bluuebunny/crossref_metadata_2025 huggingface dataset:
Anamorphic, afocal, imaging beam reshapers
Authors: Chastang Jean-Claude A. , Dony Fuad , Goodman Douglas S.
Published: February 2023

Anamorphic afocal imaging with arbitrary principal magnifications and object–image distance can be achieved with two spherocylindrical lenses. Associated with such systems is only one pair of conjugate planes, as opposed to an infinite number for rotation-symmetric afocal combinations. A paraxial study of these anamorphic afocal systems will be presented, along with some useful formulas. This will be supplemented by examples of ray traces and aberration studies. We will describe an application involving the reshaping of excimer laser beams, for coupling to a subsequent system, from a rectangular to a square cross section for the enhancement of beam uniformity.
Dual-function adaptive neural networks for photonic implementation
Authors: Petrisor G. C. , Jenkins B. K. , Chin H. , Tanguay A. R.
Published: February 2023

We present an adaptive neural-network model in which each neuron unit has two inputs, a single potential, and two outputs. This network model can exhibit general functionality, although it uses only nonnegative values for all signals and weights in the interconnection. In this dual-function network (DFN), each output is a distinct nonlinear function of the potential of the neuron. Each neuron-unit input receives a linear combination of both outputs from any set of neurons in the preceding layer. A learning algorithm for multilayer feedforward DFN's based on gradient descent of an error function and similar to backward-error-propagation learning is presented.
Optical pseudoinverse neural network
Authors: Li John X. , Yu Francis T. S.
Published: February 2023

Pseudoinverse is a linear mapping algorithm that produces minimum-squared errors. Pseudoinverse neural networks (PNNs) implement this algorithm by using neuralnetwork components in a two-layer structure. The first layer with N neurons is trained with a Kittler-Young transform and a pseudoinverse transform by using a set of training images from all image classes. As a result, the outputs of the first layer are the matching scores between input images and the basis images of different classes. A MAXNET of M neurons is built in the second layer of the PNN to pickup the maximum matching score. In the MAXNET, the interconnections between neurons are inhibitory with a value of -a, where a <1/M and the connections of the neurons to themselves are 1. High-space-bandwidth-product operation is possible because the number of interconnections is only M × N in the PNN. In our experiment, a optical PNN with 16 384 neurons is built, and pattern recognitions of 128 × 128 images are performed. Furthermore, the PNN does not suffer from spurious outputs, which can produce no-match results.
Photonic components for neural net implementations using incoherent-coherent holographic interconnections
Authors: Asthana P. , Chin H. , Nordin G. , Tanguay A. R. , Petrisor G. C. , Jenkins B. K. , Madhukar A.
Published: February 2023

A novel photonic architecture for neuralnetwork implementation was recently proposed,1 which incorporates a hybrid incoherent/coherent recording and readout scheme for the formation and utilization of highly multiplexed volume holograms. In this paper we discuss three of the essential optoelectronic components integrated within this architecture: volume holographic interconnections, multifunction spatial light modulators (SLM's), and two-dimensional incoherent/coherent source arrays.2 The volume holographic interconnections use a novel double angularly multiplexed incoherent/coherent recording and reconstruction technique that minimizes both the recording-induced and readout-induced crosstalk inherent in conventional fan-out/fan-in interconnections, permits incoherent summation of interconnection-weighted inputs, and optimizes overall interconnection throughput efficiency. Multifunction optoelectronic SLM's are used to implement dualchannel two dimensional neuron unit arrays and thus incorporate the detection, amplification, functional implementation (e.g., sigmoidal response), and optical modulation required in the neuron unit planes.
Glass waveguide directional couplers fabricated by a two-step purely thermal ion-exchange technique
Authors: Hashizume H. , Kobayashi S. , Sato S. , Seki M.
Published: February 2023

Here we report fundamental characteristics of directional couplers made by a two- step purely thermal ion-exchange. A large number of directional couplers with 11-20 µm axial separations (gap widths are 0-10µm) and 0-10 mm coupling-waveguide region lengths were fabricated. The ion-exchange process used T1 and K ions. The coupling lengths at 1300 nm and at 1550 nm wavelengths were estimated to be 2-55 mm and 2-18 mm, respectively. The relation between the coupling length and the axial separation was fitted well to an exponential function. The excess losses, including one coupling loss with a single-mode fiber for > 14µm axial separation, were all within 0.7 dB. The polarization dependency of the branching ratio of 3-dB couplers with half the coupling length was evaluated to be < ±2%. For the temperature change from −40°C to 85°C, the variation of the branching ratio measured with unpolarized light was as low as < ±1%.
Optical AND Gates Using Vertically Integrated Surface Emitting Laser-Phototransistors
Authors: Chan W. K. , von Lehmen A. , Florez L. T. , Harbison J. P. , Nguyen C. K.
Published: February 2023

Vertical cavity surface emitting (VCSE) lasers are potentially important in the area of optical processing where two-dimensional, addressable arrays of these lasers are envisioned. Although the addressing can be electrical, the required number of connections will ultimately limit the array size and their packing density. Optical addressing not only will eliminate the need for most of these connections, but will provide a natural interface with the input data which will already be in the form of optical patterns. In addition to optical addressing, optically implemented logic operations at each pixel will be useful and will eliminate the need for extra electronics. For example, with a laser that turns on if and only if both of two inputs are on (logical AND), one input pattern can gate the other. In this paper we will describe the first optically addressable VCSE lasers and the first optical AND gate with VCSE laser output.
Constraint on the incidence angle and thickness of a transparent film on an absorbing substrate to achieve a given reflectance for incident, unpolarized light
Authors: Giardina Kurt A. , Azzam R. M. A.
Published: February 2023

At a given wavelength, we determine all possible solution pairs (ϕ, d absorbing substrate that achieve a given unpolarized-light reflectance Ru. The trajectory of the point that represents a solution pair in the ϕ- d plane depends significantly on the extinction coefficient of the substrate and on whether Ru is or the normal-incidence reflectance

R
¯

O

of the uncoated substrate. When Ru

R
¯

O

, the specified reflectance is achieved over a limited range of ϕ. At the least possible incidence angle, the film thickness ≅ 1/8th wave, with the exact equality holding if the substrate is transparent. As an application of these results we consider SiO2 films on Si detectors that produce Ru = 0.75, 0.6667, and 0.50 at laser wavelengths of 337, 488, and 633 nm. If the first three detectors of the four-detector photopolarimeter (FDP) are coated to have these reflectance levels, with the reflectance diminishing in the direction of propagation of the light beam, and the last detector is anti-reflection-coated (e.g., with a quarter-wave Si3N4 layer), equipartition of energy among the four detectors is accomplished for incident unpolarized light. Such condition is desirable in the operation of the FDP.1 The ellipsometric parameters of the coated surfaces and the determinant of the FDP instrument matrix are also calculated.
High-contrast thin-film polarizers for Nd:glass laser systems
Authors: Smith Douglas J. , Jin Michael S. , Chrzan Z. Roman
Published: February 2023

Thin-film polarizers are essential for efficient frequency conversion of high-energy lasers used for inertial fusion energy experiments. Many polarizer designs appear in the literature. Designs for single-wavelength devices are best compared by examining both the contrast ratio (Tp/Ts) and the throughput (Tp) as a function of the angle of incidence. A design using tantalum pentoxide/silicon dioxide is optimized for use at 1054 nm. These materials can be accurately controlled during deposition and have favorable damage characteristics. A method is described for accurate calibration of a physical thickness monitor in a planetary deposition system. A reflectometer modified to automatically measure the angular spectrum of contrast and throughput is essential for fine-tuning the design. Contrast ratios exceeding 1000:1 with throughput greater than 0.96 are realized on polarizers as large as 35 cm. The results for polarizers up to 60 cm (30 cm clear aperture) are presented. Performance of the polarizers on the 24-beam OMEGA laser is summarized.
Data and theory of colorimetric purity discrimination
Authors: Yeh Tsaiyao , Smith Vivianne C. , Pokorny Joel
Published: February 2023

We developed a model using the critical axes from Boynton and Kambe to describe the discrepancy in purity-discrimination data measured from white, ΔP(white), and from the spectrum, ΔP(spectrum). In this study, we used a computer-controlled four-channel Maxwellian view system to investigate the model predictions. For five normal observers, we measured chromatic discrimination steps along the tritan and R/G axis, purity-discrimination functions from white (0.3536,0.3545), and purity-discrimination functions from the spectrum. A double-random staircase, temporal forced-choice paradigm was used. The luminance levels varied from 2.86 to 286 td. In confirmation of the model, the ΔP(white) thresholds were similar to classical data, and the ΔP(spectrum) thresholds at a fixed luminance level depended on the individual observer's tritan discrimination threshold. The data also showed that test luminance level had a major effect on ΔP(spectrum) but only a minor effect on ΔP (white). Furthermore, we observed that a common TVI template cannot describe discrimination changes with both chromaticity and mean luminance. We refined the chromatic discrimination model to account for the main trends of the colorimetric purity data.
Discrimination and sensation in the opponent colors channels
Authors: Calkins David J.
Published: February 2023

"Indiscriminability action spectra" of the red/green opponent channel can be measured by using a foveally presented 500 ms raised cosine without spatial edges. These spectra represent lights that are rendered indiscriminable at a cone-antagonistic locus. I found that mid-waveand long-wave low-frequency stimuli falling on the same contour, when presented simultaneously on an intense 578 nm adapting field, cancel the "green" and "red" sensations, respectively, elicited by each. That is, the isocancellation contours of the red/green channel are identical to the indiscriminability spectra. Also, using the low-frequency stimulus, I isolated a short-wave mechanism that codes a single "violet" both at and above threshold. Lights between 400 and 489 nm, which fall on the same indiscriminability contour up to 2 log units suprathreshold, are indiscriminable. This single "violet" is distinct from a single "blue" elicited by a second short-wave mechanism whose sensitivity is suppressed by a 578 nm adapting field. This mechanism is manifestly opponent since the color it codes is cancelled by an appropriate yellow low-frequency light.
Second-harmonic generation in laser-assisted poled polymeric materials
Authors: Cao X. F. , Yu L. P. , Dalton L. R.
Published: February 2023

A new laser-assisted poling method was introduced to fabricate organic polymeric materials for second-order nonlinear optical applications. This method provides selective and controllable poling in organic polymers. The large orientation order of nonlinear optical molecular units was evidenced in laser-assisted poled polymers. As a result, polymer thin films with a large second-harmonic nonlinearity can be fabricated. From the measurements of second-harmonic generation in thin-film geometry, second-harmonic coefficients were found to be d33 = 168 ± 18 pm/V and d33/d13 = 7 ± 2 at 1320 nm. Experimental results indicate the improvement of molecular alignment by laser-assisted poling methods in comparison with the nonlinear properties of the same material poled with tradition poling scheme. We have also incorporated nonlinear optical function units into photoinduced, cross-linking linear polymer chains. Long-term stability of the molecular orientation was achieved by fixing the aligned nonlinear units with the cross-linking technique. Because of the selective poling ability, laser-assisted poling techniques can be used to fabricate nonlinear channel waveguides, grating input couplers, and waveguides for quasi-phase-matching second-harmonic generation.
Physiological basis of photometry
Authors: Lee Barry B.
Published: February 2023

The human photopic luminous efficiency function, the basis of photopic photometry for over 50 years, may be derived from several psychophysical tasks. These tasks are sometimes assumed to tap a "luminance channel" in the visual system, but the physiological identity of this channel has been controversial. The physiological basis of two photometric tasks will be discussed. For flicker photometry, there is strong evidence that cells of the phasic, magnocellular system of the primate visual pathway form the substrate. Not only can photometric properties, such as additivity and transitivity, be demonstrated in this pathway, but also odd psychophysical effects, such as that seen when the relative phase of two flickering lights changes, find a precise correlation in the responses of these cells. This makes it unlikely that cells of the parvocellular system contribute to this task. For another photometric task, the minimally distinct border, evidence for M-pathway cells as the physiological substrate is also compelling, implying that this pathway is a major contributor to form vision. It is parsimonious to suppose that the M-pathway is involved in other photometric tasks, such as resolution photometry.
Stable soliton and nonsoliton three-dimensional propagation of intense light by multiple-beam interference in Kerr materials
Authors: Barthelemy A. , Colombeau B. , Froehly C. , Reynaud F. , Vampouille M.
Published: February 2023

Intense laser beams of usual shape (gaussian profile and circular symmetry) carrying more than a critical power are known to break up into several self-focused spots when propagating through homogeneous Kerr type nonlinear media. This chaotic instability prevents all the previously envisaged applications of the intensity controlled refactive index changed exhibited by Kerr materials. When the nonlinear propagation is restricted to two dimensions, for example in a planar waveguide, it has been shown, some years ago that soliton effects induce stable self guided beams at suitable intensities. This communication presents a new kind of geometrical intensity profiles that are stable as well for the two-dimensional as for the three-dimensional cases. These structures consist in the interference pattern of four (or at least two) copropagating beams, coming from the same laser sources and overlapping into the nonlinear medium. We report experimental results showing the use of this technic for (i) the increase of the intensity threshold before the growing of self-focusing instability and (ii) generating two-dimensional soliton beams. At higher intensity levels, distortions are introduced by the self-bending of beam trajectories due to the contribution of the enveloppe of the intensity input pattern to the refractive index profile. Intensity controlled self deflection has been observed and, when combined with a spatial filter, applied to the clipping of the more intense part (5 ps) of 30 ps pulses. The control of the beam spatial shapes during their nonlinear propagation offers a new way to avoid optical damages resulting from self-focusing, for example in very high power laser amplifiers. On an another side it opens the use of bulk Kerr media for achieving the optical processing of intense pulsed laser radiation. This processing can rest on geometrical as well as on temporal self phase modulation effects. The last limits come from the appearance of stimulated scatterings. Recent experiments on stimulated Raman scattering suggest to us that they could be probably overcome by giving to temporal pulses beatings the same role as the previously presented beam interferences.
Ionization of D2O at 10.6 µm
Authors: Xu G. , Decker J. E. , Hou M. , Chin S. L.
Published: February 2023

The fundamental processes surrounding the interaction of intense laser pulses with atoms is well advanced. Recently attention has been turned to similar interactions involving molecules.1 We describe some results of the ionization of D2O molecules by intense CO2 laser pulses with a duration of 1.5 ns at 10.6 µm and an intensity of 1012 W/cm2. Time-of-flight spectra in the present experiment demonstrate fragmentation rich in structure, a marked difference from experiments performed with pulses of 100 ns duration.2 The major peaks in the spectra, which include D+, DO+, (DO)2+, (D2O)2+, etc., and proposed processes will be discussed. Negative ions have not been detected. The proposed sequences will be verified by correlation calculations now in progress.
Compact multichannel Fourier-transform spectrometer with a Savart-plate interferometer
Authors: Kawata Satoshi , Hashimoto Mamoru
Published: February 2023

We have proposed a Fourier-transform spectrometer that uses a multichannel detector and a shearing interferometer.1,2 Because this type of spectrometer contains no moving parts, it has many potential applications, including use as a compact sensor for field use and for time-resolved spectroscopy. In this paper, we present another version of multichannel Fourier-transform spectrometer. In this spectrometer, the radiation to be analyzed is split by a Savart-plate (a birefringent-prism combination) into two beams, and the two beams are recombined on the array detector, where they form forming an interference fringe (interferogram). The interferogram is electronically scanned (read out) and is Fourier-transformed in a computer to reconstruct the spectrum. Because these optics form a source-doubling Fourier transform, the extent of sample/source does not reduce the fringe visibility. As a result, a large field of view is attained. The optical system of the developed spectrometer is compact and stable, and it is easily aligned because of the in-line optical arrangement of the interferometer, which uses only one Fourier-transform lens. The optical system is about 200 mm long uses a Rutile Savart-plate (15 × 15 × 15 mm3). Experimental results of near-infrared defuse-reflectance spectra will be shown for several samples.
Fourier-transform emission spectroscopy
Authors: Frum C. I. , Engleman R. , Bernath P. F.
Published: February 2023

The vibration-rotation spectrum of silicon monosulfide, an important astrophysical molecule, has been observed in emission between 640 and 800 cm–1 using the Fourier-transform spectrometer associated with the McMath Solar Telescope at Kitt Peak. Gas-phase SiS was produced by the reaction of solid silicon with silicon disulfide, SiS2, in an alumina heat pipe oven. More than 2400 lines were assigned to four isotopomers (28Si32S, 28Si34S, 29Si32S and 30Si32S). The data for all the isotopomers series were fitted together using the mass-reduced Dunham expression including Watson's Born-Oppenheimer breakdown coefficients. The infrared spectrum of the antisymmetric stretching mode, v3, of BeF2 has been observed in emission near 1530 cm-1. Gas-phase BeF2 was produced by heating solid beryllium difluoride to about 800°C in a heat pipe oven. The spectra were recorded at a resolution of 0.005 cm–1 using a KC1 beam splitter and Si:As detectors.
Design overview of the high-resolution imaging spectrometer
Authors: Smith S. Terese
Published: February 2023

The newly emerging field of imaging spectrometry is driving the interest for remote sensing instruments that image the Earth's surface in contiguous spectral bands. The High Resolution Imaging Spectrometer (HIRIS) is a facility instrument for "Mission to Planet Earth" and will be flown on the first of NASA's Earth Observing System (EOS) platforms. HIRIS is a pointable instrument and images the surface of the Earth with 30 m nominal spatial sampling. The instrument disperses light by use of prisms to obtain 10 nm nominal spectral sampling from 0.4 mm to 2.45 mm. The instrument requirements are discussed. The baseline optical design and the trade-offs made in arriving at that design are presented. This publication was prepared by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.
Novel diode-pumping schemes for near-IR rare-earth lasers
Authors: Esterowitz Leon , Stoneman Robert C. , Rosenblatt Gregg H.
Published: February 2023

Solid-state lasers are being considered for an increasing number of applications in which the laser radiation would be directed over inhabited regions. Eyesafe lasers such as the Raman shifted Nd 1.06 µm or the Er 1.5 µm have therefore received much attention recently. In this talk we will consider two interesting alternatives to such eyesafe laser systems. Both of these systems utilize thulium as the active laser ion in which the lower laser level is an excited state. The Tm3+ 3H4 3F4 transition at 1.5µm, however, is normally self-terminating due to the long lower level lifetime (-10 ms) relative to the upper level lifetime (-1 ms). As a result CW laser emission can only be obtained by depopulating the 3F4 level. This has been done in two systems: 1) a Tm, Ho:YLF crystal in which energy is transferred from the Tm ion to the Ho ion, which is then lased at 2 µm and 2) a Tm, Tb:YLF crystal in which a cross-relaxation process between the Tm and Tb ions depopulates the Tm 3F4 level without requiring a cascade laser process. These four level CW lasing schemes can also provide tunable CW operation and may provide other advantages over three level eyesafe laser systems.
Effects of scattering on photorefractive dynamics
Authors: Maniloff Eric S. , Johnson Kristina M.
Published: February 2023

Because of their high angular selectivities and diffraction efficiencies, photorefractive crystals are attractive media for implementing many optical-computing architectures. The temporal dynamics of the photorefractive effect must be understood before successful implementations of computing architectures using photorefractive multiplexed holograms can be realized. Previous theoretical analyses of the photorefractive effect have not taken losses into account. These losses result from absorption and/or scattering effects. When recording holograms in photorefractive lithium niobate, scattering is frequently a major effect, and the scattered power may exceed the diffracted power. It is therefore impossible to accurately match experimentaland theoretical results without including scattering in the theoretical analysis. Experimental investigations have monitored the dynamics of both the diffraction efficiency and the losses during the recording process in iron-doped lithium niobate crystals. After the dependence of the loss on the recording time is measured, a theoretical fit to the recording and erasure dynamics for single holograms may be accomplished. Our results will be presented and discussed, along with their influence on the recording of multiplexed holograms.
Optical coatings with radially controlled reflection intensity and phase shift
Authors: Emiliani Gabriele , Piegari Angela
Published: February 2023

An interesting application of optical coatings in the laser field requires cavity mirrors with a particular reflectance profile (i.e., a Gaussian profile) along the coating radius. However, these devices generally introduce a phase distortion in the wave front of the laser beam. Real improvement in laser performance depends on controlling both the reflection intensity and phase profile. Traditional design procedures and thin-film deposition techniques are aimed at producing coatings with defined reflectance values at different wavelengths but uniform reflectance on the coating surface. In this work, the reflection and transmission intensity and phase at a single wavelength are examined, and a suitable design method for obtaining desired radial profiles is proposed. The phase front is generally required to be flat along the radius while, at the same time, the reflection intensity either decreases continuously from the coating center to the outside or has a jump at a particular radius value. Such performances are obtained with thin-film multilayer coatings in which one of the layers has a profiled thickness. This radially variable thickness is achieved by the aid of a properly shaped mask in a sputtering deposition apparatus. Coatings for Nd:YAG and CO2 lasers are examined.
Deposition of optical multilayer coatings with automatic error compensation: I. Theoretical description
Authors: Sullivan Brian T. , Dobrowolski J. A.
Published: February 2023

The manufacture of complicated optical coatings can be a challenge when they consist of many layers of unequal thicknesses and when the deposition technique employed does not produce dense layers. Errors in the deposited layers can lead to a complete breakdown of the monitoring of subsequent layers. The best chance of success is with a process in which the construction parameters of layers are evaluated as soon as the lasers are deposited and in which the construction parameters of the remaining layers are then reoptimized to compensate for any errors that are made. This paper describes a versatile program developed at the National Research Council of Canada for calculations on systems composed of dielectric and absorbing (porous) films and fot the real-time control of their manufacture. For porous layers, an effective-medium theory is used to model the optical constants in vacuum and in air. In the simulation mode of the program, random errors are applied to the construction parameters of the layers. The best monitoring strategy for the manufacture of a given multilayer is established on the basis of statistical information obtained from a number of these simulations. In this paper, the results of calculations on the effectiveness of various monitoring strategies will be presented for several different multilayers. The interfacing of the program with the deposition equipment and the experimental results obtained will be the subject of another paper.
Rod contributions to peripheral red–green color discrimination
Authors: Nagy Allen L. , Doyal Jeffrey
Published: February 2023

We have compared color discrimination thresholds for long-wavelength spectral lights presented to the fovea and to the peripheral retina. Results obtained in the fovea are similar to those obtained by other investigators. Threshold increases as the test wavelength is increased. The slope of the threshold-versus-wavelength function decreases as the stimulus field is moved further into the periphery. Peripheral thresholds are significantly higher on a blue background bright enough to desensitize rods, but they are not bright enough to raise foveal thresholds, suggesting that rod signals contribute to the peripheral thresholds. However, the shapes of the threshold-versus-wavelength functions obtained on the background differ in the fovea and the periphery, suggesting that differences between foveal and peripheral functions are not produced entirely by rods. Foveal and peripheral functions are similar in shape if the peripheral thresholds are obtained with a larger test field.
Effect of stimulus size on the detection of complementary colors
Authors: Iivanainen Antti , Rovamo Jyrki
Published: February 2023

We studied how much desaturating color had to be added to blue or red in order to perceive complementary color, i.e., yellow or blue–green, respectively. Thresholds were measured in an eye preadapted to blue or red at eccentricities of 0–15° in the nasal visual field. The CIE chromaticity coordinates of blue or red were subtracted from the chromaticity coordinates corresponding to the complementary color thresholds to obtain the threshold differences (dx, dy) in chromaticity coordinates. With constant stimulus size, dx and dy decreased for both colors when eccentricity increased, indicating that thresholds decreased with increasing eccentricity for a constant size stimulus. When the stimulus was M-scaled by reducing its size toward the fovea in inverse proportion to ganglion-cell sampling density, dx and dy were independent of eccentricity for blue, except in the fovea, where more desaturating color was needed. For red color, M-scaling failed to make dx and dy independent of eccentricity at any eccentricity tested.
Polymer films for three-dimensional memory applications
Authors: Haskal Haim M. , Connolly James J.
Published: February 2023

We report the recording of holographic relief gratings in dye-in-polymer films previously developed for optical disk applications.1 Recording was performed with a frequency-doubled Q-switched Nd:YAG laser in a Mach–Zehnder interferometer configuration. Efficiencies in the first diffraction order of 3–4.5% were obtained. Strong diffraction into the second order was observed, which indicates a nonsinusoidal grating profile. We monitored grating formation during writing by means of an auxiliary He—Ne laser. The grating starts forming rapidly after the application of the laser pulse. Diffraction then reaches a maximum, after which the polymer cools off and relaxes to form a permanent grating. The polymer film can be used as the building block for a stratified-volume holographic medium.2 We have studied by computer simulation the storage capability of the artificial three-dimensional memory medium. The discrete nature of the medium leads to a multiplicity of Bragg angles in which the separation between peaks is dictated by the interlayer distance, and the width of the peaks is dictated by the overall structure thickness. The number of multiplexed holograms that can be stored and read out unambiguously in a three-dimensional memory application is equal to the number of layers in the structure.
Refractive solution for a diffraction-free beam
Authors: Thewes Ken , Karim Mohammad A. , Awwal Abdul Ahad S.
Published: February 2023

Diffraction-free beam will alleviate the problems of beam spreading when the energy of beam is being transferred to a target. Recently, Durnin1 has shown that a Bessel beam can propagate in a diffraction-free mode. A holographically generated diffraction-free beam suffers loss because of its limited efficiency. Refractive systems have already been designed for circularly Gaussian to circularly uniform2 and annularly Gaussian to circularly uniform beam transformation. By using a similar approach, we designed a refracting system capable of transforming a circularly Gaussian laser beam to a Bessel beam with almost unity efficiency. The surface slope, radii of curvature and other important parameters are optimized for ease of fabrication.
Saturation of chromatic increments on intense achromatic backgrounds
Authors: Drum Bruce , Sternheim Charles E.
Published: February 2023

Drum1 measured threshold-versus-adapting-intensity (TVI) functions for chromatic increments on achromatic backgrounds. The TVI slopes became greater than unity at background levels above 4 log trolands (log td) for stimulus wavelengths across the visible spectrum. Because only one background level above 4 log td was tested, however, the detailed shapes of the curves and the full extent of the steepening could not be resolved. We now report more detailed TVI measurements at four test wavelengths (430, 490, 575, and 660 nm) and background illuminances at 0.2 log-unit intervals from 4.0 log td to 5.6 log td. Foveal, 2° diameter test stimuli were presented for 1 s on a concentric, perceptually white (5128 K color temperature), 7° diameter, steady background. Thresholds were obtained by the method of adjustment, after which the test stimulus illuminances were increased 0.6 log-unit and the subject estimated the percentages of red, yellow, green, blue, and white. Average TVI slopes for two subjects were 2.75 for 430 nm, 1.55 for 490 nm, 1.15 for 575 nm, and 1.4 for 660 nm, which is in qualitative agreement with published estimates of the ratio of chromatic to achromatic sensitivity. Also, the percentage of white apparent in the suprathreshold increments generally increased with increasing background illuminance despite substantial increases in excitation purity. These findings imply that steady, intense achromatic backgrounds can produce response saturation in color-oppo-nent mechanisms.
Color appearance in peripheral retina: effects of white surround on size scale
Authors: Abramov Israel , Gordon James , Chan Hoover
Published: February 2023

Hue and saturation scaling were used to measure the appearance of spectral lights as a function of stimulus size at loci spaced across the horizontal meridian. At a given locus, each hue (red, yellow, green, and blue) grew as a function of stimulus size up to some asymptotic value. Growth functions fitted to the hue data were used to derive the sizes of the "perceptive fields" of the hue mechanisms. We had previously investigated the size-scales of these fields by using stimuli presented on a dark background: Field sizes for all mechanisms increased with eccentricity, this increase was greater on the temporal than on the nasal retina, and the retinal size-scales of the different hue mechanisms were not the same. We now report the results obtained from repeating the study with stimuli embedded in a white surround. The main effects of the white surround were as follows: Sizes of perceptive fields of all mechanisms decreased at all peripheral loci, apparent saturation decreased for foveal stimuli but increased for peripheral stimuli, and short-wavelength redness increased everywhere.
Investigation of the cryogenic distortion of beryllium mirrors
Authors: Gossett Ernest W.
Published: February 2023

The 0.5 m consortium mirror, which was fabricated as a solid and tested to 100 K1, has been lightweighted and retested to 20 K. The mirror was machine lightweighted to 80% of a solid with an areal density of 23 kg/m. The light-weighted mirror displayed a distortion pattern reminicent of the raw material processing, the same as seen in the solid. The BRDF was measured at 0.5145 and 3.39 μm to 0.5° and at 10.6 μm to 3°.
Three-dimensional stacked-layer optical memory using electron-trapping materials
Authors: Jutamulia Suganda , Storti George M. , Seiderman William , Lindmayer Joseph
Published: February 2023

Electron-trapping (ET) materials are optical storage materials developed by Quantex. When ET materials are exposed to visible light (e.g., 488 nm), electrons from the ground state will be excited and then captured by thermally stable traps. Subsequent exposure to IR light (e.g., 1064 nm) excites and releases the trapped electrons to the ground state with the emission of orange-to-red light. We have investigated a new architecture that is based on a stacked layer scheme. In this architecture, a two-dimensional page memory is individually stored in a particular ET layer by means of visible light. The layer can be selectively read by using IR light. In contrast to the volume holographic approach, the two-dimensional emission from the ET layer is directly detected as the recalled page memory. The page memory can be written by properly imaging the page composer onto a specific layer with blue laser light at 488 nm. To read out the memory on a specific layer, a slice of 1064 nm IR beam is addressed into the ET layer from the side of the stacked-layer medium. The orange emission (630 nm) corresponding to the written page memory at that layer is emitted as a result of the IR stimulation.
Absolute phasing of segmented mirrors
Authors: Ruquist Richard
Published: February 2023

Very large space-borne telescopes have primary mirrors made of several independent segments that must be aligned to a fraction of a wavelength for optimum performance. All proposed solutions for such phase alignment appear to have some limitations. For example, gradient (tilt) sensors may control the figure of each individual segment but are insensitive to piston error between segments, whereas complementary segment-to-segment edge capacitance gauges can eliminate piston error but require absolute calibration. We show that absolute calibration of the mirror segments may be achieved by optimizing the intensity of the focused light, if the initial errors are less than about one wavelength. Implementation requires computer processing of a time series of focal-plane, single-detector intensity measurements as the various segments are dithered. The key issue addressed in this paper is that all numerical optimization techniques yield local optima rather than global optima, and numerical methods for distinguishing one from the other do not exist. We find that a comparison of the optimized focal-plane intensity or Strehl ratio for wide and narrow light spectra may be used to distinguish local and global optima and may provide a means to scan through local optima to reach the global solution.
The influence of a λ/4-plate location in a laser oscillator/amplifier system with a phase-conjugate mirror
Authors: Kuo Yung-Sheng , McIver John K.
Published: February 2023

The use of a phase-conjugate mirror in a double-pass oscillator/amplifier laser system has received a lot of attention because the phase-conjugate mirror can correct some of the optical aberrations introduced by the laser amplifier. To reduce the feedback of the amplified pulse to the oscillator, an optical isolator must be used. A commonly used isolation system is the combination of a λ/4 plate and a linear polarizer. Because the amplifier rod(s) often has thermally induced birefringence, the amount of feedback will depend on the location of the λ/4 plate. We observed that the feedback is smaller when the λ/4 plate is located in front of the amplifier system (two Nd:YAG rods) than when it is behind the amplifier system. A matrix theory describing the birefringent effect is developed to explain the experimental result. The ratio of feedback intensities corresponding to the λ/4 plate's being behind versus being in front of the amplifiers depends on the ratio of the depolarization coefficient to the linear-polarized amplification coefficient.
Modal properties of nonlinear parabolic graded-index optical guides
Authors: Gagnon L. , Paré C.
Published: February 2023

We study the propagation modes in nonlinear planar and circular media that have a transverse parabolic index profile.1 The first mode profiles, as well as their dispersion curves, are calculated numerically. In particular, one observes a splitting of some linear degenerate modes and cutoff of nonlinear modes because of self-focusing limits. A numerical scheme (beam propagation method) is also used to study near-modal propagation under the paraxial approximation. Those results are compared with an approximate analytical calculation based on the variational principle.2 This approach is not limited to small nonlinearities; it describes quite well the amplitude-dependent quasiperiodic propagation observed numerically. Furthermore, it reproduces the modal dispersion curves in a simple way. These results can also be applied to the study of nonlinear radiation modes of the free three-dimensional paraxial wave equation.
Response of a self-pumped phase-conjugate mirror for two mutually coherent inputs
Authors: Honda T. , Matsumoto H.
Published: February 2023

Photorefractive self-pumped phase conjugation is attractive for its simplicity and high reflectivity with low-power light sources. In order to realize its potential applications, it is important to study its response. So far the response of a phase-conjugate wave has been described with its rise time. It has not studied how the phase-conjugate wave responds when the spatial structure of an input probe wave is changed dynamically. We investigated the response of the phase conjugate wave by using two mutually coherent input beams, which can be regarded as components of a probe wave, and by introducing sinusoidal phase changes into one of them with varied frequencies. Each input beam has a power of 6 mW at the wavelength of 515 nm. A BaTiO3 crystal was employed as a self-pumped phase-conjugate mirror.1 By measuring relative phase between the two output beams, which can be regarded as components of a phase-conjugate wave, we found the response characteristic represented by a time-lag of first order, which is similar to RC circuit. The response time thus determined was 0.32 s, which was much shorter than the rise time of 30 s obtained with the same condition.
Nonlinear-optical response in suspensions of organic and inorganic colloidal systems
Authors: Schuster P. R. , Viands C. A. , Potember R. S.
Published: February 2023

The third-order nonlinear optical response of various colloidal suspensions has been investigated. The transmissive properties of these systems are of particular interest in terms of the speed of the switching response, the switching threshold, the recovery time, and the dynamic range over which optical density is generated. We have seen resonant and non-resonant behavior in the nonlinear response of these materials. These suspensions are composed of both inorganic and organic materials homogeneously distributed within a dielectric matrix. In certain studies, these materials have been synthesized as charge-transfer complexes by using an inorganic electron donor combined with an organic electron acceptor. Our results concerning the third-order nonlinear optical properties of these materials; our development of methods for the enhancement of their nonlinear optical response will also be reported.
Efficient coupling of multiple diode laser arrays to an optical fiber
Authors: Fan T. T.
Published: February 2023

Diode lasers are efficient sources of laser radiation, but their coupling to an optical fiber has been limited to applications that require low power. Here we demonstrate that three high-power diode lasers can be coupled with high efficiency into a single multimode optical fiber by geometric multiplexing. In principle, many more diodes could be used and tens of watts of power could be obtained from a single fiber with incoherent multiplediode input. We have coupled three highpower diode arrays to a 200 µm core, 0.2 N.A. optical fiber with 59% efficiency and have obtained 700 mW at the output of the fiber for 1.19 W at the input. Based on the properties of the beams from these high-power diode laser sources, it should be possible to efficiently couple over 100 of these lasers to this optical fiber and obtain tens of watts of deliverable power. Calculations show that the number of identical sources that can be efficiently coupled to an optical fiber is proportional to the square of the product of the core diameter and numerical aperture.
Femtosecond group-velocity dispersion in optics
Authors: Takiguchi Yoshihiro , Alfano R. R.
Published: February 2023

Group velocity dispersion (GVD) is a well-known phenomenon that causes pulse broadening of femtosecond pulses propagating through dispersive materials. Femtosecond spectroscopy is becoming commonplace, and one must consider the effect of GVD in optical components such as mirrors, lenses, prisms, glass plates, glass cells, dielectric-coated mirrors, nonlinear crystals, liquid samples, solid samples, and detectors, each of which shows GVD effects. In this presentation, broadening effects are numerically calculated for GVD in various optical components by means of the Drude refractive-index model. Beam trajectories in various optical components, such as lenses and prisms, are simulated to evaluate the material thickness, which determines the broadening. For example, the ratio of duration times between the incident pulse tin and the output pulse tout through a dispersive plate is calculated from (tout/tin)2 = 1+(BL/tin2)2, where B is a coefficient that depends on material characteristics and L is the thickness of the plate. For a 1 mm thick BK7 glass plate, a 10 fs laser pulse at 600 nm will broaden to be 22.83 fs with B = 2.052 × 10–25. Even a 100 µm thick KDP nonlinear crystal broadens a 10 fs pulse to 10.21 fs. Details of femtosecond pulse broadening will be presented for lenses, prisms, water, and air.
Distributed three-dimensional computers based on holographic single-mode interconnects
Authors: Jannson Tomasz , Jannson Joanna , Lin Freddie
Published: February 2023

The recent intense interest in highly parallel optical interconnects in the United States, Europe, and Japan has been stimulated by the recent trend toward increasing the integration between very-large-scale integrated electronics and optics in order to implement high-bandwidth and high-speed processing/storage density. This is particularly important in highly distributed three-dimensional computer architectures, where massive parallelism is required at the processor level. Conventional electric interconnects can only be of a local nature and can only have low parallelism. In the area of highly distributed three-dimensional architecture, POC has demonstrated the first integration of single-mode, glass integrated optics with multiplexed volume holoplanar (waveguide) gratings1,2 and volume total-internal-reflection holographic couplers (making use of a 1:4:8 optical bus and 1:32 fan-out). In this article, we discuss the hardware aspects of the optical interconnect, which uses multiplexed planar holograms.3 Component issues (laser sources, modulators, switches, interconnects, detectors, waveguides, and couplers) and system issues (power budget, bandwidth, wavelength sensitivity, and reconfigurability) are particularly important.
Space-invariant optical fan-out components for large-array generation
Authors: Taghizadeh M. R. , Turunen J. , Miller J. M. , Vasara A. , Westerholm J.
Published: February 2023

Space-invariant holographic fan-out elements are important in most parallel optical processing and computing networks: These components can, for example, deliver biasing power for an array of optically bistable logic gates and can supply an array of point sources in the input plane of any space-variant interconnect. The primary figures of merit characterizing the performance of any optical-array generator are the diffraction efficiency and the array uniformity (reconstruction error). When the number of beams in the array is large, the size of the smallest feature becomes an important fabrication consideration. Using these figures of merit, we compare the performance of different binary-phase (Dammann grating) and multiple-phase kinoform Fourier-domain holograms generating large beam arrays. The fabrication tolerances of Dammann gratings and kinoforms are evaluated by a statistical approach, and a technique for maximizing the minimum feature size in the structure of Dammann gratings is discussed. The latter is important not only as a fabrication consideration but also because Fourier optics can be expected to fail if features smaller than about 5λ are present. Experimental results are presented on the largest space-invariant array generators reported so far: a conventional 201 × 201 beam Dammann grating, a modified 128 × 128 Dammann grating, and a 32 × 32 kinoform.