bluuebunny/crossref_metadata_2025 huggingface dataset:
Sawtooth contrast sensitivity: decrements have the edge
Authors: Bowen R. W. , Pokorny Joel , Smith Vivianne C.
Published: February 2023

We measured temporal contrast thresholds for positive and negative sawtooths to test for asymmetry in sensitivity to light offset vs light onset. Since mirror-image sawtooth waveforms have identical amplitude spectra and differ only in phase, they also offer a test of the idea that sensitivity to a waveform is governed only by the amplitude of the Fourier fundamental. The stimulus was a 1.8° diam circle, mean retinal illuminance of 500 townsends (Td). Threshold contrast for the sawtooths (positive ramp or fast-off and negative ramp or fast-on) was measured at frequencies from 2 to 26 Hz. A sine-wave contrast sensitivity function was also determined over the same range. Observers were more sensitive to fast-off sawtooths than to fast-on by 0.05–0.16 log unit for stimuli of 2–13 Hz. At higher frequencies, differences were not systematic. This incremental/decremental asymmetry was confirmed with other waveforms. Sensitivity to fast-on sawtooths could be predicted from sine-wave contrast sensitivity with evidence of second harmonic intrusion at very low frequencies. Greater sensitivity to fast-off sawtooths suggests a response to the temporal structure of a waveform vs its spectral content and is consistent with the hypothesis of parallel on and off psychophysical channels.
Developmental changes in spatial scale
Authors: Swanson William H. , Birch Eileen E.
Published: February 2023

Development of spatiotemporal mechanisms during infancy was studied by measuring temporal contrast sensitivity of eighteen infants at 2.1, 8.3, and 33 Hz using 1.0-cycle/deg spatially localized patterns. A large increase in contrast sensitivity between 3 and 7 months of age was found at 8.3 Hz but not at 2.1 or 33 Hz. The data were analyzed in terms of a model using multiple spatiotemporal mechanisms which change in spatial scale between 3 and 7 months of age. Of the mechanisms sensitive to 1.0 cycle/deg, those with bandpass temporal tuning appear to increase in sensitivity more rapidly than those with low-pass temporal tuning.
Double-layer thin-film reflection phase retarders
Authors: Perilloux B. E.
Published: February 2023

Given a substrate and incidence angle, combinations of refractive indices for two transparent layers are determined that provide a specified differential phase shift and equal p- and s-polarization reflectances. The method utilized to determine this constraint on the film indices has been published.1 For nonideal retarders, with polarization-dependent reflectances, a numerical method is described that finds all film thickness pairs that achieve a specified differential phase shift for given indices and incidence angle. From these film thickness solution pairs, the thickness pair that provides the most equal p- and s-polarization reflectances is plotted for discrete film-index pairs. Both the ideal and nonideal solutions are plotted simultaneously for an absorbing and nonabsorbing substrate, incident angles of 30, 45, and 60°, and 90 and 180° reflection phase retardation angles.
New software for evaluating optical constants of absorbing films
Authors: Hanada Yoshiyuki , Yamamoto Yuji , Nakai Hidemi , Enjouji Katsuhisa
Published: February 2023

The optical constant evaluation technique for absorbing films has been newly developed. This technique can handle absorbing films, which are used for solar controlling films, with sufficient accuracy. In this technique, we assumed that the absorbing film has a double-layer structure. For example, a stainless steel film is assumed that consists of a metal layer and a surface oxidized layer, and this is supported by the surface analysis using SIMS. The advantage of this technique is that it can evaluate not only complex refractive indices but also thicknesses of metal (nitride) and surface oxidized layers. Another advantage is that only spectrophotometer and monochromatic ellipsometer measurements are necessary to calculate the optical constants in a wide range of wavelength. The optical constants of various film materials such as stainless steel, chromium, titanium nitride, silicon carbide, and so on were obtained using this technique. The errors are small enough so that optical properties of the multilayers for solar controlling films can be predicted with sufficient accuracy. For example, the spectral reflectance of a two-layer system (air/titanium nitride/stainless steel/glass) which was evaluated from those optical constants agreed well with measured values within a 3% error.
Polarization-sensitive coatings for optical devices
Authors: Sargent R. B. , Horowitz F. , Macleod H. A.
Published: February 2023

The columnar structure associated with conventionally deposited thin films has been extensively documented. The columns resulting from normal-incidence evaporation are oriented normal to the substrate, and the main optical effects on normal-incidence illumination are a reduction of refractive index and film inhomogeneity.
Efficient algorithm for calculating CGHs of line-segment objects
Authors: Manuar Omar A. , Kiely Aaron B. , Lettieri Thomas R.
Published: February 2023

The fast Fourier transform, although efficient, for calculating computer-generated holograms (CGHs) of objects in the form of 2-D arrays, is less useful with other types of object. In the work reported here, the interest was in developing an efficient algorithm for calculating Fourier transform CGHs of objects composed of a number of line segments. First, the object is restructured by approximating each line-segment angle ϕ by the closest angle ϕ′ in a set of standard angles whose arctangents are ratios of integers. (This significantly reduces the number of trigonometric functions to be performed.) Next, the line segments are grouped by ϕ′ and by center to exploit mathematical symmetries inherent in the sinc function (the Fourier transform of a single line segment). The Fourier transform is then performed on each segment, and the final hologram, represented by amplitude and phase matrices, is a summation of the individual line-segment transforms. The CGHs are encoded using the binary detour phase technique, printed with a laser printer, and then photoreduced into a 35-mm slide film. The reconstructed images of 2-D line-segment objects show multiple orders due to slight oversampling of the Fourier transform. The reconstructions of 3-D ot,ects, composed of 2-D line-segment objects spaced along the optical axis, show real images at different locations near the focal point of the reconstruction beam. Alternatively, virtual images may be seen by addition of a viewing lens placed after the reconstruction lens. The application of this algorithm to real-time metrology of optical surfaces and to 3-D holographic displays is currently being investigated.
Degenerate four-wave mixing in composites containing small metallic particles
Authors: Bloemer Mark J. , Ashley Paul R. , Mcdonald Joseph K. , Christensen Charles R.
Published: February 2023

Composite materials containing small metal particles exhibit third-order nonlinearities of the same magnitude as found in composites containing CdS
x
Se1–
x
microcrystals. For metal particles the largest nonlinearities occur in the vicinity of the surface plasmon resonance. For the work reported here gold microparticles were embedded in a gelatin matrix to study degenerate four-wave mixing (DFWM) in both bulk and thin-film forms. The gelatin has a higher index of refraction (1.55) than most glasses and low propagation losses making it suitable for waveguide studies. The gelatin was spin coated in aqueous solution with the water later removed by baking. Thin-film thicknesses were ~1 μm. The metal particle concentration was adjusted to optimize the conjugate signal relative to absorption losses. Guided wave propagation loss ranged from 2 to 6 dB/cm. The DFWM reflectivity was measured as a function of the pump intensity at frequencies near the plasmon resonance. The plasmon resonance was found from absorbance spectra obtained with a spectrophotometer. Metal particle sizes were determined using a scanning electron microscope. Reflectivity data and fabrication procedures are presented as well as a comparison to other composite materials.
Laser-induced grating spectroscopy of Cr3+-doρed garnets
Authors: Powell Richard C. , Hashmi Faqir M. , Suchocki Andrzej , Durville F. , Boulon G.
Published: February 2023

Laser-induced grating measurements were made as a function of laser power and write beam crossing angle for various temperatures between 10 and 300 K on Cr3+ ions in Gd3Ga5O12 (GGG), Gd3Sc2Ga3O12 (GSGG), and GGG mixed with Ca, Mg, and Zr ions. Population gratings were produced in the Cr3+ ions, and the diffusion coefficient describing energy migration among the Cr3+ ions was determined from the grating decay rate. The energy migration was found to increase as the temperature was raised for GGG and to decrease with decreasing temperature for GSGG. This difference is attributed to the differences in the crystal field splittings of the excited states in the two hosts. Enhanced energy diffusion was observed in the multiply doped GGG sample. Contributions to the laser-induced gratings from absorption and dispersion changes were determined, and this was used to provide information on radiationless relaxation and excited state absorption processes. For long writing times, long-lived changes in the refractive index were observed and attributed to optically induced color centers.
Effects of a finite outer scale of turbulence on the spatial spectrum of phase fluctuations
Authors: Winker David M.
Published: February 2023

Kolmogorov turbulence theory predicts an inertial range of turbulence where the power spectrum for refractive-index fluctuations follows a 5/3 power law. In theoretical studies the large-scale limit of the inertial range is often taken to be infinite, although this is a nonphysical assumption. In recent years a number of measurements of the outer scale have been reported, usually of the order of 5–10 m, but none is directly applicable to propagation studies. There are currently several projects to develop 8-m class telescopes, and it seems that for these large scale optical systems the effect of the outer scale may become significant. The Zernike decomposition of atmospheric optical turbulence is derived for the case of a Kolmogorov spectrum modified by the presence of a finite outer scale. The results indicate significant attenuation of tilt and low-order aberrations on medium to large telescopes if the path-integrated effective outer scale is of the order of 5–10 m. The sensitivity of an experimental technique for direct measurement of the outer scale is calculated.
Non-Gaussian correlation effects in coherent anti-Stokes Raman spectroscopy
Authors: Lau Albert M. F. , Farrow Roger L.
Published: February 2023

We propose a new approach to the analysis of stochastic processes with non-Gaussian statistics: the expansion of stochastic processes in terms of first and higher powers of Gaussian components (like a basis set). This approach is applied to treat the non-Gaussian correlation effects observed in coherent anti-Stokes Raman scattering (CARS) measurements performed on the O(18) transition of nitrogen using frequency-doubled pump-laser fields.1 A proper account of these effects is critical to the accuracy of CARS measurements on species concentrations. By comparison of our calculated results with experimental data at 500 Torr, the field statistics of the pump lasers are first determined and then used to make further predictions at 4500 Torr, where the Raman relaxation time is comparable with the time scale of the pump–laser fluctuations. In both cases, calculations based on this approach give much better agreement with experiments than previous theories.1,2
Effect of thermal light scattering fluctuations on two-wave mixing in optical Kerr media
Authors: Rogovin D. , McGraw Robert , Gavrielides A.
Published: February 2023

Two-wave mixing, or coherent beam combination, is of considerable interest to the nonlinear optics and laser physics communities. One approach, of particular interest to this study, involves irradiating an optical Kerr media with two nondegenerate laser beams. The finite response time of the Kerr material ensures that any laser-induced grating will lag the interference pattern formed by the two nondegenerate laser beams and thereby allow energy transfer from the high-frequency beam to the low-frequency one. For such media, thermal light scattering fluctuations give rise to thermal noise gratings which can transfer energy from one wave to the other. Since such gratings are random in nature, their effect is to introduce fluctuations in the two-wave mixing process itself. We examine the influence of such thermal noise gratings on two-wave mixing and determine the SNR for this process in the nondepleted pump approximation.
Loss compensation using Raman scattering in a multichannel soliton-based optical fiber communication system
Authors: Wang L. K. , Yang C. C.
Published: February 2023

To overcome the effects of fiber loss in a soliton-based communication system, optical amplifications using stimulated Raman scattering have been widely investigated. The idea is to input periodically along the fiber cw lasers with a slightly higher frequency compared with that of the signal. In a multichannel wavelength-multiplexing system, amplification parameters must be chosen carefully to compensate for the fiber losses in all channels. In this consideration, the Raman conversion among channels has to be taken into account. Here we consider a two-channel system and write two coupled equations in the sense that the net integrated gain is equal to the net integrated loss in an amplification period for each channel. By using an approximated curve for a Raman gain coefficient, those equations can be solved for deciding the required input pump intensity and wavelength. Numerical simulations have shown almost complete compensation for both channels if the amplification period is properly chosen. Also, the importance of the Raman conversion between two channels is clearly demonstrated.
Proposed method of measuring inner scale of atmospheric turbulence and C n 2
Authors: Andrews Larry C. , Phillips Ronald L.
Published: February 2023

An optical wave propagating through a random medium with a finite inner scale of turbulence can lead to larger values of the scintillation index than observed when the inner scale is vanishingly small. Calculated values of the refractive-index structure parameter

C
n
2

based on a direct short path measurement of the scintillation index need to be adjusted for nonzero inner scales. Analytic expressions for this correction factor are now available for both plane waves1 and spherical waves (not yet published).
Nonlinear effects in bulk semiconductor-doped glasses
Authors: Delong K. W. , Gabel A. , Seaton C. T. , Stegeman George I.
Published: February 2023

In the past few years, glasses doped with micro-crystallites of semiconductor material have been proposed as candidates for the fabrication of nonlinear optical switching and modulation devices because of their reasonably strong nonlinear response, subnanosecond response time, and ease of waveguide fabrication. We investigated these glasses using nonlinear transmission measurements and degenerate four-wave mixing. We have done these measurements on a time scale that is longer than the relaxation time (~100 ps-1 ns), of the order of the relaxation time, and shorter than the relaxation time (15-ns, 80-ps, and 30-ps laser pulses, respectively). We have also demonstrated four-wave mixing in a single-mode planar waveguide,1 an important first step toward nonlinear waveguide devices. We compared the experimental results to a theoretical model. The model uses the powerful plasma theory of Banyai and Koch2 to model the semiconductor response. The comparison indicates that a carrier-dependent relaxation time is necessary to explain the data. Whether this is a radiative-type recombination or an Auger-type process is unclear. We also explore the effect of two-photon absorption on the model.
Pump field modulation of resonance fluorescence in semiconductors
Authors: Lindberg Markus , An Sunghyuck , Koch Stephan W. , Sargent Murray
Published: February 2023

We investigate the resonance fluorescence spectrum of a bulk semiconductor subject to an injection current and an arbitrarily intense electromagnetic wave. We assume that the electronhole system is in quasiequilibrium due to the rapid carrier-carrier intraband scattering. The analysis is based on the generalized Bloch equations1 for semiconductors. Although the fast carrier scattering heavily damps the electronic coherence, it nevertheless allows the medium to follow adiabatically the relatively slowly varying field fluctuations. As a consequence, the resonance fluorescence spectra reveal asymmetric dips generated by pump scattering off carrier-density pulsations induced by the interference between the pump and vacuum mode. Similar to the two-level resonance fluorescence and probe absorption, the semiconductor probe absorption coefficient equals the difference between the resonance fluorescence and reabsorption coefficients. The results are important for nonlinear semiconductor spectroscopy and semiconductor laser instabilities.
Saturable absorption in semiconductor-doped glass waveguides
Authors: Finlayson N. , Banyai W. C. , Fazio E. , Villeneuve A. , Seaton C. T. , Stegeman George I. , Cullen T. C. , Ironside C. N.
Published: February 2023

Strong absorption saturation has been observed in single-mode channel waveguides fabricated in CdSxSe1-
x
semiconductor-doped glass by K+–Na+ ion exchange. At wavelengths below and close to the band gap of the semiconductor the transmission of the waveguide can be increased to several times the small-signal value. However, the waveguide never exhibits unity transmission. The saturable absorption properties of the waveguide are effectively modeled by a four-level system. Hercher has given equations describing the steady-state transmission of an optically thick sample of such a system.1 Unity transmission cannot be attained in the four-level system even at high intensities due to absorptive transitions between the upper levels (i.e., free-carrier absorption). Typical transmission curves for different values of the waveguide small-signal transmission have been calculated using the model. Good qualitative agreement is observed between the features of the experimental and theoretical curves. An important consequence of these results is that all-optical guided-wave devices fabricated in these glasses will exhibit considerable losses even in the high-intensity regime due to free-carrier absorption.
Scattering of a plane wave with a film with a self-defocusing nonlinearity
Authors: Liu Yi-Fan , Leung K. M.
Published: February 2023

The scattering of a plane transverse-electric electromagnetic wave with a nonlinear dielectric thin film, which is embedded between two semi­infinite linear media, is theoretically studied. We assume that the nonlinear film can be characterized by an intensity-dependent dielectric constant with a negative Kerr coefficient, and the wave is monochromatic. Exact analytical solutions to Maxwell’s equations for the fields are derived in terms of the Jacobian elliptic sine function. The solutions contain four integration constants, and they are determined by imposing the necessary boundary conditions on the fields. We also find that the reflection and transmission coefficients can exhibit optical bistable and multistable behaviors as a function of the intensity of the incident wave. For a given film thickness and at particular values of the incident intensity, induced transparency and induced resonances can also exist. (12 min)
Local normal mode analysis of waveguide grating couplers
Authors: Weller-Brophy Laura A.
Published: February 2023

A variety of analytical formalisms and numerical techniques have been used to describe guided-radiation mode coupling by waveguide diffraction gratings. Motivated by the development of integrated optic devices such as grating couplers and DFB lasers, the focus of this work has been on the case of normal incidence, where the projections of the mode propagation vectors in the plane of the waveguide are parallel to the grating vector. Recent interest in the use of grating couplers at non­normal incidence, as in the case of focusing grating couplers, has led to the extension of previous analyses to the more general case of oblique incidence.12 We present the results of a local normal mode analysis of shallow periodic surface corrugation grating couplers for the case of non-normal incidence.2 Our results are compared with those obtained using an ideal mode expansion as well as to the results of the quasioptical technique employed by Wlodarczyk and Seshadri.1 It is shown that all the formalisms predict TE-TM and TM-TE mode coupling for the case of oblique incidence. We consider the effects of such coupling on the operation of straight-line and focusing grating couplers.
Multifractal spectrum of quasiperiodic optical multilayers
Authors: Chow Lee , Penny Iain , Guenther Karl H.
Published: February 2023

Kohmoto et al.,1 proposed recently an experiment to probe the photon localization in optical multilayers. We investigated the possibilities of experimental verification of photon localization in a 1-D quasiperiodic layer structure. Conventional deposition techniques for thin films are not well suited because of the imperfect microstructure of these films. In contrast, low-voltage reactive ion plating deposition produces very dense homogeneous films with smooth interfaces, as assumed in the theory. We deposited multilayers consisting of high H and low L index materials according to the truncated Fibonacci sequence which can be written as a quasi-Fabry-Perot filter (CB)2A(BC)2 with A = HLHH, B = LHHL, and C = ALA. Because of the quasiperiodicity, a fractal transmission curve results in theory. In practice, the refractive-index dispersion changes the above quasiperiodic structure. To investigate this influence, we used Ta2O5, TiO2, and ZrO2 with different dispersion for the H layers with nondispersive SiO2 for the L layers. We present the first results of this study.
Electrooptic switches using ferroelectric liquid crystals
Authors: Clark Noel A. , Handschy M. A. , Meadows M. R. , Roosma L.
Published: February 2023

Electrooptic switching in ferroelectric liquid crystals (FLCs) produces large changes in their refractive index. This change, typically 0.15, is useful for optical switches that operate via total internal reflection (TIR) in contrast to most other electrooptic devices, both solid state and liquid crystal, that use variable retardance. We present experimental observations on both bulk optic and waveguide FLC devices that utilize TIR. Our devices are typically two state having one state where the incident light is below the critical angle and another state where the critical angle is decreased so that the same incident light is beyond critical. Application of 10 V/μm across an FLC film can accomplish switching between these two states in tens of microseconds. The advantages of the bulk optic device include its very high off-state extinction (~106) and the independence of its on-state transmittance on wavelength. The advantages of the wavelength device include the very short interaction length it requires enabling its integration into very dense optical switching arrays.
Analysis of the dielectric behavior of ferroelectric liquid crystals
Authors: Parneix J. P. , Legrand C.
Published: February 2023

An analysis of the dielectric response of ferro-electric liquid crystals at the

S
A

−

S
C
⋅

transition temperature is presented. The dielectric permittivity

(

ε
∗

=

ε
′

−
j

ε

′
′

)

was measured as a function of frequency in the planar (bookshelf) and homeotropic geometries, respectively. The frequency range was 5-109Hz. To obtain these measurements, a new dielectric cell was designed allowing a direct optical check of the sample alignment during the experiments. The data are consistent with previously published theories which show that in addition to the usual dielectric relaxation processes of conventional liquid crystals appearing in the high-frequency range of the dielectric spectrum, two modes dominate the dielectric response in the low-frequency range connected with the existence of long-range polarizationP.The first mode is often called the Goldstone mode. It is only apparent in the

S
c
⋅

phase and is connected with the inphase fluctuations of the phases of the tilt angleθand the polarizationP.The second one is the soft mode which is only observed close to the transition in the two phases. The inphase fluctuations ofθandPamplitudes are responsible for this mode existence. The frequency and temperature dependences of the amplitudes and relaxation frequencies of these two modes are investigated and compared to the data. The analysis yields values for molecular parameters which are consistent with previously reported values.
Forward scattering correction for light transmission through desert aerosols
Authors: Walker Philip L.
Published: February 2023

Desert aerosol size distribution measurements taken at China Lake, CA, along with a wind-blown dust model from AFGL indicate that desert dust consists of three lognormally distributed modes. The smallest, composed of combustion products, peaks at a diameter of 0.1 μm. An intermediate mode, composed of dust, peaks at 0.6 μm, the largest particles being 10 μm. These modes are wind speed independent. The largest particle mode peaks at 10 μm depending on wind speed. Attenuation for these aerosols may not follow Beer’s law for short wavelengths because of forward scattering generated by the larger particles. This work ascertains those conditions for which forward scattering is important by computing an effective extinction coefficient for a 1-km path over the spectral range of 0.4–12 μm as a function of wind speed and visibility and graphically comparing it to the Mie computed extinction coefficient.
Enhanced backscatter peaks from rough surfaces
Authors: Kim Min-Joong
Published: February 2023

Enhanced backscatter peaks in the diffuse envelope of the scattered radiation from a singlescale 2-D metallic randomly rough surface were first reported by O’Donnell and Mendez.1 The surfaces, which were made by etching a photoresist coated substrate with laser speckle patterns and coated with gold, had a mean slope of the order of 1. This statistical characteristic of the surfaces exhibiting enhanced backscatter peaks made the available scattering theories unsuitable for comparison to experimental data. In an attempt to alleviate this situation, a set of scattering experiments was carried out using a series of surfaces with similar 1/e correlation length but with varying surface height variance; the surfaces thus ranged from having a small mean slope to a large mean slope. In addition to the above-mentioned experiments, Stokes's were measured, allowing one to express completely the polarization state of the scattered light and more specifically that of the enhanced backscatter peak.
Diffraction properties of periodic arrays of dielectric cylinders
Authors: Magnusson R. , Shin D.
Published: February 2023

Diffraction gratings operating in the Raman-Nath diffraction regime (i.e., thin structures) have generally multiple diffracted output waves for a single incident wave. The distribution of energy among the diffracted waves is found to be critically dependent on the grating shape. This applies to both bulk-modulated (or planar) gratings and surface-modulated (or surface-relief) structures. For some applications, it is of interest to produce structures with multiple diffracted waves of approximately equal intensities. A particularly simple approach to achieve this is to use periodic structures consisting of arrays of dielectric cylinders. Our purpose is to present a simple theory to describe the diffraction behavior of periodic dielectric cylindrical arrays. Integral expressions are given for the complex amplitudes of the diffracted waves. A simple approximate formula for the diffraction efficiency of the zeroth order is presented. The model is evaluated experimentally, and good agreement is found. The diffraction regime in which multiple diffracted waves with similar intensities exist is defined quantitatively via a single parameter.
Diffraction from fractally serrated circular apertures
Authors: Kim Y. , Grebel H. , Jaggard D. L.
Published: February 2023

We investigate far-field diffraction from fractally serrated circular apertures. This investigation has potential use in pattern recognition, remote sensing, and radiation pattern synthesis. Fraunhofer diffraction patterns from these serrated circular apertures are exactly calculated. Then the bandlimited Weierstrass function, which possesses fractal characteristics within limited ranges, is used to model the rough boundaries along a circular aperture. Subsequently, the Fraunhofer diffraction pattern from this fractally serrated aperture is evaluated, and the effects on the diffraction pattern due to each scale size of the bandlimited Weierstrass function are examined. The diffraction effects due to each scale size are explained using the conservation of momentum. We also relate fractal descriptors such as the fundamental spatial frequency and fractal dimension to the diffraction patterns. In particular, the fundamental spatial frequency determines the angular distribution of the diffraction pattern. On the other hand, the radial distribution of the diffraction pattern is characterized by fractal dimension. Results of computer simulations and optical demonstrations are presented.
Nonspecular changes in partly coherent beams on reflection by layered media
Authors: Simon R. , Tamir T.
Published: February 2023

Past studies have determined that fully coherent beams undergo nonspecular changes on reflection by multilayered media. These changes involve lateral, focal, and angular shifts of the beam axis and a magnification of the beamwidth.1 By using Gaussian Schell-model beams, we examine such nonspecular effects in the case of partly coherent beams. We find that only the angular shift is affected by the presence of incoherence, while the other three nonspecular effects are identical to those in coherent Gaussian beams having the same beam-waist size. On the other hand, we show that the coherence length, the far-field diffraction angle, and the degree of global coherence are also changed by the reflection process. However, all these nonspecular changes are correlated so that the degree of global coherence multiplied by the far-field diffraction angle yields a factor that is preserved as an invariant quantity by the reflection process.
Optical transform patterns of nested polygons
Authors: English R. Edward , George Nicholas
Published: February 2023

We compute and measure diffraction patterns of nested polygonal apertures. A nested polygonal aperture comprises concentric polygonal strips (alternating transparent and opaque) of decreasing size. The key to writing a simple closed-form solution lies in decomposing the polygon into elemental triangles having a gratinglike structure. We present results for the particular case of a regular pentagon; here the elemental building blocks are gratinglike segments. First, we compute the optical transform of these gratinglike segments. Then we combine them appropriately to arrive at a formula for the diffraction pattern of a nested pentagonal aperture. The solution is especially well suited for computer calculation, and we show the results of such a calculation. Examining the diffraction pattern over a wide dynamic range (70 dB down from the diffraction peak) reveals fascinating low-intensity features. The combined effect of the gratinglike structure and the segment edges produces double-nested pentagons in the diffraction pattern. These features have been observed and measured experimentally.
Acuity-luminance functions in retinitis pigmentosa
Authors: Alexander Kenneth R. , Derlacki Deborah J. , Fishman Gerald A. , Peachey Neal S.
Published: February 2023

Optotype acuity was measured as a function of chart illumination in patients with retinitis pigmentosa (RP) to characterize more completely the degree of foveal impairment in this night-blinding disorder. Acuity-luminance functions were obtained from twenty RP patients who had 20/40 or better Snellen acuity, minimal or no posterior subcapsular cataracts, and no observable foveal lesions, as well as from ten age-similar normal observers. Subjects viewed modified Bailey-Lovie charts through an artificial pupil and an appropriate correction in a phoropter with illumination ranging from −1.1 to 5.2 log Td. Results were analyzed with a hyperbolic equation: in which MAR is the measured minimum angle of resolution, A is the asymptotic value of MAR, I is the chart retinal illuminance, s is a semisaturation parameter, and m is a slope parameter. The RP patients showed normal values of logs but had increases in logA and logm that were correlated significantly (r = 0.65). These findings indicate that (1) the greater the acuity loss of the RP patients at high luminances, the proportionately greater their acuity deficit at low luminances; (2) the patient’s acuity reductions result from a mechanism other than a decreased quantal catch.
Reversibility of contrast sensitivity changes in treated open-angle glaucoma
Authors: Ginsburg Arthur P. , Faye Eleanor E. , Sponsel William E.
Published: February 2023

Visual field reversibility, not uncommon in treated chronic glaucoma, is well-documented in individuals and groups. Contrast sensitivity is proving to be valuable for diagnosing and treating glaucoma suspects and patients. Presented here are cases of substantial contrast sensitivity reversals, measured with the Vistech Consultants Vision Contrast Test System (VCTS), in patients receiving topical drug therapy and, in one case, trabeculotomy. The phenomenon of predominately midfrequency contrast sensitivity losses in glaucoma patients is evident. These patients exhibit significant posttherapeutic changes in their contrast sensitivity curves. Contrast sensitivity deficits appear to be reversible and may even be anticipated in response to treatment. Possible visual mechanisms behind the contrast sensitivity changes are discussed. Furthermore, the inherent lack of midfrequency sensitivity of low-contrast optotypes suggests caution in their use to evaluate contrast sensitivity losses and therapeutic changes in glaucoma patients. The contrast sensitivity reversals, which may or may not be accompanied by visual field reversals, can occur in both those patients treated with drugs and those who undergo surgery. It is apparent that changes in contrast sensitivity and visual fields can provide useful clinical information to evaluate glaucoma patients and their responses to therapy.
Photopigment densitometry with a scanning laser ophthalmoscope
Authors: Elsner Ann E. , Burns Stephen A. , Webb Robert H.
Published: February 2023

We have used a confocal scanning laser ophthalmoscope (cSLO) to measure human photopigment density as a function of retinal location. The cSLO produces 20 × 17° video images of the fundus, which are digitized (8 bits) for subsequent analysis. In each session, one laser was selected as the bleaching and test beam, while another (790 nm) was used to image the fundus during dark adaptation or pigment regeneration. To obtain two-way densities, fundus images were stored at 10-s intervals following exposure to the bleaching beam. Image realignment is easily attained at the two-pixel level. Measurement artifacts were primarily due to reflections from retinal structures, such as the fovea, the internal limiting membrane, and the nerve fibers. External reflectance standards were digitized in each image to control for dark current and temporal changes in the detector or laser. We investigated internal reflectance standards also, such as vessel contrast and reflections from the scleral crescent, if present. Infrared images do not afford a suitable reference for changes over the retina, since these images exhibit contrasts and reflections different from images taken at visible wavelengths. A 2-mm confocal collection aperture typically gives lower two-way density estimates than the 12.5-mm confocal aperture. This is consistent with findings that the tightly confocal arrangement is selective for retinal surface features. Two-way optical densities referred to 555 nm were 0.27-0.45 for the central 0.4°.
Restoration of retinal images taken through cataract
Authors: Peli Eli
Published: February 2023

An optical model for imaging the retina through cataract has been developed. The images are treated as sample functions of stochastic processes. From this model a homomorphic Weiner filter can be designed that will optimally restore the cataractous image (in the mean/square error sense). The design of the filter requires a priori knowledge of the statistics of either the cataract transmittance function or the noncataractous image. The cataract transmittance function can be estimated from the cataractous image of the retina and the assumption that it is low pass in nature. The statistics of the noncataractous image may be estimated using an old precataractous photograph of the retina, which is frequently available. Implementation of this restoration technique in a variety of modes has been effective with clinical photographs. The best results were obtained with short-space enhancement using averaged short-space estimates of the spectra of the two images.
Optical fabrication issues in excimer laser keratomileusis
Authors: Chastang Jean-Claude , Hanna Khalil , Asfar Louis , Samson Jean
Published: February 2023

The ablation characteristics of the output of an ArF excimer laser at 193 nm when applied to the corneal tissue have received much attention because they offer the prospect of correcting visual errors by actually reshaping the cornea. The reshaping of the cornea is done by projecting onto the cornea the image of a small aperture, which is in effect etched onto the cornea with every pulse of the laser. The extent and type of correction under consideration (myopia, hyperopia, astigmatism) determine the shape of the aperture as well as its trajectory onto the cornea. The summation of the elementary ablations over the cornea yields the global required ablation. Mathematical developments explaining how the shape of the apertures as well as their trajectories are determined to obtain a given correction are explained. Optical components other than the cornea could be machined in an analogous manner.
Self-bending of a cw beam in sodium vapor
Authors: Swartzlander G. A. , Yin H. , Kaplan A. E.
Published: February 2023

We report the first observations of the cw self-bending effect1 using an asymmetrical laser beam propagating in sodium vapor and discuss some concerns of practical and physical importance. The laser frequency was detuned below the D2 resonance until the maximum self-bending angle was observed. At ~200°C the nonlinear refractive index was found to be predominantly Kerrlike (Δn ≃ n
2
I) at experimental peak intensities up to ~220 W/cm2. This result is inconsistent with our numerical calculations of the saturation of the anomalous dispersion that includes power-broadened hole-burning of an inhomogeneously broadened two-level system,2 which predicts strong saturation of Δn. By analyzing either the self-deflection angle or the intensity at a single point in the far-field region as the input power was varied, we were able to determine that n2 ≃ − 10
−
7 cm2/W. Self-deflection angles as large as 5.9 mrad or eight times the diffraction angle were observed, which is more than enough for some useful applications such as resonatorless optical bistability, optical switching, and interconnecting, nonlinear optical coupling, and radiation protection, the latter of which we have demonstrated.
Recovery of excitation Intensity dependence in pulsed focused beams
Authors: Ruyten Wilhelmus M. , Lewis J. W. L.
Published: February 2023

We present the recovery of excitation intensity dependence from spatially and temporally averaged data as an inversion problem. Thus cross sections and line shapes are obtained as a function of local instantaneous intensity rather than peak intensity or pulse energy. In the nonsaturated regime, actual and experimental cross sections are related by a Volterra integral equation. For exponential intensity profiles, the problem is solved by Abel inversion. For mildly nonlinear cross sections, inversion results are obtained from the moments of the excitation density function. For the most general case, inversion by collocation is discussed, in particular by the direct-inversion approach. In the saturation regime, the problem becomes nonlinear in the time coordinate and has to be reformulated so as to include a saturation parameter. It is shown how inversion results can be obtained under the constraint of the constant spectral area under the line profile, yielding also a value for the saturation parameter. Our treatment should allow the extension of such diagnostic schemes as two-photon laser-induced fluorescence into the saturation regime, maintaining calibration while enabling a higher SNR.
Considerations Involved in the Design of an Optical Digital Computer
Authors: Huang Alan
Published: February 2023

The prime concern in the design of an optical digital computer is "Why?". Optical bistability is faced with the same question. If optical bistability is to compete with other switching technologies solely in terms of speed and power then its development will be haunted by the constant advances in silicon technology.
Optical Bistability in CuCl
Authors: Hönerlage B. , Bigot J.Y. , Levy R.
Published: February 2023

As it is well known from nonlinear optics, the dielectric function

ε(

Q
˜

,ω)

and the resulting polariton dispersion are functions of the excitation intensity. Since in CuCI biexcitons with energy EBi may be created by the absorption of two photons provided by different light sources,

ε(

Q
˜

,

Ω
)

depends on the density of photons with frequency ωℓ, defined such that.
Optically Induced Changes in the Faraday Rotation Spectra of the Ferromagnetic Semiconductor CdCr2Se4*
Authors: Sanford Norman A.
Published: February 2023

Chromium chalcogenide spinel semiconductors have gained attention because of the strong interaction between their electronic and magnetic systems. CdCr2Se4, the most extensively studied Cr spinel, is ferromagnetic and orders at 130 K. The optical absorption edge is found to red shift for temperatures below the Curie point(1). Faraday rotation spectra measured near the absorption edge are highly dispersive with peak rotation increasing and shifting to the red as temperature is reduced. In particular, the rotation spectra scanned at fixed temperature display zero crossings characteristic of the temperature (T less than TC). The red shifting of both the absorption edge as well as the rotation dispersion result from increased magnetic order with reduced temperature(2).
Observation of Bistability in a Josephson Device
Authors: Muhlfelder Barry , Johnson Warren W.
Published: February 2023

We have been building devices with two Josephson junctions coupled together by a transmission line or waveguide. We have found that these devices can exhibit a type of bistable behavior not seen before in other Josephson devices. The observed behavior appears to have certain similarities to optical multi­stability.
Theory of Multistability in Josephson Junction Devices
Authors: Drummond Peter D. , Muhlfelder Barry , Johnson Warren W.
Published: February 2023

The existence of phase-transition like behavior in Josephson junctions is well known. However most studies of the theory of these transitions are restricted to numerical calculations, owing to the nonlinearities of the Josephson equations in the regions of usual interest. Approximate analytic techniques that do exist are often restricted to regions where the oscillations are nearly sinusoidal.
Self-Beating Instabilities in Bistable Devices
Authors: Martin-Pereda J.A. , Muriel M.A.
Published: February 2023

Since the observation of optical bistability, several papers have discussed the effect of a delayed feedback on instabilities pointing out that the transmited light from the system can be periodic or chaotic in time under certain conditions. This phenomenon was confirmed by Gibbs et al.1 in hybrid bistable optical devices with PLZT as electrooptical material. Ukada et al.2 have reported similar effects in LiNbO3. In this case a coaxial line was employed as delay. A sustained oscillatory optical output is show to appear under the instable condition. Moreover, as we have shown previously,3 similar effects can be obtained from liquid crystal cells under suitable conditions, In this paper we extend these results giving an analytical model of some of the obtained oscillatory optical outputs.
Empirical and Analytical Study of Instabilities in Hybrid Optical Bistable Systems
Authors: Pereda J.A. Martin , Muriel M.A.
Published: February 2023

In this paper we analize the instabilities of electrooptic bistaole devices with delayed feedback, giving the instability condition for oscillation to appear. This condition will be given for the two types of curves more commonly used, namely Iout VS. IIn and transmission versus voltage.
Cyclotron Bistability of Electrons in Vacuum and Semiconductors
Authors: Kaplan A.E.
Published: February 2023

The feasibility of an optical cyclotron bistability of free electrons in vacuum as well as of conductive electrons in semiconductors is discussed. It was recently shown by us1 that the cyclotron bistability of the free electrons can be based on the dependence of a cyclotron frequency of forced oscillations on the relativistic mass of the electron and, hence, on its momentum (or kinetic energy). It was also suggested that1 the analogous effect could be feasible in semiconductors whose conductive electrons have a particularly strong dependence of their effective masses on energy (or momentum) of their excitation. The main advantageous features of the cyclotron bistability in semiconductors is that (i) the effective mass of electrons in some semiconductors (e.g. InSb) is very small which results in a considerable decrease of a required magnet field for a given resonant frequency, and (ii) the nonlinearity associated with conductive electrons in semiconductors is by many orders of magnitude larger than the relativistic nonlinearity of free electrons, which allows for a fairly low critical pumping intensity, even if taking into consideration a faster relaxation time in semiconductors.
Absorptive Optical Bistability with Laser Amplitude Fluctuations
Authors: Kuś M. , Wódkiewicz K. , Gallas J. A. C.
Published: February 2023

In this paper we discuss the influence of laser fluctuations on the hysteresis cycle in Optical Bistability. For the simplest case of an Absorptive Optical Bistability in a good cavity driven by an external laser light with non-white Gaussian amplitude fluctuations we derive a Fokker-Planck equation in the limit of large laser linewidth and good amplitude stabilization. This Fokker-Planck equation has a nonconstant diffusion term which shifts the most probable values of the steady state probability distribution from its deterministic positions. From the form of the steady state solution of the Fokker-Planck equation with non-white amplitude fluctuations we discuss the relative stability of the bistable branches. As in the case of quantum fluctuations the random amplitude of the laser field leads to a small range of values of the injected laser intensity in which the two bistable peaks have a comparable area. The transmitted field averaged with respect to the stationary distribution function coincides with one of the two deterministic branches except on the narrow transition region where we have large fluctuations.