bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical subharmonics excitation of free cyclotron electrons
Authors: Kaplan A. E.
Published: February 2023

Relativistic nonlinear optics1 of free electrons in a magnetic field predicts the existence of strong nonlinear effects with very low power of driving radiation. Even small relativistic effects may result in a hysteretic resonance either at the main cyclotron frequency Ω, predicted in Ref. 2 and experimentally observed in Ref. 3, or at the optical frequencies ω1 and ω2 when ω1 − ω1, = Ω or ω1 − ω1 = 2Ω (multiphoton resonances1 of different orders). Here we show theoretically that yet another nonlinear optical effect in such a system is feasible; this effect consists in the generation of higher-order subharmonics Ω of optical field with frequency ω when ω = nΩ where n ≥ 2 is the integer. The critical amplitude of the laser field required for the subharmonic excitation of the nth order is E
cr
= E0ρ(n), where E0 = 2eΩ2/3c2 and ρ(n) is a slowly increasing function of n; ρ(2) = 1. For λ0 = c/2πΩ = 1 mm, the amplitude E0 corresponds to an intensity as low as ~2 × 10−10 W/cm2. Therefore, the cyclotron motion of electrons in a microwave range can be excited at a very high-order subharmonic of a driving laser radiation in infrared or even visible ranges with a very low driving power. This phenomenon may prove to be very important in establishing coherent links between optical lasers and atomic or molecular microwave clocks.
Real-time intensity inversion by four-wave mixing in Bi12SiO20
Authors: Wooder N. J. , Dainty J. C.
Published: February 2023

The intensity dependence of wavefront reflectivity in four-wave mixing in photorefractive materials is highly nonlinear. Use of this nonlinearity can produce interesting image modifications such as image intensity inversion. Intensity inversion, i.e., lout ∝ 1/lin, is obtained when the intensity of the signal beam, lin, is very much greater than the total intensity of the reference and readout (pump) beams.1,2 We have observed inversion for a dynamic range of the signal beams between 10:1 and 100:1 using bismuth silicon oxide as the nonlinear medium. Experimental results showing the extent of inversion as a function of the beam intensities, interaction angle, and applied voltages are presented.
Flow-field visualization by holographic interferometery in iron-doped lithium niobate crystals
Authors: Mitchell J. H. , Magnusson R. , Black T. D. , Wilson D. R.
Published: February 2023

Photorefractive crystals are promising recording media for a variety of applications including holographic interferometry. This is due to properties such as instantaneous hologram formation (self-development), high-data storage capacity (3D storage), high sensitivity and resolution, erasability and reusability, etc. In this paper, experimental production of interferograms using double-exposure holography in crystals of lithium niobate is reported. The methodology necessary for recording and retrieving flow-field information using photorefractive holographic recording in these crystals is discussed as well as the critical parameters involved, such as crystallographic orientation, crystal doping levels, ratio of reference to object beam power, and the required exposure energy levels. Experiments using lithium niobate crystals with various iron-doping levels in both reflection and transmission geometry have been performed. Various phase objects such as a nozzle discharge from a nitrogen bottle and airflow over an airfoil have been recorded. Qualitative results showing the reconstructed interferograms obtained via this technique are presented and compared with corresponding results obtained using photographic film as the recording medium.
Infrared characterization of thin-film mesh filters with submicron features
Authors: Schimert Thomas R. , Byrne Dale M. , Case William E.
Published: February 2023

The utility of periodic metal screens or mesh filters for spectral and polarization selectivity from microwave to far-infrared wavelengths is well documented in current literature. Ordinary diffraction is avoided by making the period of the screen less than the wavelength of incident radiation. Under this geometrical constraint, only a single directional mode will propagate; all other diffractive orders are evanescent. Most recently, electron-beam microlithography has made possible the fabrication of periodic metal arrays operating in the middle-infrared spectral region.1,2 We describe the measured optical properties of selected infrared mesh filters and compare these data with theoretical predictions. Determining the induced current on the screen is a fundamental element of the scattering problem. Here the finite conductivity of the metal plays an important role.
Resonant nonlinear optical response of 1-D excitons
Authors: Orenstein J. , Greene Benjamin I. , Millard R. R. , Williams L. R.
Published: February 2023

The nonlinear optical properties of polymeric semiconductors have recently come under intensive study due to increasing interest in optical signal processing. The nonresonant nonlinear optical constants of polydiacetylene-PTS have previously been well characterized. In this paper we present results on the resonant nonlinear optical response of PTS. One measurement was performed using the transient grating technique. Two 1.97-eV pulses were overlapped at the sample to form an intensity grating. A reflectivity grating developed which was probed by a third time-delayed pulse. The magnitude of the reflectivity change per absorbed photon was extremely large, corresponding to a nonlinear refractive index, n2, of 3 × 10−2 (MW/cm2)−1. The recovery time of the system following pulsed excitation was 2.0 ± 0.2 ps. We interpret our results in terms of a model in which the nonlinear response is entirely due to the dynamics of the singlet exciton in PTS. We describe a straightforward extension of the ideas developed by Schmitt-Rink, Chemla, and Miller for a 2-D exciton system to 1-D.1 Using their "phase-space filling” model, the magnitude of n2 allows us to determine the Bohr radius of the exciton to be 30 Å, which is in excellent agreement with theoretical predictions. In addition we discuss a simple offshoot of this model which gives a good quantitative description of nonresonant response of PTS as well.
Visual system constraints in local image processing
Authors: Mitra Sunanda
Published: February 2023

The biological hardware of the human visual system has been modeled by conformal retinocortical projections. Such a complex-log transformation implies certain invariances in the pattern of stimulation of the visual cortex, thus retaining the characteristic features of a scene to be reconstructed from primal sketches. Assuming the human visual system uses Fourier domain descriptions for image reconstruction, evaluation of the modulation transfer function (MTF) of the visual system (i.e., eye-retina brain) provides us with important clues to biological image processing. Experimental evaluation of human MTFs in the presence of local obscuration demonstrates the constraints on spatial frequency response imposed by local receptive-field structures of the retina. The effect of such constraints on spatial frequency response in image processing and image reconstruction are addressed.
Short optical pulses in the focal region
Authors: Sherman George C.
Published: February 2023

The extensive theory available on the wavefield present in the focal region of optical systems deals exclusively with monochromatic waves. Since optical systems are now being utilized to focus very short optical pulses, it will be useful to extend the theory into the time domain. This paper presents an analytic approximation in the time domain for the wavefield in the focal region of a very small f/No. system valid when the pulse is very short. In contrast to the monochromatic case, it has proved possible to evaluate the propagation integrals in terms of known functions. The solution expresses the wavefield as a superimposition of one-half of a spherical pulse in front of the focal plane converging toward the focal point and a cylindrical pulse converging toward the optic axis for early time. At later time, there is one-half of a spherical pulse behind the focal plane diverging away from the focal point and a cylindrical pulse diverging from, the optic axis. On crossing the focal plane, the spherical waves pass to zero abruptly. The total field is continuous at the focal plane, however, because the cylindrical wave has a discontinuity there of equal magnitude with opposite sense.
Optimal imaging concentrators based on the ratio of encircled energy criterion
Authors: Idell Paul S.
Published: February 2023

We investigate the effects of spatial coherence on the design of optimal imaging concentrators where the ratio of encircled energy (REE) in the image plane is used to gauge concentrator performance. Using the REE criterion, we develop an apodization procedure which provides optimal light concentration for source fields possessing arbitrary states of spatial coherence and for arbitrary detector configurations. Our solution for the optimal pupil screen invokes the use of a generalized Fredholm-type integral equation whose integral kernel (and weighting function) are determined by the pupil field cross-spectral density function and the detector configuration in the image plane. We illustrate the effects of source coherence on the optimal apodizer design through the use of several numerically computed examples. These examples indicate the range of field coherence conditions over which concentrator performance will be improved through apodization. For the case that multiple-detector concentrators are considered, we investigate the onset of eigenvalue degeneracy in the integral eigenvalue problem and discuss its effects on the optimal pupil function solution.
Discrimination of the center position of a circle exceeds discrimination of the center position between two dots for stimuli beyond a critical size
Authors: Hirsch Joy , Groll Susan L.
Published: February 2023

Spatial discriminations that are finer than the center-to-center spacing of foveal photoreceptors (hyperacuity) are readily observed for 1-D spatial tasks such as Vernier offset, spatial frequency and line separation discriminations, and bisection tasks. We introduce a new task where the just- noticeable difference in offset from the center of circle Δc is measured. Circle center discriminations were measured over a range of circle radii and compared to just-noticeable differences in bisection between two dots Δb with separations equal to the circle diameters. The data show that Δb and Δc were equivalent for small stimuli (radii or bisection distance were approximately ≤0.025° of visual angle). For stimuli larger than this critical size, performance on the 2-D circle task Δc progressively exceeds performance on the 1-D bisection task Δb. These results demonstrate that the human visual system is able to exploit a 2-D spatial parameter (area) to achieve a hyperacuity advantage.
Induced internal noise in visual decision tasks
Authors: Burgess Arthur E.
Published: February 2023

Many previous visual signal detection and discrimination experiments have been interpreted using the concept of noise internal to the human observer. This noise is best characterized by an equivalent input noise spectral density that depends mainly on display luminance.1 This internal noise component has been assumed to be independent of external (display) noise. Experiments are described showing that there is another component—induced internal noise—that increases in proportion to increasing external noise. The induced component dominates the other (constant or independent) component when the display noise is easily visible. The experiments were done in two ways: by comparing decisions for multiple passes through noise-limited digital image sets and also by using the same noise in both alternatives of a two- alternative forced choice decision. Induced noise estimates were the same in both cases. It was found that the induced internal noise spectral density was ~60 % of the external noise density. The results can be explained by a model quasi-ideal observer that is not able to precisely use prior information about signal parameters. The model includes a source of random signal parameter jitter about mean values followed by a maximum likelihood decision strategy.
Effects of pictorial noise interfering with visual detection
Authors: Van Meeteren A. , Valeton J. M.
Published: February 2023

To evaluate the potential gain of noise suppression techniques, visual detection of sine wave gratings in Images with additive fine and coarse grain pictorial noise was investigated. An important part of the threshold elevations caused by pictorial noise can be explained in terms of masking. The threshold elevation can be reduced by about a factor of 7 through intelligent image processing. In addition to masking by similar noise components the detection of low spatial frequency target detail can also be hindered by high spatial frequency noise components. Correspondingly the detection of lower spatial frequencies can be moderately improved by blurring.
High resolution spectroscopy of xenon using coherent narrowband XUV radiation generated by four-wave mixing
Authors: Cooper David G. , Mcilrath Thomas J.
Published: February 2023

Absorption transitions were scanned by pulsed, narrowband, tunable coherent XUV radiation generated by two-photon resonant four-wave mixing in krypton. The four-wave mixing was accomplished by focusing two collinear beams into a chamber containing 1–5 Torr of krypton with a few Torr of argon added to Improve phase matching. One input beam was fixed at 2166.67 Å, corresponding to the 4p6 1S0 →4p5 5p[2 1/2]2 two- photon resonance in krypton. The other beam was the visible or near-IR output of a pressure- tuned dye laser. The XUV wavelength was calculated from measurements of the input wavelengths using a Fizeau-type wavemeter. Because very little xenon was required for absorption, both the generation and absorption of the XUV could be done in the same chamber, eliminating the need for differetial pumping. Thus, static pressure measurements allowed accurate determination of the xenon number density. Two well-defined absorption paths were established by a coated capillary array beam splitter for the XUV. The two signals were ratioed to obtain intensity profiles which were independent of the input intensities, and accurate cross sections were then calculated.
Rydberg atom wave packets localized in the angular coordinates
Authors: Yeazell John A. , Stroud C. R.
Published: February 2023

The quantum theory of atoms is based on a Hamiltonian which is just that of the classical Kepler theory of planetary orbits. In spite of this common foundation, the predictions of quantum theory ordinarily do not much resemble those of classical theory. Even in the limit of large quantum numbers the energy eigenstates of quantum theory do not look at all like the classical elliptical orbits. Recently, Parker and Stroud1 have shown that it is possible to excite a Rydberg atom wave packet whose radial dependence resembles the classical ideal of a particle traveling in an elliptical orbit. In this paper we discuss the formation of a wave packet in the polar and azimuthal angles by the coherent excitation of Rydberg states with the same principal quantum, but with a distribution of the angular momentum quantum numbers. When this wave packet is formed of the Rydberg states of an alkali atom the connection with classical theory is again striking. The wave packet precesses due to the core polarization, just as the classical elliptical orbit precesses due to an added r–4 perturbing potential.
Wind and backscatter measurements with the NOAA injection-lock infrared Doppler lidar
Authors: Hall Freeman F.
Published: February 2023

The NOAA Doppler lidar has been recently upgraded with a 2-J/pulse injection-lock laser that provides a 13-dB increase in energy over the previous hybrid design. Frequency stability of the new laser is demonstrated by the consistencies in sequentially recorded wind profiles to better than 0.1 m/s when scans are made within 1 min of each other. Comparison with tower anemometers also agrees well to within 0.2 m/s. Backscatter profiles at 10.6 μm show occasional, very clean layers in the upper troposphere where the scattering coefficient, beta, is <1.0E-11 l/(m sr). These layers have been confirmed using a ruby lidar, where scattering ratios of 1.1 compared to Rayleigh are measured. The sparse population of large aerosols in these clean layers does not compare well with much higher turbidity measured in 1981, 1982, and 1983 with the hybrid lidar. We conclude that there is great variability from one year to the next in large aerosol population in the upper troposphere. Possibly the El Nino climate anomaly in 1982 and 1983 caused a more dusty atmosphere than normal.
Analysis of intrapulse chirp in CO2 laser oscillators
Authors: Berger Russ G. , Moody Stephen E. , Thayer W. J.
Published: February 2023

Optical radar techniques using heterodyne detection require coherent frequency-controlled laser operation. In laser oscillators, frequency drift is caused by change in the index of refraction within the resonator. Pulsed CO2 lasers can have significant intrapulse chirp due to three time varying sources of refractive index: thermally induced gas density variations, electron plasma density, and anomalous dispersion when operating off line center. Previous work has focused on the first two of these effects.1,2 Since the anomalous dispersion effect is dependent on the frequency shift off line center, this source of chirp can be controlled somewhat by judicious use of off-line-center operation, which can partially compensate for the effect of the other chirp sources. Using a computer simulation of the fields within both stable and unstable resonators, a quantification of the frequency drift dependent on an appropriate average of the index of refraction within the resonator has been accomplished.
White-light image subtraction using a liquid crystal television
Authors: Chao T. H. , Cai L. Z. , Chen M.
Published: February 2023

A white-light processing technique for optical image subtraction using a liquid crystal television (LCTV) spatial light modulator is described. Real-world scenes are fed into the LCTV through a TV camera. The input image is then processed by a dual-channel white-light optical processor. A pair of double-grating interferometers is inserted into the Fourier plane of the optical processor such that the output image is modulated by two sets of complementary achromatic fringe patterns, each possessing the same spatial frequency but shifted by a half-period. Two sequential exposures are needed for coding the difference between the two input scenes onto one photographic film. Each of the exposures is taken through one of the grating interferometers. The coded difference image can be obtained by bandpass filtering of the coded photographic transparency.
Electrooptical linear transformation processing system
Authors: Yu Francis T. S. , Cao M. F. , Lu T. W.
Published: February 2023

A microcomputer-based optical linear transformation processing system is described. This system utilizes two patially parallel addressable magnetooptic spatial light modulators and a CCD detector to perform high speed electrooptical operation. A systolic array processing scheme is employed in this system to implement various linear transformations, for example, discrete Fourier transformation, discrete Hilbert transformation, chirp-Z transformation, and many others.
Spatial frequency matching in complex stimuli
Authors: Olzak Lynn A. , Thomas James P.
Published: February 2023

Spatial frequency discrimination can be either facilitated or reduced by the addition of a grating mask to each test component, depending on the separation between mask and test frequencies. At small separations, performance is facilitated, probably due to unique beat patterns. At larger separations, performance is reduced. Reductions in performance might be explained if the mask introduces noise into the system; alternatively, the mask may alter the apparent spatial frequency of the test gratings, reducing the apparent difference between them. These possibilities were explored in a two-interval spatial frequency matching task. In the first interval, the test stimulus was repeatedly presented. A given test stimulus was composed of a vertical sinusoidal grating, either alone or masked by another frequency component. In the second interval, a sinusoidal grating of variable spatial frequency appeared. For each block of trials, the observer chose one component of the test stimulus to match. Blocks were repeated until the observer was satisfied that all distinct components had been matched for a given test stimulus. Matches were determined by averaging matches obtained by two randomly interleaved, independent staircases. The results provide information about the cues used in the complex discrimination task and are interpreted in relation to the discrimination data by means of a simple model.
Artistic transformations in image processing
Authors: Glasser Adrian , Howland Howard C.
Published: February 2023

We have examined certain transformations, linear and nonlinear, which transform frame-grabbed black-and-white photographic images into artistic renditions of the original. Such transforms resemble sketches, sketch and wash renditions, or mosaics. Generally these transforms involve a large reduction in information of the original photographic image, and we have attempted to measure this reduction using coding algorithms. The reverse, increase in information when an artist creates a painting from a sketch, was also evaluated. Lastly, we also studied the importance of the information retained and discarded in the recognition of faces in a series of artistically transformed, frequency filtered images. We conclude that information necessary for recognizing faces (and many other objects) is broadly and redundantly distributed throughout the spatial frequency spectrum.
Squeezed state experiments in sodium vapor
Authors: Maeda Mari W. , Kumar Prem , Shapiro Jeffrey H.
Published: February 2023

Squeezed states of light exhibit phase-sensitive quantum noise which falls below the semiclassical shot noise limit. We report results from experiments in sodium vapor to observe squeezed light. In a single-beam experiment, a dye laser beam transmitted through sodium vapor was homodyned. Phase-sensitive noise on the radio frequency off­set modes was observed at or above the semiclassical limit.1 In a two-beam correlation experiment, the transmitted probe and the reflected con­jugate beams in forward four-wave mixing were direct detected. Although this configuration does not generate squeezed light, the subtracted photo­current exhibits subshot noise fluctuations.2 Phase-insensitive noise above the semiclassical limit was observed with a strong positive correlation between the probe and the conjugate photo­currents. In a squeezed state experiment, a probe-conjugate combination mode of forward four-wave mixing was homodyned.3 With the input beam blocked, the noise showed nonclassical phase-sensitivity with a minimum of 0.2 dB below the vacuum state limit. When only the probe or the conjugate beam was homodyned, the noise remained phase-insensitive near the vacuum state level.
Conversion of Poisson photons into sub-Poisson photons by the action of electron feedback
Authors: Capasso Federico , Teich M. C.
Published: February 2023

Poisson photons may be converted into sub-Poisson photons by the action of an electron current configured in an external feedback loop. The generation mechanism involves single-photon transitions so that the source can be made arbitrarily sub-Poisson. Unlike previous schemes, nonlinear optics is not invoked. A useful configuration involves a photon emitter illuminating a detector/ source combination in a closed-loop system. Two solid-state implementations of the detector/source are suggested. One makes use of electronic dipole transitions between the energy levels of a quantum-well heterostructure; the other operates by electrons impact-exciting electroluminescent centers.
New high gain staircase photoconductors and observation of sawtooth-to-stalrcase transition in compositionally graded heterostructures
Authors: Capasso Federico , Tu C. , Mohammed K.
Published: February 2023

Staircase heterostructures have recently been proposed as a means of achieving noise-free photomultiplierlike avalanche gain and repeated velocity overshoot. No experimental study of transport in such structures has so far been reported. In this paper we report the first investigation of carrier transport in a staircase potential configuration. The latter is obtained by appropritely biasing an MBE compositionally graded multilayer AIGaAs structure contacted by two n+ regions. The graded gap undoped region consists of three layers each graded from x = 0 to x = 0.2 over a distance of 5000 Å. A new photoconductive gain phenomenon which is peculiar to these graded materials is found. Dramatic differences in the photoconductivity are observed as the band diagram changes from a sawtooth to a staircase configuration, with increasing bias. In the staircase conduction band configuration electrons have high velocity while holes are slowed down and partially trapped by virtue of the valence band steps. This leads to high current gain (≥ 104). In the sawtooth configuration, on the other hand, the opposite occurs and the gain dramatically decreases (≤ 10). By engineering the staircase band diagram the performance of the photoconductor (gain and gain-bandwidth product) can be tuned over a very wide range. Other device applications are also discussed.
Comparison of three techniques for measuring optical constants of dielectric films
Authors: Garcia Marie F.
Published: February 2023

Three independent techniques for the measurement of the optical constants of a single dielectric layer on a glass substrate are compared for Al2O3, ZrO2, TiO2, NdF3, and LaF3. The first technique, inspired by Abeles,1 compares the reflections from coated and uncoated surfaces in both polarizations until a balance is obtained. This yields n values at a single visible wavelength with an accuracy of ±0.005. This method is useful over a wide range of film thicknesses. The envelope method employs reflectance and transmittance data over a wide wavelength range. An inhomogeneous model derives the optical constants, the thickness, and the inhomogeneity of the dielectric layer as a function of wavelength, with a precision in n of just under ±0.02 absolute and in k from ±2.5 × 10−4 at short to ±5 × 10−4 at long wavelengths.2 If the index and thickness of the film are large enough to allow waveguiding, the measured coupling angle yields the effective index N incorporating the actual index and thickness and provides n values with an accuracy of ±0.001. Although the three techniques have their differences, they produce comparable results for n, k, thickness, and degree of inhomogeneity. This comparability provides a checking mechanism for these parameters and allows insights into the deposition process.
Raman solitons in optical fibers
Authors: Druhl Kai
Published: February 2023

Soliton propagation in optical fibers for signals with a single carrier frequency has important applications in optical communications. Raman solitons involve signals with at least two frequencies (pump and Stokes). They show the features of pulse narrowing and intrinsic amplification and are promising for new communication technologies. Their propagation in Raman media with homogeneous broadening is well understood.1
Intensity discrimination with twisted birefringent optical fibers
Authors: Winful Herbert G. , Hu Andong
Published: February 2023

Intensity-dependent polarization effects in birefringent optical fibers have been used by several workers to achieve pulse shaping and intensity discrimination. In that application, the low intensity parts of a pulse transmitted through the fiber are blocked by an output polarizer while the high intensity part, which undergoes nonlinear polarization rotation, is transmitted. We recently reported a theory of this effect which shows that for fibers with well-defined principal axes, nonlinear polarization changes cannot occur if the input polarization is along a principal axis and the intensity is below the critical value for the fast axis instability. Experimentally, it has been noted that the virtually unavoidable twists present in any real fiber play an important role in determining the output polarization state. In this paper we present a theory of intensity-dependent polarization changes in twisted birefringent fibers. The theory takes into account the twist-induced circular birefringence and shows that twist can enhance the nonlinear transmission of fiber-optic devices that rely on nonlinear birefringence.
Image sampling density reduction below that of Nyquist
Authors: Cheung Kwan F. , Marks Robert J.
Published: February 2023

A technique to uniformly decimate samples in a multidimensional low-pass bandlimited signal without information loss is presented. In many cases, the overall sampling density can be reduced below the Nyquist density1 and ultimately to the hyper-area of the support of the function's spectrum. Two methods to regain the deleted samples are discussed. Both regain samples in forms of linear interpolations. The specific case of sampling images obtained through systems with circular pupils is addressed. An analysis of the noise sensitivity of the restoration is also presented.
Image restoration from the signed Fourier magnitude using generalized projections
Authors: Levi Aharon , Yudilevich Eitan , Habetler George , Stark Henry
Published: February 2023

We consider the problem of restoring an image from the phase-sign function (the so-called one-bit of phase) and the Fourier magnitude using the method of generalized projections. A formal obstacle to implementing projection methods to obtain a solution is that the set of functions with a prescribed phase-sign function, while convex, is not closed. To close the set we add an appropriate set of limit functions and then show that the algorithm does not converge to one of the added limit functions (a good feature of the algorithm). While other algorithms exist for retrieval from signed magnitude, the advantage of generalized projections is that a certain type of error reduction property is assured—provided that the algorithm does not stagnate in a trap (a local minimum) or a tunnel (a region where sets are nearly parallel). To the best of our knowledge this claim is not made by competing algorithms.
Limits to lightness constancy
Authors: Sewall Laura , Kersten Daniel
Published: February 2023

The limits to lightness constancy can be measured by the accuracy with which human observers estimate the reflectance of an object as a function of various illumination conditions. Our paradigm is analogous to traditional psychophysical methods used for signal identification, with the reflectance representing the signal and the illumination serving as noise. We used computer graphic techniques to simulate monochrome scenes consisting of a plane grid of square pieces of paper with various initial reflectances. The squares were then non-uniformly illuminated. We measured the ability of observers to correctly identify the reflectance of a randomly chosen patch by selecting a matching piece of paper from a standard palette, also simulated. Performance was measured as a function of the number of patches, number of possible reflectance values, illumination contrast, and illumination spatial spectrum. With uniform illumination, observers could accurately identify only six reflectance values for the three conditions varying in number of patches. However, within this range of reflectance patches, reflectance identification was robust over the range of illumination contrasts and spatial frequencies tested. These results suggest interesting constraints to be considered in the formulation of algorithms for lightness constancy.
Nature of the interference pattern produced on reflection at a phase-conjugate mirror
Authors: Jacobs Arturo A. , Tompkin Wayne R. , Boyd Robert W.
Published: February 2023

We have repeated the classic experiment of Wiener,1 which established the nature of the standing-wave pattern produced by reflection at the surface of a metallic mirror, with the metallic mirror used in his experiment replaced by a phase-conjugate mirror. We find that the positions of the fringes produced by interference between the wave incident on the phase-conjugate mirror and the wave leaving the mirror depends on the phase of the incident wave. This result is in contrast to that obtained through the use of a metallic mirror, in which case the interference pattern is found to be independent of the phase of the incident wave. The origin of the different behavior in these two cases lies in the fact that the phases of the waves that pump the PCM provide a reference through which phase information carried by the signal wave can be obtained. The experimental results are in excellent quantitative agreement with recent theoretical predictions.2
Vision psychophysics applied to clinical research problems
Authors: Massof Robert W.
Published: February 2023

Ophthalmologic disorders have been characterized and classified almost exclusively on the basis of morphologic criteria. With the exceptions of visual acuity and visual field measures, measures of visual system functions have, until very recently, played only a minor role in clinical diagnosis, determining the natural course of disease and evaluating the efficacy of treatment. However, the past few years have witnessed a growth in the application of modern vision psychophysical theories and techniques to the study of clinical problems. For example, rod afterimage detection latency experiments and models have recently been applied to test hypotheses regarding early abnormalities in rod transduction kinetics in retinitis pigmentosa. The flash-on-flash paradigm and models for visual adaptation have recently been applied in determining the etiology of threshold elevations in age- related macular degeneration and other retinal disorders. The Stiles-Crawford effect and waveguide models have been used to evaluate receptor disorientation in exudative maculopathies. Hyperacuity techniques and models have been used to evaluate metamorphosia and degenerative changes in the retinal receptor mosaic.
Infrared laser-induced desorption of NO and CO from alumina substrates
Authors: Weber W. H. , Poindexter B. D.
Published: February 2023

We present results of laser-induced desorption experiments on layers of CO and NO physisorbed at low temperatures (5-40 K) on fire-polished alumina substrates. The radiation source is a line-tunable CO laser capable of operating on over 400 lines in the 1500-1900-cm−1 region with a cw output power on the strong lines of 0.3-0.5 W. The experiments are carried out in a bakable UHV chamber with coverages of about a monolayer. The desorbed molecules are detected with a quadrupole mass analyzer operating In a time-of-flight mode. The desorption yields from both molecules show a broad, nonresonant (wavelength-independent) behavior. Additionally, NO shows a strongly resonant peak at 1843 cm−1 that we attribute to the direct excitation of the NO stretch mode. Effective temperatures for the desorbed molecules are obtained by fitting the time-of-flight data to a Boltzmann distribution. These vary from approximately the substrate temperature to 10-20 K higher, depending on the laser fluence and the substrate temperature.
Optical time-domain beam former implementations
Authors: Rolsma P. B. , Griffin Richard D. , Lee J. N.
Published: February 2023

A time-domain beam former spatially filters signals by weighting, delaying, and coherently summing the outputs of an array of sensors. Since a wavefront propagating across the array arrives at different sensors at different times, this operation can steer a maximum-response axis (or beam) of the array toward the propagation direction of the wavefront and discriminate against uncorrelated background noise. Since the transmission medium is often nondispersive (e.g., in sonar), the delays are independent of frequency; thus, this technique works well for broadband signals. We have built an eight-element eight-beam delay-sum beam former using a total internal reflection spatial light modulator as an electrical-to-optical transducer for the sensor signals, a commercial liquid-crystal television (LCTV) and the necessary optical elements as a crossbar switch, and a time-integrating photodetector array. A microcomputer was used for storage and control. The experimental beam-response pattern for hard-clipped (i.e., binary) input signals was obtained and compared with the calculated beam pattern. The throughput of this system was limited by the time response and instabilities of the LCTV. For improved response we are building a partial-sum beam former using optical fiber connections and a charge-transfer-device detector.
Phase discrimination in the normal and amblyopic fovea
Authors: Banks Martin S. , Bennett Patrick J. , Gubrud Gregory A.
Published: February 2023

Several investigators have observed anomalies in the encoding of spatial phase in amblyopic eyes. We adapted the paradigm of Field and Nachmias1 to examine amblyopic phase encoding in greater detail. Two normal observers and two with anisometropic amblyopia viewed stimuli composed of a fundamental and second harmonic added in various phases. The stimuli were presented foveally. For each eye tested, the spatial frequency of the fundamental was set to the peak of the CSF. The stimuli were Gaussian-damped and presented in a 2IFC discrimination paradigm. When the stimuli were in fact different, they differed only in the polarity of the second harmonic (180° shift). Thresholds were measured by varying the contrast of the second harmonic. Only two mechanisms were required to account for foveal phase discriminations in nonamblyopic eyes. The odd-symmetric mechanisms were slightly less sensitive than the even-symmetric mechanisms. The amblyopic data were also consistent with the two-mechanism model, but the odd-symmetric mechanisms were distinctly less sensitive than the even-symmetric. The difference between odd and even sensitivity was correlated with the depth of the amblyopia. These results suggest that the phase-encoding anomalies observed in the amblyopic central visual field may reflect a diminished sensitivity (or reliability) among odd-symmetric mechanisms. The pattern of results in the amblyopic fovea is similar to that observed in the peripheral visual field of normal obsevers (2). For the two amblyopic eyes, the results were similar to those observed between 20° and 40° eccentric in normal eyes.
Through the looking glass…
Authors: Yariv Amnon
Published: February 2023

We can look through cloudy glass, correlate, subtract, and convolve images in real time, we can amplify coherent beams and make length insensitive resonators and also store and recall images associatively. I attempt to show how all these wonderful things can be accomplished using the tools and concepts of the field of phase conjugate optics.
Forward-degenerate four-wave mixing in absorbing liquids and liquid crystals
Authors: Guha Shekhar , Chen W. P.
Published: February 2023

The large third-order nonlinear susceptibility [χ(3)] arising from thermally induced effects in absorbing liquids and liquid crystals (106 or more times greater than that of CS2) can easily be used to demonstrate and study four-wave mixing processes with low-power lasers. The absorbing liquids provide some advantages over the widely used photorefractive materials in obtaining optical phase conjugation because of their easy availability, low cost, and flexible physical properties. Moreover, the underlying physical mechanism of the thermally induced nonlinearity is one of the best understood of all the nonlinear optical processes, so direct comparison with theory is possible.
Optical pulse propagation in a multiple resonant dispersive Lorentz medium
Authors: Shen Shioupyn , Oughstun Kurt Edmund
Published: February 2023

To obtain a more complete understanding of the effects of temporal dispersion on the propagation dynamics of optical pulses in a physically realistic medium, we have examined the classical problem of dispersive pulse propagation in a Lorentz model medium that is characterized by two separate resonance frequencies. Both an input delta-function pulse and an input unit step-function modulated signal with carrier frequency ωc are considered. In each case the dynamic evolution of the propagated field is described in terms of the dynamics of the saddle points in the complex ω plane that are associated with the complex phase function appearing in the integral representation of the field. The appearance of a new precursor field, separate from the well-known Sommerfeld and Brillouin precursor fields, is shown to appear when the two resonance frequencies of the medium are sufficiently separated. Finally, the signal velocity that is characteristic of the field contribution oscillating at the applied carrier frequency ωc is obtained. These results are illustrated with numerical solutions that depict the entire evolution of the propagated field.
Bragg holography in the XUV region
Authors: Jannson Joanna , Yeung Peter C.
Published: February 2023

A new approach to XUV optics is analyzed based on the holographic fabrication of optical elements, including imaging optics, gratings, lenses, and mirrors. The single-step direct holographic registration of interference patterns produced by two coherent electromagnetic waves is considered in the XUV region for obtaining the desired transmission and reflection of Bragg holographic structures. For this purpose, the properties of the holographic material as well as the applicability of currently available laser sources in terms of their coherence, power, and pulse rate are analyzed. By using the well-known model of XUV wave propagation,1 two types of Kogelnik's holographic structure are considered for this spectral region, namely, the so-called lossy gratings and mixed gratings. It can be shown that, in spite of high values of the linear absorption coefficient of the recording medium (~5 × 103 cm−1), even the purely lossy gratings (where only the real part of the refractive-index modulation is taken into account) can lead to relatively high diffraction efficiencies of more than 50%. Finally, the results of Kogelnik's dynamic theory for XUV Lippmann-Bragg structures are compared with the standard multilayer dynamic models by extending the author’s earlier analyses2 to the XUV region.
Recent advances in the spectroscopy of platinum hollow cathodes
Authors: Engleman Rolf
Published: February 2023

High resolution spectra of platinum hollow cathodes have been obtained in the region from 220 nm to 5 μm using the Kitt Peak Fourier transform spectrometer (KPFTS).1 An earlier analysis of the visible and ultraviolet spectra yielded precise energy levels for neutral platinum (Pt I).2 More detailed analyses, based on the fine structure of each transition and due to the six naturally abundant isotopes, have resulted in values for the isotopic and hyperfine splitting coefficients for Pt I. In addition to several parity-forbidden transitions, some new energy levels have been found. A comparison with theoretical predictions has also been made. The spectrum of singly ionized platinum, Pt II, has also been analyzed in considerable detail. That analysis remains incomplete since allowed transitions connecting the ground state and several low-lying even levels occur only in the near vacuum ultraviolet where the KPFTS cannot operate. Attempts to complete the analysis of Pt II are described. A discussion of the platinum hollow cathode spectrum as a vacuum ultraviolet wavelength standard is presented, as well as the importance of certain Pt II transitions to astrophysical problems.
Mechanical rotating mirror isolator for large laser-fusion systems
Authors: Zhou Feng , Hu Shaoyi , Chen Qinhao , Deng Ximing
Published: February 2023

We have designed a high-speed rotating mirror isolator, which is basically contained by a rotating mirror and a spatial filter. The incident ray is reflected by the rotating mirror and scans an input lens. Only the main pulses can get through the hole at the optical focus to the output lens of the spatial filter. The optical system has been carefully designed, so the output ray from the isolator is restored and is as static as the incident ray.
Detection of ultraweak chemiluminescence of human urine with an intensity difference for nonsmokers and smokers
Authors: Inaba Humio , Yoda Binkoh , Saeki Akio
Published: February 2023

This paper reports for the first known time the measurement of ultraweak spontaneous chemiluminescence, generated without any external excitation, from human urine samples similar to blood.1,2 with an ultrahigh-sensitivity photon-counting system that was developed recently using a selected photomultiplier operated in optimum conditions.
Chemical production and reaction of metastable N(2D) for short-wavelength chemical lasers
Authors: Nikolai W. L. , Jensen R. C. , Coombe Robert D.
Published: February 2023

Metastable N(2D) is selectively produced (yield ≥ 85%) in the reaction of oxygen atoms and cyanogen radicals. We have made oxygen atoms at densities >1015 molecules cm−3 via the reaction of fluorine atoms with water. Yields approach 100% and modeling indicates scaling to short-wavelength chemical laser (SWCL) device levels is possible. We have also produced cyanogen radicals via the reaction of fluorine atoms with HCN and will present our results on the rate constant, CN yield, and scaling potential for this reaction. This latter category includes measurements of the rate constants for reaction of CN with various species we envision will be present in a SWCL device. N(2D) reacts rapidly with Cl2 and is constrained by spin and orbital angular momentum conservation to produce NCl(b,a). We present our results on NCl(b,a) yields and quenching by species envisioned to be present in a SWCL device.
Theory of thick and thin reference gratings for enhanced detection of acoustic waves
Authors: Magnusson R. , Black T. D.
Published: February 2023

Acoustic waves propagating in elastic media are used for many practical devices such as acoustooptic modulators, beam deflectors, and switches. The generation and detection of acoustic waves is also important in the study and characterization of materials. Typically, acoustic waves produce small effective refractive-index variations and can, thus, be difficult to detect by simple optical probing. It has been shown that use of stationary reference gratings can greatly facilitate the detection of these waves. In this paper, the application of thick (Bragg diffraction regime, i.e., two diffracted waves) and thin (Raman-Nath diffraction regime, i.e., multiple diffracted waves) sinusoidal phase reference gratings is considered for enhanced detection of acoustic waves. The coupled-wave theory is used to analyze the thick-grating case, while the transmittance approach is used for the thin-grating case. Simple, analytical expressions are obtained that describe the diffraction characteristics in each case. It is shown that thick reference gratings produce a purely sinusoidal temporal light-intensity modulation while thin gratings, in general, produce nonsinusoidal modulation.