bluuebunny/crossref_metadata_2025 huggingface dataset:
Methods for the generation of volume holograms via computer
Authors: Keller Paul E. , Gmitro Arthur F.
Published: February 2023

Because of the potential for high interconnectivity, several researchers have designed and implemented optical systems using volume holograms (e.g., the synaptic interconnects of neural networks). So far, this work has concentrated on optically generated holograms (i.e., holograms recorded by using interferometric techniques). Optical generation of the volume hologram often presents challenges in both the recording stage and the reliability of the playback stage. We are investigating the potential of generating the volume hologram by computer. In a computer generation approach, the volume hologram is discretized and described as a 3-dimensional array of voxels (volume elements) similar to the 2-dimensional array of pixels used to describe a planar hologram. The fundamental issues of this approach are to properly model the forward diffraction problem, to develop a procedure to encode the desired interconnections, and to determine a method of fabricating a discretized volume structure. This talk outlines the basic considerations involved in the generation and fabrication of volume holograms by computer.
All-optical finite state machine controller with holographic control-store ROM
Authors: Heuring V. P. , Morozov V.
Published: February 2023

This paper will describe an all-optical state machine controller for controlling optical processors and processes. It is based on clocking control words from a holographic ROM. The controller is microcoded and includes the capability of unconditional and conditional branching. It has a capacity of 1024 control words, each of which may contain information for controlling arithmetic and logic processors and optical memories, as well as containing next address information. We will describe a prototype device that functions as a sequential counter. The controller functions in the traditional manner: an ad dress is presented as parallel optical beams to an optical address decoder. The decoded address selects a single holographic control word, which contains both control and branching information. The controller is timed by two optical clock signals that control output of the decoded address and sequencing of the next address information. We estimate operating speed at >100 MHz.
Parallel algorithms for an all-optical Boolean matrix ALU
Authors: Morozov V. , Heuring V. P.
Published: February 2023

We describe algorithms for parallel matrix and vector manipulation using a novel, all-optical arithmetic and logic unit (ALU). The ALU permits repeated parallel Boolean operations on an N × N matrix. Control of the ALU is by means of an optical control unit that has its microcontrol store in a holographic ROM. The ALU includes several storage registers for use as accumulators and for storage of operands and results, and it uses holographic interconnects to accomplish several special purpose arithmetic and logical shifting operations. The algorithms to be presented include one for Boolean matrix multiplication that allows the multiplication of two N × N matrices in N machine clock cycles, a process that is O(N3). We also present an algorithm for performing arithmetic addition of N pairs of N digit integers in N + 3 machine clock cycles. The ALU can be programmed to perform arbitrary matrix and vector operations.
Light scattering from adjacent Raman-Nath and Bragg gratings with arbitrary frequency ratios
Authors: Chatterjee M.R. , Chen S.-T.
Published: February 2023

Larson et al.1 have recently reported studying the characteristics of a surface acoustic wave via optical scattering from a parallel ultrasonic setup in which the surface wave acts as a Raman-Nath grating and the scattering is controlled and monitored by a bulk (Bragg) grating placed adjacent to the surface wave. The acoustic frequencies are typically assumed to be simple harmonics or subharmonics, which may not always reflect a practical situation. An earlier study2 had focused on the parallel ultrasonic problem from a multiple plane wave scattering perspective. In that study, simple harmonic frequency ratios were also assumed and both cells were chosen to be either at or near Raman-Nath. In this paper, we examine the diffraction effects associated with adjacent Raman-Nath and finite-Q Bragg cells (and their reverse order) in which the acoustic frequencies may be either simple harmonics or arbitrary. It is seen that analytical solutions are extremely difficult for the latter case, especially for a Raman-Nath/Bragg configuration. Numerical cases for variable

α
^

and δ values (where δ is an arbitrary phase factor between the cells) are examined in some detail.
Geometric interpretation of acousto-optic interaction with three-dimensional light and sound fields
Authors: Liu Z.C. , Mehrl D.J.
Published: February 2023

We present a novel approach for analyzing acousto-optic diffraction, applicable to 3-D sound and light fields. The technique decomposes light and sound fields as a linear superposition of plane waves. A geometric model of 3-D acousto-optic interaction, based on the wave-vector diagram, can be used to generate a system of equations that fully describe the interacting plane waves of light and sound. The geometric model offers an intuitive look into 3-D acousto-optic interaction without any implicit assumptions except weak interaction. The angular plane wave spectrum of the diffracted light can be found by solving the system of equations together with a single numerical integration over the product of the incident light and sound spectra. This form of solution coupled with the 2-D FFT algorithm offers the possibility of numerically computing the diffracted light field from arbitrary incident light and sound fields. Results are presented and compared with those from ray-tracing methods.
Fluorescent confocal microscopy of semiconductor microstructures
Authors: Brown Thomas G. , Kulawiec Andrew W. , Olofsson Lars , Smith Warren E.
Published: February 2023

Problems exist in characterizing high-frequency disordering in semiconductor microstructures, such as those used in quantum-well lasers. Global quantities, such as quantum efficiency and spectral characteristics averaged over the entire sample, are usually measured without detailed determination of their spatial distribution. High spatial resolution can be obtained with transmission electron microscopy, but the sample is sacrificed and the parameters of interest are measured only indirectly by using electron interactions. The use of a confocal microscope to image the fluorescence of a high-frequency (0.4 μm) spatially disordered quantum well is demonstrated. The distribution of the radiative recombination and the efficiency of the disordering process can be directly inferred with this approach. The technique has application to the fabrication and optimization of resonant-periodic-gain semiconductor lasers.
Dynamics of the spontaneous emission of an atom into the photon-density-of-states gap
Authors: Sánchez-Mondragón J. J. , Nabiev R.
Published: February 2023

We consider the dynamics of the spontaneous emission of a two-level atom embedded into a periodic layered dielectric structure. When the resonant atomic frequency lies within the photon-density-of-states gap (DOS) of width Γ, the atom spontaneous emission becomes fully inhibited for times tΓ ≥ 1. We discuss its enhancing by tuning the atomic resonance with a one mode microcavity. In the λ/4 shifted distributed feedback microcavities, which possess a δ function in the DOS, the spontaneous emission has damped Rabi oscillations and the damping depends on r and the gap depth.
Photonic properties of nano/micro-engineered photonic lattices
Authors: Gourley P. L. , Warren M. E. , Wendt J. R. , Vawter G. A. , Brennan T. M. , Hammons B. E.
Published: February 2023

We have characterized electron-hole recombination and the spontaneous and stimulated emission properies of photo-pumped photonic lattices formed by etching periodic unit cells in epitaxial (Al,Ga)As semiconductor microcavities. The lattices were fabricated by the conjunction of molecular beam epitaxy, photo/electron-beam lithography, and reactive ion beam etching. A variety of lattices corresponding to different cell shapes, sizes (2-7 μm), and spacings (0.2 to 2 μm) were investigated. Stable lasing modes were observed for arrays with high lattice gain factors (0.8 to 1.0) and cell Fresnel numbers between 2 and 6. These lattices had a lasing threshold that exhibited a minimum at 270 to 290 K, where the optical modes and electron-hole recombination were studied. The far field emission in these lattices provides a direct mapping of the optical Bloch waves in the lattice and shows evidence for inhibited emission at the Bragg condition where a photonic band gap is predicted. The electron-hole recombination time for GaAs lattices varied from 200 to 400 ps as the cell spacing increased from 0.2 to 1.0 μm.
Photon localization in radially distributed dielectric resonators
Authors: Brady David , Papen George , Sipe John
Published: February 2023

Electromagnetic propagation is inhibited over the complete solid angle for a finite range of frequencies, and localized modes arise in perfect dielectrics with radially periodic indices of refraction. The electromagnetic properties of such structures are similar to periodic photonic band structures, but radial perturbations scatter weakly away from the Bragg resonance and yield a gap for arbitrarily weak index perturbations. The simplest radial perturbation is δn = Δn
o
cos(Kr). In 3-D, this perturbation causes narrow gaps and true localized modes. 2-D systems are constructed by radially perturbing the effective index of slab waveguides. True photon localization is not possible in purely dielectric 2-D systems, but high-Q transparent resonators can be constructed. We discuss solutions to the vector Helmholtz equation under radial dielectric modulation and describe resonance spectra and scattering in 3-D and 2-D structures. We discuss the fabrication of 2-D structures.
Atomic emission rates in photonic band structures
Authors: Dowling Jonathan P. , Bowden Charles M.
Published: February 2023

There has been a great deal of interest lately in periodic dielectric materials that exhibit photonic band structures. One of the more interesting features of such a substance is its ability to alter the emission rate of probe atoms embedded in the periodic lattice. Large enhancements and complete inhibition of emission rates can be obtained. It has been known for some time that the influence of a cavity on atomic emission is essentially a classical effect. Hence, we develop a general classical treatment of radiation rates in an inhomogeneous medium. Our results agree with those of a fully quantum calculation, and are applied to a simple scalar model of a dipole in a one-dimensional periodic lattice of the Kronig-Penney type.
Observation of gain induced by partially correlated stochastic optical fields in two-level atoms
Authors: Anderson M. H. , Vemuri G. , Cooper J. , Smith S. J. , Zoller P.
Published: February 2023

We have measured the absorption of a weak, stochastic field in the presence of a strong, degenerate stochastic pump that saturates the 3S1/2(F = 2, m
f
=2) → 3P3/2(F = 3, m
f
= 3) transition in atomic sodium. The probe is a time delayed replica of the pump field, and the net field obeys non-Markovian phase diffusing statistics. The absorption (gain) of the probe field was measured as a function of the time delay. We use cw lasers and impose phase diffusing statistics (δ-correlated frequency fluctuations) with a system of electro-optics. The time delay is provided by lengths of optical fiber. Our results agree well with a recent theory for atomic response to non-Markovian fields, valid for arbitrary strengths and bandwidths of the pump field and a weak time delayed probe. For both pump and probe fields resonant with the transition, we observe maximum gain for a probe time delay of approximately 0.8 lifetimes of the upper state (γ−1).
Hexagons and squares due to counterpropagation in Kerr media
Authors: Geddes J. B. , Indik R. A. , Moloney J. V. , Newell A. C. , Firth W. J.
Published: February 2023

Spontaneous pattern formation has been observed experimentally when two counterpropagating laser beams interact in sodium vapor. We report investigations into the nature, stability, and range of patterns in such systems. The model is an anti-reflected slab of Kerr medium, irradiated from each side by smooth, constant input fields-plane waves or Gaussian beams. Two transverse-dimensional numerical simulations have produced a rich variety of patterns. On the self-focusing side, hexagons are preferred and we find that these patterns persist to about 15% below the linear threshold intensity both with and without the wavelength-scale index grating. These results are in general agreement with our analysis and with hexagon dynamics in other situations such as fluid convection. A new phenomenon not present in typical hexagon structures is the occurrence of a Hopf bifurcation, through which the hexagon pattern destabilizes. On the self-defocusing side, squares are the favored pattern. Simulations including the index grating indicate that above threshold they are stable while below threshold they are unstable and are replaced with the homogeneous plane-wave state.
Using p-i-n/HBT photoreceivers for very high speed communications
Authors: Lunardi L. M. , Chandrasekhar S.
Published: February 2023

We have used the heterojunction bipolar transistor (HBT) as the device technology to perform the electronic functions in monolithically integrated photoreceivers. Our approach has been motivated by the fact that HBTs have already demonstrated high-speed performance, even with relaxed design rules, and by noise analysis, which suggests that bipolar transistor-based preamplifiers will have sensitivities favorable for optical communication systems. We will present our results of p-i-n photodetectors integrated with HBT-based preamplifiers realized in the InP/InGaAs material system. Sensitivity measurements at high bit rates confirm that the performance of these monolithic receivers is close to that of the best p-i-n hybrid receivers.
Long-wavelength InGaAs MSM-HEMT receiver OEICs
Authors: Hong W. P. , Chang G. K.
Published: February 2023

Our recent progress in researching receiver OEICs based on InGaAs metal-semiconductor-metal (MSM) photodetectors and high-electron-mobility-transistor (HEMT) amplifiers is reviewed. We have built three different receiver OEICs for different system applications. The basic fabrication process was OMCVD growth on a patterned substrate by which the epitaxial layer structures of a MSM photodetector and HEMT are grown sequentially on prepatterned InP substrates in one growth run. Both MSM photodetector and HEMT are based on InAlAs/InGaAs heterostructures in which InGaAs is a light absorption layer of the MSM photodetector and a channel layer of the HEMT. This integration technology represents a major step toward achieving high-performance and low-cost light-wave receiving components.
Switching energy dependence on the input beam size in the VSTEP optoelectronic switch
Authors: Beyzavi K. , Devlin G. E. , Linke R. A. , Ogura I. , Numai T. , Kasahara K.
Published: February 2023

One form of the VSTEP device is a bistable light activated thyristor with an optically active region, between two AlGaAs/ GaAs heterojunctions, for light emission. We report a nearly linear dependence of the optical switching energy E
sw
on illumination area showing a factor of 5 decrease in the minimum E
sw
as the spot size is reduced 10 times from the full device area. This effect is explained by noting that the inner p layer is completely depleted and the mobility of the photogenerated holes, injected into this region as part of the current flow mechanism, is very low. For small illumination areas and sufficiently high powers, the device can be made to switch on (initially, only in this small area) in a time that is short compared with the lateral spreading time (~400 ns). The total optical energy required to accomplish this is linearly dependent on the illumination area in this limit. For lower power densities, when switching times are longer than this characteristic time, E
sw
becomes independent of the spot size. We see evidence of this behavior in the data. Calculations of E
sw
for the fully illuminated device show good agreement with the measurements.
InAlGaAs/InGaAs MQW modulators operating at 1.06 μm on GaAs substrate for opto-electronic computing
Authors: Fan C. , Shih D. , Hansen M. , Wieder H. H. , Esener S. C.
Published: February 2023

Strain-relaxed InAlGaAs/InGaAs MQW device arrays with an exciton absorption peak at 1.06 μm are reported. The array will be used in flip-chip bonded Si/GaAs smart pixels operating at the wavelength corresponding to the emission of diode pumped solid state Nd-YAG lasers. The MQW devices are designed for both electro-optic modulation and detection in the pixels, while the logic functions are implemented by Si CMOS circuits. MQW modulators operating below the GaAs band edge have been demonstrated with strained GaAs/InGaAs MQWs on GaAs substrates. However, the indium content required for operation at 1.06 μm is about 25%, which results in a 2% lattice mismatch between InGaAs and GaAs. In this work, MQW structures are constructed by lattice-matched InAlGaAs/InGaAs multi-layers of the same indium content in both quaternary and ternary materials. The misfit strain from GaAs substrate was accommodated by a compositionally step-graded InAlGaAs buffer with each 0.3 to 0.5 μm thick step representing a less than 10% change in the indium composition. The band gap of each InAlGaAs layer was adjusted to be the same as that of GaAs by controlling the aluminum content. The preliminary results show an electro-absorption of 2500/ cm at 1.06 μm with an applied field of 3 × 105 V/cm.
Second and third harmonic generation by reflection from Langmuir-Blodgett films of a new organic material
Authors: Srinivasan R. , Venkateswarlu P. , He K. X. , Hyde H. W. , Penn B. G. , Frazier D. O.
Published: February 2023

SHG and THG signals were observed by reflection from the Langmuir-Blodgett monolayer of a Sec-butyl derivative of 4-methyl-6-nitro-2-quinolinamine. A floating monolayer was obtained by spreading chloroform solutions on ultrapure water and the subsequent evaporation of chloroform. The monolayer was deposited on a suitably treated glass slide at a compression rate of 100 cm2/min and a pressure of 12 mN/m. The 1064 nm fundamental wave emanating from a Nd:YAG laser was incident at a 45° angle on the monolayer surface, with the length of the substrate in a vertical plane. Signals were observed at 532 nm (SHG) and 355 nm (THG). When the sample was rotated by 90° in a vertical plane, the SHG signal vanished and the THG signal became much smaller. SHG and THG signals were also observed by reflection from a L-B film of 20 monolayers. When this sample was rotated by 90°, there was no significant difference in the intensity of the signals. The values of χ2 and χ3 were determined to be 10−6 and 5 × 10−4 esu, respectively, by using standard relations.
Picosecond degenerate two-wave mixing
Authors: Dutton T. E. , Rentzepis P. , Rogovin D. , Shen T. P. , Scholl J.
Published: February 2023

We examine transient, degenerate two-wave mixing by using picosecond laser pulses to create orientational index gratings. A phase shift between the electromagnetic and material index gratings can be created with degenerate laser beams through nonlinearities that exhibit a finite response time. This requires that the response time for the nonlinear material and the laser pulse time be compatible. The specific mechanism for phase shift arises from the time delay that the nonlinear material exhibits to incident laser pulses, and it serves as a mechanism for energy transfer. We have examined this phenomenon experimentally in CS2 and found good agreement between theory and experiment. The theory has been extended to treat situations in which the medium is irradiated by very high power pulse beams, and the saturation characteristics of this phenomenon have been determined. Additionally, the change in laser pulse shape and the detailed physical characteristic of the optical index gratings responsible for energy transfer for saturation conditions have been investigated.
Two and three photon absorption in C60/C70 solutions
Authors: McLean D. G. , Schmitt M. G. , Brant M. , Sutherland R. L. , Brandelik D.
Published: February 2023

We have performed nonlinear absorption measurements at 532 nm and 1064 nm in solutions of C60/C70 (95%/5%) in CCl4. Our nonlinear transmittance data at 532 nm agrees with the data reported in Ref. 1, where optical limiting was attributed to triplet-triplet absorption. Our data is observed to fit very well the expected behavior for two photon absorption at 532 nm. The measured β = 2.44 cm/ GW at a concentration of 0.020 mM. The 1064 nm nonlinear transmittance data fits a three photon rather than a two photon absorption dependence. The measured γ = 0.0347 cm3/GW2 at a concentration of 0.31 mM. This indicates a fifth order nonlinearity at 1064 nm, which was also observed in degenerate four wave mixing in a C60 film at comparable irradiances (1-10 GW/cm2).2
Nonlinear interaction of multiple waves in an optical fiber
Authors: Judy Arthur , Hart Darlene , Roy Rajarshi
Published: February 2023

Four wave mixing interactions between two pump waves and multiple sidebands in a single mode fiber are investigated. Two tunable dye lasers are used to generate pump waves that are input into a polarization maintaining fiber. A video camera interfaced to a spectrometer allows us to study both single shot and averaged spectra at the fiber output. Predictions from the nonlinear Schrödinger equation with dual frequency input are compared with those from a simplified model of wave propagation that employs ordinary differential equations (ODEs) and assumes monochromatic waves. In particular, we study a conservation relation that was discovered in the ODE model and examine its validity for different experimental regimes. Analytic approximations, numerical solutions, and experimental observations are compared for various values of detuning and power of the input pump waves.
Calculations of Raman conversion and beam quality of high intensity laser beams in air propagation
Authors: Lin Ying , Kessler Terrance J. , Lawrence George N.
Published: February 2023

Very high intensity laser beams used in laser-fusion experiments are subject to rotational Raman conversion, which generates a Stokes beam—initially by spontaneous Raman scattering and subsequently by stimulated Raman amplification. At the typical irradiance level of gigawatts per square centimeter, the laser may be significantly depleted over several tens of meters. Accurate calculation of the degree of Raman conversion is essential for the design of the device but requires detailed treatment of the combined effects of aberration, spontaneous noise, nonlinear amplification, and diffraction. A wave optics calculation is required but is very difficult because the Fresnel numbers are very high (in the range 1,000 to 10,000). The transient behavior needs four-dimensional calculations. Inevitably aberrations in the upstream part of the beam lead to some fluctuations in intensity. Even very weak hot spots in the laser, because of the amplifications of about exp(30), generate strong hot spots in the Stokes beam. We show these hot spots typically dominate the process and lead to very significant spatial coherence of the Stokes beam and a concomitant decrease in the modeling difficulties.
Electromagnetic scattering by a circular groove in a ground plane
Authors: Kok Yon-Lin
Published: February 2023

The problem of electromagnetic scattering by a circular-grooved corrugated ground plane is treated in a cylindrical coordinate system (ρ, ϕ, z), where the solution assumes a 2π periodicity in direction. Thus, the solution can be expanded in a Fourier series in ϕ and can be decomposed into two orthogonal polarizations according to vector field theory. They are the fast polarization, Hϕ = 0 and the slow polarization, Eϕ = 0. Furthermore, these two polarizations can be uniquely determined by Eϕ and Hϕ, respectively, each represented in the form of an integral involving Bessel functions. For the nth mode in the Fourier series expansion, they are where r
n
(ξ) is the unknown function amenable to electromagnetic boundary conditions. It is found that r
n
(ξ) can be constructed by another series of Bessel functions through the techniques of Hankel transforms. The coefficients of the series can be determined by enforcing the continuity of tangential fields in the groove aperture. Simulation results will be presented to show that the boundary-value techniques are efficient and computationally stable.
Novel diffraction techniques for metrology of etched silicon gratings
Authors: Krukar R. H. , Naqvi S. S. H. , McNeil J. R. , Franke J. E. , Niemczyk T. M. , Hush D. R.
Published: February 2023

A rigorous coupled wave model is used to generate simulated laser scatter patterns from diffraction gratings etched to various depths into a silicon wafer. The multivariate statistical analysis techniques of inverse least squares, classical least squares, principal component regression, and partial least squares are calibrated by using the simulated scatter data to predict the grating height. The same data set is also used to train a multilayer perceptron implementation of a neural network to similarly predict the grating height. Cross validation is used to evaluate the performance of each method. After the calibration, training, and validation phases, measured scatter patterns produced by structures are analyzed. The analysis not only addresses the inverse scatter problem in several ways but also indicates the preferred technique.
Inverse problems with quasi-homogeneous random media utilizing scattered pulses
Authors: Fischer D. , Cairns B.
Published: February 2023

Inversion formulas are presented for determining the two-point spatial correlation function of the dielectric susceptibility of a quasi-homogeneous1 random medium. The method requires that the medium be illuminated by plane-wave pulses and that the time resolved intensity profile of the scattered field in the far zone be known for all directions of incidence and all directions of scattering. The solution yields expressions for both constituent factors of the two-point spatial correlation function of the medium, namely the strength of the dielectric susceptibility and its degree of spatial correlation. We illustrate our analysis by some examples.
Uncertainty relations and interferometers
Authors: Hillery Mark , Mlodinow Leonard
Published: February 2023

As was originally pointed out by Caves, squeezed light can be used to increase the accuracy of interferometric phase measurements. This analysis was carried further by Yurke, McCall, and Klauder, who used group theory to examine the ultimate sensitivity of conventional interferometers and also those constructed from four-wave mixers. Here we consider interferometers composed of mixtures of beam splitters, four-wave mixers, and degenerate parametric amplifiers. We show that each interferometer can be characterized by an uncertainty relation whose minimum uncertainty states can be used to explore its ultimate accuracy. The variables in the uncertainty relation are quadratic in the mode operators, which allows us to connect the study of improved interferometric measurements to recent work on higher-order squeezing.
Textured metal baffles for stray light suppression in rugged systems
Authors: Johnson Edward A. , Blatchley Charles B. , Wyman Charles L. , Breault Robert P.
Published: February 2023

Summary not available at press time.
Scalable wideband optical networks
Authors: Brackett C. A.
Published: February 2023

Multiwavelength optical networks of many forms that use wavelength to create concurrent network interconnections on passive optical media such as stars, buses, and rings have been proposed and in part demonstrated. These networks have virtually all suffered from the limitation of not being scalable to large numbers of access nodes. We describe how to overcome this limitation and to produce truly scalable and modular multiwavelength networks having capacities far surpassing that of star-based networks by the use of wavelength routing to produce maximal wavelength reuse, wavelength translation to reduce blocking, and multihop switching to provide packet based network access at gigabit-per-second rates. The result is network architecture in which the number of access nodes is independent of the number of wavelengths used.
Direct detection of Gaussian state light
Authors: Shapiro J. H. , Sun K.-X.
Published: February 2023

The quantum theory of photodetection is applied to the direct detection of multi-mode Gaussian-state light, with particular attention to the mean photocurrent and the photocurrent noise spectrum. Gaussian-state light comprises squeezed-state light plus additional classical Gaussian noise. By extending the familiar Gaussian moment-factoring formula of classical statistics to the antinormally ordered characteristic function of Gaussian-state light, the first and second moment photocurrent statistics for such illumination are shown to be completely characterized by knowledge of the mean function, the phase-sensitive correlation function, and the normally ordered correlation of the input light. The theory delineates the condition under which the strong-mean-field approximation is applicable to direct detection of such beams, i.e., it tells us when a direct detector yields the same noise spectrum as that of an in-phase homodyne detector. Numerical results are presented for the noise spectra of a squeezed amplifier, i.e., an optical parametric amplifier with signal-injection-induced gain saturation.
Propagation of high-energy laser beams through evaporating aerosols
Authors: Zardecki Andrew
Published: February 2023

The pioneering work of Reilly and Wallace in the early 1980s led to a spectacular understanding of laser—aerosol interactions. Research has focused, on the one hand, on the description of the vaporization process and the associated hydrodynamic phenomena. On the other hand, on the basis of semi-analytic and Monte Carlo techniques, predictive numerical algorithms have been constructed. They enable one to study the broadening and distortion of laser pulses in the process of vaporization, thermal blooming, turbulence, burning, and plasma formation. This paper summarizes the basic physics underlying the process of single droplet vaporization and cloud recondensation. Experiments performed at Los Alamos National Laboratory on laser propagation through clouds will be described. We also formulate the hydrodynamics in the region surrounding the droplet. The propagation algorithm developed under the forward scattering approximation—supplemented by the energy conservation condition—allows us to study the pulse distortion and the laser-assisted imaging in the evaporating clouds. We assess the significance of turbulent mixing and recondensation in a cleared channel. In addition, the effects of high-energy pulses on the burning of carbon particles and plasma formation in metallic aerosols will be discussed.
Time dependence of the internal and scattered intensity of a dielectric sphere illuminated with a pulsed Gaussian beam
Authors: Khaled E. E. M. , Chowdhury D. Q. , Hill S. C. , Barber P. W.
Published: February 2023

The timedependent internal and scattered intensities of a dielectric sphere illuminated with a pulsed beam are presented. The incident beam is Gaussian in both space and time. The center of the beam is positioned inside, on the edge, or outside the sphere. The center frequency of the pulse is usually chosen so that the sphere is on or near a morphology-dependent resonance (MDR). The time-dependent fields at points inside or outside the sphere are calculated by inverse transforming the frequency spectrum. The frequency spectrum at each point is calculated by using the incident field spectrum and the transfer function at that point. The transfer function is the steady state field at the point of observation as a function of incident frequency. The steady state fields are calculated by using a combination of the plane wave spectrum technique and the T-matrix method. The primary factors determining the time dependence of the internal intensity are the position at which the intensity is computed; the position, spatial width, and temporal width of the incident Gaussian beam; the detuning of the center frequency of the pulse from the nearest high-Q MDR frequency; and the lifetime of the nearest high-Q MDR. The results help in modeling nonlinear optics in droplets.
POINTS: technology for micro-arcsecond optical astrometry
Authors: Noecker M. C. , Babcock R. W. , Phillips J. D. , Reasenberg R. D.
Published: February 2023

We discuss the technology requirements for the POINTS optical interferometric instrument. Angular resolution of 5 × 10−6 arcsec (25 prad) by using an interferometer with a 2-m baseline requires internal distance metrology at the few picometer level and precise starlight fringe splitting. We have shown long term stability of two picometers in measurements on a Michelson-type distance gauge; we will soon test a design for point- to-point distance measurements. Full-aperture metrology of the starlight path has shown promising results with the first prototype zone-plate mirror, which diffracts part of the incident light to an auxiliary focus. Other applicable technological areas include broadband mirrors and beam splitters with stable phase shift and polarization properties, high-efficiency broadband detector arrays, thermally stable glasses and structural materials, integrated optics, a stable and robust laser source in the near infrared, supersmooth surfaces, and precision glass assemblies.
Modified method of laser beam collimation using Talbot interferometry
Authors: Ganesan A. R. , Venkateswarlu Putcha
Published: February 2023

A modified method of testing laser beam collimation is presented. The method is based on self-imaging coupled with the Moiré phenomenon. A Ronchi grating of low frequency (about 50 to 100 lines/in.) is placed in the beam to be tested such that the grating lines make an angle δ with the horizontal. Self-images (Talbot images) of this grating are formed at certain well defined planes. A right angled prism is used in the retroreflecting mode to project the folded self-image onto the actual grating. The grating lines in the projected self-image would make an angle minus δ with the horizontal. The Moiré fringes are observed through a beam splitter placed between the grating and the collimating lens. For a collimated beam the Moiré fringes are parallel to the roof-edge of the prism, which is seen as a bright line; otherwise, they are rotated with respect to this reference orientation. The technique has a built-in reference and does not require precise alignment or measurement of the grating orientation.
Optical fiber preamplifier in lidar detection
Authors: Salisbury Michael S. , McManamon Paul , Watson Edward , Mark Martin , Duncan Bradley
Published: February 2023

A ratio for direct detection and heterodyne detection has been developed for an in-house 1.06-μm lidar system at Wright Laboratory. A signal-to-noise ratio formula has also been developed for direct detection and heterodyne detection with a rare earth doped optical fiber preamplifier incorporated into the lidar system. With the fiber preamplifier in the system, the return signal is amplified by a power gain factor G, but the fiber preamplifier also adds a noise term to the signal-to-noise ratio as a result of the spontaneous emission inherent in this type of optical amplification. This noise that is added by the spontaneous emission limits the benefit that the fiber preamplifier will have on system sensitivity. The spontaneous emission noise will have a different impact on the direct detection scheme than it will on the heterodyne detection scheme because of the presence of the local oscillator in the heterodyne case. The effect of the spontaneous emission is examined in detail for both detection schemes. An experimental setup for incorporating the fiber preamplifier into the lidar system is given, and results of sensitivity comparisons are discussed.
Faraday anomalous dispersion optical transmitter for high stability frequency locking of laser diodes
Authors: Gallant M. R. , Shay T. M.
Published: February 2023

Frequency stabilized diode lasers are required for optical communications, laser spectroscopy, and remote sensing. Two conventional techniques for frequency stabilization are optical feedback and optoelectronic feedback. Optical feedback is achieved by use of a partially transmitting mirror, which creates an external cavity diode laser system. A frequency selective element, such as an étalon, a birefringent tuner, or an interference filter, placed in an external cavity will provide frequency stabilization and linewidth reduction of the diode laser. Optoelectronic feedback requires complex electronics to stabilize the laser diode.
Optical implementations of the wavelet transform
Authors: Riasati Vahid R. , Berinato Robert J. , Abushagur Mustafa A. G.
Published: February 2023

The theory of the wavelet transform (WT) is discussed as it relates to nonstationary signals. Two optical architectures are presented for the implementation of the WT. The optical time and space integrating implementations of the WT allow the use of space to simultaneously present the function under analysis to a series of variable pass-band filters. Space integrating architectures allow the use of space to represent a range of frequencies as a bank of filters. On the other hand, time integrating architectures have the ability to change the integration time to provide the necessary variation of frequency across the spatial extent of the beam to implement the WT.
Wavelet based optical signal detection in a dense target environment
Authors: Zhang Y. , Katz A. , Kenterakis E. , Li Y.
Published: February 2023

Signal processing in a dense target environment has been found useful in applications such as medical diagnosis and weather forecasting. It was proved that the echo from the assemblage of targets is described by where D(x, y) is the target density, s(t) is radar signal, and x and y are the distance and velocity, respectively.
Propagation of an ultrashort pulse through a dispersive medium
Authors: May M. , Morhange J. F. , Hirlimann C.
Published: February 2023

In the slowly varying envelope approximation, a quasi-monochroma tic light wave of central angular frequency ωo propagates through a dispersive material at the group velocity. This approximation fails in the case of ultrashort pulses for which the temporal frequency components of the envelope are of the same order as ωo. The concept of group velocity cannot be used in this case since the signal envelope suffers a strong distortion. To describe the propagation of such pulses, we propose a mathematical time-frequency decomposition of the incident light amplitude into elementary components of same duration τ
a′
each centered at a frequency Ω lying in the Fourier spectral range of the original pulse. Each wavelet component F(Ω, t) is given by the convolution between the Ω Fourier component and an analyzing Gaussian function, whose spectral width will determine its duration. The original pulse is retrieved by integrating F(Ω, t) over the frequency. This method is applied to a representation of the propagation of a 3 fs light pulse through a quartz plate. We will study the deformation and the time enlargement of the pulse versus τ
a
and the thickness of the plate, taking into account the strong dispersion of the group time characterizing each wavelet.
Squeezing in a double-sided optical parametric oscillator with arbitrary output couplings
Authors: Prasad Sudhakar
Published: February 2023

In a recent work,1 the influence of arbitrary values of output-mirror transmission on the quantum noise and squeezing in a degenerate optical parametric oscillator (DOPO) with a single output mirror was studied. The work being presented here is a theoretical extension of that research to the case of a DOPO in a double-sided cavity with arbitrary transmission coefficients for the two output mirrors. Additionally, the pump field will be allowed to have amplitude and phase noise. Both intracavity and extracavity fields will be treated for a variety of squeezing characteristics of the input fields entering the DOPO cavity. The dependence of squeezing of the output and intracavity fields on the spatial phase, which determines the locations of the nodes and antinodes, of the average pump field will also be analyzed. As in Ref. 1, the generalization of the good-cavity results to arbitrary quality cavities is highly nontrivial.
Instabilities in a laser with injected atomic coherence
Authors: Bergou J. , Zhang J.
Published: February 2023

We discuss the influence of injected atomic coherence on laser dynamics. The nonlinear equations of motion for the intensity and phase give the dependence on external parameters (inversion, amplitude of the atomic coherence, and cavity-field detuning). Depending on the inversion, there can be one or three steady-state solutions corresponding to a given value of the injected coherence. The situation is analogous to optical bistability, the atomic coherence playing the role of the injected field. For zero detuning the upper, laser-like branch starts at zero value of the injected coherence and a numerical stability analysis indicates that it is the only stable solution, the lower branch being everywhere unstable. For finite detuning the upper branch starts at a finite threshold value of the injected coherence. For coherences smaller than this threshold the system exhibits oscillatory behavior that corresponds to a stable limit cycle in the phase plane of the laser quadrature variables. The intensity fluctuations of the laser exhibit antibunching for sub-Poissonian pumping statistics.
Nonlinear theory of pump coupled micromasers
Authors: Bergou J. , Bogar P. , Hillery M.
Published: February 2023

Two micromasers are coupled by sharing a common pump beam. A stream of excited atoms first passes through one micromaser and then enters a second one. The steady state of the second micromaser exhibits a second threshold at θ2= 2. The second threshold is accompanied with a jump of π in the phase of the second micromaser. For higher values of the pump parameter θ new branches of the steady-state intensity keep appearing. In certain parameter regions the phase of the second micromaser locks to that of the first and exhibits correlated emission laser-like noise quenching. In other regions the intensity fluctuations exhibit antibunching. The approach to steady state is also highly nonclassical. There are sharp jumps of magnitude π in the phase of the second micromaser and the intensity tends to overshoot before they settle to their steady-state value. In this transient regime the system exhibits phase noise squeezing.
Measurements and models of the motion aftereffect
Authors: Sachtler Wendelin L. , Zaidi Qasim
Published: February 2023

Sensitivity to motion was measured by the percentage of trials in which an observer reported seeing motion of briefly presented high-contrast sinusoidal gratings moving over a range of velocities. The psychometric curve was remeasured following adaptation to a grating moving in one direction for an extended period of time. Adaptation shifted the minimum of the psychometric curve towards the direction of the adapting stimulus and made the curve asymmetric. The shift was smaller when the adapting field was larger than the test. In a second set of experiments we measured the effect of motion adaptation on contrast thresholds for moving gratings of different sizes. Threshold elevation was maximal when adapting and test sizes matched. We present a mechanistic model of the motion aftereffect that consists of independent multiplicative gain controls in motion-sensing mechanisms tuned to different rates of motion. In addition, we discuss a model of size effects in motion adaptation that invokes diffuse inhibitory connections among motion-sensing mechanisms.
Computer generated holograms for large deflection angle optical interconnects
Authors: Nakkar Mouna , Stack Jared , Welch W. Hudson , Feldman Michael R.
Published: February 2023

Although many papers have recently been published on computer generated holograms (CGHs) or diffractive optics for optical interconnects, most research has concentrated on connections that involve relatively small angles. Small angle connections require relatively low CGH spatial frequencies and can be implemented efficiently with many CGH design and encoding methods. Large angle connections, however, are needed to implement long distance interconnects with a high connection density. For example, an optically interconnected multichip module system is currently under development. Connection lengths of up to 40 mm and angles as large as 27° are needed. For such large deflection angles, the CGH spatial frequencies are so large that with conventional encoding methods only two phase levels can be employed, and the resulting diffraction efficiency through two successive holograms is limited to a maximum value of 16%. Therefore we developed a new encoding method that allowed us to increase the number of phase levels in the CGH, thereby increasing the diffraction efficiency.
Differential signaling in optical interconnects and logic
Authors: Stirk C. , Wagner K.
Published: February 2023

The advantages of differential signaling in binary communication and logic systems are high reliability and speed; the main disadvantage is the additional hardware required. For optical interconnection network and digital optical logic systems, we describe simple hardware implementations for differential signaling and analyze their impact on the system's reliability and performance. Model non-idealities include finite contrast, shot and thermal noise, scattering, diffraction, and aberrations. In contrast to the limits of direct detection, we describe a crossbar whose size is independent of modulator contrast ratio and threshold logic circuits scalable to high fan-in.
Modified signed-digit quaternary arithmetic using optical symbolic substitution
Authors: Alam M. S. , Jemili K. , Karim M. A.
Published: February 2023

Modified signed-digit (MSD) arithmetic can be efficiently performed by using two-step symbolic substitution (SS) for carry-free addition and borrow-free subtraction, where the to-be-added pair of numbers is first mapped into an intermediate pair such that the addition of the latter pair will prohibit carry propagation. Kozaitis1 presented the addition rules for a higherorder (two-bit) SS scheme allowing four bits to be processed at the same time. However, this technique depends on the length of the bit string, thereby producing an unnecessary constraint on the computation speed for operations involving long operands. To incorporate more information in fewer digits and at the same time perform arithmetic operations independent of the length of the bit strings, in this paper we study the higher-order SS technique employing MSD quaternary arithmetic. The necessary SS rules for both addition and subtraction using the proposed technique have been derived by taking into consideration a pair of reference bits from the next-lower-order bit position. Finally, the performances of the higher-order MSD binary, trinary, and quaternary arithmetic with the optical SS technique are compared.