bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunable far-infrared laser spectra of planar supersonic jets
Authors: Blake Geoffrey A.
Published: February 2023

Hydrogen bonds are ubiquitous in nature. It is hardly surprising, therefore, that since their discovery over 70 years ago hydrogen bonds have aroused tremendous interest. The most direct route to the analysis of these bonds involves detection of their vibrational modes which occur in the far-infrared, a region long referred to as the gap in the electromagnetic spectrum. Indeed, unlike techniques at both longer and shorter wavelengths, tunable far-infrared spectroscopy is a very recent development. Previous work in this region was performed with line tunable lasers coupled with eigenstate tuning through the application of large electric or magnetic fields. The resulting resonance spectra are quite complicated, the coverage is poor, and the necessity of predicting zero-field constants from high-field data often renders the observed transitions unassignable. Add to these difficulties the problem of simply producing sufficient quantities of the weakly bound clusters for spectroscopic study, and it is easy to see why our knowledge of such systems is so limited.
Airborne astronomy: laser spectroscopy takes off
Authors: Betz A. L.
Published: February 2023

Astronomical spectroscopy in the far infrared (FIR) between 150 and 400 μm has previously relied on instruments that use interferometric techniques and are consequently wavelength sensitive. Such spectrometers are generally limited to resolutions below 1 part in 104 because of physical size constraints and the extended angular sizes of observed sources. Heterodyne spectrometers, on the other hand, are frequency sensitive and not subject to these resolution constraints. Radio astronomers have long used heterodyne techniques to achieve resolutions exceeding 1 part in 106, which are required to resolve velocity-broadened profiles of atomic and molecular lines in interstellar gas clouds. The development of laser heterodyne techniques now makes equivalent observations in the FIR possible. Spectrometers using optically pumped FIR lasers as local oscillators (LOs), and GaAs diodes as mixers now operate regularly aboard NASA’s Kuiper Airborne Observatory. The laser LOs oscillate on fixed molecular transitions, but spectroscopic tunability can be achieved within the intermediate frequency output bandwidth of the mixer (generally up to 15 GHz). Heterodyne spectroscopy has proved valuable for astronomical observations of the fine-structure line emission from neutral atomic carbon (809 GHz) and ionized carbon (1900 GHz) as well as the J = 7-6 (807-GHz) and J = 17-16 (1956-GHz) rotational lines of CO.
Operational characteristics of a planar InGaAs avalanche photodiode in near-IR photon counting detection
Authors: Imai S. , Mashiko S. , Asai K. , Inaba H.
Published: February 2023

Development of techniques and systems for ultraweak light detection in the near-IR region ranging from 1 to 2 μm is very attractive and useful not only for optical communications and optical data processing but also for other applications such as spectroscopy, life sciences, and biotechnology. We report some experimental results of the basic operational characteristics in a IR photon counting scheme for a planar InGaAs avalanche photodiode (APD), which is primarily developed for high-speed optical fiber communications. The APDs used in the experiment are FPD13U81WS (Fujitsu) of which the operative diameter is 80 μm. This APD was cooled to a temperature of 77 K to effectively reduce dark pulses below ~1000 counts/s. Then the APD was dc biased to 99% of breakdown voltage (V
b
= 47.20 V at 77 K). Pulse-height distributions of both the dark and signal pulses were analyzed by changing various operational conditions. Based on the measurement results we obtained, some evaluations were also made of the SNR, a quality factor, and the excess noise multiplication factor for this APD. The minimum detectable optical power was estimated to be ~1 × 10−14 W with an averaging time of 100 s. The linearity of the count rate for signal pulses for this device was maintained between nearly 1 × 10−11 and 1 × 10−14 W.
Comparison of superlattice avalanche photodiodes with different layer thicknesses
Authors: Worchesky T. L. , Horst S. C.
Published: February 2023

We have examined the photoresponse and avalanche multiplication of several GaAs/AlGaAs superlattice avalanche photodiodes. The diodes were made of material from four separate MBE-grown wafers containing superlattices with periods of 200, 400, 700, and 1000 Å. Each diode contained twenty periods of the superlattice. We compared the effect of the superlattice period with background doping density in the avalanche region and capping layer thickness on the avalanche process. These structures have exhibited gains up to 100.
Improved temporal resolution in diffusion driven photodetectors
Authors: Kostenbauder Adnah , Siegman A. E.
Published: February 2023

We recently demonstrated a photovoltaic detector based on the Dember voltage and optical interference effects.1 In brief, we created an interference pattern in a semiconductor with two electrodes. The interference pattern is positioned to generate a photocarrier grating with a maximum density at one electrode and a minimum at the other. The Dember voltage associated with this density difference decays at the same rate as does the photocarrier grating (i.e.,

D
a

k
g
2

). In effect, this device substitutes the time that it takes for a photocarrier grating to decay for the transit time. In the devices discussed previously, the grating period was limited to 1.4 μm by imaging optics and resulted in response times of a few tens of picoseconds. Here we report measurements on a new generation of these detectors that allow the grating period to be reduced to 0.1 μm and which have greatly reduced electrical parasitics. These devices are made from 500-Å silicon on sapphire wafers contacted to an electrooptic wafer. The second wafer allows us to perform electrooptic sampling and is required because these devices are photovoltaic and consequently cannot be used as a sampling gate.
A 100-Gbit/s optical tapped delay line
Authors: Bao Yufei , Anemogiannis Emmanuel , Verber Carl M.
Published: February 2023

We present design procedures and performance calculations for an integrated optical 8-bit tapped delay line device to be fabricated on a 3-in. lithium niobate (LNO) wafer. It is composed of electrooptic and holographic diffraction gratings and, under the limitation of 1-μm lithography, can be designed to operate at data rates exceeding 100 Gbit/s. Analysis for both TE and TM modes, which includes the effects of off-axis propagation in the uniaxial LNO crystal, is discussed. Potential use includes code generation, time division multiplexing, and matrix multiplication.
Development of a multiple-branch step-index tapered waveguide coupling device
Authors: Cox H. L. , Ashley P. R.
Published: February 2023

A multiple-branch tapered channel waveguide has been developed for coupling GaAs semiconductor laser source radiation into a multichannel Ti:LiNbO3 optical array modulator. The step-index guiding wave region was fabricated by first rf sputter depositing Corning 7059 glass on Corning 2947 microscope slides, which were used as the substrate material. A shadowing technique was used during the sputtering process to produce a slowly increasing taper along the direction of propagation in the waveguide. Strip-channel waveguides were formed by masking off the guiding wave region and dry etching using an ion milling technique. The initial input channel is designed to collect radiation efficiently from the GaAs laser source. This initial input channel is then divided into two identical single-mode branches. After a distance each branch is divided into an additional set of identical single-mode branches. This process is repeated until the number of branches equals the number required for input into the array modulator. Losses produced by this multiple-branching geometry are discussed along with optimization of the branching geometry.
Bandpass filtering in BaTiO3
Authors: Pugliese Lenore , Morris G. Michael
Published: February 2023

White light images are used to perform real-time spatial filtering in BaTiO3 in two different geometries. White light images act as spatial filters by erasing certain frequency components of photorefractive Fourier transform holograms. As a result, these frequency components are suppressed in the reconstructed holographic images. In both geometries filters are illuminated using a commercial slide projector and imaged into the crystal. The two geometries differ in the method employed to read the hologram. In one of the arrangements, a separate read beam is needed in addition to the object Fourier transform and plane-wave reference beam. The other geometry is self-reading employing only the object beam and a strong self-pumping reference. Although the self-reading system is virtually self-aligning, its filtering characteristics differ from the four-wave mixing setup. With only minimal changes these arrangements permit electronic generation and positioning of spatial filters.
Multiple-exposure holograms stored and reconstructed with equal diffraction efficiency In photorefractive media
Authors: Strasser Arden C. , Johnson Kristina M.
Published: February 2023

Several optical computing and interconnection architectures have been demonstrated which rely on storing multiple-exposure holograms in volume photorefractive media. In addition, photorefractive materials are used as storage media for optical associative memories and adaptive neurallike networks. One potential problem with these materials is that holograms stored with equal energies reconstruct images with unequal brightness. Holograms recorded later in a multiple-exposure reconstruct brighter than holograms recorded earlier in the superimposition. Staebler et al.1 showed that the diffraction efficiency of the 100th hologram stored and fixed in a multiple-exposure recording in Fe-doped LiNbO3 reconstructed four times as bright as the tenth hologram recorded in the superimposition. Trial and error attempts to compensate for this effect resulted in an order of magnitude difference in brightness between the first and last reconstructed images.
Dynamics of a ring resonator utilizing photorefractive gain and loss
Authors: Martin Peter J. , Lininger Diana M. , Anderson Dana Z.
Published: February 2023

We have built a unidirectional ring resonator which uses barium titanate crystals for both gain and saturated loss. One photorefractive crystal provides gain via two-beam coupling in a conventional unidirectional ring configuration.1 A second crystal couples light out of the resonator using two-beam coupling, thereby producing loss. The dynamics of this resonator are investigated by observing the temporal buildup of the radiative power in the resonator. The intensity-dependent rates for grating formation are different for the two photorefractive crystals and are also dynamically changing due to the time-varying radiative power in the resonator. In turn, the radiative power in the resonator is dependent on the time-dependent grating strengths in the crystals. This interplay between grating formation and optical feedback is investigated.
Double phase-conjugate mirror using photorefractive BSO crystal
Authors: Xu Kebin , Xu Haiying , Hong Jing
Published: February 2023

Various phase-conjugate mirrors based on four-wave mixing in photorefractive crystals have been proposed and demonstrated recently. A double phase-conjugate mirror (DPCM), which through a transmission grating mechanism phase conjugates two input beams simultaneously impinging on opposite sides of a photorefractive crystal BSO is shown. We report on the successful operation of the DPCM and analyze its properties theoretically. Uses of the device in image processing are demonstrated.
Low-loss SiO2-Ta2O5 thin film optical waveguides with a wide range of refractive-index controllability
Authors: Shuto Keizo , Sekine Satoshi , Suzuki Senichi , Ueoka Yasushige
Published: February 2023

Low-loss optical waveguides made of mixed thin films of SiO2–Ta2O5 have successfully been fabricated by the rf magnetron sputtering method on thermally oxidized silicon substrate. The film exhibits wide controllability of refractive index by changing the composition ratio of SiO2 and Ta2O5, which is attained by controlling the input rf power into each SiO2 and Ta2O5 target during cosputtering. Thermal annealing is applied to the films after deposition. This process gives a remarkable decrease in propagation loss. Experimental results show that the refractive index is controlled in the wide range between 1.46 and 2.12 measured at 0.633-μm wavelength. This is linearly proportional to the mixture ratio of the two target materials. Propagation losses as low as 0.2–0.3 dB/cm at wavelengths of 0.633, 1.30, and 1.55 μm, are obtained by annealing the films at 400°C. Three-dimensional waveguides have been fabricated by a RIBE technique. Well-confined single-mode wave propagation is observed for the waveguide consisting of a rectangular core SiO2–Ta2O5 guide surrounded by an SiO2 cladding layer. The use of 3-D waveguides in a directional coupler is discussed.
Laser ablation of high Tc material in the presence of an oxygen flame
Authors: Hill W. T. , Hansen A. , Neifeld R. A. , Gunapala S. , Liang G. , Croft M. , Shaheen S. A. , Ginley D.
Published: February 2023

Excimer laser ablation was used to prepare thin films from bulk high-T
c
material. In previous studies we investigated the systematics of the ablation process by monitoring the thickness and composition of the thin films produced as a function of laser fluence and deposition angle. These studies indicate that material is primarily ejected from the target surface in a highly collimated plume. We have enhanced our studies by adding a fluorescence monitor and a dc biased rf oxygen plasma to our apparatus with which we have studied the fluorescence spectra of the plume at various positions within the plume. The results of this investigation are presented together with our latest results associated with high-T
c
film preparation.
Diffusion approximation and its similarity transforms for estimating laser light absorption in tissue
Authors: Welch A. J.
Published: February 2023

The accuracy of the diffusion approximation was examined by comparing it with more accurate solutions of radiative transfer theory for 1-D geometry. The forward and backward fluxes computed with the diffusion approximation are appropriate for both high and isotropic scattering cases. However, there are errors associated with the fluence rate. Lower fluence rates are computed in the subsurface region of a slab of tissue even though fluxes are estimated accurately. Radiance patterns are highly anisotropic at the boundary or near the source, and the diffusion mode is not proper in this region. As absorption and anisotropy of scattering increase, deviations increase. For high absorption, errors are smaller in terms of the total fluence rate since the diffuse fluence rate is much smaller than the collimated fluence rate. For highly forward scattering, negative reflectance and fluence rates may be computed. For anisotropic scattering, transforms of optical coefficients using similarity relations and the delta-Eddington approximation improve accuracy. Estimations of reflection and transmission are much improved, especially with the delta-Eddington approximation for the Henyey-Greenstein phase function.
Analysis of diffusely reflected light from human tissue in vivo
Authors: Bonner Robert F. , Nossal R.
Published: February 2023

The theoretical formulas presented in the previous paper (THD4) have been applied to the analysis of optical surface measurements made from living human and canine tissues. From measured in vivo surface intensity profiles Γ (ρ) of a variety of tissues, the characteristic absorption and scattering parameters were obtained using the theoretical formulas. By this approach, the depth dependence of photodynamic light dose in a patient’s metastatic melanoma was determined and corroborated by biopsy following treatment. Also, the empirical dependence on fiber separation of remote sensing of microcirculatory blood flow by laser Doppler velocimetry was found to be consistent with theory (mean path length as a function of ρ, 〈n|ρ〉〉. Finally, the analytical expression for Γ(n, ρ), the probability that a photon will be emitted at ρ after a path length n (or time t = n/c
i
), was shown to predict the temporal distribution of emergent light at large ρ following picosecond laser pulses. The theoretical formulas thus are useful both in designing and interpreting noninvasive optical remote sensing measurements in vivo.
Two-photon spectroscopy of the F1∏g and f3∏g states of molecular fluorine
Authors: Faris Gregory W. , Bischel William K.
Published: February 2023

In the interest of developing a sensitive detection technique for molecular fluorine, we attempted two-photon-excited ionization detection of the F1∏
g
state. The frequency-doubled output of a Nd:YAG-pumped dye laser was Raman shifted and the third anti-Stokes line selected with a Pellin-Broca prism. This light at around 207 nm was focused into a cell containing ~120 Torr of 10% F2 in He gas mixture. The ions produced were detected with a pair of electrodes biased to 500 V and amplified with a charge amplifier. High-resolution spectra of both the F1∏
g
state and the near-lying f3∏
g
state were obtained. The f3∏
g
state, a spin-forbidden transition from the ground state, is of interest because it is thought to be the upper level of the F2 laser transition at 157 nm, possibly the spectrally brightest source in the VUV today. In a recent theoretical investigation1 of the f3∏
g
state in fluorine it was found that the 157-nm laser transition could not be conclusively assigned. We are currently attempting to observe VUV fluorescence from the two-photon excited f3∏
g
state. If this experiment is successful, it would definitively assign the upper level of the F2 laser, allow further spectroscopy measurements of this important level, and demonstrate a fluorescence-based detection technique for molecular fluorine.
Potential of ( 5 ) 1 Σ g + state of Na2 by two-step excitation spectroscopy
Authors: Yan G.-Y. , Sterling B. W. , Schawlow A. L.
Published: February 2023

We report a detailed study of a Rydberg state of Na2,

(
5
)

1

Σ
g
+

, by means of cw two-steep excitation spectroscopy

(
5
)

1

Σ
g
+

←

A
1

Σ
u
+

←

X
1

Σ
g
+

; 270 levels in the state were measured with high resolution. These levels are located between 32,500 and 35,400 cm1.
Optical properties of β-quinol clathrates in the far infrared
Authors: Ryan J. C. , Plant D. V. , Adler C. L. , Lawandy N. M.
Published: February 2023

Clathrate compounds are ideal systems for the study of quantum confined atoms and molecules. Experimental and theoretical studies of β-quinol clathrates with a variety of guest atoms and molecules have been performed. A harmonic potential with quartic perturbation has been used to model the β-quinol cage seen by the guest atom or molecule to explain comparable far-infrared transition probabilities from quantized states of the clathrate cage for noble gas atoms and simple homonuclear and heteronuclear diatomics.1 Predictions of overtone absorption cross section and third-order nonlinear susceptibilities have been made based on this model. Experiments were aimed at determining overtone cross sections and third harmonic generation susceptibilities. The overtone and fundamental excitation of N2 and Xe clathrates were studied using a cw CH2F2 laser at 184.6 μm and several CO2 TEA laser-pumped superfluorescent emissions of NH3 and D2O. In addition, third harmonic generation was studied in Xe clathrates using MW/cm2 sources as the fundamentals just below the n= 0 → 1 transition at 43.5 cm−1.
Spatially localized Rydberg electron wave packets
Authors: Yeazell John A. , Mallalieu Mark , Stroud C. R.
Published: February 2023

The quantum theory of atoms is based on a Hamiltonian which is just that of the classical Kepler theory of planetary orbits. In spite of this common foundation, the predictions of quantum theory ordinarily do not much resemble those of the classical theory. However, there are atomic states which do behave classically. We have excited and detected an atomic electron wave packet that is localized in the polar and azimuthal angles.1 The wave packet is formed through the coherent superposition of Rydberg states of atomic sodium. The superposition is achieved by short-pulse optical excitation of the atom in the presence of a strong rf field. The wave packet is detected by dc field ionization. The ionization rate of such a wave packet depends on its angular localization (the angular width and orientation with respect to the dc field). A classical model of the ionization predicts this behavior.
Optical diagnostic development for high-current pulsed glow discharges
Authors: Kirman G. , Hartmann W. , Dominic V. , Liou R. L. , Hsu T. Y. , Gundersen Martin A.
Published: February 2023

Optical diagnostics used in the study of fundamental processes occurring in a high current (104-A/cm2) pulsed glow discharge are discussed. Temporally and spatially resolved spectroscopy and laser-induced fluorescence spectroscopy have been used to determine the population distribution of the excited states and the emission line shape in a high-current hydrogen discharge that is typical of a high-power plasma switch. When combined with appropriate models these measurements give information about the plasma energy, plasma density distribution, and transport properties. Laser-induced fluorescence spectroscopy can also be used to identify impurities in the discharge plasma giving information related to the plasma-surface interactions. These data provide quantitative information for the development of microscopic models of the plasmas in pulsed power devices including plasma lenses for high-energy physics applications, high-power switches, and engineering of new plasma loaded devices.
Diode lasers and arrays
Authors: Streifer William
Published: February 2023

This tutorial discusses the principles of operation of III–V semiconductor diode lasers, the use of distributed feedback, and high-power laser arrays. The semiconductor laser is a robust miniature versatile device, which directly converts electricity to light with very high efficiency. Uses in pumping solid-state lasers and in fiber-optic and point-to-point communications are reviewed.
One- and two-dimensional arrays with uniform intensity distribution
Authors: Buus Jens
Published: February 2023

Insufficient mode discrimination combined with spatial hole burning is a major problem in the development of coherent laser arrays. This problem is reduced if the array is designed to have a uniform intensity distribution. We describe how uniformity can be achieved in end emitting 1-D arrays and surface emitting 2-D arrays.
New phenomena show effects of luminance motion on stereoscopic motion and on color motion
Authors: Chang Jih Jie , Julesz Bela
Published: February 2023

Stereoscopic motion involves binocular disparity and luminance. In general, binocular and luminance contours of objects move in synchrony, thus sending identical direction signals to binocular disparity and luminance channels. It is possible, using random-dot stereograms, to generate independent directions of motion for luminance dots and cyclopean surfaces. To help illustrate our point, we refer to Ramachandran and Anstis (1986), who raised the question of what would happen if the leopard and the spots on the leopard’s body were to move in opposite directions. Would we still be able to see where the leopard is going? The phenomena we have observed showed that smooth coherent cyclopean movement, in both the frontoparallel and the toward-away direction, can be seen only if luminance motion exists. This suggests that stereoscopic motion is processed by separate binocular disparity and luminance motion units. In the case of color motion, we investigated if motion direction, that is defined solely by color, can be seen under equi-luminant conditions. Instead of using the isoluminant values for different colored dots, we randomized the luminance of the red and green dots in a random-dot cinnematograms to achieve equiluminance. Under these conditions, motion direction which is based solely on color correspondence cannot be perceived. Therefore, like stereoscopic motion, color motion is processed by separate color and luminance motion channels.
Alternative representations of visual space
Authors: Arditi Aries
Published: February 2023

The visual field is generally defined as the set of directions from which light is visible to a single eye, while the term binocular visual field has been used to refer either to a composite of the two visual fields, to the set of points on the fixation surface visible to either eye in binocular viewing, or to the portions of the visual fields that the two eyes share. These 2-D representations are geometrically inadequate for representing visual space in the most typical viewing conditions, yet they are used widely in vision science and related disciplines for precisely that purpose. Two alternative graphic constructs that are useful in representing the field of view are described: the 3-D volume visual field and the retinocentric binocular field. Both can be computed from the two monocular visual fields, given minimal assumptions, and are useful tools for developing hypotheses about many aspects of visual and visuomotor behavior.
What we learn to see in random-dot stereograms
Authors: O’Toole Alice , Kersten Daniel
Published: February 2023

In six experiments, we examined some properties of the learning effects reported for random-dot stereograms. The first three experiments offer a controlled replication of the retinal position-specific learning found by Ramachandran (1976) and a reexamination of the issue of random-dot pattern learning. Experiment 1 replicated the position-specific learning effect. Experiments 2 and 3 offered evidence that observers learn the monocular random-dot patterns and that this learning facilitates the depth percept. This result indicates that the traditional claim that random-dot stereograms are devoid of monocularly recognizable or useful forms should be reconsidered.
Testing of the maximum-likelihood method in restoring fluorescence micrographs and other noncoherent imagery
Authors: Holmes Timothy J.
Published: February 2023

We report on some early testing of a maximum-likelihood-based image-restoration algorithm which has been adapted from nuclear-medicine imaging. Potential uses Include noncoherent imaging systems where, for example, the object being imaged is a self-luminous source. This broad class of systems includes certain types of astronomical and infrared systems, although this presentation focuses on the use of fluorescence microscopy. The testing that is reported has involved both computer simulation of superresolving image restoration and experimentation with the restoration of a real image obtained from a defocused camera. This testing has involved a qualitative assessment of restored images, a quantification of mean square error in the restored Images and in the restored Fourier transforms of the images, and a quantification of resolution In these images. The potential for superresolution and bandlimited-spectrum extrapolation has been shown in these simulation tests, while the defocused-camera experiment has given some preliminary evidence of feasibility with real data.
Direct measurement of ultraweak photon emission from human breath using a highly sensitive photon counting technique
Authors: Kobayashi M. , Usa M. , Ichimura T. , Asai K. , Inaba H.
Published: February 2023

It is known that biological tissues and cells exhibit ultraweak photon emission of the order of 10-14 W or less without external or artificial stimulation. Most of these phenomena so far are known to be associated with lipid peroxidation and processes involving active oxygens and relevant free radicals. The detailed mechanisms of such ultraweak photon emission are now being studied in our group. As part of this research, we are investigating ultraweak emission, called biophoton, originating from human beings, and we have detected the chemiluminescence of human breath without the addition of any other substance. Human breath contains various sorts of molecules, thus reflecting the pulmonary condition.
Optical spectroscopy of a single ion at the Dicke limit
Authors: Bergquist J. C. , Diedrich F. , Itano Wayne M. , Wineland D. J.
Published: February 2023

A single Hg+ ion that is confined in an rf (Paul) trap can be laser cooled so that the amplitude of its motion is much less than an optical wavelength (the Dicke limit for optical transitions).1 More recently, we used the technique of sideband cooling to reach the zero point of motion.2 This realizes for the first time, we believe, the fundamental limit of laser cooling and the ideal of an isolated atomic particle at rest in free space to within the quantum mechanical limits imposed by the surrounding apparatus. In both limits, Doppler effects to all orders become negligible, the interrogation time is arbitrarily long, and the fundamental shot noise limit of a single atom is readily attained. We report these results and our progress toward the 2S1/2—2D5/2 282-nm transition with a resolution approaching the 2-Hz natural linewidth.
Sustained self-pulsation of cw operated Y-coupled diode laser arrays
Authors: Defreez R. K. , Yu Nu , Bossert D. J. , Elliott Richard A. , Winful H. G. , Welch D. F.
Published: February 2023

Streak camera observation of the time evolution of the near-field radiation pattern of flared Y-coupled diode laser arrays is reported. The arrays exhibit sustained self-pulsation at frequencies up to 4 GHz In CW operating conditions.
Optical implementation of a two-dimensional adaptive neural network
Authors: Wu Shudong , Lu Taiwei , Yu Francis T. S.
Published: February 2023

Two-dimensional neural networks based on the Hopfield model were proposed by Farhat and Psaltis1 and Caulfield.2 Their models require a large size of spatial light modulator or a large number of holographic elements. We propose a similar neural architecture, which uses a high-resolution video monitor as the programmable associative memory mask, and a moderate size SLM as an input matrix. An array of lenslets is used to provide the interconnections between the associative memory mask and the input matrix. With this architecture, an adaptive neural network of large size can be easily synthesized, and the limitations of low spatial bandwidth product and small dynamic range of available SLMs can be alleviated. To increase the system capacity, accuracy and speed, orthogonal projection algorithm, adaptive masking, and thresholding are used. This proposed system has the capability of improving the robustness and fault tolerance.
Space-variant optical intercorrects via multifaceted planar holograms
Authors: Gmitro Arthur F. , Keller Paul E.
Published: February 2023

One approach to implementing the space-variant interconnections needed for optical neural networks is to use a multifaceted hologram where each node has a dedicated subhologram, or facet, that encodes the interconnection pattern for that node. This approach was used to build an 8 × 8 node neural network for a simple associative memory problem and an 8 × 8 node neural network for a sixteen input winner-take-all network. The design approach for these holograms is presented, and the performance of the system in terms of diffraction efficiency and interconnection accuracy is discussed.
New architecture for optical fiber devices: power couplers and mode controllers
Authors: Sasaki Issei , Yoneta Masaji
Published: February 2023

This paper presents a new type of architecture for creating various optical devices applicable to optical fiber communication and optical fiber sensor systems. Power couplers and mode controllers are selected here for example targets. We use fibers only as the constituent material of such devices without any other optical component.
Recognition of articulated objects using a neural net architecture
Authors: Pentland Alex P.
Published: February 2023

The problem of recognizing complex articulated objects seems to require nonlocal nonhomogeneous computation. As a result, it is more difficult to imagine a neural net architecture that performs such a task. To gain insight into this problem we developed a prototype system for recognizing relatively complex articulated objects from their projected 2-D silhouettes by use of a massively parallel network of relatively simple processors. The computation is accomplished by breaking the recognition process down into a series of progressively more abstract estimation problems, each of which can be solved by local interaction between relatively simple computational units.
Combined optical-microelectronic realization of neural network models
Authors: Agranat A. , Neugebauer C. F. , Yariv Amnon
Published: February 2023

We describe a new generic approach for realizing neural network models. Schematically the basic system consists of a special purpose electronic integrated circuit—the neural processor (NP) and a 2-D spatial light modulator (SLM). The synaptic efficacies matrix is stored on the SLM and loaded in parallel into the NP. This is done by imaging the contents of the SLM onto an array detector which acts as the input unit of the NP. The NP processes the state of the network by using the synaptic efficacies supplied by the SLM. Several different architectures for the NP are described which enable the construction of networks with both binary and analog neurons, analog programmable synapses, and either synchronous or asynchronous updating. The expected properties of these systems are discussed based on the state of the art of microelectronic signal processing and SLM technology. It is shown that networks with 102–103 neurons can be built with update rates of typically 10 kHz for the complete networks. Finally, preliminary experimental results are described.
Spectroscopic diagnostics and atomic physics experiments in tokamak plasmas
Authors: Rowan William L.
Published: February 2023

As for other tokamaks, spectroscopy of the plasma produced in the Texas Experimental Tokamak (TEXT) has resulted in significant contributions to both atomic and plasma physics. The identification of magnetic and electric dipole transitions in highly ionized species allowed the determination of energy levels while increasing the availability of emission lines for plasma experiments and for use as standards in other atomic physics studies. Collisional rate measurements provided benchmarks for atomic theory and the basic data for implementation of some plasma diagnostics. Complementing the usual plasma physics role as a tool in the study of impurity behavior or ion energy transport, spectroscopy is now also employed in the study of plasma turbulence, MHD stability, and the nonthermal effects of rf heating. As accuracy requirements for some of these measurements increase, active spectroscopic techniques are displacing the familiar passive ones. The experiments which illustrate this review were all conducted on TEXT and are the work of physicists from a number of laboratories. They are chosen to emphasize advances in physics and to describe the critical role of spectroscopy in plasma physics.
Development of a pulsed dye laser system for tokamak diagnostics
Authors: Thomas Mary K. , West W. P. , Thomas D. M.
Published: February 2023

The current density profile (CDP) diagnostic system on the Texas Experimental Tokamak (TEXT) has been used to measure poloidal magnetic fields in the plasma using laser-induced fluorescence of a radially injected 100-keV lithium beam. A new method, based on laser enhanced attenuation of the injected Li beam and time-of-flight signal analysis, is being developed. To obtain the needed spatial and spectral resolution, the diagnostic requires a laser output at a wavelength of 667.1 nm, a bandwidth of <1 GHz, peak power of >20 W, and a pulse length of <10 ns at a 1-MHz rep rate. To achieve these requirements, an acoustooptic cavity dumper will be added to an existing symmetric z-shaped cw dye laser. The z-shaped cavity has previously demonstrated the required bandwidth and longitudinal mode structure, while a conventional cavity with a dumper has previously shown the required pulse length, rep rate, and peak power. This paper discusses details on the basic approach of the diagnostic measurement and presents details on the performance of the pulse laser system.
Narrow linewidth unstable resonators
Authors: Cooper D. , Dexter J. L. , Tankersley L. L. , Reintjes John F.
Published: February 2023

We have previously demonstrated that a feedback ring in an unstable resonator can be useful in providing narrow bandwidth radiation across the full available aperture of the resonator. In this configuration the light traveling in the forward direction in the ring passes through frequency-narrowing etalons while it is collimated and is then coupled back into the main resonator with a lens to match the divergence requirements. It is subsequently coupled out of the cavity with a scraper mirror, forming the output beam. The reverse wave in the ring passes through the etalons while converging or diverging. It is apertured at the focus of the lens, restricting it to the Fresnel core of the cavity. It thus does not appear in the output radiation, although it can affect the extraction efficiency by saturating the gain in the core. We examine the effect that the reverse wave has on the extraction efficiency and linewidth for cavity geometries involving symmetric and asymmetric rings and ones in which the light is coupled into and out of the ring by either a beam splitter or a polarizer. Use of a polarizer combined with a 90° rotator in the ring and a quarterwave plate in the main cavity allows complete separation of the forward and backward modes of the ring. Results indicate that when the modes are completely decoupled by the polarizing elements the extraction efficiency is relatively low but increases if the quarterwave plate is removed, allowing the forward and backward modes to mix on alternate cavity passes. We also compare the effect of a backward wave suppressing mirror on the extraction efficiency.
Reducing the effects of backscattering on the correlations of a He-Ne ring laser
Authors: Wang L. J. , Mandel Leonard
Published: February 2023

It has recently been shown theoretically1 that increasing both the loss and gain of a two-mode ring laser so as to maintain the working point leads to reduced backscattering effects, even though the absolute backscattering rate remains unchanged. In principle, the intensity cross correlation should change from positive to negative values, which it would have with zero or very low backscattering. By introducing a variable loss element in the form of a rotatable glass plate into the ring laser cavity, we have been able to confirm several of the theoretical predictions experimentally. In particular, we demonstrate the change from negative to positive intensity cross correlations as a knife-edge is progressively inserted into the laser beam.
Surface acoustic waves: optical depolarization in noncoplanar conditions
Authors: Graver W. R. , Mayer W. G. , Ngoc T.
Published: February 2023

Optical depolarization resulting from the interaction with a surface acoustic wave (SAW) has been investigated for conditions where the acoustic beam is not in the optical plane of incidence. Contributions to the scattered optical field include the corrugation of the surface and the elastooptic effect at the surface in the case where the SAW propagates in fused silica and the optical wave propagates in air. The depolarization is investigated as a function of the optical incident angle θfor −90 < θ <90° and as a function of the acoustic out-of-plane angle φ,for 0 < φ <90°. Four initial-to-final polarization states are studied, S to S, P to P, Sto P, and P to S. Scattering cross sections for 0 < K/k <0.1 (where K and k are the acoustical and optical wavenumbers, respectively) are generated and discussed. Functional relationships between the surface corrugation and the elastooptic effect are also evaluated with regard to their contributions to the scattered field. A Jones matrix describing the four polarization states is defined. From this, a Stokes matrix is developed and evaluated with respect to the scattering cross-sectional values.
Quad-phase-only filters for pattern recognition
Authors: Hansche Bruce D. , Dickey Fred M. , Mason J. Jeff
Published: February 2023

Motivated by the introduction of fast binary spatial light modulators such as the magnetooptic devices by Semetex and Litton, research in binary phase-only filters (BPOFs) has been active. Many techniques have been suggested for selecting a particular real binary representation of a desired complex filter function.1,2 All the resulting BPOFs represent real functions, which implies certain limitations. Among these limitations is a Hermitian impulse response, which means that correlation filters represented as BPOFs cannot discriminate between a target function and its mirror image. This presentation introduces the quad-phase-only filter (QPOF), which consists of the binarized real and imaginary parts of the desired filter function G(f): The SNR performance of the QPOF is considered, and it is shown that, for certain classes of target image, the QPOF performance is superior to the BPOF. A detour phase implementation is presented, which has some advantages over a two-beam interferometric implementation. Among these are a simpler single-beam optical system and tolerance of device phase errors. Both simulated and optically implemented results are presented.
Coherent surface emitting 2-D diode laser arrays using grating coupling
Authors: Lurie M. , Amantea R. , Butler Jerome K. , Carlson N. W. , Evans G. A. , Hammer J. M. , Palfrey S. L.
Published: February 2023

First, we describe a monolithic surface emitting 2-D laser array that produces coherent emission from more than 50% of its surface. Surfaces up to 5 × 0.06 mm have been achieved. Second, we show the importance of accurate interpretation of coherence in determining array performance and illustrate with calculations and data for our arrays.
High-power coherent laser diode array
Authors: Welch David F.
Published: February 2023

The progress of laser diode array research presents tremendous potential for high-power coherent lasers. Output powers of 38-W cw and wall plug efficiencies of greater than 50% could combine to produce very high-average-power laser systems. Currently one of the remaining technologies needed to be developed is the stable locking of the individual array elements into a coherent source resulting in a single lobed far-field pattern with a high Strehl ratio.
Infrared flash kinetic spectroscopy of free radicals
Authors: Moore C. B. , Bergman R. G. , Chen I-C. , Darwin D. C. , Johnston H. S. , Guo Y. , Wasserman E. P. , Young A. T.
Published: February 2023

Two IR flash kinetic spectrometers are described. Both use nanosecond pulsed UV lasers to produce high concentrations of reactive species. These are then probed by tunable cw IR lasers. High-resolution spectra of singlet and triplet states of CH2 and of HCO are presented. Measurements of reaction rates and of product quantum yields are described for several reactions important in atmospheric and combustion chemistry with particular emphasis on the dynamics of radical-radical reactions. The reactivity of the coordinatively unsaturated organometallic intermediate cyclopentadienylcobaltmonocarbonyl (CpCoCO) to a variety of ligands is studied in both gas and liquid phases.
Rotationally resolved inter-Rydberg spectroscopy of Ar2
Authors: Kane D. J. , Eden J. G.
Published: February 2023

Experiments utilizing inter-Rydberg spectroscopy to obtain laser excitation spectra of

Ar

2

3

Σ
u
+

(

1
u

,

0
u
−

)

formed in a pulsed corona discharge are described. By monitoring the atomic Ar fluorescence (4p → 4s) fed by the dissociation of higher-lying Rydberg states, high J(>30) rotational states have been resolved for several of the

A

π
u

5
p

(

0
g
−

,

1
g

,

2
g

)

←
A

σ
g

4
s

(

1
u

,

0
u
−

)

)

Rydberg band heads in the 497-530-nm region. Preliminary analysis of the rotational series shows that B
e
for the upper and lower states generally agree with presently accepted values.
Two-dimensional motion analysis: Information In the nodes of moving plaids
Authors: Perrone John A. , Stone Leland S.
Published: February 2023

In a recent model for the measurement of 2-D image motion, each 2-D sensor responds to edge motion and generates multiple outputs representing a subset of all possible edge velocities.1 A second stage determines which output is the correct edge velocity by using a cosine weighted voting scheme. Voting is carried out over the whole field, and the winning vote determines the final output direction. In the majority of cases involving uniform motion over the whole image, this scheme detects the correct velocity of the pattern as a whole and solves the aperture problem. For certain patterns, however, the model output departs significantly from that predicted by the constraint line solution.2,3 In particular, for moving plaids made up of two unequal contrast sine wave gratings of different orientations, the model predicts a bias in the perceived direction of motion. Data are presented that show that this Is consistent with human psychophysical results. We show that in the case of unequal contrast, the nodes in a plaid become skewed. Their asymmetric shape is responsible for the directional bias in the model output and may be involved in the perceptual bias as well. Our findings suggest a reassessment of the constraint line solution and the role of the nodes in the determination of the direction of motion of plaids.
Visual field asymmetries for coherence thresholds with dot pattern stimuli
Authors: Drum Bruce , O'leary David
Published: February 2023

We investigated the effects of added noise on the visibility of dot pattern stimuli as a function of the visual field position using the pattern discrimination perimeter.1 The stimuli were 20 × 20-dot patches of nonrandom dots embedded in a field of dynamic random dots. The dots subtended 15 min of arc, and the black/white dot ratio was 1/1 for both stimulus and surround. The stimuli were located on the four principal diagonals at an eccentricity of 12.7°. The stimulus pattern was either an upward-scrolling spatially random pattern presented for eight surround frames or a static checkerboard presented for only one surround frame. The surround frame rate was 15 Hz for the scrolling stimulus and 1.875 Hz for the checkerboard; thus stimulus duration was 0.533 s for both patterns. Coherence thresholds were measured with a staircase procedure by randomizing known percentages of stimulus dots per surround frame. Checkerboard coherence thresholds were higher for the superior than the inferior field, in agreement with asymmetries typically reported for luminance increment thresholds. Scrolling coherence thresholds, however, were lower for the superior than the inferior field, suggesting that motion detection mechanisms are more sensitive for the superior field, whereas spatial pattern detection mechanisms are more sensitive for the inferior field. A control experiment confirmed this finding for downward, leftward, and rightward scrolling stimuli, but thresholds were surprisingly lower for upward scrolling than for the other three directions, regardless of position.