bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise performance of photorefractive crystal holograms
Authors: Song Q. Wang , Banerjee Partha P. , Liu Jaw-Jei
Published: February 2023

We analyze the temporal and spatial nature of the diffracted light from a photorefractive volume hologram under the influence of electronic noise in the material. Because of this noise, the holographic grating within the crystal is not strictly periodic; in other words, it has random fluctuations in both amplitude and period. Gaussian beam illumination at the nominal Bragg angle is assumed. The reason for this choice is that we can now evaluate not only the temporal statistics in the diffracted light, but also its spatial randomness. This quantitative evaluation achieved through defining a system transfer function that relates the output diffracted light to the input in the spatial frequency domain. For light nominally incident at the Bragg angle, this transfer function may be derived by Fourier transforming the paraxial wave equation in the presence of interaction terms. Estimation of spatial randomness is not possible to calculate assuming plane wave illumination since one cannot monitor transverse fluctuations along its wavefront. By using first- order approximation, the temporal and spatial noise ratios are obtained. Their dependence on reading time, reading beam intensity, grating spacing, and temperature are predicted.
Self-trapped exciton enhanced photostructural transformation in AsSe fiber glass
Authors: Schmid A. W. , Kim M. , Cerqua K. , LaCourse W. D.
Published: February 2023

Arsenic chalcogenide glasses for IR fiber and data storage uses exhibit photoinduced structural transformations when irradiated by below-band- gap light. We demonstrate that these transformations are enhanced by irradiating at a self-trapped exciton (STE) resonance wavelength. Rayleigh and Raman signals show that STE decay leads to instabilities among metastable structural states in bulk glass. With time constants of the order of seconds, these instabilities may switch abruptly into states of increased order. By varying the relative concentration in these binary compounds, we control the availability of the initial STE forming state. These measurements provide evidence that photoinduced structural transformations in arsenic selenides occur at 1-5 W/cm2 irradiation levels.
Multichannel filtering as the first step of visual processing
Authors: Malik Jitendra
Published: February 2023

A summary was not available at time of publication.
Fabricating the perfect zone plate for x-ray optics by minimizing placement errors in electron beam lithography
Authors: Anderson Erik H. , Kern Dieter , Boegli Volker
Published: February 2023

Fresnel zone plate lenses are used in a wide variety of x-ray optical instruments for imaging, forming small x-ray probes, etc. A zone plate consists of a concentric ring of alternating transmissive material with opaque (and/or phase shifting) material. For diffraction-limited lens performance, the placement of the zones is critical. The maximum placement error should be less than a small fraction (i.e., 1/4) of the smallest zonewidth. For the highest resolution zone plate, with smallest zonewidths of 30-40 nm, achieving the required placement accuracy is a challenge. New techniques have been developed to measure placement errors in electron beam systems, and measurements on IBM’s VS-6 high resolution electron beam lithography tool show small but nonzero errors. Small amounts of drift from thermal and other sources can cause serious placement errors during the zone plate's exposure time.
Proposal for a QND which-path measurement using photons
Authors: Yang S. , Raymer M. G.
Published: February 2023

A scheme is proposed for experimentally achieving the famous two-slit gedanken experiment using photons. A particle’s quantum pathways can interfere to produce fringes in the probability for the particle to be found at some location. If the path taken by the particle is experimentally determined, the complementarity principle says that the fringes must disappear. To carry out this experiment with photons is difficult because normally the act of determining a photon’s location destroys it. We propose to overcome this by putting a type-II optical parametric amplifier (OPA) in each arm of a Mach-Zehnder interferometer and observing fringes at the output. An OPA responds to an input photon by increasing its probability to produce a pair of photons, one having polarization orthogonal to the input photon.
Air refractive-index measurement using two-color methods
Authors: Matsumoto Hirokazu , Zhu Yucong , Fujima Ichiro , O'ishi Tadanao
Published: February 2023

In precision distance measurement, one of the error sources is the changes of the refractive index of air along the optical path. Two methods are given for estimating the refractive index of air, based on the difference in optical paths between two lasers transmitting at different wavelengths. A long-arm two-color fringe-counting interferometer is developed by using a stabilized 633-nm He-Ne laser and a diode-pumped 1064-nm YAG laser.
Single-point optical turbulence thermosonde system
Authors: Hoover C. , Walters D. L.
Published: February 2023

Small random variations in the index of refraction of the atmosphere produce atmospheric turbulence. Since the index of refraction of air is a function of the atmospheric density, it is possible to measure the index of refraction structure parameter from vertical temperature and pressure differences of an ascending or descending balloon. In the past, two probes connected differentially were used for this measurement. The Naval Postgraduate School has developed a single probe, high speed thermosonde system. Results from this system are presented. This system can be coupled with an acoustic sounder for high resolution, low altitude turbulence profiling.
Chaotic dynamics of infrared lasers
Authors: Cardimona D. A. , Kovanis V. , Sharma M. P.
Published: February 2023

Far-infrared (FIR) lasers have recently proved to be effective tools for the experimental investigation of nonlinear laser dynamics. We derive the equations that model two types of FIR lasers: one depicting an NH3 laser using a three-level scheme and the other depicting a CH3F laser using a four-level scheme. We next perform a systematic study of the time development of the field, the medium polarization, and the molecular inversion, and then present the Fourier spectra. The routes to chaos are investigated using a linear stability analysis and a Lyapunov exponent calculation.
Spatio-temporal window in illusory contour perception
Authors: Kojo Ilpo , Ravamo Jyrki
Published: February 2023

The best known example of illusory contours is the Kanizsa triangle consisting of three disks with a sector removed. The disks and sectors are arranged so that they form the comers of a triangle. Although the sides of the triangle are not physically present, they are clearly visible. In our experiments the inducing disks of an illusory (Kanizsa) triangle were presented sequentially. We varied the sizes and/or distances of the disks and asked the subjects whether they saw the triangle or only a temporal sequence of disks. The subjects adjusted the duration of presentation to find out the longest (critical) duration that allowed the perception of the illusory triangle.
Spatial scaling of absolute and relative movement discrimination
Authors: Makela Pia , Whitaker David , Rovamo Jyrki
Published: February 2023

The technique of spatial scaling provides a method by which the rate of decline in performance in any psychophysical task can be determined as a function of eccentricity. The main advantage of the technique is that no prior assumptions regarding the size of peripherally presented stimuli need to be made. We measured thresholds for discriminating the direction of movement of an object that underwent an instantaneous displacement either to the right or left. No stationary references were present in the rest of the visual field. The rate at which performance changes with eccentricity is conveniently denoted by E2 which represents the eccentricity at which foveal stimulus size must double to maintain equivalent performance.
Detection of band-pass filtered patterns in noise
Authors: Nasanen Risto , Kukkonen Helja , Rovamo Jyrki
Published: February 2023

Contrast energy thresholds were measured for noisy band-pass filtered Sloan letters K, H, O, and a plus pattern (+) at various center frequencies and bandwidths. Computer graphics were used to produce the stimuli on a computer monitor. In the center of the screen was a model stimulus without noise. On its right and left side was a window containing white static noise. One of the noise windows also contained the stimulus to be detected. The observer had to indicate, by pressing one of two keys on a computer keyboard, whether the stimulus was on the right or left side. A 2AFC method and unlimited viewing time was used.
Contrast sensitivity as a function of luminance: effects of area and spatial frequency
Authors: Mustonen Juvi , Rovamo Jyrki , Nasanen Risto
Published: February 2023

Using gratings with various areas (A) and spatial frequencies (f < 4 c/deg, where the attenuating effect of the transfer function of eye optics is negligible) we measured Michelson contrast sensitivity as a function of retinal illuminance (l). At high luminance levels contrast sensitivity (S) was independent of retinal illuminance obeying Weber’s law, whereas at low luminance levels S = k × l–0.5 obeying the DeVries-Rose law.
Do we have the technology to build a diffraction-limited soft x-ray telescope?
Authors: Küchel Michael F.
Published: February 2023

For a relatively small mirror diameter of 250 mm and a wavelength of 10 nm, the theoretical diffraction limit is as low as 0.01 arcsec. On the other hand, a surface figure error and irregularity of ~0.5 nm rms must be reached if the Strehl ratio should be high. We present results of wavefront measurements, where a repeatability of 0.2 nm and an absolute accuracy for the shape of > 1 nm have already been reached for such minors The key to a successful telescope is a two-mirror design with only very slight deviations from ideal spheres. We assume that these mirrors could be manufactured with classical polishing technology, with which a very smooth surface without pronounced gradient errors in any spatial frequency region could be achieved. Experience shows that, in this case, the most dominant wavefront errors are longscale, e.g., of the type of spherical aberration, astigmatism and coma, which could be compensated by proper misalignment of the telescope. For this, a setup is necessary where the wavefront error of the telescope could be tested interferometrically in double pass.
Testing high N.A. convex spherical surfaces
Authors: Creath Katherine , Hariharan P.
Published: February 2023

Interferometric tests of convex surfaces for large N. A. lens systems often present serious problems. These surfaces can be tested quite simply by making use of the aplanatic imaging properties of a spherical surface. Using a Fizeau interferometer, the reference surface N.A. is chosen so that the surface under test can be filled when the beam from the interferometer is directed to converge on the further aplanatic point of the test surface. Refraction will direct the beam to the closer aplanatic point. After the beam is reflected back from the closer aplantic point, the rays will be normal to the reference surface of the interferometer if the test surface is perfect. To perform this test, the test lens needs to have a thickness so that the back surface is at the closer aplanatic point.
Invariant pattern classification using an optical coordinate transformation system
Authors: Asselin Daniel , Arsenault Henri H.
Published: February 2023

An optical system using rectangular-to-polar coordinate transformation can be used for rotation invariant pattern recognition and classification. We have constructed an optical device to accomplish the coordinate transformation. The output of this device is imaged onto a liquid crystal light valve and Fourier transformed, then sent to a neural network and compared to stored invariant values. The coordinate transformation system uses a nonregular sampling array to minimize effects caused by the nonregular sampling resulting from a rectangular to polar transformation.
Forming a clear picture of holograms
Authors: Sillyman Sheldon S.
Published: February 2023

In recent years, there has been a glorification of the capabilities of holography on television and in motion pictures. An exhibit dealing with holography would therefore be popular with the general public. Demonstration of the making of a hologram would provide the public with the realistic yet still fascinating uses for holograms that presently exist. A display could be built that demonstrates the fabrication of a simple transmission hologram using a laser, beam splitter, lenses, mirrors, and a film plate arranged either on an optical alignment bench or possibly in a sandbox for stability. The display would reside in a totally dark environment.
Holographic disk line scanner using a holoplate
Authors: Hasegawa Shin-ya , Iwata Shigetake , Kayashima Shigeo , Maeda Satoshi , Yamagishi Fumio , Nakashima Masato , Inagaki Takefumi
Published: February 2023

An achromatized all-holographic straight-line scanner for use in laser diode printers has been developed. The scanner consists of a compact holographic disk and a new holoplate and needs no other auxiliary optics to scan and focus the laser beam. Conventional holographic scanners having optical power suffer from scanning-beam aberration and chromatic aberration caused by mode hopping of the laser diode. To make a low-cost holographic line scanner more practical, resolution as high as 400 dpi must be attained. Moreover, scanners free from chromatic aberrations, especially in scan direction, need to be developed. To meet the requirements, we devised a simple holographic-disk scanner using a holoplate. Our holoplate compensates for shifts in position of the scanning beam caused by the laser diode hopping modes in both scan and cross-scan directions. High resolution can be obtained by using a compound optical system having a variable spatial-frequency disk and a holoplate.
Optical 2-D permutation tor convolution of 1-D long data streams
Authors: Li Yao , Zhang Yan , Kanterakis E. , Katz A. , Lu X. J.
Published: February 2023

Radar, sonar, and communications often require that long data streams containing, perhaps, more than one million data points be convolved or correlated. Conventional digital electronic computers with serial processing hardwares are not capable of handling such operations in real time. Although various mathematical models exist that decompose long data streams into a set of shorter streams to be processed in parallel for convolution/correlation, the actual digital electronic hardware to implement these algorithms may be too complicated. In this paper, a number-theoretic transform algorithm that is suitable for an optical implementation is studied for performing hybrid convolution/correlation of long data streams. The 1-D input and reference data streams are permuted to form arrays of shorter data sequences in 2-D formats, which are then optically convolved/correlated via a standard Fourier optics method. The 2-D convolution/correlation obtained result is finally shuffled back to obtain the 1-D convolution result.
Suppression of phase fluctuations in stimulated Brillouin scattering
Authors: Moore Thomas R. , Gaeta Alexander L. , Boyd Robert W.
Published: February 2023

We have performed an experiment to study the stability of the phase of the Stokes wave generated by stimulated Brillouin scattering (SBS). Abeam from a single-mode Nd:YAG laser of 400-ns duration was split into two beams of nominally equal energy. Each of the beams was directed through a focusing lens into identical but independent Brillouin cells. The SBS reflections from the cells were interfered with each other, and the resulting interference pattern was imaged onto an optical multichannel analyzer to provide a time-integrated record of the interference pattern. Surprisingly, the time-integrated interference pattern shows large depth of modulation, even though the Stokes pulse duration is 250 times longer than the phonon lifetime.
Hybrid mode-locking of a Styryl 9 dye laser using a nonlinear mirror
Authors: Bi J. Q. , Proctor M. , Hodel W. , Dupertuis M. A. , Beaud P. , Schutz J. , Weber H. P. , Martin D. , Morier-Genoud F. , Reinhart F. K.
Published: February 2023

We have hybridly mode-locked a Styryl 9 dye laser using a nonlinear mirror that consists of a 200-nm bulk GaAlAs (5% Al content) layer grown on a linear Bragg mirror. The dye laser is synchronously pumped by compressed and frequency doubled Nd:YAG laser pulses (3.5-psec pulses, 200-mW average power). With regular mirrors the pulses have durations of 900 fsec and extended wings lead to a time-bandwidth product p = 0.64. The replacement of one mirror by a nonlinear mirror leads to a significant mode-locking improvement and pulse shortening without the need for an external cavity. Best performance of the laser is obtained near the band-edge of the GaAlAs material. At 836 nm, practically bandwidth-limited 220 fsec pulses (p = 0.44) are generated with an average output power of 15 mW. To our knowledge this is the first time that a bulk GaAlAs semiconductor instead of a multiple quantum well structure has been used for modelocking. The bulk GaAlAs material has a high saturation energy and requires no additional treatment for the reduction of the carrier recombination time. It simply acts as a slow saturable absorber.
Analysis of picosecond and femtosecond pulse dye laser amplifiers
Authors: Jiang Shuang-Hua , Casperson Lee W.
Published: February 2023

When dealing with the ultrashort pulse (picosecond to femtosecond duration) amplification by dye laser amplifiers, the rate equations fail to explain the light-matter interaction adequately as the pulse duration approaches the phase coherence time of the amplifying medium. In our research, a semiclassical model was developed and used for such short pulse amplification processes. The pulse evolution, pulse energy gain, pulse duration and other parameters were investigated. Solutions were compared with results based on the rate equation treatment, i.e., without considering the phase memory effects.
Investigation of the 2-D to 0-D transition in quantum wells under high magnetic fields
Authors: Stark J. B. , Knox W. H. , Chemla D. S.
Published: February 2023

Optical transitions near the band gap of semiconductors are dominated by the electron-hole (e-h) correlation which results in large excitonic enhancement. They exhibit quantum size effects whenever the dimensions of a semiconductor structure are of the order of the bulk exciton radius, ao. Recently quasi-2-D excitonic effects have been investigated extensively in quantum well (QW) structures of high optical quality.
Femtosecond coherent absorption changes in CdSSe quantum dot-doped glasses
Authors: DeLong K. W. , Yumoto Junji , Uesugi Naoshi
Published: February 2023

We report what we believe to be the first observation of coherent transient absorption changes in glasses doped with quantum dots of CdS0.12Se0.88. These observations were made at room temperature with on-resonant laser pumping. We observe a transient bleaching on the high energy side of the pump center wavelength, and a transient absorption increase on the low energy side. The transient effects last for a time about equal to the pump pulse duration, 80 fsec, after which real carrier generation masks the effects. The results can be qualitatively explained by a spectral shift in the direction predicted by the optical Stark effect. This was a pump-probe experiment where the 622-nm pump center wavelength was on the long wavelength side of the lowest energy transition in the quantum dots but still well within the absorption band. The radii of the microcrystallites ranged from 20 to 40 Å, and T2 in similar samples was estimated to be 60 fsec or less. Although the laser pulsewidth is longer than the dephasing time in the sample, we were still able to see coherent effects.
Multiple mechanisms for the detection of reflection symmetry in brief exposures
Authors: Tyler Christopher W. , Hardage Lani , Miller Richard
Published: February 2023

Reflection symmetry is a pop-out image feature which receives preferential visual processing compared with, say, repetition or rotation symmetry (Julesz, 1971). We sought to examine the mechanisms underlying such processing, since its neurophysiological properties are unknown. Reflection symmetry was imposed on a multilevel random image on a Macintosh II computer. Dynamic noise was generated by random assignments to the lookup table for the random image. For opposite contrast symmetry, bright dots in one half field image were matched with symmetric dark dots in the other half. Forced-choice thresholds for symmetry detection were measured as a function of the width of nonsymmetric masking strip around the symmetry axis, forcing detection by features progressively further from the axis. For dynamic noise images, symmetry could be detected in ~120-msec presentations, while 1-sec presentations allowed detection up to masking widths of ~20 arcmin. On the other hand, in static images (sandwiched between dynamic fields) symmetry could be detected in ~60-msec presentations, while 1-sec presentations allowed detection up to much greater masking widths (~5°). This implies a static symmetry mechanism both more sensitive and operating over much larger cortical distances. Opposite contrast symmetry showed longer detection times in both static and dynamic noise, and its masking width was extremely narrow (~3 arcmin) in dynamic noise, implying a third neural mechanism.
Illusory Mach bands: visual artifacts or tokens of perceived illumination changes?
Authors: Osbourn Gordon C.
Published: February 2023

Illusory Mach bands have long been regarded as artifacts of edge-enhancing mechanisms, yet key properties have remained unexplained. We present a quantitative model that treats Mach bands as the useful end products of a hypothesized mechanism for distinguishing certain illumination and reflectance changes in a scene. The model mechanism selectively locates illumination changes associated with shadow penumbra boundaries and labels these with Mach bands while suppressing detection of other types of image boundaries (e.g., abrupt object edges) and high frequency image noise. The noise suppression mechanism requires a penumbra contrast sensitivity maximum from general principles alone that matches published data. Model calculations on both idealized intensity patterns and video images demonstrate that the key spatial and spatial-frequency characteristics of Mach bands are quantitatively accounted for. The long-puzzling absence of Mach bands at abrupt edges (where typical edge enhancers produce maximal responses) also follows directly from the model mechanism and is associated with the ability to distinguish cast shadow illumination changes (with penumbra edges) from reflectance changes at abrupt object boundaries in an image. The useful detection selectivity and noise suppression properties required by the Mach band model suggest the operation of a distinct component of the visual system that contributes to lightness perception.
The marriage of photorefractive and semi-conductor devices for optical computing
Authors: Paek Eung Gi
Published: February 2023

Photorefractive volume holographic recording materials have been widely used in various applications, such as holographic memories, optical interconnect, optical neural networks, and signal/image processing. Recent advances in semiconductor devices, especially surface-emitting microlaser arrays, allow a lot of flexibility and compactness, which traditional single, bulky laser-based optical systems lack. When the two technologies are married, a wide variety of new applications may become feasible. In this talk, we will show some of the possible applications of optics utilizing both devices. First, we will describe a volume holographic memory that can be rapidly accessed by using a beam steering optics that consists of a microlaser array and a collimating lens. Second, we will demonstrate a compact and robust holographic correlator that can possibly be integrated into a small scale by using semiconductor technology. Finally, we will describe a new method of all-optical image transmission through a single-mode fiber by using a two-dimensional multi-color surface-emitting laser diode array and a volume hologram. By using the method, a 2D image can possibly be transmitted in parallel at the speed of light, without requiring any intermediate electronics, such as a video camera or display devices, that result in a speed bottle-neck and high power consumption. A preliminary experimental result to prove the concept is demonstrated.
Reciprocal MTF/LSF information from experimental data in diffraction limited systems
Authors: Calvo M. L. , Chevalier M. , Lakshminarayanan V. , Mondal P. K.
Published: February 2023

Study of resolution criteria for two line images in diffraction limited systems under incoherent illumination is of importance in robotic vision and visual system models. We are interested in the discrimination of lines, edges, and formalism. The line objects can be represented in terms of derivatives of Heaviside functions. The line spread function (LSF) is expressed in terms of Struve functions of the first kind. Data on experimental LSFs are obtained by Fourier transforming the experimental MTF. The results are fitted to theoretical LSF distributions where losses in the transfer of energy are taken into account (by using Conrady criteria). The location and number of zeros specify the characteristics of the system, namely, the presence of aberrations as well as possible extra correlation with additional factors. The reciprocal LSF/MTF data are discussed, and the importance of information on the first and second derivatives of the resolution threshold distributions is underscored.
Growth and characterization of mixed photorefractive crystals, Bi12Si1-xTixO20
Authors: Yeh T. S. , Hu L. J. , Lin S. P. , Lin C. H. , Tu S. L. , Yang S. J. , Hsu K. Y.
Published: February 2023

This paper describes the growth and photorefractive characteristics of a series of single crystals from solid solution Bi12Si1-
x
Ti
x
O20 of various compositions (x varies from 0.0 to 1.0) in 10-20 mm diameter and 20-40 mm long, that were successfully grown by the Czochralski method. The axial temperature gradient was kept higher than 50°C/cm and the growth rate was kept lower than 0.5 mm/h to prevent cellular growth and inclusions. X-ray phase analysis (XPA) and differential thermal analysis (DTA) have been applied to study the phase diagram of the Bi12Si1-
x
Ti
x
O20 system. The XPA results indicated that all specimens consist of single phase with the sillenite structure and that the concentration dependence of the unit cell parameter was close to linear. The DTA results showed that the liguidus temperature of the samples decreased as the content of Bi12TiO20 increased. From the crystallization and above analysis we confirmed that the unstricted solid solution had occurred in the melts of Bi12Si1−
x
Ti
x
O20. The two wavemixing technique has been applied to characterize photorefractive properties of the crystals, including the photorefractive grating recording and erasing speeds and diffraction efficiency. The diffraction efficiency of a He–Ne probe beam from the grating developed by two argon laser beams was measured to be three times as high as that of pure Bi12SiO20.
Effect of the dynamics of carrier transport on the nonlinear optical properties of hetero-n-i-p-i’s
Authors: Jupina Michael , Mahgerefteh Daniel , Garmire Elsa , Hasenbelg Tom , Kost Alan
Published: February 2023

Previous measurements in a n-i-p-i structure with InAs/GaAs superlattice quantum wells in the i regions seemed to indicate that the field-screening nonlinearity saturates at low intensities I ~ 5 W/cm2. We present evidence here that carriers that are "stuck" in the wells near this intensity can escape beyond I ~ 15 W/cm2 so that field screening turns on again. We used a sample grown by migration enhanced epitaxy and having 12 periods of n-i-p-i doped GaAs with three InAs/GaAs quantum wells in each i region. The quantum wells were periods of a superlattice grown to be (InAs)2(GaAs)5. The spectrum of the nonlinear transmission, ΔT/T, was measured by using 50-s pulses from a cw Ti-sapphire laser tuned near the exciton absorption peak at 970 nm. For I = 0.1 W/cm2 to I = 103 W/ cm2 the exciton absorption peak has a blue shift, compatible with photo-carrier field screening. The magnitude of ∆T/T increases with light intensity in a nonlinear way, with plateaus near I = 5 W/cm2 and I = 150 W/ cm2. We will show that this intensity dependence reflects the change in the ability of carriers to escape the wells as the built-in field decreases with increasing intensity.
Optical scatter from fused silica: a comparison to Rayleigh-Rice scattering theory
Authors: Black J. Paul
Published: February 2023

Angle resolved scatter measurements were performed on fused silica superpolished substrates. The total scatter from these substrates is caused by surface, near surface, and bulk scatter. The total scatter from the substrate was measured at 0.633 μm with the Phillips Laboratory scatterometer. Bulk scatter was measured by a method independent of the surface and near surface scatter. The measured bulk scatter was subtracted from the total scatter. The angular profile of the residual scatter compares favorably to the optical factor in the Rayleigh-Rice interface scatter theory. The optical factor, a term in the theory dependent on index of refraction and source and detector polarization, was then removed from the residual total scatter. The remaining scatter was integrated to determine the total integrated scatter for incident beam angles of 25°, 40°, 60°, and 80°. The resulting integrated values were corrected for the variation in transmitted power according to the Fresnel equations and were plotted versus the incident angle. The plotted curves demonstrate that the method developed to measure the scatter combined with analysis using Rayleigh-Rice theory allow the strength of near surface scatter to be estimated.
Interaction of two optical beams at a symmetric random surface
Authors: Gu Zu-Han , Escamilla H. M. , Mendez E. R. , Maradudin A. A. , Lu J. Q. , Michel T. , Nieto-Vesperinas M.
Published: February 2023

Recently, specular enhancement has been shown. In this paper, we present an experimental and theoretical study of the scattering of two coherent optical beams from a symmetrical random surface. It is found that in addition to the two sharp peaks corresponding to the enhancements in the specular directions, there is a third peak due to the interaction of the two optical beams at the surface.
Determination of angular surface scattering from measurements of range-resolved laser radar cross section
Authors: Shirley L. G. , Hallerman G. R. , Vivilecchia J. R.
Published: February 2023

Knowledge of a material's surface scattering properties is of interest in many fields, e.g., in relating laser radar signatures to the surface properties and underlying shape of a scattering object. The range-resolved cross section U(z) is a signature that carries a great deal of information about the object. It depends on the surface scatter through the monostatic reflectance distribution function f(θ), where θ is the local angle of incidence. We recently demonstrated a technique for measuring U(z) to submillimeter resolutions by flood illuminating the object with a wavelength-scanning Ti:sapphire laser beam and analyzing the fluctuating speckle intensity. In this paper, we begin with an object of known shape, such as a sphere, and calculate the relationship between U(z) and f(θ) analytically. We use axially symmetric objects, illuminated along the axis of symmetry, so that each value of range z maps into a single value of θ. This allows measurements of U(z) to be converted into measurements of f(θ). The signal-to-noise ratio at large θ can be improved by using elongated objects, such as ellipsoids. We compare these results with conventional measurements of f(θ) and find good agreement.
Macroscopic quantum fluctuations in stimulated Raman scattering
Authors: Scalora M. , Bowden C. M. , Haus J. W.
Published: February 2023

We examine beam pointing fluctuations that arise when the Stokes field is initiated from vacuum fluctuations. Using a model that includes diffraction and pump depletion, we use stochastic boundary conditions to solve for the fields. We present results with one and two transverse coordinates and compare them with experimental observations. Using a Gaussian input pump beam, we find that δK, a measure of the transverse fluctuations, is essentially a linear function of Fresnel number, in both the linear and nonlinear regimes, with larger values in the latter case. For low Fresnel numbers, we find that our theory is in excellent agreement with experiment when one or two transverse coordinates are used. For larger Fresnel numbers, quantitative agreement with experiment is obtained only if both transverse coordinates are employed in the calculation.
Properties of films produced by modulated-dc-magnetron sputtering
Authors: Pond B. J. , Du T. , Sobczak J. , Carniglia C. K.
Published: February 2023

Reactive-dc-magnetron sputtering has been demonstrated as a viable technique for producing dense films with improved mechanical properties. Recent advances in this process, such as deposition at low pressures and elimination of arcing on the target surface, have resulted in the deposition of films with improved optical properties. Films produced by this technique have very low scatter and absorption values that are comparable to those of ion-beam-sputtered films. Single-layer films of SiO2, Al2O3, Ta2O5, and TiO2 have been deposited and analyzed. The optical and mechanical properties of these films are compared with those of films deposited by ion-beam sputtering and electron-beam evaporation. The films deposited by dc-magnetron sputtering are homogeneous and have excellent index repeatability. This makes it possible to achieve near-theoretical performance in the spectral characteristics of multilayer coatings. A number of multilayer coatings have been produced by this technique, and some of these have physical thicknesses greater than 10 μm. The sensitivity of these coatings to the relative humidity of the surrounding environment was measured, and they were extremely stable.
Performance evaluation of interceptor seeker technologies and system concepts using an integrated radiance throughput model
Authors: Wyman Charles L. , Andrzejewski Joseph , Calhoun Ronnie
Published: February 2023

An extensive development program for hypersonic interceptor seeker systems and component technologies has been underway within the community for some time. Seeker system concepts using various combinations of window and sensor technologies are traded and compared by using a recently developed integrated radiance throughput model. The model provides a rapid means of medium fidelity performance evaluation over the entire dynamic range of interceptor/target engagement scenarios. Previous efforts to perform trades and performance evaluations were done piecemeal. Thorough comparisons considering complete engagement scenarios is inefficient when performed piecemeal. The throughput model was initially conceived to provide comparative performance analysis for new and existing window materials. It consists of numerous modules to simulate the operational and engagement environment. Several of these modules consist of or draw upon existing programs to analyze elements of that environment. These include LOWTRAN, SIRRM, OSC, CFD CODES, AERO-OPTIC CODE, and PHONONB. The throughput model has evolved into a means of complete seeker performance evaluation. Several typical component and system concept trades that have been recently performed are presented. An animated video demonstrating results over a typical range of parameters is presented.
All-optical WDM networks
Authors: Saleh Adel A. M.
Published: February 2023

With the recent developments in tunable lasers and filters, star couplers, wavelength-routing multiplexers, low-noise optical amplifiers, and even wavelength changers, optical WDM technology is now emerging as the most flexible and efficient technique for accessing the vast bandwidth of the optical fiber. It permits a large number of independent users to communicate over the same network at a staggering overall throughput without a significant degree of coordination. When envisioning the use of this technology to construct an optical network of national or international extent, it is desirable to keep the signal path all optical from source to destination to offer the network users the flexibility of using virtually arbitrary signaling formats and modulation rates. To realize this goal efficiently it is essential that the network architecture be hierarchical, e.g., local area networks (LANs) interconnected by metropolitan area networks (MANs), which, in turn, are interconnected by a wide area network (WAN) of possible global extent. The subnetworks in such a hierarchy should be decoupled in such a way as to allow optical frequency reuse. Thus, optical frequencies used for local communications within a given LAN could be reused within any other LAN without interference. This increases the overall network capacity, conserves signal power, and simplifies network management and fault isolation.
Fluorescence from a single atom interacting with antibunched light
Authors: Lyublinskaya Irina , Vyas Reeta
Published: February 2023

Statistical properties of fluorescent light from a single two-level atom driven by a beam of antibunched light are discussed in the weak field limit. Fields generated by realistic open systems with pumping and dissipation are chosen to be the models for antibunched light. As examples, we consider fields produced in intracavity second harmonic generation and in the homodyned degenerate parametric oscillator. These fields can be described in terms of real Gaussian random processes with coherent components. Analytical expressions for fluorescent light intensity and second order intensity correlation function in the steady state are derived. Effects of driving field correlations, detuning, and parameters characterizing the driving field on the statistics of scattered light are investigated. It is found that over a certain range of parameters characterizing the driving field the second order intensity correlation function may vanish at non-zero time. These and other interesting features will be discussed.
Analytical solution to the master equation for atomic damping by a squeezed vacuum
Authors: Schmitt H. A. , Mufti A. , Sargent M.
Published: February 2023

An algebraic solution to the problem of atomic damping by a sqeezed vacuum is presented. The master equation is solved by exploiting its formal similarity with the S-matrix equation and using group theoretical techniques. The solution is expressed in terms of elementary functions, allowing a wide range of parameters to be studied. This method allows us to calculate quantites such as expectation values and variances without solving many coupled differential equations. The effects of several physical parameters, such as the number of thermal photons and the magnitude and phase of the squeezing parameter, are illustrated graphically. In particular, we find that it does not seem to be possible to get squeezing in one of the quadratures nor to get minimum-uncertainty squeezing.
Squeezed amplification with cavity detunings: noise behavior
Authors: Sun K.-X. , Shapiro J. H.
Published: February 2023

Optical parametric amplifiers (OPA's) and optical parametric oscillators (OPO's) can exhibit squeezed amplification when an injected signal beam is used to elicit small-signal gain saturation. This paper extends previous work on OPA/OPO noise behavior under signal injection. Doubly resonant and triply resonant, single-ended cavities are considered in the good-cavity limit. Owing to the nonlinear coupling between the signal and idler beams within the cavity, both are sensitive to the detuning of each beam from its respective resonance. Signal and idler output noise spectra are found by linearizing the quantum coupled-mode equations about the classical mean-field solutions. Cavity detunings lead to frequency dependent phase shifts between the low-noise and high-noise quadratures of both the signal and idler beams. Moreover, the phase of the low-noise quadrature need not coincide with that of the corresponding mean field. The resulting large-signal, signal-to-noise ratio improvement afforded by squeezed amplification is therefore sensitive to the cavity detunings. The effects of classical excess noise on the pump beam and the injected signal beam are also considered.
Combined heterodyned fiber optic ESPI and velocimeter system using a dithered servo technique
Authors: Harvey David , McBride Roy , Doval Agel , Valera Jesus D. , Jones Julian D. C.
Published: February 2023

We describe a diode laser powered fiber optic based system for vibrational analysis that incorporates the benefits of electronic speckle pattern interferometry (ESPI) and laser velocimetry. Through phase locking of the common reference arm to the motion of a single point on the target by using the velocimeter output, the combined unit allows automatic heterodyning of the ESPI system and limited compensation for unwanted random out of plane motion of the test object. As the velocimeter point is tracked across the surface, a signal containing the vibrational information but independent of the power level returned from the target and the fringe visibility is obtained by using a dithered servo technique. The frequency shifting is then applied either by using a fiber optic piezoelectric phase modulator in the reference arm or by shifting of the source wavelength through direct modulation of the diode laser injection current. The system was thus able to be successfully demonstrated on a range of surface types, including those showing large spatial variations in reflectivity.
Picosecond infrared measurements in condensed matter
Authors: Rothberg Lewis
Published: February 2023

Difference frequency mixing of amplified femtosecond visible pulses with white light continuum radiation produces relatively broadband infrared pulses (~10 meV), whose bandwidth is determined by the phase matching bandwidth of the difference frequency crystal. This radiation is easily tuned over a broad range (hundreds of meV) by angle tuning of the crystal. One application is the study of photogenerated charge carriers in the quasi-one-dimensional organic semiconductor trans-polyacetylene. Beause of the strong electron-phonon coupling, electrons and holes are dressed by the lattice leading subgap levels (0.45eV). Using transient mid-infra-red spectroscopy, we can observe the subpicosecond lattice deformation as well as measure gemmate recombination dynamics and interchain excitation probabilities. These data have been used to understand the photoconductivity and nonlinear optical properties of polyacetylene. Up-conversion gating of long tunable narrowband infrared pulses by an amplified subpicosecond laser is particularly valuable for subpicosecond vibrational spectroscopy. For example, the behavior of the CO ligands can be tracked during organometallic photochemistry to provide information about their cooling, rebinding, and reorientation. Issues such as the solvation of catalytically active metal carbonyls in solution and the pathway by which CO enters and exits hemoglobin are addressed.
Mt. Pinatubo volcanic aerosol effects on the remote sensing of sea surface temperature
Authors: Nagaraja Rao C. R. , Zhang Nian
Published: February 2023

The stratospheric volcanic dust cloud resulting from the eruption of Mt. Pinatubo in June 1991 has adversely affected the retrieval of sea surface temperature from the upwelling infrared radiances (≈3.7,10.8, and 11.9 µm) measured by the Advanced Very High Resolution Radiometer onboard the NOAA polar orbiting satellites. Correction algorithms to restore the capability of sea surface temperature retrieval during such volcanic dust episodes have been developed by combining model simulations of the radiative effects of volcanic aerosols with shipboard and buoy measurements of sea surface temperature and the NOAA operational aerosol product. The operational implementation of the correction algorithms will be discussed, accompanied by examples of the restored sea surface temperature fields.
Bayesian estimation of the magnitude of an optical field from its intensity
Authors: Fienup J. R. , Thelen B. J.
Published: February 2023

For several problems in optics it is necessary to estimate the magnitude of an optical field from a photon-limited measurement of its intensity (squared magnitude). An example is wavefront sensing from one or more measured intensities using an iterative transform algorithm such as the Gerchberg–Saxton algorithm. The maximum-likelihood estimate of the intensity and the minimum mean-squared error estimate of the intensity is simply the measured photon-limited intensity. The square root of the measured intensity is the maximum likelihood estimate of the magnitude, but it has a negative bias in that the square root of the intensity systematically underestimates the magnitude. We show that there exists no unbiased estimator for the magnitude. Other estimators, such as the square root of (1 + intensity), where intensity is in terms of number of detected photons, perform better than the square root estimator, as do some Bayesian estimators that use an assumed prior probability distribution for the intensity. The Cramer–Rao lower bound on the mean-squared error in estimating the magnitude is 1/4, and all of the above estimators have a mean-squared error close to 1/4 when the intensity is large but significantly differ from 1/4 when the intensity is small. The analysis is also given for intensity measurements with a background bias.
Proto-objects: an intermediate-level visual representation
Authors: Finkel Leif H. , Sajda Paul
Published: February 2023

One of the major functions of intermediate-level vision is object discrimination—grouping stimuli into “things.” We propose a model in which the outputs of early visual processing are first grouped into proto-objects, which are then linked into objects. Proto-objects are defined as bounded, simply connected, and spatially continuous surfaces with associated surface attributes such as depth, color, and texture. We have constructed a physiologically based neural network implementation of this model that discriminates objects based on the extraction of depth from occlusion. We provide detailed mechanisms for binding edges and lines into contours, segementing contours of different objects, binding surface attributes to surfaces, and binding contours and surfaces together. Together, these processes identify proto-objects in the scene. The representation of a proto-object is distributed across multiple visual maps. Proto-objects are discriminated by strictly feedforward processing, but they are linked together to form objects by reentrant feedback from higher level areas. The linking processes depend upon both surface cues (depth) and contour cues (good continuation). Extensive simulations demonstrate that responses of the model are similar to human psychophysical responses to both real and illusory stimuli.
Recoded higher order MSD numbers for fast symbolic substitution
Authors: Awwal A. A. S. , Islam M. N. , Karim M. A. , Cherri A. K.
Published: February 2023

The recoded signed-digit, modified signed-digit (MSD) number system is found to be more efficient than the normal MSD system in terms of hardware complexity. When implemented optically by using a content addressable memory, the number of rules to be implemented is much lower than that obtained by the MSD scheme for the addition/subtraction operation. Higher order symbolic substitution is an attempt to reduce the number of individual hardware modules by processing more numbers in parallel. This work combines the merit of higher order processing and that of recoding to obtain efficient symbolic substitution.