bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin of the subpicosecond nonlinear responses in simple liquids
Authors: McMorrow Dale , Lotshaw William T. , Kenney-Wallace Geraldine A.
Published: February 2023

New data are presented on the optical Kerr effect (OKE) of several organic molecular liquids using 65-fs optical pulses centered at 633 nm. Four dynamically distinct responses are observed in every liquid composed of molecules that possess a permanent polarization anisotropy. These include an instantaneous response that follows the laser pulse intensity autocorrelation, an ultrafast component with a 1/e time constant of < 170 fs, an intermediate response with τ1/
e
of 400-600 fs, and a slower response commonly associated with orientational diffusion. In addition to these nonresonant contributions to nonlinear susceptibility, low-frequency intramolecular vibrations may be resonantly driven by the different Fourier components of the femtosecond laser pulse. In such cases the temporal evolution of these vibrational modes is directly observed superimposed on the nonresonant signal contribution. The OKE transients are discussed in terms of a simple model for molecular motion with inertial effects included explicitly. This analysis, in conjunction with the wealth of information available from frequency domain light-scattering experiments and molecular dynamics simulations, enables us to make definitive statements as to the origin and nature of the observed subpicosecond responses.
Multipass amplifier using a confocal resonator pair
Authors: Fork Richard L.
Published: February 2023

A multipass optical amplifier is described which makes use of the properties of a coupled pair of approximately confocal resonators. The departures of each resonator from the confocal condition, the relative orientation of the resonators, and the direction and convergence of the incident beam to be amplified can be varied to select a particular multipass arrangement. In general, these adjustments cause an incident light beam to pass alternatively through the two resonators and finally emerge after a number of traversals, which depends on the particular small departures of each resonator from the confocal condition. There are two basic configurations. In one configuration all the successive beam paths pass through one common crossing point which also coincides with the beam waists of the two resonators. In the second basic configuration, there are two spatially separated common crossing points, each of which coincides with the beam waist of one of the two resonators. A typical round trip transit time is ~2 ns. A number of variations of these basic configurations are discussed. Some allow a progressive change in the beam waist at the common crossing points, and some include dispersive elements which allow spectral filtering and group velocity dispersion correction.
Strehl ratio for spherical aberration: a ray picture
Authors: Ojeda-Castaneda J. , Furlan W. D. , Sicre E. E.
Published: February 2023

We apply the phase-space representation known as the Wigner distribution function to associate amplitudes to the paraxial rays. In this way we are able to give a geometrical optics ray picture of the Strehl ratio. Tolerance criteria for focus errors and spherical aberration are specified in terms of the amplitude for the paraxial rays which intersect the optical axis. We show that for certain pupils, the amplitude of the rays that cross the optical axis at an angle θ are identical to the values of the optical transfer function at the spatial frequency α = 2θ/λ.
Finite-length line spread function
Authors: Dallas William J. , Barrett Harrison H.
Published: February 2023

Any linear shift-invariant imaging system can be completely described by its point spread function (PSF) or its optical transfer function (OTF). If the system has rotational symmetry, the full 2-D PSF or OTF is not needed, only a radial line through either the PSF or the OTF. Alternatively the line spread function (LSF), the image of an infinite line, may be used as the 1-D description. There are, however, important imaging systems that are not well described by the LSF. One reason for failure of the LSF description is that the system may have a relatively small region of isoplanaticity so that a long input line is not permitted. We present here an alternative 1-D description of the system which we term the finite-length line spread function (FLSF). The FLSF is the image of a finite-length line. The relation of the FLSF to the PSF and the OTF is conveniently described by a new integral transform.
Incoherent image reconstruction from multiple-laser-speckle patterns
Authors: Fienup James R. , Goodman R. S. , Idell P. S.
Published: February 2023

By averaging over the power spectra of many far-field speckle intensity patterns scattered by a laser-illuminated rough object, one can, after subtraction of a dc term, estimate the autocorrelation of an incoherent image of the object. Equivalently, by averaging the autocorrelations of the many speckle patterns, one can, after subtraction of a bias term, estimate the squared modulus of the Fourier transform of the incoherent image. Then one can reconstruct the incoherent image, or equivalently retrieve the Fourier phase, using a phase retrieval algorithm such as the iterative transform algorithm. Image reconstruction is facilitated by the non-negativity constraint that is valid for incoherent images.
Speckle correlation measurements of stone decay in the deterioration of monuments
Authors: Hinsch K. , Gulker G. , Holscher C. , Wolff K.
Published: February 2023

The study of stone decay is of great importance in actions for the preservation of monuments. Many deterioration processes are accompanied by corresponding changes in the microstructure of the stone surface. Thus a quantitative method is required which is sensitive enough to detect the minute changes in the microtopography of the stone face. Optical solutions to this task utilize surface information obtained in a scattered-light speckle field. Surface changes are measured as changes of the according speckle pattern. To obtain a quantitative measure for the similarity of patterns an optical speckle correlation is performed.
Shuffle communication component for optical parallel computing
Authors: Lohman G. E. , Lohmann A. W.
Published: February 2023

A shuffle communication network serves to connect many individual processor elements in a parallel computing system. Previous optical implementations of the so-called perfect shuffle consisted of macroscopic classical components such as lenses, prisms, and a beam splitter. Other shuffles, especially the inverse perfect shuffle, require highly structured deflecting elements. We implemented such a shuffle, which contains highly structured phase gratings.
Demonstration of switched holograms for optical interconnect
Authors: McManus J. B. , Putnam R. S. , Caulfield H. John
Published: February 2023

We report the construction of a device intended for programmable optical interconnection of multiple processors in a highly parallel computer. This device, which we refer to as the Holoswitch, is based on an array of solid optical switches (liquid crystal polarization switches and polarizing beam splitters), which direct a set of optical beams toward any of a selection of holograms. Each hologram, when selected, deflects the input beams toward an array of detectors or collection optics with any desired prerecorded permutation. We expect that, out of the enormous number of permutations that are possible with many (~1000) input channels, only a tiny subset represents useful interconnection patterns in a computer. Thus a modest number of holograms is sufficient for many parallel computing algorithms. We describe the construction of a prototype device with nine different interconnection patterns recorded on a single 4- × 5-in. DCG hologram. Each permutation pattern handles 64 optical channels in an area of 4 cm2. Switching the liquid crystal cells allows a global change of the interconnection pattern in ~50 ms.
Segmented mirror adaptive optics system
Authors: Downie John D. , Goodman Joseph W. , Ennis David
Published: February 2023

An adaptive optics system that utilizes a segmented mirror as the active component is described and discussed. The mirror is a 10-in. diam spherical mirror composed of 13 independently controllable segments of equal area. The system linearity and control laws are discussed assuming a modal wavefront expansion. Two approaches to modal aberration expansion are briefly outlined using (1) Zernike polynomials as the basis set and (2) a modified set of Zernike polynomials. Both approaches allow calculation of the coefficient vector with a matrix–vector multiplication if a fixed sampling geometry is used. Assuming the employment of Zernike polynomials in the wavefront expansion, the feedback matrix G which governs actuator movement in the presence of measured aberration is computed. The mirror fitting errors to the Zernike polynomials are then estimated, and a finite number of polynomials are chosen which can be adequately corrected.
Optical computer for dynamic magnetic resonance imaging
Authors: Gmitro Arthur F. , Gindi Gene R. , Tresp Volker
Published: February 2023

An optical computing system for the video-rate reconstruction of computed tomography images has been constructed. A modification of this system allows for the reconstruction of magnetic resonance (MR) images. Several fast scanning methods for MR are appropriate to this reconstruction approach and, when coupled to such a system, afford the possibility of real-time dynamic MR imaging.
Real-time computed tomography
Authors: Tresp Volker , Gmitro Arthur F. , Gindi Gene R.
Published: February 2023

The parallel and rapid processing of optical computing can be exploited for the high-speed reconstruction of computed tomography images. Our system implements the filtered backprojection algorithm using an incoherent optical system for the backprojection. A video camera integrates the filtered backprojections, and the reconstructed image can be directly displayed on a video monitor. The filtering operation can alternatively be performed by a heterodyne space-integrating acoustooptic convolver, a surface acoustic wave filter, or a digital finite impulse response filter. We present images reconstructed by our system, discuss system performance, and compare the different filtering methods. In connection with a fast CT scanner our system makes the real-time observation of dynamic events possible.
Statistical properties of stochastic and chaotic optical signals
Authors: Abraham Neal B. , Das B. , Tarroja M. F. H.
Published: February 2023

We have measured (or computed) time-series, second-and higher-order correlation functions, correlation dimensions, and amplitude and intensity spectra to compare and contrast chaotic laser signals (from experiments with a single-mode He-Xe 3.51-μm laser and numerical simulations of unstable inhomogeneously broadened single-mode lasers and numerical results for the Lorenz-Haken model for single-mode homogeneously broadened lasers) with stochastically fluctuating signals measured at the output of an amplified spontaneous emission source and a computed sine wave with added phase noise. We find important similarities and points of distinction in addition to the expected result that stochastic signals would show no evidence of a finite correlation dimension while chaotic signals would show a small fractal value for the correlation dimension.
Symmetric self-electrooptic effect device
Authors: Lentine A. L. , Hinton H. S. , Miller D. A. B. , Henry J. E. , Cunningham J. E. , Chirovsky L. M. F.
Published: February 2023

We demonstrate an integrated symmetric self-electrooptic effect device (S-SEED) consisting of two quantum well PIN diodes electrically connected in a series. The device acts as a bistable optical memory element with individual set S and reset R inputs and complementary outputs (optical S-R latch). The switching point is determined by the ratio of the two inputs, making the device insensitive to optical power supply fluctuations when both power beams are derived from the same source; i.e., it solves the problem of critical biasing common to most optically bistable devices.
Multiple-reflection effects in hemiellipsoid reflectometers
Authors: Snail Keith A.
Published: February 2023

Collecting mirror reflectometers such as the Coblentz hemisphere and the hemiellipsoid are useful for measuring diffuse reflectance and transmittance. The three primary sources of systematic error in these instruments are: optical aberrations (and associated overfilling of the detector), nonuniform angular response of the detector, and multiple reflections between the sample and detector. In previous work, Snail1 derived an approximate upper bound for the magnification of a hemiellipsoid and suggested using an inverted nonimaging2 compound parabolic concentrator to eliminate the angular response of the detector. This paper considers the effect of multiple reflections between the sample and detector of a hemiellipsoidal mirror reflectometer. For a point sample and point detector, multiple reflections can be included in the throughput equation analytically. The result is a power series. For finite sized detectors and samples, a ray tracing approach must be used. In addition to reporting on such a ray tracing study, techniques for correcting for and/or minimizing multiple-reflection effects are discussed.
Interface of optical design programs to CAD/CAE/CAM software
Authors: Wise Timothy D.
Published: February 2023

CAD/CAM systems permit the manufacture of real physical parts on a milling, or other shop, machine which has received its instructions from the design system. However, a persistent problem has been the lack of a link between the optical CAD software and mechanical CAD software. A past paper described software which bridges this gap by producing an International Graphics Exchange Standard (IGES) file from the neutral plot files of the optical model. This IGES file can then be directly read into the mechanical drafting and design programs, ANVIL and GEOMOD. Although the latest enhancements to this older interface are addressed, the main thrust is the description of three completely new capabilities: (1) the ability to read directly NASTRAN-generated strain data for optical surfaces into the optical design program CODE-V, (2) the direct passage of a standard lens prescription in CODE-V to the program APART for stray light analysis, and (3) the entry of mechanical drafting data directly into APART via IGES files. This last interface is particularly exciting because it allows, for the first time, a completely graphic entry of structural data into an optical analysis program. A description of the typical procedures used to accomplish the transfer of data is provided along with several examples. Plans are presented to use these new software links to achieve paperless manufacture of optomechanical systems. Since the current algorithms have been designed with an eye on eventual improvements, an assessment of current limitations and future enhancements is also included.
Subwavelength resolution using near-field diffraction
Authors: Goodell J. B.
Published: February 2023

Spatial frequency response as predicted by Fraunhofer optics is not the ultimate optical resolution limit. Very near-field diffraction fields, within even Fresnel zones, offer the means of exceeding the Rayleigh limit by an order of magnitude or more using no imaging optics but placing and maintaining sending and receiving elements in very near-field zones. Optical diffraction in the very near-field zone is discussed, and successfully operating the 18-bit absolute optical encoder working at a 0.65-μm wavelength light which easily resolves a 0.1-μm displacement is described in detail. The LSB length on the 3.28-in. Gray codes track is in fact 1 μm and thus requires at least 0.25-μm resolution, which is beyond the capability of even high numerical aperture optics.
Orientation selectivity of dichoptic adaptation for chromatic and luminance gratings
Authors: Chan Hoover , De Valois Karen K.
Published: February 2023

Binocular mechanisms analyzing oriented equiluminant color- and luminance-varying sinusoidal grating patterns were studied using a dichoptic adaptation paradigm. In all conditions, space-averaged chromaticity and luminance remained constant. Fusion was maintained through the use of strong binocular contours and nonius lines. The spatial frequency of both test and adaptation patterns was 2 cycles/deg. Contrast sensitivity was determined using the method of adjustments. When an equiluminant chromatic adaptation pattern was presented to one eye and an equiluminant test pattern to the other eye, the adaptation effect showed orientation selectivity. There was little adaptation effect when a chromatic pattern was used as the test with a luminance adaptation pattern or vice versa. We conclude that the binocular chromatic mechanism is similar to that seen monocularly and that there is little binocular interaction between chromatic spatial information and luminance spatial information.
Facilitation of chromatic discrimination by a temporally displaced luminance pedestal
Authors: Eskew Rhea T. , Stromeyer Charles F. , Kronauer Richard E.
Published: February 2023

When a purely chromatic stimulus (foveal 1° test on uniform field) is accompanied by a spatially coincident luminance change, the threshold for chromatic detection is about half of what it is without the luminance pedestal. Here we report experiments in which the test and pedestal are varied in duration and separated in time. With a 30-ms pedestal and a 200-ms test, the pedestal must precede the test by <100-ms SOA or facilitation does not occur. Maximum facilitation is reached at or slightly after test onset, and when the pedestal is presented near the end of the test flash, masking occurs rather than facilitation. The masking indicates a powerful rebound or chromatic contrast effect induced by the offset of these very weak chromatic test lights. The perception of test and pedestal presentations as a single event is necessary but not sufficient for facilitation to occur. These results may be used to constrain theories of how luminance contours can improve chromatic discrimination.
Development of an ultrasensitive photon counting system and its use in measurements of ultraweak plant bioluminescence
Authors: Kobayashi M. , Mashiko S. , Scott R. Q. , Saeki R. , Ichimura T. , Inaba H.
Published: February 2023

The study of spontaneous light emission without external or artificial stimulation in biological tissues and cells in vivo is impeded by the extremely low intensity of such bioluminescence in many subjects and systems of interest. The aim of our research project is the research and development of improved means of detecting these biophoton phenomena and the study of ultraweak bioluminescence. We describe here recent developments in both highly sensitive photon counting techniques and ultraweak bioluminescence and chemiluminescence spectroscopy.
Optical symbolic logic
Authors: Cathey W. Thomas
Published: February 2023

Optical systems for implementing optical expert systems have been designed and simulated. Components of the system have been built and tested. The concept, optical system used, and types of Al problem that can be solved with the current system are described. The current research results are reviewed, and future plans are outlined. Results of other optical symbolic logic experiments are also presented. These experiments are based on the use of polarization to carry the information through the system.
Spatial frequency dependence of the color of monochromatic light
Authors: Hayhoe Mary M. , Williams David R.
Published: February 2023

We report here a striking dependence of the color of monochromatic light on the spatial proper ties of the stimulus. The subject matched the color of a uniform field to that of a monochromatic grating. The grating and matching field were alternated at 0.5 Hz, and the luminance profile of the field was a 2-D Gaussian (σ = 36 min of arc). Gratings were unity contrast interference fringes with wavelengths of 457, 477, 502, 515, or 633 nm, and the matching field was a mixture of a white near illuminant C and an incoherent variable wavelength monochromatic light. Subjects adjusted the intensity and wavelength of the monochromatic light and the intensity of the white to make a match.
Spatial distinctness measure for peripheral colored borders
Authors: Blatherwick Peter , Hallett Peter E.
Published: February 2023

A novel spatial method is used to measure the distinctness of peripherally viewed chromatic and achromatic borders. The method determines the degree to which sharp (step-edged) borders must be blurred to be just noticeably different, using Gaussian blur and forced choice. Stimuli consist of 0.5-s duration, centrally fixated disks inserted in backgrounds of another color. This configuration provides maximal border length and large color fields. One achromatic and three isoluminous chromatic borders are tested at five retinal eccentricities from 1.25 to 20° and at both low photopic and mesopic levels of illumination. Blur thresholds for low photopic achromatic borders can be scaled to inverse cortical magnification functions. Chromatic border distinctness for yellow-blue (tritan metamers) is poor below about 2.5° eccentricity and is very poor for red-green (isoblue cone) above 10°. Chromatic border distinctnesses are otherwise comparable with each other but are degraded relative to achromatic at all eccentricities. Mesopic blur thresholds are larger than photopic, the lower eccentricities being more affected in all cases other than red-green, which becomes worse mesopically at high eccentricities as well. The possibility of contributions by rods is discussed.
Calculation of harmonic radiation from atoms subjected to strong laser fields and the possibility of nuclear excitation
Authors: Solem J. C. , Biedenharn L. C. , Rinker G. A.
Published: February 2023

The Hamiltonian for an electron in an effective atomic coulomb field and a strong laser field is If we restrict the operator r to diagonal elements in the principal quantum n, solutions can be approximated by substituting for r, where K is the Coulomb symmetry generator (Runge-Lenz vector). An extraordinary result is that the electron's response is orthogonal to E0: there is no component of the dipole in the E0 direction.
Optical properties of microcrystalline silicon/silicon oxide multilayers
Authors: Persans Peter D. , Abeles B.
Published: February 2023

We report optical absorption and electroabsorption measurements on silicon microcrystallites with dimensions from 40 to 100 Å. Silicon microcrystals of well-defined dimensions were prepared by thermal annealing of periodic amorphous multilayers consisting of amorphous silicon and silicon dioxide sublayers prepared by plasma-assisted chemical vapor deposition. The crystallite size is controlled by the thickness of the amorphous silicon sublayers. This novel class of material possesses many properties intermediate between bulk crystals and disordered or amorphous materials. Optical absorption for hν < 3 eV is significantly higher than that of bulk crystals possibly due to absorption in interstitial material between crystallites. Relaxation of Δk = 0 crystal momentum rules for optical transitions leads to broadening and shift of critical points in optical modulation spectra. Quantum confinement of electronic states may also lead to energy shifts in optical spectra.
Optical processing in photorefractive GaAs
Authors: Cheng Li-Jen , Gheen Gregory
Published: February 2023

GaAs is the most technologically important compound semiconductor for electronics and optoelectronics. It also has the potential to become an important material for optical processing in the near-IR range. This paper discusses this potential. Although the figure of merit n3r/ϵ of GaAs is comparable with those of BSO, BaTiO3, and SBN, the photorefractive effect of GaAs measured so far is considerably smaller than those of these oxides. Because of the cubic crystal structure with optical isotropy and adequate electron-optical tensor, beam interactions in photorefractive GaAs can create special polarization effects which have not been observed in the photorefractive oxide crystals. Use of these polarization effects can make GaAs crystals become an effective optical processing medium with unique advantages in spite of the small photorefractive effect. This potential has recently been demonstrated by the observation of spatial light modulation in LEC-grown un doped semi-insulating GaAs with beam coupling.
Survey of the optical and other physical properties of infrared optical materials
Authors: Browder James Steve , Ballard Stanley S.
Published: February 2023

A comprehensive collection of the properties of more than 100 materials useful in IR instrumentation has been prepared for a forthcoming handbook of IR optical materials. Existing sources of data, such as the standard handbooks and other compilations, have been liberally consulted. Current and recent journals have been searched. The data are presented in convenient form for rapid location by the user. Additionally, this presentation highlights gaps in the available data, which are of special interest and importance for the newer materials. For many properties, graphs and bar charts provide a ready comparison among competing materials. Data are ordinarily given for room temperature and sometimes for 77 K. Broader variations of properties with temperature are included when available and pertinent.
Quantum and thermal noise of solitons in optical fibers
Authors: Drummond P. D. , Carter S. J.
Published: February 2023

We develop a quantum theory of propagation in dispersive nonlinear media via a quantized field theory and a coherent state expansion. The resulting stochastic nonlinear Schrodinger equation includes both quantum fluctuations and thermal noise due to refractive-index fluctuations in the medium. The theory can describe either cw propagation with dispersion or soliton propagation. In the cw case, enhanced squeezing occurs with anomalous dispersion. This is reduced by thermal noise, just as it is in the normal dispersion case. The noise-induced reduction in squeezing is more severe with normal dispersion owing to the intrinsic lack of phase matching in the normal dispersion regime. With anomalous dispersion, the cancellation of nonlinear by linear dispersion allows squeezing to occur over a wide bandwidth even in the presence of thermal fluctuations. Our theory is also able to treat soliton propagation in the anomalous dispersion case. A substantial degree of pulsed squeezing is obtained, and we point out that an optimal detection scheme requires a pulsed local oscillator. Results for the effects of thermal noise on soliton propagation are presented, in which case improvement is obtained by reducing the soliton time duration.
Smart optical pattern recognition
Authors: Caulfield H. John
Published: February 2023

Artificial intelligence applied to hardware such as an optical pattern recognition system is the method such a system uses to optimize its preference in view of its endowments and limitations. Human vision, for example, has strong learned components. Two people with physiologically identical vision systems would undoubtedly see differently because they have self-programmed themselves differently. Likewise humans learn to accommodate for injuries, imperfections, degradation, etc.
Ultrafast optical arithmetic architecture with symbolic substitution algorithms
Authors: Louri Ahmed , Hwang Kai
Published: February 2023

The Inherent parallelism of optics opens new frontiers for parallel processing.1 This fact coupled with the difficulty of VLSI technology is handling the communication needs placed by the parallel computing requirements has generated great interest in digital optical computing. One parallel technique proposed for optical processing is symbolic substitution. We first present algorithms for performing optical digital arithmetic using the signed-digit representation.2 This number system is well suited for optical symbolic processing due to its carry-free addition and subtraction. The addition/subtraction processing time is independent of word length; it depends only on the characteristics of the optical devices used. Second, we present the substitution rules to carry out addition, subtraction, multiplication, and division. Third, we give several approaches to implement such an optical processor as well as discuss their design trade-offs. The proposed processor is a carry-free highly parallel system aimed at exploiting the inherent and unique ability of optics to process information in two space dimensions. Finally, we present a speedup analysis and compare it to an electronic implementation.
Effects of nonlinear phase shift due to stimulated Brillouin scattering in single-mode fibers
Authors: Waarts R. G. , Friesem A. A. , Hefetz Y.
Published: February 2023

Stimulated Brillouin scattering (SBS) is one of the most dominant nonlinear effects in coherent transmission through single-mode fibers. The gain of SBS is always accompanied by a nonlinear phase shift in accordance with the Kramers-Kronig relations between the real and imaginary parts of the nonlinear index of refraction. Such a phase shift may lead to distortion of signals in a coherent transmission line. We investigated the frequency-to-amplitude modulation conversion of a frequency modulated signal counterpropagated by a strong pump wave. For a frequency separation between pump and signal wave corresponding to the frequency of the acoustic phonons (~20 GHz at a wavelength of 820 nm) a strong AM signal was detected. This AM signal was measured as a function of the frequency separation for different pump intensities and parameters of the modulation. Results for fibers with different index profiles leading to a different Brillouin interaction bandwidth are presented. These results are in good agreement with an exact analytical model.
Extremely sensitive laser diode direct detection optical communication system for intersatellite links
Authors: Sun X. , Davidson Frederic
Published: February 2023

A semiconductor laser diode direct detection optical communication system suitable for use in an intersatellite communication link was constructed, and its performance was measured. The system used Q = 4 pulse position modulation (PPM) to transmit binary source data at a rate of 25 Mbit/s and contained a low-noise silicon avalanche photodiode (APD) as a photodetector. Use of the conventional Gaussian model for the output of the low-noise APD (RCA C30902S) was shown to be inappropriate under low-background radiation levels because its use caused a severe underestimate of the optical APD gain and an overestimate of a system bit error rate. A numerical procedure was developed that made use of the Conradi distribution for the APD output which gave good agreement with the results of the experimental measurements of system performance. A slot clock recovery subsystem was also provided in the receiver. It consisted of a nonlinearity which is easy to implement and a narrow bandpass filter centered at the slot clock frequency. Use of the recovered timing signal showed no penalty in the minimal input optical power required to maintain a specified error rate. The system achieved a bit error rate of 10−6 at a received signal level corresponding to an average of 60 detected photons per transmitted information bit (120 photons per PPM symbol).
Spatial mode matching efficiencies for heterodyned GaAlAs semiconductor lasers
Authors: Winick K. A. , Kumar P.
Published: February 2023

The performance of an optical heterodyne receiver is strongly influenced by the degree to which the signal and local oscillator beams can be spatially matched in both amplitude and phase at the detector. Any mismatch reduces the IF signal power and consequently the SNR. The ratio of IF signal power obtained in the presence of a mismatch to that obtained when there is no mismatch is referred to as the spatial mode matching efficiency. Several authors have performed theoretical studies to determine the mode matching efficiency as a function of system parameters, including signal/local oscillator beam angular misalignment, signal/local oscillator beam size differences, and detector-to-spot size ratios. Experiments to quantitatively measure mode matching efficiencies, however, are few. We experimentally measured these efficiencies when two independent GaAlAs semiconductor lasers were heterodyned on a high-speed silicon PIN photo-detector. The experiments have also been repeated using a single frequency-modulated GaAlAs laser, which is self-heterodyned with the aid of an unequal path length Mach-Zehnder interferometer. In the former case, maximum repeatable efficiencies of 75% were obtained. In the latter case, these values increased to ~90 %.
Schematic eye for the 30-day old myopic chicken
Authors: Schaeffel Frank , Howland Howard C.
Published: February 2023

Recently, the chicken eye has become an important model for artificial myopia. A large body of data is available which describes morphological changes in the eyes of young chickens which occur in response to altered visual experience (mainly visual deprivation). Also, development of the refractive state has been studied extensively. However, no attempt has yet been published to predict changes in the refractive state from the changes in the ocular dimensions which were observed following experimental treatment. We used various techniques (infrared photoretinoscopy, infrared photokeratometry, A-scan ultrasound, frozen sections, transscleral images, refractometry, and nonparaxial ray tracing) to develop a schematic eye for the 30-day old chicken. Based on the schematic eye, the refractive state was calculated from morphological data in both normal and ametropic chickens and compared to the refractive states actually measured.
Design considerations for an amateur camera viewfinder
Authors: Fantone Stephen D.
Published: February 2023

The Polaroid Spectra camera contains an unusual telescopic viewfinder comprised of injection-molded components and glass mirrors. The camera’s geometry required a radical departure from the reversed Galilean form typically found in inexpensive cameras. The result is a viewfinder which is over 150 mm in length, has an eye relief of 17 mm, and a magnification of 0.5, covers a full field in excess of 54°, and yet presents a cross section at the front of the camera of <18 × 12 mm. The Spectra's reverse telephoto design includes seven lenses, five aspheric surfaces, and two prisms as well as a four-mirror erecting system. High-volume manufacturing techniques required a design which allows for automated assembly and testing.
Primate ganglion cells: types, distribution, and pathways
Authors: Rodieck Robert W.
Published: February 2023

Until recently, little was known of the different cell types of the primate retina, other than from Golgi studies of cells seen in transverse section. The development of an in vitro preparation, which allows identified cells to be intracellularly injected with a marker able to reveal their full dendritic morphology, has greatly increased our understanding of the distinct ganglion cell types present.
Features in the optical transform of a serrated aperture or disk
Authors: Beal Madeleine M. , George Nicholas
Published: February 2023

In the context of pattern recognition, we describe the optical transform patterns that are obtained from either a roughened circular aperture or a disk with an irregular edge. This topic is of interest both in studying the effects of rough apertures in an optical system and as an approximate model for particulate analysis. A statistical analysis is used to establish the effect of the roughness on the optical transform.
Wavefront calculation from a hologram
Authors: Yang C.W. , Xiang L.Q. , IH C.S.
Published: February 2023

It has become increasingly important to include a hologram or HOE in an optical system for serious applications. It is, therefore, necessary to calculate quantitatively the wavefront reconstructed from a hologram. We have tried two methods to perform the calculation1: the optical path difference method; the tangent plane intersection (TPI) method. For holograms with simple geometries, such as those with planar or spherical waves, both methods yield the same results. For general holograms, particularly for those with small f/Nos. and large aberrations, the results are quite different. Our experiments show that the TPI method produces results more consistent with the assumptions. We are unable to explain why these two methods yielded different results.
Intensity-dependent absorption in barium titanate
Authors: Brost George A.
Published: February 2023

An intensity-dependent absorption in photorefractive barium titanate has recently been reported. This effect results in nonsymmetric behavior of the two-beam coupling gain coefficient. Various characteristics of the intensity-dependent absorption coefficient have been measured. These include temperature dependence and temporal behavior. To date there has been no theoretical treatment of these phenomena. This paper discusses the intensity-dependent absorption via a model in which the absorption is accounted for by the existence of shallow traps. These traps, which are unoccupied at room temperature, become filled by free charge carriers generated by the interaction of the laser light with deep trap impurities that are also present. The rate equations for these interactions are presented and solved. The results are compared with and shown to be in good agreement with experimental results.
Material parameters study in photorefractive barium titanate using Raman-Nath diffraction patterns
Authors: Ditman L.S.
Published: February 2023

We present results from measurements obtained using Raman-Nath diffraction patterns from laser-induced gratings in single crystals of barium titanate. Analyses of these patterns lead to determination of grating and material parameters. The experimental technique consists of passing a probe laser beam parallel to the planes of a grating formed via the photorefractive effect from the interference pattern of coherent laser writing beams which intersect in the crystal. The Raman-Nath diffraction pattern which is observed on a screen placed beyond the interaction region consists of multiple modes angularly separated and located symmetrically about the zero-order (undeflected) mode. The angle of deflection of a particular mode is a function of the ratio of probe beam wavelength to grating spacing in the crystal; the intensity of a particular mode is a function of refractive-index modulation depth. For a fixed angle between the input write beams, the grating spacing in the crystal is varied by rotating the crystal with respect to the input write beam angles. By observing relative intensity changes of the various modes, a best fit of the data to the squared Bessel function curves describing Raman-Nath diffraction gives a value of refractive-index modulation depth. This value in turn leads to the determination of the space charge field and charge concentration.
Phase-only filters implemented on amplitude-modulating spatial light modulators
Authors: Kenkel Jeffrey , Cartwright Steven
Published: February 2023

Phase-only filters are useful for matched filtering and other forms of Fourier-plane filters. Although these filters may be implemented simply on a phase-modulating spatial light modulator (SLM), it is also possible to use amplitude-modulating SLMs, even ones without grey-scale capability. Simple filters encoding two and three phase states are presented. These filters provide useful correlations even with a limited number of resolution points.
Pseudorandom apertures for incoherent image processing
Authors: Cartwright Steven , Flannery David , Milkovich Mary
Published: February 2023

It is well known that effective transfer functions for incoherent imaging can be synthesized by subtracting two images. However, most such schemes suffer due to the difficulty of choosing appropriate apertures with sufficient light throughput. Pseudorandom sequences have anticorrelation properties that make them attractive for optical processing. By using a phase (rather than amplitude) aperture, effective blocking of undesired frequencies is accomplished while maintaining a totally clear aperture. The trade-off is that the spectral bandwidths of the illumination must be restricted.
Optical joint transform correlation using analog phase-only filters
Authors: Lanteigne David J. , Hudson Tracy D.
Published: February 2023

Optical joint transform correlation exploits the interference of two side-by-side coherently illuminated objects. One object is a reference; the other could be a real-time input to the correlator. Optical Fourier transformation of the object plane for two similar objects produces a fringed interference pattern, with the fringe spacing inversely proportional to the object spacing. Nonlinear coherent-to-coherent conversion by a spatial light modulator in the Fourier plane, followed by inverse Fourier transformation, yields paired correlation spots symmetric about the optical axis. Unlike classical correlators, no complex (phase and magnitude) filters are required, only coherent input and reference objects. The spatial light modulators suitable for the nonlinear conversion, such as magnetooptic and liquid crystal devices, map amplitude objects into phase objects. The effects of this mapping on the correlation were investigated by recording joint transform filters on a phase-only holographic recording medium with nonlinear exposure characteristics. The resulting correlations were observed; SNR and overall optical efficiency were found to compare favorably with the output of classical VanderLugt correlators.
Linear phase differentation by image subtraction
Authors: Ojeda-Castaneda J. , Mosso A. , Vazquez A.
Published: February 2023

Image subtraction techniques are powerful tools for detecting small changes in medical images, aerial pictures, and other scenes. By employing suitable optoelectronic devices, the incoherent subtraction technique can provide a fast method for image detection with simultaneous difference processing. Here we propose an incoherent technique of image subtraction for rendering visible in a linear fashion the first derivative of the phase structure. Our procedure consists of subtracting incoherently two images of the same phase object. Each image is spatial filtered by different methods, and it is recorded independently. The spatial filters are novel.
QMF pyramids: a new class of orthogonal pyramid transform
Authors: Adelson Edward H. , Simoncelli Eero
Published: February 2023

We have developed a new class of pyramid transform using quadrature mirror filter kernels. Unlike Gabor transforms, the basis functions are orthogonal and the coefficients are readily computed. Unlike ordinary pyramids, there is no increase in the number of samples needed to represent an image, and the sampling functions are identical to the basis functions. Good localization can be achieved in space, spatial frequency, and orientation. We have derived QMF pyramids for square, quincunx, and hexagonal decimation grids; each has its own set of kernels and its own advantages. By placing the representation in a pyramid structure one can achieve highly efficient computation.
Simple model of the early visual pathways
Authors: Hofmann Martin I. , Hallett Peter E.
Published: February 2023

The model consists of discrete units, both spatial and temporal. The outputs are also restricted to discrete values and are nonlinear functions of the input. Units are arranged in three levels: (1) analogous to the photoreceptors, the image is sampled by a hexagonal array of units; (2) analogous to the center-surround-type cells, each unit is excited by nearby receptor units and inhibited by more distant units; (3) analogous to simple cells in the visual cortex, the units receive excitatory input from a band of center-surround units and inhibitory input from adjacent bands to produce a series of six orientation selective units. An important feature at level (3) is connectivity between the orientation selective units. In a local region of space excitatory connections exist between similarly oriented units and inhibitory connections between orthogonally oriented units. Consequently the properties of level (3) units are modified as the system iterates. The effect of this position-orientation interaction is to sharpen the tuning curves for both orientation and spatial frequency selectivity. The outputs of the units in level (3) may also serve as a basis for simple texture discrimination.
Investigation of broadband absorption by O3 in intracavity dye laser spectroscopy
Authors: Brobst William D. , Allen John E.
Published: February 2023

A parametric study of intracavity absorption by a gas-phase broadband absorbing species has been carried out using a cw dye laser. Absorption by ozone in the weak visible Chappuis band system guaranteed that the intracavity absorption linewidth was much greater than the multimode dye laser emission bandwidth, providing an essentially constant optical loss for all the oscillating longitudinal cavity modes. High spectral resolution of the dye laser emission showed the change in mode intensity due to the presence of additional loss was best characterized by the absorptance (Δl/l0). Use of this form allowed quantification of the absorption via a modified Beer-Lambert relationship. Enhancement of absorption over conventional techniques was observed to be strongly dependent on the laser power, having a value in excess of a factor of 600 near the lasing threshold. Comparison is made to narrowband intracavity absorption by the visible bands of NO2, providing the first direct quantitative observation of both broadband and narrowband intracavity absorbers with the same experimental apparatus. In addition to providing another direct sensitive optical detection method in laboratory studies of O3, the results yield further information for the comprehensive theoretical analysis of standing-wave multimode dye lasers.
Nonresonant satellite holes produced by persistant spectral hole burning of KCl : NO 2 −
Authors: Ambrose W. P. , Sievers A. J.
Published: February 2023

Persistent spectral holes may be burned into the IR vibrational spectrum of

NO

2
−

ions matrix isolated in alkali-halide lattices. The holes are formed when ions, which are resonantly excited by a tunable diode laser, occasionally reorient in the lattice. The frequency shift and inhomogeneous broadening of the vibrational mode both result from lattice strains. A hole burned in a spectral feature arising from low-frequency librational levels in combination with the bending mode of

NO

2
−

impurities in KCl at low temperatures (~800 cm−1) not only produces a hole at the laser frequency but also produces a hole in every other transition. The nonresonant spectral hole positions and shapes are highly correlated to the resonant hole position and shape. The hole burning results indicate that the inhomogeneous broadening in these bands is caused by a distribution of symmetrically split librational levels.
Spatial coherence of semiconductor lasers and laser arrays
Authors: Durkin Peter , Wilson Kimberley , Dente Gregory
Published: February 2023

We have developed a simple method for measuring the spatial coherence at the output facet of semiconductor lasers and laser arrays. The method uses a double slit to interfere two points (x and x′) of a device nearfield and to produce Young’s fringes in the far field. We then measure the fringe visibility for a series of points. If the visibility is high for all possible pairings (x, x′), we are assured that the array is operating predominantly in a single transverse mode; however, if the visibility varies over the series it is evidence of multiple modes. For the multimode case, if we assume that the device output can be represented as an unlocked superposition of transverse modes, we can use the measured visibility to determine the relative power in each mode.