bluuebunny/crossref_metadata_2025 huggingface dataset:
Binocular Inhibitory interactions
Authors: Blake Randolph
Published: February 2023

With his invention of the stereoscope in 1838, Wheatstone observed two remarkable perceptual phenomena produced by dichoptic stimulation. One was stereopsis, the compelling sense of depth that occurs when similar half-images stimulate noncorresponding areas of the two eyes. The other was binocular rivalry, the alternating periods of monocular suppression produced by dissimilar stimulation of corresponding areas of the two eyes. By its very nature, binocular rivalry implies the existence of inhibitory interactions between the two eyes. Binocular rivalry can be construed as the default outcome when the binocular visual system fails to establish correspondence between the two monocular images. This presentation summarizes (1) the stimulus conditions that trigger rivalry (i.e., the features used in the establishment of correspondence); (2) various means (e.g., eye movements) for measuring alternations in dominance during rivalry; and (3) evidence bearing on the putative locus of rivalry. In addition, the relation between rivalry suppression and other forms of binocular inhibition is discussed. Finally, the role of top-down influences on rivalry will be considered. It is concluded that rivalry is triggered by rather unrefined stimulus features and that it operates at a relatively early stage of visual processing.
Optical nonlinear properties of thin-film waveguides based on Cd(S,Se)-doped glasses
Authors: Patela Serqiusz , Jerominek H. , Tremblay R. , Delisle C.
Published: February 2023

Optical nonlinear properties of the waveguiding structures consisting of thin films of Corning 7059 glass deposited by rf magnetron sputtering onto Cd(S,Se)-doped glass substrates (Schott long-pass filters) have been studied utilizing the effect of power-dependent prism coupling. The experiments were performed at a wavelength of 0.4880 μm with an argon-ion laser working in both cw and mode-locked (1-ns pulse duration) regimes. In’ both cases a limiting action in prism coupling was observed. Moreover hysteresis (output vs input light intensity) was observed with a pulse illumination. The changes in mode coupling angles with the variation of the input intensity were measured and the data obtained were utilized to determine both the sign and the value of the nonlinearity. We have also performed introductory studies on the technology of waveguides fabricated by sputtering of Cd(S,Se)-doped glasses onto optical linear glass substrates. The most recent progress in our research is presented.
An incoherent optical correlation system for median filtering
Authors: Ochoa Ellen , Allebach Jan P. , Sweeney Donald W.
Published: February 2023

Median filters are widely used in image processing because they remove impulsive noise while preserving edges. They are one example of a class of filter known as order statistic filters which require a ranking of pixels within the filter window. When only one of the ordered pixels (the i th pixel) is then selected as the output of the filter, the result is called the i th ranked-order operation. The median filter of window size N is therefore an (N + 1)/2 ranked-order operation while the maximum and minimum filters are, respectively, Nth and 1st ranked-order operations.
Quadratic optical associative memories
Authors: Psaltis Demetri , Park Cheol Hoon
Published: February 2023

An associative memory can be thought of as an array of discriminant functions that maps a selected set of input vectors x to a prescribed set of output binary vectors y. We discuss the use of quadratic discriminant functions of the following form as building blocks for constructing optical associative memories: Quadratic associative memories provide a dramatic increase in storage capacity, defined as the total number of associations that can be stored in the tensor of weights w
ijk
, compared to the commonly used linear associative memories because of an increase in the available degrees of freedom. We will discuss two separate methods for storing information in quadratic memories and describe corresponding optical systems for implementing these memories. The first scheme utilizes volume holography to store associations of 1-D vectors. The 3-D volume hologram is used to store and implement the third rank tensor of weights. The second method utilizes planar holograms for information storage in conjunction with square-law nonlinearity to calculate the required quadratic expansion.
Holographic implementation of a neural network model
Authors: Paek Eung Gi , Psaltis Demetri
Published: February 2023

Simplified models for the way information is stored in neural networks consist of two major components: neurons and interconnections among the neurons. Information is stored in the interconnections and the operation of the neurons themselves is often modeled as thresholding. An optical architecture is described and experimentally demonstrated that utilizes a microchannel spatial light modulator (MSLM) to optically simulate a 2-D array of neurons that can represent 2-D patterns and holograms to implement the interconnection among the pixels in the array. Two separate holograms are used and each is fabricated as a multiplexed Fourier transform hologram of a set of images. The optical system is configured so that when an input image matches one of the patterns stored in the first hologram, the associated image from the second hologram is reconstructed and imaged onto the MSLM which thresholds it. For the case of autoassociations the input and output images are the same and feedback can be used by imaging the output of the MSLM back through the optical system.
Frequency multiplexing
Authors: Sirat Gabriel Y. , Maruani Alain D.
Published: February 2023

Recently, J. J. Hopfield described a simple model for the operation of neural networks. A Hopfield processor consists of a vector-matrix multiplier and a nonlinear feedback. Farhat and Psaltis have proposed an optical implementation of this model and emphasized a natural link between neural processing and optics. In this paper we present a modification of the Hopfield model, a memory composed of M vectors of, respectively, N bits. We define an equivalence class U (M), for each vector V (M). A probe vector is close to the vector V (M) if it is close enough (in the Hamming sense) to one of the shifted versions. The data are reorganized into S classes, class S containing the vectors shifted by S bits. For each class S we define a validation switch, which is a threshold version of the Hopfield energy. It can be shown that by a proper choice of the switch parameters, the latter is on for class S if and only if the probe is close to version S of one of the memories. Assuming the switch is on for class S, if the probe is shifted back by S bits and injected into a Hopfield processor, it will converge to vector V (M).
Defect detection in silicon by optical beam-induced reflectance
Authors: Carver Gary E. , Michalski John D.
Published: February 2023

Microstructural flaws near the surface of a silicon wafer generally impair the successful manufacture of integrated circuits. Detrimental defects such as stacking faults, dislocations, and metallic precipitates are often 1-2 µm in size. In the semiconductor industry, these defects are usually revealed by destructive chemical etching procedures. The scientific community has explored several schemes for detecting defects in silicon. Most systems excite a sample with a beam of electrons or photons and then monitor phenomena such as electrical conductivity, microwave absorption, acoustic or thermal-wave scattering, inductive coupling, or surface photovoltage. No system appears to be capable of detecting 1-µm sized defects in silicon via a completely nondestructive measurement. We have developed an electrooptical system based on a pump-probe laser arrangement to satisfy these requirements. The system excites a wafer surface with a focused visible pumping laser. Holes and electrons generated by the pump alter the optical constants of silicon in the infrared. A second laser then probes the infrared reflectance of the photoexcited area. Electrically active defects consume the photoexcited carriers and reduce the magnitude of the optically induced change in infrared reflectance from levels observed in a nondefective crystal. Stress-induced changes in mobility can also lead to defect contrast.
Dynamic response of photorefractives to time-varying fields
Authors: Vachss Frederick , Hesselink Lambertus
Published: February 2023

The behavior of holographic recording and read out in photorefractive media under steady-state excitation has been extensively investigated in the last decade. Recent applications of photorefractive materials in time-dependent image processing however have utilized both time-varying images and the alteration of photorefractive response through the application of time-varying electric fields. Thus far, however, analyses of the photorefractive effect in these input conditions have been restricted to the quasi-steady-state limit and are thus only strictly valid for sufficiently low excitation frequencies.
Instabilities due to quantum multiwave mixing
Authors: Sargent Murray
Published: February 2023

Given one oscillating mode in a laser or an optical bistability cavity, can other modes build up, that is, is single-mode operation unstable? The answer depends on an interplay of spontaneous emission, saturated gain, and four-wave mixing processes that permit one or more sidemodes both to be resonant with cavity modes and to have more gain than loss. We discuss this problem for cavities containing one- or two-photon two-level media subjected to a classical wave of arbitrary intensity and one or two weak quantized sidemodes. While a single sidemode may have gain, two sidemodes symmetrically placed about a strong pump mode can have greater gain due to four-wave mixing contributions sometimes called combination tones. The theory is valid for the buildup of sidemodes from quantum noise until the sidemodes begin to saturate. Subsequent dynamics including chaos must be handled by a theory that allows all modes to saturate. The same physical mechanisms are important in saturation spectroscopy and control the generation of squeezed states in a cavity. However while the instabilities depend on sidemode gain and spontaneous emission, the generation of squeezed states of the vacuum avoids these phenomena, depending solely on quantum combination tones.
Chaotic behavior of laser oscillation output in a ring cavity
Authors: Lu Weiping , Tan Weihan
Published: February 2023

We have studied the laser oscillation output in a ring cavity when the oscillation frequency resonated with the medium frequency. The dynamics of the system is described by Here I(t) and W(t) are the normalized intensity and population difference, respectively, α is the gain coefficient, and the parameters Q and Γ = −InR characterize the losses in the cavity.
Optimization of the photorefractive properties of BaTiO3
Authors: Klein M. B.
Published: February 2023

Photorefractive materials offer great promise for a variety of applications in adaptive optics and optical data processing. BaTiO3 is a particularly promising material, primarily because the very large value of the electrooptic tensor component r42 yields correspondingly large values of grating efficiency, beam coupling gain, and four-wave mixing reflectivity. At present, commercial samples of BaTiO3 have a relatively long photorefractive respone time, typically 0.1-1.0 s at an intensity of 1 W/cm2. For many applications, response times <1 ms are needed. To develop techniques for improving the response time and other photorefractive properties, it is first necessary to understand the physical origins of the photorefractive effect in BaTiO3. We begin by reviewing recent experiments intended to identify the photorefractive centers in BaTiO3 and to measure their concentrations. We also review energy level models which have been proposed, as well as the corresponding charge compensation relations. The two basic approaches to improving the response time in BaTiO3 are doping during growth and treatment of existing crystals in a reducing atmosphere. We analyze the influence of both of these approaches on the respone time and describe the results of recent experiments on both doped and reduced crystals.
Framework for optical computing: a personal view
Authors: Athale Ravindra A.
Published: February 2023

The use of optics in computing has taken many forms over the last 25 years, it ranges from optical data storage and fiber-optic local area networks to all-optical digital computers and optical realizations of neural net models. The first two examples represent a mature, widely accepted use of optics in computing while the latter examples represent speculative and highly controversial use of optics in computing. In between the two extremes are systems with various levels of development and acceptability, such as matched filter correlators, acoustooptic processors, and optoelectronic interconnects for electronic computing systems. I seek to categorize various computing systems—optical, electronic, or hybrid—according to the operations that they perform (e.g., number crunching, symbolic inferences, signal preprocessing, etc.) and the class of computing systems (e.g., analog, linear, digital, or quasilinear) that they belong to. Within each category, a hierarchical organization of algorithms/architectures, higher-order operations, elementary operations, and computational primitives can be introduced. This framework will then be useful in organizing the various aspects of the use of optics in computing. Such a taxonomy will presumably help in analyzing the comparative advantages of optics over electronics and of one scheme for optical computing over another. It is also hoped that such a framework will serve as a guide for future directions of research.
Parallel algorithms for matrix algebra problems on shift-connected digital optical single-instruction multiple-data arrays
Authors: Drabik Timothy J. , Lee Sing H.
Published: February 2023

Shift-connected digital optical single-instruction multiple-data (SIMD) arrays1 comprise a 2-D (N × N) array of 1-bit logic/arithmetic elements with optical inputs and outputs, a memory that stores binary images, and hardware to perform arbitrary, programmable space-invariant shifts on data images as they are brought from memory to the logic array. Results of logic operations are returned to the memory in parallel. Such a shift-connected array can efficiently perform multiples of dense matrices or of sparse matrices possessing a multidiagonal structure from which algorithms for matrix inversion, partial differential equations, and eigenvalue problems can be assembled. Multiplication of an
N
vector by an N × N dense matrix requires computation time proportional to K2, where K is the number of bits of precision desired, and memory proportional to K. Multiplication of an
N
2 vector by an N2 × N2 sparse matrix with multidiagonal structure corresponds to accumulating weighted, shifted versions of an N × N array of numbers. Computation time required is proportional to DK2, where D is the number of nonzero diagonals. Memory required also depends linearly on D. Because shifts across multiple processing elements are available, 2-D shift-connected arrays can easily be programmed to have 3-D or 4-D topologies as well.1 Multiples by sparse matrices arising from the discretization of continuous problems in two to four dimensions can be optimally performed on a processor array with the same dimensionality. The case of implementing these algorithms derives from the 2-D parallelism and global data movement capability of optical systems.
Image bearing photorefractive oscillators
Authors: Fischer Baruch , Sternklar S. , Weiss S.
Published: February 2023

We demonstrate photorefractive oscillations between two BaTiO3 crystals with intracavity phase and amplitude modulation and multimode fibers. Two configurations are discussed. In one, two semilinear passive phase conjugate mirrors (PPCMs) are placed in tandem, and the first PPCM is pumped externally. This excites all the other beams, i.e., the other three beams of the first PPCM and all four beams of the second, causing the buildup of oscillations between the two crystals, even in the presence of a slide or multimode fiber between the crystals. In the second configuration, two double-phase conjugate mirrors face each other with a slide placed between them and each is pumped separately by different image bearing beams which may be derived from separate lasers. Oscillations build up which support the three different images simultaneously. The automatic self-tracking of the oscillating beams is due to the self-induced gratings in the crystals, allowing the oscillators to support a large bandwidth of transverse modes in the cavities. Applications in real-time image processing are discussed.
Short-lived phenomena observed in Comet Halley
Authors: Lynch D. K. , Russell R. W. , Rice C. J.
Published: February 2023

Infrared (2–10.3 μm) and visual observations of Comet Halley made prior to perihelion at the Mt. Lemmon Observatory (NASA and U. Arizona) reveal at least three types of short-lived events: (1) On 8 Nov. 1985 (UT) an expulsion of materials resulted in both infrared and visible brightness changes lasting several hours. (2) Between 10 and 13 Jan. 1986 (UT) the comet was observed to increase in brightness by factors of 2.5, 4.3, 4, and 3.8 at wavelengths of 2.3, 3.6, 4.6, and 10.3 μm, respectively. (3) During the same period in January the comet tail underwent a wagging mode, i.e., the position angle first increased by 10° and then decreased by 8°.
Point source sensitivity of astronomical imaging arrays in space
Authors: Ftaclas Christ , Silverglate Peter
Published: February 2023

A space telescope produces a diffraction-limited point spread function (PSF) with ~84% of the energy confined to the central peak. Imaging arrays generally produce asymmetric PSF with less centrally concentrated energy. This effect tends to degrade sensitivity when sky background is taken into account. Thus resolution goals are better met by highly thinned arrays and sensitivity goals by highly filled arrays. For phased arrays, fill factor breaks the quadratic relationship between resolution and sensitivity characteristic of monoliths, and it is possible to choose configurations in which an increased collecting area produces gains in resolution and sensitivity at predetermined levels, a desirable feature for modular configurations. We have also examined the desirability of heterodyne and speckle imaging vs direct imaging. While both heterodyne and speckle imaging produce relaxed telescope tolerances, the loss in sensitivity associated with heterodyne and speckle imaging does not justify their use.
Do color difference thresholds depend on the wavelength or hue appearance of stimuli?
Authors: Nilsson Thomy H.
Published: February 2023

Hue and color brightness difference thresholds were measured by the method of adjustment at thirty wavelengths. These wavelengths were tested in ascending and descending orders on successive days. As a result, on half of the trials each wavelength was preceded by a shorter wavelength, on the other trials preceded by a longer one. The hue evoked by each wavelength was measured systematically. The hue appearance of each wavelength was found to be altered by the order in which the wavelengths were tested. These hue changes did not alter the hue discrimination function: i.e., hue difference thresholds were largest around 530 nm regardless of whether that wavelength appeared to be green on descending wavelength days or yellow-green on ascending wavelength days. Hue discrimination depends on wavelength and not on hue. On the other hand, the color brightness discrimination function tended to shift with wavelength as the appearance of those wavelengths shifted in hue: i.e., when testing from 425 to 625 nm, brightness difference thresholds reached a maximum at 555 nm which was reported as yellow; when testing from 655 to 425 nm, this peak shifted to 575 nm while yellow shifted to 580 nm. Color brightness discrimination depends mostly on hue not wavelength. These results suggest that (1) color appearance and color discrimination are mediated by separate mechanisms; (2) hue discrimination is mediated by mechanisms that are proximal to the receptors; (3) color brightness discrimination is mediated more centrally than hue discrimination.
Ultrasound-assisted evaporation of optical thin films
Authors: Hwangbo C. K. , Jacobson M. R. , Macleod H. A.
Published: February 2023

The effects of ultrasound-assisted deposition (UAD) of ZrO2, Ta2O5, and MgF2 films on their optical and structural properties have been investigated. The glass or fused silica substrates (with areas ~25 cm2) are attached with Torr-Seal to tubular piezoelectric transducers, which are, in turn, clamped to stationary tooling within a Balzers 510 evaporation plant. The transducers are driven by an ENI 2100L rf power amplifier with a 10-kHz to 12-MHz bandwidth and a power output of around 150 W. Radiative heating of the substrates, with and without ultrasound, was also performed to distinguish between purely thermal and ultrasonic effects. Results thus far indicate that ultrasonic powers above 100 W are required to induce detectable changes in UV absorption and vacuum-to-air shifts of the spectral profile. At substrate temperatures (T
s
) near ambient, UV absorption in UAD films is equal to or slightly higher than in conventionally deposited (CD) films. For T
s
above 100°C, UV absorption tends to increase for UAD vs CD films; baking tends to lower the absorption, indicating that UAD films are oxygen deficient. No changes in crystal structures at high T
s
as measured by x-ray diffraction, in surface roughness as observed with Nomarski microscopy, and in robustness as determined by controlled exposure to high temperatures and humidities, were noted.
Properties of SnTe transparent conductive IR optical coatings
Authors: Knoll R. W. , Pawlewicz W. T. , Mann I. B.
Published: February 2023

We describe basic properties of SnTe thin films produced by sputtering and by flash evaporation. The unusually high carrier concentration and favorable transmission characteristics of this semiconductor allow its use as a transparent conductive IR coating material. Transmission better than 70% (including substrate losses) was achieved in some cases for SnTe coatings containing an SiO2 antireflection coating. SnTe coatings tuned for optimum optical performance had resistivities of ~2.7E-4 Ω cm. Carrier mobilities ranged up to 800 cm2/V s. SnTe optical performance and electrical properties were found to be very sensitive to SnTe stoichiometry and to coating purity. Properties and stability were also sensitive to substrate surface quality (roughness). The dependence of optical transmission, electrical resistivity, and carrier mobility on Sn content is described. Effects of substrate temperature and postdeposition heat treatment on these properties are also discussed.
New type of optical bistability
Authors: Chen Jutao , Liu Yupu , Wang Zhijiang
Published: February 2023

A new type of active optical bistability is described: frequency bistability as well as light intensity bistability. The device is quite simple—a laser with a passive filter. The gain medium of the laser is homogeneously broadened and has a broad fluorescence spectrum much greater than the longitudinal mode interval. The passive filter, in fact, is a set of mirrors with reflectivity varying with frequency. Its center frequency, that is, the frequency of maximum reflectivity, is different from that of the gain medium. The mechanism of this bistability is making use of the nonlinearity of both gain medium and passive filter vs frequency.
Effect of applied electric fields on beam coupling in ferroelectrlcs
Authors: Gookin Debra M. , Gross G. W.
Published: February 2023

Ferroelectrics, such as BaTiO3, have large electrooptic coefficients which make them useful photorefractive materials. Diffraction efficiencies in photorefractive materials are improved by the application of electric fields. In ferroelectrics, as in nonferroelectrics, the improvement in diffraction efficiency is attributable to increased drift. However in ferroelectrics at least one other mechanism contributes to the effect of electric fields on beam coupling. When an electric field is applied to a ferroelectric, even at room temperature, some polarization reversal (reversal of the c axis) takes place. Both mechanisms can cause the direction of optical gain to switch. We present a theory of the interaction of electric fields with ferroelectric materials and the consequences of these interactions on optical beam coupling via two-wave mixing.
New method for conoscopic observation of crystals
Authors: Warenghem M. , Grover C. P.
Published: February 2023

This interferometric method has been devised for the simultaneous determination of the optic axis and thickness of a birefringent sample. It is analogous to the conventional microscope conoscopy, however it has the advantage of providing observations over a very large angle of incidence by using simple equipment. On the other hand, similar studies by usual methods would require expensive microscope objectives and condensors and a rather cumbersome image analysis method for quantitative measurements. Furthermore, the short working distance for a high numerical aperture objective prevents the insertion of any additional piece of equipment such as a heating stage needed for specialized studies. In this method the fringes of birefringence are obtained by scanning the field of observation. This has been achieved by successively varying the angle of incidence of the illuminating narrow beam of light. The fact that the zeroth fringe associated with the crystal optic axis is the widest, enables us to label unambiguously the orders of the fringes and to determine the fractional order with a high precision. The method has been dubbed as scanning conoscopy and has been used for accurate determination of Freedericksz transition and anchoring energies in nematic liquid crystals.
Optical systems to scan laser beams
Authors: Grey David S.
Published: February 2023

Perhaps the most common lens arrangement used in conjunction with laser scanning is a beam expander, one or two scan mirrors, then an image forming lens group designed for anterior aperture stop. The numerical aperture ranges from ~0.03 for typesetting to ~0.25 for circuit board trimming. The system has inverse vignetting, image mapping is usually F/theta or F/sin(theta), telecentricity may or may not be specified, and it may or may not be achromatized. A line image perpendicular to the scan direction may or may not be required at the scan mirror. Another family uses acoustooptical scan elements. The design problem there is to create a ray-trace model to verify performance and especially to compute assembly tolerances. (Invited paper, 25 min)
Grating-adaptation aftereffects and cone-rod Interactions
Authors: Buck Steven L. , Knight Roger
Published: February 2023

Aftereffects of adaptation to spatial grating stimuli have been studied intensively in photopic vision over the last 20 years. However, it was shown only recently that such aftereffects also occur when the adapting grating modulates only rods or cones and the test grating modulates only the other receptor type, suggesting the adaptation of some portion of a pathway shared by rod and cone signals.1 We show here that the site of adaptation displays both orientation and spatial-frequency tuning. We measured photopic luminance-modulation thresholds (not contrast-modulation thresholds) for resolving square-wave and sine-wave gratings after adaptation to scotopically detected gratings at 7° eccentricity. Test gratings were 670 nm and 200-ms duration. Adapting gratings were 490 nm, 0.67-Hz counterphase flickered, and presented for 120 s before the first test stimulus and for 3 s before subsequent test stimuli. The interaction aftereffect was found to have an orientation tuning half-bandwidth at half-maximum of 15-20° and a spatial-frequency tuning half-bandwidth at half-maximum of less than an octave.
Phase-dependent sensitivity to heterochromatic flicker: subject differences in color-normal males
Authors: Swanson William H. , Pokorny Joel , Smith Vivianne C.
Published: February 2023

We measured sensitivity to sinusoidal temporal modulation as a function of the relative phase of two equally luminant chromatic sources. We previously reported data for three observers at a range of temporal frequencies (OSA 1985); now we report data for a range of observers at a single temporal frequency. The stimuli were presented in a two-channel Maxwellian view system employing red (625-nm) and green (564-nm) light-emitting diodes (LEDs). The two sources were matched by heterochromatic flicker photometry, and their mixture was metameric to ~600 nm. The radiance of the LEDs was controlled by computer-driven electronic circuitry that provided a linear response up to 900 td/LED. A 350 td, 2° test field was superimposed on 8°, 600-nm adapting fields of 100 and 1000 td. We measured modulation sensitivity to 6-Hz flicker for eighteen phases from 0° to 340° and computed an axis of symmetry. Color-normal males had phase axes in the range of 123–173° and 112–156° for adapting fields of 100 and 1000 td (that is, stimulus condition red-leads-green gives minimum sensitivity). In comparison, color-defective males had phase axes of 176–184°. We discuss the data in terms of cone density ratios.
Thin films and instrumental polarization
Authors: Chipman Russell A.
Published: February 2023

A general method for calculating the polarization effects of thin films on the instrumental polarization of symmetrical optical systems is presented. This method treats the coated optical surfaces as weak spatially varying polarizers and sums the surface contributions to determine the overall instrumental polarization. The Fresnel and thin-film equations for the interfaces are expanded in a Taylor series which describe the amplitude, phase, dichroism, and birefringence as functions of the angle of incidence. Using paraxial optics, these low-order surface polarization contributions may be readily summed to determine the variation of instrumental polarization for arbitrary paraxial ray paths. The resulting polarization behavior displays a close correspondence to the wavefront aberrations of geometrical optics and are thus called polarization aberrations. Suggestions for thin-film designs which compensate for instrumental polarization follow naturally.
Discovering natural object categories
Authors: Bobick Aaron
Published: February 2023

We assume that visual object recognition occurs by mapping incoming visual data onto a set of object categories. A claim is made that the world is structured in such a way that allows a definition of natural classes and that these classes should be the basis for visual categorization. Therefore, a vision system that is to perform successful visual categorization in the natural world must be able to recover these natural classes.
Supercontinuum laser pulse profile characterization and compression
Authors: Ho P. P. , Li Q. , Jimbo T. , Alfano R.
Published: February 2023

The temporal distribution of supercontinuum at different wavelengths generated by propagating an intense picosecond laser pulse through condensed matter was measured by a streak camera. Experimental results indicate that the Stokes continuum is at the leading edge and the anti-Stokes continuum is at the trailing edge of the laser pulse. The total output laser pulse duration was broadened in the condensed medium due to the group velocity dispersion. However, a 10-nm bandwidth selected from the supercontinuum has a slightly narrow pulse duration than the incident laser pulse envelope. This is attributed to the generation mechanism of the self-phase modulation process and the substructure of the incident laser pulse. Using a negative dispersion transmission holographic grating pair, a selected 10-nm band from a supercontinuum laser generated from an 8-ps laser pulse has been compressed down to ~1 ps.
Photoluminescence dynamics of the layered GaSe semiconductor under Intense picosecond laser-induced shock waves
Authors: Lu X. Z. , Rao R. , Doukas A. , Willman B. , Lee S. , Alfano R. R.
Published: February 2023

The generation of intense picosecond laser- driven shock waves in the layered GaSe semiconductor and simultaneous probing of the sample using another picosecond laser to study the shock- induced phenomena are discussed. In unshock condition, at low probe intensity, spontaneous emission is observed while at high probe intensity stimulated emission is observed. Under laser- induced shock pressure, 20-nm spectral shift of spontaneous emission and sixfold decrease in the intensity of stimulated emission have been detected. By careful band-shape analysis, both spontaneous and stimulated emission is attributed to the exciton-exciton scattering process. The red shift of the spontaneous emission is caused by the shrinkage of GaSe band gap under shock pressure. The quenching of the stimulated emission is explained on the basis of stimulated absorption by the electron-hole recombination process.
Characteristics of picosecond pulses generated from a synchronously pumped dye laser system
Authors: Bao Xiaoyi , Wu Cunkai
Published: February 2023

We present the mode-locked equation with a third-order expansion of the gain. The equation can deal with the problem which cannot be solved by a second-order treatment.
Wave packet analysis of the multimode Jaynes-Cummings model
Authors: Parker Jonathan , Stroud C. R.
Published: February 2023

A spontaneously decaying two-level atom in an evacuated high-Q cavity undergoes Rabi oscillations. This phenomenon has been observed experimentally as enhanced or inhibited spontaneous emission. In the standard Jaynes-Cummings model the atom is assumed to interact with only a single cavity mode. By retaining the infinite set of cavity modes the propagation of the spontaneously emitted radiation may be calculated. Such an analysis yields a clear physical picture of Rabi oscillations. These vacuum-field Rabi oscillations are compared with Rabi oscillations of a one-electron atom induced by coherent radiation. We show that the same wave packet analysis explains both types of Rabi oscillation. The limit in which a multimode cavity may be approximated as a single-mode cavity is discussed.
Test of Bell’s Inequalities using Rydberg atoms
Authors: Oliver Brian J. , Stroud C. R.
Published: February 2023

An experimental test of Bell’s inequalities using two-level atoms is proposed. The test is analogous to that proposed by Bohm but, instead of using spins and Stern-Gerlach magnets, two-level atoms and resonant pulses are used. Two atoms excited to a common Rydberg state, but traveling in different directions, are introduced into a microwave cavity. The microwave field resonantly couples two Rydberg states and excites the atoms into a correlated state. The atoms then pass out of the cavity and into separate interaction regions where resonant microwave fields rotate their Bloch vectors through angles directly corresponding to the angles of orientation of the Stern-Gerlach magnets in the spin experiment. State selective ionization is then used to determine whether each atom is in the upper or lower Rydberg state. State selective ionization of Rydberg states has been demonstrated with an efficiency approaching 100% so that tests of Bell’s inequalities which are even more stringent than those using cascade photon polarization may be possible.
Spatial frequency discrimination in simple and compound gratings
Authors: Thomas James P.
Published: February 2023

These experiments examine how spatial frequency discrimination is altered by the addition of new frequency components. All stimuli were vertical gratings, windowed horizontally by a Gaussian function. Simple gratings contained a single component: a narrow band of frequencies. Compound gratings contained two such components.
Role of lateral inhibition in determining the shape of the contrast transducer function
Authors: Lawton Teri B. , Tyler Christopher W.
Published: February 2023

The ratio of inhibition to excitation in visual re­sponse changes as a function of spatial frequency. The ratio varies from ~1.0 at low spatial frequencies to 0 by ~10 cycles/deg. Therefore, the effect of lateral inhibition on the shape of the contrast transducer function can be investigated by varying spatial frequency and masking contrast. We examined this hypothesis by presenting brief contrast increments in 0° phase to a steady back­ground grating having the same spatial frequency as the test grating. We explored the effects of spatial frequency across a 6-octave range, masking contrasts across a 7-octave range, and short and long stimulus durations on the contrast masking function. A 2 AFC procedure was used to measure the contrast threshold. The shape of the contrast transducer function derived from these data changed significantly as the spatial frequency of the test and background gratings varied from O. 25 to 20 cycles/deg. The results can be interpreted to imply that the contrast transducer pre­cedes the site of lateral inhibition.
Objective evidence for opponent-orientation processing
Authors: Regan D. , Regan M. P. , Price P.
Published: February 2023

Two gratings inclined at a small constant angle Δθ° were superimposed. Recordings were taken from electrodes located over visual cortex while one grating was counterphase-modulated atF1, Hz and the other atF2Hz. The evoked potential included several discrete nonlinear frequency components of frequencies (nF1±mF2),nandmbeing integers. These frequencies were very precisely specified; bandwidths were no more than 0.008 Hz. Then the superimposed gratings were rotated bodily around the clock. A cross-modulation component that was independent of spatial phase reached maximum amplitude for horizontal and vertical orientations, fell to minima within 20° of horizontal and vertical, and showed a submaximum at oblique orientations.
Ultrasqueezed light via multifrequency pumping
Authors: Schumaker Bonny L.
Published: February 2023

The fundamental and simplest kind of squeezing (broadband squeezing) is produced by pumping a nonlinear medium at a single frequency. The observables squeezed are the electric-field quadrature phases defined relative to the pump frequency. Their measurement requires homodyning against an optical-frequency (the pump frequency) local oscillator. When the medium is pumped at several different frequencies (equally spaced), different kinds of observables exhibit squeezing. Their measurement requires further homodyning, against a radio-frequency (the pump frequency spacing) local oscillator, and, for four or more pump frequencies, against subsequent lower-frequency local oscillators. For a given total pump power, it is possible to achieve greater squeezing by distributing the pump power over several (at least three) different pump frequencies than by pumping at a single frequency. The drawback is that a more sophisticated detection scheme is required (i.e., further homodyning) to measure the maximum squeezing (less squeezing is produced in more easily measured observables, such as the electric-field quadrature phases). The required further homodyning at rf and lower frequencies is straightforward to accomplish, however, and the advantages of using lower pump powers at each optical frequency can be substantial, especially in mediums such as optical fibers, where large pump powers bring with them substantial added noise sources.
Impact Ionization across the band-edge discontinuity in superlattices and its applications to solid-state photomultipliers
Authors: Capasso Federico , Allam J. , Cho A. Y. , Mohammed K. , Malik R. J. , Hutchinson A. L. , Sivco D.
Published: February 2023

We report the observation of a new avalanche phenomenon in superlattices. This effect is characterized by a large ratio of the multiplications for holes and electrons implying β ≫ α and is very different in nature from the previously studied band-edge discontinuity assisted ionization in quantum wells. The i region of our p+in+ structures, grown by MBE, consists of an undoped (n ≃1015 cm−3) Al0.48ln0.52As/Ga0.47ln0.53As superlattice. Six wafers with well and barrier thicknesses ranging from 100 to 470 Å and a number of periods varying from 20 to 50 were studied. In addition similar MBE structures with an AISb/GaSb superlattice were also grown. The electron and hole initiated gains (Me and Mh) were determined using standard techniques. It was found that Mh ≫ Me. Ionization ratios β/α in excess of 102 have been deduced which are the highest observed in any III–V material. All the experimental data can be explained in terms of a new mechanism, impact ionization across the band-edge discontinuity. There are concentrations of electrons and holes dynamically stored in the conduction and valence band wells which can easily approach 1016 cm−3 in our structures, at fields ≲ 105 V/cm. Consider now a carrier (e.g., a hole) photoinjected into the structure; after gaining energy in the barrier layers it can impact-ionize one of the holes dynamically stored in the low gap layers out of the well across the valence band discontinuity. Electrons may of course impact-ionize electrons out of the wells but since ∆EC(≃0.5 eV) is more than twice ∆Ev, the electron ionization rate is much smaller than the hole ionization rate which explains why the holes are multiplied much more than the electrons. New solid-state photomultipliers based on this phenomenon are discussed.
Single-mode conversion by magnetic linear birefringence four-layer magnetooptic waveguides
Authors: Canal F. , Hernandez J.
Published: February 2023

The propagation modes in a four-layer magnetooptic waveguide have been calculated, assuming that both the intermediate layers are anisotropic, as a function of the permeability and permittivity tensors of the material. Mode conversion for a plane magnetooptic waveguide consisting of a double-layer thin-film epitaxially grown on a substrate and placed in the air, where the active element corresponds to the top layer, has been analyzed. This structure makes it possible to obtain single-mode propagation which is of great importance in the making of optical devices.
Exact semiclassical theory of four-wave mixing
Authors: Prior Yehiam , Levine A. M. , Chencinski N. , Schreiber W. M. , Weiszmann A. N.
Published: February 2023

Nonlinear perturbative susceptibilities have been used successfully to analyze experiments in nonlinear optics for two decades. By its very nature, a perturbative approach is limited to a small value of the expansion parameter, and nonlinear susceptibilities are not useful for strong saturating fields. Presently, a theory is presented for the treatment of FWM which is applicable to arbitrary strength of the input fields, both on and off resonance. The field harmonic time dependences are removed by a transformation to the proper rotating frame, and the resulting eigenvalue problem is solved numerically. Several new effects are predicted. For strong fields resonance frequencies are shifted and lines are split (similar to the ac Stark effect). When such a split line is acted on by another strong field (a phenomenon not studied so far), a new effect of stirring is observed, which results in the broadening and merging of the two separate components. A new extra resonance appears which is induced by the strong field and is present even in the absence of any collisions or other dephasing processes or of laser phase fluctuation. This new extra resonance is a new member in the family of extra resonances which were discussed in various previous publications.
Adaptive orientation-sensitive enhancement of striated patterns based on a visual model
Authors: Peli Eli
Published: February 2023

An adaptive algorithm for the enhancement of patterns consisting of families of curved lines was implemented. The algorithm was designed to simulate the human visual system’s ability to detect and follow such patterns even in adverse conditions. Sections of a striated pattern that are not perceivable alone may be detected if viewed contiguous to suprathreshold parts of the same pattern. The algorithm implements filters that are well localized in both the space and spatial frequency domains. These bandpass, orientationsensitive fan filters are similar in point spread functions to responses recorded from visual cortical cells. The filters are used both to detect the orientation of the striation in a small window and to enhance the image in that orientation. To speed up calculations and reduce error rates, the search for orientation is limited to a small angular range based on orientations previously found in neighboring, overlapping windows. The results of application of the algorithm to low-contrast striated patterns and to noisy images are presented. Difficulties and solutions to the problems encountered in windows with multiple orientations are discussed.
Color sensations of noncomplex images
Authors: McCann John J.
Published: February 2023

This paper describes psychophysical matches and computer models of simple color and lightness displays. These noncomplex displays include simultaneous contrast, step gradient, and other targets. The study compares color sensations-—measured by visual matching, and spectral reflectances—measured radiometrically. In addition, different computational models of color sensation are tested for their ability to predict color matches for these targets. Unlike complex images in which color sensations are highly correlated with radiometric reflectances, noncomplex images exhibit local spatial interactions that generate sensations poorly correlated with radiometric reflectances.
Ultrahigh speed Schottky barrier and PIN photodiodes
Authors: Wang S. Y. , Carey K. W. , Kolner B. H. , Collins D. M.
Published: February 2023

With the advent of using light as the carrier frequency the trend is toward high speed transmitters and receivers to capitalize on the high bandwidth afforded. We have been concentrating on the receiver end and particularly the photodiode. GaAs Schottky photodiodes fabricated on molecular beam epitaxy have demonstrated —3-dB bandwidths in excess of 100 GHz at a wavelength of 600 nm. For longer wavelengths, 1.06 and 1.30 μm, we have developed a front side illuminated double heterostructure InP/GalnAs/InP PIN photodiode with the —3-dB bandwidth in excess of 18 GHz. This device bandwidth is insensitive to wavelength in the 1.06–1.6-μm range. In addition, the dark current is <100 pA at the operating voltage of —4 V for a 50-μm diam device with a 25-μm diam bondpad. High speed characterization techniques using electrooptic sampling, a microwave spectrum analyzer, and standard sampling are discussed. Growth techniques of the PIN photodiode using atmospheric organometallic vapor phase epitaxy are also discussed.