bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity discrimination on simple and complex backgrounds predicted by a gradient model
Authors: Lawton Teri B. , Ramirez Carlos , Koch Christof
Published: February 2023

Correlation and gradient models predict different responses to moving sine gratings of varying contrasts. For small contrast values, correlation models predict a quadratic dependence of velocity discrimination on contrast, whereas for gradient models velocity discrimination is independent of contrast. Drifting sine gratings that optimally activated the movement detection system were used to determine the temporal frequency needed to see drifting test gratings moving faster than a comparison sine grating of the same spatial frequency. The contrast of the gratings was varied between 1 and 20%. The temporal frequency was varied between 5 and 20 cycles/s. The spatial frequency of test and comparison patterns varied from 0.5 to 8 cycles/deg in 1-octave intervals. Test and comparison patterns were presented for 200 ms with a 500-ms interval using a temporal two-alternative forced-choice procedure. For 15–20 cycles/s, where flicker and not left–right movement was seen, there was some dependence on contrast. These results were found for velocity discrimination relative to backgrounds composed of either uniform mean luminance or single- or multiple-spatial-frequency components. Velocity discrimination thresholds are in agreement with the gradient model of movement discrimination but do not support simple correlationlike models. However, by normalizing the output of the spatiotemporal models approximately, a contrast-independent measure of velocity can be derived. These results can be predicted by neural networks composed of the paired even- and odd-symmetric simple and complex cells found in magnocellular pathways.
Links in acoustooptics: past to future
Authors: Korpel Adrianus
Published: February 2023

In perhaps no other field than acoustooptics have so many concepts been rediscovered and so many devices reinvented. The reason for this is that, with the appearance of the laser, acoustooptics suddenly changed from an esoteric mathematics discipline into a relevant engineering technology. In the rush to exploit useful applications, ranging from beam deflectors to signal processors, it was often easier—and always more exciting—to reinvent new devices rather than read old articles. Also, mathematics had dressed the once earthy body of acoustooptics with layer on layer of increasingly frivolous theories that applied to decreasingly realistic models. It, therefore, often made good sense to start all over again guided by physical intuition. Unavoidably then, many concepts were rediscovered, such as the Debye-Sears wave vector diagram of phase synchronous interaction, Brillouin’s rescattering interpretation of multiple orders, and Van Cittert’s cascaded grating approach to strong interaction. As regards experiments, devices, and systems, a similar situation developed, as exemplified by the repeat (along modern lines) of Ali’s frequency shift measurement, the reemergence of the Scophony system of TV display, and the rediscovery of Ocolicsanyi’s highly original ideas about signal processing. I trace some of the links that connect present-day acoustooptic theory and practice to the past and speculate on how they may extend into the future.
Acoustooptic technique for beam scanning and beam formation In phased array radars
Authors: Riza Nabeel A. , Psaltis Demetri
Published: February 2023

This paper introduces an optical technique for generation of phased array antenna drive signals for single and continuous mode beam scanning and beam formation. An optical system using two acoustooptic devices, imaging optics, and an array of high-speed detectors is used to generate the correctly phased signals. The required phase change on each detector is brought about by a frequency change in the acoustoptic device drive signal, which in turn maps frequency changes to changes in angular deflections. This results in a spatial frequency change on the detector plane. The detector array samples the generated phase distribution to produce the driving currents for the antenna elements. The Doppler shift in the acoustooptic interaction in the Bragg cells is used to produce the high-frequency carrier signal for the rf antennas. The use of optics eliminates expensive and bulky microwave frequency mixers. This processor can be operated up to a 10-GHz radar carrier frequency and provides system advantages such as single-parameter scan control, multiple-beam scanning, graceful degradation of antenna beam pattern with component failure, small-system losses, low-power requirements, and small size. The processor can be built in either bulk or integrated forms.
Effects of crosstalk in multichannel acoustooptic Bragg cells on optical signal processors
Authors: Lin Shih-Chun , Boughton R. Scott
Published: February 2023

Multichannel acoustooptic Bragg cells have been proposed for correlation, spectrum analysis, phased array signal processing, and optical computing. Concerns were expressed on the effects of crosstalk in the multichannel Bragg cells due to acoustic spreading and rf interference on the systems performance. We have evaluated several high-performance multichannel TeO2 Bragg cells to determine their suitability for our advanced hybrid optical signal processing needs. Crosstalk, among other parameters, was measured and found to be around −30 dB. We report our recent measurements of the effects of the crosstalk of these multichannel TeO2 Bragg cells on multichannel AO correlators, convolvers, and spectrum analyzers, which form the basic building blocks for some advanced architectures. Experiments were done on a coherent space-integrating correlator that was used for broadband beam forming and a similar convolver for digital multiplication by analog convolution. Results showed that the signal in a quiescent channel due to crosstalk from the neighboring activated channel were significant and could cause false alarm and bit errors. Experiments with an AO rf spectrum analyzer also showed significant extraneous spectral components due to crosstalk from neighboring channels. Details of the study are presented.
Light-Induced scattering in photorefractive crystals
Authors: Kebin Xu , Haiying Xu , Jing Hong
Published: February 2023

We discuss the scattering induced by the photorefractive crystals Fe:LİNbO3 and BaTiOa, both theoretically and experimentally.
Measurement of the photorefractive phase shift using two-beam coupling
Authors: Cudney R. S. , Bacher G. D. , Pierce Robert M. , Feinberg Jack
Published: February 2023

When two coherent plane waves interfere within a photorefractive crystal, the resulting periodic intensity pattern causes a periodic modulation of the refractive index of the crystal. For the case of purely diffusive transport of the photorefractive charges, there is a Δϕ = 90° phase shift between the intensity pattern and the refractive-index pattern. However, if there is any externally applied or internally generated (by the photovoltaic effect, for example) dc electric field in the crystal, the phase shift Δϕ will differ from 90°. We present a method for accurately determining the phase shift Δϕ and thereby the magnitude of any dc electric fields inside the photorefractive crystal. We use two- beam coupling in the crystal to deplete an already weak probe beam by an intense pump beam. The phase of the probe beam is weakly modulated sinusoidally at a frequency ω, causing a variation in the transmitted intensity of the probe beam. By measuring the ratio of the ω and 2ω components of the transmitted beam, the phase shift Δϕ may be obtained.1 We use this technique to measure the steady state and time-evolving phase shift Δϕ in barium titanate and lithium niobate crystals.
Spatial light modulation using two-wave mixing properties of photorefractive materials
Authors: Gilbreath G. C. , Davidson F. M.
Published: February 2023

A design is presented which combines concepts of 2-D spatial light modulation with photorefractive coupling for a subsystem applicable to optical communications. Laser diodes are the transmitters of choice in laser spacecraft communications. However, the outputs from these devices are not directly usable in that massive bulky conventional optics are required to correct and direct a given beam. Furthermore, beam characteristics change with time and in some applications, due to channel effects, affecting SNRs and overall system efficiencies. Hence a means to not only replace heavy bulky optics with lightweight optical elements but to modify these optics in situ in real time is highly desirable.
Optical constants for various rough silver thin films
Authors: Varnier Francoise , Mayani Nicole , Rasigni Georges
Published: February 2023

The surface structure characterization our team has developed for several years (based on microdensitometer analysis of shadowed surface replicas) proved to be very powerful in topography restitution and in determination of statistical parameters (surface roughness rms height, autocovariance length) of any microrough surface, such as thin evaporated films. An extensive surface roughness investigation of silver films evaporated on various fluoride undercoatings was achieved. Then, a set of those statistical parameters connected with silver films is available, the values of which lie in a very large range. In addition, the optical properties of those silver films were determined. Those results allowed us to study the silver film optical constants’ values vs the film’s statistical parameters. It is then possible to deduce the optical constants of a thin silver film when its roughness approaches zero. Moreover, the dip in the optical reflectance near the surface plasmon energy was measured and related to the statistical roughness parameters of the deposit.
Measurements of absorption losses in TIO2 films by a collinear photothermal deflection technique
Authors: Commandre M. , Pelletier E.
Published: February 2023

We review the principle of photothermal deflection for measuring absorption losses in TiO2 films. A collinear arrangement gives the best sensitivity for the detection of losses in a low absorbing film deposited on a transparent substrate. The nineteen TiO2 films produced by seven different processes (electron-beam evaporation, ion assisted deposition, ion beam sputtering, ion plating) of the 1986 OSA Annual Meeting are measured by this technique. The extinction coefficients of the different films do not show obvious correlation with the deposition method. An important fact is that we have detected a variation in absorption as a function of time on some layers. This absorption shift is connected with the illumination conditions of the sample under study (wavelength, 600 nm; incident power, 750 W/cm2). Experimental results over time are given. The evolution of the photothermal signal is very different from one sample to another. This phenomenon is partially reversible and can be modified by annealing.
New mirror absorption measurement technique using substrate surface deformation
Authors: Webb Jeffrey I. , Wieman Carl E. , Anderson Dana Z.
Published: February 2023

The absorption of a mirror coating can be measured by observing the frequency shift and mode coupling In a resonator. These changes are caused by deformation of the mirror substrate as the light energy is absorbed. We model the substrate as a right circular cylinder and consider only expansion in the length of the cylinder, as expansion in the radial direction is small compared to the laser spot size. The deformations of both a uniform absorption across the surface of the mirror as well as a point absorption are computed analytically. The frequency shift and mode coupling of a cavity with one of the deformed mirrors are calculated by perturbation techniques, and the findings are compared with experimental results using high-finesse power buildup cavities. For 1 W incident on a resonator with BK7 mirror substrates, a finesse of 3000, 10-ppm absorption, and a 0.4-rhm spot size, we calculate a maximum deformation of 120 Å. For a Zerodur substrate in the same conditions, the lower thermal expansion coefficient reduces the deformation to 1.7 Å.
Performance characteristics of coherent 2-D grating surface emitting diode laser arrays
Authors: Carlson Nils , Evans G. A. , Amantea R. , Palfrey S. L. , Hammer J. M. , Lurie M. , Carr L. A. , Hawrylo F. Z. , James E. A. , Kaiser C. J. , Kirk J. B. , Reichert W. F.
Published: February 2023

The power-current characteristics and efficiencies of coherent two dimensional n × 10 grating surface emitting surface emitting diode laser arrays have been experimentally measured as a function of n. the number of Injection-coupled sections in the array. It has been found that the threshold current density as n increases.
Microchannel heat sinks and microlens arrays for high-average-power diode laser arrays
Authors: Walpole James N. , Liali Z. L. , Diadiuk V. , Missaggia L. J.
Published: February 2023

To utilize effectively large-scale monolithic 2-D arrays of diode lasers for high average output power, microchannel heat sinks and microlens arrays are needed. The heat sinks are required to dissipate heat loads of several hundred W/cm2, while the microlenses permit collection and concentration of the array output for optical pumping of solidstate lasers and improve the till factor (and hence the beam pattern) in coherent operation of arrays.
Single-lobed operation of gain-guided laser diode arrays
Authors: Stone R. E. , Gacusan L. Z. , Wang S. C.
Published: February 2023

High-power phased array laser diodes typically emit multilobed far-field patterns. For many practical applications, a single-lobed diffraction-limited far-field beam pattern is most desired. Various schemes1,2 have been used to modify the multi-lobed far-field pattern into a single lobe.
Spectral properties of cancerous and normal human breast and lung tissues
Authors: Tang G. C. , Pradhan A. , Wenling S. , Alfano R. R.
Published: February 2023

Transient state, excitation spectra, and time- resolved spectroscopic dynamics from normal and cancerous human breast and lung tissues have been studied and are presented. The spectral profiles obtained from samples excited with the second and third harmonic of a picosecond pulse Nd:glass laser were different for normal and cancerous tissues. The main peaks at ~450 nm were shifted, while the subsidiary peaks of normal tissues smoothed out in the cancerous tissues with less structure. The excitation spectra for the three different emission wavelengths at 520, 550, and 600 nm corresponding to the three peaks in the normal tissue fluorescence spectra were measured. The overall excitation spectra showed broad UV and visible bands with differences between the cancerous and normal tissues. The dynamic profiles of the fluorescence spectra were measured using photoexcitation by 350- and 530 nm light from a picosecond pulse Nd:glass laser and a streak camera detection system. The kinetic profiles showed faster decay times for the cancerous tissues compared with normal tissues. The spectroscopic differences were attributed to changes in flavins, porphyrins, and the surrounding media.
Modeling reflectance changes during retinal photocoagulation
Authors: Pflibsen Kent P.
Published: February 2023

A model for retinal laser photocoagulation dosimetry has been developed in which a fundus reflectance and a thermal damage model have been coupled together. The fundus reflectance model utilizes two reflecting layers in the fundus anterior to the choriocapillaris, Lambert-Beer’s law attenuators for the ocular media, retinal pigment epithelium (RPE), and choriocapillaris, a Kubelka-Munk homogeneous scatterer/absorber for the choroid, and a reflecting layer for the sclera.1 The thermal damage model contains a light propagation routine, a thermal diffusion routine, and a rate description of the thermal damage process. The interface between these two models incorporates a third model in which light scattering by fundus tissues changes as a function of the predicted volume of damaged tissue.
Photorefractive crossbar switching applied to associative memories
Authors: Wilde Jeff , Hesselink Lambertus
Published: February 2023

Recent interest in neural network models for parallel distributed processing is stimulating much interest within the optics community, in particular, on the feasibility of optical associative memories.1 We illustrate how a set of spatially multiplexed volume holograms recorded in a photorefractive crystal constitutes an optical crossbar switch that globally interconnects a two-layer neural network.2 We focus on the use of the network to provide associative memory and show that the mathematical operations involved in distributed memory storage and recall can be optically implemented in a very natural fashion within the framework of photorefractive holography. These operations include vector outer products, linear combinations of outer-product matrices, and matrix-vector multiplication.
Photorefractive crystals as trainable neural network interconnects
Authors: O'Callaghan M. J. , Anderson D. Z.
Published: February 2023

We have performed experimental studies of a hybrid electronic/optical neural network where interconnections are implemented optically using a photorefractive crystal. This system1 consists of a laser, liquid crystal television (LCTV) screen, photorefractive crystal, and CCD light detector array to implement a two-layer feed-forward neural network. A microcomputer reads the CCD array and controls the LCTV. The pixels of the LCTV represent a set of input neurons (which spatially modulate a laser beam). A holographic grating within the crystal forms the neural network interconnections (via diffraction) and the CCD array corresponds to a set of output neurons. The holographic grating is trained using adaline learning, also known as the delta rule.2 A 1-D training image (64 pixels wide) modulates a laser beam which then passes through the crystal. A computer compares the spatial profile of diffracted light seen at the 256-element CCD array with the desired output. A 64-pixel wide corrective image modulates a second laser beam which intersects the first, and the grating evolves in response to the overlapping images. This procedure is repeated many times for each input image to be learned.
Optical neurocomputing using liquid crystal spatial light modulators
Authors: Zhang Ling , Bigner Jack , Cotter Lise , Johnson Kristina M.
Published: February 2023

The significant feature of neurocomputers is their highly interconnected architectures. Fast switching speeds are not essential. Therefore, the devices required to build these computing networks have the design specifications of low-energy dissipation and the need to scale with network size. Nematic and ferroelectric liquid crystals have the characteristics of low switching energy (subpicojoule), large size (commonly used in flat panel displays), and sufficient operating speeds (milliseconds to microseconds).
Total noise and nonclassical states
Authors: Hillery Mark
Published: February 2023

The total noise of a state is the sum of the fluctuations in the real part of the field amplitude and those in the imaginary part. It is a measure of the total fluctuations in the field amplitude and is a minimum for coherent states. Several examples of nonclassical fields are considered, and it is shown that as nonclassical behavior increases so does total noise. For example, total noise increases as a state becomes more squeezed or as the photon statistics become more sub-Poissonian. This result is then generalized by using the concept of nonclassical distance. Nonclassical distance δ is a measure of the extent to which the behavior of a field state differs from that of classical states. A lower bound for the total noise is derived which is an increasing function of δ. This means that the more nonclassical a state is the greater its total noise must be.
Optical Implications of a new quantum correlation result
Authors: Arthurs E. , Goodman M. S.
Published: February 2023

Recent advances, particularly in the area of quantum optics, have caused heightened interest in the fundamental limitations on the achievable accuracy that may be obtained in measuring quantum mechanical systems. We present a quantum correlation result and a noise commutation relation for correlated quantum systems. The measurement of quantum system observables requires the correlation of these micro-observables and the measuring apparatus (usually a macroscopic system). The noise commutation relation is applied to quantum measurements leading to a generalized Heisenberg uncertainty relation. The generalized Heisenberg uncertainty relation yields a lower bound on the inherent unavoidable extra noise in quantum measurements, which is due to the measuring process itself. To indicate the utility of the noise commutation relation, two different applications in optics are discussed. The first, an application of the generalized Heisenberg uncertainty relation, indicates how a model-independent noise limit for balanced homodyne detection can be obtained. Another application is discussed in which the noise commutation relation is applied to develop a model-independent lower bound for the inherent noise of a quantum optical linear amplifier.
Bragg condition for asymmetric dielectric surface-relief gratings
Authors: Moharam M. G.
Published: February 2023

Holographic planar gratings are fabricated by inducing perturbation in the refractive index (permittivity) in the medium. The Bragg condition for slanted or unslanted holographic gratings is given by 2nL cos(ϕ ‒ θ) = λ0, where L is the grating period, ϕ is the slant angle, θ is the angle of incidence measured in the grating medium, λ0 is the free-space wavelength, n is the refractive index of the grating medium neglecting the grating modulation. This approximation is generally valid since the index does not vary through the grating thickness and the index modulation is very small. Surface-relief gratings are fabricated by producing periodic perturbation in the surface of the grating medium. The above Bragg condition may be used for symmetric surface-relief gratings (ϕ = 90) in the form 2L sinθ0 = λ0, where θ0 is the angle of incidence in air. For asymmetric gratings, the average refractive index or permittivity of the grating varies though the grating thickness and is significantly different from the refractive indices of two regions forming the grating. The slant angle of the grating and the grating period needed in the Bragg condition are not defined. In this work, a condition for maximum diffraction efficiency for asymmetric surface-relief gratings is proposed. The predicted angles of incidence for maximum diffraction efficiency for several grating profiles are compared with the exact angles obtained using the rigorous coupled-wave analysis. Satisfactory agreement is shown for both TE and TM polarization for the various grating profiles considered. The proposed condition is shown to be a reliable indicator of the maximum efficiency.
Short-pulse pumping of photoionization driven XUV lasers
Authors: Barty Christopher P. J. , King D. A. , Yin G. Y. , Hahn K. H. , Field J. E. , Young J. F. , Harris Steve E.
Published: February 2023

Utilizing chirped pulse amplification, we have developed a 3-J 15-ps 1.06-μm laser source for the study of XUV lasers. The laser system consists of a Q-switched and mode-locked Nd:YAG oscillator configured to produce 220-ps pulses. The peak of the Q-switched pulse train is attenuated to 2 μJ and focused into a 47-cm single-mode optical fiber. Self-phase modulation in the fiber spectrally broadens and chirps the pulse. The output of the fiber is recollimated and relay imaged through a set of four Nd:YAG and three Nd: glass amplifiers. The narrowband Nd:YAG amplifiers significantly reshape the pulse and limit the output to 3 J in 100 ps. Compression to 15 ps is accomplished by two nearly parallel 1200-groove/mm gratings separated by 14 m. The 6.5- × 8.0-cm beam is focused in a line at ~65° incidence onto a grooved heavy metal target. The resulting plasma-produced soft x rays photoionize the atomic vapor which surrounds the target. With small angle adjustments of the final grating, synchronous traveling-wave pumping is achieved along the line focus. We have observed an increase in the optimum pressure for a small signal gain in the 108.9-nm Xe Auger system commensurate with the decrease in pulse length. Studies of Auger lasers in Cs and Kr and photoionization lasers K and Na are presented.
X-ray holographic microscopy using photoresists
Authors: Jacobsen Chris , Howells Malcolm , Rothman Steve , Kirz Janos , McQuaid Ken
Published: February 2023

Soft x-ray holographic microscopy offers the promise of producing images of hydrated biological specimens at a transverse resolution of a few hundred angstroms.1 Using a soft x-ray undulator National Synchrotron Light Source and a monochromator and spatial filter pinhole, we coherently illuminate our specimen (air-dried rat pancreatic zymogen granules) and recording medium (a photoresist) with 25-A soft x rays.2 By using the Gabor holographic geometry, we are able to bypass the technological difficulties of making high-resolution x-ray optical elements. The processed holograms are enlarged with an electron microscope and digitized, and a reconstructed image is obtained numerically using a computer. In this manner, we obtained images of air-dried rat pancreatic zymogen granules which exhibit sub-1000-A resolution and which yield information not available in 100-keV electron or optical images of similarly prepared specimens.
Reduction in visual science
Authors: Hardin Clyde L.
Published: February 2023

Suppose that we have a complete utopian understanding of the workings of the nervous system. Would we thereby know all that there is to know about subjective sensory experience? It has been maintained that we would not and that although sensory experiences are caused by brain events, they cannot be identical with them. We shall consider three arguments that purport to lead to this conclusion and discover that each of them is defective. It will then be argued that the question of whether sensory experiences are identical with brain events is empirical, to be settled by future science. An affirmative answer requires that the phenomenology be properly regimented and shown to be isomorphic with an appropriate subset of neural processes. Although the realization of these conditions must be regarded as utopian, contemporary visual science has made progress in this direction.
Channel models of vision and the principle of parsimony
Authors: Massof Robert W.
Published: February 2023

There is a plethora of models in vision psychophysics that are of the same class and are designed to account for the results of detection and discrimination experiments in the spatial, temporal, chromatic, and luminance domains. This class of model, called channel models, is captured in the general expression where c1,(t, x, y) is the space-time response of the ith channel, 0[ ] is a space-time operator that reduces c1,(t, x, y) to a space-time constant (e.g., peak detector, power detector), n is a dimensionless parameter derived from the slope of the empirical psychometric function, and d is the threshold for detection or discrimination.
Ultrafast optoelectronics
Authors: Auston David
Published: February 2023

Optoelectronic devices and measurement techniques now operate at speeds ranging from picoseconds to hundreds of femtoseconds, have a dynamic range that extends from microvolts to kilovolts, are virtually jitter-free, and can make measurements in a wide variety of circuits, devices, and materials without requiring direct electrical contacts to the samples under test. This tutorial summarizes recent work on this topic emphasizing the basic device and measurement concepts and the diverse uses in electronics, materials science, and communications.
Progress in electrooptic sampling of highspeed devices and integrated circuits
Authors: Valdmanis J. A.
Published: February 2023

The rapidly increasing speed and complexity of current and future electronic circuitry has in many cases exceeded the capabilities of conventional all-electronic testing techniques. The need for high-speed noninvasive testing of integrated circuits is on us. By turning to optically based techniques, we can exploit the availability of picosecond and subpicosecond laser pulses to make electrical measurements. This paper reviews the latest refinements and applications of the electrooptic sampling technique, which utilizes optical pulses directly as sampling gates in electrooptic materials. It is currently the fastest (<300-fs resolution, >1-THz bandwidth) measurement technique available for electronic circuits and does not require vacuum for operation. Electrooptic sampling can be applied to a wide variety of circuits and devices and, when configured as an optical probe, can noninvasively interrogate internal nodes of complex integrated circuits. We discuss many measurement applications ranging from the basic physics of subpicosecond electrical pulse generation and the high-speed properties of high T
c
superconductors to integrated circuit probing on GaAs, silicon, and ceramic substrates.
Constraints on sensitivity of linear visual neurons
Authors: Watson Andrew B.
Published: February 2023

Many visual neurons linearly combine signals from the receptors or from other cells which themselves form linear combinations of receptor signals. In both cases, if the noise that limits cell performance is confined to the receptors, the peak sensitivity of the cell is entirely determined by the magnitude of the receptor noise and the normalized shape of the cells’ receptive field. This simple result may be used to estimate the receptor noise from the sensitivity of retinal or geniculate cells as well as to predict sensitivity of higher-order cells from that of lower-order cells. Consequences of this constraint are illustrated for actual primate geniculate and cortical cells and for model cortical cells.
Critical analysis of filter models of spatial vision
Authors: Klein Stanley A. , Levi Dennis M.
Published: February 2023

Filter-based models predict the general form of bisection threshold as a function of separation.1,2 Here we examine several limitations of those models. (1) Our old data1 and new densely sampled bisection data showed a single cusp corresponding to separations between 2 and 3 min. Depending on assumptions about the number and spacing of the filters, models predict either too many or too few cusps. (2) Filter models predict the wrong perceived width in certain conditions. Consider a two-line separation judgment in the presence of a cosine grating mask whose spatial frequency is one-half of the nominal spatial frequency of the white line pair and with the lines at the zero crossings surrounding the grating peak. Filter models predict that the perceived separation of the lines will be narrower compared to the perceived separation with an opposite polarity mask. The experimental data, however, show the reverse. (3) Filter models tend to predict separation discrimination thresholds that are, in general, lower than observed. For the viewprint model this is particularly true at wide separations.
Noise gratings recorded by single and double beams in silver halide emulsion
Authors: Riddy G. D. G. , Solymar L.
Published: February 2023

A set of experimental results is presented showing the conversion of an input beam into scattered radiation by noise gratings recorded either by a single beam or by two beams of varying beam ratio. In the latter case the conversion into noise is strongly dependent on whether the angular range of the replay beam is in the vicinity of that of the strong beam or of the weak beam. A previously published theory,1 representing the scattered radiation by a very large number of plane waves and assuming a nondepleted transmitted beam, is generalized. The theory presented is valid for high efficiency but needs a numerical solution of the resulting coupled wave differential equations. Curves for the angular variation of the replay beam are shown both for single-and double-beam recording and compared to the experimental results. The effect of processing the silver halide material is also discussed.
Surface relief holograms and holographic optical elements in sensitized polystyrene
Authors: Sperley K. M. , Schellenberg F. S. , Willson C. G. , Levenson Marc D. , Brock P.
Published: February 2023

Poly(tBOC)styrene is a sensitive (<0.5-mJ/cm2) photodeformable holographic medium that supports high-efficiency surface relief gratings and moderate efficiency index gratings. The development of the holograms is especially simple, requiring only that the medium be heated to ~100°C for 2 min. The diffraction efficiency for the first order in reflection is higher than 10% for spatial frequencies below 500 lines/mm, but there is no regime where a linear relationship exists between exposure and efficiency. This medium is eminently suitable for the production of holographic optical elements intended for use in the ultraviolet. An off-axis zone plate made by aluminizing a relief hologram fully depletes the zero-order beam and produces a first-order focused spot within 30 % of the diffraction limit. Such tightly focused beams can be used for ablating patterns in many materials.
Infrared recording with commercial plastics
Authors: Calixto Sergio , Menchaca Carmen
Published: February 2023

Several plastics have been used to record IR interference patterns when a CO2 laser was used as a light source. Recording materials were in the form of PMMA thin films (20-60-μm thickness) and Lexan and acrylate blocks (4-5-mm thickness). Thin films presented different transmittance, depending on their thickness, blocks absorbing completely IR radiation. To characterize the media, interference gratings with different spatial frequencies were recorded. Modulation of the recording material during exposure time was monitored by measuring diffraction efficiency when a He-Ne laser beam was sent to the recording area. Permanent gratings were recorded with the three materials, maximum diffraction efficiencies of ~20% for red light were obtained. One characteristic of Lexan was the possibility of recording transient gratings which showed diffraction efficiencies of the order of 1.5% when exposure times of ~80 ms and power densities of ~28 W/cm2 were present. This method is a means to detect information carried by IR wavelengths by using visible light. Finally, the response of these IR recorded diffractive elements when IR light is used in the reconstruction step has been studied.
Raman spectra of TICaBaCuO high-temperature superconductors
Authors: Krantz M. , Rosen H. J. , Macfarlane R. M. , Lee V. Y.
Published: February 2023

The room temperture first-order Raman spectra of the TI2CaBa2Cu2Ox (2 CuO2-layer) 2122 phase and the TI2Ca2Ba2Cu3Ox (3 CuO2-layer) 2223 phase with respective superconducting transition temperatures of 100 and 125 K are presented. The weak Raman scattering efficiency of the essentially single 2122 phase and predominantly 2223 phase samples produces spectra with a considerable number of partially overlapping phonon peaks between 350 and 650 cm−1 and a few at lower frequencies. Comparison with Raman spectra of the impurity phase candidates BaO2, BaCuO2, CaCuO2, TI2O3, TICa5Cu6 allow identification of the intrinsic Raman modes of both superconducting phases. Factor group analysis of the tetragonal unit cells of both phases, space group 14/mmm, yields the mode classifications and the atoms involved in the modes of A
g
symmetry which are expected to be the strongest. Similarities between the spectra of the 2223 and 2122 phases and comparison with the well-characterized YBa2Cu3Ox Raman spectrum suggest mode assignments for the high-frequency modes of A
g
symmetry involving O motion.
Effect of oxygen stoichiometry on softening of Raman active lattice modes in YBa2Cu3Ox
Authors: Rosen H. J. , Krantz M. , Macfarlane R. M. , Lee V. Y.
Published: February 2023

Temperature-dependent frequency shift and linewidth data of the Raman active 337-nm−1 CuO2 in-plane bond-bending mode have been measured for five different oxygen stochiometries between x = 7.00 and x = 6.14 in polycrystalline samples. Softening and line broadening effects observed for the x = 7.00 sample are sharply reduced for x = 6.87 even though the superconducting transition temperature is similar. With a further reduction of oxygen content below x = 6.68, both the soft mode behavior and the line broadening effects completely disappear. These unexpected results could suggest a large variation in the interaction between the electronic system and the lattice as the oxygen content is varied.
Searching for superreflectance in a high Tc superconductor mirror coating
Authors: Wei David T.
Published: February 2023

Just as the dc magnetic field is excluded from a superconductor in the Meissner effect,1,2 the exclusion of high-frequency radiation should give rise to total, reflection, in a high T
c
superconductor, superreflectance (R = 100%) is theoretically shown as a direct result from vector potential formulation below the energy gap. Reflection remains strong up to the plasma frequency. The refractive indices and penetration depth of the radiation are also derived. The superreflectance mirror has yet to be made, with inhomogeneity, impurities, and less than optimal surface condition as the main obstacles. An ion beam sputtering method is proposed to coat a superconductor film on crystalline substrates. This process has reduced the surface irregularities, consistently produced 99.995% of reflectance from optical interference coatings, and holds the most potential in producing superreflectance.
4×4 Acoustooptic photonic space switch with multicasting capability
Authors: Huang P. C. , Stephens W. E. , Banwell T. C. , Reith L. A.
Published: February 2023

A 4 × 4 crossbar space switch was constructed using a vector-matrix multiplier architecture.1 A vertical array of acoustooptic cells was utilized to deflect and steer four GRIN-lens collimated input beams horizontally through free space to a 4 X 4 matrix array of collection GRIN lenses. This array focuses the deflected beams into an array of four 4 X 1 multimode combiners vertically oriented to sum the optical power, thereby forming the cross-points of the array. This configuration has been shown capable of multicasting and wired-OR operations.
Generation of squeezed states of light by intracavity frequency doubling
Authors: Pereira S. F. , Xiao Min , Miller J. D. , Kimble H. J. , Hall J. L.
Published: February 2023

We have generated squeezed states of light by the process of second harmonic conversion within an optical cavity resonant at both fundamental and harmonic frequencies. The experiment consists of a standing-wave cavity containing a crystal of lithium niobate doped with magnesium oxide and driven by the field from a frequency-stabilized Nd:YAG laser (incident power, ~10 mW). The total field reflected from the cavity illuminates a pair of high quantum efficiency photodiodes, whose individual photocurrents are summed. Observations of squeezing are made by analyzing the spectral density of fluctuations for this sum photo-current while the cavity detuning is scanned through resonance. An intensity regulator holds the reflected light intensity constant during the scan by control of the incident light level. Reductions in photocurrent fluctuations of 12% relative to the vacuum-state or shot-noise level are achieved for frequency offsets near 4 MHz. Since significantly higher degrees of squeezing are predicted by our theoretical analysis, we discuss those processes that currently limit the observed noise reduction, including phase noise produced by the intracavity crystal in the absence of nonlinear conversion.
Nondegenerate four-wave mixing in a squeezed vacuum
Authors: An Sunghyuck , Sargent Murray
Published: February 2023

Gardiner1 treated the problem of the decay of two-level systems in a squeezed vacuum. To a good approximation, he found that the Maxwell-Bloch equations are modified simply by having different inphase and inquadrature relation rates. Resonance fluorescence2 and probe absorption have been studied in such a vacuum. We describe nondegenerate four-wave mixing as derived using standard Fourier series methods but with two transverse decay constants. For a highly squeezed vacuum, we find sharp resonances in the probe absorption coefficient and suppression of population pulsation contributions. These resonances are very sensitive to changes in the pump/vacuum relative phase. We average the probe absorption and coupling coefficients over pump spatial holes and solve the coupled mode equations to find the four-wave mixing reflection coefficient. We find that the reflectivity peaks and dips are smaller than in unsqueezed vacuum.
Instability in a cw ring optical parametric oscillator
Authors: Wong N. C.
Published: February 2023

Above-threshold operation of a cw phase-matched triply resonant ring degenerate optical parametric oscillator (OPO) as a function of the pump intensity is theoretically analyzed. The internal pump photon number is clamped at approximately the threshold level. As the pump is increased, additional pump photons are converted into signal photons until an instability point is reached when the internal signal photon number is 4 times the internal pump photon number. Above the instability point the steady state becomes unstable due to competition between the two processes of parametric downconversion and upconversion, each requiring a different relative phase. While this is very similar to the instability of second harmonic generation inside a cavity, this OPO instability has not been pointed out before. When internal losses and nondegenerate signal and idler are included, we obtain a similar conclusion. If the ring cavity is replaced with a special standing-wave configuration, cw operation is stable at all pump levels because the two processes can coexist. This has important implications in current squeezing experiments in which single-ended (basically ring) cavities are preferred and in monolithic ring OPO as efficient tunable radiation sources. The design parameters for a stable ring OPO are discussed.
Imaging with kinoform optical elements
Authors: Buralli Dale A. , Morris G. Michael
Published: February 2023

The optical characteristics of both paraxial and nonparaxial design kinoforms are reviewed. A comparison of the aberration properties of each design indicates that the choice of design depends on the application. For collimation or collection at large apertures, the nonparaxial design is necessary. In spite of the presence of spherical aberration, however, in some cases the paraxial design is preferred. As an example of the potential usefulness of the paraxial design, a flat-field planar kinoform landscape lens free from third-order coma and astigmatism is designed. Due to the inherent large amount of chromatic aberration in diffractive optics, this lens is limited to monochromatic operation, but the restrictions on aperture and field angle from the remaining monochromatic aberrations are approximately the same as for a conventional refractive lens. Theoretical predictions are compared to experimental results from the two different types of kinoform, with particular emphasis on diffraction efficiency and image quality.
Routine computation of diffraction PSF for complicated optical design
Authors: Stamnes Jakob J. , Heier Halvor
Published: February 2023

Over the last ten years we have been developing a computer program for the efficient and accurate routine computation of the diffraction point spread function. The computation is accomplished in a two-step procedure in which one first employs ray tracing to compute the wavefront error in the plane of the exit pupil and to determine the shape of the vignetted pupil. Then one uses the standard Kirchhoff diffraction theory combined with the SSP method1,2 for numerical integration to compute the field in the region of the image. The method does not rely on the small angle approximation and works well for a pupil of general shape. The diffraction patterns are presented as contour maps or graphs of intensity or phase of the field near focus. Routines for computing the optical transfer function from the diffraction patterns are also discussed.
Generation of 420-nm emission by direct frequency doubling of injection-locked GaAIAs array output using KNbO3
Authors: Chun Myung K. , Goldberg L. , Weller J. F.
Published: February 2023

Direct second harmonic generation using a GaAIAs laser diode and KNbO3 offers the possibility of efficient generation in the 400-450-nm spectral range. However, the SHG efficiency using laser diodes has been limited in the past by their relatively low available power output and/or poor spectral and beam quality. Recently, significant progress has been made in obtaining a diffraction- limited beam from a high-power laser diode array by injection locking.1 A single-lobe far-field beam with 70-80 % of the output power contained in the diffraction-limited lobe has been demonstrated in a 500-mW gain-guided laser array.2 The high electrical to optical conversion efficiency, high-power and diffraction-limited output characteristics of injection-locked arrays make them suitable sources for SHG. With 180 mW of cw array output coupled into a temperature tuned KNbO3, 0.24 mW of 420- nm output was obtained. The a-cut 3- X 3.7- X 6- mm KNbO3 crystal was mounted in a thermoelectrically temperature-controlled enclosure. A linearly polarized output of array at 842.5 nm was phase matched noncritically at -22.75°C with a measured halfwidth of temperature tuning range at 0. 5.°C. The results correspond to a 30-dB improvement over previously demonstated power in cw SHG using laser diode sources.3
Optical parametric conversion of picosecond pulses in KTiOPO4
Authors: Vanherzeele Herman
Published: February 2023

KTiOPO4 (KTP) is a widely used material for frequency doubling 1,06-μm Nd:YAG lasers. Here we report the first demonstration of single-pass optical parametric generation and frequency difference mixing with picosecond pulses in hydrothermally grown KTP. The laser system utilized for this work consists of a cw mode-locked Nd:YLF laser (1.053 μm), which both synchronously pumps a single jet dye laser and seeds a Nd:YLF regenerative amplifier (RA). The dye laser emits 1-ps pulses, tunable from 0.57 to 1 μm. The output of the RA is first amplified up to 75 mj in a double-pass linear Nd:YLF amplifier, then spatially filtered in vacuum, and finally frequency doubled (20 mj in a 30-ps pulse at 526 nm) for pumping a three-stage dye laser amplifier. The dye laser amplifier typically generates picosecond pulses at the millijoule level. For the parametric generation experiments the high-power 526-nm beam was used as the pump. We have investigated two schemes: (1) the conventional configuration, in which the output of the generator is built up from noise in the nonlinear crystal, and (2) parametric generation, seeded by the dye laser. In the frequency difference mixing experiments, the amplified dye laser output is mixed with the remaining 1.053-μim beam of the amplified Nd:YLF to generate IR pulses at longer wavelengths. The KTP crystals were cut parallel to the natural (201) or (011) faces for propagation in the X-Z or Y-Z planes, respectively. For both cuts, the normal to the entrance face makes an angle of 58.8° with the Z axis. The tuning range of the parametric generator is 0.6-4.3 μim. Over this entire range, we found the experimentally observed phase matching angles to be in good agreement with the ones calculated from Sellmeier equations.1 A typical energy conversion efficiency of the (nonseeded) parametric device is 10% for a 5-mJ pump in 20-mm long crystals. Optical damage in KTP does not present a problem for these applications. We measured a damage threshold of 30 GW/cm2 for 30-ps green pulses (10-Hz repetition rate).