bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser diode as a temporal coherence controllable source
Authors: Tai Anthony M. , Subotic Nikola S.
Published: February 2023

The spatial coherence of a light source can be easily controlled by varying the source size. The temporal coherence of a light source, on the other hand, has proved to be much more difficult to control. The dependence of the laser diode emission wavelength on temperature offers an opportunity for direct control of their temporal coherence. By modulating the Injection current, temperature fluctuations in the semiconductor junction produce a controlled wavelength drift In the emitted radiation. The amount of wavelength drift can be varied by regulating the depth and period of the modulation which over the integration period translates into variable spectral bandwidths. Thus, a wide range of temporal coherence lengths can be synthesized by appropriately modulating the laser diode current. Possible applications of the technique are described.
Phase conjugation of nonstationary optical signals
Authors: Tataronis John , Saleh Bahaa E. A.
Published: February 2023

The generation of phase conjugated replicas of optical signals has been the subject of many theoretical and experimental studies. Phase conjugation of harmonic signals is a byproduct of certain nonlinear processes such as degenerate four- wave mixing and stimulated Brillouin scattering. Although conjugation of steady signals is well established, the possibility and the effectiveness of conjugating unsteady signals remain largely unexplored. When the envelope of an optical signal varies, new physical phenomena in the conjugation process arise. As previously shown,1 dispersion in the conjugation process distorts the phase conjugate replica of a pulsed signal. Distortion appears even if the response of the medium to the applied optical signal is instantaneous.
Near-field effects of apodization and spherical aberration
Authors: Allred Daniel B. , Mills James P.
Published: February 2023

The effects of Gaussian apodization with −0.8 waves of spherical aberration on a coherent optical system were examined. The area of study was in the near-field concentrating on the areas near the focus in the Fresnel region of an f/12 system using optical wavelengths. Computer predictions were made for four cases: unapodized-unaberrated, apodized-unaberrated, unapodized-aberrated, and apodized-aberrated. Predictions were made for cross-sectional planes perpendicular to the optical axis using Fourier optics. Meridional plane predictions were produced using a numerical integration method of determining the Kirchhoff integral.
Interferometry with the European Very Large Telescope
Authors: Merkle Fritz
Published: February 2023

In the present Very Large Telescope (VLT) linear array concept four independent telescopes of the 8-m class are coupled together. This offers the unique possibility to operate the telescopes as an optical and/or infrared long base-line interferometer. The first target for an interferometric operation is the infrared range from 5 to 20 μm and later a gradual expansion to shorter wavelengths. In the interferometric mode the gain of the 8-m diam single apertures of the VLT is only given, if adaptive optics is used for a real-time partial or full phase compensation of the degradations due to atmospheric turbulence. When the condition atmospheric coherence area > telescope diameter is not fulfilled, adaptive optics is a technique to restore full coherence over the whole pupil. The gain for the SNR in interferometry goes at least with the inverse cube of the point spread function. Therefore, no other parameter can bring about such an improvement. The correction problem is extremely severe at visible wavelengths due to the high temporal and spatial frequencies of the fluctuations. Instead of several thousand subapertures required in the visible for a full correction, only 100-200 subapertures have to be corrected in the infrared case. Additional to the phasing of the individual telescopes, the whole array has to be phased. In a system with independently mounted telescopes the longitudinal position of the pupil images and the effects of pupil foreshortening have to be corrected in addition to the pure path-length correction.
Image reconstruction for misaligned optics using phase diversity
Authors: Paxman R. G. , Fienup J. R.
Published: February 2023

A segmented-aperture telescope such as the Multiple Mirror Telescope (MMT) will suffer from phase errors unless the segments are aligned to within a small fraction of a wavelength. Such a coherent alignment of the segments is very difficult to achieve in real time. An alternative is to record the images degraded by phase errors and restore them after detection using phase-retrieval techniques. This paper describes the use of Gonsalves’ phase-diversity method (which was previously used to combat atmospheric turbulence) to correct imagery blurred by a misaligned MMT. Two images are simultaneously recorded: the usual degraded image in the focal plane and a second degraded image in an out-of-focus plane. An iterative gradient-search algorithm finds the phase error of the telescope that is consistent with both degraded images. The final image is obtained by a Wiener-Helstrom filtering of the degraded image using the retrieved phase errors. The results of reconstruction experiments using simulated data including the effects of noise are shown for the case of random piston phase errors on each of six segments.
Use of single-mode fibers in an optical Interferometric array
Authors: Shaklan S. , Roddier F.
Published: February 2023

We have found that single-mode fiber optics can provide a simple and effective means of interfering the light collected by separate telescopes. Using several meters of fiber in each arm of a Mach-Zehnder interferometer, we observed the effects of dispersion, temperature, and birefringence on the broadband interference pattern. Dispersion and temperature effects are slow, differential (seen in each arm of the interferometer), and easily corrected. The much more serious problems caused by birefringence, which can have wavelength-dependent, wavelength-independent, and temporal components, can be eliminated by monochromatically monitoring the polarization in low-birefringence fiber or by using high-birefringence fiber. In the low-birefringence case, polarization control can be accomplished by elastooptically inducing birefringence,1 and in the high-birefringence case, two detectors, one for each eigenpo-larization, will be needed. In either case, the visibility of interference fringes can be made independent of effects introduced by the fiber optics.
Analysis of the initial field and energy flux in absorbing optical waveguides
Authors: Lakshminarayanan Vasudevan , Calvo Maria Luisa
Published: February 2023

We present an exact formulation of the electromagnetic field incident on an optical waveguide. From this formulation, the expression for the critical angle is derived as a natural consequence. Expressions for the total fraction of power confined within a waveguide are analyzed using parameters associated with the absorption properties of the waveguide. An explicit equation for the fraction of energy confined within a waveguide supporting two sets of modes is also presented and discussed.
Inhomogeneous thin films
Authors: Jacobsson Roland
Published: February 2023

The status of inhomogeneous thin films is reviewed, in particular from the viewpoint of uses of optical interference coatings. Analytical and numerical calculation methods are treated and applied to a survey of the general properties of these films, including their suitability as starting designs for multilayer filters consisting of homogeneous films. Next, theoretical and experimental work on homogeneous mixtures, which is the basis for the fabrication of inhomogeneous films, is reviewed together with the various approaches used to fabricate mixtures and inhomogeneous films. After treating optical methods of characterization of inhomogeneous films, existing and potential applications are reviewed.
Fabrication of arbitrary Index profiles
Authors: Hall R. L. , Southwell W. H. , Gunning W. J.
Published: February 2023

The use of very thin layers in the design of advanced thin-film devices has been proposed as a method of generating arbitrary index profiles.1 Thin layer pairs deposited sequentially and in the correct ratio of thicknesses have been shown to exhibit, as far as the incident light is concerned, an effective index that lies between the index values of the constituent materials. However, the deposition of these layers presents a considerable challenge to the coating engineer since the thicknesses of these layers are much less than the wavelength of light. In addition, some designs may require a thickness tolerance of 1 % or less. These requirements cannot be met using standard optical or crystal thin-film monitors. This paper describes a system used for the fabrication of filters that incorporate such layers. Ellipsometric monitoring techniques are discussed that allow the accurate measurement of very thin optical films. The results of several advanced filter designs are presented.
Manufacture of optical quasi-inhomogeneous layer systems
Authors: Dobrowolski J. A. , Ranger M. , Brown J. , Ho F. C. , Grant P.
Published: February 2023

It is now possible to design optical thin-film systems with almost any desired spectral transmission curve. Some of the synthesis methods used for that purpose yield solutions in the form of inhomogeneous layers. These can then be approximated by multilayer systems consisting of very many, very thin films of two materials only. Other methods provide such quasi-inhomogeneous solutions directly. Because they were difficult to implement in practice, such layer systems were, until now, of academic interest only. This paper describes equipment which has been especially designed for the realization of such multilayers. It is based on the constant rate evaporation of two materials. The construction parameters of the quasi-inhomogeneous layer system are automatically translated into a set of instructions for the control of the deposition by a microcomputer. Experimental results are presented to illustrate the process.
Derivation of a new matrix for an inhomogeneous dielectric thin film
Authors: Bovard Bertrand G.
Published: February 2023

Varying the refractive index of a thin film from one boundary to the other is a very appealing design approach for new types of coating with higher performance. An exact expression for the amplitude reflection coefficient of a single inhomogeneous layer has been given by Sossi in the particular case where there is no refractive-index discontinuity at the layer boundaries.1 Nevertheless, the most efficient way to calculate the optical properties of a coating remains the matrix method where each layer is characterized by a 2 × 2 matrix. Although matrices have been listed in the literature for particular refractive-index profiles,2 no general expression has ever been given. Until now, the only general way to deal with inhomogeneous layers has been to consider each layer as a stack of numerous homogeneous sublayers and to multiply all the corresponding matrices. We introduce a new matrix characterizing any type of inhomogeneous layer, which can easily be included in the traditional programs and allows the calculation of the optical properties of any stack of inhomogeneous and homogeneous layers.
Theory and experiment on the nonlocal radial dependence of laser-induced molecular reorientation in a nematic film
Authors: Khoo I. C. , Yan P. Y. , Liu T. H. , Finn G. M. , Michael R. R.
Published: February 2023

We present a quantitative theoretical and experimental study of the transverse dependence of nematic liquid crystal axis reorientation by a laser beam of beam sizes that are comparable to the liquid crystal film thickness. As a result of the interplay between the boundary torques and the torques exerted by the molecules outside the laser beam on the molecules within the laser beam, interesting nonlocal effects arise. The natures of the torque balance equations and the solutions for the reorientation profile are very different for laser polarizations that are normal, or obliquely inclined, to the director axis. If the laser polarization is perpendicular to the director axis there is a threshold intensity for reorientation to occur. The relative width of the reorientation profile (with respect to the laser beam waist) can be larger (or smaller) than unity depending on whether the laser beam size is smaller (or larger) than the film thickness. On the other hand, if the beam polarization is not normal to the director axis, the width of the response is always larger than the laser beam waist. These nonlocal behaviors have profound effects on transverse optical bistability switching behaviors and switching intensities.
Dispersion of nonlinear index of refraction of CS2
Authors: Mohebi M. , Soileau M. J.
Published: February 2023

We have measured the nonlinear refractive index of CS2 in the 9-11-μm spectral region. We employed the same technique used in Ref. 1, which is to monitor the onset of whole beam self-focusing by observing the photoacoustic signal in an optically thick cell of room temperature, liquid CS2. The departure of the acoustic signal from linear growth with incident power marks the critical power for the onset of nonlinearity. It is experimentally verified that the phenomenon is power dependent as expected from self-focusing. The value of n2 is then calculated from the theoretical model2 of self-focusing. In all measurements the intensity on the axis was smaller than the calculated threshold intensity for Brillouin scattering. The backreflection is also monitored to make sure the Brillouin scattering is not playing a role in the phenomenon. Our previous1 measurement of n2 in CS2at 10.6 μm was an order of magnitude larger than the reorientational n
2
in the visible and near infrared. In this series of experiments we find the maximum n2 to be [0.9 ± 0.2] × 10−9esu at 10.24 μm which is about five times greater than n2 at 10.6 μm. Such large dispersions are indicative of resonance processes. Further experimental studies are required to understand the microscopic processes responsible for the observed dispersion in n2.
Binary pattern classification using optical phase conjugation
Authors: Little Gordon R. , Gustafson Steven C.
Published: February 2023

An elementary binary pattern classifier has n binary input variables and one binary output variable. The input variables may be identified with image pixels so that there are 2n possible input patterns. Classification or specification of the binary output is required for m of these patterns; the remaining patterns are do not cares. For m > 2n and large n (e.g., n ≥ 64), classifiers using all-electronic combinatorial logic techniques generally require numerous decision elements and complex interconnections. These requirements may lead to limited performance in areas such as processing speed and noise tolerance. Classifiers based on holographic associative memory techniques and the use of optical phase conjugation have potential for providing substantial performance improvements in these areas. In particular, analytical and computer simulation results indicate that phase conjugation with thresholded gain may significantly impove the ability of holographic associative memory processors to correctly classify numerous noisy or highly cross-correlated binary patterns. This indication may be attributed mainly to the fact that an additional well-interconnected decision surface can be inserted in a classifier by a thresholded phase conjugator.
Optical processor for adaptive neural networks
Authors: Johnson John L. , Gregory Don A.
Published: February 2023

The behavior of an optical processor architecture having three input images and one inhibited output image is described. It is applied as a major building block of an adaptive, self-organizing two-slab pattern classifier from the Grossberg neural models. Laboratory experiments are presented which indicate that the pattern enhancement, normalization, and inhibitory convolution effects required by the neural model may be achieved with a liquid crystal light valve such as the one produced by Hughes. This device is shown to give an intensity response similar to the fundamental nonlinear neural response required by the Grossberg models. A hybrid electrooptic design using current technology is proposed for the implementation of the complete adaptive pattern classifier.
Metrology for image evaluation of a microlithographic optical system
Authors: Brunner T. A.
Published: February 2023

State-of-the-art microlithographic optical systems are normally evaluated by measuring developed photoresist patterns. Unfortunately, the highly nonlinear and variable resist characteristics complicate the quantitative evaluation of imagery with such techniques. A new approach for directly obtaining the image profile uses 0.4-µm wide slits of fluorescent material on a silicon wafer.1 These slits are accurately scanned by the interferometrically controlled stage of a step-and-repeat system as fluorescence intensity is monitored. This paper presents image profiles of 1.2- and 0.8-µm objects at various field positions and focus parameters. Lens distortion data, relative to the laser stage grid, are shown. Atmospheric pressure variations were found to cause observable changes in the best focus parameter (0.17 µm/Torr) and in the lens reduction error (1 ppm/Torr). Finally, the relative vibration between image and wafer has been measured as position vs time, in contrast to normal accelerometer techniques which lose sensitivity at low frequencies.
Scanning polarization/interference contrast microscopes with linear sensitivity
Authors: See C. W. , Iravani M. Vaez
Published: February 2023

Many available techniques for microscopy depend, for their proper operation, on object related polarization variations of the interrogating light. Examples of such systems include the polarization microscope and the Nomarski differential interference microscope. The output signals from these systems are directly proportional to cos(δϕ), where δϕ is the change in the phase of the orthogonal polarizations of the light beam due to object features. For a small value of δϕ, the strength of the output signal depends on the square of this variation and thus the sensitivity of the system is greatly limited.
Observation of diminished specular reflectivity in self-pumped photorefractive conjugators
Authors: Pepper David M.
Published: February 2023

There has been considerable interest recently in the physics and potential applications of self-pumped phase conjugate mirrors using various photorefractive materials. In spite of the intense interest in one particularly appealing device—the internally pumped phase conjugate mirror1—its operation is not well understood. As an aid in improving our understanding of this device, we have measured the specular reflectivity from the input face of a crystal of BaTiO3 during self-pumped operation. Measurements were performed (at λ = 5145 Å) as a function of the angle of incidence for both linear polarization states. For the s-polarization state—which does not lead to self-pumped conjugation—we find good agreement with the standard Fresnel reflection relations. However, for the p-polarization state, the specular reflectivity drops from the standard Fresnel reflection value (e.g., ~15% at near-normal incidence) to ~2%—a value less than that for an air-glass interface. The temporal dependence of the drop in the specular reflectivity correlates well with the conjugate-wave build-up time. By angularly dithering the crystal—thereby destroying the photorefractive-induced gratings—the p-polarization reflectivity is restored to its standard value. A phenomenological model involving destructive interference of the specular component2 via internally reflected fields gives reasonable agreement with experiment.
Investigation of the photorefractive behavior of chrome-doped GaAs using two-beam coupling
Authors: Albanese Giovanni , Kumar Jayant , Steier William H.
Published: February 2023

Recently, there has been considerable interest in the photorefractive properties of semiconductors1,2 because of the possible applications in optical data processing and phase conjugate optics. We have made measurements, at 1.06 µm, of the grating formation time and the two-beam coupling gain as a function of intensity, grating wavelength, and applied voltage. The GaAs sample has a chrome concentration of 1017 cm−3, dark resistivity of ~300 MΩ cm, and dimensions of 10 × 10 × 5.5 mm. The applied electric field and the polarization vector were along the [111] direction. The inverse of the grating formation time varies linearly with intensity in accordance with theoretical predictions. For an incident laser intensity of 35 mW/cm2, the grating formation time is 1.5 ms and increases to 1.8 ms on application of 6 kV. The gain increases with intensity and saturates. The saturated gain and the intensity required for saturation both increase with applied voltage. A maximum gain of 0.5 cm-1 at a grating spacing of 0.9 pm was measured with no voltage applied which leads to a trap concentration of 1015 cm−3. An applied voltage of 6 kV yielded a maximum gain of 0.9 cm−1 at a grating spacing of 1.2 µm. It was observed that reducing the intensity decreases the gain and, at the same time, shifts the maxima of the gain curves to higher values of grating spacing both with and without an applied voltage.
Theoretical and experimental study of frequency detuning in photorefractive oscillators
Authors: Fischer Baruch , Sternklar S. , Weiss S.
Published: February 2023

Recent reports of self-frequency detuning in a passive phase conjugate mirror (PPCM) have led to some speculations concerning the underlying mechanism for this nondegenerate oscillation. We have developed a theory1 of self-frequency detuning in various photorefractive oscillators and report on an experimental study2 using BaTiO3 in the semilinear PPCM and ring PPCM configurations. The detuning is shown to depend on the dc electric field on the crystal, optical phases in the oscillator cavity, and light intensity in the crystal. Our results also indicate the existence of an internal electric field in the crystal.
Controlling the frequency shift of a self-pumped phase conjugator
Authors: Jiang J. P. , Feinberg Jack
Published: February 2023

When the phase-conjugate replica of an optical beam is generated by traditional four-wave mixing with external pumping beams, the frequency of the phase-conjugate beam is fixed by the frequencies of the three input beams. In self-pumped phase conjugation, there is only one input beam, and the frequency of the output beam is free to roam. In photorefractive materials, this frequency difference between the incident and output beams is typically a few hertz. We present a method for controlling this frequency shift in the self-pumped phase-conjugate mirror that uses a ring configuration1 in photorefractive barium titanate. We show that two-beam coupling of an additional control beam with either of the optical beams already present in the ring cavity can alter the frequency of the phase-conjugate beam. We show that the control beam can alter the nonreciprocal phase shift2 of light propagating around the ring and thereby alter the frequency of the phase-conjugate beam. We also calculate the magnitude and the sign of the expected frequency shift as a function of the intensity, direction, and frequency of this control beam.
Optical-origin drift and whole-error distribution of a fringe-counting interferometer
Authors: Chen Ming-Yi
Published: February 2023

Various kinds of fringe-counting interferometer have been successfully used for line standard calibration and precision positioning, etc. The accuracy of these systems has been claimed to within one ten-millionth or so in many papers. Although the description of error sources and evaluation of measurement accuracy was the main part of these papers, the strict relationship among the errors has not yet been clearly revealed. The reason is simply that for a fringe-counting interferometer two boundary conditions should be considered: the original optical path difference between reference and measurement arms is usually not equal to zero, and the interference order corresponding to the original path difference is set at zero at the beginning of the measurement.
Evaluating the resolution of plane diffraction gratings using a real-time digital interferometer
Authors: Chin Wen-Hong , Lin Zhong
Published: February 2023

The methods currently used for evaluating the resolving power of a plane diffraction grating are: recording the shape and halfwidth of a spectral image by the 546.1-nm mercury line or 632.8-nm He–Ne laser, and measuring the flatness of the diffracted wavefront interferometrically. The method discussed in this paper is that the plane grating under test is measured using a real-time digital wavefront interferometer, the relative intensity distribution of the spectral image is calculated, and the resolution is obtained. The main advantages of this method are: (1) the resolution is free of the errors introduced by the instrument in the conventional resolving power test; (2) the relationship between the resolution and the shape of the diffracted wavefront is made clear.
Calculation of the Raman depolarization ratios for the breathing vibrant modes of pyridine adsorbed on silver sol particles
Authors: Jiang Ping , Zhang Chunping , Zhang Guanyin
Published: February 2023

In surface-enhanced Raman scattering experiments the depolarization ratio for the breathing vibrant modes of the pyridine molecule adsorbed on a metal surface is ρ > 0.5, which is much larger than the free pyridine value of ρ < 0.05. To examine the influence of colloid aggregation on the Raman depolarization ratio, we consider the colloid particles as two spheres each with a radius of R (R ≪ λ) and calculate the Raman depolarization ratios for the breathing vibrant modes of pyridine adsorbed on silver sol particles.
Submillimeter wave plasma diagnostics
Authors: Luhmann N. C.
Published: February 2023

The millimeter and submillimeter wave portions of the spectrum are ideally suited to the determination of fusion plasma properties such as density, internal magnetic fields, temperature, and wave spectrum. This has motivated the development of low noise receivers and imaging arrays as well as a variety of sources (lasers, solid-state multipliers, and gyrotrons) which is the major focus of this paper. Recent advances including tomographic phase and polarization imaging are described.
Millimeter and submillimeter wave astronomy
Authors: Phillips Thomas G.
Published: February 2023

The interstellar medium consists of diffuse clouds and dense clouds containing atoms, molecules, and dust particles at temperatures ranging from 3 to several hundred kelvins. The dense cloud gas particles are mostly molecular and the species found vary from simple molecules such as H2, CO, CS, HCN, etc. to heavy types such as the cyanopolyynes. Molecules other than symmetric ones, such as H2, have dipole moments and can be observed through their rotational transitions which lie in the millimeter and submillimeter bands. The emission line strengths as seen by large ground radio telescopes are usually in the 0.1-10 K range in terms of equivalent blackbody emission. Therefore, sensitive heterodyne detectors are used where noise temperatures are only about ten times the quantum limit. The most sensitive types employ SIS detector elements, which can be used in conjunction with focal plane antenna structures such as bow-ties. Many studies have been carried out including molecule identification, temperature and density measurements, and studies of dynamics of gas clouds in our galaxy and other galaxies.
Optical techniques at millimeter wavelengths
Authors: Compton Richard C. , Rutledge David B.
Published: February 2023

Millimeter systems have evolved as scaled-down versions of existing microwave technology.1 As the operating wavelength decreases, the components become smaller, more difficult to build, and very expensive. At these high frequencies, waveguide and transmission lines become lossy and are restricted in the power they can carry. Optical components, like lenses, can be used to overcome many of these problems. A typical quasi-optical system might consist of a primary lens which focuses radiation onto a secondary substrate lens.1 On the back side of the substrate lens sits an antenna which couples the incident radiation into a small detector. Calculations made using a modified diffraction integral predict efficiencies as high as 70% for infinitesimal dipoles in these systems. In practice bow-tie antennas are used because of their broadband properties. Measurements and calculations for the bow-tie show several interesting phenomena. Log-periodic antennas have also been studied and show excellent performance. Quasi-optical design can be extended to multielement imaging systems. Arrays of bow-ties have been analyzed, fabricated, and measured.2 A major difficulty in an array is accessing the signal from each element. This problem can be avoided by using an array in which each element has its own lens. The lens has the effect of magnifying the size of the receiving antenna allowing smaller antennas to be used. This frees up more space on the substrate for running wires to each element.
Improving the convergence of transverse ray aberration series
Authors: Forbes G. W.
Published: February 2023

Transverse ray aberration series are simply the Taylor series of functions which specify the configuration of a ray after passage through an optical system in terms of the initial configuration. These series are expansions about some specified base ray—the axis for a symmetric system. As is typical of Taylor series, the accuracy of aberration series (truncated at a particular order) deteriorates as the configuration of the initial ray moves away from the base ray. If the accuracy becomes inadequate, an obvious response is to compute the series to higher orders. This approach, however, relies on the assumption that the region of convergence of the series encloses the region of interest. In practice, using the conventional series for systems designed to image plane objects (possibly at infinity), this assumption is often invalid. The limited convergence of these series has hitherto restricted their use to the analysis of systems with (at most) moderate fields and apertures. The selection of an unconventional set of ray parameters as the arguments of the aberration series is shown to yield (i) convergence over the entire region of interest for more demanding systems (e.g., systems with half-fields of, say, 70°) and (ii) remarkable improvements in the accuracy of the truncated series.
Nonimaging pump cavity for a laser
Authors: Kuppenheimer J. D. , Winston R.
Published: February 2023

Nonimaging optics provides a design tool for determining the precise shape of a pump cavity which couples all the radiation coming from the flashlamp into the laser rod. The design principle for the optimized cavity can be summarized as follows: extreme rays of a predetermined angle emerging from the light source are made to be incident on the laser rod at a predetermined angle by reflection from the appropriately shaped cavity. In this way, all radiation within the desired etendue is transferred from lamp to rod. Moreover, the irradiance on the laser rod is uniform. Commonly used pump cavity configurations are elliptical or have diffusely reflective walls. Accordingly, three cavity designs were evaluated experimentally: (1) a silver-coated aluminum cavity with an etendue preserving geometry; (2) a silver-coated aluminum cavity with an approximate elliptical geometry designed for the same rod and pump configuration as the etendue cavity; and (3) a commercially available diffuse-reflection laser pump cavity. The threshold and slope efficiency of each configuration were compared. The lasers were passively O-switched and the outputs used as a measure of the pump uniformity. In each case, the nonimaging cavity showed the best overall performance.
Simultaneous objective and subjective measurements of fixation disparity
Authors: Kertesz Andrew E. , Lee Hyo J.
Published: February 2023

Fixation disparity is generally used to describe the inexactness of binocular fixation. Typically fixation disparity is measured subjectively by the extent of binocularly perceived misalignment of dichoptically (one to each eye) presented Nonius lines. It is customary to obtain fixation disparity measurements as a function of stimulus disparity resulting in a fixation disparity curve. These curves (that purport to measure vergence error or, equivalently, the magnitude of sensory compensation to assure fusion) are used to characterize binocular disorders as well as prognostic indicators for orthoptic therapy. In previous experiments we found significant differences between subjective and objective measurements of cyclo-fusional response.1 We have, therefore, decided to perform simultaneous objective (eye movement measurements during binocular viewing and cover–uncover test) and subjective (Nonius line displacement) measurements of horizontal and vertical fixation disparities as a function of stimulus disparities. All our stimuli contained a fixation point. We found significant differences between the objective and subjective measurements. These differences render the Nonius line method an unreliable indicator of fusional performance or sensory status.
Toward a general model of binocular Interaction
Authors: Cogan Alexander I.
Published: February 2023

A recent model1 of binocular interaction in human vision was tested at the differential luminance threshold; it was also used to fit the data of Birch2 on suprathreshold contrast matching. The quantitative model was quite successful in predicting the relations among monoptic, binoptic, and dichoptic effects, both at threshold and for the suprathreshold task. The threshold experiment was similar to that of Cohn and Lasley,3 and their observations were replicated. It will be shown, however, that these observations do not indicate the operation of two independent binocular channels, as proposed by Cohn and Lasley.3 On the present model1 all binocular stimuli, of whatever interocular polarity, are processed in the same bilateral either-eye channel, where excitatory summation is reduced by reciprocal inhibition. In addition, same-polarity (binoptic) stimuli evoke a fused binocular response that is purely excitatory. The model offers a unified qualitative explanation for diverse binocular phenomena, including the Julesz-Tyler neurontropy.4
Real-time Image recognition by partially coherent light
Authors: Javidi Bahram
Published: February 2023

A real-time image recognition system that can perform complex signal detection under partially coherent illumination is presented. The unique features of the correlator are that the target under study may be a diffusely illuminated real object, and the real-time correlation signal is produced using a narrowband extended light source. The system employs an optical correlator used with a spatial light modulator (liquid crystal image transducer). Pattern recognition experiments using naturally illuminated real objects are provided and the effects of partially coherent illumination on the spatial phase variations in the output wavefront of the device are investigated. Such nonuniformities may arise from nonflatness and mismatch of various output layers in some liquid crystal image transducers which can degrade the performance of the correlator. The experimental results indicate that the distortion effects present in the output surface of the device can be reduced by relaxing the coherence requirements of the system. A quantitative analysis is presented to study the effects of partially coherent illumination on the real-time correlation signal.
Performance of conventional and composite matched filters with error correction
Authors: Green Charles , Cheung Kwan F. , Atlas Les E. , Marks Robert J.
Published: February 2023

Computationally, composite matched filters (CMF) require logarithmically fewer operations than conventional matched filters.1 In cases where the conventional matched filter is optimal, however, the corresponding CMF is not. The performance of the CMF can be enhanced by the addition of redundant computation for error correction purposes. We accomplish this with the use of linear error correcting block codes. The performance of these augmented CMFs is compared with that of the conventional matched filter both analytically and by simulation.
Polychromatic real-time pattern recognition using a liquid crystal television
Authors: Yu Francis T. S. , Lin T. W. , Jutamulia S.
Published: February 2023

Recently, the low-cost black-and-white liquid crystal TV has been applied to real-time optical signal processing. In this work a color liquid crystal TV was used as a spatial light modulator to perform polychromatic real-time pattern recognition. The pixel structure of the LCTV display panel provides multiple Fourier spectra of the input signal. An individual polychromatic Fourier spectrum consists of several colors corresponding to the polychromatic light used. Particular color filters were placed prior to the individual Fourier spectrum in order to synthesize monochromatic holographic matched spatial filters. The phase variation of the display panel obscures the spatial-invariant processing to a certain degree. However, two-color optical correlation has been performed successfully in a simple polychromatic pattern recognition.
Photodetector spectral response comparator: design and applications
Authors: Houston Jeanne M.
Published: February 2023

We have developed a monochromator-based spectral comparator for the purpose of photodiode calibration and research. The comparator is used for measurements of reflectance, absolute response, and quantum efficiency. Some of the unique features of the instrument are its narrow bandpass, its low light scattering in the ultraviolet, and its wavelength accuracy. In addition the data taking process for the comparator has been completely automated. Some of the experiments that we have been able to do because of these instrument features are an accurate measurement of the absolute response of a photooptically corrected detector, and the measurement of the internal quantum efficiency of a group of photodiodes. We describe this instrument and the experimental results.
Initial operating characteristics of the Mark III stellar interferometer
Authors: Shao Michael , Colavita M. Mark , Staelin D. , Johnston K. , Hughes J.
Published: February 2023

The Mark III interferometer is a two-element stellar interferometer with four fixed base lines that uses active optical systems to keep optical path differences well below a wavelength of light for phase coherent operation. The instrument is designed to be used on a regular basis for astronomical observations as well as a test bed for technology development of instruments for phase coherent interferometric imaging and astrometry. Open loop pointing of the two siderostats is accurate to ~10 sec of arc, within the field of view of the star tracker. Closed loop operation of the star trackers should coalign the beams to ~0.2 sec of arc. As the interferometer base line rotates with the earth, the time varying optical path difference between the two siderostats and the star is compensated by an optical delay line. The delay line is controlled by a laser interferometer and can be set with an accuracy of ~10 nm over a range of 20 m. The optical path difference from the beam combiner to the star via the two arms is determined by measuring the phase of the stellar fringe pattern. The stellar fringe tracker is designed to compensate for optical path fluctuations due to turbulence to ~λ/8. Initially, the interferometer will be used for wide angle astrometry. The addition of an imaging capability is planned.
Ion-assisted deposition of fluoride optical thin films
Authors: Targove J. D. , Bovard B. G. , Lehan J. P. , Messerly M. J. , Weng C. C.
Published: February 2023

We prepared optical thin films of several fluoride materials using ion-assisted deposition. The materials were selected for their transmittance in the near ultraviolet and include LaF3, CeF3, NdF3, and cryolite. We investigated the effects of the ion species, beam energy, and beam current density on thin-film properties.
XPS analysis of IAD fluoride films
Authors: Kennemore Charles M. , Gibson Ursula J.
Published: February 2023

Investigation of the core electron binding energies by x-ray photoelectron spectroscopy (XPS) allows the determination not only of the elemental composition of the film but also the detection of the various compounds of the constituent elements due to the measurable shift in the electron binding energies associated with chemical bonding.
Multichannel holography for particle field tomography
Authors: Zhao Dazun , Mei Wenhui
Published: February 2023

This is another use, based on an earlier application,1 of spatial multichannel holography. A particle field can be examined by measuring its parameters layer by layer when reconstructing its hologram. But the fact that, at the image plane of a certain layer, defocused images of particles of other layers also appear disturbs the measurement. Multichannel holography can reduce the disturbance by shortening the focusing depth of images. To demonstrate: a particle field is simulated by a stack of nine glass plates and on one surface of each plate many small ink spots are spattered randomly. The stack is illuminated by a laser beam scattered from a large piece of ground glass and an off-axis hologram is taken. Reconstructed images of layers from that hologram and from an ordinary one (particle field is illuminated by a point source during recording) are compared with each other and with their corresponding true distributions on the plates. We find the former show much less disturbance. The same conclusion is obtained when images of tilted cross sections are compared.
Zone plates for x-ray microscopy at 300-Å resolution
Authors: Burge R. E.
Published: February 2023

Zone plates with outermost zone width ≥300 Å have been fabricated by high-resolution E-beam writing in carbon contamination resist. The replication of a range of such zone plates into gold has been successful. The zone plates have been tested in scanning x-ray microscopes using synchrotron radiation at both Brookhaven and Daresbury, U.K. The latter microscope is a new development with a scanning stage having a fine step size of 100 Å. The design and performance of the new scanning microscope are discussed, as are the practical problems of zone plate fabrication and scanning x-ray microscopy as the point-to-point resolution improves. The further development of soft x-ray imaging is considerably aided by theoretical considerations of the optical properties of diffracting elements incorporating the 3-D structure, i.e., including the effect of the zone plate thickness. An integral formulation we have developed for this thick slit problem makes use of the circular zone-plate symmetry and also provides a possible route toward the solution of the inverse problem in zone plate design.
Possibility of high-resolution Fresnel zone plates for x-ray application by spatial frequency multiplication
Authors: Yun Wenbing
Published: February 2023

Analysis shows that the interference pattern of two diffracted orders of a zone plate is another zone plate pattern. The smallest spacing of the interference pattern can be several times smaller than that of the parent and thus corresponding improvement in spatial resolution can be gained. The demonstration of the scheme using a visible light laser and studies with a soft x-ray source lead us to think that fabricating zone plates with spatial resolution as small as 200 Å may be possible.
Direct measurement of dispersive nonlinearities in GaAs
Authors: Lee Y. H. , Rhee B. K. , Chavez-Pirson A. , Gibbs Hyatt M. , Gossard A. C. , Wiegmann W.
Published: February 2023

Nonlinear refractive-index changes in GaAs are obtained at room temperature by measuring shifts of Fabry-Perot (F.P.) transmission. The 299-Å multiple-quantum-well GaAs sample was sandwiched between two dielectric mirrors (90% reflectivity) to form a F.P. etalon (finesse =10). The pump beam was tuned to 821 nm and modulated to obtain 1-μs pulses at 10 kHz. The photoluminescence from a focused pump spot at the GaAs etalon was used as a broadband probe source. Since the photoluminescence is due to carriers generated by a pump beam, the pump and probe beams automatically align themselves. The fast electronic nonlinearity exhibited blue shifts (negative index changes) of the F.P. transmission peaks, while the slow thermal nonlinearity showed red shifts (positive index changes). Nonlinear index changes were calculated from the measured shifts of the F.P. peaks for different pump intensities. A self-consistent F.P. phase function for this calculation was obtained assuming lengths of 2.9 and 1.5 μm for the GaAs and air gap, respectively. Optical bistability was most easily observed for the region of large index change (873-878 nm). The slow nonlinear index changes below the band gap showed nonresonant characteristics rather than resonant, saturable behavior.
Quantum optics of particles: distinctive features of a Hanbury Brown-Twiss experiment with electrons
Authors: Silverman M. P.
Published: February 2023

Interference experiments characterized by the degree of first-order coherence (Young’s fringes, Fresnel, and Fraunhofer diffraction, etc.) have been performed with massive particles, in particular electrons and neutrons, as well as with light. Optical intensity interference or correlation experiments characterized by the degree of second-order coherence have not yet been performed with particles. The theory for such experiments shows striking differences in the behavior of electrons compared with that of light deriving from the differences in quantum statistics and charge. Photons are neutral bosons. They can be prepared in states that exhibit bunching, no bunching, or antibunching; they are unaffected by the presence of electromagnetic potentials. Electrons are charged fermions. Theory indicates that they exhibit antibunching regardless of the coherence of the source, and that their degree of second-order coherence can be influenced by electromagnetic fields through which they do not pass. A remarkable example is the Hanbury Brown-Twiss experiment with electrons that have interacted locally with the vector potential of an inaccessible magnetic field. The electron intensity correlation at two detectors is shown to be sensitive to the confined magnetic flux; experimental conditions differ considerably from those of the well-known Aharonov-Bohm effect.
Individual differences in interocular differences
Authors: Shevell Steven K. , Humanski Richard A.
Published: February 2023

A given visual stimulus viewed monocularly with one eye can change in perceived color when viewed monocularly with the other eye. We report here the magnitude of interocular difference for many observers. In the color perception task, observers adjusted a mixture of 540- and 660-nm lights for equilibrium (neither reddish nor greenish) yellow. Measurements were made over a test-field radiance range of 2.4 log units in each of three adapting conditions: (1) dark adaptation, (2) 10 troland, 660-nm adaptation, and (3) 100 troland, 660-nm adaptation. In some sessions the test was presented steadily, and in others it was briefly flashed (200 ms). The results show reliable differences between an individual’s two eyes, with the average difference between the eyes varying substantially from one observer to the next. In comparison to dark adaptation, a chromatic adapting field increases the magnitude of both the interocular difference itself and the variability of the interocular difference across observers. One implication of these results is that (monocularly measured) color perception differences between observers, which of course are differences between eyes as well as between people, should be evaluated relative to differences between eyes of single observers.