ORCID Profile
0000-0002-8936-4358
Current Organisation
Tufts University
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Publisher: Optica Publishing Group
Date: 07-1991
Publisher: Optica Publishing Group
Date: 09-1992
Publisher: Optica Publishing Group
Date: 11-1981
DOI: 10.1364/OL.6.000519
Abstract: A theory of phase conjugation in asymmetric materials that allow a phase shift between the grating and the light-interference pattern is developed. We find that when this phase is nonzero, maximum phase-conjugate reflectivity occurs for unequal pump intensities. The conditions for self-oscillation are studied.
Publisher: SPIE
Date: 28-05-2002
DOI: 10.1117/12.468338
Publisher: AIP Publishing
Date: 15-09-1985
DOI: 10.1063/1.96073
Abstract: We report photorefractive passive phase conjugation of GaAlAs laser radiation at 815–865 nm and Ar+ laser radiation at 1090 nm. A ring passive phase conjugate mirror was used with BaTiO3 as the real-time holographic gain medium. With GaAlAs lasers phase conjugate reflectivities of up to 16% uncorrected for Fresnel losses were recorded. Effects of the strong associated feedback to the laser and attempts at mode locking are described. At 1090 nm the reflectivity remains approximately the same, but with a significantly longer time constant.
Publisher: MDPI AG
Date: 26-11-2021
DOI: 10.3390/RS13234794
Abstract: Many Indonesian forests have been cleared and replaced by fast-growing cash crops (e.g., oil palm and rubber plantations), altering the vegetation structure of entire regions. Complex vegetation structure provides habitat niches to a large number of native species. Airborne laser scanning (ALS) can provide detailed three-dimensional information on vegetation structure. Here, we investigate the potential of ALS metrics to highlight differences across a gradient of land-use management intensities in Sumatra, Indonesia. We focused on tropical rainforests, jungle rubber, rubber plantations, oil palm plantations and transitional lands. Twenty-two ALS metrics were extracted from 183 plots. Analysis included a principal component analysis (PCA), analysis of variance (ANOVAs) and random forest (RF) characterization of the land use/land cover (LULC). Results from the PCA indicated that a greater number of canopy gaps are associated with oil palm plantations, while a taller stand height and higher vegetation structural metrics were linked with rainforest and jungle rubber. A clear separation in metrics performance between forest (including rainforest and jungle rubber) and oil palm was evident from the metrics pairwise comparison, with rubber plantations and transitional land behaving similar to forests (rainforest and jungle rubber) and oil palm plantations, according to different metrics. Lastly, two RF models were carried out: one using all five land uses (5LU), and one using four, merging jungle rubber with rainforest (4LU). The 5LU model resulted in a lower overall accuracy (51.1%) due to mismatches between jungle rubber and forest, while the 4LU model resulted in a higher accuracy (72.2%). Our results show the potential of ALS metrics to characterize different LULCs, which can be used to track changes in land use and their effect on ecosystem functioning, bio ersity and climate.
Publisher: SPIE
Date: 18-08-1995
DOI: 10.1117/12.217014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 1984
Publisher: AIP Publishing
Date: 08-12-1986
DOI: 10.1063/1.97280
Abstract: We measure the spectral characteristics of an external cavity semiconductor laser which uses a phase conjugate mirror for its external reflection. This device has significant advantages over the conventional external cavity system owing to the self-aligning nature of the phase conjugate mirror. The fiber delay line self-heterodyne technique is used to measure the fundamental linewidth for single mode operation of this device. It shows the linewidth to be at least as narrow as the instrumental resolution of 100 kHz.
Publisher: IOP Publishing
Date: 24-10-2008
Publisher: The Optical Society
Date: 02-12-2010
DOI: 10.1364/OE.18.026499
Publisher: Elsevier BV
Date: 02-1988
Publisher: AIP Publishing
Date: 12-1985
DOI: 10.1063/1.96352
Abstract: Because the ring and semilinear passive phase conjugate mirrors use dynamic transmission holograms, they are insensitive to vibration and may be pumped with light of short coherence length or with picosecond mode-locked laser light. Experimental demonstrations of these modes of operation are described.
Publisher: AIP Publishing
Date: 25-09-1995
DOI: 10.1063/1.115419
Abstract: SrxBa1−xNb2O6 films have been epitaxially grown on MgO substrates by a single-source plasma-enhanced chemical vapor deposition (PE-CVD). Exceptionally high quality of the epitaxial films was observed as indicated by high-resolution synchrotron x-ray diffraction imaging. The films exhibit waveguiding behavior with values of refractive index and the linear electro-optic coefficient r51 close to those of bulk crystals.
Publisher: Beilstein Institut
Date: 05-04-2013
DOI: 10.3762/BJNANO.4.25
Abstract: Atomic force microscopes have become indispensable tools for mechanical characterization of nanoscale and submicron structures. However, materials with complex geometries, such as electrospun fiber networks used for tissue scaffolds, still pose challenges due to the influence of tension and bending modulus on the response of the suspended structures. Here we report mechanical measurements on electrospun silk fibers with various treatments that allow discriminating among the different mechanisms that determine the mechanical behavior of these complex structures. In particular we were able to identify the role of tension and boundary conditions (pinned versus cl ed) in determining the mechanical response of electrospun silk fibers. Our findings show that high-resolution mechanical imaging with torsional harmonic atomic force microscopy provides a reliable method to investigate the mechanics of materials with complex geometries.
Publisher: Wiley
Date: 19-11-2011
DOI: 10.1002/POLB.23003
Publisher: AIP Publishing
Date: 06-1983
DOI: 10.1063/1.93800
Abstract: A passive phase conjugate mirror based on four-wave mixing in an optical ring cavity is described. Unlike previously demonstrated passive phase conjugate mirrors it generates only one of its pumping beams by nonlinear optical interactions, the other being provided by feedback of the probe after transmission through the nonlinear medium. The results of a theory yielding phase conjugate reflectivity and oscillation thresholds are presented together with an experimental demonstration of phase conjugation in barium titanate and strontium barium niobate. The device is self-starting by four-wave mixing, and has an oscillation threshold lower than that of other previously demonstrated passive phase conjugate mirrors with similar ease of alignment. The operation of a device which generates nonconjugate oscillation beams is also reported.
Publisher: Optica Publishing Group
Date: 03-1995
DOI: 10.1364/OL.20.000432
Abstract: We implement a random-walk scattering model in a nonlinear beam-propagation code to simulate fanning in photorefractive crystals. The characteristics of the scatterers were verified by comparisons of the measured firstorder statistics of the scattered intensity with a theoretical expression of the probability-density function based on a random-walk scattering model. Both the size and the separation of the scatterers can be varied, enabling us to tailor our numerical simulations to experimental measurements of non lified and lified scattering. We show that a one-dimensional model does not accurately simulate lified scattering for crystals with a nondiagonal electro-optic tensor and that surface scattering alone may not account for the angular dependence of the lified scattering distributions.
Publisher: Springer Berlin Heidelberg
Date: 2010
Publisher: AIP Publishing
Date: 08-1982
DOI: 10.1063/1.93489
Abstract: We report here a novel laser resonator with the ability to correct for intracavity phase distortions. The optical cavity employs a passive (self-pumped) phase conjugate reflector to provide this capability.
Publisher: Springer Science and Business Media LLC
Date: 11-09-2007
Publisher: SPIE-Intl Soc Optical Eng
Date: 1993
DOI: 10.1117/12.147723
Publisher: Optica Publishing Group
Date: 15-10-1995
DOI: 10.1364/OL.20.002075
Abstract: A laser beam propagating in a photorefractive crystal generates a refractive-index profile that deflects the beam to one side. This nonlinear deflection can be balanced by total internal reflection at the crystal surface to produce self-induced photorefractive surface waves. Theoretical and experimental evidence for this effect is given.
Publisher: AIP Publishing
Date: 28-04-1997
DOI: 10.1063/1.118820
Abstract: We describe in this letter a novel approach to obtain a tunable midinfrared (mid-IR) laser output. By applying quasiphase-matched difference frequency generation in a periodically domain inverted LiNbO3 crystal placed inside a Cr3+:LiSAF laser cavity, more than 50 mW of mid-IR output was generated using only 1.8 watts of red diode or dye laser pumping. Wavelength tuning of the mid-IR signals from 3.3 to 4.2 μm was demonstrated by tuning only the wavelength of the Cr3+:LiSAF emission, without the need to reorient the LiNbO3 crystal for domain period adjustment.
Publisher: SPIE-Intl Soc Optical Eng
Date: 1993
DOI: 10.1117/12.147722
Publisher: AIP Publishing
Date: 06-1985
DOI: 10.1063/1.335314
Abstract: We report experimental and theoretical studies of the use of the photorefractive effect in the design of optical limiters. Preliminary results indicate extinction coefficients of at least 98–99% with 1 J/cm2 transmitted before steady state is reached.
Publisher: Optica Publishing Group
Date: 15-08-1990
DOI: 10.1364/OL.15.000897
Abstract: The photorefractive transmission grating ring self-pumped phase-conjugate mirror is shown to be formally equivalent to a double phase-conjugate mirror with internal losses and equal-intensity input beams. These mirrors are also equivalent to a self-pumped phase conjugator consisting of a photorefractive crystal with one face highly reflecting. This result shows that all transmission grating self-pumped phase-conjugate mirrors, with the exception of the linear self-pumped phase conjugator, are topologically equivalent to a double phase-conjugate mirror. No similar equivalence can be shown for the reflection grating ring phase conjugator.
Publisher: Optica Publishing Group
Date: 08-1997
DOI: 10.1364/OL.22.001141
Abstract: Optical aberrations that are due to high-speed turbulence in the aero-optical regime are corrected with optical phase conjugation based on coherent population trapping in sodium vapor. Experimental measurements of an unheated, forced helium jet in air have demonstrated aberration correction by a factor of 7.8 at a forcing frequency of 18kHz with an optical power gain of 32.
Publisher: AIP Publishing
Date: 08-06-1998
DOI: 10.1063/1.121496
Abstract: Highly (110)-oriented and (100) nearly epitaxial 0.7PMN-0.3PT thin films were deposited on (1012) sapphire and (100) LaAlO3 substrates, respectively, using a dip-coating method. Optical waveguide characterization and electro-optic effect measurements of the film on sapphire substrate were demonstrated. Low propagation loss of 4.1 dB/cm and high quadratic electro-optic coefficient of 0.75×10−16 (m/V)2 were obtained at wavelength of 632.8 nm. Epitaxial PMN-PT thin films will be suitable for integrated optic devices.
Publisher: IOP Publishing
Date: 23-07-2007
Publisher: Elsevier BV
Date: 07-1990
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7SM00446J
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 1995
DOI: 10.1109/50.350646
Publisher: American Chemical Society (ACS)
Date: 28-03-2008
DOI: 10.1021/BM701235F
Abstract: Silk-based biomaterial systems have been previously explored for a variety of medical and nonmedical materials needs. The unique biophysical features of silks provide options to generate highly tailored structures and morphologies with this unique family of fibrous proteins. To exploit these features, we have optimized the all aqueous processing of silk fibroin into novel surface nanopatterned protein materials. We have exploited control of this nanomorphology to optimize the optical features of these silk protein systems. We demonstrate control of surface morphology down to 125 nm, with fidelity over large length scales. This surface nanopatterning allows the silk protein to be formed into diffractive optics such as diffraction gratings, pattern generators, and lenses due to novel aqueous processing into optically clear materials via control of beta sheet crystallinity. Further, we incorporate biological components, such as hemoglobin and the enzyme peroxidase, during the process of forming the silk diffraction gratings. The ambient processing of the silk protein in water, in combination with these bioactive components, allows these entrained molecules to retain activity and provide added functions and selectivity to the optically active silk films. Thus, combinations of biochemical and optical readout is feasible and provides in a single, disposable/all degradable element with both spectral discrimination and biological function. These new surface nanopatterned, bioactive silk protein-based material systems offer a unique combination of features potentially useful for a range of biosensor needs, particularly when considered in concert with the remarkable mechanical properties of these proteins, their biocompatibility, and controllable biodegradation.
Publisher: Optica Publishing Group
Date: 03-1994
DOI: 10.1364/OL.19.000320
Abstract: We show numerically that a solitonlike propagation behavior in a self-focusing nonlinear fiber array can be used for efficient optical switching. Initial phase modulation of only five fibers is used for switching control.
Publisher: AIP Publishing
Date: 14-08-2006
DOI: 10.1063/1.2335983
Abstract: Cantilevers are commonly used in microelectromechanical systems for sensing and optical switching applications. The authors demonstrate the use of optical tweezers for all optical actuation of a tapered optical fiber used as a cantilever and to drive it as a micromechanical oscillator. A fiber optic confocal detection system is used to monitor backscattered trapping light to sense the position and oscillation characteristics of the cantilever. Potential applications include optical switching and dynamic reconfigurability of photonic circuits.
Publisher: Elsevier BV
Date: 05-1992
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2007
Publisher: SPIE
Date: 12-09-2013
DOI: 10.1117/12.2027155
Publisher: AIP Publishing
Date: 15-10-1982
DOI: 10.1063/1.93652
Abstract: We report the results of a theoretical and experimental investigation of a passive (self-pumped) phase conjugate mirror. This device is based on real time holography in materials which allow a spatial phase shift between the refractive index grating and the light interference pattern. An imaging experiment is reported showing the phase conjugating nature of the device. The holographic medium used was a single crystal of barium titanate.
Publisher: Optica Publishing Group
Date: 2006
DOI: 10.1364/OE.14.001933
Abstract: We present a photonic band gap (PBG) structure (or nonlinear photonic crystal) design for terahertz (THz) wave parametric generation, whose component materials have a small refractive index difference in the near infrared and a large index difference for THz waves. The structural dispersion of such a PBG structure is strong in the THz range but negligible in the optical range. The former allows the phase-matched pump wavelength to be placed in the near infrared to eliminate two-photon absorption of the pump and signal beams. The latter leads to a crystal layer fabrication tolerances of a few micrometers and traditional polishing methods are suitable for device fabrication. The added design flexibility also allows the use of the most efficient crystal orientations.
Publisher: Optica Publishing Group
Date: 12-2089
DOI: 10.1364/OL.14.001297
Abstract: A method for achromatic volume holography is described using a combination of material and grating dispersion. With barium titanate as the dispersive material, a bandwidth of 250 nm is realized. The device may be used for broadband phase conjugation and image reconstruction.
Publisher: Optica Publishing Group
Date: 11-1996
Publisher: Optica Publishing Group
Date: 04-2003
DOI: 10.1364/AO.42.001820
Abstract: We demonstrate, what is to the best our knowledge, a new method for studying the motion of a particle trapped by optical tweezers in this method the trapping beam itself is used as a confocal probe. By studying the response of the particle to periodic motion of the tweezers, we obtain information about the medium viscosity, particle properties, and trap stiffness. We develop the mathematical model, demonstrate experimentally its validity for our system, and discuss advantages of using this method as a new form of scanning photonic force microscopy for applications in which a high spatial and temporal resolution of the medium viscosity is desired.
Publisher: SPIE
Date: 09-11-1993
DOI: 10.1117/12.163565
Publisher: American Physical Society (APS)
Date: 09-1990
Publisher: Optica Publishing Group
Date: 07-1985
DOI: 10.1364/OL.10.000359
Abstract: We describe the experimental measurement of phase-conjugate reflectivity versus various ratios of input-beam intensities in photorefractive barium titanate and strontium barium niobate crystals. The experimental results are compared with the theoretical prediction from the coupled-wave theory. Three different methods to measure the nonlinear coupling constant of the crystal are also presented and compared.
Publisher: AIP Publishing
Date: 29-05-1989
DOI: 10.1063/1.101161
Abstract: A dynamically reprogrammable optical interconnect is demonstrated using temporally multiplexed writing beams in photorefractive double phase conjugation to achieve arbitrary fan-out and fan-in. Applications to neural networks and image transmission through thick distortions are discussed.
Publisher: Wiley
Date: 11-07-2022
Abstract: Vegetation canopy height is a relevant proxy for aboveground biomass, carbon stock, and bio ersity. Wall‐to‐wall information of canopy height with high spatial resolution and accuracy is not yet available on large scales. For the globally consistent TanDEM‐X data, simplifications are necessary to estimate canopy height with semi‐empirical models based on polarimetric synthetic aperture radar interferometry (PolInSAR). We trained the semi‐empirical models with s led GEDI data, because the assumptions behind the application of such simplifications are not always valid for TanDEM‐X. General linear as well as sinc models and empirical parameterizations of these models were applied to estimate the canopy height in tropical landscapes of Sumatra, Indonesia. Airborne laser scanning (ALS) data were consistently used as an independent reference. The general simplified models were compared with the trained empirical versions to assess the potential improvement of the empirical parameterization of the models. The residuals of the different canopy height models were further evaluated in relation to land use and structural information of the vegetation. Our results indicated that the empirical parameters substantially improved the estimation from a root‐mean‐square‐error (RMSE) of 10.3 m (55.8%) to 8.8 m (47.7%), when using the linear model. In contrast, the improvement of the sinc model with empirical parameters was not substantial compared to the general sinc model (7.4 m [40.4%] vs. 6.9 m [37.5%]). A consistent improvement was observed in the linear model, whereas the improvement of the sinc model was dependent on the land‐use type. Structural attributes like the canopy height itself and vegetation cover had a significant effect on the accuracies, with higher and denser vegetation generally resulting in higher residuals. We demonstrate the potential of the combined exploitation of the TanDEM‐X and GEDI missions for a wall‐to‐wall canopy height estimation in a tropical region. This study provides relevant findings for a consistent mapping of vegetation canopy height in tropical landscapes and on large scales with spaceborne laser and SAR data.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-1993
DOI: 10.1109/68.205630
Publisher: Springer Science and Business Media LLC
Date: 02-1991
DOI: 10.1007/BF00357669
Publisher: Optica Publishing Group
Date: 10-1996
Publisher: Optica Publishing Group
Date: 09-1987
DOI: 10.1364/OL.12.000714
Abstract: We describe semi-self-pumped photorefractive phase-conjugate mirrors based on the unidirectional ring resonator and the double phase-conjugate mirror. Their applicability to thresholding phase conjugation and one-way imaging through distortions is discussed.
Publisher: Elsevier BV
Date: 08-1991
Publisher: Elsevier BV
Date: 05-1991
Publisher: Optica Publishing Group
Date: 11-1995
DOI: 10.1364/OL.20.002252
Publisher: AIP Publishing
Date: 04-2007
DOI: 10.1063/1.2719626
Abstract: This article presents a simple and novel method for the fabrication of cylindrical microchannels in polymer or biopolymer substrates. This process results in highly regular, cylindrical microchannels, suitable both to the transport of liquid and the transmission of light. This method eliminates issues associated with positioning tolerances characteristic of conventional fabrication techniques, such as soft lithography. Such devices hold great promise in the field of biomedical engineering by providing a true cylindrical profile for microflow studies and vascular modeling, as well as the ability to optically analyze injected biological s les. An evaluation of these devices is performed by real time optical imaging of blood flow.
Publisher: Elsevier BV
Date: 11-1978
Publisher: Optica Publishing Group
Date: 11-1994
Publisher: Optica Publishing Group
Date: 02-05-2008
DOI: 10.1364/OE.16.007161
Abstract: We report broad bandwidth, mid-IR supercontinuum generation using a sub-cm (8 mm) length of highly nonlinear tellurite microstructured photonic crystal fiber (PCF). We pump the fiber at telecommunication wavelengths by using 1550 nm, 100 fs pulses of energy E=1.9 nJ. When coupled in the PCF, these pulses result in a supercontinuum (SC) bandwidth of 4080 nm extending from 789 to 4870 nm measured at 20 dBm below the peak spectral power. This bandwidth is comparable or in excess of previously reported spectra for other nonlinear glass fiber formulations despite the significantly shorter fiber length. In addition, besides offering a convenient pump wavelength, short fiber lengths enable smoother SC spectra, lower dispersion, and reduced material absorption at longer wavelengths making the use of this PCF particularly interesting.
Publisher: Optica Publishing Group
Date: 05-1995
DOI: 10.1364/OL.20.000982
Publisher: AIP Publishing
Date: 15-05-1982
DOI: 10.1063/1.92944
Abstract: We report the use of Sr1−x Bax Nb2O6 as an efficient holographic four-wave mixing medium. We have used this material in a continuous wave phase conjugate mirror with reflectivity exceeding unity, and in a phase conjugate resonator.
Publisher: Optica Publishing Group
Date: 05-1989
DOI: 10.1364/OL.14.000462
Abstract: We report the design and operation of a photorefractive ring self-pumped phase conjugator using total internal reflection in strontium barium niobate. Phase-conjugate reflectivity and fidelity are measured and compared with those of the conventional total-internal-reflection phase conjugator.
Publisher: Optica Publishing Group
Date: 09-1991
DOI: 10.1364/OL.16.001313
Abstract: We report self-pumped optical phase conjugation in which the pumps are self-induced as standing waves in a linear Raman laser. Self-pumped reflectivities approaching 5% are obtained for input intensities of 20 W/cm(2). This low optical input intensity combined with predicted submicrosecond response times suggests that the resonant Raman interaction may provide the basis for a promising new class of nonlinear-optical material.
Publisher: Optica Publishing Group
Date: 10-1994
Publisher: AIP Publishing
Date: 17-05-1999
DOI: 10.1063/1.124057
Abstract: The structural and quadratic electro-optic properties in lead magnesium niobate titanate thin films have been systematically studied as a function of the fraction x of lead titanate. (110)-oriented, pyrochlore-free PMN–PT films with PT contents around morphotropic phase boundary compositions, which have a propagation loss as low as 3 dB/cm and a high electro-optical (EO) coefficient of 1.32×10−16 (m/V)2, have been fabricated on (1012)-cut sapphire substrates. The EO measurements show that the PMN–PT is a highly promising electro-optic material.
Publisher: IOP Publishing
Date: 07-12-2006
Abstract: The miniaturization of optical devices and their integration for creating adaptive and reconfigurable photonic integrated circuits requires effective platforms and methods to control light over very short distances. We present here several techniques and objects that we have developed to harness light at the sub-micrometer scale. These new tools include planar photonic crystal on nonlinear chalcogenide glasses, tapered silica fibres, optofluidics, and optical trapping. Their association could provide the basic building blocks of completely new architectures and platforms that would have an impact on numerous applications, from optical logic to sensing.
Publisher: AIP Publishing
Date: 15-08-1985
DOI: 10.1063/1.96159
Abstract: A self-pumped phase conjugating mirror in conjunction with a traveling-wave acousto-optic modulator can be used to derive a spatially undisplaced frequency translatable optical beam. One can also obtain a beam consisting of multiple optical frequencies spaced by twice the modulator drive frequency. We find that the appropriate measure of the phase conjugating mirror’s ability to retroreflect a moving optical beam can be its response (writing) time, its memory time, or the ratio of the two, depending on how the beam is moving.
Publisher: Wiley
Date: 03-02-2015
Publisher: AIP Publishing
Date: 15-05-1989
DOI: 10.1063/1.101187
Abstract: We report here for the first time the demonstration of self-pumped phase conjugation in photorefractive semiconductors using 1.32 μm light. Using an ac field technique to enhance the gain coefficient in InP:Fe and a single input pump beam, phase conjugate reflectivities of 11% were measured using an input beam intensity of less than 1 mW/mm2. These results open up many possibilities for using photorefractive semiconductors in applications with low-power infrared diode lasers.
Publisher: Optica Publishing Group
Date: 1986
Publisher: Optica Publishing Group
Date: 07-1986
DOI: 10.1364/OL.11.000455
Abstract: A GaAlAs semiconductor laser with feedback from a barium titanate photorefractive ring passive phase-conjugate mirror can be made to perform repeating or nonrepeating frequency scans over a 10-nm range toward either the blue or the red. The direction of scanning and whether the scans repeat may be controlled by adjusting the overlap of the interaction beams in the crystal. This overlap region may be adjusted so that the diode frequency spectrum, originally occupying about 10 longitudinal modes, scans and narrows as the conjugate signal builds up, coming to rest often in one, but sometimes two or three, longitudinal modes as a result of self-generated distributed-feedback effects. We also report similar effects caused by feedback from the total-internal-reflection passive phase conjugate mirror. The alignment-control mechanism of the ring mirror is, however, not available in this case.
Publisher: Optica Publishing Group
Date: 19-09-2005
Abstract: We introduce a novel method of attaining all-optical beam control in an optofluidic device by displacing an optically trapped microsphere through a light beam. The micro-sphere causes the beam to be refracted by various degrees as a function of the sphere position, providing tunable attenuation and beam-steering in the device. The device itself consists of the manipulated light beam extending between two buried waveguides which are on either side of a microfluidic channel. This channel contains the micro-spheres which are suspended in water. We simulate this geometry using the Finite Difference Time Domain method and find good agreement between simulation and experiment.
Publisher: Elsevier BV
Date: 10-2021
Publisher: Optica Publishing Group
Date: 12-1987
DOI: 10.1364/OL.12.001029
Abstract: Two-beam coupling in photorefractive BaTiO(3) is used to perform time differentiation of time-varying coherent phase and litude images. Differentiation of one-dimensional signals and two-dimensional images is performed.
Publisher: Optica Publishing Group
Date: 1993
Publisher: AIP Publishing
Date: 12-05-1986
DOI: 10.1063/1.97009
Abstract: We report experimental demonstrations of the use of a photorefractive barium titanate ring passive phase conjugate mirror in the coherent coupling of two GaAlAs diode lasers. By cooling the crystal towards its tetragonal to orthorhombic phase transition, we were also able to achieve infrared photorefractive phase conjugation with gain.
Publisher: Optica Publishing Group
Date: 07-1982
DOI: 10.1364/OL.7.000313
Abstract: An exact solution of a nonlinear model of holographic four-wave mixing is derived. An expression for the reflectivity of a phase-conjugate mirror with depleted pumps is presented. We find that such a phase-conjugate mirror may exhibit bistability.
Publisher: SPIE
Date: 08-04-2004
DOI: 10.1117/12.519481
Publisher: Optica Publishing Group
Date: 15-11-1995
DOI: 10.1364/OL.20.002276
Publisher: Optica Publishing Group
Date: 15-09-1991
DOI: 10.1364/OL.16.001442
Publisher: Optica Publishing Group
Date: 15-02-1992
DOI: 10.1364/OL.17.000297
Abstract: We carried out an experimental study to verify a proposed theory for achromatic volume holography using dispersive compensation in photorefractive barium titanate crystals. Compensation of the phase mismatch was observed and was consistent with the theory.
Publisher: Optica Publishing Group
Date: 07-1985
DOI: 10.1364/OL.10.000353
Abstract: We find experimentally and explain theoretically that in a resonator bounded by two phase-conjugate mirrors (PCM's), unlike in resonators with one PCM and one conventional mirror, the oscillation frequency differs from that of the pumping beams. Using BaTiO(3) for the PCM, we find extremely small deltaomega/omega approximately 10(-15).
Publisher: Optica Publishing Group
Date: 09-2004
DOI: 10.1364/OL.29.002046
Abstract: Cascaded nonlinear optical interactions are analyzed for their potential to overcome quantum-defect related limitations on the efficiency of terahertz wave difference-frequency generation. The dispersion of ZnTe permits phase-matched production of a series of Stokes lines from two initial near-infrared beams. As the pump beams run down the Stokes ladder, the number of terahertz photons continually increases. A potential improvement by a factor of 5 is demonstrated in a 0.26-cm-long crystal by use of 25-MW/mm2 pumps at a wavelength of 824 nm.
Publisher: SPIE
Date: 10-05-1996
DOI: 10.1117/12.239482
Publisher: Optica Publishing Group
Date: 06-1997
DOI: 10.1364/OL.22.000769
Abstract: We observed optical gain as great as 30 with nearly distortion-free beam propagation in optically dense sodium vapor, using four-wave mixing. Moreover, 15-dB classical noise correlations were seen in the lified probe and conjugate beams. To achieve this performance in such a strongly absorbing medium, one must suppress unwanted absorption and self-focusing effects. This is accomplished with coherent population trapping.
Publisher: Optica Publishing Group
Date: 04-1988
DOI: 10.1364/OL.13.000324
Abstract: We solve the undepleted-pumps photorefractive four-wave mixing equations for the case of orthogonally polarized pump beams. Advantages over the parallel-polarized-pumps case include the potential for reflectivity enhancement and easy isolation of the conjugator from the source. The phase-conjugate reflectivities for both the parallel and orthogonally polarized pump beam cases were measured with a BaTiO3 crystal, and the results support our theoretical predictions.
Publisher: Optica Publishing Group
Date: 15-02-2002
DOI: 10.1364/OL.27.000264
Abstract: The techniques of confocal microscopy and optical tweezers have shown themselves to be powerful tools in biological and medical research. We combine these methods to develop a minimally invasive instrument that is capable of making hydrodynamic measurements more rapidly than is possible with other devices. This result leads to the possibility of making scanning images of the viscosity distribution of materials around biopolymer-producing cells. 100 x 100 images can be taken with 0.5-microm spatial resolution in 3 min. An image of the viscosity distribution around a pullulan-producing cell of Aureobasidium pullulans is shown as an ex le.
Publisher: American Chemical Society (ACS)
Date: 14-02-2013
DOI: 10.1021/JA312647N
Publisher: Optica Publishing Group
Date: 07-1995
DOI: 10.1364/OL.20.001459
Abstract: The effectiveness of laser beam cleanup with photorefractive two-beam coupling is evaluated. We compare the measured effectiveness of the method with that of spatial filtering and find that the method works well for a highly aberrated beam approximately 700 times diffraction limited, whereas for moderately aberrated beams the effectiveness of the method is the same as that of spatial filtering.
Publisher: AIP Publishing
Date: 1995
DOI: 10.1063/1.359357
Abstract: Charge carrier competition between the gratings produced in degenerate four-wave mixing in bismuth silicon oxide reduces steady-state diffraction efficiency, suppresses several processes of transient diffraction efficiency, and changes the concavity of reflection grating development.
Publisher: Optica Publishing Group
Date: 08-2002
DOI: 10.1364/OL.27.001357
Abstract: The use of optical tweezers to measure micrometer-resolution velocity fields in fluid flow is demonstrated as an extension of a scanning confocal viscosity microscope. This demonstration is achieved by detection of the motion of an optically trapped microsphere in an oscillating laser trap. The technique is validated by comparison with an independent video-based measurement and applied to obtain a two-dimensional map of the flow past a microscopic wedge. Since the velocity is measured simultaneously with the trap relaxation time, the technique requires no fluid-dependent calibration and is independent of the trap stiffness and the particle size.
Publisher: Optica Publishing Group
Date: 15-05-1991
DOI: 10.1364/OL.16.000747
Abstract: We present an optical signal-processing technique for additive noise reduction that uses the noisy signal and a Gaussian reference beam to produce an adaptive Wiener filter. We experimentally demonstrate an improvement from 1 to 8 in the signal-to-noise ratio by using nonlinear gain in two-beam coupling in barium titanate to transmit 50% of the signal and 6% of the noise.
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-10765
Abstract: & & Accurate characterization of land use and land cover (LULC) is important in a rapidly changing environment such as the Indonesian tropics. Over the past 30 years, native tropical forests have been cleared and replaced by fast-growing cash-crops, such as oil palm and rubber plantations. This change in land use dramatically alters the vegetation structure of the entire region. Vegetation structural complexity is highly variable in tropical forests, and provides habitat to a large number of native species. In addition, vegetation structure has an impact on micro-climate and the exchange of greenhouse gases (GHG), water and energy. Measuring vegetation structure in the field can be costly and time consuming, particularly in remote, inaccessible areas of tropical forest. In contrast, Airborne Laser Scanning (ALS) can provide very detailed three-dimensional information on forest structure without the need to reach remote areas in the field. Here, we aim to study the potential of ALS-derived measures of structural complexity as ecological indicators to highlight differences in forest structure across a gradient of LULC in Sumatra, Indonesia. We analysed the structural complexity of four main LULC types relevant to the region: tropical secondary forests, rubber agroforests, oil palm plantations and shrublands. Several structural metrics have been extracted from ALS data over 136 circular 0.1 ha plots (34 plots per LULC type): top height, height percentiles, rumple index, leaf area index (LAI), effective number of layers (ENL), vegetation cover, number of gaps. Results from a Principal Component Analysis (PCA) indicated number of gaps to be a major driver associated with the occurrence of oil palm plantations, while higher values of key structural metrics, such as top height, LAI and ENL were strongly linked with the presence of secondary tropical forest plots. Furthermore, a clear separation in metrics behaviour between forest and oil palm plots was evident from the pairwise comparison of these metrics, with rubber and shrubland plots behaving similarly to either forests or oil palm plantings according to different metrics. Our results show clear distinctions in several structural attributes among different LULC, which indicate the need for careful considerations regarding the impact of land-use change on ecosystem functioning, bio ersity and climate.& &
Publisher: Elsevier BV
Date: 09-1992
Publisher: Optica Publishing Group
Date: 04-1986
DOI: 10.1364/OL.11.000242
Publisher: Optica Publishing Group
Date: 04-1986
DOI: 10.1364/OL.11.000239
Publisher: SPIE
Date: 28-12-2005
DOI: 10.1117/12.651733
Publisher: AIP Publishing
Date: 15-11-1984
DOI: 10.1063/1.95046
Abstract: Bistability and hysteresis have been observed in a photorefractive passive phase conjugate mirror. A threshold basis for the effect is presented and the results of an experimental demonstration of the device are given.
Publisher: AIP Publishing
Date: 15-03-1982
DOI: 10.1063/1.93144
Abstract: We report here the demonstration of several new optical oscillator configurations including a unidirectional ring oscillator and a self-pumped phase conjugate mirror. The gain medium is BaTiO3, pumped by a 632.8-nm He-Ne laser at power levels down to 50 μW.
Publisher: Elsevier BV
Date: 02-1999
Publisher: AIP Publishing
Date: 29-11-1999
DOI: 10.1063/1.125299
Abstract: Erbium-doped Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN–PT) thin films were grown on (10 1̄2) sapphire substrate with a purpose of developing an active optical material combining both the large electro-optic (EO) effect and lasing or lification functions. Strong characteristic Er3+ intra-4f shell emission around 1.54 μm is observed at room temperature and a compositional quenching occurred at where the Er content is larger than 0.5 mol %. The introduction of Er in PMN–PT decreased the EO effect, but the EO coefficient still maintain a reasonable value, which is about 0.4×10−16 (m/V)2 at Er content of 0.5 mol %. These results indicate that Er3+-doped PMN–PT can be a potential candidate for integrated optic active devices.
Publisher: AIP Publishing
Date: 06-04-2009
DOI: 10.1063/1.3099935
Abstract: We investigate numerically and experimentally all-optical control of particles inside water filled, silica, hollow-core photonic crystal fiber (HC-PCF). We use an optical trapping beam focused outside the fiber, through its microstructure, perpendicular to the HC-PCF and independent of the guided fiber core mode. Finite difference time domain simulations model trapping through HC-PCF microstructure: trapping along the length of the HC-PCF is well maintained despite the significant effects due to scattering of the HC-PCF core structure. Trapped silica microspheres inside a HC-PCF is demonstrated experimentally as a reversible, reliable technique to control particles in fiber independent of the guided fiber mode. We observe a broadband attenuation of the HC-PCF transmission upon loading a silica microsphere into the fiber core.
Publisher: AIP Publishing
Date: 24-05-1999
DOI: 10.1063/1.124080
Abstract: We have demonstrated a large photorefractive effect in thin-film polycrystalline (Pb, La) (Zr, Ti)O3 (8.5/65/35) fabricated by metalorganic chemical-liquid deposition. With an applied external electric field, this film exhibited a high photorefractive diffraction efficiency measured by degenerate four-wave mixing. Poling phenomena and depolarization processes in the film were also investigated.
Publisher: Optica Publishing Group
Date: 10-1989
Publisher: AIP Publishing
Date: 27-02-2006
DOI: 10.1063/1.2181204
Abstract: We introduce a class of highly compact refractometers integrated onto a planar microfluidic geometry that demonstrates high resolution refractive index measurements in 50μm fluid channels utilizing a Fabry–Perot cavity formed between resonant Bragg grating reflectors. This cavity forms a resonant peak in the transmission spectrum which is dependent upon the refractive index of the fluid in the microfluidic channel. We demonstrate this class of refractometer using optical fiber Bragg gratings to provide high resolution, intracavity losses are minimized using integrated collimating optics. The refractometer can resolve refractive index changes of 0.2% and is simulated using coupled mode theory.
Publisher: Optica Publishing Group
Date: 07-1990
Publisher: Optica Publishing Group
Date: 15-12-1991
DOI: 10.1364/OL.16.001984
Abstract: We describe two-beam coupling and temporal encoding experiments in barium titanate. Volume gratings are created in the photorefractive material by 50-fs optical pulses. Information in the writing pulses may be encoded as spatially distributed volume gratings in the crystal. Femtosecond temporal waveform reconstruction is demonstrated.
Publisher: Elsevier BV
Date: 04-1990
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2000
DOI: 10.1109/50.848389
Publisher: Springer Science and Business Media LLC
Date: 2011
Publisher: SPIE
Date: 18-10-2004
DOI: 10.1117/12.558203
Publisher: IEEE
Date: 10-2006
Publisher: Optica Publishing Group
Date: 08-1991
DOI: 10.1364/OL.16.001183
Abstract: Photorefractive two-beam coupling with reduced spatiotemporal coherence is investigated both theoretically and experimentally. Limited spatiotemporal coherence results in spatially limited grating regions. Theoretical predictions of the beam-coupling behavior in two symmetries are supported by experimental results.
Publisher: Proceedings of the National Academy of Sciences
Date: 13-11-2001
Abstract: Collagen is a key fibrous protein in biological systems, characterized by a complex structural hierarchy as well as the ability to self-assemble into liquid crystalline mesophases. The structural features of collagen influence cellular responses and material properties, with importance for a wide range of biomaterials and tissue architectures. The mechanism by which fibrillar collagen structures form from liquid crystalline mesophases is not well characterized. We report positive printing of collagen and a collagen-like peptide down to 30–50-nm line widths, using the atomic force microscopy technique of dip-pen nanolithography. The method preserved the triple-helical structure and biological activity of collagen and even fostered the formation of characteristic higher levels of structural organization. The “direct-write” capability of biologically relevant molecules, while preserving their structure and functionality, provides tremendous flexibility in future biological device applications and in proteomics arrays, as well as a new strategy to study the important hierarchical assembly processes of biological systems.
Publisher: AIP Publishing
Date: 09-1985
DOI: 10.1063/1.96147
Abstract: Frequency detuning effects in photorefractive oscillators are used in a new type of (passive) interferometry which converts optical path length changes to frequency shifts. Such an interferometer is potentially more accurate than conventional interferometers which convert optical path length changes to phase or intensity changes.
Publisher: AIP Publishing
Date: 15-07-1982
DOI: 10.1063/1.93431
Abstract: We demonstrate one-way optical field imaging through a distorting medium using a four-wave mixing implementation of real-time holography. Information can be transmitted at an arbitrarily fast rate as long as the mixing medium can respond to changes in the distortion.
Publisher: American Physical Society (APS)
Date: 11-1996
Publisher: Elsevier BV
Date: 04-1992
Publisher: AIP Publishing
Date: 20-09-2010
DOI: 10.1063/1.3486157
Abstract: In this paper, we report on gold nanoparticle (GNP) doped silk films as an implantable and degradable heating element activated by light, which can be potentially used for wireless powering of implanted microdevices. Proof-of-concept experiments have been conducted by casting a GNP doped silk film on a miniature thermal-power chip, which generates ∼20 mW when illuminated by a green laser with an output power of 450 mW/mm2 at 532 nm.
Publisher: Optica Publishing Group
Date: 15-05-1994
DOI: 10.1364/OL.19.000743
Abstract: We analyze the circumstances under which a real-time hologram written with litude-modulated beams behaves as a linear mixer. We calculate nonlinear correction terms that can be used to analyze the linearity of a variety of photorefractive time-integrative devices.
Publisher: AIP Publishing
Date: 15-04-1984
DOI: 10.1063/1.94924
Abstract: Passive phase conjugation of up to six lines (457, 476, 488, 496, 501, and 514 nm) of the all lines output of an argon ion laser is reported. Imaging characteristics and reflectivity measurements are given. In general, multiline operation results in some loss in both reflectivity and image resolution. This work opens the possibility for passive phase conjugation of full color images.
Publisher: SPIE
Date: 31-08-2006
DOI: 10.1117/12.679856
No related grants have been discovered for Mark Cronin-Golomb.