bluuebunny/crossref_metadata_2025 huggingface dataset:
Learning algorithms in neural networks
Authors: Widrow Bernard
Published: February 2023

With suitable training, layered neural networks can be made insensitive to pattern rotation, translation, scale, perspective, etc., while being responsive to pattern scale.
Optical properties of mammalian tissue
Authors: Wolbarsht M. L. , Shi D. X. , Gomes E.
Published: February 2023

The high-water absorption peak α at 2.94 µm (>10,000 cm−1, specific absorption depth of ~1 µm) makes exact spectroscopic measurements difficult to achieve. Measurements of films thin enough (~1 µm) to have adequate transmission for reliable detection require accurate estimation of the thickness of the film. Thicker samples may have more reliable thickness measurements, but corresponding overall transmission is too low to be measured accurately. Measurement problems increased by absorption peak shifts with higher temperatures. All these are important considerations in predicting the penetration depth of incident radiation and the amount of tissue ablated in a real surgical situation. A model is given to indicate what kinds of tissue removal per laser pulse can be expected in a given situation. Scattering is included, although unlikely in this spectral region, but to allow comparison with laser ablation at shorter wavelengths.
Local and asymmetric interconnections using volume holograms
Authors: Gu Xiang-Guang , Psaltis Demetri
Published: February 2023

Volume holograms provide the possibility for very high density storage of the interconnecting weights in an optical neural computer. The number of connections that can be stored in a hologram of volume V can approach N3 = O(V/λ
3
). We have shown previously how N3/2 out of N2 pixels can be selected as fractal sampling grids at the input and output planes so that all connections can be independently implemented by the volume hologram. We derive the sampling grids for arbitrary N
d
→N
3–d
mappings for any 1 ⪯ d ⪯ 2, and we extend these ideas to the use of volume holograms for the implementation of local connectivity. If each pixel in a 2-D array of M units is to be arbitrarily interconnected to its C neighbors, the total number of connections is MC. We show that the volume required for the implementation of the local connectivity scheme we describe is O(MC).
Compact architectures for adaptive neural nets
Authors: Athale Ravindra A. , Stirk Charles W.
Published: February 2023

A compact optical architecture capable of implementing a number of adaptive neural net models is described. Compact architectures do not involve traditional optical imaging systems and are potentially rugged, easily constructed, and scalable. The critical devices of the generic architecture include 1-D electrooptic modulators and detectors to implement the neural processing elements along with the Pockels readout optical modulator to encode the analog weights. The architectural advances include an input-output compatible method of handling both positive and negative values for the elements of the neuron activation vectors and the synaptic weight matrices during learning and recall. These hybrid architectures are capable of implementing linear and nonlinear associators with adaptive learning algorithms.
New materials for ferroelectric liquid crystal mixtures
Authors: Geelhaar Thomas , Krause Joachim , Reiffenrath Volker , Wächtler Andreas
Published: February 2023

Physical properties of typical molecular structures for ferroelectric liquid crystal mixtures are discussed. New nonchiral SmC substances and chiral dopants are introduced.
Molecular orientation of ferroelectric liquid crystal on a rubbed surface
Authors: Sakai H. , Uchida Tatsuo
Published: February 2023

One of the most important problems of ferroelectric liquid crystals (FLCs) is their difficulty in obtaining homogeneous as well as bistable alignment. Concerning this problem, Clark et al. recently clarified that the FLCs generally have a chevron structure, that is, a bend structure of the smectic layer, which causes formation of the zigzag domain and an undesirable decrease of the azimuth angle between bistable orientational directions.
Silicon VLSI-compatible ferroelectric liquid crystal light modulator process
Authors: Drabik Timothy J. , Gaylord Thomas K.
Published: February 2023

The development of optically interconnected VLSI and wafer-scale systems has as a prerequisite the existence of a light modulator technology compatible with logic circuit technology that will enable the unconstrained placement of a large number of logic-driven light sources on a die or wafer. Integrated lasers, multiple-quantum-well electroabsorption modulators, and organic electrooptic materials exhibit high speed but are sufficiently mature to permit system prototyping, especially in silicon. Ferroelectric liquid crystals (FLCs) possess low switching energies and driving voltages in the surface-stabilized cell configuration1 and are, therefore, well matched to the output characteristics of silicon CMOS logic gates. Rapid development of faster materials is under way with switching times of 3 μs at 15 V/μm available now. We present a procedure that incorporates fabrication of most components of a reflective surface-stabilized FLC light modulator cell into an unmodified bulk CMOS process flow. The reflective electrode and 1-1.5-μm thick spacer can be obtained by specifying features in the mask description of the die. Light sources can thus be placed in the same manner as transistors. The only postprocessing steps that need be applied to the silicon die are the application of an aligning layer to ensure proper smectic layer orientation and assembly of the cells with a common transparent cover electrode.
Schemes for construction of low f/No. HOE objective lens for the infrared
Authors: Chen Hsuan , Chen Ming-Yi
Published: February 2023

The theory and technique of using a doublewavelength shift recording scheme for the fabrication of diffraction-limited low f/No. holographic objective and collimating lenses were proposed previously,1,2 Basically, the recording was done in two steps in two different wavelengths. A phase compensating corrector plate was first fabricated holographically at the shortest wavelength. The corrector plate was subsequently read out with the light of the intermediate wavelength. The light diffracted from the corrector plate interfered with a spherical wave and was recorded as the final HOE to be used in the longest wavelength. In each step of the recordings, the geometry was kept straight to the configuration that was free from all Seidel aberrations. Using this technique, we fabricated an infrared HOE objective lens for using at the wavelength of 830 nm with very low aberration. The experimental result agreed quite well with the theory we developed in the earlier work.
Optical pyramidal image processing using mathematical morphology
Authors: Eichmann George , Lu Chao , Zhu Jianxin , Li Yao
Published: February 2023

Pyramidal image processing (PIP) is a form of multiresolution analysis in which a primary image is decomposed into a set of different resolution image copies. Pyramidal processing aims to extract and interpret significant features of an image appearing at different resolutions. Because of using a large number of multidimensional convolutions, the existing digital software PIP implementations are very time-consuming. Recently, morphological filtering (MF)-based image processing and analysis, because of its simplicity of operation and its direct relationship to the shapes of an image, have been widely studied. Using a MF method, the implementation of PIP is proposed. By using a set of well-structured masks, a primary image is decomposed into a sequence of resolution image copies. Pipelined and parallel algorithms are suggested for these morphological PIP (MPIP). Using various linear and nonlinear optical methods, various optical MPIP structures are described.
Iterative electronic halftoning procedure
Authors: Broja Manfred , Wyrowski Frank , Bryngdahl Olof
Published: February 2023

Different types of binarization procedure exist which can be used to convert a graytone image into a halftone picture. Dither methods are based on sequential pointwise decisions between the original distribution and the binary result. Furthermore, digital processing allows active and integrative concepts. Error diffusion techniques are sequential realizations which incorporate local processing. We discuss halftoning by global processing. Our scheme is based on an iterative Fourier transform algorithm with control of constraints in the image as well as its spectrum. We will show how the image on one hand and the texture formed by quantization noise on the other hand can be influenced and shaped. Variation of the basic constraints is discussed and experimental results shown.
Associative polarization-encoded optical shadow-casting: applications in image processing
Authors: Awwal A. A. S. , Karim M. A.
Published: February 2023

Gray-level image processors need more than just two bits for the inputs. For the specific case of image addition, it is necessary for the carry to propagate so as to yield the correct binary output. In the original optical shadow-casting work of Tanida and Ichioka,1 this was realized by copying the input bits of the gray-level images into different spatial locations, but the scheme finally resulted in a nonbinary analog output. In the current work using a polarization-encoded optical shadow-casting system,2 the carry propagation is accomplished simply by means of encoding (using polarization codes) the inputs and sources. Both serial and parallel outputs are shown to be realizable using the polarization-encoded optical shadow-casting system. The system is unique in that it acts like an associative memory wherein certain portions of the available memory locations are shared by more than one output. The associative nature of mapping of information in the input pixel subcells makes this system highly efficient in terms of memory saving.
Pseudocolor-encoding method with reflecting filter
Authors: Tian Weijian , Si Gongcai , Tian Zhiwei
Published: February 2023

Up to now, the typical optical system for pseudocolor-encoding processing is a Fourier-transform system which is usually called a 4-f system. A new optical processing system with a reflecting filter and just one single Fourier transform lens is presented. The authors also give the satisfactory experimental results of pseudocolor photos for some medical x-ray films and analyze its principle theoretically. As we use the reflecting system of double-beam or a more than two-beam optical system, the synthetic technique1 of different preprocessing for each individual path may be utilized effectively.
Study of the problems in a phase-encoding plate of a silver halide film
Authors: Tian Zhiwei , Rong Xingfu , Ye Shuitang , Yang Hui
Published: February 2023

The information loss in the modulating process of the phase-encoding plate is analyzed by means of the H-D curve of silver halide film, which shows that there exist some limiting conditions1 for certain regions of information processed, and information loss is inevitable. Utilizing the special characteristics of silver halide film, we describe a new technique for enhancing and reserving the wholeness of required information. We also suggest a further application of the multiexposure phase-encoding plate and present relevant experimental results, which seems to be a good way of enriching the output colors.
Infrared gradient-index design and materials
Authors: Moore Duncan T.
Published: February 2023

Gradient-index materials have been developed to transmit in the near- and far-IR portions of the spectrum. Gradient-index germanium/silicon has been developed by Czochralski crystal growths, and chemically vapor-deposited zinc selenide/zinc sulfide has been produced. These two new materials provide unique opportunities for designers of IR optical systems. Due to the unusual dependence of the chromatic aberration and Petzval field curvature on the gradient, it is possible to design more simplified optical systems than possible with aspheres or holographic elements.
Image anomalies In thermal imaging systems: what they are and how to get rid of them
Authors: Fischer Robert
Published: February 2023

The cryogenically cooled detectors used in thermal imaging systems are in effect looking at thermal or heat sources in object space. Any uniform change in the thermal irradiance over the field of view will reduce somewhat the system sensitivity. However, a far more severe and sometimes devastating problem occurs when the thermal irradiance changes or modulates across the field of view. This can cause false images, bright bands, and other cosmetically undesirable effects, which in the worst cases can be tracked or otherwise processed by the system as if it were a real image. These effects are especially evident in scanning systems, and we show how the basic scanning geometries can lead to these image anomalies if appropriate care in the optical as well as the mechanical design is not taken.
Computer-aided design of a new compact video rate optical scanner
Authors: Dent Virginia J.
Published: February 2023

The compact video rate optical scanner (CVROS) is the product of several years of research and development at Kollmorgen Corp. Today it is a fully functional unique configuration for a compact IR scanner. A detailed discussion of the scanner concept can be found in Ref. 1. Several state-of-the-art technologies made it possible to transform the CVROS from a concept into operational hardware including a computer-aided optical design. In particular, Optical Research Associates CODEV optical design package was used on a VAX 8350 to simulate and evaluate the scanner. This presentation discusses the unusual methods of system modeling employed and several of the analyses performed using CODEV. In the CVROS system, vertical scanning of the scene is done with an oscillating plane mirror, while a rotating disk, with a set of concave micromachined spherical mirrors around its periphery, provides scanning in the horizontal direction.
Conceptual and neuronal plasticity in visual processing
Authors: Churchland Paul M.
Published: February 2023

The substantial dependents of perceptual processing on one’s prior conceptual set is by now a familiar theme. I here explore the possibility of radical changes in the character and content of one’s perceptual processing, changes occasioned by radical changes in one’s background conceptual framework. Recent research into learning, categorization, and perception in artificial and neural nets provides new ground for this exploration and new insights into the nature of both conceptual and perceptual plasticity in living creatures.
Uses of photoconductlve, photoemissive, and electron-beam sampling in high-speed circuit characterization
Authors: Halbout Jean-Marc
Published: February 2023

Recent advances in process technology and better understanding of design and scaling principles have led recently to the realization of very high-speed LSI and VLSI circuits. These circuits have gate delays well under the 50-ps mark and characteristic feature and wiring interconnect sizes smaller than 1 μm. Circuits built today are already beyond the testing capabilities of conventional equipment, both in terms of their capability to access internal nodes and in terms of their temporal resolution. On-chip wiring delays must also be accurately measured to ascertain the critical timing necessary to the operation of complex high-speed circuits. Characterization techniques are urgently needed to answer these challenges, both at the level of single device characterization and for contactless in situ probing of complex circuits. In addition, for digital devices which operate inherently in a nonlinear large-signal regime, it is most desirable to complement the frequency domain characterization as is now practiced with a direct time domain characterization, which reflects more closely the operation of the devices in their applications. The ultrafast laser technology provides attractive solutions to high-speed electrical characterization through several techniques which have been developed in the past years. This paper concentrates on reviewing three of these techniques: photoconductive sampling for single-device characterization, photoemissive sampling for probing voltage on interconnect lines on circuit or packages, and photoelectron electron-beam probing which brings the already well-developed electron-beam circuit probing technology into the picosecond regime and is particularly well suited to contactless probing of voltages in the LSI and VLSI environment with high-density circuits at minimal linewidth.
Coplanar vacuum photodiode for measurement of short-wavelength picosecond pulses
Authors: Johnson A. M. , Bokor J. , Simpson W. M. , Storz R. H.
Published: February 2023

A vacuum photodiode is the most elementary photoelectric detector. Such a device is sensitive to photon energies which exceed the photocathode work function in accord with the classical photoelectric effect. For vacuum ultraviolet and soft x-ray radiation, photoelectric quantum yields in excess of 50% can be reached.1 With a carefully designed external circuit, the response time of such a detector is limited by the diode capacitance. The present state-of-the-art rise time in a commercial biplanar vacuum photodiode2 is 60 ps.
High-mobility cadmium-telluride photoconductive switch generating electrical pulses of <0.5-ps duration
Authors: Nuss Martin C. , Kisker D. W. , Smith P. R. , Harvey T. E.
Published: February 2023

Electrical pulses of only 480-fs duration have been generated using polycrystalline films of CdTe grown by UV-enhanced metal organic chemical vapor deposition (MOCVD). The photoconductor was integrated in a coplanar transmission line with a 10-μm linewidth and spacing. The electrical pulses were generated in a sliding contact geometry and probed via reflection-mode electrooptic sampling in a small LiTaO3 crystal dipped into the fringing fields of the transmission line. A pulse duration of 560-fs (FWHM) with a 490-fs rise time and a 450-fs 1 /e fall time was measured. Deconvoluting the response of the electroptic sampling technique, we arrive at a pulse duration of 480 fs. For comparison, an 830-fs duration (FWHM) was measured for a radiation-damaged silicon-on-sapphire (SOS) photoconductive switch in the same geometry, demonstrating the superior switching speed of MOCVD CdTe.
New derivation of Feder’s third-order aberration expressions
Authors: Evans Eric D. , Collins Stuart A.
Published: February 2023

This paper presents a clear and rigorous derivation of Feder’s well-known equations for the third-order aberrations. The derivation starts with Born and Wolf’s version of a Hamilton's angle characteristic for a single spherical surface. We then derive the addition theorem of aberrations and write expressions for the third-order ray aberrations of n-surface systems. Finally, we write the aberration expressions in terms of axial and chief rays and derive Feder’s numerically efficient equations for the third-order aberrations.
Photonic switching devices
Authors: Silberberg Yaron
Published: February 2023

Photonic switching devices are required to route or switch an optical signal without translating it first to an electrical signal. Their main attraction is in the ability to handle optical signals in a transparent way: the format and data are set by the network terminals. Three different families of photonic switches can be defined according to the switching mechanism. Mechanical switches physically move fibers to route a signal. They are inherently slow but can be ideal for specific applications. Electrooptic switches using integrated optics are faster and more versatile. Some integrated optics technologies have been developed to the point that they can be tested in actual system experiments. We review the different kinds of electrooptical switching device, their principle of operation, and their typical parameters. All-optical switches are controlled by the light itself through a nonlinear optical interaction. All-optical devices could be extremely fast, and switching times of the order of 100 fs have been recently demonstrated. However, all-optical switches are still in their infancy. Several concepts have been proposed and demonstrated, yet their potential depends critically on the development of suitable nonlinear media. We describe some of these experiments and the problems facing this technology.
Demonstration of a high-dimensionality optical local area network switch
Authors: Perrier Philippe A. , Prucnal Paul R.
Published: February 2023

Many classical switching architectures have been considered for optical space-division switches.1 Although some of these architectures have been implemented with dimensionality as large as 8×8, the fabrication of larger optical switches based on 2 × 2 optical switching elements may be difficult.
Crossed resonator configurations for photonic switching
Authors: Capron Barbara A. , Holm David A.
Published: February 2023

A possible device concept for photonic switching is the crossed resonator in which two Fabry-Perot resonators with perpendicular cavity axes enclose a nonlinear medium. Light entering one of the cavities can modify the light exiting the other cavity by altering the refractive index of the medium. This configuration has been proposed for use as an optical logic gate.1 In this work we also demonstrate its potential as an optical switch and transistor. We model the device following the single Fabry-Perot cavity work for steady-state fields of Miller2 and for pulsed inputs following Bischofberger and Shen.3 We assume the medium has a Kerr nonlinearity with an intensity-independent background absorption. Using parameters for the organic polymer polydiacetylene (PTS) etched into an optical waveguide, we find differential gains of greater than three for steady-state input fields of reasonable powers and that this device in certain regimes behaves like an optical transistor. For the time-dependent case, we model the medium temporal response by the Debye equation using the medium response time for PTS. We present results for input pulses of varying intensity and duration.
Ganglion cell pathways for rod acuity
Authors: Fairchild Mark D. , Lennie Peter
Published: February 2023

We examined the acuity of the human rod system pyschophysically to establish whether the parvocellar P or magnocellular M pathway carries high-frequency spatial information in scotopic vision. We measured visual acuity for smalt patches of sinusoidal grating at a range of eccentricities in temporal retina. When the targets were detected via rods, visual acuity ranged from 5.3 cycles/deg at an eccentricity of 5-2.9 cycles/deg at an eccentricity of 30°. We also calculated the highest spatial frequency that could be reliably resolved by the mosaics of Pand M cells and found that visual acuity of the rod system is too high to be supported by the M-ganglion cells. The psychophysical acuity is also lower than the Nyquist limit for P-ganglion cells. This implies that the high-frequency information for scotopic vision is carried in the P-cell pathway and that visual acuity is limited by the sizes of the receptive fields of individual cells, not by their separation. This conclusion is corroborated by our failure to find aliasing in scotopic vision, despite our finding clear aliases when corresponding measurements of acuity were made in photopic conditions.
In situ emulsion preswelling for holographic color control
Authors: Walker Julie L. , Benton Stephen A.
Published: February 2023

Deliberate variations of emulsion thickness between holographic exposures and reconstruction produce a range of output wavelengths from a fixed exposure wavelength, a technique known as pseudocolor multicolor reflection holography. The usual methods require the removal of the film or plate from the holographic setup between exposures for imbibition of a swelling agent, followed by drying and replacement, so that retention of the swelling agent forces a physical increase in the thickness of the emulsion. However, the density (and hence the thickness) of the gelatin binder can also be varied by changing its electrolytic environment. By immersing the holographic emulsion in a suitable solution, allowing it to come to a new equilibrium thickness, and exposing it with a long-wavelength laser, shorter wavelength reconstructions can be obtained without removing the film or plate from the setup. Careful changes of solution can make a precise sequence of swellings possible, producing multiple reconstruction colors from a set of constant-wavelength recordings. Here we describe pretreatments of the emulsion that make rapid and stable equilibria possible and swelling bath sequences that produce color primaries suitable for full-color computer-graphic holographic imagery.
Far-infrared properties of oxide superconductors
Authors: Sievers A. J.
Published: February 2023

Measurements of the IR properties of the new oxide superconductors are being made both to characterize the electrodynamic properties in the normal state and to identify the energy gap and possible electron coupling mechanisms in the superconducting state. Using optical and IR Fourier transform spectroscopic techniques, reflectivity and direct absorption measurements have been made on bulk sintered materials, thin films, and single crystals of these high T
c
materials over an extended frequency interval. Kramers-Kronig and mode analysis of these data give the real and imaginary parts of the frequency-dependent conductivity, a quantity which can be compared directly with theoretical predictions. For the sintered materials the anisotropic grain effects must be unfolded from the conductivity before the energy gap can be identified. Comparing all these data for the superconducting state with the predictions of BCS theory shows that absorption occurs at frequencies below the apparent electromagnetic energy gap and that the effective gap position depends on the sample texture.
Ultrafast optical time division multiplexing/demultiplexing using nonlinear Fabry-Perot etalons
Authors: Friberg Stephen R. , Zhang Lei , Li Chun-Fei
Published: February 2023

One factor limiting interest in optical bistable devices is their relatively slow speed. For example, GaAs/AIGaAs MQW nonlinear etalon devices have switch-on times of 1 ps1 but switch-off times in excess of 150 ps.2 Similarly, ZnS and ZnSe thermal etalons can switch on more quickly than they switch off because of slow thermal relaxation times. This places a revere restriction on rates of operation. To circumvent this problem, we propose the use of nonlinear etalons in an optical time division multiplexing/demultiplexing system and describe a transmitter (two nonlinear etalons and an optical delay line) that can produce optical pulses as short as the etalon switch-on times. Pulses from the transmitter for each channel are coupled in a time sequence into a waveguide. The process is repeated after the etalon carrier-recombination (thermal relaxation) time has elapsed. Demultiplexing is carried out in a similar way. Etalon time division multiplexing results in bit rates much larger than possible for individual devices. For GaAs/AIGaAs etalons with 150-ps recombination times, bit rates from 6.7 to 500 Gbit/s should be obtainable, depending on the number of channels used. We experimentally demonstrate the feasibility of the multiplexing and demultiplexing schemes using ZnS thermal etalon devices.
Measurement of the nonlinear refractive index in a bistable laser diode
Authors: Calvani Riccardo , Caponi R.
Published: February 2023

The optical bistability (OB) behavior of a semiconductor Fabry-Perot (F.P.) cavity, biased around threshold, has been employed to evaluate the optical device parameters.1 In the present work, this approach was experimentally applied to measurements of the nonlinear refractive-index coefficient n2 in OB operating conditions.
New ferroelectric liquid crystal beta switch design
Authors: Mcruer R. , Hesselink Lambertus , Goodman Joseph W.
Published: February 2023

A beta switch is a 2 × 2 crossbar cell, which is the building block for many interconnection networks (i.e., Clos-Benes, Spanke). A new optical beta switch design based on the ferroelectric liquid crystal total internal reflection switch is investigated for use in dynamic optical interconnection networks. It exhibits low crosstalk and can be driven by only a few volts. Crosstalk, loss, and scaling characteristics are discussed in the context of the device cascadability.
Nonlinear long-fiber interferometer for measuring light intensity
Authors: Saito Shigeru , Imoto Nobuyuki
Published: February 2023

To try to demonstrate a quantum nondemolition (QND) measurement of photon number,1 we built a nonlinear interferometer system with a 10-km polarization-maintaining fiber. (In theory, this fiber length is nearly optimum for 1.5-μm operation.) The optical Kerr effect allows a signal beam intensity to change a probe beam phase, which can then be read out by the interferometer. A modified ring interferometer structure and feedback stabilization enabled the 1,32-μm probe to read the intensity of the 1.06-μm signal beam. We measured a χ(3) value in this fiber of3.6× 10-33(1.4×10-33)MKS when the polarization of the signal beam is coincident with (perpendicular to) that of the probe beam. The interferometer output spectrum displayed large noise peaks due to guided acoustic-wave Brillouin scattering (GAWBS)2 in the fiber. GAWBS was also observed in 5-km conventional single-mode fibers in various interferometer configurations. The coexistence of two different kinds of GAWBS (polarized and depolarized) makes it particularly difficult to obtain QND measurements. We conclude that a QND measurement system free from GAWBS noise requires differential phase detection of two pulses having the same polarization state.
Second harmonic piezooscillator
Authors: Bao Xiaoyi
Published: February 2023

In the laser mode-locking technique, the higher harmonic acoustooptic modulators have been widely used. This method can use a thicker transducer to produce higher modulation frequency, which avoids the difficulty in thinning of the transducer. Especially, with the request of high modulation frequency for the pump laser, it is more difficult to generate a thinner transducer. But the conventional concept said that this kind of high harmonic modulator could only work on the odd harmonic.1,2 It is impossible for the piezooscillator to work on the even harmonic. However, we find experimentally that the LiNbO3 and dense flint glass acoustooptic modulator can work at the second harmonic for the first time as far as we know. We have made three modulators; all have the phenomena of the second harmonic. At the same time, we also prove theoretically that this kind of piezooscillator, which has one unfree end (this end is welded on the dense flint glass), may have non-odd harmonic. Using the second harmonic modulator, the second harmonic mode locking of an Ar+ laser has experimentally been demonstrated. Un-doubtedly, this will have important significance for the development of the acoustooptic mode-locking technique of an Ar+ laser.
Frequency shifts of spectral lines produced by scattering from a fluctuating medium
Authors: Foley John T. , Wolf Emil
Published: February 2023

It has been shown1 that when a spectral line whose profile is Gaussian is incident on a time-independent medium whose refractive index varies randomly with position in a prescribed manner, the spectrum of the scattered field is also Gaussian but is shifted in frequency and narrowed. It has also been shown that relative to the case when the scattering medium is completely spatially uncorrelated, the shift is always toward lower frequencies.
Radiated spectrum from partially correlated dipoles
Authors: Gamliel Avshalom , George Nicholas
Published: February 2023

The effects of source correlations on the radiated spectrum have been discussed in connection with scalar sources. We examine the spectrum of the field radiated by two linear dipoles that are partially correlated. The dipoles are assumed to be linearly polarized in the same direction and have identical spectra. Expressions are derived for the radiated spectrum, the total emitted power, and the directivity. We illustrate our results by calculating the radiated spectrum for some particular choices of the frequency-dependent correlation functions and by comparison with the well- known limiting cases of fully correlated and uncorrelated dipoles.
Image processing applications of binary image algebra
Authors: Huang K. S. , Jenkins B. K. , Sawchuk A. A.
Published: February 2023

Digital optical computing is well suited to image processing tasks because of its parallelism and massive computational capability. Binary image algebra (BIA) provides a systematic parallel mathematical structure for developing parallel optical numerical array computation and image processing algorithms. A BIA representation and comparison of different kinds of parallel optical binary arithmetic (including symbolic substitution arithmetic) are discussed in Ref. 1. Here we extend this study to image processing applications.
Phase distortion compensation in a joint Fourier transform correlator by phase conjugation
Authors: Yu Francis T. S. , Wu Shudong , Mayers Andrew
Published: February 2023

In a coherent image processing system, the input object must be free from phase distortion. Unfortunately, most real-time spatial light modulators suffer from phase distortions. Liquid gates can be used to compensate for external distortion but do not remove internal nonuniformities in the devices. Holographic elements can correct phase distortion but require critical alignment. This paper investigates the use of a phase conjugate wave compensating technique to correct for phase distortions in a joint Fourier transform correlator. Because the object beam passes through the objects twice, the contrast of the objects is increased. In the experimental setup, a BSO crystal was utilized as the phase conjugating mirror. The experimental result verified that the phase conjugating technique can compensate for the phase distortion in a joint transform correlator.
X-ray scattering at near normal incidence
Authors: Hastings J. B.
Published: February 2023

Although the theory describing the production of x rays from relativistic particles has been known for some forty years, x rays from electron synchrotrons and storage rings have not been routinely available until the last few years. These broadband, extremely intense, and collimated sources of x rays have made possible new and exciting studies heretofore untried. One such area is the scattering of x rays at angles near normal incidence. There have been studies carried out in the laboratory at near normal incidence, but these have been confined to the precise determination of d-spacings and strain in several prototypical systems.
Bisection of illusory spaces
Authors: Banton Tom A. , Levi Dennis M.
Published: February 2023

Electrophysiological investigation has shown that illusory contours arise in V2 but not in V1.1 This study investigates the fineness of localization in areas 18 and higher by measuring the ability of human observers to bisect a space defined by illusory lines. Subjects viewed a bisecting space formed by either an illusory square, an implied square, or two real lines. A test line was briefly presented within the bisecting space. The subject determined whether the test line appeared to the left of, to the right of, or at the point of bisection. Illusory contours produced thresholds 10-20% smaller than implied contours when the bisecting space was between 1 and 7°. Outside of this range, illusory and implied thresholds were similar, but illusory contours were difficult to perceive. Thus, when visible, illusory contours provide information improving localization ability. When the illusory contours were strong, thresholds were at most a factor of 2 worse than real-line thresholds. This surprising similarity suggests that the spatial grain of the cortex when area 17 is bypassed is only slightly coarser than that of area 17.
Remembered referent in separation discrimination and Vernier acuity tasks
Authors: Burbeck Christina A. , Swift Dan J.
Published: February 2023

In the single-interval paradigm, which is commonly used in separation discrimination and Vernier acuity studies, a single stimulus is presented on each trial, and the observer reports how that stimulus compares to a remembered referent. In separation discrimination, the referent is the average separation. In Vernier acuity, it is collinearity. The problem is that, if uncertainty about the remembered referent is large, the computed threshold can be an overestimate of the true threshold, whereas if it is small, it can be an underestimate. Our experiments were designed to determine the effect on threshold of using remembered referents in these two tasks. We compared thresholds obtained with a remembered mean (single-interval paradigm) and with a presented mean [two-interval forced choice (2IFC)]. We found that for separation discrimination, the single-interval paradigm yielded a slightly higher threshold than did the 2IFC paradigm, whereas for Vernier acuity, the reverse was true. In terms of signal detection theory, this implies that the variance of the remembered referent is smaller (relative to the variance of the test stimuli) for Vernier acuity than for separation discrimination. Given the naturalness of the Vernier acuity referent (collinearity) and the arbitrariness of the separation discrimination referent, this explanation seems plausible.
Time-dependent behavior of stimulated rotational Raman scattering in air
Authors: Pennington Deanna M. , Henesian Mark A. , Hawkins Raymond J.
Published: February 2023

We describe the results of experiments designed to study the spectral and temporal dynamics of stimulated rotational Raman scattering (SRRS) in air as a function of intensity, pulse shape, and pulse length.1 Our experiments were performed using one arm of the Nova laser at Lawrence Livermore National Laboratory at a wavelength of 1053 nm. A collimated spatially uniform beam (11.5-cm diameter) was propagated over a 75-m air path to a diagnostic station. Data were obtained for nominally square and ramped temporal pulse shapes, 1 and 2 ns in length, with intensities ranging from 1.7 to 3.3 GW/cm2. Time-resolved spectra were recorded using a 1-m spectrometer close-coupled to a film-backed streak camera. Experimental results indicate that the initial pulse shape is most influential in the evolution of SRRS. Differences of up to 50% in the temporal onset and intensity of SRRS for ramped and square pulses of equivalent average intensity have been observed. Numerical simulations of the laser and Stokes pulse evolution have been performed including pump depletion and multiple rotational transitions. These calculations are found to be in good agreement with experiment. Experimental results and additional modeling are discussed.
New family of Gaussian amplitude functions that are exact solutions to the scalar Helmholtz equation
Authors: Landesman B. Tehan , Barrett H. H.
Published: February 2023

A new family of exact closed-form solutions to the scalar Helmholtz equation is presented. The 0,0 order of this family represents a new mathematical model for the fundamental mode of a propagating Gaussian beam. The family consists of nonseparable functions in the oblate spheroidal coordinate system that are separable in a complex coordinate system and can easily be transformed to a different set of solutions in the prolate spheroidal coordinate system where the 0,0 order is a spherical wave. This transformation consists of two substitutions in the coordinate system parameters and represents a more general method of obtaining a Gaussian beam from a spherical wave than assuming a complex point source on-axis. Finally, each higher-order member of the family of solutions possesses a Gaussian amplitude along with a finite number of higher-order terms, all of which vary on propagation.
Statistical stabilities of colliding pulse mode locking in Nd:YAG lasers
Authors: Huang Liu , Jiang Zhu-Qing , Yao Yu-Qiu
Published: February 2023

There are two ways to improve the statistical characteristic of a passively mode-locked solid-state laser system: The first is to rearrange the initial noise intensity distribution into a more regular distribution by using an intracavity modulator, as has been done in the active–passive mode locking. The second way is to improve the discriminating ability of the saturable absorber. This improvement can be accomplished by simple modification of the geometrical configuration of the laser system, such as the colliding-pulse mode-locked (CPM) laser with an antiresonant ring.
Phase dynamics in a bidirectional ring laser
Authors: Abraham Neal B. , Hoffer L. M. , Lippi G. L. , Weiss C. O.
Published: February 2023

Bidirectional ring lasers when detuned can exhibit spontaneous intensity pulsations ranging in form from alternating square waves to periodic and chaotic waveforms. Numerical studies of a model with adiabiatic elimination of the polarization show that the optical frequencies of the two modes are not constant but change during the pulsations. Square wave pulsations cause dramatic frequency shifts as the signal changes from growing to nearly constant (at the steady state value) to decaying. More irregular intensity pulsations are accompanied by more complex pulsations in the optical phase. Intensity measurements of far-IR bidirectional ring lasers using the 81- and 153-μm lines in NH3 find many similar pulsation patterns. Heterodyne measurements of the field amplitude of the FIR laser permit reconstruction of the optical phase in real time and reveal that similar optical frequency shifts occur. More complex and smoothly varying frequency changes accompany the more complex pulsation patterns. The remarkable similarity between the far-infrared laser behavior and the results of the model for lasers with adiabatic elimination of the polarization dynamics suggests that the fundamental dynamic behavior of the bidirectional ring laser may be captured by a reduced set of dynamic equations even when an adiabatic elimination cannot be directly justified from first principles.
Influence of colored noise on the first laser threshold
Authors: Zeghlache H. , Mandel P.
Published: February 2023

The neighborhood of the first laser threshold is studied when the pump parameter is swept slowly in time and in the presence of noise. The good cavity limit approximation is taken. The study is performed in the spirit of the bifurcation theory approach, the equation being taken first order in a linear stability analysis.1 The noise is added in a phenomenological way, and two kinds of noise are considered, additive noise and multiplicative noise, depending on the physical origin of the noise. The purpose of our calculation is to determine the actual position of the laser first threshold which can be significantly different from the static noiseless threshold. The effect of the different parameters of the system, such as the sweeping rate, the initial position of the sweep, the intensity and color of the noise, and the threshold condition, is investigated. This analytic investigation determines the relevant combination of parameters and leads to comparison with previous analog and numerical analysis.2,3
Trends in infrared optical design
Authors: Abel Irving R.
Published: February 2023

First-generation forward looking IRs (FLIRs) currently in operation satisfy present requirements for a dependable night vision camera but fall far short of their potential to provide much higher thermal sensitivity and reliability as well as lower cost. Field coverage requirements call for optomechanical scanning of a focal plane containing only a few detectors. Inherent in this requirement is a complexity imposed by the need for high-speed scanners and special related considerations of pupil formation, narcissus control, and cold shield efficiency. The development of second-generation systems to overcome the limitations of current FLIRs is largely dependent on advancements in focal plane technology. Second-generation focal planes are characterized by a very large number of detectors arranged either in a linear array or in a 2-D mosaic and in both cases integrated with on-focal plane electronics. As a result, the requirement for optomechanical scanning is either reduced to a single dimension at a relatively low frame rate or eliminated entirely. To realize fully the potential for increased thermal sensitivity, reliability, stability, and lower cost, optical systems are being compactly configured to maximize cold shield efficiency over a wide angle and passively athermalized to achieve stability of focus.
All-reflective infrared target simulator design
Authors: Shafer David
Published: February 2023

A wide-angle unobscured mirror system is described which has a flat focal plane and a distant external real pupil out in front. The system acts as a collimator for an infrared target that is placed in the focal plane. Its external pupil is then matched to the pupils (usually interior to them) of test devices, e.g., infrared tracking systems, seeker heads. The system has been built with an 8-in. unobscured aperture and has a measured spot size of 0.05 mrad (10 arc sec) over most of the flat 8 × 8° square field of view. Several interesting design principles were used, which are explained, which allowed the design to consist of one centered conic mirror and several spherical mirrors.
Observation of temporal coherence modes in stimulated Raman scattering
Authors: Raymer Michael G. , Li Z. W. , Walmsley I. A.
Published: February 2023

By use of a streak camera, the temporal variations of light pulses generated by stimulated Raman scattering have been observed when the pulse duration is of the order of the inverse Raman linewidth. In this regime, which is intermediate between transient and steady state, the pulse shapes undergo large shot-to-shot variations due to the effects of quantum moise. It is found that some of the pulses bear a strong resemblance to the temporal coherence modes, i.e., the eigenfunctions of the two-time field autocorrelation function.1 Probability distributions for the energy content of each of these modes are negative-exponential functions of energy. This explains why isolated modes are sometimes seen on a single shot.
Spatial correlation of Stokes generation in transient stimulated Raman scattering
Authors: Kuo S. J. , Raymer Michael G.
Published: February 2023

We have carried out an experiment to study the spatial correlation of the Stokes pulses in transient stimulated Raman scattering. The spatial pattern of Stokes pulses is known to fluctuate from shot to shot due to the buildup of the pulses from quantum noise. We have measured a series of spatial profiles of the Stokes intensity for different Fresnel numbers and Raman gains. A correlation area of the Stokes pulses is obtained by calculating the autocorrelation function of an ensemble of the intensity profiles for each set of parameters. The measured results are compared to existing theories.1