bluuebunny/crossref_metadata_2025 huggingface dataset:
Space-charge fields in volume holographic interconnections
Authors: Baek W. S. , Lee H.
Published: February 2023

Criteria for optimal implementation of the volume holographic interconnections utilizing photorefractive materials are presented. To study the photorefractive recording mechanism which yields optimal implementation of the volume holographic interconnections, the Kukhtarev's nonlinear differential equations are resolved into a number of algebraic equations by expanding the electric field and free-carrier density into their complex Fourier series. Analytic solutions of the steady state spacecharge fields in photorefractive materials are derived for small light intensity at large modulation depth. Numerical solutions for the photorefractive crystal BSO are also obtained by utilizing Powell's method without the assumption of small laser intensity, and they are compared with the analytic solutions in both cases of stationary light interference patterns and moving light interference patterns. The intermode space-charge fields generated by a pair of light interference patterns in photorefractive materials, which may cause the second-order crosstalk problem, are described. The data regions are obtained in which the effects of intermode space-charge fields are suppressed and the criteria for optimal implementation of volume holographic interconnections are satisfied.
Optical interconnect using free space optics
Authors: Dickinson A. , Prise M. E. , Craft N. C. , Chirovsky L. M. F. , D'asaro L. A.
Published: February 2023

Integrated free space optical interconnect has the potential to provide a large number of high speed connections between electronic integrated circuits. The overall optical arrangement is briefly described. We intend to use a single laser or a pair of lasers to power an interchip connection with several hundred communications channels. Differential optical encoding will be used to provide higher speed and eliminate referencing problems. We propose using reflective GaAs quantum well modulators as output ports. Energy requirements of such modulators are very low and their fabrication on silicon substrates has been demonstrated. We have tested arrays of differential modulators with 5-µm diam windows fabricated on GaAs substrates at frequencies up to 1 GHz with no high frequency roll-off. As optical input ports we propose using silicon photodetectors which are fully compatible with the standard CMOS silicon integrated circuit process. We have fabricated a test chip with a variety of differential amplifier circuits and photodiodes using a production facility. The photodiodes have sizes of 5 × 5 µm and 10×10 µm. The circuits have been tested and shown to run at 140 MHz with 100 µW of optical input power.
Nonlinear optical processes in lower dimensional conjugated structures
Authors: Garito Anthony F.
Published: February 2023

Electron-electron interactions and electron correlation in effectively reduced spatial dimensions markedly determine the unusually large nonlinear optical properties of conjugated organic and polymer structures. Experimental and theoretical studies have been extended to nonresonant nonlinear optical processes originating from real population of π-electron excited states by direct optical pumping. For qua-si-1-D chainlike structures, the nonresonant second-order and third-order susceptibilities increase by orders of magnitude and may even change sign when one-photon, or two-photon, 7r-electron excited states are populated. Thus, for example, with the fundamental frequency at 1.17 eV (λ = 1.06 µm), the microscopic third harmonic susceptibility γxxxx(−3ω;ω,ω,ω) along the 1-D axis of an eight-site chain is 33,237, and–207 × 10−36 esu when the ground state, first one-photon excited state (11Bu), and first two-photon excited state (21Ag) are, respectively, occupied. Compared to the ground state, excited state nonlinear optical properties exhibit new optical resonances and windows from dc to optical frequencies. Thus, by optical pumping into a designated state within an excited state manifold of a 1-D or 2-D structure, second-and third-order optical properties can be controllably selected to greatly enhance their magnitude, or even change their sign, over desired frequency ranges. In turn, the recent development of new nonlinear optical structures can be broadened and expanded to include nonlinear optical and electrooptic properties originating from real population of not only the ground state but also excited electronic states.
Ellipsometry of zinc sulfide films deposited in ultrahigh vacuum
Authors: Atkinson Ronald , Lee King H. , Lissberger Paul H. , Manzoor Tahir
Published: February 2023

The salient features of an automatic ellipsometer suitable for studying the nucleation and growth of zinc sulfide films in ultrahigh vacuum are described. The instrument is operated automatically in a selfnulling classical mode by means of two Faraday cells driven by currents with both ac and dc components. Sensitive measurements of the dc components in the null condition provide values of two functions δψ = ψ − ψ0 and δΔ = Δ − Δ0, where ψ0 and Δ0 are the initial values of the usual ellipsometric functions ψ and Δ for the uncoated glass substrate surface. The refractive index and thickness of the growing films are deduced from a plot of [δψ, (δΔ)2]. A point P on the [δψ, (δΔ)2] curve represents a film of thickness d and refractive index n, where n is obtained from the slope of OP and d from its length. The ellipsometric functions and optical parameters of the growing film are related to structural parameters via the Volmer-Weber model for film growth on amorphous substrates. Such growth proceeds around islands or nuclei; and in the simplest form of the model, the nuclei are assumed to be spherical and their surface number density fixed ab initio.
Optical transforms for objects in natural illumination
Authors: Wang Shen-Ge , George Nicholas
Published: February 2023

In earlier work an optoelectronic hybrid consisting of a twin-imaging interferometer with crossed roof prisms, a Fourier transform achromat, a CCD array, and a digital computer was described. Spatial cosinusoidal optical transforms can be recorded for rough objects using bandlimited white light. We describe optical metrology and feature extraction using this system. If we consider an idealized amplitude transmittance t(x,y), the advantage in the white light system is that it measures the spatial transform of |t(x,y)|2. In cases where the phase portion contributes a signal that is of little or no interest, clearly the white light transform can be preferable, say, to a system that measures and transforms t(x,y). We describe two separate experiments. For optical metrology, we measure the film grain scattering from commercially available color negative film of various ISO ratings and at different densities. In a separate series of experiments we measured the optical transform pattern that results from printouts of various digital halftones, i.e., the analog of film grain scattering in the electronic printing industry. Finally, we conclude with a discussion of pattern recognition using this white light system combined with neural network software.
Optimal apodization of acoustooptic power spectrum analyzers
Authors: De Koker E. , Van Rooyen E.
Published: February 2023

Interferometric spectrum analyzers offer improved performance over power spectrum analyzers but not without a substantial increase in complexity. In this paper a technique for improving the performance of power spectrum analyzers is presented. The intensity profile of the input light beam controls the level of the sidelobes in the detection plane as well as the resolution of the analyzer. This profile, together with acoustic attenuation also controls the instantaneous dynamic range by suppressing acoustic nonlinearities. The most common criterion used for determining the resolution of an acoustooptic spectrum analyzer is the Rayleigh criterion. The application of this criterion requires two signals of the same power, a condition which rarely occurs in practice. A condition more likely to occur is that the signal powers vary extensively and require a large dynamic range. It is for this reason that the use of the Rayleigh criterion in spectrum analysis is not recommended. A different criterion is suggested and shown to be more appropriate. The most general weighting function used is Gaussian. This function is evaluated by using the suggested criterion for resolution shown not to be optimal. An optimal weighting function is determined incorporating the effect of acoustic attention and acoustic nonlinearities. This is shown to exert an appreciable influence on system specifications and design.
Generalized line broadening and saturation behavior
Authors: Rosenberger A. T.
Published: February 2023

One characteristic normally used to distinguish inhomogeneous broadening from homogeneous broadening is the saturation behavior occurring when irradiation takes place at line center. The usual behavior found is that the absorption coefficient decreases as a negative power of 1 + I/Isat; a power of −1 indicates homogeneous broadening and a power of −½ denotes inhomogeneous broadening. It is shown here that, in the rate equation limit, this behavior is followed in most cases even though the homogeneous and inhomogeneous absorption profiles can have any line shape. The homogeneous line shape, in particular, need not be Lorentzian; its line center saturation behavior will be the same as that of a Lorentzian, however. If the inhomogeneous broadening is due to a distribution of atomic center frequencies, in the inhomogeneous limit the usual line center saturation behavior will be found no matter what the combination of homogeneous and inhomogeneous line shapes. However, if the broadening is inhomogeneous because of a distribution, among the individual atoms, in any property of the absorption profile other than center frequency (for example, the homogeneous linewidth), the saturation properties are not as simple, and in fact the inhomogeneous limit may not even exist.
Grating-surface-emitting laser arrays
Authors: Evens G. A. , Carlson N. W. , Lurie M. , Hammer J. , Palfrey S. L. , Amantea R. , Bour D. P. , Butler J. K.
Published: February 2023

In the last several years, considerable work has been directed toward developing surface-emitting semiconductor lasers such as the vertical cavity, etched 45° facet, and grating-coupled surface emitter (GSE). In this paper we review the grating-coupled approach to surface-emitting semiconductor lasers, which has demonstrated monolithic integration of over one hundred semiconductor lasers into a coherent array with the capability of electronic beam steering. Coherent operation is obtained by mutual injection coupling in one direction and evanescent coupling in the other. The threshold current density and efficiency of these lasers are approaching that of conventional cleaved facet lasers. Transparent substrates allow junction down mounting for improved thermal packaging. GSE arrays have been fabricated with wavelengths ranging from 0.77 to 0.88 µm using the AlGaAs material system, from 0.88 to 1.05 µm using strained-layer GaInAs quantum wells, and at 1.3-1.5 µm using the GaInAsP material system. To obtain the ultimate performance from the GSE arrays will put significant demands on the layer uniformity of the semiconductor structure and the fabrication processes. Uses for GSE lasers include incoherent 2-D arrays for pumping solid state lasers, high speed interconnects for integrated circuit chips, and space communications.
Three-dimensional surface curvature from binocular stereodisparity
Authors: Wildes Richard P.
Published: February 2023

Consider a binocular stereosystem that observes a curved surface patch. Owing to the geometry of the situation, markings on the surface (e.g., texture) will be imaged differently to the two views. An analysis of certain aspects of this situation is presented. More specifically, the analysis concentrates on the relationships between a surface's 3-D curvature and the differentially projected images of its surface markings. The analysis is based on: (i) following surface features as they are subjected to disparate projection, and (ii) establishing the relationships between the resulting disparity and surface curvature.
Direct computation of 3-D shape and motion invariants
Authors: Weinshall Daphna
Published: February 2023

Structure from motion often refers to the computation of inverse optics from a matched sequence of images. However, as is suggested by human vision, a depth map of a surface is probably not a good representation for storage and recognition, a more concise representation seems necessary. In addition, recovering the exact function of the surface and the motion parameters is computationally expensive, serial, and sensitive to errors. Obviating this computation, I first show that the sign of the normal curvature in a given direction on a given point in the image can be computed from a simple difference of slopes of line segments in one image. This simple operator is an example of a hyperacuity task which the visual system can perform with higher, precision, an order of magnitude better than visual acuity. Using this result, local surface patches can be classified as convex, concave, cylindrical, saddle point, or planar. This is done by repeating the basic sign operator at different orientations, a natural operation to many known biological architectures. At the same time the translational component of the optical flow is obtained, from which the focus of expansion can be computed (which is important for navigation, for example).
Giant four-wave mixing amplification in Kerr nonlinear medium with dispersion
Authors: Law C. T. , Kaplan A. E.
Published: February 2023

We have shown previously that two strong laser beams (with the same frequency) counterpropagating in a Kerr nonlinear medium with linear dispersion become un stable when their intensities exceed a certain threshold.1 We demonstrate here that the system exhibits large (theoretically unlimited) amplification of a probe beam when the two pumping beams have their intensities slightly below the threshold. This is in contrast to the conventional phase conjugation due to four-wave mixing in a nondispersive Kerr nonlinear medium. The mechanism of amplification in our system can be explained in terms of positive distributed feedback from the Kerr nonlinear index grating formed by two strong pumping laser beams in the presence of dispersion giving rise to a light-induced distributed-feedback resonator. This feedback is attributed to the fact that the weak beams with both signal frequency, ω + δ, and conjugate frequency, ω − δ, propagate with phase speed different (due to dispersion) from that of a pumping wave with frequency ω, which triggers the exponentially increasing energy exchange between weak and strong beams at the nonlinear index grating (this energy exchange is prohibited in nondispersive media). When the probe frequency approaches a frequency of one of the longitudinal modes of the light-induced distributed resonator, and the pumping intensity approaches the threshold of instability, the resonant amplification increases infinitely; for presently available laser intensity stabilities, amplification as large as 104 is feasible.
Stress control of ZnSe thin films
Authors: Sobczak J. , Pond B. J. , Carniglia C. K. , Dafoe M. F.
Published: February 2023

Thin films of ZnSe commonly have a compressive stress when deposited on fused silica substrates. We have found that this stress decreases if oxygen is admitted to the coating chamber during deposition. At a pressure of ~1.4 × 10-4 Torr, the stress changes from compressive to tensile and at this pressure stress-free films can be made. Similar results have been attained by ad mitting nitrogen or argon to the chamber. This suggests that the cause of the change in stress is not chemical but rather physical in nature.
Stress measurements of transparent optical materials using a beam scanning modulated transmission ellipsometer
Authors: Hayden Joseph E. , Jacobs Stephen D.
Published: February 2023

The principle of operation of the modulated transmission elipsometer (MTE) stress measurement technique and some specific thin film and bulk material systems that have been studied using the MTE are discussed. The MTE is an optical setup that uses a highly sensitive polarization modulation technique and an x-y galvanometer scanner for high speed mapping of internal stress birefringence in transparent optical materials. The MTE can measure stress generated retardances of the order of 0.01-160 nm in areas of from 50 × 50 μm to 100 × 100 mm. This system also has the unique ability to recognize and actively subtract optical component stress by imparting a controlled retardance bias on the laser beam. The output can be displayed as a line scan, 3-D plot, or a color contour plot. The MTE has been used to observe internal stress in dielectric thin film/substrate systems such as Cu, Ta2O5, and Si, in various transparent substrate materials. Thin film multilayers of MgF2 and ZnS on BK-7 substrates have been examined for stress as a function of predeposition and postdeposition parameters. The effects of stress on transparent Cu thin films on a glass substrate were studied by repeatedly stress mapping the system for varying levels of current through the Cu. Stress research has also been done on bulk materials such as strengthened glass, polymers, Nd:doped laser glass, and electrooptic crystals. The MTE has allowed us to compile a continually growing data base on the causes and effects of internal stress in thin film and bulk materials.
Improving mechanical properties of optical thin films by ion assisted deposition
Authors: Gao Yang , Cheng Weiming , Zhou Pengfei , Zhuang Songlin
Published: February 2023

Several optical coatings were produced by ion assisted deposition (IAD) and their mechanical properties were investigated using four different methods. The experimental results are summarized here:

(1) Eleven kinds of film were produced by IAD; they are a seventeen-layer dielectric interference filter of ZnS/MgF2; an antireflection coating of MgF2 on a plastic substrate, some oxide films such as ZrO2, TiO2, and SiO2; some metallic films such as Ag, Al, and Cu; some metal bandpass films for energy efficiency.

(2) Compared with those deposited by PVD, all the films by IAD with proper parameters have better mechanical properties, with increased abrasion and corrosion resistance, as well as improved adhesion and security.

(3) SEM photographs showed that IAD had effectively reduced the affected width of scratches on the film surface. This means that the mechanical properties and hardness of the films have been improved.

(4) With the IAD technique, we can obtain firm and fine films on plastic substrate without heating and it is difficult to obtain them by the PVD technique.

(5) The XRD, TEM, and TPDS analyses showed that the reason for improving mechanical properties by IAD is that bombardment particles can increase collecting density, improve microstructure, and facilitate crystallization of coating; and for some films, bombardment with different ions has different effects on the properties of films.
Acousto-electrooptic effects in SAW devices
Authors: Semendy Fred , Garvin C. , Decusatis C. , Das P.
Published: February 2023

Both acoustooptic (AO) and electrooptic (EO) interactions can be generated simultaneously in piezoelectric crystals to produce an acousto-electrooptic (AEO) effect. AO devices have been developed for performing convolution, correlation, and matched filtering; EO devices may be used for pulse compression and matrix processing, as well as many other applications. An AEO effect can give not only an additional port for information, but also overcome individual limitations and be used for all the above applications. A theoretical description of AEO interaction in the Bragg regime, based on superposition of surface acoustic waves (SAW) and EO interdigital transducers was reported previously.1 Longitudinal and transverse components of the propagating SAW and applied electric field were considered separately to account for the anisotropy of the crystals. Coupled mode theory was then applied to predict features of the resulting diffraction.
Anomalous erasure of photorefractive holograms in LiNbO3
Authors: Brady David , Raguin Dan , Kagan David , Psaltis Demetri
Published: February 2023

The Kuktarev band transport equations predict exponential decay in the space charge field associated with photorefractive holograms erased with uniform illumination. We have found, in contrast, that in certain conditions the amplitude of the space charge field, monitored via the diffraction efficiency, can increase dramatically before eventually decaying when a hologram is erased by uniform Bragg mismatched light. This effect can be explained using the multiple active trap model proposed by Valley in 1983. We describe experiments demonstrating this effect in LiNbO3. We analyze the effect in the context of the multiple trap model and consider its effect on the recording process. The use of volume holographic media for high density information storage requires multiple exposures. We consider the difficulties the multiple trap model creates for multiple exposure recording in photorefractive materials.
Comparison of methods for measuring titanium nitride film stoichiometry
Authors: Hillendahl James W.
Published: February 2023

Titanium nitride plays an important role in architectural optics and has great potential for visible and infrared precision optics. Characterized by unusual hardness and durability, titanium nitride has many of the optical properties of metals. But optical and physical performance depend critically on achieving near-stoichiometric conditions. Direct and indirect methods are compared for assessing thin film stoichiometry. Direct methods include Rutherford backscattering (RBS), Auger, and x-ray fluorescence. Indirect methods include measuring electrical properties (bulk resistivity), optical constants (ellipsometry), and color (CIE, Lab Hunter). Data obtained for sputtered titanium nitride films using these methods are correlated with results of hardness and abrasion tests (Taber Abraser, MIL-Spec Eraser Test, coefficient of friction scratch test, and indentation methods).
Distortion: the culprit exposed
Authors: Shafer David
Published: February 2023

Jan Hoogland has shown that fifth-order Petzval curvature is often the limiting aberration of a high-performance design, although this fact is often masked by higher-order astigmatism. I have shown that this fifth-order Petzval curvature is usually caused by pupil aberrations—mainly coma of the chief ray—within the lens. This same pupil aberration is intimately connected to the third-order distortion of the system, which is also a chief ray aberration.
Computational theory of shape from shading and motion
Authors: Pentland Alex
Published: February 2023

I describe a closed-form solution to the problem extracting shape information from image shading that uses only biologically plausible linear filters together with point nonlinearities. I then describe how, by adding a temporal dimension to this simple shape from shading mechanism, it may be extended to produce estimates of surface reflectance, object rotation, and surface shape from the photometric effects of object motion.
Perception of shape from shading
Authors: Ramachandran Vilayanur S.
Published: February 2023

Since the time of Leonardo Da Vinci there has been very little research on how human observers perceive shape from shading. Our experiments suggest that shading is a primitive visual dimension that is extracted relatively early in visual processing. More recently, our research has focused on the question of how information about shading interacts with other visual functions such as motion, occlusion, stereopsis, symmetry, and perceptual grouping. We find that (1) In extracting shape from shading the visual system incorporates the single light source constraint; i.e., it assumes that there is only one light source illuminating most of the image. This is especially true for different parts of a single object. (The rule can sometimes be overridden for multiple objects.) (2) Tokens defined by shading can be used for perceptual grouping and segregation. (3) Occlusion boundaries (e.g., illusory contours) strongly influence the extraction of shape from shading. Chromatic borders, on the other hand, are completely ineffective. (4) Shading can provide an input to motion perception.
Multiple-beam lensing and deflection of picosecond pulses in semiconductors
Authors: Dubard J. , Cui A. G. , Smirl Arthur L.
Published: February 2023

We investigate the lensing and deflection of a weak picosecond pulse by symmetric and asymmetric refractive index profiles induced in doped and undoped Si and GaAs by a second pulse. Here, two 30-ps pulses at a wavelength of 1.064 μm are incident on the surface of the sample with a small angle between the two beams and an adjustable time delay between the two pulses. The absorption of the first pulse (by single- or two-photon absorption) creates a symmetric or an asymmetric index profile. The second pulse is simultaneously or subsequently defocused and/or deflected as it propagates through the sample by the spatial index profile created by the first pulse. We discuss several geometries in which we use these effects to construct multiple-beam optical limiters, and we carefully compare the performance of these devices with more conventional singlebeam devices operated in similar conditions. Finally, we illustrate the use of these phenomena in multiple-beam geometries as spectroscopic tools for measuring the sign and magnitude of nonlinear refractive index changes. Again, we compare these multiple-beam spectroscopic techniques with their single-beam counterparts.
Multiple filter compact coherent optical correlator
Authors: Upatnieks Juris , Abshier James O. , Christensen Charles R. , Stensby John
Published: February 2023

A compact coherent optical correlator with thirty parallel filters and a filter maker were designed, fabricated, and tested. Two holographic optical elements were used to each form fifteen Fourier transforms. These elements performed a number of functions that would require several conventional elements, thus reducing the overall correlator size. The correlator had a real time input via a liquid crystal light valve and an image intensifier in front of it for operation at low light levels. A computer controlled filter maker automated the filter recording process.
Optical disk based architectures for pattern recognition and neural network implementation
Authors: Neifeld M. A. , Yamamura A. , Kobayashi Seiji , Psaltis D.
Published: February 2023

Optical disks have emerged as attractive candidates for both memory and SLM elements in optical information processing architectures. The features which make optical disks particularly well suited for these types of application include their large storage capacity (>1010 bits), parallel readout capability, convenient scanning mechanism, and their computer addressability. We have previously described disk based image correlators which can compare a 2-D input with as many as 40,000 computer specified reference images per second. In this paper we present two specific applications of optical disk based architectures. First we describe a disk based correlation architecture for use in a handwritten character recognition system.
kth law nonlinear matched filters
Authors: Javidi Bahram
Published: February 2023

We describe a nonlinear matched filter based image correlator that uses nonlinearity at the Fourier plane to threshold the linear matched filter function. The linear matched filter is expressed as a bandpass real function with amplitude and phase of the Fourier transform of the reference signal. The nonlinear matched filter is produced by applying the bandpass matched filter function to a kth law nonlinear device. The nonlinear matched filter is determined in terms of the nonlinear characteristics of the device. We have shown that the nonlinear matched filter can be considered as a sum of infinite harmonic terms.
Nonlinear phenomena in optical waveguides
Authors: Silberberg Yaron
Published: February 2023

This tutorial concentrates on third-order nonlinear effects in waveguides and waveguide structures and their applications to all-optical devices. The nonlinear response of few-mode guided wave structures is reviewed. In particular, the principles of operation of nonlinear interferometers, directional couplers, birefringent fibers, and waveguide junctions are explained and recent experimental demonstrations of these systems are reviewed.
Optimization of three- and four-element lens systems by minimizing the caustic
Authors: Al-Ahdali Issam , Shealy David L.
Published: February 2023

For an imaging optical system it is, in general, desirable to transform a collection of point sources of light into point images distributed over the focal plane with the appropriate magnification. In practice this is achieved by varying the lens system parameters such that the spread of a bundle of rays from each object point over the image plane has been minimized. A new generalized ray tracing program has been constructed to calculate the principal curvatures of the wavefront associated with a bundle of rays as it passes through an optical system. The caustic surfaces are formed by an optical system and can be determined from the results of the generalized ray tracing program. In this study, the caustic surfaces are used to construct a merit function that describes the spread of the caustic surfaces from an ideal image point. The caustic merit function has been used to optimize a large collection of three- and four-element lenses. The performance of the optimized systems has been evaluated for different field angles by comparing the rms blur circle radii of lenses designed by conventional techniques. Results indicate that minimizing the caustic merit function reduces the rms blur radii over the field of view and the total aberrations of the lens system.
What Objects will Fuse Stereoscopically?: An Experiment and Equipment Description
Authors: Swift Dan J. , Smith Robert A. , Panish Steven C.
Published: February 2023

We describe a new design for a haploscope. A plug-in board for a pc computer drives a pair of liquid-crystal shutter glasses in synchrony with the vertical retrace interrupt of an EGA monitor. In this manner, alternate frames are displayed independently to each eye. This format allows any stimulus that can be generated with EGA graphics to be displayed stereoscopically at 60 Hz (30 Hz for each eye). This equipment permitted us to quickly and easily perform the following experiment. Four "objects", all squares, were tested for their ability to fuse stereoscopically: (1) subjective contours that were generated with different inducing figures for each eye, (2) squares of fine texture surrounded by coarser texture with different random patterns for each eye, (3) random forms defined solely by motion, and (4) forms defined by vertical lines for one eye and horizontal lines for the other, all surrounded by random patterns of the same mean luminance. All conditions have in common the property of allowing no point-by-point luminance correlation. While there was much inter-subject variability, both overall and between conditions, the results showed that stereopsis for such objects is possible, but difficult (Ramachandran et al., Nature. 1973). Condition 4 was best, but it may have allowed some effective luminance correlation resulting from the well-known neon effect. Condition 1 was the worst, presumably because it had no physical forms to be fused.
Large Optical Nonlinearities Arising from Space-Charge Layers in GaAs/AlAs Staggered Alignment Superlattices
Authors: Olbright G. R. , Klem J. , Hadley G. R. , Fu W. S. , Binder R. , Koch S. W.
Published: February 2023

We present here the first observation of quasi steady-state optical nonlinearities associated with absorptive and dispersive changes in GaAs/AlAs "Type-Il" superlattices. The nonlinearity arises from space-charge layers (holes at the Γ-point in GaAs and electrons at the X-point in AlAs layers). Using pump/probe spectroscopy we have observed a deep saturation, >80% (Δa = -50,000 cm−1), and blue shift >20 meV, of the heavy-hole exciton at low temperature (10 K). The basic underlying many-body effects are a) microscopic space-charge potential and b) dynamical correlations within each plasma, the latter being the dominant nonlinearity. A numerical calculation of the appropriate Bethe-Salpeter equation for the optical polarization within the screened Hartree-Fock approximation yields good agreement with the experiment data. The dominant sources of the heavy-hole shift are found to be phase-space effects, whereas the dynamical screening contributions are less important in the relevant density range. Correponding nonlinear-dispersive changes are computed by Kramers-Kronig transformation. In the transparency region of the superlattice, a large index change of Δn~−0.2 for 2000 Å of active material and a few milliwatts excitation is observed. Potential applications of the observed nonlinearity and a new class of electroabsorption modulators based upon our observations of the above phenomena are discussed.
Surface-Emitting Microlaser Diode Arrays: A Live Demonstration
Authors: Jewell J.L. , Lee Y.H. , Scherer A. , McCall S.L. , Harbison J.P. , Florez L.T.
Published: February 2023

We have achieved electrically-pumped lasing at room temperature in microresonators 1.5-5 μm in diameter on a 3×8 mm2 chip which contains several hundred thousand lasers. Yield on the chip is very high and the reliability is sufficient to allow a portable demonstration to be scheduled. The microlasers (μlasers) have an active medium containing three quantum wells of 80 Å Ing0.2Ga0.8As with 100 Å GaAs barriers. The smallest lasers thus have active material volumes <0.05 μm3. The mirrors were GaAs/AlAs quarter-wave stacks with 20.5 pairs on the bottom n-doped and 12 pairs, p-doped, on top. Additionally the top mirror had a fraction of a quarter wave AlAs, 30 Å δ-doped GaAs, and was capped by 1500 Å Au. The semiconductor heterostructure was grown by molecular beam epitaxy, and chemically assisted ion beam etching etched through the Au cap and the >5 μm heterostructure. Our setup uses white light to illuminate the etched side of the μlaser array which is imaged onto a CCD camera and displayed on a TV monitor. The shadow of an electrical probe tip used to activate the lasers is also viewed and when the top of a μlaser is contacted, its bright output is clearly seen. Translating the μlaser array underneath the probe tip allows us to "yield test" several dozen lasers in a few seconds. Lasers from all regions of the chip appear to operate quite uniformly. The number of lasers on the chip are sufficiently large to allow us to demonstrate destructive overdrive of some of the lasers without concern of running out of them. On another chip with similar μlasers we show CW operation.
All-Optical Cascadable NOR-gate with Gain
Authors: Islam M.N.
Published: February 2023

We demonstrate an ultrafast, all-optical, cascadable NOR-gate with a small signal gain of 4.5 and a switching energy of 30pJ. The three-terminal gate is based on soliton dragging in birefringent fibers and is appropriate for a clocked digital optical processor. When two orthogonally polarized solitons start coincident in time and travel along the two principal axes of a fiber, they interact through cross-phase modulation and try to travel as a unit. Consequently, the two solitons shift in time and move toward the mean velocity between the two axes. Even when one soliton has nine times less energy than the other soliton, the smaller pulse can time shift the larger pulse by several pulse widths. In a clocked digital optical system, the time shifts from soliton dragging translate into logic operations.
Properties of Holographic Relief Phase Gratings with Conic Section Profile
Authors: Langlois Pierre , Beaulieu René
Published: February 2023

In many applications, it is necessary to divide a single laser beam into N beams of similar intensity with a high coupling efficiency. This is the case for robotic vision systems, coherent summation of laser beams, multiple imaging, security systems or coherent addition of detector signals in heterodyne detection. Binary phase gratings have been employed with success for such applications when the number of beams (N) is relatively small (≤9). But as N is increasing the fabrication of these gratings becomes impractical and costly. Fiber gratings, made with optical fibers placed side by side and embedded in epoxy, also give interesting performances for large N (≥25). However fiber gratings cannot be custom made with a specified pitch since they depend on the fiber’s diameters available.
Refractive-Index Dispersion for F-doped Silica Glass
Authors: Yamada N. , Honda K. , Kondo S. , Fujii T. , Segawa H. , Tsukuma K.
Published: February 2023

We investigated the far UV refractive indices of F-doped SiO2 glass. The relationship between the refractive index dispersion and F content was revealed in the wavelength range of 230-350 nm. F-SiO2 glass was prepared by the SiF4 gas pressure sintering of SiO2 powder compacts. F content in the resultant glass increased with increasing SiF4 gas pressure. For example, the F content was measured to be 2.1 wt. % at 1 atm SiF4 and 3.7 wt. % at 3 atm SiF4 The refractive indices were measured using the bulk glass specimen (15 × 15 × 15 mm) by means of the minimum deviation method in wavelengths of 235-546 nm. F doping was effective to decrease both the refractive index and the dispersion. The dependence of refractive index on F content was represented as a formula of Δn/n = -0.31c and the dependence of its dispersion was determined as ΔD/D = -1.47c at 250 nm where c is the concentration of F (wt %) and D is dispersion. The resultant data was fitted to a 3-term Sellmeier dispersion relationship and discussed on UV absorption edge of F-doped and pure SiO2 glass.
History and scientific objectives of the Hubble Space Telescope mission
Authors: Boggess Albert
Published: February 2023

The goal of orbiting an astronomical telescope with very high quality optics was established near the beginning of NASA's history. Its most forceful and persuasive early advocate was Lyman Spitzer, who played a major role in setting both the scientific and technical objectives and in obtaining the support required to carryout the project. Feasibility and engineering studies were begun in the 1960s, culminating in 1977 in contracts for construction of the telescope and its supporting spacecraft by Perkin-Elmer Corp, and Lockheed Missiles & Space Co., respectively. The demanding engineering task of producing a 2.4-m aperture telescope and associated pointing control capable of maintaining 0.1-sec of arc image quality throughout exposure times of hours led to some early delays in the launch date, and the flight was delayed further as a result of the Challenger tragedy. Now scheduled for launch in early 1990, the HST will carry out research on topics ranging from atmospheres of planets within our solar system to evolution of galaxies and the distance scale and age of the Universe. Most exciting of all will be the discoveries resulting from images with an order of magnitude higher resolution than have been possible before.
Load distributions beneath grinding and polishing laps
Authors: Parks Robert E. , Greenberg Reid
Published: February 2023

It is well known that when two hard bodies are rubbed together with an abrasive slurry introduced to promote wear, the two wearing surfaces become complementary mating spherical surfaces. In addition, it is known empirically that the radii of the surfaces depend on the relative motion between the two bodies. We assume the wear rates of the surfaces obey Preston's equation, that is, wear is proportional to the relative velocity times the pressure between the surfaces. We then calculate the pressure between the surfaces as a function of the shapes of the surfaces and their relative motion.
Unscreening digital stored halftone images by logic filtering
Authors: Fan Zhigang
Published: February 2023

We present a new method for retrieving a continuous-tone picture from a digitally created and stored halftone image. It gives substantially better detail than the traditional low pass filtering approach. If the screen parameters are known (or estimated), the pixel value of the halftone (black or white) reveals the possible grey range of the pixel value (above or below the threshold) in the original continuous-tone image. The grey range obtained here is broad. It is narrowed down by logic filtering. The logic filtering is basically an operation combining the grey range data in the neighborhood of a pixel. Its adaptive nature makes it possible to remove the screen effects while retaining the edge information.
Multiple scattering of light by neighboring spheres
Authors: Chen T. W.
Published: February 2023

The multiple scattering of light by two or more neighboring dielectric spheres is analyzed with the approximation that the propagation of light inside the spheres is a rectilinear motion in the average direction of initial and final waves. The rectilinear propagation results in interesting consequences: it yields certain symmetry properties in the scattered waves with respect to the orientations of dielectric spheres; it gives the threshold angle for multiple scattering processes which provides a simple criterion for the spheres to mutually interact significantly; it results in a useful sum rule which relates the many sphere systems to an effective single sphere system, and provides a quick (but approximate) way for calculating the scattered light by the complex system. These are derived theoretically and are numerically verified by comparing with the exact calculations in some simple cases.
Sensitometry and scattering characteristics of a holographic photopolymer
Authors: Stone Thomas , George Nicholas
Published: February 2023

Basic sensitometry and scattering characteristics are presented for the DMP-128 holographic photopolymer manufactured by Polaroid Corp. The refractive index modulation is studied as a function of exposure for a variety of spatial frequencies (0, 10, 100, 1000, 5000 mm−1). DMP-128 is capable of very large refractive index modulations, of the order of 0.2, at high spatial frequencies. Scanning electron micrographs reveal a globular microstructure consisting of balls with diameters of the order of 0.04-0.1 μm, and these balls give rise to index modulation as a result of variations in their packing density. The appearance of these scanning electron micrographs is very similar to those of solgel glasses. Performance characteristics of a wavelength-scanning technique for simultaneously measuring the average bulk refractive index as well as the thickness and loss constant of a thin film emulsion or photopolymer coating are presented in detail. At high spatial frequencies diffraction efficiency is used to estimate refractive index variations by comparison with a thin grating decomposition model. Another aspect of this investigation is the scattering level of the microscopic index inhomogeneities that comprise the recording. Using a wide angle scatterometer devised for such measurements, we have observed very low scattering in photopolymer gratings.
Diffusion-driven reciprocity failure in photopolymer holography
Authors: Lanteigne David J.
Published: February 2023

Photopolymer compositions used as holographic recording media are of interest for their promise of good sensitivity and excellent diffraction efficiency. A typical composition consists of a sensitizing dye, reactive monomer, and inert matrix. Light initiates polymerization, resulting in formation of a volume phase hologram. The mechanism of grating formation involves both periodic modulation of the medium's molar refractivity and its mass density. Experiments with Polaroid's DMP-128 medium show that a latent grating is formed immediately on exposure, and that the diffraction efficiency of the latent grating changes with time.
Rainbow holography using external spatial filters for chromatic corrections
Authors: Grover C. P.
Published: February 2023

A promising method using external spatial filters is described for the chromatic correction of images from transmission holograms produced in white light. The spatial corrective filter or screen represents a 1-D random diffuser and is characterized by the sinc function describing the Fourier transform of its amplitude transmittance. Holograms of nondiffuse or specularly reflecting objects, for which the far field diffraction pattern can be approximated to the delta function, have been considered for chromatic corrections by these spatial filters. However, the technique is also applicable to opaque 3-D objects coated with ret- roreflective materials. By using suitable optics the image of the object illuminated with a parallel beam of laser light is formed downstream with respect to the Fourier plane. The hologram is recorded in a plane suitably positioned with respect to the image plane. When reconstructed with a conjugate wave a real image of the Fourier transform plane is obtained downstream with respect to the real image of the object. In white light a highly blurred image is obtained on a ground glass screen placed in the plane of the image. Now let the corrective spatial filter screen be placed in the plane of the real image. It would produce a slitlike distribution containing the object information in the Fourier plane. A chromatic corrected image is then obtained in the same manner as in the rainbow holographic reconstruction process.
Real time deformable mirror joint transform correlator
Authors: Florence James M. , Polley Michael O.
Published: February 2023

A real time joint transform correlator system implemented using deformable mirror device (DMD) spatial light modulators is described. The system uses a 128 × 128 element line addressed DMD light modulator to input images at both stages of a standard joint transform architecture. The DMD light modulators are electrically addressed at video frame rates and are driven directly by CCD video camera. One of these cameras provides the square law detection at the output of the first stage of the system that is critical for joint transform correlation operation. Electronic interface circuitry between the two stages of the system provides for the comparison of various binarization and thresholding schemes on the joint transform intensity fringe structures.
Projective effect of a Ronchi ruling with an extended light source
Authors: Chen Po-Hsin , Chang Ming-Wen
Published: February 2023

In the production of moire fringes by the obstruction theory, the relationship between the light source and a single Ronchi ruling is observed. A uniform extended light source is imaged by a TV camera with the insertion of a grating between light source and camera. The image of the light source overlaps the projection of the grating. When the grating moves away from the light source, the image pattern varies periodically with the change in distance between light source and grating. The effect can be explained with geometric optics imaging theory combined with the geometric projection principle of the point source to an obstructing object.