bluuebunny/crossref_metadata_2025 huggingface dataset:
Airborne particulate scatter measurements at multiple wavelengths: a comparison with Rayleigh theory
Authors: Black J. Paul
Published: February 2023

Scattering of airborne particulates has been observed at 0.442 μm and 0.633 μm. The observations were compared to Rayleigh scattering theory with excellent agreement. The angular scatter patterns of these particulates were measured with a p-polarized and an s-polarized incident beam. The detector polarization was the same as that of the incident beam as the detector was scanned in angle. The fourth power wavelength scaling law of Rayleigh particles was compared to the measured particulate scatter. The average index of refraction and particle diameters are calculated for these particles. The scatter from these particulates is a noise source that limits the sensitivity of optical scatterometers at specific angles of operation.
New method of arc suppression for reactive-dc-magnetron sputtering
Authors: Williams F. L. , Nusbaum H. D. , Pond B. J.
Published: February 2023

Modulated-dc-magnetron sputtering offers a novel solution to problems associated with arcing on the surface of the sputtering target. Arcing has been identified as a main contributor to defects in thin films produced with low-pressure reactive magnetron-sputtering deposition. By biasing the target with a de potential that is modulated at ultrasonic frequencies, sputtering-target arcing is eliminated so that coatings with fewer defects are produced. In the technique presented here, the output from a de power supply is directed into a modulator circuit that switches the output according to a frequency and duty cycle set by a waveform generator. Thus, the output from the modulator is a time-varying electric potential with its most negative value equal to the output of the power supply and its minimum value equal to zero. Arcing on the sputtering target ceases when the switching frequency exceeds a certain threshold value (typically 10-30 kHz) that is dependent on the deposition parameters. Since modulated-dc-magnetron sputtering is effective at frequencies that are significantly less than the standard rf-sputtering frequency of 13.56 MHz, complications in coupling energy between the power supply and the sputtering target are avoided. Therefore, the efficiency of the sputtering process is dramatically improved compared to rf sputtering.
Effects of post-deposition baking on stress of magnetron-sputtered single-and multilayer films
Authors: Pond B. J. , Du T. , Sobczak J. , Carniglia C. K.
Published: February 2023

Thick multilayer coatings deposited by dc-magnetron sputtering cause an unacceptable level of stress-induced distortion in coated components. This is because all the dc-magnetron-sputtered films in our studies had a relatively high compressive stress. The compressive stress in sputtered films is due to bombardment of the growing film by energetic species. Previous studies have shown that the compressive stress of ion-beam-sputtered films was reduced by using post-deposition baking. This stress modification technique was used to reduce the compressive stress of dc-magnetron-sputtered single-and multilayer films. The materials investigated in this study were SiO2, Al2O3, Ta2O5, and TiO2. The films were baked at temperatures between 200 and 300°C (392 and 572°F) for approximately 3 h. The amount of change in the stress was dependent on the material and the baking temperature. Thick multilayer films with a total stress near zero were produced bu using this technique.
Quantum efficiency of laser dyes in aerogels
Authors: Gokturk Halit S. , Hart Timothy R.
Published: February 2023

Aerogels are highly porous materials that can be made with pores that have characteristic dimensions as small as 10 nm. A laser dye solution absorbed into small pores of an aerogel serve as a good example of a quantum confined molecular system. In this research two representative laser dyes, Rhodamine 6G and Rhodamine B, were chosen and their fluorescence quantum efficiency values were investigated when solutions of these dyes were absorbed in silica aerogels. Significant increases in the quantum efficiency values were observed for the dye solutions in the aerogels as compared to the bulk solutions (0.89 to 0.99 for Rh6G and 0.37 to 0.77 for RhB). The increase in the radiative quantum efficiency indicates a decrease in the rate constants of non-radiative processes taking place between different energy levels of the dye molecules when they are confined into silica pores. This change can be attributed to an interaction between the dye molecules and the surface of the pores.
Laser-induced fluorescence spectra of equilibrium sulfur vapor
Authors: Billmers Richard I. , Davis Jon P. , Smith Allan L.
Published: February 2023

Sulfur vapor at high temperatures and low pressures should contain mostly S2. The absorption and fluorescence spectra of S2 have been measured extensively over the past century, usually at temperatures well above 600°C. In this study we were interested in the fluorescence spectra at temperatures between 600 and 700°C, where there is a small amount of S3 present according to thermodynamic predictions. The time-integrated fluorescence spectra in this temperature range show the expected vibrational progression for S2 with some very weak extraneous features. The temporal decay curves exhibit double-exponential behavior, indicating the presence of two fluorescing components. The ratio of the amplitudes of these two components changes with temperature and pressure similar to the S2/S3 concentraton ratio predicted by the thermodyanamic model. We were able to separate the spectral contributions from each of the components by using time-resolved fluorescence spectroscopy. The short-time spectra match the vibrational progression expected from S2. At longer times, the S2 contribution vanishes and a much weaker vibrational progression is observable. The spacing in this progression matches well with one of the vibrational mode spacings for S3.
Squeezed amplification with cavity detunings: mean-field behavior
Authors: Sun K.-X. , Wong N. C. , Shapiro J. H.
Published: February 2023

Optical parametric amplifiers (OPA's) can exhibit squeezed amplification when an injected signal beam is used to elicit small-signal gain saturation. This paper extends previous work on OPA mean-field behavior under signal injection. Doubly resonant and triply resonant, single-ended cavities are considered in the good-cavity limit. Owing to the nonlinear coupling between the signal and idler beams within the cavity, both are sensitive to the detuning of each beam from its respective resonance. Signal and idler output mean fields are found by solving the nonlinear coupled-mode equations and are numerically evaluated for a variety of detunings and injection levels. Gain saturation is shown to occur for both beams and to be dependent on the cavity detunings. Comparisons are made with experimental results obtained from a doubly resonant MgO-doped, LiNbO3 OPA/OPO.
Design of achromatic holographic optical elements
Authors: Morris J. E. , Yang H. , Hangzo N. , Feldman M. R. , Rowlette John
Published: February 2023

Holographic optical elements (HOEs) have been widely used in various applications, such as collimating a beam from a laser diode and coupling light into an optical fiber. However, typical HOEs, because of their diffractive nature, suffer from severe chromatic aberration that imposes a strict requirement on the laser diodes and the environment in which they operate. The effect of chromatic aberration is more severe for HOEs with small f-number. This problem was addressed by using the recently developed radially symmetric iterative discrete on-axis (RSIDO)1 encoding method. For example, one HOE was designed for a 13 nm optical wavelength range that corresponds to 0-60°C temperature fluctuation. For an eight phase level HOE with an f-number of 1 a diffraction efficiency of 78% has been achieved in computer simulations with small efficiency variation within the specified wavelength range. The HOEs have been fabricated, and the experimental results will be compared to those of the simulations.
How to reduce thermal resistance of top-surface-emitting vertical-cavity diode lasers
Authors: Osinski Marek , Nakwaski Wlodzimierz , Stohs Jonathan
Published: February 2023

It is well known that excessive heating has serious negative effects on cw characteristics of vertical-cavity surface-emitting lasers (VCSELs), most notably on their output power and overall efficiency. Thus, optimization of the device design aimed at minimizing its thermal resistance is of great practical importance. Usually, extensive numerical calculations are necessary to calculate thermal resistance of VCSELs.1 Consequently, design optimization can be very computation intensive. We have developed a simple analytical approach,2 valid for top-surface-emitting devices mounted p-side up, that allows us to perform the optimization process easily. In particular, we find a relationship between the active region and the laser-die diameters that leads to minimal thermal resistance. We also show that only a marginal improvement in thermal resistance can be expected by substrate thinning in typical proton-implanted top-surface-emitting lasers.
Internal light intensity of vertical-cavity surface-emitting laser diodes
Authors: Choquette K. D. , Leibenguth R. E. , Wokosin D. L. , Zhang T. , Long J. W. , Richie D. A. , Tabatabie N.
Published: February 2023

Because of their short cavity length, vertical-cavity lasers (VCL’s) typically have only one cavity mode within the gain bandwidth, both of which red shift at different rates with increasing temperature; also, the gain falls off with increasing temperature. Thus, because of ohmic heating with increasing current injection, the VCL output will roll over and eventually cease. Using monolithic lateral photodetectors, we monitor the lateral VCL spontaneous emission and find that the internal light continues to increase with current, even after the output peaks and begins to decrease. When the laser emission ceases, the lateral emission begins to fall, presumably because of the gain decrease. Therefore the VCL maximum output is primarily limited by the cavity mode/gain spectral mismatch and is not due the decrease in gain.
Absorption and gain coefficients of modes of inhomogeneous spheres
Authors: Chowdhury D. Q. , Hill S. C. , Mazumder M.
Published: February 2023

A difficulty in applying the usual definition of gain or loss of a laser mode to the modes of a dielectric sphere is that there is a possible ambiguity in the normalization mode volume: the evanescent fields outside the sphere overlap with the radiating fields leaving the sphere. Here we show that an effective-average gain or loss for a resonant or near-resonant mode of a sphere can be computed by including the trapped external fields of a mode out to the first zero of the spherical Neuman function describing the field just outside the sphere. To verify the accuracy of the method, loss coefficients computed for layered spheres are used to estimate the Q of each mode. These estimated Q’s compare very well with exact Q’s of the modes computed analytically. Results computed by a time-independent perturbation method are also compared. Our method is used to compute a two-photon effective absorption coefficient for near-resonant excitation of a sphere. Results are shown as a function of input intensity and frequency. This method of calculating effective absorption or gain should be very useful in modeling lasing, stimulated Raman scattering (SRS), and other nonlinear processes in microspheres.
Novel applications of the polarization interferometer
Authors: Azzam R. M. A.
Published: February 2023

The freespace, nonbirefringent, polarization interferometer is one of the most versatile optical instruments. It can be used as (1) a limitless variable phase retarder, (2) an analog or binary polarization modulator, (3) a global polarization state generator of light of a controlled degree of polarization, (4) a depolarizer, (5) an ellipsometer of transmissive or reflective samples, and (6) an instrument for measuring the coherence and spectral properties of light sources when used in conjuction with a complete polarization-state detector. A brief account of each of these applications is presented.
Reconstruction of the spectrum in a Michelson interferometer with an extended radiation source by using the Hilbert–Schmidt method
Authors: Jia Yuanduo , Rong Xingfu
Published: February 2023

After reviewing various early methods of deconvolution, the Hilbert–Schmidt method (HSM) is presented to improve the capability of a Michelson interferometer. Simulation experiments were performed with an Apricot computer. The instrumental function we obtained has a very small width and has no noticeable sidelobes. Therefore the resolution is improved greatly, and the input spectrum is recovered in a Michelson interferometer with an extended radiation source. The intensity of the interferogram is increased on a large solid angle that exceeds the value permissible in FTS. The influence of random noise is also discussed, and the maximum order of the noise is evaluated.
Asymptotic description of Gaussian pulse propagation of arbitrary initial pulse width in a causal, dispersive dielectric
Authors: Balictsis Constantinos M. , Oughstun Kurt E.
Published: February 2023

Modern asymptotic techniques are applied to obtain a rigorous, uniformly valid description of Gaussian pulse propagation of arbitrary initial pulse width in a single- resonance Lorentz medium in the mature dispersion regime. This is a problem of considerable practical importance because of the current experimental capability of generating pulses with widths approaching the femtosecond regime. The description afforded by the standard asymptotic theory is shown to be in excellent agreement with two independent numerical experiments describing the propagation of ultrashort Gaussian-modulated harmonic signals with full widths at half maximum ranging from 0 (δ-function input pulse) to 0.4 fs. A generalization of the asymptotic description to broader pulses of arbitrary initial pulse width is then presented. The proposed theoretical description does not rely upon any quasimonochromatic or slowly varying envelope approximations, generalizing the results of these approaches in the limit of broad pulses, nor does it depend upon any nth-order dispersion approximation. Thus, it rigorously maintains the Kramers-Krönig relations, which are critical to the proper analysis of linear dispersive pulse dynamics.
Post-launch calibration of the advanced very high resolution radiometer for the Pathfinder project
Authors: Nagaraja Rao C. R. , Chen Jian Hua
Published: February 2023

The in-orbit degradation of channels 1 (visible; ≈0.63 µm) and 2 (near infrared; ≈0.83 µm) of the Advanced Very High Resolution Radiometer (AVHRR) onboard the NOAA polar orbiting satellites has been evaluated as part of the NOAA/NASA Pathfinder project, a component of the national climate and global change research program. The southeastern part of the Libyan desert has been used as the calibration target site in the implementation of the Staylor1 calibration technique. Examples of the application of the degradation rates to rehabilitate remotely sensed operational products, such as columnar aerosol amount and normalized vegetation index, will be given.
Optical wavelet matched filters
Authors: Sheng Yunglong , Roberge Danny , Lu Taiwei , Szu Harold
Published: February 2023

The wavelet transform decomposes a signal onto a set of basis wavelet functions that are dilated and shifted from the mother functions h(t), satisfying an admissible condition. This transform is compact in both time and frequency domains and is therefore efficient for time-dependent frequency analysis of the signal. We consider the wavelet transform as the correlations between the signal and a bank of wavelet filters, each having a fixed scale.1 Thus, the wavelet transform of a 1D signal is implemented in an optical correlator with multiple strip wavelet filters, and the wavelet transform of a 2D signal is implemented in a multichannel optical correlator. We make the matched filters recording the 4D wavelet transforms of a 2D input image for optical pattern recognition. With the isotropic Mexican-hat wavelets, the wavelet transform becomes the well known Laplacian-Gaussian operator for zero-crossing edge detection. However, we synthesize the filters by combining the wavelet transform filters and the conventional matched filters in the same Fourier plane for pattern recognition. The experimental results will be shown.
Two-dimensional optical wavelet transform for industrial inspection tasks
Authors: Sitter David N.
Published: February 2023

The wavelet transform of an image may be viewed as a series of bandpass filtered versions of the image where each bandpass filter is a scaled version of a prototype filter. It provides a method of viewing the image at various spectral resolutions. The wavelet transform is being investigated as a method for inspecting textured industrial products produced in rolls or sheets (paper, metals, etc.) for flaws. An optical method to implement the 2-D wavelet transform in parallel has been developed. A coherent optical processor is used to generate multiple bandpass filtered images of an input image. The measured output is the magnitude squared of the wavelet images, or the "scalogram." An electronic computer can then be used to analyze the wavelet images. The goal is to locate and classify flaws in products by noting significant deviations in the statistics of the wavelet images from the expected image statistics.
A joint transform correlator utilizing the wavelet transform
Authors: Katz A. , Kanterakis E. G. , Zhang Y. , Lu X. J. , Caviris N. P.
Published: February 2023

Wavelet transforms can be used to decompose a signal (image) into orthogonal components. When a small set of these components is used to form a wavelet transform sub-image, only specific characteristics of the image are retained. It is the identification of these characteristics that can be used to perform pattern recognition. A joint transform correlation system utilizing wavelet transforms is used to perform pattern recognition. An optical implementation of this system is described. Problems with respect to scale, rotation and translation are addressed and experimental results are presented.
Pump statistics and photon statistics in the micromaser
Authors: Bergou J. , Hillery M.
Published: February 2023

The statistics of the beam of excited atoms that pumps a micromaser influence the photon number distribution of the cavity field. Of the cases studied so far, regular injection statistics minimize the number fluctuations and Poisson statistics maximize them. Here we extend these studies in two directions. Previous master equations describing sub-Poissonian injection statistics were derived by using standard reservoir theory. Recently, corrections to these equations have been found that involve the commutator of the gain and loss operators. Describing the system by a discrete map, we can avoid the approximations inherent in reservoir theory. The results are compared to those of the master equation. Differences are found to be small for large photon number but increasingly important for decreasing photon number and pump beam intensity, indicating the breakdown of reservoir theory in this regime. We give an approximate expression for the photon number distribution for weak damping and discuss its connection with semiclassical theory. Finally, we generalize our treatment for super-Poissonian pump fluctuations.
Photon pair correlations and the effect of Raman scattering noise in optical fibers
Authors: Kennedy T. A. B. , Stephens J.
Published: February 2023

The propagation of a quantized radiation field in a nonlinear optical fiber is investigated by using a quantum nonlinear Schrödinger equation with Raman scattering contributions.1 Wideband photon pair correlations generated via the optical Kerr effect and the role of group velocity dispersion and Raman scattering will be discussed. Specifically, the quantum correlations of up-shifted and downshifted sidebands in the modulational instability at terahertz frequency detuning from the pump lie outside the GAWBS region, but they are influenced by the low frequency region of the Raman gain curve, which introduces an asymmetry between the sidebands. The effects of this asymmetry on photon pair correlations and twin beams will be discussed.
The role of cue quality in depth perception from multiple cues
Authors: Young Mark J. , Johnston Elizabeth B. , Landy Michael S.
Published: February 2023

Perceived depth of rotating ellipsoids and elliptical cylinders was examined with depths specified by motion, texture, and stereo independently manipulated. The combined depth estimate was a linear function of each cue. By manipulating the reliability of individual cues we found that the weight assigned to a cue depends upon its quality. Using only texture and motion, we found that when cue reliability was reduced, the weights summed to less than one and perceived depth decreased. To offset the extraneous cues from the flat display that may account for the remainder of the weight and reduce perceived depth, we improved the display by adding a stereo cue. In displays with sufficient high quality depth information, pilot experiments indicate that the weight subtracted from a reduced quality cue is redistributed among the remaining depth cues rather than being assigned to flatness. Extraneous cues may also play a role in Loomis and Eby’s (ICCV, 1988) finding that the perceived depth of ellipsoids specified by motion alone decreased as the angle between the line of sight and the rotation axis decreased. Using stereoscopic movies of textured ellipsoids, we find that the overall depth percept does not diminish for rotations about axes nonorthogonal to the line of sight until we approach the degenerate case (rotation about the line of sight). Thus, when there are rich depth cues, perceived depth does not decrease as a result of reducing the reliability of one of the depth cues.
The function of topography in the visual pathway
Authors: Carman George J.
Published: February 2023

Such basic functions of vision as stereopsis and kineopsis can be accomplished through the use of topographic mappings of the visual field, such as those seen in the primate visual pathway. In binocular or motion parallax viewing, parallax cues to depth are contained in pairs of images that differ locally by a combination of translations, rotations, and dilations. These generalized disparities can be represented by a pair of scaler harmonic potentials defined on the visual field. These potentials are used to determine a flow of visual information that nulls these disparities so as to fuse the pair of images. The values of these potentials at each point of the visual field are computed through use of a Green’s function, which contains an explicit specification of a composition of conformal mappings of the visual field. These mappings may be interpreted as a sequence of topographic transformations of the visual field and are qualitatively similar to those seen in the lateral geniculate nucleus (LGN) and the primary and secondary cortical areas (V1 and V2) of the primate visual pathway.
Energy computations in motion and texture
Authors: Werkhoven Peter , Sperling George , Chubb Charles
Published: February 2023

Energy is a phase-independent measure of stimulus strength. We show that an energy computation (that is, the energy of the spatiotemporal spectrum of some possibly nonlinear stimulus transformation) determines perceptual strength in three domains: (1) motion that is carried by luminance (first-order motion), (2) motion that is carried by textural properties (second-order motion), and (3) texture orientation in ambiguous spatial displays. We explore the hypothesis that perceptual strength in all three domains is governed by the same energy algorithm; it is merely applied to different transformations or to different cross-sections of a spatiotemporal stimulus. We generate ambiguous stimuli with competing motion paths (or competing texture orientations) and measure the psychometric functions that describe the perceptual dominance of one of the stimulus components as a function of its contrast. These measurements are repeated at different contrast levels of the competing component. From these data, we infer (a) the nature of the strength computation and (b) the exponent of the power function that describes the growth of equivalent internal noise with stimulus contrast. We find that all three domains are served by energy computations. The exponents of the noise-growth power functions are strikingly similar within an observer in all three domains, although exponents for different observers differ widely. We conclude that similar energy algorithms govern first-and second-order motion strength in space-time and orientation strength in a purely spatial domain.
Large array interconnection by photorefractive correlation
Authors: Ford Joseph E. , Fainman Yeshaiahu , Lee Sing H.
Published: February 2023

We present experimental results for an optical array interconnection network using the correlation matrix-tensor multiplier (CMTM) algorithm, where the phase-encoded input array is optically convolved with a control image holding the interconnection weights. Two-dimensional arrays can be interconnected with complex gray-level weights by using binary phase-only spatial light modulators. The CMTM algorithm allows graceful accommodation of limited modulator size by trading off control image bandwidth for output signal-to-noise ratio (SNR). The correlation was performed by photorefractive four-wave mixing, and the interconnection information was stored in a single exposure of each control image. The control images were displayed with binary phase-only patterns etched into quartz. Multiple interconnection patterns were prestored as color-multiplexed volume reflection holograms in z-cut LiNbO3. Fast reconfiguration between interconnection patterns is possible by using a wavelength tunable source, decoupling both the modulation and switching speeds from the slow photorefractive response. Experimental results confirmed theoretical predictions that the algorithm works best for densely connected networks, with a large fan-in to each output. Interconnection of up to 4096 inputs and outputs was demonstrated by using such dense interconnection patterns. An aggregate average SNR of over 200 was obtained for 1024 inputs and outputs.
Design of a 2 × 2 bit multiplier and N×N bit PIPO shift register by using a butterfly interconnection network
Authors: Iftekharuddin K. M. , Karim M. A.
Published: February 2023

The complexity of the very large scale integrated circuits can cause great constraints on intrachip and interchip communication capabilities. In comparision, a free-space interconnection network such as a butterfly interconnection has the advantage that it does not require magnification of the input arrays.1 Further, it may be used to realize all of the logic functions and operations that have already been obtained by using perfect-shuffle.2 Herein, we show a novel approach for realizing a 2 × 2 multiplier and then extend the technique for realizing an n-bit parallel-in parallel-out (PIPO) shift register using sequential logic gates.
Arithmetic processing using higher-order modified signed-digit symbolic substitution
Authors: Alam M. S. , Awwal A. A. S. , Karim M. A.
Published: February 2023

Among the various nonbinary number systems introduced for solving the bottleneck of carry propagation, modified signed-digit (MSD) arithmetic1 appears to be the most promising because it provides parallel, carry-free addition and borrow-free subtraction with storage complexity proportional to the length of the bit string. In MSD carry-free addition schemes, the pair of numbers to be added is first converted into an intermediate pair such that the addition of the latter pair will not generate any carry. In this paper, we extend the higher-order symbolic substitution (SS) technique to incorporate the MSD numbers. The propos d method ensures that both addition and sub traction operations can be implemened in only two steps, irrespective of the number of bits to be processed, thus saving a tremendous amount of computation time. Further, a new set of carry-free SS rules that are based upon checking a pair of reference bits from the next-lower-order bit position is derived. Finally, a content-addressable memory based optical implementation for the proposed scheme is also suggested.
Non-interferometric reconstruction of partially coherent sources
Authors: Kowarz Marek W.
Published: February 2023

Most existing techniques used to determine the properties of a partially coherent source require interferometric measurements of the cross-spectral density of the field produced by the source. We examine the circumstances under which the interferometric measurements may be replaced by measurements of the spectrum of the field in two or more planes. This approach bears some similarity to a method sometimes used in connection with the phase retrieval problem. In order to provide some insight into such noninterferometric reconstructions, we first consider the simple case of a Gaussian Schell-model source. We then examine some more general types of sources.
Transforming a circular laser beam into a square or trapezoid-almost
Authors: Sweatt William C.
Published: February 2023

An aberrated laser beam will change shape as it propagates. We can use this phenomenon to transform a collimated, uniform-intensity, round beam into a square beam with rounded corners and a fairly uniform intensity. The square beam can be recollimated because no rays cross each other. A similar transformation that turns a circular beam into a trapezoidal shape with rounded corners has been found. These aberrating elements can be fabricated by using binary optics technology. [Opt. Eng. 31(2), 245]
HCI tropospheric abundance from very high resolution ground based infrared solar spectra
Authors: David Shelle J. , Goldman Aaron , Rinsland Curtis P. , Murcray Frank J.
Published: February 2023

Very high resolution (0.004 cm–1) solar spectra near 3000 cm 1 have been collected from the ground at Mauna Loa, Hawaii, and Denver, Colorado. The R(1) line of the H35Cl (1–0) vibration- rotation band at 2925.9 cm–1 is included in these spectra. A non-linear least squares program has been used to analyze the HCI feature for column abundance. Although this program does not directly determine the vertical distribution of HCI, the tropospheric mixing ratio of HCI must be substantially reduced from the standard profile in order to accurately fit the line.
Ground based ultraviolet/visible spectroscopic measurements of stratospheric trace gases
Authors: Mount George H.
Published: February 2023

Ground and aircraft based measurements in the ultraviolet and visible spectral regions have provided critical information about the composition and time evolution of stratospheric trace gases. The technique has been especially useful in detecting nitrogen and chlorine species important to the interpretation of the Antarctic ozone hole and is now being used to measure changes in trace gas composition of the stratosphere that affect ozone depletion. Many molecular species possess highly structured absorption spectra, and measurement of their stratospheric abundance can be accomplished by observation of the scattered sunlight in the zenith sky during the day or the Moon at night; diurnal changes can be measured over a 24 h period. The technique was first developed in the 1970's and has now reached a level of sophistication such that absorptions as low as 0.02% absorption can be measured in less than 5 min integration time. New instrumentation under development to make these measurements will be discussed, as will the advantages and disadvantages of this method.
Space charge waves in photorefractive materials
Authors: Solymar L. , Shamonin M. S.
Published: February 2023

The dispersion characteristics of space charge waves propagating in a photoconducting material are derived. It is shown that both forward and backward waves can propagate depending on the materials parameters. Special cases include the low attenuation space charge waves used in the past for interaction with acoustic waves. The interaction with optical waves is investigated when the photoconductor is also an electro-optic (i.e., photorefractive) material. It is shown that power can be transferred from the optical waves to the space charge waves and vice versa. Experiments conducted in the past on two-beam interactions are reinterpreted in terms of new types of interactions that involve space charge waves. New experiments for the excitation and detection of space charge waves are proposed.
Reflection-grating based photorefractive phase conjugator and ring resonator
Authors: He Q. Byron , Campbell Scott , Yeh Pochi , Shen Dezhong
Published: February 2023

Photorefractive materials, such as BaTiO3, KNbO3, SBN, etc. are known to exhibit high nonlinearity at low optical intensities. High fidelity optical phase conjugation and various optical resonators have been demonstrated in a variety of photorefractive crystals.1 Most of these phase conjugators and oscillators are based on the transmission type of gratings, which are relatively slow depending on the kind of crystal and optical intensity used. Reflection gratings, on the other hand, have the potential to respond faster than the transmission grating because the photo-induced charges move much shorter distances in the photorefractive materials. Recently, a self-pumped phase conjugator based on the reflection gratings in KNbO3 has been demonstrated to achieve a millisecond response time.2 In this paper, we present a systematic study on the reflection-grating based two beam coupling, self-pumped phase conjugation and, for the first time, unidirectional ring oscillations in the Fe-KNbO3 crystal. Fast response time has been observed experimentally in both two beam coupling and unidirectional ring oscillation. Good phase conjugate fidelity has been achieved from the self-pumped phase conjugators.
Contrast-modulation flicker in the short-wavelength cone system
Authors: He Sheng , MacLeod Donald I. A. , Stockman Andrew
Published: February 2023

When an unresolvable grating of high retinal contrast is presented intermittently by modulating its contrast at constant average luminance, observers experience uniform field flicker. For long-wavelength cones, this contrast-modulation flicker can be seen for fringe periods almost as small as the diameter of a cone, implying no substantial neural spatial integration prior to the compressive or sensitivity-regulating nonlinearity responsible. We now report that the short-wavelength cone system, despite its greater spatial integration than the other cone systems, can generate contrast-modulation flicker for spatial frequencies as high as 50 cpd, a value comparable to that of the other cone systems in the same retinal area. Spatial resolution at the nonlinear site is in all cases apparently limited by the size of the cones. Likewise, little temporal filtering (in the range up to 15 Hz) precedes the S cone nonlinearity: evidently the reduced sensitivity for rapid flicker seen by S cones is due to postreceptoral limitations.
Picosecond pulse power generation in high power, AlGaInP visible diode lasers
Authors: Mayes Mark G. , Tatum Jim A. , Serreze H. B. , MacFarlane Duncan L.
Published: February 2023

High power visible diode lasers have recently produced cw output powers in excess of 1 W.1 These devices may be used to create picosecond pulses of high peak power in a number of ways, including gain switching, resonantly driving a sustained oscillation, and mode-locking with an external cavity. We will describe our experimental results, aiming mostly to provide a contrast among the different methods. Self mode-locking, for example, gives a longer pulse over a smaller operating region than an rf driven configuration, but offers a relatively noise-free, inexpensive option for generating visible, 500 psec pulses. A multimode, rate equation theoretical model gives us a quantitative understanding of the laser dynamics, and this work will also be presented.
Linear and nonlinear effects in efficient green and blue surface normal second harmonic generation AlxGa1–x As resonant periodic waveguides
Authors: Zou L. C. , Malloy K. J.
Published: February 2023

We designed resonant periodic waveguides for output enhancement of counterpropagating surface normal second harmonic generation (SNSHG). The waveguides consist of alternating λ(2ω)/ 2 layers of materials with high and low χ(2) and n(2ω) which we refer to as the "generating" and "spacing" layers, respectively. Our model assumes the excited source elements in the generating layers emit SH fields; the same process is weaker in spacing layers that offer proper phase shift to get in phase enhancement at the output surface. We designed Al0.7Ga0.3As/Al0.9Ga0.1 As waveguides for 532 nm and 475 nm. High Al AlGaAs was used because of the absorption loss of SH fields, especially to blue light. However, nonzero χ(2) of spacing layers become the most important loss mechanism. The relative importance of other losses, such as absorption to the SH field and reflection at interfaces determined by admittances at 2ω, was also considered. The samples are currently being grown by MOCVD and available experimental results will be reported.
Competitive optical learning with winner-take-all modulators
Authors: Wagner Kevin H. , Slagle Timothy M.
Published: February 2023

The optical implementation of modern neural network learning models such as competitive learning networks, resonance correlation networks, and back propagation networks requires a wider range of neuron behavior than a simple saturating threshold non-linearity. However, optical implementation of neurons that incorporate non-local, non-linear functions such as shunting inhibition, winner-take-all, and history-dependent behavior is beyond the capability of conventional optical devices. A new class of light modulator has been developed that combines the flexibility of analog and digital electronic VLSI circuits, optical detectors, and the switchable electo-optic capabilities of liquid crystal materials. In this paper we will show how these liquid crystal/VLSI modulators can be used in optical implementations of these learning networks.1 We will discuss in detail a competitive optical learning network that uses LC/VLSI winner-take-all neurons on fractal grids to program adaptive volume holographic interconnections.2
Large scale simulations of an optoelectronic neural network
Authors: Sharpe J. P. , Johnson K. M. , Robinson M. G.
Published: February 2023

With improving optical device technology it is now possible to consider constructing very large optoelectronic neural networks containing of the order of 1000 fully interconnected neurons. Whether such systems will work, though, depends on the quality of the optical devices and the network architecture. A recent study has indicated that a 200 neuron single layer polarization logic network can operate under the constraints of presently available spatial light modulators.1 In this paper we will extend this study to examine the effect of device limitations on the performance of single- and multilayer networks containing up to 1000 fully interconnected neurons. We consider the effect of nonlinearities, contrast ratio, and quantization noise in the weight matrix and the effect of noise at the inputs and outputs on the convergence rate and number of patterns that can be classified.
Infant cone morphology and visual acuity
Authors: Brown Angela M.
Published: February 2023

Infant visual performance is much worse than that of adults. According to one account,1 the striking morphological immaturity of infant foveal cones contributes directly to the poor vision of infants. This explanation depends on the assumption that infants use their immature foveal cones to control visual performance. In another account,2 immaturity of the foveal cones contributes indirectly to poor visual performance by forcing the infant to use the (relatively mature) extrafoveal retina to do tasks the adult does foveally. To decide between these two views, I used morphological data on human and macaque infants to estimate the amount of light absorbed by the foveal and extrafoveal cones. The fraction of the retinal surface over which photons may be absorbed was constant with age in the macaque extrafoveal retina, and equal to the fraction for human adults. All other data were from humans.
Programmable optical neural networks
Authors: Owechko Yuri
Published: February 2023

We have developed an optical neurocomputer for implementing neural networks based on real-time holography in photorefractive materials. Optical techniques show great promise for implementing neural network models because of the parallelism, connectivity, and high storage capacity of optics. It is generally agreed that optics will most likely be used for implementing very large neural networks that are impractical to simulate or implement electronically. In our system weighted connections between neurons are recorded in barium titanate as photorefractive holograms. We have virtually eliminated distortion and crosstalk between holograms by using beam fanning to distribute each connection weight among many angularly and spatially distributed photorefractive gratings. We have successfully demonstrated several optical neural networks including the Perceptron Bidirectional Associative Memory (BAM) and back propagation with a single hidden layer. All of these networks were implemented on the same hardware using a single crystal and SLM by simply changing the software. We have demonstrated networks with up to 7,000 neurons, 800,000 weights, and PC bus-limited learning rates of up to 106 connection updates per second.
Method of convex projections for image enhancement and restoration
Authors: Sezan M. Ibrahim
Published: February 2023

The method of projections onto convex sets (POCS) is an interative method that finds a feasible solution consistent with a number of a priori constraints. POCS has found applications in numerous fields ranging from astronomy to neural networks. Here we focus on the application of POCS in image restoration and enhancement. In image restoration and enhancement problems, a priori constraints are defined on the basis of the measured data as well as on the degradation operator, the noise statistics, and the actual image distribution itself. For each constraint, a closed convex set is defined. An estimate of the actual image distribution is defined as a member of the intersection set and is determined by successively projecting an initial estimate onto the constraint sets. After a brief review of the fundamentals of POCS, we discuss the application of POCS to two problems: (i) restoration of images degraded by both blur and noise, and (ii) resolution enhancement of image sequences by reconstructing high-resolution still frames from a sequence of images at a lower spatial resolution.
Monte Carlo simulation of the quantum master equation for vacuum, thermal, and squeezed reservoirs
Authors: Zoller Peter
Published: February 2023

We discuss Monte Carlo simulation of the quantum master equation in terms of system wave functions undergoing a sequence of quantum jumps based on the delay function for the occurrence of the “next jump”.1-3 The formalism can be applied to calculate the density operator and correlation functions (spectra) in quantum systems with a large number of degrees of freedom. We present the formalism and applications to (i) a multilevel atom undergoing spontaneous emission including mechanical light effects (in particular, laser cooling in the quantum limit), (ii) coupling of an atomic system to a squeezed vacuum, and (iii) cavity QED problems with coupling to thermal and squeezed baths.
Decay of quantum coherence using quantum trajectories
Authors: Carmichael H. J. , Tian L. , Kochan P.
Published: February 2023

In the quantum trajectory approach an open quantum system is represented by a stochastic pure-state wave function. The mixed-state density operator that satisfies the usual master equation is recovered from the quantum trajectories by performing either an ensemble average or, for stationary systems, an average over time. This unraveling of the master equation dynamics into pure-state trajectories provides new insight into the decay of quantum coherence in systems that are open to the environment. Under some conditions macroscopic superposition states are preserved as macroscopic superposition states along individual trajectories, but are reduced to mixtures by the trajectory average. Under other conditions one of the states in a macroscopic superposition becomes dominant (in amplitude) over the other along each quantum trajectory. We discuss the mechanisms that produce these dynamics and assess the implications for the observation of Schrodinger cat states in optics experiments. We present results for some specific examples of macroscopic superposition states generated by a cavity QED system. The system involves a small collection of atoms in an optical cavity driven by a coherent laser field. Under strong-coupling conditions this system produces a variety of Schrodinger cat states whose precise form depends on the number of atoms, the method of excitation (through a cavity mirror or from the side), the initial state of the atoms, and the position of the atoms in the cavity.
Monte Carlo wave-function solution of the spectrum of Rb in a 1-D optical molasses
Authors: Lett Paul D.
Published: February 2023

A Monte Carlo wave-function approach is used to calculate the spectrum of resonance fluorescence as well as the momentum and position distributions of an 85Rb atom in a one-dimensional standing-wave optical field (“optical molasses”). The problem includes the 16 states of the F=3 to F′=4 transition and sufficient momentum states (~100) to accurately reproduce the momentum distributions expected from polarization-gradient cooling. In addition, the trapping of these cold atoms in optical potential wells formed in some polarization configurations is demonstrated. Dicke-narrowed spectra with sidebands representing transitions between bound states in the optical potentials result. The problem is in some sense “too large” to permit solving for the spectrum by using more traditional techniques. A comparison with recent 1-D experiments measuring the spectrum of 85Rb is made. Some insights into atomic dynamics can also be gained by examining the evolution of the atomic wave packet in time.
Schottky-barrier focal plane arrays
Authors: Kosonocky Walter F.
Published: February 2023

This paper reviews the progress in the development of infrared image sensors with Schottky-barrier detectors (SBDs). Schottky-barrier focal plane arrays (FPAs) are infrared imagers that are fabricated by a well established silicon VLSI process; therefore, at the present time they represent the most advanced technology for large-area high-density focal plane arrays for many SWIR (1 to 3 μm) and MWIR (3 to 5 μm) applications. SBD line sensing arrays with up to 4096 × 4 elements and 2048 × 16 TDI elements were developed, and SBD staring (area) arrays with up to 1040 × 1040 elements have been reported. PtSi SBDs represent the most established SBD technology for applications in the SWIR and MWIR bands. At an operating temperature of 77 K, the dark current density of PtSi SBDs is in the range of 1.0 to 4.0 nÅ/cm2. Pd2Si SBDs were developed for operation with passive cooling at 120 K in the SWIR band. IrSi SBDs have also been investigated to extend the application of Schottky-barrier FPAs into the LWIR (8 to 10 μm) spectral range. Because of very low readout noise, the IR-CCD imagers with PtSi SBDs that have quantum efficiency of 0.5% to 1% at 4.0 μm are capable of 300-K thermal imaging with a noise equivalent temperature (NEΔT) from 0.033 to 0.15 K for operation at 30 frames/s and f/1.0 to f/2.8 optics.