bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring amplitude probability distribution for photon number-operator eigenstates
Authors: Yurke B. , Stoler D.
Published: February 2023

In parametric downconversion, pump photons are converted into pairs of signal and idler photons. A photodetector counting photons in the idler beam can be used to gate a homodyne detector in the signal beam so that it is on only when an n-photon wave packet enters its input. The probability distribution for the charge delivered by the homodyne detector has the same form as the position probability distribution of a harmonic oscillator in its nth energy eigenstate. In particular, the probability distribution exhibits fringes. We have calculated the visibility of these fringes for the case when both the photodetector and the homodyne detector have less than unit quantum efficiency. By reducing the photon flux in the signal and idler beam sufficiently, the effect of idler photodetector loss on the fringe visibility can be made negligible. The degree to which the fringes have been degraded then depends only on the inefficiency of the homodyne detector. For the case n = 1, the fringe is still visible when the homodyne detector efficiency is 0.5. Hence the proposed experiment should be feasible with existing technology.
Some thoughts on the feasibility of optical data base machines
Authors: Berra P. Bruce
Published: February 2023

Many very large data bases (VLDB) currently exist in industry, business, and government. To access, update, protect, and in general manage these VLDB require an enormous amount of computing power both in terms of hardware and software. A field that has received considerable research and development attention over the last 20 years is data base machines. The main objective of a data base machine is to improve greatly the performance of data base functions by maximum utilization of parallelism and hardware advances. While commercial data base machines exist, their impact has not been so great as originally expected. Unlike other fields of computing, in data base management considerable data are processed only to be discarded later. This coupled with large data volume (gigabytes to terabytes) mandate a storage hierarchy, and magnetic disks form the backbone of this hierarchy. However, the data rates from magnetic disks are only of the order of 3 Mbytes/s, which severely limits the performance of such systems. On the other hand, the potential data rates from optical disks are of the order of 300 Mbytes/s using multibeam reads. These data rates can easily be accommodated with optical interconnections for input to an optical processor. This optical processor must be able to perform rudimentary data base operations on the data prior to transforming it to electronic form, which insures that much richer data are input to the electronic computer. The optical storage system, interconnections, and optical processor form the basis of an optical data base machine. The underlying issues involved in the conceptual design of such a machine are discussed.
Synthesis of digital holograms by direct binary search
Authors: Allebach Jan P. , Seldowitz M. A. , Sweeney Donald W.
Published: February 2023

Since Lohmann proposed his detour phase method for holographic encoding in 1966, methods for encoding the complex-valued object wavefront into a real non-negative hologram transmittance function have proliferated. However, these traditional methods generate suboptimal holograms and fail to utilize fully the device resolution. We have developed a new method for hologram synthesis, direct binary search, that efficiently utilizes the available hologram resolution.
Two-dimensional high-spatial-frequency binary dielectric gratings
Authors: Moharam M. G.
Published: February 2023

Recently, it has been shown theoretically and experimentally that high-spatial-frequency rectangular-groove (binary) dielectric gratings exhibit zero reflectivity. This means that a high-spatial-frequency periodic surface on a dielectric behaves like an antireflection surface. Thus damage-prone thin-film antireflection coatings can be replaced by a grating directly on the optical element. Antireflection coatings for a substrate where the thin-film refractive index is difficult to synthesize can now be made. In these high-spatial-frequency gratings, the periodicity is less than the light wavelength in the medium. Thus all diffracted orders other than the zero order are evanescent and cut off.
Effects of pixel interaction in SLM-based optical correlators
Authors: Horner Joseph L. , Gianino P.D. , Dillon R. , Warde C.
Published: February 2023

Currently available spatial light modulators (SLMs) inevitably have an inactive area around each pixel and electrical or optical interaction between each pixel. We examine the effects these phenomena have when the SLM is used in an optical correlation system, both as an input device and as the reference function in the Fourier plane. The effects are quantified through the SNR and full width at half-maximum of the correlation plane signal through a computer simulation of the problem.
Diameters of presumed cone apertures in human retina
Authors: Curcio Christine A.
Published: February 2023

The cone entrance aperture is thought to be located in the inner segment. Little is known about changes in cone inner segment diameter (CISD) across the entire human retina. The degree to which the increase in CISD with eccentricity offsets decline in cone density to maintain total quantal flux per unit retinal area is unknown. Gradients in refractive index along the length of CIS were viewed directly in cleared retinal whole mounts using Normarski differential interference contrast microscopy. Individual CISs are optically resolvable from their neighbors at a level slightly vitreal to the CIS ellipsoid–myoid junction. CISD at this presumed aperture level and the proportion of retinal area occupied by apertures aa were measured from the fovea of one and the periphery of four young adult retinas previously mapped for cone density. CISD increased sharply from 2.3 μm at the foveal center to 6.5 μm at 1 mm (3.6°) and slowly from there to a maximum of 8.5–9 μm near the ora serrata. aa decreased approximately threefold across the retina from 69 to 78% in the foveola to a plateau of 20–35% in the midperiphery to far periphery. Over this eccentricity range, the cone density declined fortyfold. These results predict different eccentricity dependencies for visual functions explained by the density of cones and those explained by the number of photons available to cone photopigment.
Optical self-locking of semiconductor lasers
Authors: Hollberg Leo , Dahmani B.
Published: February 2023

We report on recent advances made with an optical self-locking technique that is used to stabilize the frequency of semiconductor lasers. The self-locking of the lasers to separate stable Fabry-Perot cavities is achieved by arranging to have optical feedback only at the resonance of the reference cavity. Using this method laser center frequencies are stabilized and linewidths are reduced significantly, from 20 MHz to <20 kHz. Experiments have been performed with standard single-frequency commercial lasers operating near 850 nm. The spectral characteristics of the frequency noise of the optically locked lasers are determined by heterodyne as well as interferometric techniques. These measurements provide information about the changes in the frequency spectral noise density when the laser optically self-locks. Both the long-term and short-term frequency stabilities of the lasers are measured. In addition, we describe techniques for scanning the frequency of the optically locked narrow linewidth lasers. Limitations of the method and contributions of systematic effects which can pull the frequency of the laser away from the stable cavity resonance are considered.
Past, present, and future of semiconductor-diode lasers
Authors: Streifer William
Published: February 2023

Semiconductor-diode lasers have already had a major impact on several fields of optics. These devices, which are compact, robust, convenient, inexpensive, and highly efficient, are currently manufactured at the rate of well over one million monthly. This year marks the twenty-fifth anniversary of the first demonstrations of the semiconductor-diode laser. We review the evolution of the semiconductor laser with special emphasis on identifying novel devices and milestones. The current state of the art is then discussed, a brief review of applications is presented, and the future potential of the diode laser and associated devices is considered.
Optical sum-frequency generation in proton exchanged LiNbO3 and LiTaO3 channel waveguides
Authors: Sanford Norman A. , Dyes W. A. , Connors J. M. , Mahapatra A.
Published: February 2023

Optical sum-frequency generation has been observed in channel waveguides produced by proton exchange in LiNbO3 as well as LiTaO3 substrates. Simultaneously coupling 5-mW cw from a Nd:YAG laser operating at 1.32 µm and 8-mW cw from a second Nd:YAG laser operating at 1.06 µm into a channel waveguide formed in a Z-cut LiNbO3 substrate resulted in sum-frequency generation in the yellow. The sum-frequency output emerges from the waveguide as Cherenkov radiation. Second harmonic radiation from both inputs also emerges as Cherenkov radiation but is spatially separated from the sum-frequency output. The power produced at the sum frequency as well as the second harmonic at 1.32 µm is approximately equal to 0.25 µW resulting in a combined red-yellow output of 0.5 µW. Similarly, coupling 1-mW cw at 0.840 µm from a laser diode in conjunction with the 1.06-µm input into the same waveguide gives sum-frequency generation in the blue. Conversion efficiency depends on modal content, wavelength, and scattering. A guide which supports one or two modes at 1.32 µm is more efficient in both sum frequency and second harmonic generation if simultaneously pumped at 1.06 µm than the same guide pumped with the combined input at 0.84 and 106 µm.
Timing uncertainty for receivers in optical clock distribution for VLSI
Authors: Clymer Bradley D. , Goodman Joseph W.
Published: February 2023

Optical interconnection techniques have been suggested to reduce signal skew in clock distribution for silicon VLSI chips. One optical approach for clock distribution is to holographically map an optical signal from an off-chip source to several photoreceivers within small functional cells on a chip surface. Within each functional cell, the clock is distributed via short surface wires with negligible delays. In such a system, there are two sources of timing uncertainty: a static uncertainty due to fabrication-related variation of transistor parameters between identically drawn receivers on a chip and a timing jitter due to phase noise at each receiver.
Multistate self-electrooptic effect devices
Authors: Lentine Anthony L. , Miller David A. B. , Henry J. E. , Cunningham J. E. , Chirovsky L.M.F.
Published: February 2023

We present multistate self-electrooptic effect devices consisting of electrically connected PIN diodes with quantum wells in the intrinsic regions. By connecting several (for example, N) of these diodes in series with a voltage source, the resultant device has N states, each of which consists of the diode with the least incident optical power having high transmission and the others having low transmission. Like the symmetric SEED, which is a special case of this device when N = 2, the devices are insensitive to optical power supply variations, have time sequential gain, and have good input/output isolation. Therefore, these devices solve many of the critical biasing problems commonly associated with multistable devices. We have measured the characteristics of this device for three such diodes and also demonstrated a special case of this device where two quantum well PIN diodes in series with a n-p-n transistor acts as an electrically enabled S-SEED.
Experimental study of SBS beam combination physics
Authors: Carroll David , Johnson Roosevelt , Pfeifer Shirley J. , Moyer Richard
Published: February 2023

A comprehensive experimental investigation of phase locking between two beams by stimulated Briliouin scattering (SBS) was conducted. The objective was to determine the conditions in which good coupling and aberration correction could be achieved and identify the underlying physics issues governing this process. A spatially filtered Molectron Nd:YAG laser, doubled to 532 nm, was used as the pump source. Tests were conducted over a wide range of parameters including bandwidth (100 MHz-15 GHz), f/No. near-field and far-field separation between beams, power ratio between beams, and optical path difference relative to the laser coherence length. Experiments were conducted with and without applied aberrations. Diagnostics included Mach-Zehnder interferometers, CCD cameras (far-field), and ghost beam joulemeter measurements. Ranges of near-field and far-field separation over which good phase-locking and piston-error correction have been determined. It was found that alignment tolerances were relaxed for decreased near-field separation, and the locking range was increased for Increased pump beam aberration.
Excitons in GaAs/(Al,Ga)As superlattices with coupled wells
Authors: Song J. J. , Jung P. S. , Yoon Y. S. , Tu C. W. , Vreeland T. , Nieh S.
Published: February 2023

Various new electrooptic device concepts have recently been proposed which utilize the electronic energy band structures in semiconductor superlattices. The energy bands and excitons in superlattices have not received as much attention as those in quantum wells. A series of high-quality GaAs/(Al, Ga)As superlattice samples have been fabricated to have varying barrier widths using MBE. These samples have been analyzed by transmission electron microscopy to determine the layer thicknesses. Excitation spectroscopy at 5 K was employed to study the energy subband and exciton structures in superlattices. In thin barrier superlattices, well-to-well coupling significantly affects the miniband structures and excitonic states. We report here our observations of the spectral changes associated with coupling of the wells in superlattices. Minor peaks and bumps appeared in addition to the major heavy-hole and light-hole exciton peaks. Striking changes in these exciton spectra were detected with a small change (20 Å) in the barrier widths. From these structures, exciton binding energies in superlattices were derived and found to depend on the barrier layer width. Some of the minor peaks are attributed to the excitons formed at the Brillouin zone edge.
Computer-controlled optical system for fabricating multifacet interconnection holograms
Authors: Huang K. S. , Sawchuk Alexander A. , Jenkins B. K. , Weber A. G. , Wang C. H. , Glaser I. , Chavel P. , Wang J. M.
Published: February 2023

One major reason for developing optical computers is to overcome the communication bottle­necks of electronic systems by using optical interconnections. Holographic interconnections offer a high degree of flexibility because a hologram can be used to perform the function of a multiple lens or grating. We describe how we construct a computer-controlled optical system to fabricate multifacet interconnection holograms for 3-D digital optical circuits and demonstrate how we program the exposure energies, positions, and interconnection patterns of subholograms for achieving very flexible interconnections.
Use of the joint transform in smart correlation filter generation
Authors: Dymek Michael S. , Conner Phil W. , Sun Tsishung
Published: February 2023

Design of smart filters for programmable hybrid optical/digital correlators generally requires execution of sophisticated algorithms in a time-consuming computer program. The performance of the actual correlator hardware is often disappointing, because overly simplified and idealized models of the optical components are usually assumed during filter design. We suggest a technique in which both a computer and the front half of the hybrid correlator itself are combined in a joint transform configuration to provide accurate feedback about the optical system during filter design. Differences between the phase and amplitude of a reference image and its various scaled and rotated distortions are detected in the filter plane and decoded from the joint transform fringe patterns using spatially local operations. The differences can be applied to design filters that give more predictable correlator performance.
Features and information fusion in multiple sensor object recognition
Authors: Roggemann Michael C. , Mills James P. , Rogers Steven K. , Kabrisky Matthew
Published: February 2023

Automatic pattern recognition using multiple sensors offers a promising approach to many pattern recognition problems. Among the many research issues which remain are determination and extraction of useful information from the imagery and fusion of the information derived from multiple sources. The technique being investigated applies the Dempster-Shafer theory of evidence1 to information in the form of features extracted from multiple sensor views of a scene. Features are extracted from segmented regions of a database of real corresonding IR and absolute range images. Multiple sensor features are represented through mass functions for fusion using Dempster’s rule of combination. The resulting mass distributions are evaluated to determine an estimate of class membership for each region.
Inverse scattering for optical waveguides with imperfect boundaries
Authors: Kim Y. , Grebel H.
Published: February 2023

The electromagnetic inverse scattering problem is concerned with reconstructing a scattering medium based on remotely obtained scattered data. Here we assess inverse scattering techniques applied to waveguides with imperfect boundaries. The fundamental difficulties for applying inverse techniques to optical waveguides arise from the fact that waveguides allow only eigenmodes to propagate.
High-resolution measurement of strato-spheric trace species
Authors: Farmer C. B.
Published: February 2023

The atmospheric trace molecule spectroscopy (ATMOS) instrument is a Fourier transform spectrometer developed for use in space in studying the physics and chemistry of the earth’s upper atmosphere by absorption spectroscopy. The instrument, which is capable of scanning the 2.5–16-µm spectral region with a resolution of 0.01 cm‒1 in 2 s, was flown on Spacelab 3 (29 Apr.–6 May 1985). The spectra obtained from this flight yielded the vertical abundances of many trace molecular species between the altitudes of 10 and 130 km. Several of these gases, which are important to studies of the stratospheric ozone balance, had not been observed previously.
Numerical analysis of the precursor fields in linear dispersive pulse propagation
Authors: Wyns Philippe , Foty Daniel P. , Oughstun Kurt E.
Published: February 2023

A fast accurate algorithm for the numerical evaluation of Laplace transform-type integrals is presented and applied to the numerical analysis of the precursor fields in linear dispersive pulse propagation for a Lorentz medium. Both the delta function pulse and the unit step-function modulated signal are considered. These results are compared with the results given by modern asymptotic techniques, demonstrating the ability of this numerical method to resolve accurately the extremely high frequency structure associated with the onset of the Sommerfeld precursor field. This algorithm then provides a useful technique for the investigation of any space–time region of the transient field structure associated with dispersive pulse propagation for any given dispersion relation of appropriate form without the need for performing a complicated asymptotic expansion. It also provides a useful comparison for the asymptotic theory in those important cases that warrant such a detailed analysis.
Amplified spontaneous emission in a Ti:Al2O3 amplifier
Authors: Schulz P. A. , Wall K. F. , Aggarwal R. L.
Published: February 2023

Recently the time dependence of gain in a Ti:Al2O3 amplifier was measured.1 It was shown that the decay of gain was much more rapid than expected if only spontaneous decay was responsible for depletion of the upper state. Although it was believed that amplified spontaneous emission (ASE) might be responsible for this difference, the apparent difficulty of calculating the effect of ASE inhibited pursuit of this conjecture. A rate equation has been used to demonstrate that ASE can quantitatively explain the fast decay. In this model, the gain of the amplifier is e
γ
, where γ obeys the time-dependent spatially integrated equation The three terms on the right-hand side of this equation describe the spontaneous emission rate, pump rate, and stimulated emission rate caused by the input to the amplifier and by ASE, respectively. Excellent fits of the experimental data have been obtained using only one parameter Ω, the effective solid angle for ASE. The fitted parameter is in good agreement with geometrical estimates.
Interferometric slope measurement technique for detection and measurement of silicon crystal lattice defects
Authors: Selberg Lars A. , Hoge Thomas E.
Published: February 2023

An ac heterodyne interferometric technique for detecting crystal lattice dislocations and measuring their heights is presented. Preliminary laboratory data indicate the sensitivity of the technique for defect detection to be in the nanometer range. Crystal lattice dislocations in semiconductor wafers (sliplines) can render useless any device through which a dislocation passes. These dislocations are caused by the release of latent stresses in the lattice. The release of these stresses is brought about by the processing of wafers for device fabrication. Detection of the sliplines at an early stage is important to process efficiency.
Large color differences among achromatic colors
Authors: Cowan William , von Grunau Michael
Published: February 2023

Small color differences between simple achromatic stimuli have been understood for more than a century: extensive detection and discrimination data, including the Weber fraction, coexists with successful theories based on signal detection. Larger color differences and complex stimuli, which are more important in engineering applications, are less well understood. We have been investigating these stimuli using priming in a visual search task as our measure of color difference. The task, which depends on perceived color identity of patterns similar in complexity to letters, provides stable data with thresholds much larger than either the MacAdam ellipses or the Weber fraction. The results show evidence of stimulus categorization based on luminance with the categories anchored to the background luminance.
Guided modes of thin absorbing Langmuir-Blodgett films in symmetric structures
Authors: Ouellette Francois
Published: February 2023

The guided modes of thin absorbing Langmuir-Blodgett films of organic
dyes surrounded by identical media were studied. A symmetric waveguide
has no cutoff thickness and thus can be used to study very thin films
of only a few monolayers. The modes can be excited by the frustrated
total reflection technique using a high-index prism. The dye is
modeled as having an isolated absorption band with a dielectric
function represented by the Drode-Lorentz expression. The film is
assumed to be uniaxial with the chromophore lying either parallel to
the film or perpendicular to it. When the product of the transition
moment by the relaxation time is large enough, the real part of the
dielectric constant becomes negative at some wavelengths. For a
parallel orientation, the film then supports two modes identified as
the long-range and short-range exciton polariton modes that merge into
a single surface mode for infinite film thickness. For the
perpendicular orientation, a new type of exciton polariton mode
appears for very thin films that is not supported as a surface mode
when the thickness is infinite. Calculations show that a large
enhancement of the field in the film on excitation by a prism is
possible in many cases, opening up possible applications for nonlinear
optics.
Scaling laws for lens systems in optical computers
Authors: Lohmann Adolf W. , Erlangen U.
Published: February 2023

When designing a digital optical parallel processor one faces the question of whether to use one big lens system or many small lenses side by side. Hybrid setups, consisting of macro-lenses and lens-let arrays, are also conceivable. This raises the question of how the features of a lens system change if the geometric parameters of the lens are scaled up or down. The wavelength remains unchanged, of course. Hence wave aberrations measured in wavelengths scale linearly. We review the scaling laws and the impact on parameters such as resolution, depth of focus, space-bandwidth product, time delay (latency), weight, and price on the architecture of an optical computer.
Photoelectron Spectroscopy of Vibrationally Excited H2 E,F States
Authors: Xu E. , Hickman A. P. , Kachru R. , Helm H.
Published: February 2023

In this work we report the result of a photoionization experiment in which photoelectron energy spectra were collected following 2+1 MPI of H2 via the E,F states. The bound states studied include those at the bottom of the inner E-well (vE,F=3), at the barrier of the double potential in the inside E-well (vE,F=6) and its counterpart in the outer F-well (vE,F=7), and above the barrier (vE,F=9). The E,F state wavefunctions are not confined in one or the other potential well only. This leads to a dynamic competition between direct photoionization, autoionization and dissociation. In our experiment the photoelectrons show strong non-Franck-Condon vibrational distribution. Some of the high vibrational states of

H
2
+

are so largely enhanced that they dominate the electron spectra, for examples, the v+=13 in vE,F=6, and the v+=14, 16 in vE,F=9; the "Franck-Condon picture" is even more distorted when a mainly F-state is excited as in vE,F=7.

SUMMARY In this work we report the result of a photoionization experiment in which photoelectron energy spectra were collected following 2+1 MPI of H2 via the E,F states. The bound states studied include those at the bottom of the inner E-well (vE,F=3), at the barrier of the double potential in the inside E-well (vE,F=6) and its counterpart in the outer F-well (ve,f=7), and above the barrier (ve,f=9). The E,F state wavefunctions are not confined in one or the other potential well only. This leads to a dynamic competition between direct photoionization, autoionization and dissociation. In our experiment the photoelectrons show strong non-Franck-Condon vibrational distribution. Some of the high vibrational states of

H
2
+

are so largely enhanced that they dominate the electron spectra, for examples, the v+=13 in ve,f=6, and the v+=14, 16 in ve,f=9; the "Franck-Condon picture" is even more distorted when a mainly F-state is excited as in ve,f=7. The experient is performed with a YAG-PDL-WEX pulse laser system and a high-presure H2 Raman cell. Photoelectrons are collected in a state-of-the art high resolution TOF electron spectrometer which uses permanent magnets in the magnetic bottle design. We compare the experimental results with a theoretical calculation of cross sections which includes contributions from direct photoionization and autoionization using the nonlocal complex potential method.
Double-Resonance, Fluorescence Dip Spectroscopy of Iron Period Elements
Authors: Page Ralph H. , Gudeman Christopher S.
Published: February 2023

The high melting points and appreciable spin multiplicities of some iron period elements have made spectra of their highly-excited states difficult to obtain and interpret. However, a complete set of accurate data would facilitate studies of the chemistry and physics of transition metals. It is thus desirable to unravel the spectra with state-selective spectroscopy, preferably without an oven.
Charge-screening-induced switching in spatially multiplexed subholograms in Bi12SiO20
Authors: Asthana Praveen , Tanguay Armand R.
Published: February 2023

Spatially multiplexed subholograms have potential uses in fiber-optic interconnects and optical computing. However, because of the low dark conductivity of photorefractive materials such as bismuth silicon oxide (Bi12SiO20), charges build up around the edges of the subhologram and effectively screen out the applied dc electric field. This leads to low holographic diffraction efficiencies. Using ac fields instead of dc fields is effective in reducing the amount of charge screening, and we have observed an increase in diffraction efficiency of 2 orders of magnitude with ac fields. We have characterized the properties of spatially multiplexed subholograms in Bi12SiO20 with ac fields and investigated the effects of several different manifestations of charge screening. Our experiments show that when the write and read beams are simultaneously on and the photorefractive grating is in saturation, the diffracted intensity of the read beam is proportional to exp(−al) for I > I
s
, where I is the total intensity of the write beams and I
s
is the saturation write intensity. This permits direct modulation of the diffracted beam through modulation of the write beams and can be explained by both macroscopic and microscopic charge screening effects.
Simultaneous measurement of ultra-weak biophoton emission and bioelectrical activity from plant roots
Authors: Usa M. , Kobatashi M. , Masiko S. , Inaba H.
Published: February 2023

As a means of noninvasive and nondestructive measurement of biological functions and processes through biophoton emission, several types of extremely sensitive single-photon counting system have been developed in our research with highly efficient and specially selected photomultiplier tubes. For the purpose of studying the essential roles and fundamental mechanisms of biophoton emission in living systems from a macroscopic point of view, we have also used an electrophysiological technique which does not physically damage the specimen and succeeded in obtaining both photon counting and action potential data at the same time.
Stable diffraction-limited beam from an index-guided phase-locked array supporting high-order modes at both the array and element levels
Authors: Mawst L. J. , Botez D. , Roth T. J.
Published: February 2023

A novel index-guided array structure grown by metalorganlc chemical vapor deposition is demonstrated. The array structure is unique in that it supports a single array mode consisting of strongly coupled first-order lateral modes of each element. Nearly diffraction-limited beams are obtained to over 5 × threshold and up to 145 mW/uncoated facet.
Infernet: a neural network inference machine
Authors: Kottas James A. , Warde Cardinal
Published: February 2023

The Infernet is an architecture for an inference machine that is composed of three sections: (1) an input processor that performs specific preprocessing on the inputs; (2) an output processor for generating outputs; and (3) a hierarchical inference processor which functions as the inference engine. Each section is comprised of several neural network layers. Time-domain pulse neurons are being considered as the basic cells within the layers. Temporal waves of neural activity which are supported by the interconnection topology are being considered for encoding and accessing high-level knowledge. An optical implementation for a neural layer has been designed using two optically addressed spatial light modulators (SLMs), an electrically addressed SLM, and an electronic controller.
Transient phase conjugation In photorefractive materials
Authors: Papen George C. , Saleh Bahaa E. A. , Tataronis John A.
Published: February 2023

A frequency domain technique is used to determine the response of a photorefractive phase conjugator to a pulsed probe wave. This approach provides a useful analysis of many phenomena involving planar and nonplanar fields. The transient solution to a linearized set of equations that contains contributions from both the transmission and reflection gratings is expressed as a spatiotemporal transfer function that relates the conjugate and probe waves. Associated with this frequency domain solution is a point-spread impulseresponse function that describes how an input delta function in both time and space is distorted by the nonideal conjugation process. Numerical results show the presence of temporal ringing in the conjugate signal if the conjugator is operated near an instability. This implies that the transfer function exhibits resonances for characteristic spatial and temporal frequencies which may be controlled by an external electric field. The ability to control the resonance structure and the amount of ringing in the conjugate signal at different spatial frequencies has a number of useful applications that are reviewed. Solutions based on the fully nonlinear equations are also discussed with emphasis on how the additional nonlinear effects change the linearized stability condition.
Optical head using HOE: technology and experiments
Authors: Ih Charles , Xiang L. Q. , Zuang B. H. , Yang C. W. , Lu K. Q. , Tian R. S.
Published: February 2023

The optical head is an important and major component for optical disk drives. For the read/write optical drives, expected to be generally available soon, the optical heads using conventional design often include some bulky optical lenses and prisms. The use of HOEs can greatly reduce the component counts, size, and weight of the optical head. We expect that these will improve the performance. We describe an optical head design using HOEs. The design uses two spherical plano-convex lenses and two HOEs. The two HOEs correct the spherical aberrations of the lenses, compensate wavelength shifts up to ±5 nm, and change the elliptical beam to a circular shape. Experiments have been performed to confirm the design concept. Techniques for making the HOEs and experimental results are described.
Photodoped chalcogenides as a far-infrared holographic medium
Authors: Slinger C. W. , Zakery A. , Ewen P. J. S. , Firth A. P. , Owen A. E.
Published: February 2023

The extension of holographic techniques from the visible to the far infrared is important. Potentially, holographic diffractive elements have a large range of uses in this waveband. Examples include mirrors, lenses, filters, and beam combiners. All these elements would have similar advantages to those enjoyed by their visible diffractive analogs. The metal photodissolution effect in chalcogenide glasses shows promise as one of the few techniques for producing low-loss holographic materials for use from 0.6 to beyond 16 μm. To date, the work has concentrated on the photodissolution of silver into arsenic sulfide glasses. Both bulk and surface relief gratings can be fabricated simply using blue or UV light, either by holographic or mask exposure. The results of material characterization studies show that phase gratings with high modulation and low absorption can be produced. A coupled wave analysis using these material parameters has indicated the likely performance achievable and has shown the relative merits of the bulk and surface relief structures. Diffraction efficiencies of over 90% are possible. Both bulk and surface relief gratings have been fabricated, and measurements from them are presented and compared to the theory. The limitations of the medium are discussed, and possible solutions are considered.
Thermal wave characterization of high Tc superconductors
Authors: Rosencwaig Allan , Opsal Jon , Willenborg D. L. , Coufal Hans
Published: February 2023

Thermal wave technology has proved a very effective means for investigating the near surface region of many different materials. We have performed thermal wave imaging experiments at room temperture on sintered, thin-film, and singlecrystal samples of high-T
c
superconductor materials. These images often exhibit features not visible in an optical image. In addition, we have used the thermal wave technique to measure the local anisotropy in the room-temperature thermal conductivity of single crystals of YBa2Cu3O7−
x
. Our results indicate that the anisotropy for the thermal conductivity is very similar to that reported for the electrical conductivity.
Polarization sensitive optical elements using polysilane films
Authors: Schellenberg F. M. , Byer Robert L. , Miller R. D.
Published: February 2023

Polysilanes are long σ-bonded Si-backbone polymers with various organic side groups substituted onto each Si atom. Films and waveguides of high optical quality can be easily fabricated using conventional photoresist coating technology. These materials are transparent throughout the visible spectrum but have large (α ≈ 25,000-cm−1) UV absorptions and large optical nonlinearities. Exposure of films of poly(di-n-hexylsilane) to weak doses of polarized UV light causes selective scission of chains with dipole moments aligned with the polarization of the exposing light, inducing a weak birefringence. Exposure to larger doses causes complete photovolitilization of the film. Higher birefringence from selective chain scission can be obtained using the large two-photon absorption observed in these materials [χ(3) for the process is ≈10−10 esu]. Photoexposure at ≈15 MW/cm2 with wavelengths corresponding to twice the UV absorption produces a birefringence proportional to exposure saturating at Δn ≈ 0.03. No photovolitilization was observed; thus with films several microns thick, the exposed films could be used as waveplates with phase delays as large as λ/4. We have also used this two-photon-induced chain scission to produce polarization sensitive gratings using a standard holographic arrangement. Diffraction efficiencies as large as 1% were observed for light polarized parallel to the exposing radiation, while no diffraction was observed for orthogonally polarized light.
Four-wave mixing with surface and guided-wave excitation in thin films
Authors: Glass Nathaniel E. , Rogovin D.
Published: February 2023

A theory is presented which describes the excitation of a surface-polariton (surface electromagnetic wave) or a guided wave through the interaction of three bulk electromagnetic waves that are incident on the surface of a thin-film coating on a metal substrate. The film is modeled as a lossy dielectric (complex linear dielectric constant) with a third-order optical nonlinearity. The metal substrate is also described by a complex dielectric constant. A three-layer Green’s function method is used to calculate the Poynting vector parallel to the surface. The resonant excitation of surface waves or guided waves is calculated to occur at the sum or difference frequencies of the incident waves for certain incidence angles determined by the kinematics. One of the three incident waves may be taken as a static field to explore the effects of an applied voltage. Various wavelengths of the incident beams and of the surface or guided waves are considered.
Polarization aberrations in the optical microscope
Authors: Hansen Eric W.
Published: February 2023

A long-standing problem in polarized light microscopy has been the inability to achieve simultaneously high spatial resolution and high contrast due to the rotation of the plane of polarization at oblique interfaces between crossed polars. In such cases, the system is highly astigmatic and produces severely degraded images. The theory of polarization aberrations is applied to the analysis of three solutions to this problem: (1) reducing the system aperture to block troublesome high-aperture rays; (2) the AVEC-POL method, in which high bias compensation introduces counterbalancing aberrations; and (3) the polarization rectifier, an optical element designed to introduce equal and opposite rotations of the electric vector. It is shown that a strong linear retarder (e.g., a quarter-wave plate) following the objective lens contributes a set of circular retardance polarization aberrations which balance linear polarization aberrations from the lens. Reducing the system aperture does not make effective use of these balancing aberrations. In the AVEC-POL method, the retarder-induced aberrations act to correct the system by bringing the pupil closer to radial symmetry and uniform brightness. The polarization rectifier operates in a different fashion, although it too relies on circular retardance aberrations and possesses residual errors in its pupil function similar to AVECPOL.
Optically addressed ferroelectric liquid crystal spatial light modulator
Authors: Li W. , Kuo C. T. , Moddel G.
Published: February 2023

We designed, fabricated, and characterized an optically addressed spatial light modulator. The choices of hydrogenated amorphous silicon (a-Si:H) as photosensor and ferroelectric liquid crystal (FLC) as electrooptic material provide the device with high speed and high resolution. An a-Si:H PIN photodiode and a FLC layer are sandwiched between two glass sheets coated with transparent conducting oxide (TCO). A write image beam from an Ar laser is absorbed in the photodiode resulting in an electric field across the FLC which replicates the pattern of the write beam. The image produced on the FLC is read through cross polarizers with a light beam from a He-Ne laser reflected from the interface between the FLC and the a-Si:H. The device is powered by a square-wave voltage applied to the two TCO layers. During the forward bias part of the cycle, the FLC is erased. Under reverse bias, the FLC is written and read. We have observed the performance of the spatial light modulator including response time, contrast ratio, and resolution. These are closely related to the characteristics of the a-Si:H layer. Therefore, we analyzed in detail the response of the a-Si:H to the frequency, applied voltage, and write light intensity. We found an increase in the contrast with reduced bias voltage, which is explained in terms of the effect of a series capacitance associated with FLC and a-Si:H.
Digital holography
Authors: Lohmann Adolf W.
Published: February 2023

Ordinary holograms are made by interference experiments, digital holograms by computer and plotter. The object does not have to exist physically. Most advantages of digital holograms derive from that fact. Fundamentals and some applications are reviewed: AO display; image processing; and testing.
Advances in computer-generated binary optical elements
Authors: Swanson Gary , Veldkamp Wilfrid B.
Published: February 2023

Holographic optical elements have found their way into only a very limited number of optical systems. Two major reasons have been wavelength constraints of the recording media and the off-axis configuration needed to achieve high diffraction efficiency.
Optical Bistability and Hysteresis under Phase Conjugation in CdS Crystal
Authors: Brodin M.S. , Borshch A.A. , Volkov V.I. , Kukhtarev N.V.
Published: February 2023

The exact solution of the nonlinear equations, describing phase conjugation (PC) was obtained. Theoretical dependence of the backward wave intensity on that of interacting waves with Gaussian time shape exhibits well-pronounced hysteresis, which causes the bistable operation when total pump intensity exeeds some critical value Icr. Several hysteresis loops are expected to appear with further increase of pumping.
Optical Bistability and the Digital Optical Computer
Authors: Lohmann A. W.
Published: February 2023

Electrons are well suited for switching operations as they occur in a logic processor. But electrons are not so easy to guide from one point to another point. On that score, photons are more suitable. Recently, photons became amendable also for logic processing. Hence, the stage is set for the development of an all-optical digital computer.
The Design of an Optical Digital Computer
Authors: Prise Michael E. , Downs Maralene , Walker Sue , Streibl Norbert
Published: February 2023

Because of the recent progress in the fabrication of both devices based on the Quantum Confined Stark effect and of Optical Logic Etalons (OLE), large arrays of optical input/optical output logic gates should soon be available. We show experimentally how to generate an array of equal beams from a single laser source as power supply beams for such arrays. The alignment of these arrays of power supply beams onto devices is demonstrated. As examples a 289 beam array is imaged onto an array of Optical Logic Etalons 1.5 microns in diameter and 4 microns apart and the operation of an integrated array of 36 Self Electro-optic Effect devices is shown. We also demonstrate the experimental implementation of a simple building block for an optical digital computer based on the use of such arrays. The system does a split and variable shift operation and includes ports for the loss-less input of the power supply array and for the output. The fitting together of these building blocks into a large system is discussed, along with the possible power of such a system.
Theory of Beam Reflection, Transmission, Trapping, and Breakup at Nonlinear Optical Interfaces
Authors: Aceves A. , Newell A.C. , Moloney J.V.
Published: February 2023

We will present an equivalent particle theory which reduces the problem of interaction of an incident self-focussed channel with an interface separating two nonlinear dielectric media, to a much simpler Newtonian dynamical problem of an equivalent particle moving in an equivalent potential (Figure 1a). The theory provides the first analytic instability prediction for earlier known nonlinear surface waves. Phase portraits of the equivalent particle’s trajectories (Figure 1b) correspond directly to angles of reflection and transmission of the propagating self-focussed channel. The modular structure of the theory makes it straightforward to extend it to multiple-particle interactions and multiple interface problems. All of the theoretical predictions are confirmed numerically by solving the original modified Nonlinear Schrödinger equation describing the full problem. The theory provides quantitative estimates of radiation generated due to interaction with the interface and explains how an incident self-focussed channel can break up into multiple (reflected or transmitted) channels. Contact will be made with the familiar Snell’s law linear limit and we will demonstrate the existence, in the nonlinear case, of a sharp phase transition from total internal reflection to total transmission as a function of varying incidence angle as the scaled self-focussed channel width is decreased.
Observation of Optical Nonlinearity due to band-gap renormalization in quasi-two-dimensional structures
Authors: Levenson J. A. , Abram I. I. , Raj R. , Dolique G.
Published: February 2023

The enhancement of the excitonic oscillator strengths and excitonic non-linearities, by spatial confinement, has made already possible a novel class of exciton-based optoelectronic devices (SEED,FETOM). Numerous processes contribute to the optical non-linearity, Some involve the filling of single particle states of the Fermions that compose the excitons, while others are produced by exciton-exciton or exciton-high-density plasma interactions. Most non-linear optical experiments show a cumulative effect due to all sources of nonlinearities.