bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical outer product based on forward four-wave mixing
Authors: Lee Hyuk
Published: February 2023

Outer product is an important operation in many signal processing systems. The optical implementation of the outer product has been investigated by many authors. A new optical implementation of outer product based on the phase mismatches of forward four-wave mixing is described. This new system is compact and can be used to perform the outer product of 2-D input vectors with a large number of resolution points. Amplitudes of optical waves can be multiplied if nonlinear optics is utilized. Degenerate forward four-wave mixing is due to the third-order nonlinear effect, and the synchronism condition for the above nonlinear mixing is given by k4 = k1 + k2 – k3, where k1, k2, and k3 are, respectively, the wave vectors of the three incident plane waves, and k4 is the wave vector of the generated optical wave. In our device, one element in the first input vector and another element in the second input vector are represented by two plane waves having wave vectors k1, and k2. By controlling the wave vector k3, and thus utilizing the phase mismatches arising from the syschtonism condition, the optical outer product for any two input vectors is achieved.
Optical implementation of binary symmetric logic functions
Authors: Li Yao , Ha Berlin , Eichmann George
Published: February 2023

The binary symmetric logic function (BSLF), because of its functional invariance under the permutation of input variables, is an important class of Boolean logic operation. The diversified BSLF applications include the realization of full adder, subtractor, parity checker, text comparator, binary medium filter, and binary-weighted threshold elements. We propose optical implementations of multiple-variable BSLFs. Using a triangular array of lossless beam splitters together with optical on/off switches, an optical binary symmetric logic module (OBSLM) is experimentally implemented. The applications of the OBSLM to optical digital, symbolic, and neural computing are discussed.
Nonlinear optical correlator
Authors: Javidi Bahram , Kuo Chung-Jung , Horner Joseph L.
Published: February 2023

A nonlinear joint transform image correlator is investigated. The Fourier transform interference intensity is thresholded to provide higher correlation peak intensity and a better defined correlation spot. Analytical expressions for the thresholded interference intensity are provided. The effects of nonlinearity at the Fourier plane on the correlation spots at the output plane are investigated. The correlation signals are determined in terms of the nonlinear characteristics of the spatial light modulator at the Fourier plane. We show that thresholding interference intensity results in a sum of infinite harmonic terms. Each harmonic is envelope modulated due to the nonlinear characteristics of the devices and phase modulated by m times the phase modulation of the nonthresholded interference intensity. The correct phase information about the correlation signal is recovered from the first-order harmonic of the thresholded interference intensity.
2.92-μm erbium laser operated at 125 Hz
Authors: Schnell S. , Frauchiger J. , Luthy Willy , Weber H. P.
Published: February 2023

The use of erbium lasers for microsurgery requires a repetition rate of ~100 Hz. Such a repetition rate can only be achieved in highly doped (50%) crystals where by 4/13/2 → 4/15/2, 4/13/2 →4/9/2 cross relaxation the long-living lower laser level can be depopulated. Highly doped flashlamp-pumped YAIO3:Er has a typical laser threshold of ≈30 J for a crystal of 75-mm length and 6.35-mm diameter. 100-Hz operation would thus lead to an average pump power exceeding 3 kW, well beyond the thermal damage threshold. Therefore, a reduction of the threshold is required.
Optimization of the gain in Nd:Silica single-mode fibers
Authors: Digonnet M. , Liu K. , Shaw H. J.
Published: February 2023

The development of efficient (low pump power) optical amplifiers and sources based on rare-earth doped or other active fibers depends critically on the optical gain of the fiber, especially when three-level or low gain (e.g., nonlinear) processes are involved. In optically end-pumped fibers, the gain depends on optical energy confinement provided by the fiber and consequently on the fiber N.A. and core dimension. These dependences were investigated experimentally and theoretically to establish the range of fiber parameters which optimizes the gain. In Nd:SiO2 fibers from different manufacturers, we have measured an optical gain ranging from 0.15 to 0.4 dB/mW. These data were analyzed with a model of gain in fibers accounting for energy confinement through pump and signal mode spatial overlap. It shows that the observed gain differences are largely due to differences in the fiber index profiles as opposed to differences in doping levels. This suggests that the fiber gain can be optimized by selecting the core size and N. A. in a well-defined range, predicted theoretically and supported by gain measurements. As much as a 2–4 gain increase (and equivalent reduction in the required pump power) over what we have observed may be expected from careful fiber design.
Noise characteristics of nearly single-mode semiconductor lasers
Authors: Gray G. , Roy Rajarshi
Published: February 2023

We have developed a computer model which simulates the nonlinear Langevin equations for a semiconductor laser with one strong mode and one small side mode. With this model we are able to probe the laser dynamics over a wide range of operating powers, from below threshold, when the laser is essentially a thermal noise generator, to way above threshold. The model correctly reproduces the well-known intensity noise spectra and mode partition effects. We further calculate noise variances and intensity autocorrelation and cross-correlation functions for both modes as well as for the total power, and we compare these results to linearized theories. Finally, we calculate the laser field spectrum and investigate the effect of the side mode on the laser linewidth. All the above properties are calculated for many different values of the mode suppression ratio.
Broadband communication system using a standing wave acoustooptic modulator
Authors: Tian R. S. , Ih Charles S.
Published: February 2023

There is great need for an all-service communication system by which broadband analog and high speed digital information can be transmitted simultaneously and freely. Such a system can best be implemented with frequency-division-multiplexing (FDM). The effective bandwidth of such a system is in the multigigahertz range. Because of the enormous bandwidth, the optical fiber communication (OFC) system is a good candidate for such applications. However, because of the serious intermodulation problems, it is still difficult to provide such services using OFC. A novel method, now known as double-beam-modulation (DBM) was suggested and demonstrated using a standingwave acoustooptic modulator (SWAOM) to 216 MHz. The DBM can be implemented in many forms.1 We describe the experiments of DBM using SWAOM for frequencies beyond 1 GHz. Theoretical analyses and comparisons of DBM with conventional FDM systems are described.
Chromaticity diagram demonstrating both cone excitation and color-opponency
Authors: Scheibner Horst
Published: February 2023

The original color triangle of Maxwell (1855) is designed to show linear color mixture relations. A well-known extension of the color triangle makes reference to fundamental primaries and thereby serves as a cone excitation diagram. Here a further extension is presented showing the characteristic features of linear dichromatic and trichromatic opponent-color vision. Its constituent elements are three straight lines along which one of the perceptual criteria “no blue-yellow chroma,” “no green-red chroma,” or “no brightness” holds. These loci are the intersections of 2-D subspaces of the color space with the plane of the color triangle. Such an opponent-color triangle may be superimposed on a cone excitation diagram. Together they show the (projective) core of a linear physiological color theory, of which one important feature is the direct decomposition of a color Into chrominance and luminance.
Detection contours in tristimulus space
Authors: Olzak Lynn a.
Published: February 2023

Chromatic discrimination ellipses derived from the variability of color-matching data suggest that thresholds may in part depend on test size S, chromatic and/or luminance adaptation A, chromatic and/or luminance composition of the test T, and possibly complex interactions of these factors. We approach the problem directly by using a simple detection task and by representing thresholds as differences between field and test XYZ coordinates, i.e., as vectors in tristimulus space. Using a method of adjustment procedure, we measured detection thresholds for small test spots surrounded by a large adapting field.
Antibunched light source using cavity-enhanced emission
Authors: Carmichael Howard J.
Published: February 2023

Among the novel sources of nonclassical light that have recently been studied are a number of novel lasers. Conventional laser theory describes a classical stochastic field. I show that with a change in the standard operating conditions the conventional laser model produces nonclassical fields. Deviations from the classical description in standard laser theory are small by some inverse power of the threshold photon number. Operating conditions are designed to make stimulated emission dominant; thus laser cavities are good cavities that store photons and give a high threshold photon number. Low threshold photon numbers are achieved in bad cavities and most readily in a single-atom bad-cavity system. Such a system trades phase coherence for reduced intensity noise.
Mixed species targets for femtosecond time scale x-ray generation
Authors: Harris S. E. , Kmetec J. D.
Published: February 2023

We suggest the use of mixtures of light and heavy elements as targets for laser-driven femtosecond time scale x-ray line radiators. We assume that a tightly focused 100-fs laser pulse is incident on the surface of a mixed species target and that some fraction of the laser energy is absorbed in a skin depth of ~150 Å. Electrons in the interior (~5 × 104 Å) of the metal are heated by electron—electron diffusive energy transfer and are cooled by ionizing collisions with heavy metal atoms and also, to some extent, by thermal diffusion further into the interior. Electrons make inner shell holes in heavy metal target atoms, which in turn radiate. The preponderance of light metal allows a much higher electron temperature, and, therefore, at a given absorbed laser energy density, a conversion efficiency to x rays which can be many orders of magnitude larger for a solid density heavy metal alone.
Laser requirements for multichannel FSK heterodyne lightwave systems
Authors: Wagner R. E.
Published: February 2023

Today's research in the field of coherent lightwave systems indicates that FSK heterodyne techniques are particularly attractive for use in multichannel lightwave networks. In order for such systems to become commercially feasible, however, several laser device requirements must be met. These include improvements in laser spectral characteristics, modulation response, and packaging.
Anomalies in the frequency and temporal response of magnetooptic thin films
Authors: Mendez Antonio J.
Published: February 2023

The frequency and temporal response of several magnetooptic thin films have been measured. The thin films, formed from combinations of rare earth-transition metal (RE-TM) alloys, were supplied by their commercial developers. The measurements consisted of writing at various laser carrier frequencies, duty cycles, and incident laser powers in the presence of a bias magnetic field. The resulting laser mark is read with a continuous low-power laser beam. The laser marking consists of a change in magnetization which produces a birefringence which is measured as a Kerr rotation of the linearly polarized read laser beam. The measurements obtained in this fashion have been spectrum analyzed to determine the transfer functions as a function of the write laser parameters. We found that the transfer functions vary anomalously with incident laser parameters. The anomalous behavior can be understood in terms of the heating cycle induced by the write laser. Experimental data and their analysis are presented.
High-resolution spectroscopy of the Meinel bands of OH and OD
Authors: Abrams Mark C. , Davis Sumner P. , Engleman Rolf
Published: February 2023

The IR spectrum of the Meinel bands of the OH and OD free radicals was observed in a cold ozone-hydrogen diffusion flame using the Fourier transform spectrometer at the National Solar Observatory (Kitt Peak). Eighteen bands have been observed in the spectral region between 1900 and 9000 cm-1. Wavenumbers, intensities, line shapes, and isotope shifts have been obtained. The spectrum has been synthesized and optimal molecular parameters obtained using molecular Hamiltonians and nonlinear least-squares fitting techniques. The same spectrum has been observed in two other sources, the inductively coupled plasma and the oxyacetylene flame. Comparisons of the three spectra are being made.
Intensity and broadening coefficients dependence on temperature for the 4978-cm−1 band of CO2
Authors: Suarez C. B. , Valero F. P. J.
Published: February 2023

We report measurements of the self-broadening coefficients of the 4978-cm-1 vibrational band of CO2 as well as rovibrational line intensity parameters at a high resolution of 0.004 cm-1 by using a Bomem Fourier transform spectrometer. From these measurements, performed at several different temperatures ranging from 165 to 300 K, we have derived the temperature dependence of the linewidths. This is to provide laboratory data relevant to conditions expected by planetary and atmospheric scientists and probably to contribute to a better theoretical understanding of the temperature dependence. The line-shape parameters of interest are determined by comparing experimentally obtained and computed spectra, which comprise a nonlinear point-by-point least-squares determination of the line-center frequency, intensity, and broadening coefficient, wherein the line is modeled by the Voigt profile convolved with an instrument function. For the temperature dependence of the broadening coefficients we have found n = 0.75, where this is the exponent appropriate to the (usual) power law expression. This quantity is almost the same for different J values, except for the lower ones, where, however, we need to devote a more in-depth look at our results. For the band intensity we obtained Sband = 0.9515 cm−1/cm · atm at STP, and for the rotationless transition moment squared R2 = 0.1812 × 10-4 D.
Angle-tuned multiline stimulated Raman scattering
Authors: Bobbs Bradley , Goldstone J. A. , Johnson Michael M.
Published: February 2023

The stimulated Raman scattering gain of a multiline pump laser spanning a sufficiently wide spectral range is significantly reduced from that of a narrowband laser. This is due to destructive interference between the narrowband Raman effect and the Raman-resonant four-wave mixing effect which couples the lines together. However, this interference can be constrained to be always constructive by angle tuning of the pump and Stokes seed input beams to satisfy a phase matching condition for the four-wave mixing. The narrowband Raman gain will then be obtained. Calculations for a two-line XeF laser in a Raman conversion cell show that submilliradian beam angles can shorten the required cell length by factors of ~2, while loosening the pump intensity variation tolerance by an order of magnitude. Calculations for lasers with wider spectra indicate the potential for much larger gain increases and cell length reductions.
Penetration of plasma radiation in tissue
Authors: Weyl Guy M.
Published: February 2023

Several applications of lasers in medicine, such as laser lithotripsy and plaque removal, involve formation of plasmas. These plasmas will radiate in the IR, visible, and UV. Possible deleterious effects of plasma radiation are tissue damage by heating and chemical changes induced by deposition of UV photons. Of particular concern is the possible mutagenic effects of UV photons that can penetrate the nucleus of cells and be absorbed there.
Bit serial optical computer project
Authors: Sauer Jon , Heuring Vincent , Jordan Harry , Pratt Jonathan
Published: February 2023

We have begun one of three proof-of-principle system projects to be demonstrated recently. The design philosophy is to build, with a minimal and reliable subset of the optoelectronic components currently available, a functional stored-program digital computer system. A migration path to gigahertz speeds, with the inclusion of as yet undeveloped all-optical devices, is a central design goal. A result of this effort should be a more complete understanding of the architectural and practical design issues involved in building digital optical processors. These include construction without the benefit of optical asynchronous memory or optical cascadable logic.
Programmable optoelectronic multiprocessor vs symbolic substitution for digital optical computing
Authors: Kiamilev F. , Paturi R. , Esener S. , Fainman Y. , Lee S. H.
Published: February 2023

There is much interest in recent literature in employing symbolic substitution (SS) for general-purpose digital optical computing. We evaluate and compare the SS with the programmable optoelectronic multiprocessors (POEMs) paradigms currently under development at UCSD. First, we discovered that the computational ability of an optical SS system (without straightforward global interconnect) is essentially equivalent to a 2-D VLSI SIMD mesh connected array of small-grain processors. We can show that a SS rule can be simulated by a mesh of electronic processors using only a small number of cycles depending on the complexity of the rule. In addition, the simulation of even a very small-grain processor mesh in SS seems to require more space and time. Furthermore, SS lacks any means of implementing a RAM function because of its local interconnection topology. This implies that space–time trade-offs are hard to achieve on SS machines. On the other hand, the POEMs paradigm can implement any variation of the three parameters used to classify parallel systems: synchrony (SIMD or MIMD); topology (local or global); and granularity (small or large grain). By mapping commonly used algorithms such as FFT, sorting, and graph optimization onto a SS and POEMs architectures with global interconnection topology (e.g., hypercube), we determined that the SS approach (operated at very high clock rates, e.g., above 500 MHz) is outperformed by the POEMs (operated at much slower clock rates, e.g., 10 MHz). Therefore, the speed of the devices used in SS systems is offset by the inefficiency of the algorithms used on a locally interconnected topology.
Recent progress in the development, characterization, and theory of tunable solid-state laser media based on transition metal ions
Authors: Chase Lloyd L.
Published: February 2023

Tunable lasers employing transition metal (TM) activator ions currently cover a large portion of the near-IR wavelength region from ~700 to 2300 nm. The number of crystalline laser media suitable for these ions, particularly Cr3+, has been steadily growing. Significant improvements in the lasing properties have been difficult to obtain, however, because of problems with crystal growth and quality, nonradiative processes, parasitic absorption, and excited state absorption of laser and pump light. Recent experimental and theoretical work has provided some insight regarding these and other properties and their effects on laser operation. The experimental work includes measurements of laser slope efficiency as a function of output coupling, excited state absorption, photoconductivity, and laser-induced transient and cw gratings. Ab initio theoretical approaches have had some success in providing quantitative information regarding the positions of the energy levels of these ions and their dependence on the displacements of the neighboring ions in oxide and fluoride hosts. Utilization of the information obtained from these research efforts is resulting in improved properties of tunable TM lasers.
Multiphoton ionization and harmonic generation under strong lasers
Authors: L’huillier A.
Published: February 2023

We describe experimental observations of high-order harmonic generation in rare gases. The incident radiation field is a 1064-nm 30-ps Nd:YAG laser. A gas jet provides a 1-mm wide nonlinear medium at 15-Torr pressure. The highest harmonics detected in Xe, Kr, and Ar are, respectively, the twenty-first, twenty-ninth, and thirty-third at approximately the same laser intensity of ~3 × 1013 W · cm−2. The harmonics distribution decreases steeply from the third to fifth harmonic, then presents a nearly flat plateau with, however, some anomalies in Ar and Kr in the vicinity of discrete excited states. We examine the phase matching conditions for generation of the different harmonics: our aim is to disentangle what is due to the macroscopic properties of the medium, i.e., pressure, geometry, influencing the phase matching, and, therefore, the conversion efficiency to what is characteristic of the individual atom in an intense field, i.e., nonlinear atomic susceptibilities and polarizabilities.
Infant chromatic pupillary response similar to protanopes
Authors: Clavadetscher John E.
Published: February 2023

Previous studies have shown that red and green CRT lights that are approximately equiluminant for normal adults produce strong pupillary constrictions to both directions of exchange when one is suddenly substituted for the other. In contrast, protanopes and infants less than two months old show vigorous responses only to red → green exchanges and not to green → red exchanges of these lights. The current experiment presented red → green exchanges to three- and seven-week-old infants and to adult normals and protanopes. Among the lights tested were red-green pairs that were approximate scotopic, protanopic, and normal trichromatic matches. Protanopes and normals produced approximately equal pupillary constrictions at their respective brightness matches. The infants showed approximately equal pupillary constrictions at protanopic match luminances but quite asymmetric responses at the scotopic and normal match luminances.
Prospects for Precision Spectroscopy with Pulsed Light
Authors: Fee M.S. , Danzmann K. , Chu Steven
Published: February 2023

Characterization of the instantaneous electric field using heterodyne techniques allows a prediction of the atomic response to pulsed light, making precision spectroscopy feasible.
Linear Dichroism and Efficient Second Harmonic Generation in the Absorption Band of DAN
Authors: Looser H. , Risk W.P. , Twieg R.J. , Bjorklund G.C.
Published: February 2023

The first study of optical second-harmonic generation in the absorption band of an organic nonlinear crystal is presented. In our work, angle tuned Type-I phase-matching was achieved in the organic crystal DAN (4-(N,N-dimethylamino)-3- acetamidonitrobenzene) for fundamental wavelengths between 1000 nm and 950 nm from a CW dye laser. The generated wavelengths between 500 nm and 475 nm were well within the absorption edge of DAN, resulting in an absorption constant that varied between 21/cm and 103/cm. For characterization purposes, the absorption in this wavelength range was studied in greater detail and a large dichroism with absolute transmission varying by a factor of 107/mm was detected as the direction of propagation was changed. For a fundamental wavelength of 995 nm a detailed comparison of the achievable conversion efficiency was made between a 0.75 mm long DAN crystal and a 5 mm long crystal of KTP. At the generated 497.5 nm the DAN crystal had an optical density of 1.1, while the KTP was transparent. Despite the absorption and the smaller length of the crystal, a 4 times higher conversion efficiency was obtained than for KTP. Analysis of the data shows that the absorption band provides a significant resonant enhancement of the DAN nonlinearity. Similar results can be expected for other organic crystals provided phase-matching is possible.
Two Simultaneous Cooling Processes in "Optical Molasses"
Authors: Shevy Y. , Weiss D. S. , Ungar P. J. , Riis E. , Chu Steven
Published: February 2023

We have resolved a bimodal velocity distribution in Na atoms cooled in "optical molasses". We take this behavior as evidence for two distinct cooling mechanisms.
Multiple-Bit Long-Term Data Storage by Backward Stimulated Echo in eu3+:yalo3
Authors: Kim M.K. , Kachru R.
Published: February 2023

The backward stimulated echo has been considered as a novel high-speed high-density optical data storage method. But its potential application has been confined to transient dynamic memory because of relatively short lifetime of optical coherence inside low-temperature solids. Here we report the longest observed storage time of at least six hours in the 581.8 nm7F0-5D0 transition of eu
3+
-doped YAlO3 crystal at 2°K. The experiments are performed using YAG-pumped pulsed dye lasers, beamsplitters and optical delay lines to produce five DATA pulses, at 20 nsec intervals, and WRITE and READ pulses. The measured echo intensity as a function of storage time has exponential decay time of 3.8 hours. This very long storage time is due to the very small effective nuclear magnetic moments of Eu3+ ions, and is consistent with the long lifetime of spectral hole in this system. We also observed that the signal fidelity is not noticeably affected by the number of DATA pulses and the long storage time.
High power 52 W continuous-wave monolithic laser diode arrays
Authors: Sakamoto Masamichi , Welch David F. , Endriz John G. , Streifer William , Scifres Donald R.
Published: February 2023

In this letter we report the highest room-temperature cw output power of 52 W from a 1 cm monolithic diode laser array (2 mm aperture width) with no active cooling. The devices investigated have 20 ten-stripe lasers spaced on 500 μm centers, each occupying 100 μm of the facet length. The laser structures were grown by metalorganic chemical vapor deposition (MOCVD) and employed single quantum well separate confinement heterostructures. The wafers were processed to form gain-guided 6 μm-wide stripes on 10 μm centers defined by proton bombardment. Completed devices were tested under cw conditions. Several approached 50 W cw and the best laser attained 52 W before catastrophic degradation of the facet. The threshold current was 6 A and the slope efficiency was 0.89 W/A (57% differential quantum efficiency) up to approximately 40 W of optical power. The driving current required to attain output power of 52 W was 72 A. The electrical-to-optical power conversion efficiency attained 36% for an output power of 22 W and was 28% at 52 W.
Optical Anisotropies in Thin Films of Silver and Gold
Authors: Wilson P.W. , Abeysuriya K. , Hodgkinson I.J.
Published: February 2023

Thin films of silver and gold deposited at 45° exhibit anisotropies in normal incidence transmittance, reflectance and absorptance. The magnitudes of these anisotropies are typically about a few percent. An interesting characteristic feature, a double change in sign, is believed to be caused by the globular nature of these films during the early stages of growth. In thicker films, with a transmittance of a few percent, the magnitude of the anisotropy is essentially zero. When deposition is stopped for films in the globular state, the anisotropies change with time, more or less along a reverse deposition growth path which may include change of sign.
An Integrated Silicon Optical Modulator for High Speed Data Communications at 1.3-μm Wavelength
Authors: Hemenway B. R. , Solgaard O. , Swanson R. M. , Bloom D. M.
Published: February 2023

We report the demonstration of a new kind of optical amplitude modulator for single-mode fiber applications at 1.3-μm wavelength. This work demonstrates the feasibility of using an all-silicon device in the interface between integrated silicon circuits and local-area optical communications systems. The device is intended for use in applications where the heteroepitaxy of direct bandgap or electrooptic materials or the bonding of hybrid-circuits to silicon integrated circuits is not feasible. It is fabricated using silicon epitaxy and planar fabrication technology and is suitable for integration with other bipolar devices.
Tunable far-infrared laser spectroscopy
Authors: Evenson Kenneth M. , Jennings D. A.
Published: February 2023

Tunable far-infrared (FIR) radiation has been generated using CO2 laser difference synthesis in metal-insulator-metal diodes either from the difference between a fixed frequency CO2 laser and a tunable waveguide laser or from the difference between two fixed frequency CO2 lasers plus microwave sidebands. Our tunable FIR source is being used to make highly accurate FIR frequency measurements of stable species to serve as frequency and wavelength calibration standards, measure frequencies of transient species (including molecular ions) for astronomical searches, and study line broadening and line shape parameters especially for atmospheric spectroscopy applications. The molecules HD, HF, HCI, HBr, CO, NaH, MgH, CH3OH, ArH+, OH, and CH have been studied thus far.
Photodetectors and Q.E.D.
Authors: Gustafson T. Kenneth
Published: February 2023

No summary was available at press time.
Theoretical studies of the temporal response of the doped quantum well avalanche photodiode
Authors: Wang Yang , Brennan K. F. , Teich M. C. , Saleh B. E. A.
Published: February 2023

We present calculations of the temporal response of a doped quantum well avalanche photodiode made from the GaAs/AlGaAs material system. The calculations are based on both an ensemble Monte Carlo method and an analytic formulation based on the direct calculation of the impulse response function in terms of the density functions for the transit times. These analyses are applied to a doped quantum well structure in which single-carrier-initiated double-carrier multiplication conditions occur. The results show that the envelope of the impulse response function decays rapidly due to the negligible hole impact ionization rate, resulting in large-bandwidth operation of the device. The standard deviation of the impulse response function which results from both randomness in the gain and in the birth times is also presented. Based on these calculations, it is found that in APDs in which the hole ionization probability is small but not identically zero, that the bandwidth can still be characterized by the simple analytical expression, B = 1/2π [1/m(τ
e
+ τ
h
)], where m is the number of stages present in the device and τ
e
and τ
h
are the electron and hole transit times in each stage, respectively.
Photovoltaic array GaAs cells response driven by high-power laser diodes
Authors: Landry M. J. , Rupert J. W. , Mittas A.
Published: February 2023

We describe the performance of four Applied Solar Energy Corp. and one Varian photovoltaic-array (PVA) GaAs solar cells, one monolithic and four segmented cells. The active layers of these cells are grown using metalorganic chemical vapor deposition techniques. The cell characteristics described include (1) electrical power (EP) vs cell resistance, (2) current vs voltage, (3) optimum resistance R, (4) efficiency E, and (5) fill factor (FF) for different incident LD optical power (LP) levels, respectively. For the 1-, 2-, 2'-, 10-, and 16-V cell with LP = 1.5 W (1) the EP is 0.58, 0.49, 0.73, 0.40, and 0.23 W, (2) the short circuit current is 839, 411, 371, 67.2, and 30.6 mA and the open circuit voltage is 1.08, 2.16, 2.28, 10.45, and 16.73 V, (4) R is 1.1, 5.6, 5.9, 170, and 700 Ω, (4) E(max) is 49, 39, 46, 29, and 18%, respectively, and (5) FF is 0.655, 0.534, 0.864, 0.60, and 0.445, respectively. EP decreases with increasing cell voltage rating. At a specific output voltage, the cell current is found to increase with increasing LP. R decreases with increasing cell voltage rating. The R vs LP curves are found to fit a power relationship; R = aLP expb, where a and b are constant for a cell but different for each cell. For 0.1 W of uniform white light and nonuniform LD light transmitted through a FO, the FFs of the 2- and 16-V cells differ by 2.3 and 0.4%, respectively.
Enhanced nondestructive holographic readout in SBN
Authors: Redfield Steve , Hesselink Lambertus
Published: February 2023

We describe a novel arrangement for obtaining enhanced nondestructive holographic readout in SBN using polarization effects and modification of the applied field between recording and readout. The enhancement is most pronounced for a certain range of spatial frequencies. The readout signal first decreases in strength but subsequently grows above the starting value, approaching 100% efficiency in some cases. Over 6 h of continuous readout have been achieved with efficiency remaining strong enough to provide one billion reads with SNR exceeding 20 dB.
Holographic recording In photorefractive SBN fibers
Authors: Hesselink Lambertus , Redfield Steve , Huang Yuhong
Published: February 2023

SBN is an attractive photorefractive medium, which is difficult to grow in large bulk sizes of good optical quality. Alternatively, at Stanford we grew SBN fibers of lengths exceeding 10 cm and with a diameter of <160 μm. These fibers offer a unique environment for carrying out phase conjugation experiments, such as holographic data storage, self-phase conjugation, optical interconnects, and two-beam coupling.1 We report, to our knowledge, the first photorefractive holographic recordings in an SBN fiber. A plane wave reference and an image carrying object beam are incident on the fiber in a reflection recording geometry, where the grating vector is essentially aligned with the c axis.
Ion-assisted deposition of aluminum oxynitride thin films
Authors: Hwangbo C. K. , Lingg L. J. , Lehan J. P. , Macleod H. A.
Published: February 2023

Aluminum oxynitride thin films were made by nitrogen or the mixture of nitrogen and oxygen ion bombardment on growing Al films in an oxygen backfilled chamber. Refractive indices of AlO
x
N
y
thin films were varied from 1.68 to 1.84 at 550 nm by controlling the backfilled oxygen pressure, while the deposition and ion gun parameters were kept constant. The relationship between the optical constants and stoichiometry (x and y) was obtained. High reflectors were made using AlO
x
N
y
homogeneous step-index layers and showed no vacuum-to-air shift. From an XRD, AlO
x
N
y
thin films turned out to be amorphous.
Front surface metal coatings with protective layers by reactive ion plating deposition
Authors: Guenther Karl H. , Willey Ronald
Published: February 2023

Front surface metal mirrors made by vapor deposition of aluminum or silver onto glass substrates are widely used in optical systems. Because of their inherent mechanical and environmental weakness, they need to be protected with hard dense dielectric layers. While much research has been done in the past to optimize these protective coatings, conventionally protected aluminum and silver mirrors are still less than optimal in their environmental durability. This is due to the packing density of less than unity of the protective coatings, which allows water vapor and other adverse agents to penetrate the coatings and attack the metal film. Substantial improvements of protective layers have been reported for ion assisted deposition, which, however, may have remained in the laboratory scale. Low-voltage reactive ion plating deposition of oxides has been shown to produce very dense homogeneous films, which we applied as protective layers for aluminum and silver thin films. The technique is being used in a 32-in. standard high vacuum box coater, which makes it potentially useful for coating of large mirrors of up to 30-in in diameter.
Random walk theory of photon migration in biological tissue
Authors: Nossal R. , Bonner Robert F.
Published: February 2023

Mathematical expressions are obtained for various functions (e.g., path length and depth distributions, total reflectance, and its spatial distribution) associated with photon migration in turbid media. The models assume that photons are inserted at a point on the surface of a tissue and detected at another point on this surface (or the parallel lower surface of a slab) at a distance ρ from the point of insertion. For a homogeneous medium characterized by uniform absorption and scattering cross sections, an expression is derived for P(n|ρ), the probability density of photons emerging at surface point ρ whose path length within the media is n, given in units of rms distance between scattering events. The probability density of the corresponding transit times (t = n/c
i
) in range-gating applications is also given by this expression. Expressions for spatial distribution of diffuse surface emission, mean path length, and penetration depth of emergent photons at ρ also are derived. Analogous quantities are calculated for photons migrating within a medium having a surface layer whose absorbance differs from that of the lower bulk material. The dependence of these parameters on surface thickness is illustrated.
Two-color laser spectroscopy of titanium
Authors: Knight R. D. , Sohl J. E. , Zhu Yang
Published: February 2023

Two-color double-resonance laser spectroscopy has been used to study highly excited bound and autoionizing states of titanium. A thermal beam of Ti is first excited to a well-known intermediate state by a fixed frequency pulsed dye laser, and then a second scannable laser populates highly excited states. Either autoionization or field ionization products are detected. The combination of double-resonance excitation with ionization detection makes this an extremely sensitive and highly selective method of studying highly excited states and photoionization in transition metal elements. Our measurements indicate a substantial error in the presently accepted value of the ionization potential of Ti I, and we present data for a revised value.
Ultralow threshold current in quantum confined semiconductor lasers
Authors: Yariv Amnon
Published: February 2023

Semiconductor lasers will find an increasing use in future computer interconnect circuits. This application will see large numbers (thousands) of lasers used in a single computer. Because of the large number involved it will be mandatory to develop a new generation of lasers with ultralow threshold currents, Ith smaller than 0.1 mA. Such lasers are theoretically possible by resorting to quantum confined structures such as quantum well and quantum wire configurations embedded in optimized optical structures. We review the basic physical theory and the first round of experiments which lead to Ith smaller than 0.6 mA.
Spatial masking in the third dimension
Authors: Wilson Hugh R.
Published: February 2023

Previous research has firmly established that mechanisms tuned for spatial frequency and orientation provide the substrate for processing of monocular visual information, and it has recently been demonstrated that these mechanisms are also capable of supporting stereopsis. The present studies were accordingly designed to ascertain how disparity specific interactions among such mechanisms contribute to the processing of binocular depth information. In our paradigm the target consisted of a pair of vertically oriented bars, each with a 1.0 octave bandwidth (sixth spatial derivative of a Gaussian function). These bars were spaced so that one always appeared at zero disparity, while the second carried either a crossed or uncrossed disparity. This configuration was used to measure disparity thresholds in a two-interval forced choice procedure. Following this, the targets were superimposed on a cosine grating mask at zero disparity, and thresholds were remeasured as a function of mask spatial frequency and orientation. As a control, monocular two-bar separation discrimination was also measured using the same spatial patterns.
Neural and neurally inspired network models for vision
Authors: Maloney Laurence T.
Published: February 2023

This tutorial provides an understanding of current and past attempts to model vision using simple computing elements arranged as a network. The models examined include the highly publicized parallel distributed processing models described by Rumelhart and McClelland, the work of Stephen Grossberg, and others. The primary goal is to taxonomize, explain, and evaluate these models, measuring their capabilities against long-standing problems in vision, visual development, and computer vision.
Detecting subangstrom vibration of a rough surface using real-time holography
Authors: Bacher G. D. , Cudney R. S. , Feinberg Jack
Published: February 2023

We present two methods for detecting subangstrom periodic vibrations of an arbitrarily rough surface. In one method, the laser speckle pattern reflected off of a rough surface is focused into a photorefractive crystal of barium titanate, and the intensity of the transmitted beam is measured. A pump laser beam, coherent with the speckle beam, is also incident on the crystal so as to deplete strongly the speckle beam by two-wave mixing. Any change in either the phase or the amplitude of the speckle pattern caused, for example, by a slight displacement of the reflecting surface will modulate the overall intensity of the transmitted speckle pattern. The fractional change in the intensity of the depleted probe beam yields the amplitude of the vibration. The second vibration-sensing method uses a phase-conjugate Michelson interferometer. Here a Gaussian beam incident on a rough surface produces a speckle pattern on reflection. This complicated pattern is focused into a photorefractive self-pumped Cat conjugator. The phase conjugator converts the incident speckle pattern into its time-reversed replica, which propagates back toward the scattering surface, where it is scattered a second time to reconstruct a nearly Gaussian beam. This double pass off the vibrating surface imparts a uniform phase shift to the reconstructed Gaussian beam, which is then detected by interferometry. We can detect periodic displacements as small as 0.04 Å of a rough aluminum surface using a lock-in detector with a 1-s integration time.
Electronic and optoelectronic properties of 1.3-μm Schottky barrier LED arrays
Authors: Chan Eric Y. , Fu R. J. , Burnett A. , Hong C. S.
Published: February 2023

Schottky barrier confined 1.3-μm LED arrays have been successfully fabricated. These arrays show excellent l–V characteristics and linear L–l relationship. The spectral output of the array centers being about 1.31 μm, good uniformity in these arrays is also obtained.
Dynamics of optical switching in a nonlinear film near the total internal reflection state
Authors: Khoo I. C. , Zhou Ping
Published: February 2023

We present the results of a general theory and specific experimental observation of the time dependence of a nonlinear optical switching through a thin film that possesses an intensity-dependent refractive index. The incident laser is near the total internal reflection state. Our theory explicitly accounts for the material response time and the time evolution of both the refractive index and optical field distribution in the nonlinear film and other equally important parameters such as strong reflection feedback and interference, angle of incidence, film thickness, and laser intensities. Experimental results with both cw and pulsed lasers with various types of nonlinearity are also presented.
Optical features of acoustooptic systems
Authors: Goodell John B.
Published: February 2023

Acoustooptic system technology has expanded owing to its patent advantages in certain important signal processing operations over other methods. Optical elements are essential components of these systems but must satisfy unique constraints. For example, wavefront shapes are typically Gaussian to avoid disrupting secondary maxima, which can require unique apodization techniques. This paper examines some optical features including beam expansion techniques, aberration correction, optimum wavefront shapes, resolution limiting elements, polarization requirements and effects, and dielectric vs metallic reflectors, light sources, and the effects of the Bragg materials on wavefront properties. In general, optical tolerances are very tight, but there are important mitigating factors, mostly because of the special system properties. Certain new technologies such as molded glass aspheric lenses, solid state lasers, and crystal growing and detector arrays can greatly advance the state of the art. Included is an overview of some of these areas.
Novel 2-D acoustiooptic switch
Authors: Soos Jolanta I. , Rosemeier Ronald G.
Published: February 2023

Two longitudinal transducers were bonded 90° to each other to a GaP optical substrate. The optically transparent substrate was oriented so as to consider the same acoustooptic properties for both acoustic directions. The angular separation between a deflected and undeflected beam depends on the acoustic center frequency which can be calculated by using the Bragg equation as follows: where 2θ =angle of separation, λ = laser wavelength, and V =acoustic velocity.
Crystal growth and processing of barium titanate and potassium niobate for photorefractive applications
Authors: Wechsler Barry A. , Rytz D. , Klein M. B.
Published: February 2023

Large high-quality crystals of barium titanate (BaTiO3) and potassium niobate (KNbO3) are routinely grown by the top-seeded solution growth method and are poled by straightforward techniques. However, optimization of their photoretractive properties is a more difficult problem, requiring a substantial effort in the theoretical understanding of the mechanisms of photorefractive behavior as well as the growth, processing, and characterization of crystals given a variety of treatments. In our experiments, we studied undoped, Mn-doped, and Fe-doped crystals of both materials. Their photorefractive properties—beam-coupling gain and response time—are clearly altered by doping and postgrowth oxidation-reduction treatments. Existing theoretical models are helpful in understanding the basis of this behavior but are not yet sufficient to explain completely the observed phenomena. We describe our progress toward solving these problems, including crystal growth procedures, postgrowth processing, characterization techniques, defect modeling, and other approaches to improve the photorefractive sensitivity, such as operation at high temperature.
In vivo light dosimetry during whole bladder wall PDT
Authors: Marijnissen Johannes P. A. , Star Willem M. , Jansen Harald
Published: February 2023

A system has been developed for in vivomonitoring and control of light dose rate and dose during whole bladder wall photodynamic therapy (PDT). Through a modified cystoscope three transparent plastic catheters (1-mm i.d.) can be introduced into the bladder cavity and unfolded into three directions, ~120° apart, along the bladder wall. Into each catheter a miniature isotropic light dosimetry probe is inserted. The fibers of these probes are connected to an electronic readout system with displays for energy fluence rate and integrated light dose. The cystoscope also admits an isotropic light source connected to a laser for irradiation. The readings of the three light dosimetry probes are used to optimize the position of the light source in the optical center of the bladder and to monitor its position during treatment. The uniformity of the irradiation across the bladder wall can also be checked and adjusted. Measurements in vivoconfirm that the true energy fluence rate at the bladder wall is 5–6 times the irradiance of unscattered light (wavelength, 625–630 nm). Measurements during treatment show that controlling the light source position by intravesical ultrasound does not guarantee a uniform light dose distribution across the bladder wall.