bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear optics and connection machines
Authors: Anderson Dana Z.
Published: February 2023

Optics is a natural context in which to contemplate the implementation of connection processors. The highly communicative nature of the processing elements in these machines begs for connection mechanisms that do not interact except at (or near) the processing element. This is particularly true in systems which are globally interconnected. Lightwaves do not interact except under the attendance of a material medium, and then only weakly. Furthermore, optics lends itself very well to parallel computation. Lenses, holograms, and other optical elements can easily manipulate large arrays of data in a parallel fashion. It may be possible to implement connection machines using continuous field optical architectures. These devices offer the inherent parallelism of propagating waves and an information density in principle dictated by the wavelength of light and the quality of the bulk optical elements. Few components are needed to construct a relatively large equivalent network. Various associative memories based on optical resonators have been demonstrated in the literature. These memories recall stored information through a reconstruction of injected partial information. The memory is the first realized example of an optical device connection machine function implemented with this kind of architecture. Another example is the novelty filter.
Surface plasmon cross-coupling on corrugated thin metal films
Authors: Gruhlke R. W. , Hall Dennis G.
Published: February 2023

A thin metal film supports two surface plasmon excitations, one associated with each of the sample’s two surfaces. For an asymmetric geometry, each metal surface borders a different dielectric medium, which leads to two distinct branches of the surface plasmon dispersion relation. It is possible to phase match and hence couple these two excitations if the metal film is corrugated to form a thin grating of period Λ. Cross coupling occurs, in first order, when the grating constant k
g
= 2π/Λ. matches the difference between the propagation constants of the two surface plasmon modes for some frequency ω. We have observed this cross coupling on samples prepared by depositing thin silver films onto holographic gratings formed in layers of photoresist. Our experiments make use of the fact that photoresist exhibits a broad fluorescence spectrum under laser illumination. Surface plasmons (SP) with this same spectrum are excited at the Ag-photoresist interface by excited molecules in the photoresist. Part of this spectrum near the phase-matching frequency excites SP on the Ag-air interface, which in turn radiates via the usual grating-coupling mechanism. We report our observations of this cross-coupling effect and its dependence on the grating period and film thickness.
Millimeter-wave imaging sensor
Authors: Wilson William J. , Ibbott Anthony C. , Parks Gary S. , Ricketts William B.
Published: February 2023

A dual polarized 3-mm radiometer system, with a mechanically scanned antenna, has been built for use on a small aircraft or RPV to produce near real-time moderate resolution (0.5°) images of the ground. One of the main advantages of this passive imaging sensor is that it is able to provide surveillance information through clouds, smoke, and dust when visual and IR systems are unusable. This millimeter-wave imaging sensor can also be used for a variety of remote sensing applications such as measurements of snow cover, surface moisture, vegetation type and extent, mineral type and extent, and surface temperature and thermal inertia. The fact that the millimeter-wave sensor observes different physical phenomena makes it a valuable addition to visual and IR imaging systems.
Simple corner-reflector mixer for submillimeter wavelengths
Authors: Zmuidzinas J. , Betz A. L. , Boreiko R. T.
Published: February 2023

Corner-reflector mixers have been successfully used in heterodyne receivers at submillimeter wavelengths (100-500 μm) for a variety of applications including ground-based and airborne astronomy.1 The mixers generally consist of a long-wire (4λ) whisker antenna attached to a Schottky diode, plus a 90° corner reflector with its vertex spaced 1.2λ from the whisker.2 At shorter wavelengths near 100 μm, however, difficulties in fabricating an accurate 4λ mixer make it desirable to use longer antennas and larger vertex displacements, if such is possible without loss in efficiency. In general, the optimum position of the antenna is at the peak of the standing wave distribution of the electric field induced inside the reflector by a plane wave incident at the main lobe angle of the whisker antenna. We have found that this spacing is easily calculated for any antenna length I from the relation s = λ/2·sin(θ), where the main lobe angle is given by θ = arccos(1 − 0.371λ/I). Antenna patterns calculated from such configurations with whisker lengths between 4λ and 10λ give approximately symmetric main lobes with widths ranging from 14° to 8°. These predictions are confirmed by our measurements over a range of wavelengths. In addition, our design which inverts the traditional geometry of the whisker bend leads to a greatly simplified mixer structure with no discontinuities in the reflector surfaces.
Structure from motion in a stochastic display
Authors: Williams Douglas , Phillips Gregory
Published: February 2023

Using a 2-D stochastic display, we have observed a global 3-D percept. Our stimulus is a dynamic random-dot cinematogram in which each dot takes an independent 2-D random walk of constant step size. From one frame to the next, each dot’s direction of displacement is chosen at random from a uniform distribution of directions. When the range of this distribution is <150° the percept appears to be that of a rotating cylindrical volume whose axis of rotation is along the mean of the distribution. When the range of the distribution is >150° there is no 3-D percept. As the directional distribution of the stimulus is slowly changed, the occurrence and loss of the 3-D percept shows hysteresislike behavior. This behavior is not altered by large changes in dot density or display area, suggesting a form of local cooperativity. Our results are discussed in the context of cooperative interactions that may be involved in the recovery of structure from motion.
Improving the performance of composite matched filters
Authors: Atlas Les E. , Ritcey James A. , Cheung Kwan F. , Marks Robert J.
Published: February 2023

A composite matched filter (CMF) bank requires fewer filters than a conventional matched filter bank. Indeed, the reduction is logarithmic. When the CMF output can take on either a logic one or a logic zero, we demonstrate that the bipolar CMF with an output threshold of zero many times outperforms the binary CMF where thresholding is normally performed halfway between zero and logic one.1 For equally likely orthogonal library elements embedded in white Gaussian noise, the bipolar CMF is shown to yield minimum probability of error. A further advantage of the bipolar CMF is that the detection performance is invariant with respect to multiplication of the input by a positive constant. For optical implementation, a disadvantage of bipolar over the binary CMF is the design requirement of bipolar output encoding.
Image recognition in the presence of speckle
Authors: Marron Joseph , Morris G. Michael
Published: February 2023

Techniques for performing digital image recognition on speckled images are presented. Rather than performing speckle reduction, the speckled image is correlated directly with a reference function. Statistical properties of the correlation value are derived using the multiplicative noise model for image plane speckle. It follows that the correlation value is a Gaussian random variable. Statistical detection theory dictates that images are distinguishable when the standard derivations of the correlation values are small compared to the separation of the mean values. Several reference functions are considered for both intensity correlation and correlation for which the input speckled images are clipped. One reference function considered is the incoherent image of the desired object: another is the maximum-likelihood reference function. Experiments performed on planar rough objects indicate good agreement between theory and experiment. The best ability to discriminate is obtained using the maximum-likelihood reference function.
Stability of specular reflectance on two types of self-calibration detector
Authors: Zhang Rui Rong , Belzer Barbara J. , Zalewski Edward F.
Published: February 2023

The specular reflectance of the silicon photodiodes commonly used as radiometric standards in the self-calibration method has been studied as a function of time and cleaning procedure. The two types of photodiode studied were a group of inversion layer devices and a group of PN devices: UDT model UV100 and EG&G model UV444BQ, respectively. The reflectance loss is the largest correction factor that must be measured in the self-calibration of these devices. Consequently its variation will have the largest effect on the absolute responsivity. The measurements were performed at 482.5 nm near the region of maximum reflectance of the photodiode’s silicon dioxide antireflection coating.
Radiometric gain of microlenses
Authors: Brophy C. P. , Weiss A. K. , Noethen M. L.
Published: February 2023

Recent studies1 have indicated that an array of microlenslets with a near-unity fill factor can be used to direct light more efficiently onto an underfilled array of solid-state photosensors. Radiometric gain may be defined as the total number of rays, directed onto a photosensor area by a lenslet, divided by the total number of rays collected by a bare photosensor, assuming the same ray density. We present the results of ray-based radiometric calculations which model the collection of light by a typical objective lens onto a composite imaging array. This array consists of three optically important layers: the microlenslet layer, a transparent spacer layer, and the detector plane. The radiometric gain is presented as a function of spacer-layer thickness, f/No. of the taking lens, image spot size, and microlens cap height. Radiometric gain values exceeding three are predicted for a typical video imaging array when the lenslet is modeled as a spherical cap truncated to match the pixel area. A lower gain is predicted when an anamorphic-pillow model is assumed. Experimental verification of the spherical gap model is demonstrated for lenslets formed by baking rectangular pads of photoresist. A departure from the model's prediction at large cap heights is explained by a change in the lenslet’s shape.
Models of parallel computation and optical computing
Authors: Giles C. Lee , Jenkins B. Keith
Published: February 2023

Theoretical models of computation (automata, Turing machines, random access machines, etc.) define not only what is computable but determine how much time and/or space is required for a computation. The parallel extensions of the sequential models usually offer significant speedup in algorithm execution (not all algorithms can be parallelized, however). Real parallel computer architectures based on these parallel computation models should exhibit the same algorithmic speedup. A complexity hierarchy can be defined for parallel computation models based on the space and/or time speedup of certain classes of algorithms. In particular the parallel shared memory models1 are some of the more powerful of the parallel computation models. Their close resemblance to actual computer architectures provide guidance for real architectural design and their massive interconnection requirements are well suited for implementation in optical computing architectures. In addition, the shared memory models have recently been shown to simulate deterministic Boltzmann machines and threshold-logic Turing machines. Thus optical machines based on these parallel models can potentially exhibit the computational power of the shared memory models. These parallel computation models and their implications for optical computing are discussed.
Use of holographic memory in optical expert systems
Authors: Caulfield H. John
Published: February 2023

At the heart of an expert system is an inference engine. Within the last few months a number of workers (Warde, Szu, et al.) have shown that spatial light modulators offer the ability to make multiple inferences on multiple, uncertain inputs in parallel. Using page oriented holographic memory to store information and program the spatial light modulators allows us to process data at a rate limited only by the number of pixels per second that can be changed on the spatial light modulator. Numerical examples on capacity and speed are discussed.
Design considerations for three-terminal optically addressed MQW spatial light modulators
Authors: Esener Sadik , Lee Sing H.
Published: February 2023

Although current developments in multiple quantum well (MQW) device technology show great promise, problems remain when considered in the larger framework of processing element (PE) arrays. Spatial light modulation requires many small modulator cells (25 × 25 μm2) with low switching energy (<20 fJ/μm2), low driving voltage (<20 V), good dynamic range (> 10 dB), and integrable into large arrays (>100 × 100 PEs) with a technology compatible with detector fabrication. For digital optical processors to become viable, spatial light modulators with at least 104 processing elements operating at 100-MHz frame rate are required. Assuming ideal detection efficiency, a unity power gain, and operation near thermal limits, this frame rate results in an impractical input light power density of 100 W/cm2 for a modulator array consuming 10 fJ/μm2. To ease the optical power requirements a power gain of several hundred must be achieved. For an acceptable dynamic range the processing elements should be three-terminal devices consisting of physically separated detectors and MQW modulators and should be biased at lower energies than the energy corresponding to the excitonic absorption peak. This is in contrast to two-terminal optical bistable devices using the self-electroabsorption effect and operable only with low dynamic range. A detector with high gain is also essential for weak signals to produce larger photocurrents than the currents generated in the MQW modulator. GaAs/GaAIAs heterojunction bipolar phototransistors may be good candidates to perform the required detection functions, because of their compatibility with GaAs/GaAIAs MQW modulator technology.
Redundant number representation for optical computing
Authors: Athale Ravindra A. , Lessure Harold S.
Published: February 2023

The standard digital or binary number representation provides an exponential trade-off between the number of digits used (i.e., number of parallel optical channels required to represent one number) and the accuracy of computation achievable. For example, an 8-bit number uses eight binary optical channels but has a potential for resolving 256 (28) distinct levels. Such a trade-off, however, comes at the expense of requiring nonmonotonically nonlinear operations for performing the linear arithmetic operations of multiplications and additions. Here we propose a simple redundant number representation that will provide only a trade-off between the number of channels and the achievable accuracy while keeping the operations of multiplications of addition and multiplication in a simple linear form. Such a representation can be described by the following equation: Where a is the analog number, a represents a digit that can take on a value less than or equal to m, giving the dynamic range of the representation to be (n × m). We outline several different schemes for optically implementing multiplication and analyze their performance via computer simulations.
Optical matrix-vector multiplication using four-wave mixing
Authors: Chiou Arthur E. , Yeh Pochi
Published: February 2023

Optical four-wave mixing in nonlinear media can be employed to perform parallel matrix multiplication. In our approach, two of the input beams, each carrying a matrix information along the transverse dimensions, enter the medium and form an index grating. This grating contains information about the product of the matrix elements of these two matrices. The index grating is then read out by a reference beam. In the appropriate conditions, the diffracted beam consists of the integrated contribution from each part of the volume grating along the beam path and is proportional to the matrix product. In our experiments, transparencies were used to imprint the 5 × 5 matrix information onto the light beams. A photorefractive BaTiO3 crystal is placed at the common image plane of these transparencies. The multiplication of matrices or vectors was carried out via the degenerate four-wave mixing process inside the photorefractive crystal. This paper describes the new method and reports the first experimental demonstration of an all-optical matrix–vector multiplication in a photorefractive BaTiO3 crystal. The same technique can also be utilized to perform optical interconnection and logic operations.
Some problems caused by birefringence in dielectric mirrors
Authors: Jacobs S. F. , Johnston S. C. , Arizona U.
Published: February 2023

Birefringence in dielectric multilayer reflectors, generally caused by anisotropic structural form or strain, results in different phase shifts on reflection, depending on the state of polarization of the incident light. This phenomenon is well known, but less well known are some of the problems it causes. We describe three such problems: Upon length-tuning a low-power He–Ne laser, we observe that adjacent longitudinal modes have orthogonal polarization states. As length changes, we see abrupt changes in polarization of all modes. This can be disastrous for polarization sensitive applications, and can be avoided by choosing a laser whose mirrors have birefringence. Resonances of a passive Fabry-Perot cavity can be split, with components separately excitable by orthogonally polarized light. We observe round-trip phase shift of ~0.08 rad. The single-frequency output of a He–Ne laser may be Zee-man-split by a longitudinal magnetic field to yield two circularly polarized components whose frequency separation passes through an extremum as the laser is tuned through line center.1 To stabilize such a laser one obtains a heterodyne beat between the two Zeeman components. Unfortunately, not every laser exhibits this beat, and it is necessary to select a laser whose mirrors have very little birefringence.
Signal processing for a multispectral fringe detector for imaging
Authors: Shao Michael , Colavita M. Mark
Published: February 2023

In synthetic aperture imaging, an interferometer measures the Fourier transform of the image rather than the image itself. For a two-element interferometer with base line L, the fringe amplitude and phase is the Fourier component at spatial frequency L/λ. For an optical interferometer with a wide optical bandpass, the measured amplitude and phase is the average amplitude and phase over the bandpass. For pupil plane interferometers, the use of a wide bandpass will limit the field of view, while in an image plane interferometer, the use of a wide bandpass will lower the signal-to-noise ratio of the measurement of amplitude and phase. To preserve both signal-to-noise ratio and field of view, the fringe detector in a long base line interferometer (L/D ≫ 1, where L is the base line, D is the collecting aperture) must measure the fringe amplitude and phase at a number of wave-lengths simultaneously. For the Mark III interferometer, we are using a pupil plane configuration with a low dispersion spectrometer (λ/Δλ = 50–250) and a photon counting imaging detector. A PZT controlled mirror is used to vary the optical path length. A microcoded signal processor is used to demodulate the signal to obtain the quadrature components of the complex fringe visibility at each spectral channel.
Optimal filtering and signal processing for the Mark III Interferometer
Authors: Colavita M. Mark , Shao Michael
Published: February 2023

Some applications of optimal filter theory and other signal processing for the Mark III interferometer are presented. The Mark III interferometer is a phase-coherent Michelson stellar interferometer for astrometry and imaging, employing active optics with real-time control for automated operation. For the angle tracker, an optimal-correlation angle sensor is implemented with a PAPA photon camera and digital correlation hardware. This sensor provides an error signal with a photon-noise standard deviation up to 3.6 times smaller than achievable with a quad-cell sensor for a 2:3 aspect annular tracker aperture. This error signal feeds an optimal filter adapted to the photon rate. For the siderostat pointer, an iterated extended Kalman filter is used to update an 8-geometric-parameter siderostat model. This filter improves on the performance of the previous off-line least-squares algorithm and yields pointing residuals of ~10 sec of arc for this unencoded system. For the fringe tracker, a real-time visibility gradient algorithm is used to detect phase-unwrapping errors; in the offline processing, a Kalman filter matched to the statistics of the fringe phase provides greatly improved phase unwrapping in comparison to a conventional first-difference algorithm.
How many MacAdam ellipses are there?
Authors: Varner Denise C. , Wandell Brian A.
Published: February 2023

In a classic series of experiments MacAdam and others measured chromatic discrimination around many points in chromaticity space. They characterized these contours using ellipses. Theorists have attempted to predict these shapes from physiologically based theories (e.g., Silberstein, 1945; Stiles, 1946). Parameters of the ellipsoids may be expressed as a unique linear transformation mapping the ellipsoid into a unit sphere. Whereas this transformation has six degrees of freedom, most measurements of chromatic discrimination only vary three independent degrees of freedom in the stimulus conditions: the color coordinates of the point in color space. It is not surprising, therefore, that our analysis of the MacAdam ellipsoid parameters shows that they are confined to a small region of the 6-D space of possible parameter values. We have collected new data using disk-annuli spatial targets and different temporal waveforms to increase the dimensionality of the stimulus parameters. We ask whether the new ellipses have parameters outside the region spanned by the basic MacAdam ellipse conditions. That is, we analyze whether the parameters of the MacAdam ellipsoids are limited by the number of degrees of freedom in the stimulus conditions or by the number of degrees of freedom in the processes of visual sensitivity.
Critical flicker frequency as a function of luminance and field size in dichromats
Authors: Lutze Margaret , Smith Vivianne C. , Pokorny Joel
Published: February 2023

Critical flicker frequency (CFF) was measured as a function of luminance and field size in dichromats. The field sizes were 0.7°, 1.1°, 1.6°, 2.3°, 3.7°, and 5.5°. For a given field size, a 580-nm square wave alternation was presented from –0.35 to 4.65 log trolands in 0.5 log unit steps. The observer adapted to each luminance level for 1 min after which three descending (fusion to flicker) thresholds were collected. The median was plotted as a function of luminance. The CFF vs luminance functions for each field size were averaged separately for deuteranopes and protanopes. For both classes of dichromats, increasing field size resulted in systematic increases in CFF. For each field size, the deuteranopic and protanopic data sets could not be matched with a translation along the luminance axis, indicating the difference between the two groups is not due to the choice of 580 nm as the test wavelength. All curves showed an asymptote at high luminances which occurred consistently at a higher frequency for deuteranopes than protanopes (e.g., for the 0.7° field, the asymptote was ~45 Hz for deuteranopes and ~35 Hz for protanopes). These data are compared with other literature reports of flicker sensitivity of dichromats.
Image reconstruction in tomography using convex projections
Authors: Stark Henry , Oskoui-Fard Peyma
Published: February 2023

The method of projections onto convex sets (POCS) has been widely used in image recovery and synthesis problems but it has never been used as an actual reconstruction algorithm in tomography. Yet POCS offers certain advantages over methods such as convolution backprojection or direct Fourier inversion. What are these advantages? First, POCS does not require a particular data gathering geometry (e.g., parallel beam or fan beam projections); it can be used with any arbitrary set of projection data. Second, POCS furnishes a systematic technique for incorporating a priori information about the image. It is interesting to note that when POCS is used in its most primitive mode, i.e., the only constraints are those imposed by the line-integral projections, it becomes the well-known ART algorithm. We describe how POCS is used to reconstruct images in tomography and present computer simulations to verify the feasibility of the procedure.
X-ray microscopy: state of the art of the Gottingen microscopes and expected developments
Authors: Rudolph D.
Published: February 2023

During the past few years an x-ray microscope and a scanning x-ray microscope have been developed at the University of Gottingen using condenser zone plates and high resolution microzone plates as x-ray lenses. The experimental equipment installed at the BESSY storage ring in Berlin is described. X-ray microscopic experiments with biological specimens with a resolution of ~50 nm are described. Viability tests of spores of Dawsonia superba are discussed and estimations of lethal doses at 270- and 500-eV radiation are given. Future developments are briefly reviewed: optics for higher resolution and with higher efficiency and the development of a laboratory x-ray microscope with a plasma x-ray source.
Performance of electron beam fabricated x-ray zone plates
Authors: Ade H. , Kirz J. , Rosser R. , Vladimirsky Y. , Kern D. , Rarback H.
Published: February 2023

We tested a new generation of high resolution x-ray zone plates with the scanning x-ray microscope at the National Synchrotron Light Source.1 The zone plates were fabricated by electron beam lithography at IBM.2 They consist of gold rings on a silicon nitride window and have finest rings in the 68–100-nm range. The central region has a thick solid gold plating to enhance the signal-to-noise ratio in the foci. Collection efficiencies into first-, second-, and third-order foci were measured, and the nature of the first-order focus was examined in detail. The best zone plates showed negligible astigmatism and a first-order efficiency of ~5 %. One of these was used as the focusing element in scanning x-ray microscopy of biological specimens.
Dynamic behavior of a bistable system with modulated input
Authors: Gao Jin Yue , Narducci Lorenzo M.
Published: February 2023

We studied the dynamic behavior of a hybrid bistable system with a delay in the feedback loop when the input intensity undergoes a simple sinusoidal modulation. We found that when a small modulated input is applied to a stable steady state, the output intensity oscillates with the modulation frequency ω, the amplitude of the oscillating output has a resonant structure as a function of ω, and the maximum response develops when the driving frequency coincides with the imaginary part of the linearized eigenvalue that has the largest real part. When the parameters of the system correspond to an unstable state, the injection of a modulated input makes the output oscillation frequency different, in general, from the driving frequency, except when it approaches the fundamental frequency; here the output intensity becomes frequency locked to the input signal. In the frequency-locked region, for increasing values of modulation depth the output intensity undergoes a series of period doubling bifurcations up to chaos.
Measurements of the bandgap-resonant nonlinear refractive index of bulk and multiple-quantum-well GaAs at room temperature
Authors: Morhange J. F. , Park S. H. , Peyghambarian Nasser , Jeffery A. , Gibbs Hyatt M. , Lee Y. H. , Chavez-Pirson A. , Koch S. W. , Gossard A. C. , English J. H. , Maselink M. , Morkoc H.
Published: February 2023

We report on an experimental study of the origin of the nonlinearities and the size of the nonlinear index at various wavelengths close to the exciton resonance and the material band gap. It is concluded that for intensities required for optical bistability, the nonlinearity is mainly excitonic for MQWs with well sizes W of 50 and 152 Å which are either smaller or slightly larger than the exciton radius a. For 299-Å MQW, (W ≃ 2a), where the MQW behaves more like bulk but still has distinct excitonic features, the nonlinearity is due to the combination of exciton screening, band filling, and screening of the continuum states. For bulk GaAs, the effect of exciton is comparatively small and the latter two effects are responsible almost equally for the change in the refractive index. The measured nonlinear indices are rather similar for all these samples with the bulk GaAs and 299-Å MWQ exhibiting slightly larger Δn (change in index) for similar carrier densities (or for similar light intensities). The 50-Å MQW has a slightly smaller value of nonlinear index because the nonlinearity which in this sample is due to the saturation of the exciton resonance occurs at higher excitation intensities due to larger exciton binding energy.
Eigenvalue problems using the bimodal optical computer
Authors: Abushagur Mustafa A. G. , Caulfield H. John
Published: February 2023

Analog optics is very attractive to optical information processing and computing because of its ability to process 2-D data in parallel very rapidly, but its accuracy is low. Digital electronics is much slower but more accurate. An optical-hybrid system would be a compromise. In this paper we present a bimodal optical computer (BOC) capable of determining the eigenvalues and eigenvectors for positive definite matrices with very high accuracy and speed. This system combines the accuracy of the digital processors and the speed of analog optics. The algorithm is an iterative using the inverse power method. The effect of the condition number of the matrix on the convergence of the solution is studied. The effects of the errors in the I/O devices are analyzed and it is found that with a tolerance of 5% in the electrooptical devices solutions still converge. Also the speed of the BOC in solving this class of linear algebra problems is analyzed and compared with the digital computer.
Noise effects in optical linear algebra processors
Authors: Jong T. L. , Walkup John F. , Krile T. F. , Suzuki I.
Published: February 2023

Recently, there has been considerable interest in optical processors for performing linear algebra operations to exploit both the high degree of parallelism and speed associated with optical processing. It is important to understand, and wherever possible compensate for, the limitations imposed by sources of deterministic and random error. In this paper we consider the effects of system noise sources (e.g., light sources, modulators, and detectors) on the accuracies of basic linear algebra operations. The results of digital simulations performed to evaluate the accuracies of various optical linear algebra processors are also presented.
Near-infrared photorefractive properties of BaTiO3 and tungsten bronze ferroelectrlcs
Authors: Rakuljic George A. , Yariv Amnon , Neurogaonkar Ratnakar R.
Published: February 2023

With the ever increasing importance of semiconductor lasers which operate in the near infrared, the greater the desire for nonlinear optical devices such as phase conjugate mirrors which will function at these wavelengths. Until recently almost all devices utilizing photorefractive crystals were demonstrated using visible light only. However, since these very same crystals are also photorefractive in the 0.8-1.1-μm wavelength region,1 many of the currently known devices should also operate at these longer wavelengths. With this motivation in mind, we have proceeded to study the photorefractive properties of ferroelectric crystals such as BaTiO3, SBN:60, SBN:Ce, SBN;75, and BSKNN in the near-infrared region utilizing argon, dye, semiconductor, and YAG lasers. Specifically, we measured absorption coefficients, response times, and two-beam coupling coefficients throughout this new wavelength region and we have found significant photorefractive response in all the crystals studied. For example, we routinely measured coupling coefficients >1 cm−1 in many of the crystals with response times at 1 W/cm2 in the 0.1–10-s regime depending on the crystal and wavelength used. Throughout this wavelength range negligible absorption was detected. Finally, several theoretical models were proposed and developed to describe the broad wavelength response in these crystals.
Extended range interferometer: performance and applications
Authors: Strand Timothy C. , Katzir Yigal
Published: February 2023

The extended range interferometer uses a broadband light source to obtain a monotonically decreasing coherence with increasing optical path difference. The resulting modulation of fringe contrast is then used to resolve the inherent 2π ambiguity of phase shifting interferometers. By circumventing the phase-unwrapping problem, postprocessing is reduced to simple pixel-by-pixel operations. The technique greatly simplifies and speeds up interferogram analysis, making it possible to construct a real-time area microprofilometer. Other advantages of this algorithm over conventional phase shifting interferometers are the capability to accommodate surfaces containing steps more than a quarter of a wavelength high, as well as occlusions and other signal drop-outs. The optical front end of the system is built around a microscope equipped with a Michelson interferometer attachment. For magnifications in excess of 10×, a Mirau interferometer may be used with up to 40×. The coherence length of the light can be tailored to suit various applications by suitably choosing the filters over the tungsten source. The interference pattern is sensed by a high-resolution linear response CCD camera. Image digitization and processing are done on a commercial image processor, and a PC-based system is under development. The system has demonstrated a capability for reliable and repeatable profilometry of poorly reflective, nonmetallic surfaces. Root-mean-square repeatability error was measured as 1 /500th of maximum unambiguous range, typically ~3 nm. Applications to microprofiling of surfaces containing high spatial frequency and high slope detail are presented.
Wavefront measurement using radial shear interferometry and Zernike polynomials
Authors: Sommargren Gary E.
Published: February 2023

Radial shear interferometry is one of several methods used for measuring wavefronts. It is particularly attractive for testing aspheric optics because the fringe density can be controlled by varying the amount of shear. To be useful, however, it is necessary to be able to determine the wavefront given the measured interference pattern produced by the radial shear interferometer. The relationship between the wavefront and the measured interference pattern has, in the past, been expressed using sets of nonorthogonal polynomials. The purpose of this paper is to derive this relationship in terms of the orthogonal set of Zernike polynomials. This is attractive because the Zernike coefficients are directly related to the classical aberrations. The derived relationship is a closed-form solution that can easily be implemented on a computer. Applications and numerical examples are discussed.
Digital interferometry for flow visualization in the presence of gross periodic noise
Authors: Watt David W. , Vest Charles M.
Published: February 2023

Digital interferometry is a hybrid optical-digital two-exposure holographic technique in which the interferogram image intensity is recorded at each of several, known, discrete phase shifts. From these image data the sign and magnitude of the interferogram phase may be evaluated to a high degree of accuracy. This technique is especially useful in flow visualization because it allows visu­alization of very weak flows and aids in understanding very complex ones. In nonreal-time digital interferometry, two references are used. Reconstruction with both references creates a high contrast fringe pattern on the hologram surface. Although this may be minimized by imaging techniques, it severely degrades the interferogram in applications requiring the object to be close to the hologram. This noise causes periodic distortion of the computed phase, in some cases completely washing out the signal. However, applying image filtering algorithms to the image data can remove the noise from heavily degraded images and allow the signal to be faithfully reconstructed. We dis cuss image filtering methods and present several experimental examples including the use of this technique with pulsed laser interferometry.
Power over lasers
Authors: Shafer David
Published: February 2023

There are many aspects of lasers which require that the optical designer deal with situations that were never encountered before in prelaser days. In many cases these laser features, such as a very narrow spectral bandwidth, are opportunities for designers to propose systems that would be totally impractical with conventional light sources. , In other cases, such as high power levels, they are a challenge to the designer to find system designs which will effectively address this potential problem.
Rod influence in dichromatic surface color perception
Authors: Montag Ethan , Boynton Robert M.
Published: February 2023

By means of monolexemic color naming of the 424 primary samples of the OSA Uniform Color Scales set, it is possible to establish the centroid location in that space of the eleven basic surface colors originally described by Berlin and Kay. For normals, this results in a meaningful 3-D configuration of the centroids of categorically distinct col­ors. An extension of this work with dichromat viewing fields subtending ~3° produced a configuration of centroids remarkably similar to that of normal controls, it was hypothesized that the di­chromatic observers might be using information derived from rod excitation to supplement their remaining yellow-blue color discrimination. By the use of foveally fixated small fields or bleaching of the rods, this hypothesis was confirmed by a collapse of the 3-D array of centroids into a plane defined by yellow-blue and lightness variations.
Synthesis of distortion invariant optical correlation filters
Authors: Schils George F. , Sweeney Donald W.
Published: February 2023

A method is presented for synthesizing optical correlation filters that will detect a target image independent of position and other general kinds of image distortion. The various distortions can be rotation, scale, and perspective, or any combination of these. Most generally, any linear coordinate distortion is allowed. Since these filters do not require energy normalization, they are also intensity invariant. The design technique starts by finding a set of eigenfunctions and eigenimages for the specified target and distortion. Because these modes completely describe the target image, the correlation filter is formed from their linear combination. The spatial orthogonality of the eigenimages preserves the target information when the modes are combined. The linear combination coefficients are required to have unit amplitude, and their phases are found so that the optical system outputs a constant amplitude. Filters meeting these criteria are successfully designed by iterating between the spatial domain and the eigenfunction domain. All the target information can be extracted by the optical system if the distortion is introduced as a temporal variation of the filter. Detection of a constant intensity signature will uniquely locate input targets in parallel. We illustrate this technique with several examples.
Modulation of exciton absorption by below band gap excitation: optical Stark effect
Authors: Von Lehmen A. C.
Published: February 2023

Optical pumping in the transparent region of GaAs quantum well heterostructures produces modulation of the exciton absorption by two distinct physical mechanisms. First, photoexcitation below the band gap can produce carriers at the bandedge via phonon-assisted absorption. These carriers bleach the exciton through the effects of the exclusion principle. We have utilized this mechanism in studies of the phonon sidebands of the exciton in quantum well heterostructures. In contrast, the second mechanism is a direct interaction between the optical field and the exciton and involves no exciton or free carrier population. This is the optical Stark effect, which produces a shift of the exciton transition to higher energy. The exciton transition remains shifted only as long as the optical pump pulse is present. Hence the optical Stark effect is a new nonlinearity in quantum wells which occurs on an extremely fast time scale. In this paper we present experimental results representing both carrier-related modulation and Stark shifting o, the exciton resonance produced by picosecond photoexcitation. We describe studies of the Urbach tail and phonon sidebands and discuss the optical Stark shift in terms of a model developed for the ground state exciton transition.
Picosecond optical nonlinearities in GalnAsP
Authors: Miller A. , Manning R. J.
Published: February 2023

We report picosecond excite-probe and transient grating measurements on the alloy semiconductor GalnAsP with three different band gap energies. Pulses of 5-ps duration from a Nd:phosphate glass laser allowed excitation from band gap resonant conditions to excess energies of 0.3 eV. In the smallest gap materials, 0.86 eV, excite–probe measurements showed saturation and fast recovery within ~10 ps consistent with Auger recombination at carrier densities in excess of 2 × 1019 cm−3. Saturation of larger band gap samples (1.02 and 1.17 eV) occurred at lower laser fluences as expected, giving slower decays of ~500 ps due to radiative recombination but with an initially fast Auger component. Three pulse transient grating measurements used two excite pulses to produce a refractive grating of period 6 μm. The first-order diffraction of an orthogonally polarized probe pulse monitored the grating decay. All samples gave a decay rate of the same order ~200 ps which was faster than the decays associated with bimolecular recombination and is almost certainly due to ambipolar diffusion contributing to the washing out of the population modulation. We have thus demonstrated that nonlinear phenomena in these materials can have quite different band gap and carrier-dependent responses at 1.054 μm.
Five basic problems in machine vision
Authors: Fischler Martin A.
Published: February 2023

This paper presents the current machine vision paradigm as an attempt to solve five basic problems concerned with different aspects of modeling the physical environment from 2-D images.

These problems are:

(1) recovering scene geometry,

(2) image partitioning,

(3) object labeling,

(4) relational description in both space and time, and

(5) system architecture.

We describe the reason for the difficulty of each of these problems, and provide examples of novel approaches currently being investigated as potential solutions.
From klystrons to lasers: the Stanford connection
Authors: Byer Robert L.
Published: February 2023

The development of coherent sources of radiation has taken place in distinct steps that have involved conceptual breakthroughs. We explore the evolution of coherent sources through the past 50 years, including radio, TV, klystrons (microwaves), the maser and finally the laser.
Blue skies, red sunsets, and the green flash
Authors: Greenler Robert G.
Published: February 2023

The scattering of sunlight in the atmosphere is responsible for many beautiful sky effects. Some of these effects are a familiar part of our daily lives—the blue sky, red sunsets, and white clouds. A number of other scattering effects are less well known but can be seen by those who look. This presentation, with photographs and demonstrations, deals with naked-eye effects that we all can see.
Adaptive edge-only matching model for pattern recognition in humans and machines
Authors: Caelli Terry , Nagendran Shyamala
Published: February 2023

A procedure for the classification of patterns in terms of their critical edge features is considered. The learning phase involves: (i) an initial multiscaled edge extractor for each sample within a class; (ii) developing multiscaled prototypes within each class; and (iii) emphasizing the unique features of each class.
Experimental application of iteratively designed rotation-invariant filters for target recognition
Authors: Ochoa Ellen , Schils George F. , Sweeney Donald W.
Published: February 2023

An iteratively designed correlation filter Is used in a coherent optical system to perform recognition of targets independent of their position, rotation, or intensity. A full 3-D correlation operation is obtained by rotating the filter in the Fourier plane. The filter is designed so that the target image produces a constant-intensity response in the output as the filter is rotated, while other objects produce specklelike intensity variations. Therefore, detection consists of locating those pixels in the correlation plane which remain constant. This process requires only two data buffers, one to accumulate the intensity of each frame and one to accumulate the intensity-squared.
Propagation properties of single-mode dielectric waveguide structures: a path Integral approach
Authors: Hawkins Raymond J.
Published: February 2023

A path integral approach to the treatment of propagation problems in integrated optics is presented. This path integral formulation is obtained by exploiting the formal isomorphism between the scalar optical wave equation and the time-dependent Schroedinger wave equation. The propagation constant for the fundamental mode is obtained using the Feynman-Kac formula and a similar approach is used to obtain the propagation constant of the first-order mode. This path integral treatment of integrated optics is implemented numerically using a simple matrix multiplication method that can accommodate arbitrarily graded refractive-index profiles. Propagation constants obtained by this method are shown to be in good agreement with exact results.
Field correlations within homogeneous, isotropic, primary steady-state sources
Authors: Foley J. T. , Kim Kisik , Wolf Emil
Published: February 2023

An explicit expression is derived for the cross- spectral density function of the field generated by homogeneous, isotropic, primary steady-state sources of a wide class. It is found that, in general, the degree of spectral coherence of the field is sinc-correlated, regardless of the nature of the source correlation. The only exceptions are fields generated by sources whose cross-spectral density at frequency ω does not contain spatial-frequency components of periods 2πc/ω (c = speed of light in vacuo). These exceptional cases are shown to be associated with nonradiating, stochastic source distributions. It is found that the field produced by such a source may be correlated over appreciably larger source regions.