bluuebunny/crossref_metadata_2025 huggingface dataset:
Central mechanisms of color appearance
Authors: Shevell Steven K.
Published: February 2023

Most laboratory research on color perception involves monocular experiments. With monocular stimuli, the effects of central mechanisms that affect color perception in natural viewing may be missed or misinterpreted, since central mechanisms may respond differently when receiving neural signals from both eyes. Using binocular and haploscopic adapting fields, some properties of central mechanisms have been determined. One fundamental result is the qualitatively different effect of adapting the contralateral eye, compared with the usual monocular condition where the test and adapting lights are seen by the same eye. For example, long-wavelength adaptation of the contralateral eye causes a test to appear more reddish; this contrasts with the well-known effect of the same adapting field in a monocular experiment, where it causes the test to appear more greenish. Measurements also show that changes in color appearance caused by contralateral adaptation cannot be explained by a simple contribution to hue from the contralateral stimulus. Further, studies in which both eyes are adapted have revealed the complex nature of central mechanisms: binocular adaptation cannot be accounted for by combining the effect of adapting only the test eye with the effect of adapting only the contralateral eye. These and other results reveal an important role of central mechanisms. A function of central mechanisms consistent with the results is integration of disparate signals from the two eyes by a process that tends toward color constancy.
Optics with pulses of a few cycles duration
Authors: Knox W. H. , Stolen R. H. , Tomlinson W. J.
Published: February 2023

Recent advances in optical pulse compression have made possible the production of pulses as short as 8 fs,1 corresponding to only 3.8 cycles duration. Several interesting optical problems arise as a result of the large bandwidth which is characteristic of such short pulses. The generation of the large chirped bandwidth by propagation of an intense pulse in a short length of optical fiber appears to still be well described by the nonlinear Schrödinger equation,2 however in the compression using parallel diffraction gratings it is no longer valid to neglect the cubic phase term.3 Inclusion of this term alters considerably the compressed pulse characteristics. The dispersion of optical materials is not exactly linear with frequency, and this introduces another frequency dependent error which can affect the compressed pulse. In addition to these problems which arise in generation of very short pulses, a number of problems are encountered in manipulation of the pulse. A number of common optical elements such as wave plates and multilayer dielectric coatings are essentially useless in this regime. In fact, propagation of an 8-fs optical pulse through only a few meters of air produces significant pulse broadening.
Self-injection locking of pulsed single longitudinal- and transverse-mode alexandrite lasers
Authors: Harter D. J. , Siebert D. R. , Heiney A. J.
Published: February 2023

A solid state laser operated high above threshold cannot easily maintain single-longitudinal-mode output. However, high power single-longitudinal-mode output can be achieved by injecting a singlelongitudinal-mode pulse from a near-threshold laser into the high power laser. We have devised a resonator configuration wherein the functions of the near-threshold injecting laser and the highpower injected laser are integrated into a single laser. The self-injection-locked laser consists of a single laser head and two resonators which are selected by an electrooptical element and a thin-film polarizer. Lasing starts in the lossy resonator arm which contains the line-narrowing and tuning elements and is operated close to threshold. The lasing in this arm is detected by a photodiode which triggers the switching of the electrooptical element, thus redirecting this small line-narrowed signal into the bare-cavity arm to injection-seed the Q-switched output pulse. We have obtained >100 mJ in 40-ns pulses which are single-longitudinal and transverse modes. Higher intracavity power densities are observed without optical damage in this single-transverse-mode resonator than are usually obtained in conventional multitransverse-mode oscillators. We attribute this behavior to the more uniform spatial profile.
Evaluation of alexandrite laser materials
Authors: Stotlar S. C. , Edgett L. B.
Published: February 2023

Alexandrite for tunable lasers has been studied using optical and chemical techniques, including UV-visible spectroscopy, x-ray and electron microprobe, and chemical analysis. Material characteristics affect and limit laser performance and contribute to failure. Optical microscopy and SEM have been used to examine defects and banding. Bands are one of the most readily apparent characteristics of Czochralski-grown synthetic alexandrite. Through secondary electron image and x-ray profile (digital) data, the bands can be shown to be variations in the local doping level. The bands result from slight variations in the growth conditions, temperature drift being the most likely culprit. Defects which may induce failure in the laser rods have also been investigated. Laser damage sites are presented.
Approximate formula for the propagation constant of the basic mode in slab waveguides of arbitrary index profile
Authors: Ruschin S.
Published: February 2023

An exact analytical expression for the mode propagation constants does not exist for most of the index profile functions. Thus, numerical or graphical methods are employed even for the solution of the simplest step-index slab. The derivation of the approximate analytical formula presented is based on two facts: (1) Two waveguides can be made equivalent by changing the profile’s parameters in such a way that moments of the profile’s functions are made identical.1 (2) The cosh–2(x) profile has a particularly simple analytical solution for its eigenmode equation. The results of the approximate formula are compared with numerical results for several profiles, namely, the exponential, the Gaussian, the rectangular, and the cladded parabolic. The comparison shows agreement better than 97% for the normalized propagation constant in the single-mode range. The formula obtained can also be easily inverted to yield a simple expression of the propagation constant as a function of the profile’s width. This would be of use in cases where the width of the guide has to be designed to furnish a required value of the propagation constant.
Determination of the effective nonlinear refractive index in Si from self-defocusing and self-phase modulation
Authors: Boggess Thomas F. , Bohnert K. , Mansour Kamjou , Smirl Arthur L.
Published: February 2023

Recent development of an all-optical Si switch1 has led us to investigate a wide variety of nonlinear phenomena in this material. We have previously described our studies of the nonlinear transmission and reflection, the melting threshold, and the surface regrowth morphologies. Here, we quantify the nonlinear refraction induced in Si by the absorption of intense picosecond pulses at 1.06 μm. The temporally and spatially Gaussian profiles of the incident pulses produce a temporally and spatially dependent nonlinear refraction. Consequently, self-phase modulation and self-defocusing are evident in the transmitted pulse. The former effect manifests itself in spectral broadening and a line-center shift, while the latter provides a characteristic near-field beam deformation. A careful analysis of these phenomena has allowed us to determine the effective nonlinear refractive index associated with carrier generation in this material.
Dispersion measurements of the third-order susceptibility of organic systems
Authors: Kuzyk M. , Norwood R. , Garito A. F.
Published: February 2023

Dispersions of the third-order nonlinear optical susceptibility of organic systems were measured in the optical region using a pump-probe method. With intense Nd:YAG laser pulses (30 ps) as the pump (ω1), tunable cw dye laser radiation (ω2) was used to probe the nonlinear medium for the third-order process ω1 + ω2 − ω1 = ω2. Use of a cw probe provides referenced measurements by accounting for temporal power fluctuations in the pump beam. All beams are unfocused allowing for direct comparison of experimental data to self-focusing theory. The dispersion of the third-order electronic response can be calculated using third-order perturbation theory with respect to the zero field wave functions. We use nitrobenzene as a representative system and analyze the dispersion in terms of the frequency-dependent contributions to the third-order susceptibility due to electronic excitations, molecular reorientation, and cascading processes.
Nonlocal transverse dependence of liquid crystal director reorientation and nonlinearity induced by a laser beam
Authors: Khoo I. C. , Liu T. H.
Published: February 2023

Using both analytical and numerical techniques, we have calculated the transverse dependence of the reorientation of the director axis of a nematic liquid crystal by a linearly polarized Gaussian laser beam. The laser propagates at a small angle β with respect to the director axis direction. For this geometry, previous studies have shown that even if the optical electric field is weak in comparison with the Freedericksz field, the director axis will reorient. The reorientation gives rise to an intensity dependent phase shift. In the limit of small β and reorientation angle, the Euler equation can be solved analytically in terms of hyperbolic Bessel function integrals. A numerical evaluation of these integrals shows that, for all values of the laser beam waist compared to the thickness of the film, the transverse dependence of the reorientation has a width larger than the input laser beam waist. If the laser beam waist is comparable to or less than the thickness, the broadening is considerable (by a factor of 2 or more). We have performed quantitative experiments based on the transverse phase modulation effects. Experimental results are in excellent agreement with the theory.
Transient stimulated Raman amplification with picosecond pulse trains
Authors: Lin J. T. , Reintjes J.
Published: February 2023

We consider transient stimulated Raman amplification of trains of picosecond pulses. In this regime the gain of a single pulse is reduced from its steady-state value because of the inability of the nonlinear polarization to follow the time variations of the pump pulse. In addition oscillatory behavior of the pump and Stokes pulse amplitudes have been predicted in the transient regime in conditions of high pump depletion. When the pump radiation is in the form of a train of pulses whose separation is comparable to or shorter than the dephasing time of the nonlinear medium, increased gain can be experienced by later pulses in the train because they can grow from the material polarization created by earlier pulses. We have analyzed this type of amplification as a function of pulse spacing, pump energy, and pump intensity in the regime of high pump depletion. In addition we have considered the effects of Stark shifts of the two-photon resonant Raman level on the Stokes conversion efficiency. We find that at constant pulse intensity the conversion efficiency increases with time through the pulse train, gradually approaching steady state at low conversion efficiencies at times long compared to T2. The maximum conversion efficiency increases as the pulse spacing is decreased. If the pump depletion is too high the peak conversion of the Stokes oscillates through the train in a manner similar to the oscillations of the intensity of a single pulse. A Stark shift of the resonant level can cause reduced gain as well as introduce phase shifts on the Stokes and pump beams. The effects of these processes on the conversion efficiency are discussed.
Self-diffraction as a practical method for measuring pulse width and coherence time
Authors: Nighan W. L. , Fauchet P. M.
Published: February 2023

The simultaneous determination of the pulse width and coherence time of ultrashort laser pulses is highly desirable for the interpretation of many experiments involving nonlinear processes. We show that self-diffraction from a transient grating formed by interfering two picosecond pulses from the laser on a thin sample gives access to both quantities. This method is simple, does not require phase matching, and works best with highly absorbing materials. In our experiments, the pulses are produced by a mode-locked Nd:YAG or picosecond dye laser. The samples are thin semiconductor or dye films. We compare the self-diffraction results to those obtained by noncollinear autocorrelation. The effect of changing the absolute and relative intensity, the polarization, and pulse duration of the beams is investigated. Our data are examined in the light of a general theory recently developed by Trebino.1 We include thermal and electronic contributions to the signal. Our results are compared with the related results of Smirl et al.2 Finally, we discuss the scalability of this method to shorter pulse width and shorter wavelength and indicate an optimization procedure.
Physics and applications of room temperature excitonic electroabsorption in quantum wells
Authors: Miller D. A. B.
Published: February 2023

Quantum well systems, where electrons and holes are confined in thin (e.g., 100-Å) layers of a narrow band gap semiconductor (e.g., GaAs) by the adjacent wider band gap semiconductor layers (e.g., GaAIAs), show several interesting optical effects. In addition to making exciton absorption resonance resolvable at room temperature, the confinement results in the quantum-confined Stark effect (QCSE)1; with electric fields perpendicular to the layers of the material, the excitonic absorption shifts by large amounts (e.g., 40 meV). This effect enables high-speed modulators of micron thickness to be made.2 It can be explained as a Stark shift of the exciton energy in which the confinement inhibits the field ionization (which normally would destroy the resonance). Shifts as large as four times the binding energy can be seen at fields corresponding to 200 times the classical ionization field. The structures can also simultaneously operate as photodetectors with photocurrent proportional to absorbed power. Since absorbed power depends on voltage (field) through the QCSE, a simple electronic circuit (e.g., a resistor and bias supply) gives optoelectronic feedback which is the principle of the self-electrooptic effect device (SEED).3 Positive feedback gives optical bistability, while with negative feedback, linearized modulation and optical level shifting are possible. These devices are compatible with diode lasers and semiconductor electronics in wavelengths, power levels, voltages, materials, and fabrication, and offer very low energy operation (e.g., –10 fJ/ square micron).
Superresolving image restoration using an associative memory processor
Authors: Stojancic M. , Eichmann G.
Published: February 2023

The issue of superresolving signal and image restoration appears in many areas, such as the restoration of diffraction-limited images, geophysical prospecting, radar and sonar signal processing, biomedical imaging, image and signal bandwidth compression, reconstruction of signals and images from partial and incomplete information, etc. There is a large repertoire of different techniques and procedures available to reconstruct such images. However, most of these techniques work well only in the absence of noise. Because this is an ill-posed problem, the actual reconstruction is sensitive to noise. Recently, new optical signal and image processing techniques have been suggested that are based on associative memory processing concepts. The purpose of this paper is to explore various associative memory processor concepts applied to the superresolving image restoration problem. Results of computer simulation will be presented.
Sequential associative processing
Authors: Guest Clark C.
Published: February 2023

Associative memory (AM) is appropriate for storage of certain types of information. Conventional location addressable memory (LAM) can more efficiently store deterministic spatial and temporal patterns. A problem solving system may combine these types of memory under control of a microprogram, or context, sequencer. The solution of a problem progresses through a sequence of steps. Some steps involve decisions that refine or redirect the context of the solution process. The LAM is used to store meaningful sequences of solution steps. Output of the AM contains information associated with the input data, including the direction of the next appropriate step in the solution process. This information is used by the context sequencer to determine whether the next sequential step of the current solution path will be used or if a branch should be taken. Output of the sequencer indexes into the LAM for the next step information. Applications of sequential associative processing are presented. Implementation and integration of the component parts, the AM, the LAM, and the context sequencer are discussed.
Coherent optical eigenstate memory
Authors: Anderson Dana Z.
Published: February 2023

A high capacity associative memory would find applications in computing and perhaps lend some insight into the understanding of collective neural networks and human memory. In this work an entirely optical associative memory device is proposed. The device operates on the principle that an optical resonator employing a holographic grating can have user prescribed eigenmodes. Information which is to be recalled is contained in the hologram. Each information entity (e.g., an image of a cat) defines an eigenmode of the resonator. The stored information is accessed by injecting partial information (e.g., an image of the cat’s ear) into the resonator. The appropriate eigenmode is selected through a competitive process in a gain medium placed inside the resonator. With a net gain greater than one, the gain amplifies the field belonging to the eigenmode which most resembles the injected field; the other eigenmodes are suppressed via the competition for the gain. The principles underlying the proposed device are outlined and the issues which must be addressed are delineated.
Simultaneous and successive hue contrast
Authors: Laxar Kevin , Wooten Bill R.
Published: February 2023

Most models of simultaneous and successive hue contrast generally assume similar underlying neural processes, and most experimental results indicate that they produce similar effects. Methodology has often confounded the two effects, however. We show here that for some conditions simultaneous hue contrast yields different results than does successive hue contrast, providing evidence of different neural processes. In four experiments, the red-green null point was used as an indicator of color appearance. In the successive hue contrast condition, a unique blue background was exposed for 10 s of adaptation, followed by a yellow test flash. The null point shifted progressively toward shorter waves as the intensity of the adapting field was increased. Similar results obtained for the usual conditions of simultaneous hue contrast with the center-surround arrangement. However, for brief presentations or with the test stimulus superimposed on the background to control for stray light effects, no such shift occurred in the locus of unique yellow with a unique blue surround. Additional experiments with longer- and shorter-wave backgrounds did produce expected hue shifts, indicating that simultaneous hue contrast effects were nonetheless operative in our conditions. These results suggest that successive hue contrast requires preopponent gain changes, whereas simultaneous hue contrast requires only opponent induction.
Depth and surface inferences in line drawings
Authors: Cavanagh Patrick
Published: February 2023

When we look at a line drawing of a Necker cube, we see it as a wire frame with empty space between the black lines. With a drawing of a solid cube, however, we see each area bounded by black lines as an opaque surface with a particular orientation and depth. We examined the nature of the depth and surface inferences in line drawings by replacing the lines of the original drawings, strips of black on a white background, by lines defined by other attributes: color, texture, motion, or depth. Drawings represented by any of these attributes were able to signal shape and occlusion showing that the outline representation is analyzed at a high level, following the reintegration of the multiple representations of visual attributes such as color and motion (Zeki, 1978). Surfaces sharing the same color or texture showed no tendency to group across an intervening line; the occlusion and crossing cues provided by the intersections of contours were able to break the surface into different depth planes. Surfaces sharing common motion or depth grouped strongly, however, and often could not be seen at different depths even though separated by intervening motion or depth lines.
Inferring 3-D shapes from 2-D codons
Authors: Richards Whitman , Koenderink J. J. , Hoffman Donald D.
Published: February 2023

All plane curves can be described at an abstract level by a sequence of five primitive elemental shapes, called codons, which simply capture the relations between the extrema of curvature. The codon description provides a basis for enumerating all smooth 2-D curves. Let each of these smooth plane curves be considered as the silhouette of an opaque 3-D object. Clearly an infinity of 3-D objects can generate any one of our codon silhouettes. How then can we predict which 3-D object corresponds to a given 2-D silhouette? To restrict the infinity of choices, we impose two mathematical properties of smooth surfaces plus one simple viewing constraint. The constraint is an extension of the notion of general position and seems to drive our preferred inferences of 3-D shapes, given only the 2-D contour.
Recognition of 3-D objects from multiple views
Authors: Stark Henry , Wu Ron
Published: February 2023

Given an unknown test object and several reference classes, how do we determine which class the unknown object belongs to? The problem is more complicated when the object is 3-D and its size can vary over a broad range. Our approach is based on principles of tomography: Several views of the object are taken and reduced to projections (line integrals). The projections are Fourier transformed and mapped into a scale and rotation-invariant function via the Mellin transform and circular harmonic coefficients. The resulting function has other invariants useful in pattern recognition. A demonstration using two look-alike gears of different sizes is furnished. The technique is also useful if only partial view data of the unknown object are available. This is demonstrated as well.
Refractive-index distributions produced by interdigitated electrodes on electrooptic crystals
Authors: Glytsis E. N. , Moharam M. G. , Gaylord T. K.
Published: February 2023

Devices constructed with interdigitated surface electrodes are widely used in integrated optics to produce electrooptic switches, deflectors, and modulators as well as to launch surface acoustic waves. To be able to fabricate devices with the desired characteristics, it is essential to know the electric field that is produced in the material under the interdigitated electrodes. The spatial distribution of the electric field produced by a voltage applied to a set of interdigitated electrodes on the surface of an anisotropic crystal such as lithium niobate is calculated using rigorous electromagnetic theory. The effects of the electrode width, period, and thickness are presented. Variations with crystal orientation are analyzed. The presence of a buffer layer such as isotropic silicon dioxide is included and the effects of its thickness are presented. The resulting distributions of refractive index and strain are calculated and analyzed in terms of amplitude and harmonic content.
Measurement of the optical damage threshold of wire grid polarizers at 10.6 µm
Authors: Mohebi M. , Said A. , Soileau M. J.
Published: February 2023

We report the results of a study of the laser-induced damage threshold of wire grid polarizers for pulsed laser radiation at 10.6 µm. The polarizers were wire grids of copper or silver deposited on ZnSe substrates and overcoated with an antireflection coating. The measurements were performed using linearly polarized, normal incident, 130-ns pulses from a hybrid CO2 TEA laser. The laser was operated in the TEM00 spatial mode and single-longitudinal mode with a pulse width of 130-ns (FWHM). The beam size at the sample was 0.36 mm (FW1/e2M). Each site was irradiated only once (one on one measurement). A damage threshold of 0.8 J/cm2 (6 M W/cm2) was measured for the copper wire grid when the wires were parallel to the incident electric field (closed or low transmission condition). The damage threshold for the sample with silver wires was 2 J/cm2 (15 MW/cm2) for the same orientation. The damage threshold of both samples increased by more than a factor of 2 when the wires were oriented perpendicular to the incident electric field (the open or high transmission condition). Here we have defined the damage threshold as the lowest incident fluence (or irradiance) for which damage occurred.
Dynamics of cluster dissociation
Authors: Castleman A. W. , Keesee R. G.
Published: February 2023

Studies of cluster ionization and dissociation are of wide-ranging interest as they contribute to a further understanding of intermolecular energy flow and energy disposal following multiphoton ionization, as well as on the changing properties of matter undergoing transitions from the gas to condensed phase. A major advance in the study of unimolecular dissociation and the spectroscopy of clusters has become available through the use of multiphoton ionization methods coupled with time-of-flight reflectron techniques. Using single and two-color pulsed lasers, the excess energy introduced into a cluster can be controlled. The power of the method is demonstrated by results of recent investigations of cluster fragmentation following internal ion-molecule reactions in hydrogen bonded cluster systems. The role of dissociation and the influence of the thermochemical stability of cluster ions in affecting the appearance of magic numbers in certain cluster distributions is discussed. The application of this method in studying spectral shifts and determining ionization potentials of probe molecules following successive clustering with a solvent species is also presented.
Multilaser threshold photoionization spectroscopy of jet-cooled moles and Van der Waals clusters
Authors: Wallace Stephen C.
Published: February 2023

The dynamic properties of the excited states of polyatomic molecules show a considerable sensitivity to intermolecular interactions, both in terms of lifetimes and photoionization thresholds. Using multilaser threshold photoionization spectroscopy in conjunction with picosecond time-resolved fluorescence emission studies, it has been possible to characterize the fundamental photophysical properties of a range of model biological molecules in a supersonic beam. A number of novel features, such as conformational effects on photoionization thresholds, solvent-induced interstate decoupling, femtosecond radiationless transition rates, and cluster ion stabilization energetics are presented.
Development of spatiotemporal channels in infant vision
Authors: Wilson Hugh R.
Published: February 2023

Over the past several years a consensus has arisen regarding the spatial frequency, orientation, and temporal frequency tuning of adult visual mechanisms in both the fovea and periphery. How do these characteristics develop in the infant visual system? Discussion of this issue focuses on three major hypotheses:

(1) Infant visual development results from the progressive sensitivity increase of mechanisms that otherwise possess adult characteristics.

(2) Infant visual mechanisms are large (or low spatial frequency) versions of their adult counterparts and development consists mainly of a shift of these toward higher spatial frequencies.

(3) Infant visual mechanisms are much more broadly tuned than their adult counterparts due to reduced strength of spatial and temporal inhibition.
Saturation of green absorption in titanium-doped sapphire laser crystals
Authors: DeShazer L. G. , Eggleston John M. , Kangas K. W.
Published: February 2023

We observed a reduction in the absorption of 532-nm laser radiation by Ti:sapphire with increased laser fluence up to 3.5 J/cm2. This effect was observed for all Ti:sapphire samples studied, six crystals as of now, and is attributed to saturation of the optical transition of the Ti3+ ions. Since 532-nm radiation is used to pump Ti:sapphire lasers, it is important to know its absorption characteristics to understand completely the laser performance. However, this saturation effect is more important as an accurate method of measuring dopant ion density and absorption cross section independently. The transmittances of Ti:sapphire at 532-nm were measured with respect to incident laser fluence and fitted to a numerical saturation model using a nonsteady-state rate equation analysis based on the Franz-Nodvick approach. Upper-state fluorescence was ignored since absorption occurred on a time scale (≈10 ns) short compared to the fluorescence lifetime (≈3.2 μs). The fitted parameters were the weak-signal transmittance T0 and the saturation flux Esat (hν/σ) from which the absorption cross section and dopant ion density can be determined. For example, using a 2.1-cm Ti:sapphire sample having a weak-signal absorption coefficient of 1.58 cm−1 at 532 ran, the Esat was 7.7 J/cm2 which gave a cross section of 4.8 × 10−20 cm2 and a Ti3+ density of 3.3 × 1019 cm−3, consistent with estimates of the total Ti density.
Fundamental two-scale solution for a wave propagating in a random medium
Authors: Gozani Joseph
Published: February 2023

The fundamental solution is a result of several different analytical methods. To date, only a comparison of the scintillation index and the spectrum of intensity fluctuations (or equivalents the correlation function) has been made, with numerical simulation and experimental data. We extend the comparison of the two-scale results to the full spatial behavior of the fourth moment. We compared our results with numerical solutions obtained by the finite-difference method and found that the typical scales of the fourth moment's evolution are present.
Use of holography to measure heat transfer in high gradient systems
Authors: Owen Robert B. , Giarratano P. J. , Arp V. D.
Published: February 2023

The understanding of transient heat transfer into a confined compressible fluid is of considerable value in engine design, nuclear power plant development, and chemical engineering. Interest centers on the thermal profile, particularly as fluid expansivity and compressibility increase while approaching the critical point. Computer models which simulate this phenomena have been developed by NBS and need experimental testing. However, traditional measurement methods are indirect, while optical methods are direct, nonintru- sive, and rapid. Unfortunately, the extreme conditions of transient heat transfer and near critical conditions in the fluid boundary layer induce substantial changes in refractive indices, causing optical beam disturbances large enough to render standard phase measurements nearly useless. Even refractive techniques are difficult to apply. However, the application of holographic microscopy makes it feasible to introduce a diffusive sample beam, minimizing refractive errors. It thereby proved possible to thermally map the upper three- quarters of a boundary layer which was only a few tenths of a millimeter thick with 1-ms time resolution. In the remaining lower layer fringe packing was so extreme as to make resolution at visible wavelengths impossible.
Computer-generated holograms with speckle-suppressed reconstructions
Authors: Wyrowski Frank , Bryngdahl Olof
Published: February 2023

Computer-generated holograms possess valuable properties and offer interesting possibilities in storage and display applications. To secure a high diffraction efficiency a phase variation is superimposed on the discrete distribution to be reconstructed in the hologram construction process. A random phase distribution can be incorporated. However, it will cause speckles in the reconstruction. Wild intensity fluctuations will occur between the reconstructed sampling points. In synthetic holography other kinds of phase distribution are possible to achieve and implement.
Guided modes in uniaxial slab waveguides
Authors: Knoesen A. , Gaylord Thomas K. , Moharam M. G.
Published: February 2023

Rapidly expanding interest in the use of integrated optical waveguide circuits has revealed a lack of understanding of the optical propagation characteristics in waveguides fabricated in practical birefringent materials. The relative simplicity of guided modes in isotropic waveguides is primarily due to the decoupling of the TE and TM modes. In general, such decoupling does not exist in anisotropic structures. Even though the range of values of the propagation constants for leaky and sustained guided modes as a function of the optic axis orientation is easily determined, the accurate values of propagation constants are not.
Monitoring six-degrees-of-freedom movement with a single camera
Authors: Hilsenrath O. , Zeevi Y. Y.
Published: February 2023

The proposed method for monitoring of rigid body movement with six degrees of freedom is based on imaging the marked rigid body with a single TV camera. The cues marking the object are extracted out of one of the interlaced fields and stored as a group of pixel clouds. During the scanning time of the consecutive (complementary) interlaced field, the video input to the system is blocked and the pixel clouds are processed for cue identification and accurate localization. The position and orientation of the monitored object are computed by a single iteration (batch) method. The system is self-calibrating and determines automatically the initial position and orientation frame of reference. The location of the cues, as well as the minimal size of the cue clouds, must be discerned by the system. Only 4-6 cues have to be simultaneously detected and individually identified; the number of required cues is specified by the algorithm selected in a specific implementation.
Phasogram: image representation by localized phase
Authors: Zeevi Y. Y. , Porat M.
Published: February 2023

The importance of phase in image representation was previously demonstrated in the context of a global (Fourier) transformation. In vision where processing is accomplished by signal decomposition into localized elementary functions in the combined frequency-position space, mechanisms exist (cortical cells) which exhibit sensitivity to localized phase relationship.
Hierarchical approach for multiple object pattern recognition and detection in a noisy background
Authors: Liu Zhi-Qiang , Caelli Terry M.
Published: February 2023

Matched filtering methods are often used to detect objects in images. However, for an image scene consisting of many different patterns which are corrupted by noise, direct use of such matched filters would be very time-consuming, and the performance of the matched filter is suboptimal if the noise is nonwhite. In these cases more complex filtering processes are required which are based on the statistical characteristics of the images involved.
Finite turn-on time effects on the transient phenomena in dispersive pulse propagation
Authors: Oughstun Kurt E. , Connors Patrick T. , Sherman George C.
Published: February 2023

To study the effects of a finite turn-on time on the transient phenomena associated with dispersive pulse propagation, we consider the propagated field in a Lorentz medium due to an input hyperbolic-tangent modulated signal f(t) = u (t) sin(ωct) of carrier frequency ω
c
with initial pulse envelope where the parameter β, which is indicative of the rapidity of turn-on of the signal, is real and positive. In the limit as β → ∞ this initial envelope function approaches a unit step function. The dynamic evolution of the propagated field is described via the dynamics of the saddle points in the complex ω plane that are associated with the complex phase function appearing in the integral representation of the propagated field and their interaction with the simple pole singularities of the spectrum ũ (ω − ω
c
) of the intial pulse envelope function. This analysis shows that the precursor fields that are characteristic of the input unit step-function modulated signal will persist nearly unchanged for the input hyperbolic-tangent modulated signal for values of β of the order of δ or greater, where δ is the damping constant of the Lorentz model medium. As β decreases below δ, the precursor fields become less important and the field becomes quasimonochromatic.
Diffusion of a laser beam in turbid media
Authors: Chitanvis Shirish M. , Gerstl S. A. W.
Published: February 2023

We use the radiative transfer equation to study a laser beam propagating through a turbid medium. During the propagation, we view the beam as first scattering into a narrow forward cone, and then into a diffuse pattern. To describe this process, we propose a systematic and practical method to combine the small-angle approximation with the diffusion approximation. The method works when the scattering cross section describing scattering from aerosols can be written as the sum of a Gaussian σ
s
to describe scattering into small angles and a smooth term σ
d
to describe scattering into large/diffuse angles. We use a Green's function formalism to perform partial resummations and set up a hierarchy of approximations in the form of coupled radiative transfer equations to describe the scattering of radiation from small angles into large angles. The adjoint operator formalism then provides a simple way to obtain the net flux received by an open detector. Our approximations may be described rigorously as a power series expansion in σ0
d
/σ0
s
, the ratio of the diffusion and the forward scattering cross sections.
Applying the Kramers-Kronig relations in evaluating scattering effects in an absorptive random medium
Authors: Yang C. C.
Published: February 2023

In a passive linear medium, the principle of causality leads to the Kramers-Kronig relations. These relations relate the real and imaginary parts of dielectric permittivity through Hilbert transforms. Equivalently, there are relations between the propagation constant and absorption coefficient when a wave is propagated in such a medium. In passive random media, the real and imaginary parts of dielectric permittivity with stochastic variations also obey the Kramers-Kronig relations.
Injecting laser-locked oscillator and double-pass alexandrite amplifier with beam commutation provided by an optical circulator
Authors: Krasinski J. , Pete J. , Chin T. , Heller D. F.
Published: February 2023

A new technique is described for efficient injection locking of high power laser systems to stable but extremely weak (e.g., a few microwatts) sources.
Optically phase-locked electronic speckle pattern interferometer
Authors: Moran Steven E. , Law Robert L. , Craig Peter N. , Goldberg Warren M.
Published: February 2023

The design, operation, and characteristics of an optically phase-locked electronic speckle pattern interferometer (OPL-ESPI) are described. The OPL-ESPI sensor generates real-time equal Doppler speckle contours of vibrating objects from unstable sensor platforms with a Doppler resolution of 30 Hz and a maximum tracking range of ±5 MHz. Laboratory measurements of the sensor’s characteristics indicate a velocity tracking range of at least 8 μm/s to 8 cm/s, or a dynamic range of 40 dB. The optical phase-locked loop (OPLL) not only compensates for the deleterious effects of ambient background vibration, but also provides the basis for a new ESPI video signal processing technique which produces high contrast speckle contours. The ability to locate the OPLL lock point anywhere within the field of view of the sensor also allows examination of the spatial detail of low contrast speckle contours whose low visibility would otherwise make interpretation difficult. Since the OPL-ESPI system has local oscillator phase modulation capability, it offers the potential for detection of vibrations with amplitudes of less than a hundredth of a wavelength.
Diffraction efficiency limitations of holograms recorded in silver halide emulsions
Authors: Ward A. A. , Solymar L. , Oxford U.
Published: February 2023

Experimental measurements of the diffraction efficiencies of reflection and transmission holograms recorded in silver halide emulsions reveal an unexpected saturation in the efficiency vs exposure characteristic for high beam ratio recordings at an exposure well below the normal material saturation level. Both planar gratings and diffuse- wave holograms show similiar characteristics; the saturation effect depends on the type of processing used and is particularly significant when a no-fix process is used to minimize emulsion shrinkage. In the latter case the transmitted beam can be almost completely depleted by diffraction from noise gratings, indicating competition at recording between noise modulation and signal modulation, and it is proposed that this is the reason for reduced efficiency in all cases. The relationship between exposure modulation and permittivity modulation is quantified, and a theoretical model of the saturation effects formulated, leading to proposals for reducing detrimental effects and so to increase signal modulation and efficiency.
Spatially noncoherent wavefront reconstruction for real-time holography
Authors: Tricoles G. , Nilles J. L.
Published: February 2023

In microwave holography, time delays occur in wavefront reconstruction. Analog methods have delays in preparing scale-reduced transparencies for illumination with laser light. Digital methods have delayed in converting data to digital form, in computation, and in displaying images.
Effect of optical phase conjugation on the polarization of the transmitted image field in a multimode fiber
Authors: Zhang Yimo , Sun Yuankun , Wang Xiaochun , Li Zaichun
Published: February 2023

The image transmission through a single multimode fiber is demonstrated using a double-pass degenerate four-wave mixing (DFWM) geometry in a photorefractive crystal of Fe:LiNbO3. Also investigated are the polarization properties of the reconstructed image field. It is found that the polarization of the reconstructed image field is the same as that of the input field, even though the fiber we used is nonpolarization-maintaining.
Method of digital phase demodulation used in metrology grating technology
Authors: Wo Ju-Liang , Chan Yuan-Seng , Cao Xiang-Qun
Published: February 2023

This paper describes a new method of detecting moire signals produced by radial gratings in phase, based on digital signal processing. The system, whose core is a microcomputer, was designed to convert the moire signal in digital data. Because the technique of digital frequency analysis is used in analyzing the digital moire signal, it is possible to study quantitatively the performance figure of the moire signal and the characteristics of the driving system. By processing the digital moire signal, the phase of any point plotted on the moire contour is detected and the signal can be divided in hundreds. Instead of analog processors, the effect of digital processors may be super. In particular, it is possible to improve the accuracy of detecting radial gratings.
Quasi-evanescent waves of the total internal reflection at the lossy or gain medium
Authors: Gamo Hideya
Published: February 2023

The propagation constant

β
=
ω

μ
0

ε

in the lossy or gain medium is a complex quantity, of which the imaginary part represents damping or growing amplitude. The propagation constant in the free space

β
0

=
ω

μ
0

ε
0

is real, but the component of propagation constant parallel to the boundary surface is a complex quantity, because of the continuity of tangential components of the propagation vectors: β1
t
= β2
t
(generalized Snell’s law). Consequently, the normal component of propagation vector

β

2
n

=

(

β
0
2

−

β

2
t

2

)

1
/
2

becomes complex. By using the wave impedances ηTM= β
n
/ωϵand ηTE= ω
μ
/β
n
for TM and TE waves, we obtain the complex reflection and transmission coefficients (generalized Fresnel formulas). In the case of total internal reflection at lossless media, β2
t
is real and greater than β0, and hence β2
n
is imaginary. This is the well-known evanescent damping. In the case of lossy or gain medium, however, β2
n
becomes a complex quantity. The waves outside lossy or gain media are not perfectly evanescent but contain some radiating components. This phenomena which corresponds to the leaky surface waves will be compared with observation using an absorbing 90° prism.
Ray tracing through tandem Ronchi rulings
Authors: Horwitz James W.
Published: February 2023

In the course of our work, a problem was posed, namely, to evaluate the radiometric properties of an optical system consisting of a light source, two closely spaced Ronchi rulings, and a detector. The particular application was a glass scale that had a moving Vernier. A moire is formed between the rulings, and the motion of the Vernier causes a modulation of radiometric throughput.
Multiple aperture optical imaging
Authors: Bergey Dana J. , Mills James P. , Rogers Steven K.
Published: February 2023

The effect of multiple aperture systems on coherent and incoherent optical imaging was analyzed. Most of the effort was concentrated on the coherent imaging case. A computer program was developed that predicted the images of several simple objects as viewed through various types of multiple aperture. Objects such as edges, bars, and circles were chosen since more complicated objects can be thought of as a collection of these simple objects. These multiaperture images were produced and photographed in the laboratory. The photographs and the computer-generated plots are then analyzed to determine how the spacing, size, and number of subapertures affect the image. These images are compared and contrasted to determine what information can be obtained from them. Essential information, such as shape, orientation, position, and dimensions of the object, was looked for. Finally, the effects of the same multiple apertures on incoherent imaging are studied, and the results are compared with those of the coherent case.
Fiber-optic gyroscope using a standing-wave acoustooptic modulator
Authors: Sun Jing , Ih Charles S. , Grot Annette , Mentzer Mark
Published: February 2023

We are studying a new type of fiber-optic gyroscope and propose to utilize a standing-wave acoustooptic modulator (SWAOM) as a component of the system. When a laser beam passes through the SWAOM, two laser beams emerge: one is the diffracted first-order beam and the other is the undiffracted zeroth-order beam. The diffracted beam has two components; the frequency of one component is shifted up and the other is shifted down by the acoustic drive frequency ω
s
.