired background and associated noise. We will describe the nonlinear phase contrast measurement technique and report on its application for imaging neuronal activity. © 2011 SPIE-OSA.}, Doi = {10.1117/12.889668}, Key = {fds232529} } @article{fds350498, Author = {Claytor, K and Li, B and Samineni, P and Warren, W and Fischer, M}, Title = {Femtosecond pulse shaping enables nonlinear imaging in highly scattering materials}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, Month = {January}, ISBN = {9781557529176}, url = {http://dx.doi.org/10.1364/ls.2011.lmc5}, Abstract = {Spectral re-shaping of pulses from a mode-locked femtosecond laser allows detection of two photon absorption and self phase modulation in highly scattering materials, which permits nonlinear tissue imaging with this intrinsic contrast. © 2011 OSA.}, Doi = {10.1364/ls.2011.lmc5}, Key = {fds350498} } @article{fds349888, Author = {Li, B and Claytor, K and Warren, WS and Fischer, MC}, Title = {Optimizing shape of femtosecond laser pulses for homodyne detection of nonlinear optical signals}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, Month = {January}, ISBN = {9781557529176}, url = {http://dx.doi.org/10.1364/fio.2011.ftuq5}, Abstract = {Based on homodyne detection of weak nonlinear signals with our spectral reshaping technique, pulse shapes are optimized for fast nonlinear imaging using femtosecond mode-locked lasers. © 2011 OSA.}, Doi = {10.1364/fio.2011.ftuq5}, Key = {fds349888} } @article{fds349889, Author = {Samineni, P and Fischer, MC and Liu, HC and Yasuda, R and Warren, WS}, Title = {Nonlinear phase contrast imaging in neuronal tissue}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, Month = {January}, ISBN = {9781557529091}, url = {http://dx.doi.org/10.1364/ntm.2011.nmd3}, Abstract = {We demonstrate nonlinear phase contrast imaging in highly scattering media using rapid femtosecond pulse shaping of mode-locked laser pulses. We will also discuss potential applications of this technique for intrinsic functional neuronal imaging. © 2011 OSA: BODA/NTM/OMP/OTA.}, Doi = {10.1364/ntm.2011.nmd3}, Key = {fds349889} } @article{fds350106, Author = {Samineni, P and Fischer, MC and Warren, WS}, Title = {Cross-phase modulation microscopy}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, Month = {January}, ISBN = {9781557529176}, url = {http://dx.doi.org/10.1364/ls.2011.ltua2}, Abstract = {We report our recently developed spectral re-shaping technique for cross-phase modulation imaging, which extends widely employed phase microscopy to the nonlinear regime. © 2011 OSA.}, Doi = {10.1364/ls.2011.ltua2}, Key = {fds350106} } @article{fds232488, Author = {Samineni, P and Fischer, MC and Liu, HC and Yasuda, R and Warren, WS}, Title = {Nonlinear phase contrast imaging in neuronal tissue}, Journal = {Optics InfoBase Conference Papers}, Year = {2011}, ISSN = {2162-2701}, Key = {fds232488} } @article{fds232530, Author = {Zhang, R and Greenberg, JA and Fischer, MC and Gauthier, DJ}, Title = {Controllable ultrabroadband slow light in a warm rubidium vapor}, Journal = {Journal of the Optical Society of America B: Optical Physics}, Volume = {28}, Number = {11}, Pages = {2578-2583}, Publisher = {The Optical Society}, Year = {2011}, ISSN = {0740-3224}, url = {http://hdl.handle.net/10161/5105 Duke open access}, Abstract = {We study ultrabroadband slow light in a warm rubidium vapor cell. By working between the D1 and D2 transitions, we find a several-nanometer window centered at 788:4nm in which the group index is highly uniform and the absorption is small (<1%). We demonstrate that we can control the group delay by varying the temperature of the cell, and we observe a tunable fractional delay of 18 for pulses as short as 250 fs (6:9nm bandwidth) with a fractional broadening of only 0.65 and a power leakage of 55%. We find that a simple theoretical model is in excellent agreement with the experimental results. Using this model, we discuss the impact of the pulse's spectral characteristics on the distortion it incurs during propagation through the vapor. © 2011 Optical Society of America.}, Doi = {10.1364/JOSAB.28.002578}, Key = {fds232530} } @article{fds232515, Author = {Li, B and Warren, WS and Fischer, MC}, Title = {Phase-cycling coherent anti-Stokes Raman scattering using shaped femtosecond laser pulses}, Journal = {Optics Express}, Volume = {18}, Number = {25}, Pages = {25825-25825}, Publisher = {The Optical Society}, Year = {2010}, Month = {December}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21164927}, Abstract = {We demonstrate a homodyne coherent anti-Stokes Raman scattering (CARS) technique based on femtosecond laser pulse shaping. This technique utilizes fast phase cycling to extract nonlinear Raman signatures with a self-generated reference signal acting as a local oscillator. The local oscillator is generated at the focus and is intrinsically stable relative to the Raman signal even in highly scattering samples. We can therefore retrieve phase information from the Raman signal and can suppress the ubiquitous non-resonant background.}, Doi = {10.1364/oe.18.025825}, Key = {fds232515} } @article{fds232483, Author = {Samineni, P and Perret, Z and Warren, WS and Fischer, MC}, Title = {Femtosecond laser pulse shaping improves self-phase modulation measurements in scattering media}, Journal = {Optics InfoBase Conference Papers}, Year = {2010}, Month = {December}, Abstract = {We demonstrate that our recently developed spectral re-shaping technique improves the accuracy and precision of self-phase modulation measurements in scattering media over the conventional Z-scan method. © 2010 OSA/FiO/LS 2010.}, Key = {fds232483} } @article{fds232484, Author = {Li, B and Warren, WS and Fischer, MC}, Title = {Enhancing coherent anti-stokes Raman scattering background suppression with phase cycled structured femtosecond laser pulses}, Journal = {Optics InfoBase Conference Papers}, Year = {2010}, Month = {December}, Abstract = {We demonstrate a homodyne coherent anti-Stokes Raman scattering technique based on femtosecond laser pulse shaping (phase-cycling). This technique utilizes a self-generated non-resonant background as a local oscillator to retrieve phase information of the Raman signal. © 2010 OSA/FiO/LS 2010.}, Key = {fds232484} } @article{fds232514, Author = {Samineni, P and Perret, Z and Warren, WS and Fischer, MC}, Title = {Measurements of nonlinear refractive index in scattering media}, Journal = {Optics Express}, Volume = {18}, Number = {12}, Pages = {12727-12727}, Publisher = {Optica Publishing Group}, Year = {2010}, Month = {June}, url = {http://www.ncbi.nlm.nih.gov/pubmed/20588401}, Abstract = {We have recently developed a spectral re-shaping technique to simultaneously measure nonlinear refractive index and nonlinear absorption. In this technique, the information about the nonlinearities is encoded in the frequency domain, rather than in the spatial domain as in the conventional Z-scan method. Here we show that frequency encoding is much more robust with respect to scattering. We compare spectral re-shaping and Z-scan measurements in a highly scattering environment and show that reliable spectral re-shaping measurements can be performed even in a regime that precludes standard Z-scans.}, Doi = {10.1364/oe.18.012727}, Key = {fds232514} } @article{fds350888, Author = {Li, B and Warren, WS and Fischer, MC}, Title = {Enhancing coherent anti-stokes Raman scattering background suppression with phase cycled structured femtosecond laser pulses}, Journal = {Optics InfoBase Conference Papers}, Year = {2010}, Month = {January}, url = {http://dx.doi.org/10.1364/fio.2010.ftuf2}, Abstract = {We demonstrate a homodyne coherent anti-Stokes Raman scattering technique based on femtosecond laser pulse shaping (phase-cycling). This technique utilizes a self-generated non-resonant background as a local oscillator to retrieve phase information of the Raman signal. © 2010 OSA/FiO/LS 2010.}, Doi = {10.1364/fio.2010.ftuf2}, Key = {fds350888} } @article{fds351260, Author = {Samineni, P and Perret, Z and Warren, WS and Fischer, MC}, Title = {Femtosecond laser pulse shaping improves self-phase modulation measurements in scattering media}, Journal = {Optics InfoBase Conference Papers}, Year = {2010}, Month = {January}, url = {http://dx.doi.org/10.1364/fio.2010.fthg2}, Abstract = {We demonstrate that our recently developed spectral re-shaping technique improves the accuracy and precision of self-phase modulation measurements in scattering media over the conventional Z-scan method. © 2010 OSA/FiO/LS 2010.}, Doi = {10.1364/fio.2010.fthg2}, Key = {fds351260} } @article{fds232478, Author = {Warren, WS and Piletic, I and Fischer, M and Fu, D and Samenini, P and Matthews, T}, Title = {Nonlinear microscopy without fluorescence: Seeing the needle in the Haystack with Femtosecond pulse shaping}, Journal = {Optics InfoBase Conference Papers}, Year = {2009}, Month = {December}, ISBN = {9781557528711}, Key = {fds232478} } @article{fds232513, Author = {Fischer, MC and Raizen, MG}, Title = {Experiments on quantum transport of ultra-cold atoms in optical potentials}, Volume = {789}, Pages = {205-237}, Booktitle = {Time in Quantum Mechanics}, Publisher = {Springer Berlin Heidelberg}, Year = {2009}, Month = {December}, ISBN = {9783642031731}, ISSN = {0075-8450}, url = {http://dx.doi.org/10.1007/978-3-642-03174-8_8}, Abstract = {In this chapter, we describe our experiments with ultra cold atoms in optical potentials and show how we can address fundamental issues of time in quantum mechanics. The high degree of experimental control and the conceptual simplicity are the main advantages of our system. We start with an overview of the basic interaction of atoms and light and make the connection between atoms in optical lattices and solid state physics. While this latter connection has evolved into a major theme in physics over the past decade, at the time of this work it was still new and unexplored. After introduction of the theoretical model and the basic equations, we introduce the experimental apparatus. We then review our experiments to observe the Wannier-Stark ladder in an accelerating lattice. This system was used to study quantum tunneling where short-time non-exponential decay was first observed for an unstable quantum system. We then describe our experiments to observe the quantum Zeno and anti-Zeno effects for an unstable system that is repeatedly interrogated. We conclude this chapter with a brief outlook into the future. © 2010 Springer-Verlag Berlin Heidelberg.}, Doi = {10.1007/978-3-642-03174-8_8}, Key = {fds232513} } @article{fds232531, Author = {Fischer, MC and Piletica, I and Fub, D and Matthewsa, TE and Liuc, H and Saminenia, P and Lid, B and Warrene, WS}, Title = {Enhancing two-color absorption, self-phase modulation and raman microscopy signatures in tissue with femtosecond laser pulse shaping}, Journal = {Progress in Biomedical Optics and Imaging - Proceedings of SPIE}, Volume = {7183}, Publisher = {SPIE}, Year = {2009}, Month = {June}, ISSN = {1605-7422}, url = {http://dx.doi.org/10.1117/12.816488}, Abstract = {Nonlinear microscopies (most commonly, two-photon fluorescence, second harmonic generation, and coherent anti-Stokes Raman scattering (CARS)) have had notable successes in imaging a variety of endogenous and exogenous targets in recent years. These methods generate light at a color different from any of the exciting laser pulses, which makes the signal relatively easy to detect. Our work has focused on developing microscopy techniques using a wider range of nonlinear signatures (two-photon absorption of nonfluorescent species, self phase modulation) which have some specific advantages - for example, in recent papers we have shown that we can differentiate between different types of melanin in pigmented lesions, image hemoglobin and its oxygenation, and measure neuronal activity. In general, these signatures do not generate light at a different color and we rely on the advantages of femtosecond laser pulse shaping methods to amplify the signals and make them visible (for example, using heterodyne detection of the induced signal with one of the co-propagating laser pulses). Here we extend this work to stimulated Raman and CARS geometries. In the simplest experiments, both colors arise from filtering a single fs laser pulse, then modulating afterwards; in other cases, we demonstrate that spectral reshaping can retain high frequency resolution in Raman and CARS geometries with femtosecond laser pulses. © 2009 SPIE.}, Doi = {10.1117/12.816488}, Key = {fds232531} } @article{fds325990, Author = {Warren, WS}, Title = {Tissue imaging with shaped femtosecond laser pulses}, Journal = {Optics InfoBase Conference Papers}, Volume = {88}, Pages = {807-+}, Booktitle = {Ultrafast Phenomena XV}, Publisher = {Springer-Verlag}, Year = {2009}, Month = {January}, ISBN = {9781557528780}, Abstract = {Rapid laser pulse shaping permit detection of novel molecular signatures such as self- and cross-phase modulation or nonlinear absorption. These effects are used to discriminate between different melanins in tissue and to monitor neuronal activation. © 2009 OSA/FiO/LS/AO/AIOM/COSI/LM/SRS 2009.}, Key = {fds325990} } @article{fds350889, Author = {Warren, WS and Piletic, I and Fischer, M and Fu, D and Samenini, P and Matthews, T}, Title = {Nonlinear microscopy without fluorescence: Seeing the needle in the Haystack with Femtosecond pulse shaping}, Journal = {Optics InfoBase Conference Papers}, Year = {2009}, Month = {January}, ISBN = {9781557528711}, url = {http://dx.doi.org/10.1364/ntm.2009.nmc1}, Doi = {10.1364/ntm.2009.nmc1}, Key = {fds350889} } @article{fds232512, Author = {Warren, WS and Fischer, M and Fu, D and Ye, T and Piletic, I and Matthews, T}, Title = {New nonlinear signatures in spectroscopy and imaging}, Journal = {Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series}, Pages = {JWC1}, Year = {2008}, Month = {September}, ISBN = {9781557528599}, url = {http://dx.doi.org/10.1109/QELS.2008.4552901}, Abstract = {Ultrafast laser pulse shaping makes it possible to observe nonlinear signatures, such as self phase modulation and sum frequency absorption, at safe laser powers for tissue. Neuronal activation and melanoma diagnosis are two early targets. © 2008 Optical Society of America.}, Doi = {10.1109/QELS.2008.4552901}, Key = {fds232512} } @article{fds232534, Author = {Piletic, IR and Fischer, MC and Samineni, P and Yurtsever, G and Warren, WS}, Title = {Rapid pulse shaping with homodyne detection for measuring nonlinear optical signals}, Journal = {Optics Letters}, Volume = {33}, Number = {13}, Pages = {1482-1482}, Publisher = {Optica Publishing Group}, Year = {2008}, Month = {July}, ISSN = {0146-9592}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18594672}, Abstract = {We have designed a common-mode interferometric acousto-optic pulse shaper that is capable of shaping individual pulses differently from a mode-locked laser. The design enables the measurement of weak nonlinear optical signals such as two-photon absorption and self-phase modulation at megahertz rates. The experimental apparatus incorporates homodyne detection as a means of resolving the phase of the detected signals. The fast data acquisition rate and the ability to perform measurements in scattering media make this experimental apparatus amenable to imaging applications analogous to measurements of two-photon fluorescence using a mode-locked laser.}, Doi = {10.1364/ol.33.001482}, Key = {fds232534} } @article{fds232533, Author = {Fischer, MC and Liu, HC and Piletic, IR and Warren, WS}, Title = {Simultaneous self-phase modulation and two-photon absorption measurement by a spectral homodyne Z-scan method}, Journal = {Optics Express}, Volume = {16}, Number = {6}, Pages = {4192-4192}, Publisher = {Optica Publishing Group}, Year = {2008}, Month = {March}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18542515}, Abstract = {We developed a technique to simultaneously measure self-phase modulation and two-photon absorption using shaped femtosecond laser pulses. In the conventional Z-scan measurement technique the amount of nonlinearity is determined by measuring the change in shape and intensity of a transmitted laser beam. In contrast, our method sensitively measures nonlinearity-induced changes in the pulse spectrum. In this work we demonstrate the technique in nonlinear absorptive and dispersive samples, quantify the obtained signal, and compare the measurements with traditional Z-scans. This technique is capable of measuring these nonlinearities in highly scattering samples.}, Doi = {10.1364/oe.16.004192}, Key = {fds232533} } @article{fds232532, Author = {Emami, K and Cadman, RV and Woodburn, JM and Fischer, MC and Kadlecek, SJ and Zhu, J and Pickup, S and Guyer, RA and Law, M and Vahdat, V and Friscia, ME and Ishii, M and Yu, J and Gefter, WB and Shrager, JB and Rizi, RR}, Title = {Early changes of lung function and structure in an elastase model of emphysema—a hyperpolarized3He MRI study}, Journal = {Journal of Applied Physiology}, Volume = {104}, Number = {3}, Pages = {773-786}, Publisher = {American Physiological Society}, Year = {2008}, Month = {March}, ISSN = {8750-7587}, url = {http://dx.doi.org/10.1152/japplphysiol.00482.2007}, Abstract = {<jats:p>Early changes of lung function and structure were studied in the presence of an elastase-induced model of emphysema in 35 Sprague-Dawley rats at mild (5 U/100 g) and moderate (10 U/100 g) severities. Lung ventilation was measured on a regional basis (at a planar resolution of 3.2 mm) by hyperpolarized<jats:sup>3</jats:sup>He MRI at 5 and 10 wk after model induction. Subsequent to imaging, average alveolar diameter was measured from histological slices taken from the centers of each lobe. Changes of mean fractional ventilation, mean linear intercept, and intrasubject heterogeneity of ventilation were studied during disease progression. Mean fractional ventilation was significantly different between healthy controls (0.23 ± 0.04) and emphysematous animals at both time points in the 10-unit group (0.06 ± 0.02 and 0.12 ± 0.05, respectively). Changes in average alveolar diameter were not statistically observable until the 10th wk between healthy (37 ± 10 μm) and emphysematous rats (73 ± 25 and 95 ± 31 μm, for 5 and 10 units, respectively). Assessment of function-structure correlation suggested that the majority of the decline in fractional ventilation occurred in the first 5 wk, while enlargement of alveolar diameters appeared primarily between the 5th and 10th wk. A thresholding metric, based on the 20th percentile of fractional ventilation over the entire lung, was utilized to detect the onset of the disease with confidence, independent of whether the regional ventilation measurements were normalized with respect to the delivered tidal volume and estimated functional residual capacity of each individual rat.</jats:p>}, Doi = {10.1152/japplphysiol.00482.2007}, Key = {fds232532} } @article{fds232535, Author = {Fischer, MC and Liu, HC and Piletic, IR and Escobedo-Lozoya, Y and Yasuda, R and Warren, WS}, Title = {Self-phase modulation signatures of neuronal activity}, Journal = {Optics Letters}, Volume = {33}, Number = {3}, Pages = {219-219}, Publisher = {Optica Publishing Group}, Year = {2008}, Month = {February}, ISSN = {0146-9592}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18246134}, Abstract = {We use phase-sensitive detection of spectral hole refilling to demonstrate strong novel intrinsic nonlinear signatures of neuronal activation in hippocampal brain slices. The ability to gain access to this fundamentally new intrinsic contrast with modest power levels suggests a new approach to in vivo neural imaging. We expect that we can extrapolate our method to high spatial and temporal resolution in deep tissue while retaining the noninvasive character.}, Doi = {10.1364/ol.33.000219}, Key = {fds232535} } @article{fds232479, Author = {Liu, HC and Fischer, MC and Samineni, P and Escobedo-Lozoya, Y and Yasuda, R and Warren, WS}, Title = {Intrinsic nonlinear optical signatures of neuronal activity}, Journal = {Optics InfoBase Conference Papers}, Year = {2008}, Month = {January}, ISBN = {9781557528612}, Abstract = {Using novel femtosecond laser pulse shaping techniques and a virtually background-free detection strategy we demonstrate strong self-phase modulation signatures of neuronal activity in hippocampal brain slices without the use of exogenous contrast agents. © 2008 Optical Society of America.}, Key = {fds232479} } @article{fds232480, Author = {Fischer, MC and Liu, HC and Fu, D and Semineni, P and Matthews, T and Piletic, I and Warren, WS}, Title = {Femtosecond laser pulse shaping for molecular imaging in biological tissue}, Journal = {Optics InfoBase Conference Papers}, Year = {2008}, Month = {January}, ISBN = {9781557528612}, Abstract = {Recently developed ultrafast laser pulse shaping technology allows highsensitivity measurements of nonlinear optical effects in highly scattering media. We present applications of these techniques to extract intrinsic structural, metabolic and functional contrast in biological tissue. © 2008 OSA.}, Key = {fds232480} } @article{fds232481, Author = {Piletic, IR and Fischer, MC and Samineni, P and Warren, WS}, Title = {Accessing nonlinear contrast in imaging using rapid pulse shaping techniques}, Journal = {Optics InfoBase Conference Papers}, Year = {2008}, Month = {January}, ISBN = {9781557528612}, Abstract = {We have designed an interferometric acousto-optic pulse shaper capable of shaping individual pulses differently from a mode-locked laser. The design enables the measurement of weak nonlinear optical signals at megahertz (MHz) rates for imaging applications. © 2008 Optical Society of America.}, Key = {fds232481} } @article{fds350779, Author = {Fischer, MC and Liu, HC and Fu, D and Semineni, P and Matthews, T and Piletic, I and Warren, WS}, Title = {Femtosecond laser pulse shaping for molecular imaging in biological tissue}, Journal = {Optics InfoBase Conference Papers}, Year = {2008}, Month = {January}, ISBN = {9781557528612}, url = {http://dx.doi.org/10.1364/fio.2008.ftuy1}, Abstract = {Recently developed ultrafast laser pulse shaping technology allows highsensitivity measurements of nonlinear optical effects in highly scattering media. We present applications of these techniques to extract intrinsic structural, metabolic and functional contrast in biological tissue. © 2008 OSA.}, Doi = {10.1364/fio.2008.ftuy1}, Key = {fds350779} } @article{fds349890, Author = {Liu, HC and Fischer, MC and Samineni, P and Escobedo-Lozoya, Y and Yasuda, R and Warren, WS}, Title = {Intrinsic nonlinear optical signatures of neuronal activity}, Journal = {Optics InfoBase Conference Papers}, Year = {2008}, Month = {January}, ISBN = {9781557528612}, url = {http://dx.doi.org/10.1364/fio.2008.fwd2}, Abstract = {Using novel femtosecond laser pulse shaping techniques and a virtually background-free detection strategy we demonstrate strong self-phase modulation signatures of neuronal activity in hippocampal brain slices without the use of exogenous contrast agents. © 2008 Optical Society of America.}, Doi = {10.1364/fio.2008.fwd2}, Key = {fds349890} } @article{fds351261, Author = {Piletic, IR and Fischer, MC and Samineni, P and Warren, WS}, Title = {Accessing nonlinear contrast in imaging using rapid pulse shaping techniques}, Journal = {Optics InfoBase Conference Papers}, Year = {2008}, Month = {January}, ISBN = {9781557528612}, url = {http://dx.doi.org/10.1364/fio.2008.ftuy3}, Abstract = {We have designed an interferometric acousto-optic pulse shaper capable of shaping individual pulses differently from a mode-locked laser. The design enables the measurement of weak nonlinear optical signals at megahertz (MHz) rates for imaging applications. © 2008 Optical Society of America.}, Doi = {10.1364/fio.2008.ftuy3}, Key = {fds351261} } @article{fds232510, Author = {Fischer, MC and Liu, H and Piletic, IR and Ye, T and Yasuda, R and Warren, WS}, Title = {Self-phase modulation and two-photon absorption imaging of cells and active neurons}, Journal = {Progress in Biomedical Optics and Imaging - Proceedings of SPIE}, Volume = {6442}, Pages = {64421J}, Booktitle = {Multiphoton Micr. in the Biomed. Sciences VII, Proc. SPIE}, Publisher = {SPIE}, Year = {2007}, Month = {September}, ISBN = {9780819465559}, ISSN = {1605-7422}, url = {http://dx.doi.org/10.1117/12.698693}, Abstract = {Even though multi-photon fluorescence microscopy offers higher resolution and better penetration depth than traditional fluorescence microscopy, its use is restricted to the detection of molecules that fluoresce. Two-photon absorption (TPA) imaging can provide contrast in non-fluorescent molecules while retaining the high resolution and sectioning capabilities of nonlinear imaging modalities. In the long-wavelength water window, tissue TPA is dominated by the endogenous molecules melanin and hemoglobin with an almost complete absence of endogenous two-photon fluorescence. A complementary nonlinear contrast mechanism is self-phase modulation (SPM), which can provide intrinsic signatures that can depend on local tissue anisotropy, chemical environment, or other structural properties. We have developed a spectral hole refilling measurement technique for TPA and SPM measurements using shaped ultrafast laser pulses. Here we report on a microscopy setup to simultaneously acquire 3D, high-resolution TPA and SPM images. We have acquired data in mounted B16 melanoma cells with very modest laser power levels. We will also discuss the possible application of this measurement technique to neuronal imaging. Since SPM is sensitive to material structure we can expect SPM properties of neurons to change during neuronal firing. Using our hole-refilling technique we have now demonstrated strong novel intrinsic nonlinear signatures of neuronal activation in a hippocampal brain slice. The observed changes in nonlinear signal upon collective activation were up to factors of two, unlike other intrinsic optical signal changes on the percent level. These results show that TPA and SPM imaging can provide important novel functional contrast in tissue using very modest power levels suitable for in vivo applications.}, Doi = {10.1117/12.698693}, Key = {fds232510} } @article{fds232536, Author = {Warren, WS and Fischer, MC and Tong, Y}, Title = {Novel nonlinear contrast improves deep-tissue microscopy}, Journal = {Laser Focus World}, Volume = {43}, Number = {6}, Pages = {99-103}, Publisher = {PENNWELL PUBL CO}, Year = {2007}, Month = {June}, ISSN = {1043-8092}, Abstract = {Femtosecond laser pulse and pulse-train shaping allow detection of new nonlinear effects, with modest powers, making new biomarkers accessible and permitting deeper tissue imaging than conventional microscopy. The most developed of these technique create light at a new wavelength, which can then be separated from the exciting laser. While the two photon fluorescence (TPF) can be induced by continuous wave lasers, the vast majority of studies use short laser pulses to achieve high peak power with relatively low tissue damage from average power dissipation. Two photon absorption (TPA) and self-phase modulation (SPM) are the two most important single-wavelength effect for the purpose of tissue engineering. TPA is more effective on the intense pulses than on the weak ones, and it thus distorts the amplitude modulation, creating extra sidebands. Microscopic resolution to depths of about 1mm should be achievable in most tissues with far more physiological contrast than conventional microscopy.}, Key = {fds232536} } @article{fds232509, Author = {Kadlecek, SJ and Emami, K and Fischer, MC and Ishii, M and Yu, J and Woodburn, JM and NikKhah, M and Vahdat, V and Lipson, DA and Baumgardner, JE and Rizi, RR}, Title = {Corrigendum to “Imaging physiological parameters with hyperpolarized gas MRI” Progress in NMR Spectrosc. 47 (2005) 187}, Journal = {Progress in Nuclear Magnetic Resonance Spectroscopy}, Volume = {48}, Number = {4}, Pages = {233-235}, Publisher = {Elsevier BV}, Year = {2006}, Month = {July}, ISSN = {0079-6565}, url = {http://dx.doi.org/10.1016/j.pnmrs.2006.05.001}, Doi = {10.1016/j.pnmrs.2006.05.001}, Key = {fds232509} } @article{fds232508, Author = {Ye, T and Yurtsever, G and Fischer, M and Simon, JD and Warren, WS}, Title = {Imaging melanin by two-photon absorption microscopy}, Journal = {Proceedings of SPIE - The International Society for Optical Engineering}, Volume = {6089}, Pages = {60891X}, Booktitle = {Multiphoton Micr. in the Biomed. Sciences VI, Proc. SPIE}, Publisher = {SPIE}, Year = {2006}, Month = {May}, ISBN = {9780819461315}, ISSN = {0277-786X}, url = {http://dx.doi.org/10.1117/12.646139}, Abstract = {Multiphoton excitation fluorescence microscopy has proven to be a powerful method for non-invasive, in vivo, thick tissue imaging with molecular specificity. However, many important endogenous biomolecules do not fluoresce (NAD) or fluoresce with low efficiency (Melanin). In this report femtosecond pulse shaping methods are used to measure two-photon absorption (TPA) directly with very high sensitivity. Combining with the laser scanning microscope, this Two-photon Absorption Microscopy (TPAM) retains the penetration and localization advantages of two-photon fluorescence microscopy and permits direct observation of important endogenous molecular markers (melanin or hemoglobin) which are invisible in multiphoton fluorescence microscopy. We have demonstrated here for the first time that TPAM can successfully and more efficiently image melanoma cells and tissues and provide a good melanin contrast in optical sectioning of the melanoma lesions which are comparable to pathological histology. Combining with the two-photon fluorescence images acquired simultaneously, the distribution patterns of the melanocytes and their intratissue behavior could be studied without cutting the lesions from patients. TPAM will undoubtedly find the applications in the clinical diagnosis and biomedical research.}, Doi = {10.1117/12.646139}, Key = {fds232508} } @article{fds232476, Author = {Warren, WS and Ye, T and Fischer, M and Yurtsever, G and Li, C and Liu, H and Fu, D}, Title = {Deep tissue imaging with shaped femtosecond laser pulses}, Journal = {Optics InfoBase Conference Papers}, Year = {2006}, Month = {January}, ISBN = {9781557528100}, Abstract = {Two-photon absorption and self phase modulation can be detected deep in tissue with modest laser powers, using shaped femtosecond pulses. This permit microscopic-resolution images of biologically important targets. © 2006 Optical Society of America.}, Key = {fds232476} } @article{fds232541, Author = {KADLECEK, S and EMAMI, K and FISCHER, M and ISHII, M and YU, J and WOODBURN, J and NIKKHAH, M and VAHDAT, V and LIPSON, D and BAUMGARDNER, J}, Title = {Imaging physiological parameters with hyperpolarized gas MRI}, Journal = {Progress in Nuclear Magnetic Resonance Spectroscopy}, Volume = {47}, Number = {3-4}, Pages = {187-212}, Publisher = {Elsevier BV}, Year = {2005}, Month = {December}, ISSN = {0079-6565}, url = {http://dx.doi.org/10.1016/j.pnmrs.2005.08.006}, Abstract = {A survey capable of producing the desired physiological information from a series of polarized gas MR images is discussed. Salient requirements of an ideal radiological method for quantitative assessment of lung function are also discussed. The benefits of polarized gas MRI are clarified through a comparison with other existing modalities. The optical pumping methods for the generation of hyperpolarization and the technical aspects of gas delivery and storage are presented. Imaging techniques such as MR-based coronary angiography, and PET/SPECT tests have advanced together with extremely effective therapies and surgical procedures.}, Doi = {10.1016/j.pnmrs.2005.08.006}, Key = {fds232541} } @article{fds232552, Author = {Fischer, MC and Kadlecek, S and Yu, J and Ishii, M and Emami, K and Vahdat, V and Lipson, DA and Rizi, RR}, Title = {Measurements of Regional Alveolar Oxygen Pressure Using Hyperpolarized 3He MRI1}, Journal = {Academic Radiology}, Volume = {12}, Number = {11}, Pages = {1430-1439}, Publisher = {Elsevier BV}, Year = {2005}, Month = {November}, ISSN = {1076-6332}, url = {http://dx.doi.org/10.1016/j.acra.2005.07.007}, Abstract = {<h4>Rationale and objectives</h4>The aim of this work is to review hyperpolarized (HP) helium-3 (3He) magnetic resonance imaging (MRI) methods to measure regional alveolar oxygen partial pressure (P(A)O2) and oxygen depletion rate (R) in the lung. We point out limitations of the methods and suggest improvements to increase their accuracy.<h4>Materials and methods</h4>P(A)O2 and R can be extracted from series of HP gas images acquired during breath hold by making use of the depolarizing effect of oxygen on HP gas. To separate oxygen-induced depolarization from other depolarizing effects, several techniques can be used. We review currently used techniques and point out their advantages and limitations.<h4>Results</h4>We show that the precision of oxygen measurements depends on a variety of parameters and can vary within the measurement volume. Accuracy of the measurement also can be influenced by diffusion of oxygen and polarized 3He and generally is different for single-slice and multislice measurements. We present numerical simulations, phantom data, and in vivo data for illustration.<h4>Conclusion</h4>HP 3He MRI is a noninvasive, nonionizing, and repeatable imaging method that allows for quantitative analysis of lung function. The current techniques for measuring P(A)O2 have the potential to deliver clinically relevant functional images.}, Doi = {10.1016/j.acra.2005.07.007}, Key = {fds232552} } @article{fds232553, Author = {Haczku, A and Emami, K and Fischer, MC and Kadlecek, S and Ishii, M and Panettieri, RA and Rizi, RR}, Title = {Hyperpolarized 3He MRI in Asthma}, Journal = {Academic Radiology}, Volume = {12}, Number = {11}, Pages = {1362-1370}, Publisher = {Elsevier BV}, Year = {2005}, Month = {November}, ISSN = {1076-6332}, url = {http://dx.doi.org/10.1016/j.acra.2005.08.027}, Abstract = {<h4>Rationale and objectives</h4>Quantitative regional measurement of physiological parameters of lung may improve both early detection of asthma and its response to treatment by elucidating the characteristics of airway obstruction. Recent emergence of hyperpolarized helium-3 magnetic resonance imaging as a sensitive pulmonary imaging tool has shown great potential in capturing important structural and functional aspects of normal and diseased lungs. The objective of this study was to investigate regional ventilation changes in the mouse lung following allergen sensitization and challenge.<h4>Materials and methods</h4>A murine model of allergic airway inflammation was created in mice following allergen challenge using Af and IgE-mediated asthma. The creation of model was verified using pulmonary function test and histology. Regional fractional ventilation was then measured in the animals using hyperpolarized 3He MRI on a pixel-by-pixel basis with a planar resolution of 0.24 mm. The sensitized and healthy animals were then compared statistically to assess the potential sensitivity of this technique in detection of such pulmonary abnormalities.<h4>Results</h4>In this work, we have demonstrated for the first time the quantitative measurement of regional ventilation in normal and asthmatic mice. Results of this study show significant changes in regional ventilation in murine model of allergic airway sensitization compared with that in normal control animals.<h4>Conclusion</h4>Further development of this technique can potentially serve as a quantitative marker to investigate the physiology of allergen-induced airway hyperresponsiveness and to assist in disease treatment and prevention.}, Doi = {10.1016/j.acra.2005.08.027}, Key = {fds232553} } @article{fds232545, Author = {Fischer, MC and Ye, T and Yurtsever, G and Miller, A and Ciocca, M and Wagner, W and Warren, WS}, Title = {Two-photon absorption and self-phase modulation measurements with shaped femtosecond laser pulses}, Journal = {Optics Letters}, Volume = {30}, Number = {12}, Pages = {1551-1551}, Publisher = {Optica Publishing Group}, Year = {2005}, Month = {June}, ISSN = {0146-9592}, url = {http://dx.doi.org/10.1364/ol.30.001551}, Abstract = {We show that phase-sensitive detection of spectral hole refilling can yield information about self-phase modulation and two-photon absorption coefficients. We expect that, when applied to tissue microscopy, this technique will allow the study of endogenous molecular markers beneath the surface, even if those markers are nonfluorescent.}, Doi = {10.1364/ol.30.001551}, Key = {fds232545} } @article{fds304370, Author = {Spector, ZZ and Emami, K and Fischer, MC and Zhu, J and Ishii, M and Vahdat, V and Yu, J and Kadlecek, S and Driehuys, B and Lipson, DA and Gefter, W and Shrager, J and Rizi, RR}, Title = {Quantitative assessment of emphysema using hyperpolarized 3He magnetic resonance imaging.}, Journal = {Magn Reson Med}, Volume = {53}, Number = {6}, Pages = {1341-1346}, Year = {2005}, Month = {June}, ISSN = {0740-3194}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15906306}, Abstract = {In this experiment, Sprague-Dawley rats with elastase-induced emphysema were imaged using hyperpolarized (3)He MRI. Regional fractional ventilation r, the fraction of gas replaced with a single tidal breath, was calculated from a series of images in a wash-in study of hyperpolarized gas. We compared the regional fractional ventilation in these emphysematous rats to the regional fractional ventilations we calculated from a previous baseline study in healthy Sprague-Dawley rats. We found that there were differences in the maps of fractional ventilation and its associated frequency distribution between the healthy and emphysematous rat lungs. Fractional ventilation tended to be much lower in emphysematous rats than in normal rats. With this information, we can use data on fractional ventilation to regionally distinguish between healthy and emphysematous portions of the lung. The successful implementation of such a technique on a rat model could lead to work toward the future implementation of this technique in human patients.}, Doi = {10.1002/mrm.20514}, Key = {fds304370} } @article{fds232475, Author = {Fischer, MC and Ye, T and Yurtsever, G and Miller, A and Ciocca, M and Wagner, W and Warren, WS}, Title = {Two-photon absorption and self-phase modulation measurements with shaped femtosecond laser pulses}, Journal = {2005 Conference on Lasers and Electro-Optics, CLEO}, Volume = {2}, Pages = {968-970}, Year = {2005}, Month = {January}, ISBN = {9781557527950}, ISSN = {2162-2701}, url = {http://dx.doi.org/10.1109/cleo.2005.201992}, Abstract = {We demonstrate experimentally that phase sensitive detection of spectral hole refilling can yield information about self-phase modulation and two-photon absorption coefficients. © 2005 Optical Society of America.}, Doi = {10.1109/cleo.2005.201992}, Key = {fds232475} } @article{fds232528, Author = {Ye, T and Fischer, M and Yurtsever, G and Warren, WS}, Title = {Two-photon absorption microscopy of tissue}, Journal = {Optics InfoBase Conference Papers}, Volume = {2}, Pages = {1512-1514}, Booktitle = {Proc. of the Conf. on Lasers and Electro-Optics}, Year = {2005}, Month = {January}, ISBN = {9781557527707}, ISSN = {2162-2701}, Abstract = {Two-photon absorption microscopy (TPAM) has been demonstrated to be able to image melanin with high sensitivity. TPAM opens up a wide range of nonfluorescent molecular targets. © 2005 Optical Society of America.}, Key = {fds232528} } @article{fds232542, Author = {Ishii, M and Fischer, MC and Emami, K and Alavi, A and Spector, ZZ and Yu, J and Baumgardner, JE and Itkin, M and Kadlecek, SJ and Zhu, J and Bono, M and Gefter, WB and Lipson, DA and Shrager, JB and Rizi, RR}, Title = {Hyperpolarized helium-3 MR imaging of pulmonary function.}, Journal = {Radiol Clin North Am}, Volume = {43}, Number = {1}, Pages = {235-246}, Year = {2005}, Month = {January}, url = {http://dx.doi.org/10.1016/j.rcl.2004.09.010}, Abstract = {Recent advances in HP MR imaging contrast agents have led to novel tests of pulmonary function. Many of these tests show promise in the clinical arena.}, Doi = {10.1016/j.rcl.2004.09.010}, Key = {fds232542} } @article{fds232505, Author = {Ye, T and Wagner, W and Tian, P and Yurtsever, G and Fischer, M and Warren, WS}, Title = {Deep tissue imaging approaches by direct capture of two-photon absorption}, Journal = {2004 2nd IEEE International Symposium on Biomedical Imaging: Macro to Nano}, Volume = {1}, Pages = {668-671}, Booktitle = {Proc. IEEE Int. Symp. on Biomed. Imag.}, Year = {2004}, Month = {December}, ISBN = {9780780383883}, Abstract = {Multiphoton imaging with fluorescence detection has proven to be a powerful method for moderately deep tissue imaging (less than 1 mm) with molecular specificity. However, many important endogenous biomolecules do not fluoresce (NAD) or with low efficiency (Melanin). In this paper two femtosecond pulse shaping methods have been demonstrated to detect two-photon absorption (TPA), instead of fluorescence, with high sensitivity, which opens up a wide range of molecular targets. It also facilitates longer excitation wavelengths, which permit greater tissue penetration. Developing the imaging system by using these new methods will be also discussed. © 2004 IEEE.}, Key = {fds232505} } @article{fds232506, Author = {Warren, WS and Miller, A and Wagner, W and Ye, T and Fischer, M and Yurtsever, G}, Title = {Two-photon absorption imaging with shaped femtosecond laser pulses}, Journal = {Springer Series in Chemical Physics}, Volume = {79}, Pages = {867-869}, Booktitle = {Ultrafast Phenomena XIV}, Publisher = {Springer-Verlag}, Year = {2004}, Month = {December}, ISSN = {0172-6218}, Abstract = {Femtosecond laser pulse shaping permits background-free detection of two-photon absorption, which tends to refill spectral holes. This opens up new spectroscopic windows for monitoring tissue characteristics.}, Key = {fds232506} } @article{fds232540, Author = {Fischer, MC and Spector, ZZ and Ishii, M and Yu, J and Emami, K and Itkin, M and Rizi, R}, Title = {Single-acquisition sequence for the measurement of oxygen partial pressure by hyperpolarized gas MRI.}, Journal = {Magn Reson Med}, Volume = {52}, Number = {4}, Pages = {766-773}, Year = {2004}, Month = {October}, url = {http://dx.doi.org/10.1002/mrm.20239}, Abstract = {Magnetic resonance imaging (MRI) with hyperpolarized 3-helium gas (HP 3He) offers the possibility of studying functional lung parameters such as the alveolar oxygen concentration and oxygen depletion rate. Until now, a double-acquisition technique has been utilized to extract these parameters. A complicated single-acquisition technique was previously developed to avoid the necessity of performing two identical breathing maneuvers. The results obtained with this technique were significantly less accurate than the results obtained with the double-acquisition method. In this work, a novel, easily implemented single-acquisition sequence is presented that provides results comparable to those obtained with the established double-acquisition method. This method is demonstrated in a phantom and a pig model on a 1.5 T scanner using a 2D fast low-angle shot (FLASH) gradient-echo sequence. Numerical simulations of the time evolution of the oxygen concentration were performed. Simulation results are presented to support the experimental data. Various parameter regimes were experimentally and numerically investigated.}, Doi = {10.1002/mrm.20239}, Key = {fds232540} } @article{fds232543, Author = {Spector, ZZ and Emami, K and Fischer, MC and Zhu, J and Ishii, M and Yu, J and Kadlecek, S and Driehuys, B and Panettieri, RA and Lipson, DA and Gefter, W and Shrager, J and Rizi, RR}, Title = {A small animal model of regional alveolar ventilation using HP 3He MRI1.}, Journal = {Acad Radiol}, Volume = {11}, Number = {10}, Pages = {1171-1179}, Year = {2004}, Month = {October}, ISSN = {1076-6332}, url = {http://www.ncbi.nlm.nih.gov/pubmed/15530811}, Abstract = {RATIONALE AND OBJECTIVES: The aim of this study was to establish a standardized procedure for the measurement of regional fractional ventilation in a healthy rat model as a baseline for further studies of pulmonary disorder models. MATERIALS AND METHODS: The lungs of five healthy male Sprague-Dawley rats were imaged using hyperpolarized helium-3 magnetic resonance imaging. From these images, regional fractional ventilation was calculated and maps generated detailing the distribution of fractional ventilation in the lung. The 1.56 mm x 1.56 mm x 4 mm regions of interest were assigned on 5 cm x 5 cm field of view lung maps. Histograms were also generated showing the frequency distribution of fractional ventilation values. To compare fractional ventilation values between animals, the ventilation procedure was standardized to results from individual pulmonary function tests. Each animal's spontaneous tidal volume, respiratory rate, and inspiration percentage (percent of total respiratory cycle in inspiration) were used in their mechanical ventilation settings. RESULTS: Results were similar among all five healthy rats based on examination of ventilation distribution maps and frequency distribution histograms. Mean (0.13) and standard deviation (0.07) were calculated for fractional ventilation in each animal. However, these values were determined to be influenced by slice selection, and therefore the maps and histograms were favored in analysis of results. CONCLUSION: This study shows consistent results in healthy rat lungs and will serve as a baseline study for future measurements in emphysematous rat lungs.}, Doi = {10.1016/j.acra.2004.08.001}, Key = {fds232543} } @article{fds365591, Author = {Warren, WS and Miller, A and Wagner, W and Ye, T and Fischer, M and Yurtsever, G}, Title = {Two-photon absorption imaging and self-phase modulation imaging with shaped laser pulses}, Journal = {Optics InfoBase Conference Papers}, Year = {2004}, Month = {January}, ISBN = {1557527733}, Abstract = {We present a new method for deep tissue imaging using nonlinear optics. Specific tailored laser pulses permit measurement of two-photon absorption or self-phase modulation with modest near-IR powers (1-10 mW), giving good penetration and molecular specificity.}, Key = {fds365591} } @article{fds365772, Author = {Warren, WS and Miller, A and Wagner, W and Ye, T and Fischer, M and Yurtsever, G}, Title = {Two-photon absorption imaging with shaped femtosecond laser pulses}, Journal = {Optics InfoBase Conference Papers}, Year = {2004}, Month = {January}, ISBN = {3540241108}, Abstract = {Femtosecond laser pulse shaping permits background-free detection of two-photon absorption, which tends to refill spectral holes. This opens up new spectroscopic windows for monitoring tissue characteristics.}, Key = {fds365772} } @article{fds232539, Author = {Fischer, MC and Gupta, GC and Wang, LL and Kojima, K and Mizuhara, O and Swaminathan, V}, Title = {FEC performance under optical power transient conditions}, Journal = {IEEE Photonics Technology Letters}, Volume = {15}, Number = {11}, Pages = {1654-1656}, Publisher = {Institute of Electrical and Electronics Engineers (IEEE)}, Year = {2003}, Month = {November}, url = {http://dx.doi.org/10.1109/lpt.2003.818665}, Abstract = {We report the investigation of the performance of an interleaved Reed-Solomon forward error correction code in the presence of optical power transients for the first time. These transients were generated by adding-dropping channels in an erbium-doped fiber amplifier or Raman amplified systems.}, Doi = {10.1109/lpt.2003.818665}, Key = {fds232539} } @article{fds232551, Author = {Soole, JBD and Pafchek, R and Narayanan, C and Bogert, G and Jampanaboyana, L and Chand, N and Yu, J and Fischer, M and Ling, M and Earnshaw, MP and Kojima, K and Swaminathan, V}, Title = {DWDM performance of a packaged reconfigurable optical add-drop multiplexer subsystem supporting modular systems growth}, Journal = {IEEE Photonics Technology Letters}, Volume = {15}, Number = {11}, Pages = {1600-1602}, Publisher = {Institute of Electrical and Electronics Engineers (IEEE)}, Year = {2003}, Month = {November}, url = {http://dx.doi.org/10.1109/lpt.2003.818673}, Abstract = {We describe dense wavelength-division-multiplexing (DWDM) operation of a reconfigurable optical add-drop multiplexer subsystem module employing silica waveguide technology that is suitable for use with both fixed-wavelength and wavelength-selectable add-drop transceivers. We illustrate its use in providing modular growth in high channel-count DWDM systems.}, Doi = {10.1109/lpt.2003.818673}, Key = {fds232551} } @article{fds53148, Author = {B. Gutiérrez-Medina and M. C. Fischer and M. G. Raizen}, Title = {Observation of the quantum Zeno and anti-Zeno effects in an unstable system}, Booktitle = {The Physics of Comm.: Proc. XXII Solvay Conf. Phys.}, Publisher = {World Scientific}, Editor = {Antoniou}, Year = {2003}, Key = {fds53148} } @article{fds232550, Author = {Jianjun Yu, and Fischer, M and Chand, N and Kojima, K and Swaminathan, V}, Title = {10-Gb/s transmission over 200-km conventional fiber without dispersion compensation using the bias control technique}, Journal = {IEEE Photonics Technology Letters}, Volume = {14}, Number = {12}, Pages = {1746-1748}, Publisher = {Institute of Electrical and Electronics Engineers (IEEE)}, Year = {2002}, Month = {December}, url = {http://dx.doi.org/10.1109/lpt.2002.804668}, Abstract = {Transmission of 10-Gb/s nonreturn-to-zero (NRZ) signal over 200 km conventional single-mode fiber without any dispersion compensation was discussed. A bias control technique involving simultaneous charge of α parameter of an LiNbO3 modulator (LN-MOD) and the extinction ratio was used. It was found that when the bias is shifted and the modulated voltage on the LN-MOD is fixed the chirp and the ER are changed simultaneously.}, Doi = {10.1109/lpt.2002.804668}, Key = {fds232550} } @article{fds232503, Author = {Kojima, K and Fischer, MC and Chand, N and Klotzkin, D and Kiely, PA and Sheridan-Eng, J and Xu, Y and Tohmon, G}, Title = {Effect of reflection on un-isolated spot-size-converted 1.3 μm DFB lasers for 2.5 Gbit/s transmission}, Journal = {Conference on Optical Fiber Communication, Technical Digest Series}, Volume = {70}, Pages = {473-475}, Year = {2002}, Month = {January}, ISBN = {1557527008}, Abstract = {Spot-size-converted 1.3 μm distributed feedback laser transmitter modules for 2.5 Gbit/s transmission, were fabricated. The laser was mounted on a submount, and fiber coupling was done passively. Reflection was defined as the ratio of optical power coming back into the transmitter. The lasers satisfied the SDH/SONET requirements for 15 km transmission with strong reflection up to -16.5 dB at various locations.}, Key = {fds232503} } @article{fds376532, Author = {Kojima, K and Fischer, MC and Chand, N and Klotzkin, D and Kiely, PA and Sheridan-Eng, J and Xu, Y and Tohmon, G}, Title = {Effect of reflection on un-isolated spot-size-converted 1.3 µm DFB lasers for 2.5 Gbit/s transmission}, Journal = {Optics InfoBase Conference Papers}, Pages = {473-475}, Year = {2002}, Month = {January}, Abstract = {We have fabricated SSC-DFB laser transmitter modules, which give enough output power, and can tolerate strong reflection. They satisfy the SDH/SONET requirements for transmission up to 15 km at 2.5 Gbit/s. Because of the expected low packaging cost, the transmitter modules are expected to play a big role in the metro/access market.}, Key = {fds376532} } @article{fds232549, Author = {Shin, DS and Wang, J and Bosch, F and Kiely, PA and Chand, N and Fischer, M and Kojima, K and Kasper, BL and Peral, EM and Ransijn, H}, Title = {10 Gbit∕s transmission over 50 km nonzero dispersion-shifted fibre using 1.3 [micro sign]m directly modulated uncooled transmitters}, Journal = {Electronics Letters}, Volume = {38}, Number = {16}, Pages = {864-864}, Publisher = {Institution of Engineering and Technology (IET)}, Year = {2002}, ISSN = {0013-5194}, url = {http://dx.doi.org/10.1049/el:20020606}, Abstract = {A 1.3 μm uncooled transmitter with wide-open eye diagrams at laser temperatures of 20, 50, and 85°C is presented. Using this transmitter, it is demonstrated that 10 Gbit/s transmission is possible over a 50 km nonzero dispersion-shifted Lucent TrueWave-RS fibre. This result is compared with transmission over a 55 km standard singlemode fibre.}, Doi = {10.1049/el:20020606}, Key = {fds232549} } @article{fds232501, Author = {Yu, J and Kojima, K and Chand, N and Fischer, MC and Espindola, R and Mason, TGB}, Title = {160GB/s single-channel unrepeatered transmission over 200km of non-zero dispersion shifted fiber}, Journal = {European Conference on Optical Communication, ECOC}, Volume = {6}, Pages = {20-21}, Year = {2001}, Month = {December}, Abstract = {Single-channel 160Gb/s unrepeated transmission over 200km of non-zero dispersion shifted fiber (NZDSF) was reported using distributed Raman amplification. Clock recovery and demultiplexing were realized simultaneously by cascading a tandem electro-absorption modulator (TEAM and another EAM. When 160Gbit/s signal was transmitted over 175km fiber span, the power penalty was found to be 1.8dB.}, Key = {fds232501} } @article{fds232504, Author = {Fischer, MC and Dudarev, AM and Gutiérrez-Medina, B and Raizen, MG}, Title = {FM spectroscopy in recoil-induced resonances}, Journal = {Journal of Optics B: Quantum and Semiclassical Optics}, Volume = {3}, Number = {4}, Pages = {279-287}, Publisher = {IOP Publishing}, Year = {2001}, Month = {August}, url = {http://dx.doi.org/10.1088/1464-4266/3/4/313}, Abstract = {We report on an experimental study of recoil-induced resonances as a method of velocimetry for cold atomic samples. We present a refined experimental method that greatly improves the sensitivity of the measurement over previous experiments. Using frequency-modulation (FM) spectroscopy techniques we achieve a sensitivity that approaches the shot noise limit. In addition, we present a novel approach to deriving the line shape of the observed signal, based on the concept of quantum transport and tunnelling in motional Bloch bands.}, Doi = {10.1088/1464-4266/3/4/313}, Key = {fds232504} } @article{fds232538, Author = {Fischer, MC and Gutiérrez-Medina, B and Raizen, MG}, Title = {Observation of the Quantum Zeno and Anti-Zeno Effects in an Unstable System}, Journal = {Physical Review Letters}, Volume = {87}, Number = {4}, Pages = {040402}, Publisher = {American Physical Society (APS)}, Year = {2001}, Month = {July}, ISSN = {0031-9007}, url = {http://dx.doi.org/10.1103/physrevlett.87.040402}, Abstract = {We report the first observation of the quantum Zeno and anti-Zeno effects in an unstable system. Cold sodium atoms are trapped in a far-detuned standing wave of light that is accelerated for a controlled duration. For a large acceleration the atoms can escape the trapping potential via tunneling. Initially the number of trapped atoms shows strong nonexponential decay features, evolving into the characteristic exponential decay behavior. We repeatedly measure the number of atoms remaining trapped during the initial period of nonexponential decay. Depending on the frequency of measurements we observe a decay that is suppressed or enhanced as compared to the unperturbed system.}, Doi = {10.1103/physrevlett.87.040402}, Key = {fds232538} } @article{fds323189, Author = {Gutiérrez-Medina, B and Fischer, MC and Raizen, MG}, Title = {Observation of the quantum zeno and anti-zeno effects in an unstable system}, Journal = {Technical Digest - Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, QELS 2001}, Pages = {QPD1.1-QPD1.2}, Publisher = {Opt. Soc. America}, Year = {2001}, Month = {January}, ISBN = {9781557526632}, url = {http://dx.doi.org/10.1109/QELS.2001.962243}, Abstract = {We study the motion of ultra-cold atoms in an accelerating optical lattice. We find that the tunneling dynamics are strongly affected by repeated measurement during the non-exponential time, leading to either inhibition (zeno) or enhancement (anti-zeno) of decay.}, Doi = {10.1109/QELS.2001.962243}, Key = {fds323189} } @article{fds232548, Author = {Madison, KW and Fischer, MC and Raizen, MG}, Title = {Observation of the Wannier-Stark fan and the fractional ladder in an accelerating optical lattice}, Journal = {Physical Review A}, Volume = {60}, Number = {3}, Pages = {R1767-R1770}, Publisher = {American Physical Society (APS)}, Year = {1999}, Month = {September}, url = {http://dx.doi.org/10.1103/physreva.60.r1767}, Abstract = {We report an experimental study of the Wannier-Stark fan and the fractional Wannier-Stark ladder using laser-cooled sodium atoms in an accelerating one-dimensional standing wave of light. We prepare the atoms in the lowest motional band of the optical lattice and then impose a constant acceleration. A weak oscillatory component is added to the acceleration in order to resonantly drive interband transitions, and the number of atoms that remain in the lowest band is measured as a function of the probe frequency. The spectrum is characterized by a ladder of resonances spaced by the atomic Bloch oscillation frequency [Formula Presented] When an additional, strong ac component at frequency [Formula Presented] is added, a fractional ladder is observed with a spacing related to the electric matching ratio [Formula Presented]. © 1999 The American Physical Society.}, Doi = {10.1103/physreva.60.r1767}, Key = {fds232548} } @article{fds365339, Author = {Fischer, MC and Madison, KW and Diener, RB and Niu, Q and Raizen, MG}, Title = {Dynamical Bloch band suppression in an optical lattice}, Journal = {IQEC, International Quantum Electronics Conference Proceedings}, Pages = {239-240}, Year = {1999}, Month = {January}, ISBN = {1557525714}, Abstract = {The first observation of dynamical suppression of Bloch bands due to an AC field is presented. The system consists of laser-cooled atoms in an optical lattice. The neutral sodium atoms in the lowest band of a 1D optical lattice are trapped. The position of the potential to realize both an intense AC field and a weak spectroscopic probe is modulated in order to directly observed band suppressions. In the theoretical analysis, the quasienergies and the corresponding coupling strengths between the first and higher bands are calculated in order to generate a prediction for the experimental spectral distributions. This calculation goes beyond the single-band and tight-binding approximations, and is in good agreement with the observed spectra.}, Key = {fds365339} } @article{fds376587, Author = {Fischer, MC and Madison, KW and Diener, RB and Niu, Q and Raizen, MG}, Title = {Dynamical Bloch band suppression in an optical lattice}, Journal = {Optics InfoBase Conference Papers}, Year = {1999}, Month = {January}, Key = {fds376587} } @article{fds232547, Author = {Madison, KW and Fischer, MC and Diener, RB and Niu, Q and Raizen, MG}, Title = {Dynamical Bloch Band Suppression in an Optical Lattice}, Journal = {Physical Review Letters}, Volume = {81}, Number = {23}, Pages = {5093-5096}, Publisher = {American Physical Society (APS)}, Year = {1998}, Month = {December}, url = {http://dx.doi.org/10.1103/physrevlett.81.5093}, Abstract = {The first observation of dynamical suppression of Bloch bands due to an AC field is presented. The system consists of laser-cooled atoms in an optical lattice. The neutral sodium atoms in the lowest band of a 1D optical lattice are trapped. The position of the potential to realize both an intense AC field and a weak spectroscopic probe is modulated in order to directly observed band suppressions. In the theoretical analysis, the quasienergies and the corresponding coupling strengths between the first and higher bands are calculated in order to generate a prediction for the experimental spectral distributions. This calculation goes beyond the single-band and tight-binding approximations, and is in good agreement with the observed spectra.}, Doi = {10.1103/physrevlett.81.5093}, Key = {fds232547} } @article{fds232537, Author = {Fischer, MC and Madison, KW and Niu, Q and Raizen, MG}, Title = {Observation of Rabi oscillations between Bloch bands in an optical potential}, Journal = {Physical Review A}, Volume = {58}, Number = {4}, Pages = {R2648-R2651}, Publisher = {American Physical Society (APS)}, Year = {1998}, Month = {October}, url = {http://dx.doi.org/10.1103/physreva.58.r2648}, Abstract = {We report an experimental study of atomic motion in the Bloch band of a periodic potential. Our system consists of cold sodium atoms in a far detuned standing wave of near resonant light. We prepare the atoms in the lowest motional band, and then impose phase modulation in order to drive interband transitions. We observe Rabi oscillations between the first and second band as a function of modulation intensity and frequency. We also observe damped oscillations of the population as a function of modulation frequency, which are primarily due to a spread in Rabi frequencies over the Bloch band. © 1998 The American Physical Society.}, Doi = {10.1103/physreva.58.r2648}, Key = {fds232537} } @article{fds232527, Author = {Madison, KW and Fischer, MC and Niu, Q and Raizen, MG}, Title = {Nonexponential decay in atomic tunneling}, Journal = {Technical Digest - European Quantum Electronics Conference}, Pages = {24}, Year = {1998}, Month = {January}, Abstract = {A simple model of the band structure with a single (trapped) band separated by a bandgap from a free particle state is used to study short-time deviation from exponential decay in a quantum tunneling experiment. The system consists of ultracold sodium atoms that are trapped in an accelerating periodic optical potential created by a standing wave of light. Atoms can escape the wells via a quantum tunneling, and the number that remain is measured as a function of interaction time for a fixed value of the well depth and acceleration.}, Key = {fds232527} } @article{fds232546, Author = {Wilkinson, SR and Bharucha, CF and Fischer, MC and Madison, KW and Morrow, PR and Niu, Q and Sundaram, B and Raizen, MG}, Title = {Experimental evidence for non-exponential decay in quantum tunnelling}, Journal = {Nature}, Volume = {387}, Number = {6633}, Pages = {575-577}, Publisher = {Springer Science and Business Media LLC}, Year = {1997}, Month = {June}, url = {http://dx.doi.org/10.1038/42418}, Abstract = {An exponential decay law is the universal hallmark of unstable systems and is observed in all fields of science. This law is not, however, fully consistent with quantum mechanics and deviations from exponential decay have been predicted for short as well as long times. Such deviations have not hitherto been observed experimentally. Here we present experimental evidence for short-time deviation from exponential decay in a quantum tunnelling experiment. Our system consists of ultra-cold sodium atoms that are trapped in an accelerating periodic optical potential created by a standing wave of light. Atoms can escape the wells by quantum tunnelling, and the number that remain can be measured as a function of interaction time for a fixed value of the well depth and acceleration. We observe that for short times the survival probability is initially constant before developing the characteristics of exponential decay. The conceptual simplicity of the experiment enables a detailed comparison with theoretical predictions.}, Doi = {10.1038/42418}, Key = {fds232546} } @article{fds365773, Author = {Madison, KW and Bharucha, CF and Fischer, MC and Wilkinson, SR and Morrow, PR and Niu, Q and Sundaram, B and Raizen, MG}, Title = {Observation of non-exponential decay In quantum tunnelling}, Journal = {Optics InfoBase Conference Papers}, Year = {1997}, Month = {January}, ISBN = {1557525013}, Abstract = {We report the observation of short-time deviation from exponential decay in tunneling of ultra-cold atoms from an accelerating periodic optical potential. We measure a'flat survival probability followed by a transition to exponential decay.}, Key = {fds365773} }