bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-resolved x-ray diffraction and spectroscopy using synchrotron radiation
Authors: Mills Dennis M.
Published: February 2023

Although the pulsed nature of the radiation emitted from storage rings has for some time been exploited for studies in the visible vacuum ultraviolet region of the spectrum, only recently have synchrotron radiation users begun experiments that emphasize time resolution. Time-resolved x-ray experiments performed at synchrotron radiation sources fall naturally into two categories, those which do not depend on the actual time structure of the emitted radiation but rather rely on the high flux, and those which take explicit advantage of the modulated or pulsed nature of the x-ray beam. Although not always the case, experiments of the latter group generally have a finer time resolution and it is with these experiments that this presentation is concerned. Pulse durations of 100–1000 ps are most typical for synchrotron radiation sources with repetition rates from 0.5 to 50 MHz. These characteristics combined with the continuous spectral distribution make synchrotron radiation a highly attractive source when compared with other sources of pulsed x rays. In fact synchrotron radiation has been used both as a pump and a probe beam for the study of transient phenomena. Shorter pulses and high flux per pulse may soon be a reality with construction of advanced photon sources planned for the near future.
Experimental techniques for generation of arbitrarily shaped and phased nanosecond and picosecond pulse trains
Authors: Haner M. , Spano F. , Warren Warren S.
Published: February 2023

We have shown, in a series of recent papers, that generation of laser pulse sequences with completely controlled delays, pulse shapes, and relative phases permits selective vibrational inversion, enhances velocity resolution in gases, and differentiates between relaxation mechanisms in condensed phases. We present new results with two fundamentally different technologies developed in our laboratory to produce such pulse sequences. Nanosecond pulse shaping and phase shifting is accomplished by acoustooptic modulation of a continuous ring laser.1 We have now experimentally demonstrated pulse envelopes as complicated as Such a complicated shape cannot be generated by other methods in the literature but is needed to compensate for inhomogeneous effects in electronic transitions. We routinely generate phase shifted pulse sequences using these and simpler shapes. Picosecond pulse shaping is accomplished by transient injection locking, and currently generates 150-ps, 10-μJ pulses. We can also generate subnanosecond phase shifts.2 Our fastest pulse shaper and electrooptic modulator, in conjunction with this injection locked system, generate a digital approximation to any shape we wish with <100-ps resolution.2 These results are in agreement with our theoretical models of transient injection locking. Technological limitations of these approaches and comparison with other methods are discussed.
Cramer-Rao lower bounds on the performance of CCD optical position estimators
Authors: Winick Kim A.
Published: February 2023

The problem of optically estimating an object’s position using a charge coupled device (CCD) array composed of square pixels Δx on a side is analyzed. The object’s image spot at the CCD is assumed to have a Gaussian intensity profile with a 1/e point at a radial distance of

2

σ
s
from the peak, and the CCD noise is modeled as Poisson distributed dark current shot noise. A 2-D Cramer-Rao bound is developed and used to determine a lower limit for the mean-square error of any unbiased position estimator, and the maximum likelihood estimator is also derived. For the 1-D position estimation problem the lower bound is shown to be minimum for a pixel-to-image size ratio Δx/σ
s
of between 1 and 2 over a wide range of signal-to-noise ratios. Similarly for the 2-D problem, the optimum ratio is shown to lie between 1.5 and 2.5. As is customary in direct detection systems, it is also observed that the lower bound is a function of both the signal power and noise power separately and not just their ratio. Finally at high signal-to-noise ratios, the maximum likelihood estimator is shown to be independent of the signal and noise powers.
High-speed time-division optical switch
Authors: Su S. F. , Jou L. , Lenart J.
Published: February 2023

With the increasing deployment of optical fibers in transmission systems and the demand for high bandwidth services, such as video and high definition TV, in the foreseeable future, high-speed switching of the order of Gbit/s is desirable in telecommunications. Optical switching is one of the most promising techniques to achieve this high switching speed. However, most of the optical switching techniques developed so far belong to space-division switching, in which switching speed is not a major concern. Very few optical switching techniques, to our knowledge, are for high-speed time-division switching.
Satellite laser ranging using pseudonoise code modulated laser diodes
Authors: Norman David M. , Gardner Chester S.
Published: February 2023

Satellite laser ranging systems typically use ultrashort, high-energy pulses generated from Q-switched ruby lasers or mode-locked Nd:YAG lasers. The average power transmitted in these systems is of the order of 1 W. The range error is proportional to the laser pulse width and inversely proportional to the square root of the number of received signal photoelectrons. An alternative ranging system is proposed which uses a laser diode array as the optical source and a pseudo-noise (PN) code as the ranging signal. For a laser diode array with output power of ~1 W and nanosecond PN code chip duration, range accuracy approaches that of the pulsed laser systems. In this analysis, the maximum likelihood (ML) estimator for photon arrival times is derived for the PN code modulated system taking into account shot noise and background radiation. A correlation receiver is determined to be the optimum receiver using the ML criterion. A bound on the mean-square error of the range estimate is determined for differentiable PN code waveforms. The conditions for which this bound can be used are shown to depend on the number of received signal and background photocounts.
Optical intersatellite link computer model
Authors: Lessure Harold S. , Lawson Christopher M.
Published: February 2023

An interactive computer program has been written to aid in the definition of technologies required for optical intersatellite communication links. Input parameters are varied and the bit error rate (BER) is calculated for the link. The parameters are broken down into the following categories: laser transmitter parameters, laser pointing parameters, satellite tracking parameters, modulator characteristics, and detector performance characteristics. The model simplifies the analysis of interplay between these independently controllable parameters, allowing a rapid numerical evaluation of a configuration of interest. The model consists of six primary modules each containing between one and six subroutines. The function of the modules can briefly be described as follows:

(1) INIT initializes input parameters and admits systematic variation of a given parameter of interest;

(2) TRANSMIT calculates the power incident on the detector taking into account the transmitter power, free-space divergence loss, pointing loss, tracking loss, transmission loss through optical components, and modulation loss;

(3) BACKGROUND determines the effects of optical background from sources such as stars, the moon, the earth, and the sun;

(4) SIGNAL/NOISE calculates the detector signal-to-noise ratio (SNR) with dark current, thermal noise, shot noise, electronic noise, and optical background present;

(5) BIT ERROR calculates BER as a function of SNR for a given modulation format;

(6) DISPLAY tabulates and plots the data.
Asymmetric photoreceptor topography in the pigtail macaque (Macaca nemestrina) retina
Authors: Packer Orin , Curcio Christine A. , Hendrickson Anita E.
Published: February 2023

Asymmetries in the distribution of photoreceptor size, density, and packing order have important consequences for the intepretation of anatomic models of retinal development and models of visual function that make assumptions about the geometry of the photoreceptor mosaic. Cone density and inner segment diameter were measured in whole mounted, nondehydrated pigtail macaque (Macaca nemestrina) retinas, viewed under Nomarski optics. Highest cone densities in the foveal center of two adult animals averaged 189,000 cones/mm2. Along the horizontal meridian, there were more cones at equal eccentricities in the peripheral nasal retina than in the peripheral temporal retina. The nasotemporal ratio increased with eccentricity, reaching a maximum of 3:1. On the vertical meridian, the inferior retina was higher in density than the superior retina by a maximum ratio of 1.5:1. Cone inner segment diameter in one animal ranged from 2.6 μm at the foveal center to over 11 μm in the periphery, in all retinal quadrants. Since cones at comparable eccentricities in nasal and temporal retina have equal diameters, the proportion of peripheral retina covered by cones is greater nasally than temporally.
Measurement of visual acuity in retarded infants
Authors: Mitsuboshi Toku , Hanada Issei
Published: February 2023

Recently the PL or FPL (Tell, Fants et al.) method has been used to measure the acuity of young infants. Although these methods are effective, it is sometimes difficult to apply them to impaired or to multiply-handicapped retarded children, because they are not able to sit straight or to pay attention for any length of time. We have tried to gel the acuity from these children in a modified way or by an improved method. Quite differently from either PL or FPL, we try to get a response from the subjects themselves by using an earlier acquired cognitive task. We used this 2AFC method with some 150 children including 30 normal children, 70 handicapped retarded children, and about 50 with strabismus. We found that it is useful for the measurement of visual acuity of those children with whom it is difficult to use the classical PL or FPL method.
Clear aperture 40-mm Nd:YAG disk laser
Authors: Cao Wei-Lou , Zhang Mei-Zhen , Chen Qinhao
Published: February 2023

During the past few years, much effort has been put into developing solid-state slab lasers. Due to a limitation of the cross area of slab laser, the output power was restricted. Using the technology of the Nd:Yglass disk laser which is often used in laser fusion systems, a 40-mm clear aperture Nd:YAG disk laser has been built in our laboratory.
Photoacoustic measurements of atmospheric aerosol absorption coefficients in the ultraviolet, visible, and infrared
Authors: Ramsey-Bell Debby C. , Huffman Donald R.
Published: February 2023

Atmospheric particles affect the global climate by absorbing and scattering electromagnetic radiation. Knowledge of their optical properties at solar wavelengths (0.3–4 μm) and terrestrial wavelengths (8–20 μm) is needed. Photoacoustic measurements using broadband visible light have been previously made, resulting in values for the atmospheric aerosol absorption coefficient of 1 × 10−7m−1.1 The photoacoustic instrument has been modified for narrowband measurements in the ultraviolet through infrared regions. Absorption coefficient spectra have been obtained for atmospheric particulates collected at mountain altitudes and in Tucson, Arizona. This information has been used for identification of the absorbing material.
Complex angular momentum angular distributions for Mie scattering in the metallic limit
Authors: Nussenzveig H. M. , Wiscombe W. J.
Published: February 2023

The full angular distributions for scattering of a monochromatic plane wave by a perfectly conducting sphere, obtained by numerical summation of the exact partial wave expansion, are compared with the predictions of complex angular momentum (CAM) theory. The size parameter x = ka(where k= wavenumber, a = sphere radius) ranges from large values down to values of order unity, to determine the limits of applicability of CAM theory. A complete set of scattering data, i.e., the polarized intensities and the phase difference between the two polarizations, is plotted.
Optical design on microcomputers
Authors: Shannon Robert R.
Published: February 2023

Optical design has traditionally been a computer intensive activity. Until recently most serious lens design work was carried out using the largest computers available. Present computer power on personal microcomputers and minicomputers has exceeded the computing power of mainframes of only a decade ago, largely because of the introduction of high speed floating point processor chips. Therefore, optical design has moved to the use of these modern machines. Many of the programs currently in use are based on historical design techniques and very few have taken real advantage of the interactive nature of these small computers. A generation of programs that begin to approach the sophistication possible using these machines is beginning to appear. Direct live interaction of the designer and the program is widely used, but some new display and computation approaches are required to make it really practical. Artifical intelligence and expert system approaches have been discussed but not yet implemented in any general program. Programs which combine the lens design stage with tolerance analysis, environmental effects analysis, image evaluation, and computeraided mechanical design are available to varying degrees.
Squeezing large fortran programs into personal computers
Authors: Greynolds Alan W.
Published: February 2023

Even though it is one of the oldest programming languages around, fortran is still the language of choice in much of the scientific community. In fact, its popularity has increased with the recent availability of first class compilers and fast floating point support for personal computers. By sticking closely to the fortran-77 standard and making use of a device-independent graphics protocol, it is relatively easy to write sophisticated programs that can be executed on anything from large supercomputers to desk-top microcomputers. However, when dealing with large programs (>10,000 lines of code) with large data arrays (greater than a megabyte), limitations in personal computer hardware and software need to be addressed. A new optical analysis program of this size is currently running, with almost no modification in source code, on not only DEC VAX minicomputers but also personal computers based on both the Intel and Motorola microprocessors.
Infrared photodissociation spectroscopy of unsupported metal clusters and metal cluster complexes
Authors: Cox D. M. , Zakin M. R. , Brickman R. O. , Trevor D. J. , Reichmann K. C , Kaldor A.
Published: February 2023

The recent development of a general source to produce gas phase metal clusters using laser vaporization combined with mass selective detection techniques has enabled new studies of the fundamental chemical and physical properties of clusters as a function of their size. In our laboratory we have developed and applied a variety of experimental techniques to measure ionization thresholds, magnetic moments, and gas phase reactivities of metal clusters. We now report the first observation of infrared laser-induced dissociation (IR-LID) of metal cluster-adsorbate complexes in a molecular beam. Specifically, using a high-power pulsed CO2 laser as the infrared source, we have measured the IR-LID spectrum for the iron clusters containing chemisorbed methanol as a function of the number of iron atoms for a known number of chemisorbed molecules. For clusters which have chemisorbed only one methanol, strong IR adsorption is observed near 985 and 1075 cm-1, adsorptions presently assigned to the C-O stretch of chemisorbed methoxy radical and bridging hydrogen, respectively, i.e., the methanol is dissociatively chemisorbed. Both the feasibility and potential utility of IR-LID for characterizing metal cluster-adsorbate interactions have been demonstrated. The method is generally applicable to any cluster or cluster-adsorbate system dependent only on the availability of appropriate high-power IR laser sources.
Laser-Induced luminescence studies of matrix isolated metal clusters
Authors: Moskovits Martin
Published: February 2023

No summary was available at press time.
Diffraction of guided waves in anisotropic slab waveguides by interdigitated-electrode-induced gratings
Authors: Glytsis E. N. , Gaylord Thomas K.
Published: February 2023

Interdigitated electrode devices are widely used in integrated optics to produce phase gratings via the linear electrooptic effect. These phase gratings can diffract lightwaves and thus are capable of functioning as switches, modulators, deflectors, multipliers, orthogonal transformers, etc.
Direct measurement of effective indices of guided modes in LiNbO3 waveguides using the Cerenkov second harmonic
Authors: Sanford Norman A. , Robinson W. C.
Published: February 2023

Second harmonic generation in the form of Cerenkov radiation has been used to make direct, contact-free measurements of the effective indices of guided modes in LiNbO3 channel waveguides. X-cut substrates were used and channels, oriented along the y axis, were formed either by proton exchange or titanium indiffusion. For end-fire TE excitation, the Cerenkov harmonic is forward radiated at a shallow angle into the substrate, exits the output facet of the channel, and appears as bright bands in the far field. These bands are seen to form a one-to-one correspondence with the m-lines of the fundamental modes when a prism coupler is simultaneously clamped to the guide surface. The effective indices of the guided modes can be obtained by a simple calculation which involves only the substrate index and the angle at which the Cerenkov harmonic is radiated into the substrate.
Real-time multiple object holographic tracking
Authors: Liu Hua-Kuang , Diep Joseph , Davis Jeffrey A. , Lilly Roger A.
Published: February 2023

We describe the principle of the recognition and tracking of several objects that are moving at different directions in the same plane. This can be accomplished via a multifocus hololens and the liquid crystal TV spatial light modulator.2 A videotape demonstrating the experimental results is presented.
Video data acquisition by random scan
Authors: Zeevi Y. Y. , Hilsenrath O.
Published: February 2023

A special purpose system controlling in real time the scan pattern of a vidicon tube, converts a conventional TV camera into a versatile 2-D data acquisition system. The system architecture incorporates a scan pattern library (ROM), 2-D video map (RAM), ALU, and a special purpose vidicon driver. A scan pattern determined in real time by the host computer in an interactive mode, or alternatively selected from a scan pattern library, controls the electron scanning beam of the vidicon by means of the ALU and vidicon driver. The readout intensity information is stored in a 2-D video map. The scan path is interrupted every 40 ms by a timing controller operating in the background, before tracing of the scan path is enabled. This constraint on the repetition rate can be eliminated by utilizing other, noncapacitive types of imaging device. The main advantages of implementing the basic system in one of its possible embodiments are the high rate of visual data acquisition and the smaller memory required for storing and analyzing the data, compared with the requirements imposed by conventional scanning.
Direct linear transformation methods of triangulating from optical and SAR images
Authors: Brill Michael H.
Published: February 2023

Given an optical photograph with images of six control points (whose three-space coordinates are known), and the two image coordinates of an unknown ground point, it is possible to determine the equation of the line of sight from the camera station to the unknown point via a direct linear transformation (DLT) approach.1 To do this requires writing the projective equations for the control points in a form that is linear in the unknowns containing camera position, orientation, and (assumed affine) film distortions. These equations are written so each image coordinate of each control point appears in only one equation. The result is a linear system solvable for eleven camera variables, which can then be used with the unknown-point image coordinates to determine the line of sight. In the spotlight mode of synthetic-aperture radar (SAR), similar DLT equations are developed to determine the projection circle which is the intersection of the isorange sphere and iso-Doppler cone for a reflecting point. To avoid singularity, the Doppler equations are used to eliminate one image coordinate of each control point in the range equations, where that coordinate appears to the first power. The result is a linear system solvable for thirteen camera variables, which can then be used to determine the projection circle for an unknown ground point. Eight control points are needed for solution. Given optical and SAR images of a ground point, it is now possible to triangulate by intersecting two optical lines of sight, two SAR projection circles, or a line of sight and a projection circle, depending on the available imagery.
Invariance of spectrum of light on propagation from primary, quasi-homogeneous sources
Authors: Wolf Emil
Published: February 2023

It was shown in a recent publication1 that, in general, the normalized spectrum of light changes on propagation through free space. For light generated by sources of a certain class, which includes the usual thermal sources, the normalized spectrum was, however, found to be invariant on propagation provided that the degree of coherence of the source satisfies a certain scaling law. In this paper the analysis is extended to light from quasi-homogeneous, primary, planar sources. An analogous scaling law is derived. It is also shown that with sources of this type, a single relation exists between the spectrum of the primary source distribution and the spectrum of the light in the source plane. The results are illustrated by black-body sources.
Scattering of light by a coated bubble in water near the critical scattering angle
Authors: Billette Stuart C. , Marston Philip L.
Published: February 2023

Microbubbles in the ocean may be coated by a thin film of surfactant since such substances can be abundant in natural waters. We investigated theoretical scattering patterns for a spherical gas bubble (of radius a) coated by a film of uniform thickness h and refractive index n
f
surrounded by water of refractive index n
w
= 4/3. The patterns were computed from the partial-wave series of Aden and Kerker for ka ranging from 100 to 2500 where 2π/k is the optical wavelength in water. The corresponding range of a is 7.5 to 189 μm; h ranged from 0 to 3 μm and n
f
was typically real and equal to 1.5. Noncoated bubbles are known1 to exhibit coarse irradiance oscillations as the scattering angle θ decreases below a critical value for total reflection θ
C
= 82.8°. Anticipated coatings remove neither this coarse structure nor the superimposed finely spaced structure. The magnitude of the latter can be enhanced by the coating. The coarse oscillations are perceivably shifted toward larger θ when n
f
> n
w
. Ray optics predicts a shift in θ
C
∝ (n
f
− n
w
)h/a when h≪ a and |n
f
− n
w
| ≪ n
w
− 1. When using the irradiance near 82.8° to size bubbles, this shift in θ
c
is negligible for anticipated coating parameters.
Scattered wave inversion by a discrete backpropagation method
Authors: Chen Jei Shuan , Porter Robert P.
Published: February 2023

A discrete backpropagation method is used to reconstruct the image of an object from the measured scattered field. This inverse is based on the Kirchhoff equation in the space-time domain. Since the integral equation can be viewed as a deconvolution problem, it can be solved by means of a delay and weighted sum-algorithm. The computation is simplified by using only a few of the nearest-neighbor pairs to calculate the field along a nearby coplanar surface.
Optical transmission in disordered media
Authors: Genack Azriel Z.
Published: February 2023

Optical propagation is studied in samples of random close-packed polystyrene and titania spheres with indices of refraction n = 1.59 and n ≃ 2.8, respectively. Both spatial and temporal aspects of propagation are probed by measuring the transmission of light as a function of sample thickness as well as fluctuations in the transmitted light intensity as a function of laser frequency. Fluctuations in intensity with amplitude as large as the average intensity of light are observed within a single coherence area of a speckle pattern as the laser frequency is scanned. This makes clear the essential role of interference in transport and makes possible the measurement of the width of the distribution in the transit time of light through the sample.
Space-to-ground laser propagation
Authors: Winchester L. W. , Kopia L.
Published: February 2023

A nadir-pointing Nd:YAG laser, operating at the fundamental wavelength and the first and second harmonic wavelengths, is assumed to be in a low earth orbit ~400 km above the surface of the earth. The laser output is characterized by a pulse repetition frequency of 10 Hz, a pulse width of 0.1 μs, a divergence angle of 1.5 mrad and a variable power level. The intensity of radiation is computed as a function of altitude and laser output power using multiple scattering methods applied to an inhomogeneous planetary atmosphere. The atmospheric gas composition and concentration, turbulence, and particle concentration are treated as functions of altitude. Various

C
n
2

profiles are used to compute the effects of turbulence over the vertical propagation path from the top of the atmosphere to ground level.
Effects of finite beamwidth on laser beam propagation and scattering in discrete scattering media
Authors: Chang Hung-Wen , Ishimaru Akira
Published: February 2023

This paper deals with numerical investigations of a beam propagating and scattering in discrete random media based on the radiative transfer theory. By assuming a monochrome, unpolarized, collimated normal incident laser beam with a finite beamwidth, we derive the Fourier-Bessel transport equation in the transformed domain. This equation is expanded in terms of 2-D spherical basis functions and solved using the eigenvalue-eigenvector technique. The beam-wave solution is obtained by taking the inverse Fourier-Bessel transformation of the solutions to this Fourier-Bessel transport equation. We calculate the complete beam-wave solutions for the transmitted and backscattered specific intensity as well as the power received by a receiver as functions of the receiver field of view, the asymmetric factor of the phase function

(

μ
˜

)

, the equivalent optical thickness of the medium (τ0), the radial position of the receiver, and the ratio of the depth of the medium layer to the width of the incident beam. The results are compared with experimental data for the transmitted flux density and power of a laser beam passing through randomly distributed latex microspheres, and these results and data are found to be consistent with each other in the first-order scattering, multiple scattering, and diffusion regions.
Coordinate transformation with multiple computer-originated holograms
Authors: Cederquist Jack N. , Tai Anthony M.
Published: February 2023

To compete with electronic processing, optical processors must exploit fully their potential for noninterfering data redistribution from one plane of the processor to another. The performance of partitioned holograms with discrete subholograms is often unsatisfactory for the task of data redistribution and transformation. Some useful coordinate transformations can be performed optically with a single continuous phase holographic optical element, but many desired transformations require the use of two or more holograms to achieve adequate performance. Some new methods for designing such holograms are given. It is shown that the range of achievable transformations is much wider than previously demonstrated. The adequacy of the stationary phase approximation is examined. A theory is then developed to enable prediction of the space-bandwidth product of the transformation and of crosstalk levels. For specific applications, the required holograms were designed, generated as continuous tone holograms using a computer-controlled laser beam writer, and copied onto phase-only material to produce computer-originated holograms of high diffraction efficiency. The performance of these multiple hologram systems was then experimentally investigated and compared to the theoretical predictions.
Wavelength compensation for a holographlc/optical element
Authors: Zhuang B. H. , Ih Charles S.
Published: February 2023

The HOE (holographic optical element) offers many advantages not found in conventional optics. However, because its operation is very sensitive to wavelength, it cannot be generally used even with laser diodes whose spectrum width and/or wavelength drift may be as large as several nanometers. Also if the laser is in multimode, multiple images will be formed. Therefore simply stabilizing the wavelength of the laser diode using temperature control is generally not adequate. For some specific applications, the wavelength sensitivity can be compensated by a second hologram so that the system can function satisfactorily over a ±, –5-nm range.1 in general, when the wavelength is changed, there is an angular shift and a position shift of the image, and in addition a wavefront distortion.
Wulf-Bragg-Ewald formalism in high-efficiency Bragg holography
Authors: Jannson Joanna
Published: February 2023

The Wulf-Bragg-Ewald (WBE) formalism, generalized by using the grating vector uncertainty principle, is applied to analyze high-efficiency Bragg holographic structures. In particular, the previous approaches1,2 are extended in two directions. The first is related to the high diffraction efficiency regime (where only the first Born approximation has been considered previously). This case has broad applications related to phase materials such as dichromated gelatin or photopolymers. The second generalization applies when more than one (two or three) hologram dimensions are limited, for example, in LiNbO3 and BaTiO3 crystals used for holographic storage. It is shown in this paper that the methods based on WBE formalism can give precise predictions on hologram angular/wave-length selectivity, spectral dispersion, and multi-beam Bragg acceptance, even in the case of highly efficient ferroelectric crystal holograms where Kogelnik’s theory does not hold.
Theoretical model of reconstructed scatter noise in silver halide holograms
Authors: Riddy G. D. G. , Solymar L.
Published: February 2023

Noise gratings, i.e., gratings created by the interference between a plane wave and light scattered from that wave by inhomogeneities in a photographic emulsion, were investigated experimentally.1,2 The transmission of a replay plane wave was measured as a function of replay beam angle, and it was shown that dips in transmission were caused by recreating the scattered beam.
Beam steering and phase control via non-degenerate four-wave mixing
Authors: Schelonka L. P. , Kramer M. A. , Roller J. B.
Published: February 2023

Nondegenerate four-wave mixing in fluorescein-doped glass was used to demonstrate frequency- dependent beam steering and tilt/focus phase control. An argon-ion laser at 457.9 nm provided the probe beam and one of the pump beams. An argon-pumped dye laser, tunable from 560 to 615 nm, provided the second pump beam. The conjugate emerged at the same wavelength as the dye laser and at a frequency tunable, phase matching steering angle. It was shown conclusively that this beam was due to four-wave mixing.
Polarization recovery in phase conjugation by modal scrambling multimode fiber and the effect of applied magnetic field
Authors: Kwong Sze-Keung , Kyuma Kazuo , Yariv Amnon
Published: February 2023

We demonstrate that an optical wave propagating through a polarization and modal scrambling multimode fiber can regain its original polarization state by phase conjugation followed by reverse propagation through the medium.1,2 Such a polarization recovery phenomenon is achieved even when magnetic field is applied along the fiber.3 The experimental arrangement is described as follows: the output light from the argon-ion laser was coupled Into a graded-index multimode fiber (100-μm core diam, 20-m length). A section with a length of ~3 m of the fiber was placed in a uniform magnetic field. The output of the fiber was focused onto a BaTiO3 crystal which aligned to form a self-pumped phase conjugate mirror.4 The reflected phase conjugate light was linearly polarized along the x axis and coupled back into the fiber automatically. The polarization state of the phase conjugate light after passing through the fiber, was analyzed. The interesting and significantly new observations are that:
Optical characteristics of a cross-grating bearing 180°-shifting phase and its application
Authors: Li Zhengzhi , Shan Zijuan , Wang Dinxing
Published: February 2023

The optical characteristics of the cross-grating bearing 180°-shifting phase are studied experimentally and theoretically, with a discussion of its application.
The National New Technology Telescope as a phased array
Authors: Beckers Jacques M.
Published: February 2023

The National New Technology Telescope (NNTT) is a monolithic array of four 7.5-m diam telescopes which has a light-gathering power equivalent to that of a 15-m single-mirror telescope and an angular resolution, when phased, equivalent to a 21-m single-mirror telescope. I describe the telescope, its astronomical capabilities, the techniques which will be used to both coalign and cophase the array and to give a large phased field of view, and the plans to obtain diffraction-limited imaging at optical and infrared wavelengths. The design of the NNTT is based on the experience gained with the six-mirror Multiple Mirror Telescope which served as a prototype. The coalignment/cophasing/field of view and imaging methods planned for the NNTT apply to any close-packed array of telescopes.
Spatial factors influencing stereopsis and fusion
Authors: Schor Clifton M.
Published: February 2023

Absolute distance from the fixation point in the sagittal depth plane is the primary stimulus for fusion whereas relative disparities within and slightly beyond this range stimulate stereoscopic depth. Stereothreshold increases markedly with sagittal distance from the fixation plane. The Weber fraction describing the ratio of stereothreshold (sec of arc)/overall disparity pedestal (min of arc) increases at a rate of 0.125 with pedestal amplitudes up to 1.5°. Beyond this absolute disparity, targets appear diplopic at an unspecific distance. Stereothreshold and sensory fusion limits both increase with coarseness of fusion stimuli. The variations of stereo and diplopia thresholds with spatial frequency account for the simultaneous perception of diplopia and stereopsis in random dot stereograms. In contrast, both stereosensitivity and Panum’s fusional limit remain uniformly high at eccentric locations along the frontoparallel plane in comparison to monocular hyperacuity tasks such as Vernier acuity. Both stereosensitivity and the limits of fusion are influenced by relative position of disparate targets. As target separation decreases, stereothreshold and the fusion limit decrease according to a constant disparity/ separation gradient. At separations less than 1/4 degree, a crowding or depth averaging effect reduces stereosensitivity. Depth sensitivity appears to be enhanced at the optimal separation of 1/4 degree by a perceived depth repulsion between neighboring disparate targets. In addition to crowding and repulsion effects there is a third global interaction, in which ambiguous disparity features take on a depth appearance that is similar to or continuous with the depth stimulated by less ambiguous neighboring targets. The role that variations in binocular retinal correspondence may play in these global interactions is discussed.
Nonlinear grating coupling into InSb using a CO2 laser
Authors: Ehrlich J. E. , Li L. , Bundman P. , Seaton Colin T. , Stegeman George I. , Smith S. Desmond
Published: February 2023

We have demonstrated nonlinear grating coupling into InSb planar waveguides at room temperature using a CO2 laser. This is a thermal, positive nonlinearity causing changes in the index of refraction and thus in the Bragg coupling condition. The nonlinearity manifests itself in a shift in the angle for maximum coupling as well as a change in line shape of the coupled power-vsangle curve. The resulting asymmetry, which agrees qualitatively with the theory of Carter and Chen, leads to switching from low to high coupled intensity as the input intensity is varied.
Theory of self-phase modulations, optical switching, and transverse bistability in the transmission of a laser through a nonlinear thin film
Authors: Khoo I. C. , Yan P. Y. , Liu T. H. , Hou J. Y.
Published: February 2023

For a laser passing through an optically thin nonlinear film, the transmission can be calculated by considering only the effect associated with the nonlinear intensity-dependent transverse phase shift. The radial intensity distribution at a distance from the nonlinear film can be calculated using Kirchhoff's integral and analytically studied as a function of several optical and material parameters. It is found that the intensity distribution may be classified in terms of the diffractive phase for positive or negative nonlinearities. Accordingly, the transmitted intensity distribution can take various forms, with e.g., intensified central region with interference rings, darkened central region, and alternatively bright and darkened central region, as the input intensity is increased. The on-axis intensity can also exhibit power-limiting behavior or unidirectional switching effects. These effects have been experimentally observed. In the case of a positive feedback (e.g., with a partially reflecting mirror downstream), optical bistability in the intensity distribution (at both on-axis and off-axis regions) arises. The conditions for observing optical bistability were found to be described in a rather consistent manner in terms of the diffractive phase mentioned above.
Image recognition with the discrete rectangular wave transform
Authors: Ersoy O. K. , Kim D. Y.
Published: February 2023

The discrete rectangular wave transform (DRWT) is obtained by replacing sines and cosines in the discrete Fourier transform (DFT) by the bipolar rectangular wave function. Thus, DRWT of size N is defined as follows: where x(·) is the input data, and μ(t) is the bipolar rectangular wave function which is 1 for 0 < t mod 1 < 0.5, −1 for 0.5 < t mod 1 < 1, and 0 for t mod 1 = 0 or 0.5. The DRWT matrix contains no numbers other than ±1, ±j, and their combinations. There are also data structures for its fast computation. Since there are add operations only, its electrooptical as well as VLSI implementations are very attractive. DRWT is not an orthogonal transform, but its inverse is well defined, consisting of the complex conjugate transpose of the DRWT matrix followed by a matrix which is the direct sum of blocks of circular correlations. There are no general multiplications in the inverse transform either for N ≤ 32, when N is a power of 2. Since DRWT is both much faster and easier to implement than DFT, it is very attractive to use in applications if it also performs well in terms of various criteria such as accuracy and resolution. Our computer simulations with the method of Fourier descriptors for shape recognition indicate that DRWT performs considerably better than DFT in image recognition where the transform is used for the purpose of feature extraction. The new method using DRWT is obtained by simply replacing DFT with DRWT in the method of Fourier descriptors. In both methods, the same number of largest transform coefficients was kept, and the recognition was based on the Euclidian distances to the set of library features belonging to different reference images. Especially in the presence of white Gaussian noise, the new method is found to be considerably more accurate than the DFT method. We have also developed normalization procedures such that the new transform is invariant under translation, rotation, and scaling of the signal.
Multilayer neural net and its optical implementation
Authors: Gindi Gene R. , Gmitro Arthur F.
Published: February 2023

We present a neural net architecture that is organized as a hierarchical cascade of layers of simple threshold units. A node at layer k + 1 is connected to many nodes at layer k and thus asserts the existence of a subpattern at layer k. It is a well-known technique to cascade such layers in a compositional hierarchy so that the highest layer nodes assert the presence of complete patterns composed of many subpatterns. In our implementation, feedback links from higher to lower layers and intralevel inhibitory connections between competing subpatterns are included. If the net is driven by an appropriate iterative update scheme, it acts as an associative memory with the stored patterns as stable states. Such a structure is well suited for an optical implementation. It may be possible to decompose a given recognition task that requires space-variant connection patterns into a cascade of layers connected by space-invariant patterns. The space invariance allows 2-D node planes to be easily connected optically to other 2-D node planes. We propose an optical realization and discuss problems in the implementation of the threshold operation, the connection patterns, and the handling of negative values. Results of some simulations are presented.
Memory capacity and error-tolerance characteristics of attentive associative memories
Authors: Athale Ravindra A. , Friedlander Carl B. , Stirk Charles W.
Published: February 2023

A conventional associative memory employs correlation as a similarity measure in storage and retrieval operations. We had previously described a variant of this linear associative memory that contains a controllable, adaptive nonlinearity in the correlation domain to suppress cross-correlation noise and increase the memory capacity.1 Work by Maxwell et al.2 and Psaltis and Park3 utilized higher-order correlations to achieve the same effect. A comparative study between the use of isolated higher-order correlation terms and an adaptive nonlinearity will be carried out via computer simulations. Particular emphasis will be placed on the memory capacity and error-tolerance characteristics of the nonlinear associative memory models using different forms of nonlinearities.
Differential amplitude scanning optical microscope
Authors: Iravani M. Vaez , See C. W.
Published: February 2023

In examining a number of objects, such as those displaying small scale topography or refractive-index variations, the scanning optical microscope often results in an image of poor contrast, because the SOM produces a signal even in the absence of structural variations. The dynamic range of the system is thus not fully exploited. In this paper we present a differential amplitude scanning optical microscope (DASOM) which produces a signal only if a structural variation exists between any two adjacent points on the sample.
Stimulated light scattering in photorefractive crystals
Authors: Ewbank M. D. , Yeh Pochi , Neurgaonkar R. R. , Khoshnevisan M. , Feinberg Jack
Published: February 2023

Scattered light from a single laser beam incident on a photorefractive crystal is amplified in certain directions by two-wave mixing, producing beam fanning. A subset of the multitude of photorefractive-index gratings responsible for beam fanning is phase matched for conical diffraction. These cones of light appear with the same polarization as the incident beam and fanned light in Sr
x
Ba1
−x
Nb2O6 and with the opposite polarization in BaTiO3. Measurement of the cone angle can provide accurate values of the birefringence of the crystal as a function of wavelength. Also, the intensity distribution of the stimulated light scattering reveals the optimal orientation and spacing of the photorefractive gratings for beam coupling, as will be shown for a cerium-doped sample of Sr
x
Ba1−
x
Nb2O6 with x = 0.75. Additionally, intense stimulated scattering, reflected back toward the incident beam by the crystal surfaces, can serve as the pumping beams for four-wave mixing to generate a self-pumped phase-conjugate replica of the incident beam in both BaTiO3 and Sr
x
Ba1−
x
Nb2O6.
Instabilities of counterpropagating waves in a two-level medium
Authors: Bar-Joseph Israel , Silberberg Yaron
Published: February 2023

We have previously shown that counterpropagating waves in a Kerrlike medium exhibit spontaneous oscillations above a certain threshold intensity. The period of these oscillations was related to the medium length and to its response time. These oscillations were explained as results of parametric gain and feedback supplied by the grating formed through the nonlinear interaction. In this paper we extend the theory to a two-level medium. The complexity of the parametric interaction in this medium provides a reach spectrum of behaviors. The power exchange due to this interaction, between waves of different frequencies, is usually maximized when the frequency difference is the Rabi frequency. However, another maximum, which is smaller in magnitude, occurs in certain limits when the frequency difference is T1. Our derivation is based on performing a linear stability analysis to the steady-state solutions of the Maxwell-Bloch equations. We assumed a small signal absorption and large detuning from resonance. The solutions were studied in the limit of pure radiative broadening (T2 = T1) and rapid collisional dephasing (T2 ≪ T1). It is found that for most cases Rabi frequency self-oscillations are dominant. However, for T2 ≪ T1 and for large interaction length, we found slower oscillations, with a period of T1. We show that the results can be understood by the gain feedback model. We also discuss the effect of inhomogeneous broadening and present experimental parameters required for observation of T1 oscillations.
Effect of a transverse beam profile on the dynamics of a homogeneously broadened ring laser
Authors: Lugiato Luigi A. , Narducci Lorenzo M. , Tredicce Jorge R. , Bandy Donna K.
Published: February 2023

Most theoretical treatments of laser dynamics have been based on the plane wave approximation for the cavity field. They have also led, for the most part, to seemingly incorrect predictions for 'the instability thresholds. In an attempt to characterize the role played by the transverse intensity and phase variations of the cavity field, we have generalized the usual Maxwell-Bloch equations to include several common features that are present in experimental laser systems. We consider a unidirectional ring laser with a resonator containing spherical mirrors of arbitrary reflectivity and radius of curvature. We assume the active medium to behave as a collection of homogeneously broadened two-level systems with a transverse variation of inversion, as is normally found in typical discharge-excited systems, and we simulate the presence of a confining plasma tube with a fictitious transverse linear absorption profile, which is essentially zero everywhere except in the vicinity of the container walls. Our numerical search for the steady-state field distribution inside the cavity shows that well-behaved steady-state solutions may develop an unstable character for gain values that are not significantly higher than the ordinary laser threshold. These low threshold instabilities seem to arise as a result of a large enough mismatch between the transverse profile of the empty resonator field and of the population inversion. Bistability at threshold also seems to be part of the observed phenomenology.