bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and stability analysis of an S-tapered optical fiber-based sensor structure
Authors: Xiao Lucan , Zhang Wen , Liu Xuecheng , Lang Xianzheng , Singh Ragini , Li Guoru , Xie Yiyan , Zhang Bingyuan , Kumar Santosh
Published: February 2023

In this paper, three S-tapered fiber (STF) structures with different diameters (40, 60, and 80 µm) are fabricated using conventional single-mode fiber. First, the reproducibility of the proposed S-tapered structure is confirmed through an analysis of the diameter distribution. Considering the transmitted intensities of the three various diameter, S-tapered structures reveal that the STF with a 40 µm diameter produces more evanescent waves and is more sensitive to external refractive index variations. Therefore, the STF structure with a 40 µm diameter was evaluated for the detection of different concentration of glucose solutions, demonstrating that the structure has the potential to be utilized to develop a highly sensitive fiber sensor.
Fringe pattern analysis to evaluate light sources and sensors in digital photoelasticity
Authors: Fandiño-Toro Hermes , Aristizábal-López Yeins , Restrepo-Martínez Alejandro , Briñez-de León Juan
Published: February 2023

When experimental photoelasticity images are acquired, the spectral interaction between the light source and the sensor used affect the visual information of the fringe patterns in the produced images. Such interaction can lead to fringe patterns with an overall high quality, but also can lead to images with indistinguishable fringes, and bad stress field reconstruction. We introduce a strategy to evaluate such interaction that relies on measuring the value of four handcrafted descriptors: contrast, an image descriptor that accounts simultaneously for blur and noise, a Fourier-based descriptor to measure image quality, and image entropy. The utility of the proposed strategy was validated by measuring the selected descriptors on computational photoelasticity images, and the fringe orders achieved when evaluating the stress field, from 240 spectral configurations: 24 light sources and 10 sensors. We found that high values of the selected descriptors can be related to spectral configurations that lead to better stress field reconstruction. Overall, the results show that the selected descriptors can be useful to identify bad and good spectral interactions, which could help to design better protocols for acquiring photoelasticity images.
Analysis of image motion for optical remote sensing satellites staring imaging with area-array detectors
Authors: Peng Jiantao , He Yunsheng , Zheng Lianyu , Wang Shijie , Cheng Weiqiang
Published: February 2023

In this paper, the image motion introduced by the staring action itself during optical remote sensing satellites staring imaging with area-array detectors is studied. The image motion is decomposed into the angle-rotation image motion caused by the change of observation angle, the size-scaling image motion caused by the change of observation distance, and the Earth-rotation image motion caused by the rotation of the ground object with the Earth. The theoretical derivation of the angle-rotation image motion and size-scaling image motion is conducted, and the numerical analysis of the Earth-rotation image motion is carried out. Based on the comparison among the characteristics of the three types of image motions, the conclusion is drawn that, for general staring imaging scenes, the angle-rotation image motion is dominant, followed by the size-scaling image motion and the ignorable Earth-rotation image motion. On the condition that the image motion does not exceed 1 pixel, the allowed maximum exposure time for area-array staring imaging is analyzed. It is found that the large-array satellite is not suitable for long-exposure imaging, as its allowed exposure time decreases rapidly with the increase of roll angle. A satellite with a 12k×12k area-array detector and 500 km orbit is taken as an example. The allowed exposure time is 0.88 s when roll angle of the satellite is 0°; it decreases to 0.02 s when the roll angle increases to 28°.
Influence of Yokukansan on the refractive index of neuroblastoma cells
Authors: Baczewska Maria , Królikowska Milena , Mazur Martyna , Nowak Natalia , Szymański Jędrzej , Krauze Wojciech , Cheng Chau-Jern , Kujawińska Małgorzata
Published: February 2023

Yokukansan (YKS) is a traditional Japanese herbal medicine that is increasingly being studied for its effects on neurodegenerative diseases. In our study, we presented a novel methodology for a multimodal analysis of the effects of YKS on nerve cells. The measurements of 3D refractive index distribution and its changes performed by holographic tomography were supported with an investigation by Raman micro-spectroscopy and fluorescence microscopy to gather complementary morphological and chemical information about cells and YKS influence. It was shown that at the concentrations tested, YKS inhibits proliferation, possibly involving reactive oxygen species. Also substantial changes in the cell RI after few hours of YKS exposure were detected, followed by longer-term changes in cell lipid composition and chromatin state.
Key physical topology features for optical backbone networks via a multilayer correlation analysis
Authors: Higashimori Katsuaki , Tanaka Takafumi , Inuzuka Fumikazu , Ohara Takuya , Inoue Takeru
Published: February 2023

A communication network is a multilayer network comprising various layered technologies, and the underlying physical topology is an important aspect that determines the upper bound of overall system performance, including total communication capacity, cost, and robustness. We expect that understanding the impact of the physical topology on system performance will lead to better optical communication network design in the future, and we thus focus on clarifying the relationship between physical topology features and system performance. There have been various studies on the relationship between topology features and overall network performance. For example, the average number of hops and the cluster coefficient are well known to change network properties in complex networks. From the perspective of optical communication networks, it is known that the algebraic connectivity and average path length are related to total network capacity, and these findings have been applied in physical topology design models. On the other hand, there have been no quantitative comparisons among various topology features, and the comprehensiveness of the population from which these features are extracted is insufficient. Hence, we have developed a multilayer (physical topology and layer 1) correlation analysis framework that enables a quantitative comparison of topology features. We use this framework to numerically examine the relationships between physical topology features and the total communication capacity, cost, and robustness of optical communication networks, including graph features (especially graph spectra) that have not been investigated. The results show that the Laplacian spectral radius and geodesic distance Laplacian spectral radius are strongly related to system performance, in addition to the conventional average number of hops, cluster coefficient, algebraic connectivity, and average path length. We confirm that these correlations hold for the different network sizes and spatial nonuniformity of real optical backbone networks in different countries and regions. The results show that the average path length and cluster coefficient, or the Laplacian spectral radius and geodesic distance Laplacian spectral radius, are important guidelines for physical topology design of real optical backbone networks.
Direct and heterodyne detectors for the infrared
Authors: Spears D. L.
Published: February 2023

The performance of IR lidar and heterodyne radiometry systems is generally limited by the sensitivity of a wideband IR detector or detector array operating in either the direct or heterodyne detection mode. Here a comparison of heterodyne and direct detection for remote sensing uses is briefly described, and important differences are pointed out. Some of the design considerations for high-performance wideband photodiodes and photoconductors are discussed, including sensitivity-bandwidth trade-offs and when preamplifier noise becomes a limiting factor. A survey of available direct and coherent detectors at 10.6 μm and other IR wavelengths is presented, which includes operating requirements and sensitivities of detectors with bandwidths in the 10–2000-MHz range and cut-off wavelengths in the 5–30-μm region. Various wideband photodiodes and photoconductors using group IV, III–V, and II–VI semiconductor materials are compared.
Three-dimensional scaling of OSA uniform color scales
Authors: Man T. M. , MacAdam David L.
Published: February 2023

Three young observers judged the differences they perceived between all pairs of twenty-five colors in twelve different oblique planes formed by the OSA uniform color scales. Each observer repeated each judgment at least three times. The rms variances of the judgments ranged from 5 to 15%. For each set of colors, a 3-D configuration of points was determined for each observer, in which distances between pairs of points are, as nearly as possible, proportional to the judgments raised to a power P. The optimal value of P differed from observer to observer and from set to set of colors. For two of the observers, P was always >1.0 (as great as 1.61). For the third observer, P was 1.29 or less (as low as 0.76). The resulting rms errors of fit in the configurations were 13.8 ± 4.8%. The most successful configurations indicate (with some remarkable agreements between observers) strong curvatures of the surfaces on which the optimal configurations of the sets of twenty-five points are located. These results indicate that non-Euclidean space is needed to represent perceived color differences by geometric distances within the attainable precision of judgments.
Comparison of chromaticity discrimination ellipses
Authors: Robertson A. R.
Published: February 2023

Ellipses representing the discrimination of small color differences in the CIE chromaticity diagram have been determined recently by several investigators using surface colors (paints and textiles). When the classical MacAdam ellipses are interpolated to the same color centers they are oriented in significantly different directions. The orientation of the ellipses determined by Wyszecki and Fielder, who, like MacAdam, used colored lights, agrees better with the surface-color results in most cases. The ellipses from the various surface-color studies agree well with each other in shape and orientation, but the relative sizes for different color centers do not agree.
Free-electron lasers
Authors: Brau C. A.
Published: February 2023

No summary of this tutorial or biographical information was available at press time.
Diode-pumped Nd:YAG at 415-mW cw TEM00 10.8% total efficiency
Authors: Berger J. , Welch David , Scifres Donald R. , Streifer William , Cross Peter S.
Published: February 2023

Solid-state lasers with absorption bands between 0.7 and 0.9 μm have been efficiently pumped by AlGaAs laser diode arrays. Previously, we reported 370-mW 1.06-μm cw TEM00 output from Nd:YAG end pumped by a monolithic (SDL-2430) 100-μm laser diode array. Here we report 10.8% electrical to optical conversion efficiency for Nd:YAG at 415-mW 1.06-μm cw TEM00 output. The maximum cw output power was 465 mW (9.3% efficiency) in the TEM00 mode, which is the highest cw power generated for the efficient end pump configuration.
Effect of backscattering on the fluctuation properties of a He-Ne ring laser
Authors: Christian W. R. , Mandel Leonard
Published: February 2023

We have made a systematic investigation of the effect of reflecting light from one counterpropagating mode in a ring laser back into the other mode. In the experiment provision is made for retroreflecting a controllable fraction of the emerging optical field with variable phase back into the ring laser, while the two mode intensities, their fluctuations, and their cross-correlation are measured photoelectrically. The results of the measurements are compared to theoretical predictions based on the analytic solution of the Fokker-Planck equation in the steady state, and good agreement is found. In particular, we confirm that when the sum R1 + R2 is zero, where R1,R2 are complex backscattering coefficients, the laser behaves as if there is no backscattering in the steady state. (12 min)
Spectral response calculations of rugate filters
Authors: Southwell W. H.
Published: February 2023

All gradient-index optical filter calculations may be made using the characteristic matrix approach by dividing the index profile into many small homogeneous index layers. This attests to the versatility of the characteristic matrix technique. However, a disadvantage is the computation time required for thick filters and possibly the lack of insight for certain types of gradient-index structure. The coupled-wave theory (variation of constants) has been used to derive a closed-form expression for the reflection of filters having periodic index variation. Boundary conditions are used to account for arbitrary substrate and incident media. The total complex electric field is resolved into left- and right-traveling components. Such an approach makes it convenient to derive the amplitude reflection coefficient as well as the electric field standing waves inside the structure. The results are also used to predict an optical monitor response during deposition of such gradient-index structures. The computational time for the spectral response is independent of the number of periods or filter thickness. Consequently, for thick filters the computer computation time may be orders of magnitude faster than the characteristic matrix approach.
Scalar angular scattering theory for multilayer coatings
Authors: Zavislan James M. , Eastman Jay M.
Published: February 2023

A scalar scattering model for multilayer optical coatings is described that predicts the angular distribution of scattered light within 35° of the specular beam for incidence angles of <35°. The model predicts the scattering from coatings with uncorrelated roughness, additive roughness, or uncorrelated index variations. The scattering model treats a rough or inhomogeneous coating as a thin screen with random amplitude and phase variations. The amplitude and phase variations are related to the design of the coating and to the first- and second-order statistics of the roughness or index inhomogeneities.
Triangular coordinate graphical presentation for the optical performance of a semitransparent metal film
Authors: Apfel Joseph H.
Published: February 2023

The optical performance of an ideal thin film can be represented by a single point on a triangular coordinate graph because the sum of the reflectance, transmittance, and absorption is unity. Several examples are presented to show how the triangular coordinate graph provides a useful perspective on the interplay between the optical properties and performance of a semitransparent metal film.
Relative numbers of long-wavelength-sensitive L and middle-wavelength-sensitive M cones in the human parafoveal retina
Authors: Nerger Janice L. , Cicerone Carol M.
Published: February 2023

We present psychophysically based estimates of the relative numbers of L to M cones as a function of retinal eccentricity using the methods1 which we previously applied to the fovea. Parafoveal detection data of three trichromatic observers were used to obtain estimates of this ratio at retinal eccentricities of 0.5, 1.0, 2.0, and 4.0°. The probability of detection functions was measured for a small (2.0-6.0-min) brief (50-ms) monochromatic red test on a green background and a monochromatic green test on a spectrally mixed violet background. These conditions were selected to provide L and M cone isolation in addition to eliminating the contributions of the rods and short-wavelength-sensitive cones. Ratios were obtained in two ways: (1) by using our model to obtain best-fitting theoretical functions and (2) by comparison of the slopes of the psychometric functions. The mean L to M cone ratio was 2.10 at 0.5° and 1.99 at 1.0° eccentricity. The ratio obtained at 0.5 and 1.0° did not significantly differ from the ratio obtained in the fovea for each observer. These results indicate that the L to M cone ratio remains stable from 0 to 1.0° in the temporal retina. Our estimates of the density of cones (L + M) show a decline with eccentricity which is in good agreement with anatomical studies.
Long-wavelength insensitivity in young infants indicated by transient pupillary responses
Authors: Clavadetscher John E. , Opie Kathleen Scanlon
Published: February 2023

In adults, the pupil shows a sharp transient constriction to isoluminant chromatic exchanges. Red → green and green → red exchanges produce constrictions of about equal magnitude in normal adults but markedly different responses in adult protanopes and deuteranopes. In this study, pupillary responses were recorded from infants while they were looking at 20° schematic video faces that appeared green or red to normal adults. Ten infants were run in each age group, and each infant's responses were averaged within conditions. Three- and 7-week olds showed substantial pupillary constrictions to red → green exchanges but generally not to green → red exchanges. Most 11-week olds showed clear constrictions to both directions of exchange. Additional conditions showed that infants of all ages had clear constrictions to intensity increments produced by changing a dark face to a bright green one.
Dark-current multiplication and excess noise factor in conventional avalanche photodiodes
Authors: Hakim Nagib Z. , Teich Malvin C. , Saleh B. E. A.
Published: February 2023

The volume dark current in a conventional avalanche photodiode arises from random electron-hole pair generations in the depletion volume of the device. This process can be characterized by an average multiplication (gain) 〈M
d
〉 and an excess noise factor F
d
. Because of the randomness in the locations of the carrier generations, the gain is smaller and the excess noise factor is larger than the usual values associated with injected electrons 〈M
g
〉 and F
e
). Expressions for 〈M
d
〉 and F
d
are presented and graphically displayed. Use of these formulas in the SNR gives rise to results that differ from those obtained by assuming that the dark current multiplies in the same manner as injected carriers. The distinction can be important in the case of multiplication-noise-limited operation.
Interocular phase: its effect on binocular summation
Authors: Cogan Alexander I. , Clarke Maureen , Rossi Andrew
Published: February 2023

Assuming that the internal response to a brief change of luminance is biphasic,1 it has been proposed2 that responses to binocular stimuli must be interocularly in phase to produce a hypothetical fused effect represented psychophysically as binocular summation (e.g., at threshold). Binocular summation has been demonstrated3 for stimuli that were both spatially and temporally in 0 or 180° phase. These observations are in agreement with the model.2 To test it further, we measured differential luminance thresholds for binocular stimuli of like and opposite polarity as a function of interocular delay (SOA). Pulse duration was a parameter between 5 and 150 ms. With no delay, thresholds were lower for like than for opposite polarity stimuli: the usual finding. The relationship was reversed at a critical delay, near SOA = 50 ms. This effect was at maximum for pulses of 50-ms duration, which suggests that (1) both on and off parts of a pulse contribute to the net response and (2) there is a limit (a temporal window) of phase dependent binocular interaction.
Modifying the specificity of distortion-invariant pattern recognition filters
Authors: Ochoa Ellen , Schils George F. , Sweeney Donald W.
Published: February 2023

There are different requirements on the specificity of a correlation filter used for optical pattern recognition that depend on the particular application. For example, in industrial inspection, small differences between objects are important so the filter should be designed to be very specific. In contrast, target recognition often requires detection of a class of similar object. We have previously designed correlation filters, using a spectral iteration technique, that are invariant to perspective view, position, and intensity while remaining specific to the target object. In operation, several such holographic filters are applied to the input scene, and as the filters are changed, the output is processed for points of constant intensity. These points identify target locations. We now apply different constraints during the iteration process to modify the specificity of the filters. Methods include using fewer harmonics, apodizing the eigenvalue profile, and forcing certain harmonics to zero. We apply the filters to blurred, noisy, or partially obstructed objects.
Optical recognition of 3-D targets from an arbitrary perspective view
Authors: Schils George F. , Ochoa Ellen , Sweeney Donald W.
Published: February 2023

A small bank of optical holographic filters can be designed to recognize a 3-D object from a large solid cone of views. Invariance to image intensity and location is also exhibited. The method of design is first to decompose the set of 3-D views into a set of characteristic image components (eigenimages). These orthogonal image components contain complete information about all the object views to be recognized. An iterative method is applied to combine these eigenimages with a different relative phasing so that the information contained in them can easily be extracted when implemented optically. The iterative method produces a solution for the entire bank of holographic filters. We have found that a bank of about twenty filters is sufficient to recognize a thousand or more object views, while still retaining specificity of recognition. We discuss factors that allow recognition of the discrete training set of images as well as the continuum of intermediate views. The most important factor for continuum recognition is choosing the correct sampling of the different object views.
Integrated optical photorefractive vector matrix multiplication
Authors: Brady David , Psaltis Demetri
Published: February 2023

Vector matrix multipliers have figured prominently in optical processing architectures because the minimal processing power requirements and the global communication needs of these devices dovetail nicely with the capabilities of optics. We describe an architecture for implementing vector matrix multiplication in integrated optics. The matrix is recorded in waveguiding lithium niobate by using unguided light to write photorefractive holograms. The matrix is read out by a vector of guided beams which are diffracted into an output vector. Crosstalk between guided beams is avoided due to the Bragg matching constraint for volume holograms. The diffraction of guided beams via gratings written with unguided light is accomplished using the rotational degeneracy of Bragg matched beams about the grating wave vector. By relaxing slightly the Bragg constraint it is possible to write an N × N matrix using a signal beam modulated by a mask of N2 pinholes and a single reference beam. We present preliminary experimental results concerning multiple holograms written in waveguides from above the waveguiding plane.
Nonlinear DFBG notch filter: design considerations
Authors: Zanoni Raymond , Rochford K. , Seaton Colin T. , Stegeman George I. , Assanto G.
Published: February 2023

An integrated optical notch filter formed from two DFBGs in series is studied in detail. Tunable optical notch filters have been proposed,1 but here we consider notch filters in nonlinear optical waveguides. The notch filter is modeled using coupled-mode theory where absorption, detuning, and nonlinear saturation are included as model parameters. The limitations of both optical absorption and nonlinear saturation on device performance are presented. Also, it is shown that detuning provides some advantages and introduces some new effects due to spatial instabilities in the grating structure.
Impaired flicker sensitivity in glaucoma at 5 and 15 Hz
Authors: Brussell Edward M. , Dixon Mike , Balazsi A. Gordon
Published: February 2023

There is a growing body of evidence that deficits in flicker sensitivity are an early symptom of glaucoma. For example, Tyler1 found a large subset of patients who showed deficits principally at middle temporal frequencies. An interesting clinical implication of this finding was that screening techniques measuring either CFF or sensitivity to low frequencies might miss glaucomatous defects in many individuals. We have collected data that are consistent with Tyler’s finding using multiflash campimetry, a computer implemented technique that allows temporal resolving power to be quantified by determining the duty cycle required to detect flicker. In this study, the ability to detect flicker at 5 and 15 Hz was compared in 20 retinal locations within the central 5°. Although all observers showed greater temporal resolving power at 5 Hz, compared with 15 Hz, performance differences were exacerbated for glaucoma suspects and even more so for glaucoma patients. One way of accounting for these and Tyler's results is to assume that flicker techniques are primarily sensitive to activity in nerve fibers possessing bandpass temporal characteristics with large bandwidths.
Contrast sensitivity-luminance function in aging
Authors: Sloane Michael E. , Owsley Cynthia
Published: February 2023

We have previously reported (ARVO, 1987) that senile miosis cannot account for age-related deficits in spatial contrast sensitivity over a three-log unit range of luminance. Although the participants were free from significant media opacity, the possibility remains that their deficits could be due to differences in retinal illuminance between young and older observers. If a difference in retinal illuminance accounted for the age differences in contrast sensitivity, functions plotting sensitivity against luminance should be superimposable by a shift parallel to the luminance axis. In the present study we measured spatial contrast sensitivity under a range of luminance levels in young and old adults who were free from identifiable eye disease. Contrast thresholds for sinusoidal gratings (0.5, 2, 4, 8 cycles/deg) were measured over a three-log unit range of luminance (0.1-107 cd/m2), sampled at 0.5-log unit intervals. The contrast sensitivity–luminance functions changed as a function of test spatial frequency for both age groups. The functions at all spatial frequencies were parallel for the two age groups and could be superimposed by a vertical shift along the sensitivity axis and not by a lateral shift along the luminance axis. These data suggest that the age-related deficits in spatial contrast sensitivity are not the simple consequence of reductions in retinal illuminance produced by either senile miosis or increased light absorption by the ocular media.
Photon number distributions for an inhomogeneously broadened laser with an absorber
Authors: Mortazavi Mansour , Singh Surendra
Published: February 2023

An equation of motion for the density matrix of the field of an inhomogeneously broadened single-mode laser containing a saturable absorber is derived. Using the photon number representation this equation is solved in the steady state. High-intensity photon number distributions are obtained for the on-resonance operation of the laser. Off-resonance operation is also considered. Curves are presented to illustrate the behavior, and the results are compared with earlier investigations.
Periodic and chaotic solutions in a spin-1 model of the free-running ruby nuclear magnetic resonance laser
Authors: Chyba David E. , Meier Peter F.
Published: February 2023

Previous studies of the ruby nuclear magnetic resonance laser1 have relied on a model of the system in which the 27AI nucleus is treated as a spin-½ (two-level) system. The semiclassical model which results is reducible to two equations and so requires signal injection or modulation of a parameter to give chaotic behavior. A model involving a higher spin and more lasing levels may require a higher dimensional phase space and may, therefore, give chaotic behavior even in the free-running case. Our model is derived from a Hamiltonian for a spin-1 object in superimposed static and sinusoidally oscillating magnetic fields, incorporating also the simplest possible quadrupole interaction. The quadrupole splitting can be experimentally adjusted and is considered as a control parameter along with the excitation. With additional simplifications, a set of four equations of motion can be obtained. These reduce to the earlier two-equation model in the limit of zero quadrupole splitting. We have found period-doubling bifurcations of certain limit cycles leading to chaotic solutions. Further work is in progress, including removing some of the restrictions involved in the reduction to the four-equation system.
Pair-pumped upconversion solid-state laser
Authors: Rand Stephen C. , Pollack S. A.
Published: February 2023

A new class of laser is reported in which inversion is due to pair-mediated upconversion, quite distinct from conventional sequential one-photon or multiphoton excitation mechanisms. Upconversion of radiation is standardly accomplished by multiphoton processes relying on linear or nonlinear susceptibilities of individual atoms. However, more efficient upconversion can occur by cooperative multiatom processes involving simultaneous transitions on two or more atoms. Cooperative pair pumping in 5% Er:LiYF4 produces laser action from upconverted energy states following pumping at 1.54 µm with a flashlamp-pumped Er:glass laser on the ground to the 4/13/2 transition. Two neighboring 4/13/2 ions decay cooperatively to yield one 4/9/2 ion (which relaxes quickly to 4/11/2), competing effectively with spontaneous emission because of strong interatom coupling and long 4/13/2 lifetime. The upconversion pair process is shown for the first time to be so effective in Er:YLF that this mechanism alone can invert the 4/11/2 state with respect to lower states, generating long delays proportional to inverse pump energy in the onset of lasing.
Energy transfer in emerald laser crystals
Authors: Quarles Gregory J. , Suchocki Andrzej , Powell Richard C. , Lie Shui
Published: February 2023

Be3Al2(SiO3)6:Cr3+ (emerald) has important potential applications as a tunable vibronic laser material. The spectra of emerald exhibit structure which can be attributed to Cr3+ ions occupying three nonequivalent crystal field sites. We present here the results of characterizing the optical properties of the Cr3+ ions in emerald using time-resolved site-selection (TRSS) spectroscopy and four-wave mixing (FWM) spectroscopy techniques. The temperature and crossing angle dependence of the FWM signal decay rate are consistent with scattering of the probe beam from a laser-induced population grating of Cr3+ ions. The time evolution of the FWM signal at low temperatures is consistent with the theory of partially coherent exciton migration. The diffusion coefficient D for spatial migration of energy was determined from theoretical fits to the FWM data. D was found to increase exponentially with temperature, consistent with phonon-assisted energy transfer processes. TRSS results demonstrate the presence of short-range energy transfer between ions in nonequivalent types of site, which is significantly different from the long-range migration process probed by FWM measurements.
Information capacity of photon-number-squeezed light
Authors: Saleh B. E. A. , Teich Malvin C.
Published: February 2023

Numerous schemes have been recently suggested for generating photon-number-squeezed light. In one class of technique, initially Poisson photons are modified (using methods such as deadtime deletion, decimation, coincidence decimation, and overflow count deletion) to yield sub-Poisson photons. In another class, feedback is applied (e.g., by control of the rate of generation of photoevents) so that the resultant point process is self-exciting instead of Poisson. Are such light sources useful for optical communication? Can the channel capacity C of a lightwave communication system based on photoevent point process observations be increased by use of photon-number-squeezed light?
Beam coupling, bistability, and commutative and noncommutative behavior of self-pumping beams in BaTiO3
Authors: Venkateswarlu Putcha , Jagannath H. , George M. C. , Miahnahri A.
Published: February 2023

BaTiO3 crystal is self-pumped by coherent beams A1 and A2 from a multilongitudinal-mode Ar+ laser. The self-pumped

A
1
*

 and 

A
2
*

with a 4800-Å laser showed oscillations whose frequency increases with laser intensity. They are bistable and do not coexist. With 5145 and 4765 Å,

A
1
*

 and 

A
2
*

coexist and are stable with minor coherent pulsations. When coexisting,

A
2
*

 and 

A
1
*

are strong with a 5145-Å laser while they are very weak with 4765 Å. A mutually consistent fanning occurs so that a component of each fanned beam (A1 and A2) is incident on the other beam’s grating at the correct Bragg angle to undergo total internal reflection and get into the reverse direction of the other. Thus when A1 is shut off the detector D2 of

A
2
*

shows a sharp intensity drop and similarly the D1 of

A
1
*

, when A2 is off. The counterparts of the images at D1 and D2 are seen outside the crystal between the outgoing directions of A1 and A2. When the beams A1, and A2 with 5145 Å are incoherent, the sequence A1 + A2 does not commute with A2 + A1.
Stimulated Brillouin scattering fidelity with a variable aberrator
Authors: Schelonka L. P.
Published: February 2023

We have examined stimulated Brillouin scattering (SBS) wavefront reconstruction with a continuously variable aberrator. A tripled single-longitudinal-mode YAG laser at 355 nm was used. The 10-ns laser pulse width was approximately twice the phonon lifetime of liquid hexane (the SBS medium), and the pulse energy was varied from SBS threshold to ~20 times threshold. No light pipes or phase plates were used. The aberrator produced continuously variable optical path differences (OPDs) from 0.14λ to 2.5λ (peak to valley). For pulses with 20 times threshold energy, the SBS accurately reconstructed the wavefront, independent of pump aberration for OPDs from 0.14λ to 2.5λ. For pulses with 7 times threshold energy, the SBS accurately reconstructed the wavefront for OPDs from 0.14λ to 1.3λ, but the fidelity monotonically declined for larger OPD. For pulses slightly above threshold, the fidelity was constant for a lower range of OPDs and declined for large OPD. At all intensities, the decline in fidelity was distinct from a decline in reflectivity, which was observed as the aberrator reduced the pump focal intensity. The onset of fidelity decline always occurred during stronger aberrations than the onset of reflectivity decline.
Mechanisms of curvature discrimination
Authors: Wilson Hugh R. , Richards Whitman
Published: February 2023

Visual processing of curvature was investigated by measuring increment thresholds for curvatures from 0.3 to 25 deg−1. Discrimination of simple curve contours was compared with thresholds for both bandpass and low-pass filtered stimuli. Surprisingly, the higher spatial frequency, orientation selective mechanisms dominate curvature processing, even at low curvatures where lower spatial frequency masks come into play. Our data suggest two different types of curvature mechanism. A simple modification of Wilson's model is in good quantitative agreement with these data. A further modification is required, however, to explain curvature discrimination of Vernier edges created by offsetting the two halves of a grating. In this case, end-stopping must be made explicit using relatively small masks with broad orientation tuning.
Associative learning of a shape from a shading operator
Authors: Knill David C. , Kersten Daniel
Published: February 2023

The shading pattern over a surface provides information about the shape of the surface. The problem of deriving shape from shading, however, is underconstrained. Current modeling solutions to the problem employ heuristic local constraints on shape, such as smoothness or the umbilical point approximation, in solving the problem. The approach taken here is to assume that the constraints are embodied in the statistical structure of natural surfaces. We apply a linear associative algorithm to learn a shape from shading operator from pairs of example surfaces and images. The training set is generated using a fractal model of natural surfaces. Images are represented as contrast values at each pixel, and surfaces are represented as surface normal vectors at each pixel. The learned operator consists of two spatially localized convolution filters for computing the x and y components of the surface normal at each pixel in an image. Application of these filters to novel images results in qualitatively good reconstructions. The model is insensitive to changes in incident light flux and may easily accommodate changes in light source direction by reorientation of the filters. Due to the spatial localization of the filters, very low-frequency changes in surface shape are lost in the reconstruction. This correlates well with human perception of shape from shading away from edges.
Strategies for integrating stereo and monocular surface information
Authors: Stevens Kent A. , Brookes Allen
Published: February 2023

A continuous surface rendered monocularly by outline and surface contours is interpreted in three dimensions as having a definite shape in depth. A random dot stereogram of the same surface, devoid of monocular cues, usually conveys a more compelling 3-D impression of the surface. The natural viewing condition, of course, is a binocular projection containing redundantly consisent monocular cues.
Spatial evolution of beam profiles in an SBS amplifier
Authors: Miller Edward J. , Skeldon Mark D. , Boyd Robert W.
Published: February 2023

We have performed an experimental and theoretical analysis of how a probe beam is modified on propagation through an SBS gain medium for various input beam parameters and total gains through the SBS medium. For the case of an undepleted lowest-order Gaussian pump beam, we found that when the probe spot size is smaller than the pump spot size in the focal region, the input probe profile is essentially preserved during amplification. However, if the probe is larger than the pump, the beam is modified as it propagates through the medium and in the limit of high gain takes on the mode structure of the pump. To model these effects mathematically, we decompose the probe wave into Laguerre-Gaussian modes and solve numerically the equations describing the spatial evolution of the individual modes. The result of the nonlinear coupling is to transfer energy from the pump beam to the probe and to redistribute the energy among the probe modes. In some cases, the transmitted probe shows a pronounced ring structure.
Caustic and wave aberrations: Clairaut’s equation
Authors: Ojeda-Castaneda J. , Pons Alicia
Published: February 2023

The departures from sphericity of a wavefront can be specified by either the wave aberration function or the transversal ray aberrations. Another possibility of specifying the departures from sphericity is by considering the envelope of a set of rays. Here we indicate that the analytical form of the caustic can be obtained readily from the wave aberration function or from the transversal ray aberrations. We show that the analytical form of the caustic and the parametric expressions for ray tracing are the particular solution and the general solution, respectively, of Clairaut's nonlinear differential equation.
Analysis of loss mechanisms in silver film-diffused optical waveguides
Authors: Cox H.L. , O’Connor D. , Ashley P.R. , Morgan R.L.
Published: February 2023

A program has been developed to fabricate silver film-diffused glass, optical waveguides for use as optical couplers in optical signal processing systems. The diffusion process was assisted by applying electric fields ranging from 40 to 200 V/mm and at elevated temperatures ranging from 270 to 300°C. The graded-index profiles were analyzed using the WKB method and the effective index of refraction values measured with the prism coupling technique. Results of the WKB analysis showed that a Gaussian profile fits the effective index data best. Loss measurements of around 1 dB/cm were found for wavelengths of 633 nm or longer. However, at shorter wavelengths of 488 and 514 nm losses are substantially higher and could reach several dB/cm. One mechanism proposed for this loss is the wavelength-dependent absorption by silver aggregates or silver complexes which are present in the guiding wave layer. A strong red incoherent emission is produced in the guiding-wave layer, and this radiation is emitted normal to the waveguide surface when guided wave modes are excited at 488 nm. When 514 nm is used, this emission takes on a brownish red appearance. This emission consists of broad bands with band centers that are shifted from the excitation line by wavenumber shifts ranging from 3190 to 6475 cm-1, with 488-nm excitation and with 514-nm excitation, the shifts range from 4250 to 5320 cm-1.
Symmetry perception by optical transformation
Authors: Khadr N. , Pederson D.O. , Salamo G.J. , Weber B. A.
Published: February 2023

Real-time optical processors have long been recognized for such potential applications as optical computing, robotic vision, radar signal processing, and pattern recognition. In particular, optical processors offer a powerful alternative to electronic processors due to their ability to process in parallel a large amount of spatial information and to perform at extremely high speeds a large number of spatial operations. One example of a real-time optical processor is a simple modification of an early optical correlator proposed by VanderLugt. In a modern version of the VanderLugt processor film is replaced by a photorefractive nonlinear optical medium. The advantage of the crystal approach over traditional wet-chemical processing is that the correlation between different scenes is carried out in real time and not limited by the time needed for development or film replacement. Despite the success of modern correlators, however, they are hampered by an old but severe limitation for practical application. Even the modern correlator has not overcome the inability of traditional correlators to recognize an object independent of its size or the viewed perspective.
Combined space- and Fourier-domain moment invariants
Authors: Freeman Mark O. , Saleh B. E. A.
Published: February 2023

A moment-based pattern recognition system (in this case moment invariants) can be significantly improved by simply repeating the feature set in the Fourier domain. Moment-based feature sets in the space domain have these well-known properties: (1) they are best for distinguishing macroscopic regions of an image such as shapes; (2) high-order moments capture more information about the finer details contained in an image but are more susceptible to corruption by noise than are low-order moments. We show by theory and example that a feature set based on the low-order moments of the Fourier transform of a pattern has strengths that complement those of the usual space-domain moment-based feature sets. Improved results and a wider range of application result from using moment-based features from both domains. Basically, low-order Fourier-domain moments respond strongly to high-frequency details while ignoring the macroscopic shapes in an image. At the same time, their susceptibility to corruption by additive white noise is about the same as for low-order space-domain moments. Evidence shows that Fourier-domain moment invariants are far more useful for pattern recognition than the common ring-wedge-type features or other features based on the optical Fourier irradiance.
Dependence of grating contrast sensitivity on area, shape, and eccentricity
Authors: Rovamo Jyrki , Raninen Antti
Published: February 2023

Contrast sensitivity increases with grating area. The prime determinants of this spatial integration process are the number and length of grating bars. When grating size is expressed in square cycles (c2) calculated by multiplying grating area A by spatial frequency F squared, spatial integration in foveal vision becomes similar for all spatial frequencies.1 When the contrast sensitivity data, collected for spatial frequencies of 1.5-3 cycles/deg at the eccentricities of 0-22 deg, were plotted as a function of the number of square cycles, the increase of contrast sensitivity was similar along and across the meridians of the visual field. Also, the increase of contrast sensitivity as a function of grating value (AF
2
) was at all eccentricities similar along and across the grating bars. The only exception was the grating containing only 1cycle: in that case the increase of contrast sensitivity as a function of bar length was negligible. Although the increase of contrast sensitivity as a function of square cycles was steeper in peripheral than foveal vision, spatial integration saturated at similar grating values irrespective of visual field location. The results indicate that the reduction of contrast sensitivity, produced by dark surround for gratings consisting of a small number of square cycles, is stronger in peripheral than foveal vision, as is the case in lateral masking.
Minimum-negativity constraint applied to large data sets
Authors: Howard Samuel J.
Published: February 2023

The efficacy of a new algorithm implementing the minimum-negativity constraint1 in computing data sets of up to 64K (K = 1024) data points is demonstrated. A specific example is shown for an interferogram of 17K points taken from a rocketborne field-widened interferometer. Restoring data points to the interferogram to yield a total of 64K points, on Fourier transforming with the fast Fourier transform, produces improved resolution for the resulting 64K data points of the IR spectral lines. An example of restoration with the same interferogram involving a minor modification of the algorithm so that it is appropriate for parallel processing is also illustrated. The new algorithms may be easily generalized to two dimensions.
Image reconstruction using entropy, relative entropy, and the discrete cosine transform
Authors: Tzannes N. S. , Bodenscharz John S. , Tzannes M. A.
Published: February 2023

Previously1 we introduced the use of the maximum entropy principle (MEP) for image reconstruction of moment-coded images. The MEP and the minimum relative principle (MREP) are used in reconstructing images previously compressed by retaining a subset of the coefficients of their discrete cosine transform (DCT), a popular method of image compression since it approximates closely the ideal Karhunen-Loeve transform compression. The normal way to reconstruct such compressed images is by using the inverse DCT. The reconstructed image under the MEP is the one that maximizes the entropy of the image subject to constraints reflecting the retained DCT coefficients. Under the MREP, the reconstructed image is obtained by successive minimization of its relative entropy subject to one constraint at a time, with each solution serving as a prior for the next minimization. Both methods were applied to images compressed by DCT, and the results were compared to normal inverse DCT reconstruction. It is concluded that MEP and MREP are better than IDCT, and the improvement is attributed to the fact that these methods make no assumptions about the value of the unretained coefficients, while IDCT assumes them equal to zero.