bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical implementation in Boltzmann machines
Authors: Ticknor Anthony J. , Barrett Harrison H.
Published: February 2023

The Boltzmann machine, a hardware implementation of the simulated annealing algorithm, easily and directly takes advantage of highly interconnected systems for parallel processing. Optical systems for matrix operations and random number generation greatly relax the computational burden of the digital electronics and increase the speed by many orders of magnitude over the software implementation. The algorithm is inherently fault-tolerant, but simple use of an analog optical system for matrix operations might critically limit available dynamic range and space-bandwidth product. We therefore present a method for significantly increasing the available dynamic range with little sacrifice in the overall grain-processing speed. We also show how under some circumstances the usable space-bandwidth product of the reconstruction can be increased.
Efficient wave mixing in photorefractive BSO/BGO crystals and applications to optical signal processing
Authors: Huignard J. P. , Herriau J. P.
Published: February 2023

Photorefractive materials have been widely investigated for applications to optical signal processing; promising materials are sellenite type crystals Bi12SiO20 (BSO), Bi12GeO20 (BGO) in which fast response and high index modulation can be achieved in wave mixing experiments when the frequency of one beam is slightly shifted. This technique has resulted in large values of the exponential gain coefficient (Γ ≃ 8-12 cm-1) for optimized recording conditions (drift recording mode with an externally applied electric field E0). When the amplified incident or conjugate signal is fed back to the BSO, different types of oscillator are demonstrated in which the beam in the cavity is spontaneously frequency shifted. We review the conditions of efficient beam interaction with BSO-BGO crystals and demonstrate applications to image amplification, dynamic interconnection between fibers, ring and phase conjugate resonators. We also show that BSO-BGO crystals of different origins may exhibit significant differences in their photoconductive and photorefractive properties. This arises from noticeable differences in the migration lengths of the photocarriers and in the trapping center concentrations. We report high grating efficiencies (ηs ≃ 95%) when large electric fields (E0 ≃ 12 kV cm-1) are applied to low photoconductive crystals and nearly complete beam depletion in two-wave mixing with a moving grating (grating period Λ ≃ 20 μm).
Powdered dielectric guides for millimeter waves
Authors: Bridges William B. , Bruno William M.
Published: February 2023

Low-loss dielectric powders have been used as the core material of dielectric waveguides in the microwave and millimeter wave regions. Both flexible guides and planar circuits analogous to fiber and integrated optical components have been realized. Transmission losses <10 dB/m and ring resonator Qs of 2000 are obtained at 94 GHz. Bending losses were found to be insignificant for radii of curvature greater than a few centimeters. Directional couplers with fixed and variable coupling were investigated. Barium tetratitanate, nickel aluminum titanate, and magnesium calcium titanate were among the lowest-loss powders studied, exhibiting effective dielectric constants of 3.5-6 in packed powder form. Teflon was used as the cladding material for flexible waveguides, and Teflon, polypropylene, and polystyrene were used as rigid substrates for the planar dielectric channel waveguides.
Dichoptic hyperacuity: the precision of Nonius alignment
Authors: Levi Dennis M. , McKee Suzanne P.
Published: February 2023

The precision of Vernier alignment and Nonius alignment (dichoptic Vernier) depends on gap size. We measured thresholds for monocular Vernier and dichoptic Nonius alignment of briefly flashed short lines. Over a large range of gap sizes, monocular Vernier thresholds are approximately a constant fraction of gap size (equivalent to a constant orientation threshold).
Spectral irradiance scales based on filtered absolute silicon photodectors
Authors: Bruening Robert J.
Published: February 2023

A scale of spectral irradiance has been realized for the 400-700-nm wavelength range based on absolute silicon photodetectors with wavelengths selected by interference filters. Using this equipment, an absolute radiometric scale was produced independent of the traditional approaches to absolute radiometry based on either the thermal physics of blackbodies or absolute thermal detectors. From these data, a photometric scale of luminous intensity has been realized. The detector based scales were compared with blackbody scales by calibrating lamps relative to both scales.
Launch, assembly, and growth: drivers in giant-class space telescope design
Authors: Krim Michael H. , Wissinger Alan B.
Published: February 2023

Compelling arguments have been made by the scientific community for the development of giant-class astronomical telescopes by the early part of the next century. These systems will have base-line apertures exceeding 24 m with fill factors >25% and weights of the order of 50,000 kg. Multiple launches will be required to deliver the disassembled system to low earth orbit for final assembly prior to boosting it to a higher operational orbit. Clearly such a system can only become a reality if implementation issues such as the deployment, operation, and maintenance costs can be constrained to acceptably low levels and if the architecture of the system has sufficient flexibility to satisfy the widest possible science constituency. Several approaches to configuring giant-class telescope systems are discussed. The optimum handoff point between a fewer number of ground assembled large modules and a larger number of more real-estate efficient smaller components is presented. Aperture configuration is discussed with regard to optical performance, vehicle requirements, and other hardware implementation considerations. Finally the issues associated with transferring the observatory to its higher operational orbit and estimates of revisit times for maintenance, instrument changeout, and evolutionary modification or growth are discussed. A review of the key enabling technologies necessary to design and build, launch, and deploy such a telescope system by the early part of the next century is presented.
Successive color matching in complex fields
Authors: Cowan W. B.
Published: February 2023

In successive color matching of simple uniform colors the precision of the match declines as the time between the presentation of the reference stimulus and the presentation of the test stimulus increases. When the stimulus is more complicated more degrees of freedom must be matched. How does the match precision decline for each degree of freedom? We have examined this question using the most simple fields that are more complicated than uniform colors: grey areas with grey surrounds. Two degrees of freedom characterize the stimuli: the luminance of the center and the luminance of the surround, so the matching precision can be represented by 2-D ellipses similar to the MacAdam ellipses. These ellipses grow in a characteristic way as the time interval increases, elongating along lines of constant contrast. We conclude, at least for these simple images, that the visual system preserves contrast information more precisely than it does overall luminance information. This conclusion has implications for color reproduction, where image and reproduction are generally well separated in time and/or space. Accurate reproduction of contrast is more important for reproduction fidelity than accurate reproduction of overall brightness.
Flicker photometry: residual minimum flicker
Authors: Kaiser P. K. , Pandey Vimal Ram L. , Ayama M.
Published: February 2023

We show that when all possible optical artifacts are eliminated in a flicker photometric procedure, there is still a residual minimum flicker after color fusion occurs. The stimuli were alternated with approximately rectangular counterphase pulses and we obtained results contrary to those of a previous report where the stimuli were alternated sinusoidally. In a subsidiary test using a computer-generated counterphase cosine wave on an RCB monitor, at 70 td, one observer perceived no residual flicker but a second observer did.
Conductive coatings for the ultraviolet and near infrared
Authors: Martin Peter M. , Pawlewicz W. T. , Mann I. B. , Bennett W. D.
Published: February 2023

Conductive high transmission coatings for the UV and near IR are described. The predicted and observed dependence of coating transmission on metal layer sheet resistance and refractive index of the dielectric layer are compared. Computer-generated transmission/layer thickness maps are used for multilayer design sensitivity analysis. Coatings made from Ta2O5/Ag/Ta2O5 with the design 0.62λ/(150-220-Å) Ag/0.12λ had the best UV transmission, near 80% on glass between 330- and 450-nm wavelengths. Metal layer sheet resistance ranged from 2 to 10 Ω/sq. Coatings with Nb2O5 layers had similar transmissions, and worked best above the 380-nm wavelength. Near-IR coatings were made from Si/Ag/Si combinations. Transmissions near 80% on glass at 1400 nm were achieved by a 0.19λ/200-Å Ag/0.19λ design. The high refractive index (~3.4) of the Si layers made high transmissions possible. All coatings were fabricated by dc magnetron reactive sputtering using metal targets (Ta, Nb, Si, Ag) and either Ar or Ar + O2 gases. Even though substrate temperatures were <40°C, care was taken to prevent Ag oxidation or diffusion into the dielectric. The coatings are useful for any applications requiring high UV and near-IR transmission, high conductivity, and high-IR reflectance.
Varied line-space grating spectrometer for x-ray transfer experiments in optically thick plasmas
Authors: Hettrick Michael C. , Kahn S. M. , Craig W. , Falcone Roger
Published: February 2023

Over the next decade, several astrophysical observatories will obtain high-resolution spectra of cosmic x-ray sources. Of particular interest are accretion-powered objects, such as active galactive nuclei, in which the x-ray emitting material is optically thick and therefore cannot be studied using the well-known models developed to explain the optically thin solar corona. In our laboratory, we are attempting to simulate optical depth conditions from which astrophysical processes can be modeled, including photoabsorption, recombination, and fluorescence. A laser-produced plasma, when time-resolved to separate collisional and radiative effects, can function both as a source of soft x rays and as the ionized plasma. The newly developed spectroscopic technique of varied line-space plane gratings is used to provide high spectral resolution at grazing incidence wavelengths, while maintaining stigmatic imaging and the normal incidence focal plane suitable for use with a streak camera detector. We report preliminary results using metal target plasma sources and x-ray film at the detection plane, verifying the predicted performance of the instrument. We have successfully recorded soft x-ray spectra employing two different collecting mirrors to feed convergent light to the grating: (1) a normal incidence multilayered mirror and (2) a grazing incidence Kirkpatrick-Baez mirror system.
Optical heterodyne interferometry
Authors: Devoe R. G. , Fabre C. , Jungmann K. , Hoffnagle J. , Brewer R. G.
Published: February 2023

We describe a new approach to precision interferometry that is in principle different from previous techniques in that it is free from the systematic errors usually associated with interferometry. Optical heterodyne techniques are used to directly measure the empirical mode spacing of an interferometer over a broad (10%) frequency range. The frequency difference between any two modes can then be computed by summing the spacing of the modes that lie between them, in this way optical frequency differences of up to 50 THz can be measured without the usual corrections for mirror phase shift or diffraction. The heterodyne principle is realized by a dual frequency modulation technique which resonates 4-GHz sidebands of a stabilized dye laser with adjacent interferometer modes. The interferometer has a finesse of 20,000 and a linewidth of only 10 kHz, and measurements show that its mode spacing varies quadratically around its center frequency with a maximum deviation of a few parts in 10−8.
Optical advantages of using a moire topographic instrument on the living body
Authors: Cao Xiang-Qun , Yuan Yu-Lin , Huang Wai-Shi , Lu Jian-Ming
Published: February 2023

A moire topographic instrument has been successfully used in a clinic for making topograms of the living body. This instrument has three optical advantages: (1) its sensitivity can be adjusted; (2) the gratings adopt a suitable depth and the measurable depth is 150 mm; (3) it has smooth grating lines with outfocusing for eliminating noise. Eighty-five percent of the moire topograms of a scoliotic patient agree with the x rays.
Precise representation of bound (closed-channel) energy levels in atoms and small molecules
Authors: Ginter Marshall L. , Ginter Dorothy S.
Published: February 2023

Energy-dependent coupled-channel models are presented for atoms and diatomic molecules which can reproduce entire bound-state (closed-channel) energy level structures and associated electronic transition intensities to within the experimental uncertainties in the high resolution spectroscopic data from which the levels are derived. Discussion includes the effects of energy dependence on the close-coupled μ
α
parameters, the properties of the U
iα
elements of the frame transformation matrix describing the transformations between close-coupled and loose-coupled representations, and the effects of perturber levels outside the channel structures represented by a specific frame transformation. Examples include precise reproduction (within average experimental uncertainties of <0.2 cm–1) of the msmp3,mpnd odd-parity bound levels with J ⩽ 3 for the fourth group atoms Si, I, Ge I, and Sn I, and the electronic structures in molecular He2 associated with the (1σ
g
)2(1σ
u
)npλ and (1σ
g
)2(1σ
u
)ns,ndλ configurations.
High repetition rate amplification of femtosecond optical pulses: recent developments and applications
Authors: Knox Wayne H.
Published: February 2023

Dye laser technology allows the direct generation of optical pulses of femtosecond duration at high repetition rates (74–200 MHz). At these high rates, sensitive differential techniques can be employed for small signal analysis; however, the relatively low pulse energies available limit the applicability of such systems. Amplification of femtosecond optical pulses makes possible a wide range of new investigations in nonlinear optics, spectroscopy, and high density phenomena; however, the repetition rate is then dictated by the pump source. Operation at intermediate repetition rates (1–10 kHz) provides a new and powerful combination: high peak powers (~50,000 times higher than direct laser output) and extensive signal averaging through the use of lock-in amplifiers, differential scanning optical multichannel analyzers, and point-by-point digital techniques. The techniques involved in the amplification and detection of femtosecond optical pulses in the kilohertz regime are discussed, as well as several illustrative applications.
Optical properties of a-Ge/Si3N4 multilayer stacks
Authors: Edgerton Robert F. , Allred David D. , Van Nguyen On
Published: February 2023

A series of samples of single layers and twenty alternating thin layers of Si3N4 and a-Ge were prepared on quartz substrates by ion beam deposition. The optical transmission and reflection spectra were measured in the 300–2400-nm wavelength range. The analysis used a computer search routine to find a suitable set of values for the parameters used for describing the complex index of refraction n(λ) – ik(λ) and thickness for each layer in the multilayer stack. First, the single films were analyzed and the index n(λ), the extinction coefficient k(λ), and therefore the absorption coefficient a = [4πk(λ)]/λ for each of these materials was obtained. Second, the stack was described by ten pairs of Si3N4/a-Ge films. The thickness of the Si3N4 and a-Ge were allowed to vary, the index of refraction of the Si3N4 and a-Ge were varied, and the absorption coefficient of the a-Ge was varied. Only the absorption coefficient of the Si3N4 was held fixed at the values given by the single film study. The values of the band gap of the a-Ge were seen to change from 0.88 eV for a single layer of a-Ge (170 nm thick) to 0.97 eV for ten thin layers of a-Ge (4.35 nm) interspersed with Si3N4 films (3.68 nm). Methods of measuring the band gap that are based on incoherent light and coherent light are compared.
Measurement of thin-film elastic constants via Brillouin spectroscopy
Authors: Zanoni R. , Bell J. , Naselli C. , Stegeman George I. , Seaton Colin T. , Nizzoli F.
Published: February 2023

High resolution Brillouin spectroscopy has been used to measure the elastic constants of highly oriented thin films of cadmium arachidate. Samples of cadmium arachidate were prepared on molybdenum and glass substrates using the Langmuir-Blodgett technique. Thermally excited guided acoustic waves in the thin films were probed using Brillouin spectroscopy. The scattered light was spectrum analyzed with a high resolution tandem multipass interferometer to measure the Brillouin shifted signals. The elastic constants were estimated by fitting a model of the guided acoustic waves within a hexagonal thin film on an isotropic substrate to the Brillouin shift data. The shear elastic constant was found to be small c44 < 4.0 × 108 N/m2. The elastic constant corresponding to the longitudinal velocity along the molecular axis was quite large, c33 = 2.1 × 1010 N/m2.
Fast algorithm for discrete Fourier spectrum extrapolation
Authors: Howard Samuel J.
Published: February 2023

An effective algorithm for calculating the extended discrete Fourier spectrum for bandlimited data has been developed that has modest computer time and memory requirements. It is thus suited for the practical processing of large (16K points or greater) experimental data sets. This algorithm is an iterative procedure for numerically solving the set of nonlinear equations resulting from application of the minimum-negativity constraint (a variation of the positivity constraint) to bandlimited data. The theoretical development leading to the nonlinear equations was derived earlier by the author.1
High-fidelity phase conjugation of broadband laser radiation with stimulated Brillouin scattering using a grating disperser
Authors: Dlabal M. L. , Reintjes J. , Lehmberg R. H.
Published: February 2023

We describe the use of a grating disperser to allow effective phase conjugation of broadband radiation with stimulated Brillouin scattering. With conventional configurations the bandwidth of the pump radiation is restricted because the Brillouin reflectivity decreases when the pump bandwidth becomes wider than the Brillouin linewidth and the conjugate fidelity decreases when the coherence length becomes shorter than the effective interaction length. With our technique the pump beam is focused into a laterally extended focal region, each element of which has effectively narrowband radiation. As long as these narrowband focal-region elements carry sufficient spatial information each will provide a conjugate of the pump wave at its appropriate wavelength. Because the return beam from the Brillouin cell is a conjugate of the incoming beam it will reconstruct off the grating to form a conjugate of the beam as a whole, rather than a beam with double the dispersion. We demonstrate the performance of this technique in correcting phase aberrations using radiation at 353 nm from a XeF laser and SBS in n-hexane. Comparisons are made of performance with and without the grating disperser and results are compared with theory. In addition we present studies of the effects of various types and degrees of aberration and various amounts of grating dispersion.
Confocal scanning laser ophthalmoscope
Authors: Webb Robert H.
Published: February 2023

A confocal scanning imager moves an illumination spot over the object and moves a (virtual) detector synchronously over the image. In the confocal scanning laser ophthalmoscope this is accomplished by reusing the source optics for detection. The common optical elements are all mirrors—either flat or spherical—and the scanners are positioned to compensate astigmatism due to mirror tilt. The source beam aperture at the horizontal scanner is small. Light returning from the eye is processed by the same elements but now the polygon’s facet is overfilled. A solid state (high quantum efficiency) detector may be at either pupillary or retinal conjugate plane in the descanned beam and still have proper throughput matching. Our 1-mm avalanche photodiode at a pupillary plane is preceded by interchangeable stops at an image (retinal) plane. Not only can we reject scattered light to a degree unusual for viewing the retina, but we choose selectively among direct and scattered components of the light returning from the eye. The retinal view is surprising. One (of many) consequences is that this ophthalmoscope gives crisp and complete retinal images in He-Ne light without dilation of the pupil.
Stratified volume holographic optical elements
Authors: Tanguay A. R. , Johnson R. V.
Published: February 2023

Volume holographic optical elements are of considerable interest for applications in optical information processing and computing systems and in optical interconnect technology. Typical volume holographic optical elements are fabricated from bulk photosensitive materials, such that the holographic recording process occurs throughout the entire volume. We have investigated an alternative approach to the fabrication of such elements by employing a number of thin photosensitive layers interleaved among much thicker optically inactive buffer layers. As few as five thin but spatially separated active layers can exhibit essentially the same Bragg selectivity as a single distributed volume hologram. Performance characteristics of stratified volume holographic optical elements have been studied by the anisotropic optical beam propagation method,1 including angular alignment sensitivity, buffer layer thickness sensitivity, crosstalk, and diffraction efficiency as a function of the number of active layers and relative layer thicknesses. Such a concept may allow highly photosensitive and very fast response time materials such as multiple quantum well (MQW) structures in III–V or II–VI compound semiconductors to be used in fabricating volume holographic optical elements, even though such materials are very difficult to grow in layer thicknesses sufficient to individually exhibit the requisite thick holographic characteristics. In addition, novel and intriguing device designs can be envisioned in MQW structures by utilizing applied electric fields to tune the device absorption and phase modulation resonances.
Dual series solution to high frequency binary conducting grating
Authors: Kok Yon-Lin , Gallagher Neal C.
Published: February 2023

Very high frequency corrugated surfaces have become the object of increased study over recent years. With these structures, the period of the surface corrugation is of the order of, or much smaller than, the optical wavelengths with which they are used. Devices employing such corrugated surfaces have unusual and interesting polarization and diffraction characteristics. However, properties of these devices have only been understood by solving large systems of equations. Parameters which affect these solutions include corrugation period, depth, and duty cycle. In addition, the ratio of corrugation dimensions to optical wavelength is very significant. These parametric values also have a significant impact on the numerical stability of common techniques used for solving these grating problems. Usual methods of solution include iterative methods and the so-called mode matching methods. For parameter values of interest to us, we have found that these methods converge slowly, are subject to numerical instabilities, and sometimes require massive computation. We have adapted a method called the dual-series method which, through contour integration, avoids these difficult numerical problems. In addition, the dual-series method yields analytical expressions where other methods produce only numerical values.
Effect of filtering on the pseudocolor image
Authors: Zhuge Xiangbin , Kang Shancun , Chen Hongshan
Published: February 2023

This paper deals with, in phase modulation of pseudocolor-density encoding, the shearing function of low diffraction spatial frequency filtering of 0 or 1 class on the frequency spectrum, which causes the loss of the fine structure of the output color image and a serious smooth edge of the color image.
Model for hyperopia, myopia, and presbyopia, with suggested therapeutic remedies
Authors: McLeod Roger D.
Published: February 2023

A spatial frequency model for vision requires that the diffraction pattern representations of the Fourier transformed equivalent of object information at the focal surfaces of two quasi-monochromatic wavelength intervals are coincident with rod and cone outer receptive segments.1 A focal length and wavelength dependence is linked to the size of the Airy diffraction pattern, coherent transfer functions, and variable-sized patches at the retina. Airy diameter couples wavelength over pupil diameter. This, and the hardwiring of the retinal neurophysiology, indicate that visual tasks with changes of pupillary diameter require wavelength changes to maintain a more nearly constant relationship of Airy pattern to nerve network. Hyperopia is then a system stuck in a condition of long focal length, for which appropriate therapy consists of convergence and brightness-dependent exercises which couple in accommodation increases. Myopia is then a condition of too short a focal length, with reverse treatment strategy required. Presbyopia requires a combination of these approaches.
Far-infrared laser emission from optically pumped CH2DF
Authors: Eggers D. F. , Tobin M. S. , Daley T. W. , Lewis-Bevan W. , Gerry M. C. L.
Published: February 2023

CH2DF gas was synthesized in high isotopic purity and tested for far-IR laser emission with pumping by a CO2 laser. Five lines were found, ranging from 169.5 to 498.4 μm. Infrared absorption spectra at 0.005-cm−1 resolution and analysis of the rotational structure permit clear-cut assignment of two lines: 190.3 μm pumped by 10R46 is due to (J, Ka, Kc) of 34 1 33 → 33 1 32 in v5; 494.8 μm pumped by 10P4 is due to 132 12 → 122 11 in v6. Molecular constants are reported for these two bands, centered at 1055.544 and 938.301 cm−1, respectively. The spectra show indications of v9 centered somewhere near 1130 cm−1; unfortunately we have not yet obtained an assignment of lines due to its great weakness and overlapping by the very strong 1055 band. There are problems in finding infrared absorptions sufficiently close to the pumping lines for the other laser lines; it is possible that they may originate in molecules that are vibrationally excited before absorbing the CO2 laser radiation. Spectra of combination bands lead to parameters that are shown to support this suggestion.
Short-wavelength chemical laser research
Authors: Jones C. R.
Published: February 2023

The pursuit of short-wavelength chemical lasers (SWCL) has persisted for two decades, a fact which ought to lead us to ask some hard questions: Are there fundamental reasons underlying our limited success, or have we been unlucky? Have we been looking at the best approaches? Most importantly, what should we now be doing to invent viable SWCLs? The current research program assumes that the critical issues are the formation and maintenance of high densities of electronically excited species. We are not convinced that the conventional continuous-flow mixing approach is the most promising one. This concern is based on various limiting effects on density, including the radiative-lifetime/mixing-time problem.
Laser-induced fluorescence studies of excited state relaxation in GeF
Authors: Hinchen J. J.
Published: February 2023

The collisional deactivation of electronic, vibrational, and rotational states of GeF was studied using laser-induced fluorescence (LiF). Interest in this molecule was stimulated by the work of S. Davis who pointed out the potential of group IVA fluorides as chemical laser candidates due to large ground state splitting. Experimentally, Ge vapor evaporated by a pulsed YAG laser was reacted with F2, dilute in He, to form GeF. Pulses from a dye laser (~10 mJ, 12 ns) pumped the GeF to a specific vibrational-rotational level of the A2∑ electronic state. By scanning the laser wavelength LIF spectra were produced. Temporal decay of the fluorescence from a single excited level was used to determine relaxation rates as radiative lifetime = 1 × 106 s; V–V transfer = 1.6 × 105 s−1 Torr−1; rotational relaxation = 1 × 107 s−1 Torr−1. By saturating the pumped level and comparing the LIF to chemiluminescence the population ratio in A/X states at V = 0 was found approximately as 1/7. The formation and loss of GeF(X) was followed by observing LIF intensity as the dye laser pulse was delayed past the YAG evaporation pulse. Also, the temporal concentration changes of GeF(A) followed from chemiluminescence intensity. The results are compared to a simple kinetic model which incorporates reaction and deactivation rates.
New physical picture of the Langmuir flow effect
Authors: Yuan Xiao-Dong
Published: February 2023

By using an external cavity ring laser, the radial distribution of the Langmuir flow null shift in discharge tube capillaries has been investigated. The experimental results are not in agreement with the current picture which predicts that the gas flow is in one direction at the center of the capillary and in the other direction near the wall, with a well-known radial distribution of velocity. Now the measured Langmuir flow null shifts caused by gas flow effects are only in one direction with a new radial distribution of the gas flow velocity. We explain the experimental results by introducing a reasonable physical picture: because of electron–atom collisions in the glow discharge, the atoms at different states have different average velocities that cause Langmuir flow null shift effects quite different from the current picture.
Systems view of optical digital computers
Authors: Huang Alan
Published: February 2023

Initial efforts at building an optical digital computer involved trying to make exact optical equivalents of electronic gates and memories. The optical gates were either noncascadable or two-port devices. The optical memories were slow, expensive, awkward, and failed to use the high bandwidth, parallel communications capabilities of optics.
Age norms for the polarity of the Farnsworth-Munsell 100-Hue test
Authors: Knoblauch K. , Podgor M. , Kusuda M. , Saunders F. , Hynes R. , Higgins K. , De Monasterio F.
Published: February 2023

We have evaluated the color vision of a sample of 75 normal individuals (20–78 years old) with the Farnsworth-Munsell 100-Hue test at five illuminance levels. The data were analyzed by fitting a two-cycle sine wave directly to each cap score error distribution. The amplitude and phase of this sine wave determine, respectively, the polarity and axis of each error distribution. The results of these fits quantify the increase in yellow-blue type errors that occur with increase in age and with decrease in illuminance level. Other indices of polarity were evaluated and found to be equivalent to the one that we used. Based on our sample, we present norms for the amplitude as a function of age
Aging in visual-vestibular interactions
Authors: Elsner Ann E. , Wall C. , Johnson J.
Published: February 2023

To search rapidly for information in a scene, it is critical to make quick, accurate saccadic eye movements. Often, while making these movements, a body or head movement is required. Thus, vestibular and saccadic eye movements must be coordinated. It is known that the vestibular system can change with age; e.g., the gain of the system can decrease with age, particularly at low frequencies. However, the effects on saccadic eye movements are not understood. Using a pseudorandom vestibular stimulus (rotation about the vertical) with frequencies from 0.02 to 1.67 Hz, we have measured (a) the gain and phase of the vestibulo-ocular reflex and (b) saccade parameters. Saccade targets were three red LEDs, positioned in the center and 9° to either side. We recruited five observers, 62–69 years, who had been normal on a battery of vestibular tests 2 years prior. There was a slight loss of low frequency relative to high frequency gain, but this trend was not significant. However, the average number of saccade errors doubled while rotating vs remaining stationary. Most errors during rotation were (a) single or multistep saccades of less than half-amplitude or (b) slow eye movements.
Double phase-conjugate fiber-optic gyro
Authors: McMichael Ian , Yeh Pochi
Published: February 2023

We describe and demonstrate a new type of phase-conjugate fiber-optic gyro1 (PCFOG). PCFOGs use phase conjugation to compensate for reciprocal phase changes due to thermal and mechanical effects on the fiber, while at the same time allowing for the measurement of the nonreciprocal phase shift produced by rotation. Where the best standard fiber-optic gyros require polarization-preserving fibers and couplers to avoid polarization scrambling that is a source of noise and signal fading, PCFOGs can avoid this problem by using polarization-preserving phase conjugation.2 This has the advantage of allowing for the use of inexpensive nonpolarization preserving and even multimode fibers and components. The double PCFOG is simply an interferometer, in which both arms contain fiber-optic coils terminated by the same self-pumped phase-conjugate mirror. We have recently demonstrated rotation sensing using such an interferometer with a self-pumped crystal of barium titanate as the phase-conjugate mirror. For this demonstration, the entire interferometer was mounted on a rotary table and light was piped to the table using a fiber optic. In addition to the simplicity of the new self-pumped version of the PCFOG, it has the advantage of allowing for the use of fiber-optic coils that are longer than the coherence length of the laser to increase the sensitivity of the gyro.
Phase conjugation and pulse compression via stimulated scattering in the isotropic and mesophases of liquid crystals
Authors: Khoo I. C. , Michael R. R. , Yan P. Y.
Published: February 2023

We have conducted a detailed experimental study of stimulated scatterings of nanosecond laser pulses from thin films of nematics and smectic, and isotropic cholesteric liquid crystals. We have observed for the first time simultaneous occurrence of phase conjugation (with aberration correction capability) and optical pulse compression (with compressor ratio as high as 20 or so). The origins of the nonlinear scattering process have been studied in detail with linearly and circularly polarized beams and are found to be mostly of Brillouin nature, although Raman and orientational processes also contribute in some cases. We have also studied the process involving some guided wave geometries in thin films of nematic and smectic and observed good quality phase conjugation and pulse compression even under very severe distortion at the input end of the sample. The observed thresholds for the stimulated scattering are in the kilowatts regime, and they are compared and contrasted with observations in other nonlinear materials. In most cases, the laser power thresholds are comparable to other nonlinear liquids, but it is observed that the threshold for a particular cholesteric is unusually low. Detailed analysis and experimental results are presented.
Optical bistability in the multiple quantum well structure
Authors: Sung C. C. , Bowden Charles M. , Englund John C. , Cook James M.
Published: February 2023

The multiple quantum well structure, GaAs/GaAIAs, displays room temperature optical bistability at very low switching powers in various conditions through the temperature variation and the external voltage across the sample.1,2 We have constructed detailed models to calculate these effects. Coupled Maxwell’s equations and the heat conduction equation are solved to demonstrate how the red shift of the band gap leads to absorptive bistability. The spatial variation of the external field strength is a typical PIN junction and the experimental values of the absorption coefficient are used to obtain the bistability properties as a function of the incident frequency and the biased external voltage. The results based on the actual material constants are in good agreement with the experimental data without adjustable parameters. We also extend the previous work on the stability analysis in the mean-field approximation to this system involving complicated boundary conditions with the propagation effects.
Non-Gaussian diffusers as phase encoders in neurooptic processors
Authors: Jannson Tomasz , Karaguleff C. , Stoll H. M.
Published: February 2023

Key elements of the Northrop neurooptic processor1 include an array of nonlinear processing elements (neurons) and means for effecting space-variant interconnections (synapses) between any two of these processing elements. The latter take the form of holographic phase gratings distributed within a volume of LiNbO3. Phase encoding of processor outputs must be used to avoid Bragg cone coupling effects2 and, hence, undesired interconnect degeneracies within the LiNbO3. Phase encoding may be accomplished by using non-Gaussian optical diffusers with tunable Wiener spectra and adjustable correlation lengths within the image plane of the processor array. Diffuser design criteria include the minimization of processor output cross-correlation functions and the attainment of processor output autocorrelation functions which most closely resemble delta functions. In this paper, the analysis of an appropriate diffuser is described, and several fabrication techniques are presented. Specifically, computer-generated and optically synthesized binary diffusers derived from bandlimited Gaussian noise are discussed. Finally, an experimental setup for examining diffuser autocorrelation functions is described.
Emission spectrum of SO+ in a supersonic expansion
Authors: Hardwick J. L. , Moseley J. T. , Milkman I. W. , Choi J. C.
Published: February 2023

Using a supersonic expansion of helium and sulfur dioxide excited by a corona discharge, we have observed spectra of the A–X band system of the thionyl ion, SO+, in emission between 255 and 450 nm. The spectra are rotationally and spin-orbit cooled by the expansion, allowing features which ordinarily are highly congested to be analyzed rotationally. The derived constants have been merged with those obtained from previously published spectra of SO+, as well as from new analyses of unpublished high resolution measurements. The formation of the excited thionyl ion occurs via a dissociative charge transfer reaction between He+ and SO2, and its primary path of destruction appears to be reactions with excess sulfur dioxide. Derived constants for the A–X system of the thionyl ion have been obtained for v″ = 0–10 and v' = 0–11. These new data substantially extend the range of vibrational and rotational information available for this ion and are expected to simplify future searches at higher resolution.
Geometrical control of parameters in wedge filters
Authors: Stoner John O.
Published: February 2023

In making an optical filter to provide any desired attenuation between 0.9 and 0.001 (0.5–30 dB) in the visible and infrared, the absorbing material of choice was carbon because of its environmental stability. To obtain the desired gradation of thickness from 0 to ~1.5 μm, separated-aperture masking1 was used; motion of the source as evaporation progressed provided the necessary gradation in thickness. The maximum thickness was controlled by the source–substrate distance; stringent efforts had to be made to avoid excessive substrate heating due to the proximity of the hot source. Finally, because the stresses in evaporated carbon layers can be controlled in part by choice of the angle at which the atoms strike the surface,2 the substrate was tilted at the angle calculated to optimize the performance of the resulting filter.
Composition and structure of anodic oxide films on Hg1−xCdxTe
Authors: Seelmann-Eggebert M. , Richter H. J.
Published: February 2023

Thin films of native oxides were anodically grown on n-type Hg1−
x
Cd
x
Te (x = 0.2 and 0.3) to achieve surface passivation which is essential to the function of this narrow gap semiconductor as a high performance infrared detector. To establish a basis for correlation of the physical and chemical properties which arise from the formation of these films, we studied and identified the electrochemical reactions at the onset of anodization and analyzed the composition and structure of the resulting anodic films. For these analyses we employed angle-resolved and standard x-ray photoelectron spectroscopy in combination with electrochemical techniques, such as cyclic current-voltage measurements. We found that composition and structure of anodic films on Hg1−
x
Cd
x
Te depend significantly on two growth parameters, namely, the electrolyte (pH 4.7–13) and the density of the anodic current (galvanostatic anodization). The native oxide films grown at pH 4.7 were found to be rich in Te and Hg, and HgTe2O5 was identified as a major oxide constituent. At pH 13, CdTeO3 is the dominating native oxide; however, if the aqueous component of the electrolyte is partially replaced by ethylene glycol or a similar organic liquid, the solubility of the tellurite decreases, the HgTeO3 precipitates at the electrolytic interface of the growing film and decisively improves the physical properties of the film.
Phase density conservation in fiber-optic systems
Authors: Jannson Joanna , Yeung Peter C.
Published: February 2023

The usefulness of the phase-space concept is well recognized in understanding the propagation of electromagnetic radiation. Furthermore, the principle of phase density conservation in the form of Liouville’s theorem has been broadly discussed for solar energy concentration in systems having axial symmetry1 as well as in the case of more general non-Cartesian systems.2 The purpose of this paper is to extend the applications of the phase density conservation principle to the fiber-optics area in order to demonstrate the feasibility of fabricating new types of fiber optic coupler, connector, and beam expander. Based on Liouville’s invariant1,2 in design, such systems can potentially circumvent the aberration losses of conventional imaging or nonimaging optics, thus attaining the highest brightness (radiance) or efficiency permissible under the second law of thermodynamics. In addition, the approach of globally optimizing Liouville’s invariant (which is equivalent to maximizing the system efficiency) for the optical channels involved is analyzed. The consequences of the phase density conservation principle for low or moderate values of Fresnel number, like those in fiber-optic systems, are also discussed.
Electrooptical gaze measurement with high spatial and temporal resolution
Authors: Zeevi Y. Y. , Rosenfeld L. , Williams T.
Published: February 2023

The stringent requirements of achieving both high spatial (0.25°) and temporal (1-ms) resolution in a helmet-mounted electrooptical system permitting 2-D gaze measurements independent of head translation prohibits implementation of 2-D sensors. To meet these requirements, SRD has recently introduced a novel technique wherein two 1-D, photoelectric self-scanned arrays detect projections of the bright pupil (P) and corneal reflection (CR) images, thereby reducing the number of sampled pixels from n2 to 2n. To achieve subpixel resolution we have developed algorithms based on models of the P, CR, and iris signals. The pupil center is immediately provided with subpixel resolution once its elliptic model parameters are determined by a least-squares fit of the P-set of data. Alternatively it can be determined using the P-edges defined by the intersection of the P-model with the iris model. The P-model enables definition of its center and/or edges even in extreme cases where the CR obscures one of the latter. The distorted CR signal is first restored by subtraction of the P-model from the raw data. The set of 5–7 points of the restored CR signal is then used for computation of a Gaussian model to provide the center of the CR with 0.25 pixel resolution. Measurements with an artificial eye indicate resolution (and accuracy) of better than 0.25° at a rate of 1000 frames/s.
Surface acoustic wave diffraction of polarized light
Authors: Graver William R. , Ngoc Tran , Mayer Walter G.
Published: February 2023

In the presence of an acoustic Rayleigh wave, the surface of an isotropic solid will exhibit a physical corrugation which moves with the wave. When an optical wave interacts with the surface acoustic wave, the light is simultaneously reflected and diffracted. Earlier diffraction integral work which specifically supports this area was performed by Mayer.1 Additional development of phenomenological depolarization was later pursued by Stegeman2 and considered the intrinsic stress polarization properties of transparent materials. Sarid3 also observed pronounced differences in the line shape of light scattered by partial acoustic waves. Following this, an experimental observation of light polarization and surface acoustic waves was made by Alippi et al.4 but lacked the development of a physical model of the interaction. Experimental data are compared to our model including scattering mechanisms associated with the surface corrugation and elastooptic effects, optical incident and azimuthal angles, and acoustic intensity and frequency for S- and P-polarized input light.
Spectral narrowing of a storage ring free-electron laser using a birefringent plate
Authors: Elleaume Pascal
Published: February 2023

It has been proposed to reduce the spectral width of a free-electron laser using a birefringent plate at the Brewster angle. The linewidth can be controlled by rotating the plate. This would be particularly useful for a storage ring FEL where a linewidth of 10−5–10−6 should be achievable without significant reduction of gain. Sapphire looks like a good candidate in the 0.15–1.0-μm wavelength range.
Polynomial fitting to an aberrated wavefront by the method of averages with minimum error
Authors: Cordero-Davila A. , Diaz-Uribe R. , Rodriguez G. , Cardona-Nunez O. , Pedraza-Contreras J. , Cornejo-Rodriguez A.
Published: February 2023

For analyzing a Twyman-Green interferogram coming from an axially symmetric system, we use the method of the averages. Together with this technique we developed a method of minimizing the propagated error in the calculation of the polynomial fitting coefficients by finding the points of the domain that yield error weighting functions of minimum value.