Showing papers in "Optics Express in 2000"
TL;DR: It is shown that, in the particular case of a tightly focused, radially polarized beam, the polarization shows large inhomogeneities in the focal region, while the azimuthally polarized beam is purely transverse even at very high numerical apertures.
Abstract: Cylindrical-vector beams are of increasing recent interest for their role in novel laser resonators and their applications to electron acceleration and scanning microscopy. In this paper, we calculate cylindrical-vector fields, near the focal region of an aplanatic lens, and briefly discuss some applications. We show that, in the particular case of a tightly focused, radially polarized beam, the polarization shows large inhomogeneities in the focal region, while the azimuthally polarized beam is purely transverse even at very high numerical apertures.
1,472 citations
TL;DR: The en-face optical coherence tomography system, equipped with the 3D rendering feature acts as a valuable diagnostic tool allowing "peeling off" of transversal and longitudinal biologic material to investigate different internal features.
Abstract: We demonstrate the functionality of an en-face optical coherence tomography (OCT) system with images from the retina and skin. En-face images collected at different depths are subsequently used to reconstruct a 3D volume of the tissue. The reconstruction allows software inferred OCT longitudinal images at any transversal position in the stack. The position in depth in the stack before creating longitudinal OCT images is also adjustable, offering a valuable guidance tool for exploring the 3D volume of the tissue. This is illustrated by Quick time movies showing either depth or lateral exploration along one of two possible different directions in the stack of transversal OCT images. Sufficient accuracy of the volume rendered is obtained in 20 seconds when the system operates at 2 frames a second. The system, equipped with the 3D rendering feature acts as a valuable diagnostic tool allowing “peeling off” of transversal and longitudinal biologic material to investigate different internal features.
330 citations
TL;DR: An instrument for non-invasive optical imaging of the human brain that produces on-line images with a temporal resolution of 160 ms with real-time videos of the arterial pulsation and motor activation recorded on a 4 x 9 cm 2 area of the cerebral cortex in a healthy human subject.
Abstract: We have developed an instrument for non-invasive optical imaging of the human brain that produces on-line images with a temporal resolution of 160 ms. The imaged quantities are the temporal changes in cerebral oxy-hemoglobin and deoxy-hemoglobin concentrations. We report real-time videos of the arterial pulsation and motor activation recorded on a 4 x 9 cm 2 area of the cerebral cortex in a healthy human subject. This approach to optical brain imaging is a powerful tool for the investigation of the spatial and temporal features of the optical signals collected on the brain.
258 citations
TL;DR: The use of pulsed lasers for microprocessing material in several manufacturing industries is presented and microvia, ink jet printer nozzle and biomedical catheter hole drilling, thin-film scribing and micro-electro-mechanical system (MEMS) fabrication applications are reviewed.
Abstract: The use of pulsed lasers for microprocessing material in several manufacturing industries is presented. Microvia, ink jet printer nozzle and biomedical catheter hole drilling, thin-film scribing and micro-electro-mechanical system (MEMS) fabrication applications are reviewed.
228 citations
TL;DR: At resonance frequencies, extremely large enhancements of the electromagnetic fields occur near the surface of the particle, with amplitudes several hundred-fold that of the incident field.
Abstract: We study the plasmon resonances of 10–100(nm) two-dimensional metal particles with a non-regular shape. Movies illustrate the spectral response of such particles in the optical range. Contrary to particles with a simple shape (cylinder, ellipse) non-regular particles exhibit many distinct resonances over a large spectral range. At resonance frequencies, extremely large enhancements of the electromagnetic fields occur near the surface of the particle, with amplitudes several hundred-fold that of the incident field. Implications of these strong and localized fields for nano-optics and surface enhanced Raman scattering (SERS) are also discussed.
217 citations
TL;DR: An optical coherence microscope (OCM) has been designed and constructed to acquire 3-dimensional images of highly scattering biological tissue, and the fundamental photon noise limitation is measured and compared with theory.
Abstract: An optical coherence microscope (OCM) has been designed and constructed to acquire 3-dimensional images of highly scattering biological tissue. Volume-rendering software is used to enhance 3-D visualization of the data sets. Lateral resolution of the OCM is 5 mm (FWHM), and the depth resolution is 10 mm (FWHM) in tissue. The design trade-offs for a 3-D OCM are discussed, and the fundamental photon noise limitation is measured and compared with theory. A rotating 3-D image of a frog embryo is presented to illustrate the capabilities of the instrument.
177 citations
TL;DR: This technique provides enhancement in the visibility of subsurface structures via processing of the depolarized images obtained using polarized illumination at different wavelengths using spectral and polarization discrimination of the backscattered photons.
Abstract: Deep subsurface imaging in tissues is demonstrated by employing both spectral and polarization discrimination of the backscattered photons This technique provides enhancement in the visibility of subsurface structures via processing of the depolarized images obtained using polarized illumination at different wavelengths The experimental results demonstrate detection and imaging of a high-scattering object located up to 15-cm beneath the surface of a host chicken tissue used as the model medium
174 citations
TL;DR: A time-resolved Monte Carlo technique was used to simulate the propagation of polarized light in turbid media and the effects of the polarization state of the incident light and of the size of scatterers on the propagate of DOP were studied.
Abstract: A time-resolved Monte Carlo technique was used to simulate the propagation of polarized light in turbid media. Calculated quantities include the reflection Mueller matrices, the transmission Mueller matrices, and the degree of polarization (DOP). The effects of the polarization state of the incident light and of the size of scatterers on the propagation of DOP were studied. Results are shown in animation sequences.
149 citations
TL;DR: The dynamic performance of the adaptive optics system is investigated in detail using a diffractive wavefront generator based on a ferroelectric spatial light modulator to produce wavefronts with time-varying aberrations.
Abstract: A low cost adaptive optics system constructed almost entirely of commercially available components is presented. The system uses a 37 actuator membrane mirror and operates at frame rates up to 800Hz using a single processor. Numerical modelling of the membrane mirror is used to optimize parameters of the system. The dynamic performance of the system is investigated in detail using a diffractive wavefront generator based on a ferroelectric spatial light modulator. This is used to produce wavefronts with time-varying aberrations. The ability of the system to correct for Kolmogorov turbulence with different strengths and effective wind speeds is measured experimentally using the wavefront generator.
143 citations
TL;DR: The principle of wavelength-scanning digital interference holography is applied to three-dimensional imaging of a small biological specimen, resulting in tomographic images with narrow axial resolution.
Abstract: The principle of wavelength-scanning digital interference holography is applied to three-dimensional imaging of a small biological specimen. The images are reconstructed from a number of holograms digitally recorded while the wavelengths are varied at regular intervals, and the numerical interference of the multiple three-dimensional hologram fields results in tomographic images with narrow axial resolution. An animated three-dimensional model of the object is constructed from the tomographic images.
141 citations
TL;DR: Fits of the ModelFest data with five models are reported: Peak Contrast, Contrast Energy, Generalized Energy, a Gabor Channels model, and a Discrete Cosine Transform model.
Abstract: The ModelFest Phase One dataset is a collection of luminance contrast thresholds for 43 two-dimensional monochromatic spatial patterns confined to an area of approximately two by two degrees. These data were collected by a collaboration among twelve laboratories, and were designed to provide a common database for calibration and testing of spatial vision models. Here I report fits of the ModelFest data with five models: Peak Contrast, Contrast Energy, Generalized Energy, a Gabor Channels model, and a Discrete Cosine Transform model. The Gabor Channels model provides the best fit, though the other, simpler models, with the exception of Peak Contrast, provide remarkably good fits as well. Though there are clear individual differences, regularities in the data suggest the possibility of constructing a standard observer for spatial vision.
TL;DR: The finite-difference time-domain method with pulse response techniques is combined in order to calculate the light scattering properties of biological cells over a range of wavelengths simultaneously, providing greater geometric flexibility than Mie theory solutions.
Abstract: We combine the finite-difference time-domain method with pulse response techniques in order to calculate the light scattering properties of biological cells over a range of wavelengths simultaneously. The method we describe can be used to compute the scattering patterns of cells containing multiple heterogeneous organelles, providing greater geometric flexibility than Mie theory solutions. Using a desktop computer, we calculate the scattering patterns for common homogeneous models of biological cells and also for more complex representations of cellular morphology. We find that the geometry chosen significantly impacts scattering properties, emphasizing the need for careful consideration of appropriate theoretical models of cellular scattering and for accurate microscopic determination of optical properties.
TL;DR: Possibilities to produce sub-diffraction limited structures in thin metal films and bulk dielectric materials using femtosecond laser pulses are investigated and results on the fabrication of sub-micrometer structures in 100-200 nm chrome-coated surfaces by direct ablative writing are reported.
Abstract: Possibilities to produce sub-diffraction limited structures in thin metal films and bulk dielectric materials using femtosecond laser pulses are investigated. The physics of ultrashort pulse laser ablation of solids is outlined. Results on the fabrication of sub-micrometer structures in 100–200 nm chrome-coated surfaces by direct ablative writing are reported. Polarization maintaining optical waveguides produced by femtosecond laser pulses inside crystalline quartz are demonstrated.
TL;DR: Analytical derivatives for the dispersion equations are derived and presented for what is believed to be the first time, and a new algorithm that significantly reduces the time required to compute the derivatives is given.
Abstract: This paper discusses a numerical method for computing the electromagnetic modes supported by multilayer planar optical waveguides constructed from lossy or active media, having in general a diagonal permittivity tensor. The method solves the dispersion equations in the complex plane via the Cauchy integration method. It is applicable to lossless, lossy and active waveguides, and to AntiResonant Reflecting Optical Waveguides (ARROW’s). Analytical derivatives for the dispersion equations are derived and presented for what is believed to be the first time, and a new algorithm that significantly reduces the time required to compute the derivatives is given. This has a double impact: improved accuracy and reduced computation time compared to the standard approach. A different integration contour, which is suitable for leaky modes is also presented. Comparisons are made with results found in the literature; excellent agreement is noted for all comparisons made.
TL;DR: The properties of some purely bound plasmon-polariton modes guided by an asymmetric waveguide structure composed of a thin lossy metal film of finite width supported by a dielectrics substrate and covered by a different dielectric superstrate are presented for what is believed to be the first time.
Abstract: The properties of some purely bound plasmon-polariton modes guided by an asymmetric waveguide structure composed of a thin lossy metal film of finite width supported by a dielectric substrate and covered by a different dielectric superstrate are presented for what is believed to be the first time. The mode spectrum supported by these structures is quite different from the spectrum supported by corresponding asymmetric slab structures or similar finite-width symmetric waveguides. Unlike these limiting cases, the dispersion with film thickness exhibits an unusual oscillatory character that is explained by a “switching” of constituent interface modes. This mode switching is unique to asymmetric finite-width structures. Above a certain cut-off film thickness, the structure can support a long-ranging mode and its attenuation decreases very rapidly with decreasing film thickness, more so than the long-ranging mode in symmetric structures. Also, the cutoff thickness of the long-ranging mode is larger than the cutoff thickness of the long-ranging mode in the corresponding asymmetric slab waveguide, which implies that propagation along finite-width films is more sensitive to the asymmetry in the structure than propagation along a similar slab structure. Both of these results are potentially useful for the transmission and control of optical radiation.
TL;DR: These microscopes use ultrashort pulse excitation over large areas of the sample and allow efficient use of the high-average power available from modern ultrashorts pulse lasers.
Abstract: We demonstrate a widefield multiphoton microscope and a temporally decorrelated, multifocal, multiphoton microscope that is based on a high-efficiency array of cascaded beamsplitters. Because these microscopes use ultrashort pulse excitation over large areas of the sample, they allow efficient use of the high-average power available from modern ultrashort pulse lasers.
TL;DR: A corrugated hollow-core fiber modulates the intensity of the fundamental pulse along the direction of propagation, resulting in a periodic modulation of the harmonic emission at wavelengths close to the cutoff, increasing the harmonic yield by up to three orders of magnitude.
Abstract: We describe theoretically a new technique for quasi-phase-matched generation of high harmonics and attosecond pulses in a gas medium, in a high ionization limit. A corrugated hollow-core fiber modulates the intensity of the fundamental pulse along the direction of propagation, resulting in a periodic modulation of the harmonic emission at wavelengths close to the cutoff. This leads to an increase of the harmonic yield of up to three orders of magnitude. At the same time the highest harmonics merge in a broad band that corresponds to a single attosecond pulse, using 15-fs driving pulses.
TL;DR: It is shown that the combined effects of imperfect polarization of the transmitted laser pulse, non-ideal properties of transmitter and receiver optics and cross-talk between parallel and perpendicular polarization channels can be described by a single parameter, which is essentially the overall system depolarization.
Abstract: An algorithm for correcting instrumental effects in polarization lidar studies is discussed. Cross-talk between the perpendicular and parallel polarization channels and imperfect polarization of the transmitted laser beam are taken into account. On the basis of the Mueller formalism it is shown that - with certain assumptions - the combined effects of imperfect polarization of the transmitted laser pulse, non-ideal properties of transmitter and receiver optics and cross-talk between parallel and perpendicular polarization channels can be described by a single parameter, which is essentially the overall system depolarization.
TL;DR: A relationship between the torque and angle of orientation of the cell, showing that stable equilibrium orientations are at angles of 0 o, 180 o and 360 o and unstable equilibrium orientation are at 90 o and 270 o relative to the axis of beam propagation.
Abstract: We present a theoretical analysis of the behaviour of erythrocytes in an optical trapping system. We modeled erythrocyte behaviour in an optical trap by an algorithm which divided the cell surface into a large number of elements and recursively summed the force and torque on each element. We present a relationship between the torque and angle of orientation of the cell, showing that stable equilibrium orientations are at angles of 0°, 180° and 360° and unstable equilibrium orientations are at 90° and 270° relative to the axis of beam propagation. This is consistent with our experimental observations and with results described in the literature. We also model behaviour of the erythrocyte during micromanipulation by calculating the net force on it. Such theoretical analysis is practical as it allows for the optimization of the optical parameters of a trapping system prior to performing a specific optical micromanipulation application, such as cell sorting or construction of a cell pattern for lab-on-a-chip applications.
TL;DR: It is demonstrated that the degree of polarization of the backscattered light is sensitive to the optical properties of both layers and to layer thickness, which has applications for characterizing burns and melanoma.
Abstract: The polarization properties of light backscattered from a two layer scattering medium are investigated. Linear, circular and elliptical polarization states are considered and it is demonstrated that the degree of polarization of the backscattered light is sensitive to the optical properties of both layers and to layer thickness. Furthermore, it is shown that the polarization memory of circularly polarized light enables deeper layers to be probed whereas linearly polarized light is more sensitive to surface layers. This has applications for characterizing burns and melanoma.
TL;DR: Real-time imaging of gas leaks was demonstrated using an IR camera employing outdoor thermal background radiation and an optical filter and a gas-correlation cell matching the absorption band of the gas.
Abstract: Real-time imaging of gas leaks was demonstrated using an IR camera employing outdoor thermal background radiation. Ammonia, ethylene and methane detection was demonstrated in the spectral region 7-13 microm. Imaging was accomplished using an optical filter and a gas-correlation cell matching the absorption band of the gas. When two gases, such as ammonia and ethylene, are absorbing in the same wavelength region it is possible to isolate one for display by using gas-correlation multispectral imaging. Results from a field test on a leaking gas tanker are presented as QuickTime movies. A detection limit of 200 ppm x meter for ammonia was accomplished in this setup when the temperature difference between the background and the gas was 18 K and the frame rate was 15 Hz.
TL;DR: The confocal imaging system resolved sub-cellular detail throughout the entire epithelial thickness and provided sufficient contrast to enable quantitative feature analysis in aceto-whitening.
Abstract: High resolution, in vivo confocal imaging of amelanotic epithelial tissue may offer a clinically useful adjunct to standard histopathologic techniques. Application of acetic acid has been shown to enhance contrast in confocal images of these tissues. In this study, we record the time course of aceto-whitening at the cellular level and determine whether the contrast provided enables quantitative feature analysis. Confocal images and videos of cervical specimens were obtained throughout the epithelium before, during and post-acetic acid after the application of 6% acetic acid. Aceto-whitening occurs within seconds after the application. The confocal imaging system resolved sub-cellular detail throughout the entire epithelial thickness and provided sufficient contrast to enable quantitative feature analysis.
TL;DR: This work demonstrates a transmission of 4 x 10 Gb/s WDM channels over 1.2 km of free space in 1.55-microm band through a fiber-pigtailed collimator and enables the use of standard 100-GHz channel spacing and an optical preamplifier at the receiver.
Abstract: We demonstrate a transmission of 4×10 Gb/s WDM channels over 1.2 km of free space in 1.55-µm band. The transmitted beam is coupled into a single-mode fiber through a fiber-pigtailed collimator, which enables the use of standard 100-GHz channel spacing and an optical preamplifier at the receiver. All the received channels have Q values higher than 6.
TL;DR: An investigation of the effect of a 3D non-scattering gap region on image reconstruction in diffuse optical tomography using the Radiosity-Diffusion method and the inverse problem is solved using the adjoint field method.
Abstract: We present an investigation of the effect of a 3D non-scattering gap region on image reconstruction in diffuse optical tomography. The void gap is modelled by the Radiosity-Diffusion method and the inverse problem is solved using the adjoint field method. The case of a sphere with concentric spherical gap is used as an example.
TL;DR: It is shown that angle-dithering a second-harmonic-generation crystal that is otherwise too narrowband (that is, too thick) can yield sufficient phase-matching bandwidth and an accurate pulse measurement and is applied to frequency-resolved optical gating (FROG) and shows that accurate pulse measurements can be made using a comparatively very thick and hence narrowband crystal.
Abstract: We show that the usual phase-matching-bandwidth constraint in ultrashort-laser-pulse measurement techniques is overly restrictive. Specifically, the phase-matching bandwidth need not exceed the pulse bandwidth on every pulse. Instead, only the phase-matching bandwidth integrated over the measurement period need exceed the pulse bandwidth. We show that angle-dithering a second-harmonic-generation crystal that is otherwise too narrowband (that is, too thick) can yield sufficient phase-matching bandwidth and an accurate pulse measurement. We apply this technique to frequency-resolved optical gating (FROG) and show that accurate pulse measurements can be made using a comparatively very thick and hence narrowband crystal. An additional advantage of using a thick crystal is increased signal strength.
TL;DR: The reflective features of a water surface covered with an oil film expressed by the dependence of the reflectance on the angle of light incidence and wavelength and film thickness with respect to downward and upward light fluxes are reported.
Abstract: This paper reports the reflective features of a water surface covered with an oil film expressed by the dependence of the reflectance on the angle of light incidence and wavelength and film thickness with respect to downward and upward light fluxes. The sensitivity of the shape of these functions on the oil type appears especially strong in case of the upward light fluxes as opposed to downward fluxes.
TL;DR: These techniques in detecting neovascularization in age-related macular degeneration are investigated using a novel technique, Multiply Scattered Light Tomography, and confocal Infrared Imaging.
Abstract: A novel technique, Multiply Scattered Light Tomography (MSLT), and confocal Infrared Imaging are used to provide diagnostic information using a comfortable, rapid, and noninvasive method. We investigated these techniques in detecting neovascularization in age-related macular degeneration. The MSLT used a Vertical Cavity Surface Emitting Laser (VCSEL) at 850 nm, while the confocal imaging technique used either the VCSEL or a 790 nm laser diode. Both were implemented into the topographical scanning system (TopSS, Laser Diagnostic Technologies, Inc.) Confocal imaging with both lasers provided different information about neovascularization as a function of focal plane, and different also from MSLT.
TL;DR: In this paper, higher order guided modes in an air-silica microstructure fiber comprising a ring of six large air-holes surrounding a Germanium doped core were characterized experimentally using an intra-core Bragg grating.
Abstract: We study the higher order guided modes in an air-silica microstructure fiber comprising a ring of six large air-holes surrounding a Germanium doped core. We characterize the modes experimentally using an intra-core Bragg grating. The experimentally observed modes are then accurately modeled by beam propagation simulations using an index profile similar to the observed fiber cross section. Theory and experiment confirm the presence of “inner cladding” modes with approximate cylindrical symmetry near the core, similar to conventional cladding modes, but which strongly exhibit the symmetry of the microstructure at large radius. Such modes are useful in fabricating robust tunable grating filters and we show that the Bragg grating is a useful diagnostic to measure their effective indices and intensity profiles.
TL;DR: An all-optical binary counter composed of four semiconductor optical amplifier based all- optical switching gates that operates with bit-differential delays between the exclusive-OR gate used for modulo-2 binary addition and the AND gate for binary carry detection is experimentally demonstrated.
Abstract: We experimentally demonstrate an all-optical binary counter composed of four semiconductor optical amplifier based all-optical switching gates The time-of-flight optical circuit operates with bit-differential delays between the exclusive-OR gate used for modulo-2 binary addition and the AND gate used for binary carry detection A movie of the counter operating in real time is presented
TL;DR: Experimental three-dimensional image reconstruction of optically heterogeneous turbid media from near-infrared continuous-wave measurements shows that both absorption and scattering images of a 10x15 mm cylindrical object embedded in a 50x50 mm cylINDrical background can be reconstructed using the algorithm.
Abstract: This paper demonstrates experimental three-dimensional (3D) image reconstruction of optically heterogeneous turbid media from near-infrared continuous-wave measurements. Successful reconstruction is achieved through a full 3D finite-element based, Newton-type reconstruction algorithm. Our experimental evidence shows that both absorption and scattering images of a 10×15 mm cylindrical object embedded in a 50×50 mm cylindrical background can be reconstructed using our algorithm.