bluuebunny/crossref_metadata_2025 huggingface dataset:
Driven two-level atoms as gain media for two or more photon amplification
Authors: Zhu Y. , Morin S. , Wu Qilin , Lezama A. , Mossberg T. W. , Lewenstein M.
Published: February 2023

It is well known that driven two-level atoms can exhibit optical amplification.1 This fact has led to the recent demonstration of single-photon lasing in cell and atomic-beam type ensembles of two-level atoms.2 We show that the same simple two-level system can also be utilized as a two- or more-photon amplifying medium. The underlying physics can be understood in terms of the atom field dressed-state picture. When driven by a field detuned from the atomic resonance, significant population inversion between the dressed-state doublets can be created. In the dressed picture, single-photon lasing occurs between inverted sublevels of adjacent dressed-state doublets. Transitions between nonadjacent doublets are still inverted, but require two or more photons. In the degenerate case, the multiphoton emission frequencies differ from the single-photon emission frequency and can hence be selectively enhanced using an optical cavity. Due to the peculiar structure of dressed levels, the multiphoton emissions are all connected through near resonant intermediate states. The multiphoton emissions can also be viewed as a stimulated hyper-Raman scattering of successively higher order.
Thermal QED revivals in the Jaynes-Cummings model
Authors: Arroyo-Correa Gabriel , Sanchez-Mondragon J. Javier
Published: February 2023

We develop an exact mathematical analysis of the time evolution of the atomic inversion in the Jaynes-Cummings model when the field is initially prepared in a thermal state, where the initial state of the TLA is the ground or excited state m = ∓1.
Application of moment invariant image descriptor to neural computing
Authors: Yu Francis T. S. , Lu Taiwei , Xu Xin , Yang Robert , Li Yajun
Published: February 2023

Invariant moments can be used to describe the basic characteristics of visual pattern.1 Thus they can be employed as a criterion in measuring the performance of different neural networks. Numerical analysis of the convergence of several neural network models based on invariant moment measurement has been conducted. Moment invariant image descriptors are used to develop a shift, scale, and rotation invariant neural network.
Calibration of a two-color pyrometer with reference wavelength method
Authors: Hahn Jae Won , Hahn Jeong Kyun , Park Seung Nam , Rhee Chunghi
Published: February 2023

The concept of reference wavelength is introduced for calibration of a two-color pyrometer. With the reference wavelength method, an analytical formula of the ratio temperature for the two-color pyrometer is derived. A two-color pyrometer is constructed with a silicon photodiode and two narrowband interference filters (12-nm FWHM, 800- and 900-nm peak wavelength). For both channels, the two-color pyrometer is calibrated with the reference wavelength method. The reference wavelengths for the two channels are chosen as 803 and 903 nm, and the correction factors are calculated from the calibration results. In greybody condition which is simulated with a blackbody furnace, the measured temperature error of the two-color pyrometer is less than ±6°C in the temperature range of 700-1000°C. Also measuring surface temperature of an oxidized steel specimen contained in a vacuum furnace, the temperature error is less than ±15°C in the temperature range of 850-1000°C.
Spectroscopic techniques for studying magnetic fusion plasmas
Authors: Isler R. C.
Published: February 2023

Magnetic fusion plasmas have temperatures ranging from several tens of electron volts at the edge up to several kiloelectron volts at the center. Electron densities typically vary from 1 to 10 × 1013/cm3. Spectroscopic techniques using wavelengths from the x-ray through the visible regions are employed to measure a number of parameters.1 These quantities include, but are not restricted to, plasma temperatures, radiated power, impurity content and transport, radial electric fields as inferred from plasma rotation, neutral hydrogen densities, and rotational transforms of magnetic fields. In addition to passive spectroscopy, active techniques are used for enhancing spectroscopic capabilities. Introduction of trace amounts of nonintrinsic impurities by laser ablation, excitation by charge exchange between energetic hydrogen beams incident on highly ionized impurities, laser-induced fluorescence, and excitation of lithium introduced in a beam or as a pellet have all been employed for making one or more types of measurement. In particular, charge exchange from hydrogen beams has become widely adopted as the standard method of measuring ion temperatures, plasma rotation, and concentrations of fully ionized low-Z impurities.2
Dispersion compensation in pseudocolor transmission holographic stereograms
Authors: Andrews John R.
Published: February 2023

This paper presents a set of design rules to implement dispersion compensation for pseudocolor transmission holographic stereograms illuminated by a point white-light source. The technique proposed here1 can be considered a generalization of the "achromatic" transmission hologram described by Benton,2 which includes illumination by a point light source at a finite distance. The axial and vertical correction involves tilting of the master hologram (H1) relative to the image-plane hologram (H2),1,2 and the lateral compensation is done by a one-dimensional magnification along the lateral axis for different color contributions in the white-light reconstruction.2 Dispersion compensation for many commonly used display situations is significantly different from the dispersion compensation for a point source at infinity. For instance, as the point source moves closer to H2, the "achromatic" angle decreases, and lateral correction is required. Experimental data verify the basic analysis, and modeling of the dispersion correction demonstrates its effectiveness.
Stochastic mode-locking theory of external-cavity semiconductor lasers
Authors: Hsu Kevin , Verber Carl M. , Roy Rajarshi
Published: February 2023

A stochastic mode-locking model has been developed to study the effect of intrinsic spontaneous noise and carrier shot noise on the phenomenon of active mode-locking in external-cavity semiconductor lasers. This frequency-domain numerical model includes nonlinear carrier dynamics, population pulsation, and self- and cross-saturation of the gain and is sufficiently flexible to account for coupling of multiple harmonic field components. The computer simulation of noise follows Marcuse's approach1 except that, because of active modulation, the Langevin noise strengths are allowed to depend on the time evolution of the gain and photon number. The resulting numerical simulation models the pulse-height probability distribution and the correlation of pulse height deviations under various operating conditions, such as the bias level, modulation strength, modulation type, and frequency detuning. The array of optical pulses are also numerically sampled and averaged to reveal the detailed stable structure of pulses, including possibly the reproducible satellite peaks, as have been evidenced in other experiments.
High-gain spatial distortion limits for squeezing and quantum measurement
Authors: La Porta A. , Slusher R. E.
Published: February 2023

The single-pass parametric downconver- sion amplifier is a simple optical arrangement that is useful for squeezed-light noise reduction and quantum nondemolition measurement.1 This device is pumped by a beam with a Gaussian spatial mode profile and acts on an input mode with a corresponding spatial profile. High parametric gain is required to achieve large squeezed noise reduction or accurate quantum measurement of a quadrature component of an input field. At large gains (>3 dB) the spatial variation of the pump field causes the parametrically amplified and deamplified quadrature field components to assume strongly non-Gaussian spatial profiles and to be distorted significantly with respect to each other. We analyze this distortion in the classical limit for an input beam with Gaussian profile and find that the gain measured by homodyne or direct detection differs from the low-gain limit. In the quantum limit, the case of squeezing is considered. It is shown that, in addition to the classical modifications, noise from higherorder spatial modes are coupled into the Gaussian mode, which is measured by a homodyne detection scheme using a Gauss- ian-profile local-oscillator beam. This high- gain mode-coupling process limits the degree of squeezing that can be obtained and the accuracy for quantum nondemolition measurement.
Squeezed pulse vacuum from fiber-ring interferometer
Authors: Bergman K. , Haus H. A.
Published: February 2023

Squeezing with degenerate parametric amplification sacrifices the power needed for the pump.1 Squeezing by using the third- order nonlinearity does not necessarily sacrifice the pump power, because it remains at the same frequency as the squeezed radiation. Because the third-order nonlinearity is weak, long interaction lengths must be used, i.e., optical fibers. Past experiments with quasi excitation in optical fibers were plagued by stimulated Brillouin scattering (SBS) and guided acoustic wave acoustic Brillouin scattering (GAWBS).2 The use of pulses raises the peak power and the SBS threshold, allowing use of shorter fibers. A Mach-Zehnder interferometer configuration separates the pump from the squeezed vacuum.3 This has two advantages: the pump power can be reused as the local oscillator power, and the squeezed radiation can be measured closer to zero frequency (30 kHz) because the pump fluctuations are absent.
Quantum frequency conversion
Authors: Kumar Prem
Published: February 2023

Many demonstrations of the generation and application of squeezed light have recently been made. Progress in its application to spectroscopy,1 however, has been hampered by the lack of tunable sources of squeezed light. Present sources generate squeezing around a fixed frequency, whereas for spectroscopic applications, tunability is desirable. Here, I propose a scheme by which frequency-tunable squeezed light can be generated. I show that it is possible to change a light beam's frequency without affecting its quantum state. Consider the sum frequency process wherein a beam at ω1 is mixed with a pump beam at ω2 to generate the sum ω3 = ω1 + ω2.
Velocity measurements in supersonic reacting flows by using Doppler-shifted OH and NO fluorescence
Authors: Allen Mark G. , Kessler William J. , Davis Steven J.
Published: February 2023

Laser-induced fluorescence is an attractive technique for nonintrusive velocity measurements in supersonic reacting flow research where other optically based techniques are unfeasible. Fluorescence-based velocity measurements have been demonstrated in cold, nonreacting compressible flows by means of molecules seeded into the flow.1,2
Experimental investigation of intrinsic optical bistabiliyy in gold colloids
Authors: Parigger Christian
Published: February 2023

Composite dielectric materials, such as gold colloids, are expected to facilitate intrinsic optically bistable behavior without cavity feedback. The nonlinear response of the metallic particles has been reported1 to exhibit bistability in the local field intensity. Experimental studies were carried out with picosecond laser systems. Accurate measurements were made of the ratio of incident to transmitted energy per pulse for increasing irradiance, but the anticipated switching behavior was not observed before optical breakdown occurred. However, conventional optical switching, which decreases the ratio, was detected for aqueous gold colloids at irradiances of typically 100 GW/cm2—well below picosecond optical-breakdown thresholds. Such high irradiances are required because of the weak nonlinear optical coupling of the gold colloids.
Self-aligning micromachined structures for optical fiber attachment to integrated-optical polymer waveguides
Authors: Goel Sanjay , Naylor David L.
Published: February 2023

The coupling of an array of optical fibers with waveguides has become an important technique with the advent of integrated-optical devices and is a key issue in evaluating their manufacturability and reliability. So far, some techniques have been developed for LiNbO3 waveguides.1,2 We have designed structures for the coupling of single-mode optical fibers to polymer-based optical waveguides. A thin layerof polymethyl methacrylate (PMMA) is deposited on top of a silicon wafer coated with silicon dioxide to form a thin-film waveguide. An appropriate choice of cladding can suppress multimode loses in the waveguide by insuring singlemode operation. Matching the refractive indices of the fiber and the waveguide further reduces the reflection loses. The process of micromachining, the wet-chemical an- iosotropic etching of silicon, has been well developed.
Second-harmonic generation dependence on the spontaneous polarization in ferroelectric vinylidene fluoride/trifluoroethylene copolymer thin films
Authors: Zhang Dapeng , Zhao Ji , Gamo Hideya
Published: February 2023

The vinylidene fluoride/trifluoroethylene (VDF/TrFE) copolymer is ferroelectric at room temperature, and its Curie temperature is 90°C.1 The sample consists of a VDF(65)/TrFE(36) copolymer film of a thickness of 4/µm with transparent electrodes InO and ITO on both sides. By varying the voltage between transparent electrodes mentioned above, we observe the typical hysteresis curve of linear polarization P(2ω) vs. poling field E(0) when the incident electric field is E(ω). The linearly polarized Q-switched Nd:YAG laser beam (wavelength 1.06 µm, pulse width 200 ns, and repetition rate 1 kHz) is obliquely incident on the sample mentioned above. The second-harmonic generation reaches its maximum at the incident angle of 50°. Because the sign of the second- order nonlinear-coefficient non- centrosymmetric crystal depends on the crystal orientation and thus the poling field, we can detect the sign of second-harmonic generation by using a nonlinear reference crystal, such as KTP. The X-Y recording of second-harmonic generation or nonlinear polarization from the film versus the poling electric field E(0) is shown for various rates of change poling field. The poled VDF/TrFE copolymer is orthorhombic of class mm2, and the nonlinear coefficients can be changed as a function of the poling field.
Self-organizing neural network for computing stereo disparity and transparency
Authors: Marshall Jonathan A.
Published: February 2023

A new analysis shows how efficient representation structures for higher-level visual tasks, such as segmentation, grouping, transparency, depth perception, and size perception, can self-organize. Here, three simple adaptive algorithms are combined in parallel in a neural-network simulation. A variant of a Hebbian excitatory learning rule provides each neuron with selectivity for patterns. A Weber-Law neuron-growth rule permits the network to learn and classify patterns despite variations in their spatial scale. A new anti- Hebbian inhibitory learning rule permits superposition of multiple simultaneous neural activations (multiple winners), under strictly regulated circumstances, instead of forcing winner-take-all pattern classifications. In the case of stereo transparency, the inhibitory learning both implements a uniqueness constraint and permits coactivation of cells representing multiple disparities at the same image location. Thus, two or more disparities can be active simultaneously without interference. This behavior is analogous to that of Prazdny's stereo vision algorithm,1 with the bonus that each binocular point is assigned a unique disparity. In a large implementation, such a network would be able to effectively represent the disparities of a cloud of points at random depths, like human observers and unlike Prazdny's method.
Dynamics of monochromatic nonequilibrium phonons generated by defect-induced one-phonon absorption
Authors: Tolbert W. A. , Dennis W. M. , Yen W. M.
Published: February 2023

Defect-induced one-phonon absorption1 of far-infrared radiation is used to generate monochromatic nonequilibrium phonon populations in LaF3:Pr3+ at a range of frequencies throughout the acoustic band. The pump source for this generation mechanism is a transversely excited atmospheric-pressure CO2-laser-pumped superradiant cell. Phonon occupation numbers of order 10 are generated. Phonons are optically detected in a time-resolved frequency-selective manner by using the anti-Stokes absorption sideband of the 3P0 state of Pr3+. The lifetime of these phonons is determined and is found to obey the ω-5 dependence as predicted by the isotropic dispersionless model for anharmonic decay of acoustic phonons.2 The spectral dynamics associated with the decay of these phonons is also investigated and is compared with a rate-equation analysis that includes backfeeding of the decay products. The production of double-frequency phonons by a three-phonon confluence process is also demonstrated.
Fundamental and overtone transitions of hydrogen iodide using frequency-modulation spectroscopy
Authors: Riris Haris , Carlisle C. B. , Cooper David E. , Wang Liang-guo , Gallagher T. F. , Tipping R. H.
Published: February 2023

Frequency-modulation spectroscopy (FMS)1-3 is a sensitive form of derivative absorption spectroscopy. The technique was used with two diode-laser systems to study the fundamental and second-overtone transitions of hydrogen iodide. A lead-salt diode laser operating at 4.7μm was used to measure the line strengths and nitrogen-collisional-broadening coefficients of the P-branch of the fundamental transition. For the second overtone, a near-IR system using a single-mode InGaAs laser was used, and several transitions of the R-branch were measured. The high sensitivity of our system (1 × 10-6) facilitated the measurement of high covibrational (J = 18) transitions. The dipole-moment function and Herman-Wallis coefficients of HI were calculated, on the basis of the line strength measurements.
Two-dimensional oscillator, the two-dimensional hydrogen atom, and lossless optical beam splitter: birds of a feather
Authors: Danakas Sotiris , Aravind P. K.
Published: February 2023

We point out some striking similarities between three simple, yet fundamental, quantum systems: (1) the two-dimensional isotropic oscillator, (2) the two-dimensional hydrogen atom, and (3) the lossless two-port beam splitter. By using the quantum theory of angular momentum, we obtain the unitary transformation connecting the Cartesian and polar eigenfunctions of the two-dimensional oscillator. By similar methods, we also obtain the unitary transformation connecting the polar and parabolic eigenfunctions of the two-dimensional hydrogen atom. Finally, we show that both the preceding transformations are closely related to the unitary transformation that connects the input and output photon statistics at a lossless 50-50 beamsplitter. Thus, a close connection is established between the quantum beam splitter, recently studied by several workers1,2 and two basic quantum systems.
Vacuum-field interference and enhanced spontaneous-emission in confined structures and in the microscopic-cavity
Authors: DeMartini F. , Mataloni P. , Murra D.
Published: February 2023

The method of "Periodic-Pumping" for Spontaneous-Emission (SpE) investigation has been first introduced by our laboratory.1 This method is applied here to vacuum-confinement structures [i.e., the "microcavity"2,3 and single-mirror confinement devices]. The method consists of the detection of the effect of spatial displacement of the excitation-region in the vacuum-confined active-zone on the SpE average probability: Γ = (1/T). The method is illustrated with reference to the Fabry-Perot microcavity with spacing d = d ≡ λ/2, i.e., in "SpE enhancement" condition. There the injection-angle θ of the well-collimated coherent pumping beam (SHG by an unstable-cavity Nd-YaG laser) which interferes only once in the microcavity by singlemirror reflection, is related to the position of the center-of-mass of the active-zone. A strong effect of SpE lifetime change under θ-variation enables the study of the distribution of the self-interfering vacuum field in the microcavity.
Thresholdless laser action and inhibition of quantum correlations in a microscopic cavity
Authors: De Martini F. , Marrocco M. , Tommasini R.
Published: February 2023

The process of zero threshold laser action in stimulated emission (StE) has been first reported by our laboratory, together with spontaneous emission (SpE) anomalies.1,2 In this work a new microcavity technique aimed at the investigation of the Bose-Einstein quantum correlations between two microlasers coupled to the same quasi plane-wave microcavity k-mode, orthogonal to the microcavity mirrors and excited by two independent beams at λ = 0.53 μm SHG by a common TEM00 Nd:YAG unstable-cavity laser. In the experiment the micrometrically controlled transverse distance s is the relevant variable of the experiment. The StE radiation at λ = 0.632 μm emerging from the microcavity on the k-mode is detected through an efficient spatial filter. The measurement of the exponential thresholdless-laser gain at various coherent-pump intensities of the overall laser system leads to the functional s-dependence of a relevant quantity: the "degree of Bose-Einstein correlation" a (s, d) among the active spots1,2 excited in the microcavity. The behavior of this quantity for microcavity spacings d = [d ≡ (λ/2, 5d, 10d], demonstrates that the rapid quantum decorrelation taking place in the condition of maximum confinement, i.e., at d = d, decreases at large d values approaching asymptotically, for a macroscopic-cavity d > d, the full correlation over the entire plane-wave phase surface expected according to the common QED notion of full photon freespace delocalization. An extended theoretical account of this novel effect of fundamental atom-field interaction physics and laser physics is given on the basis of the quantum interference taking place within the StE process among the plane waves belonging to the modal k-distribution for a microcavity of finite finesse. A region in the microcavity of interaction coherence (referred to as a photon-localization: effect) is established, giving rise to a strong dependence of the quantum-mechanical interatom correlation on the parameters of the microcavity. The theoretical results are found to be in agreement with our experimental findings. General considerations on the QED concept of transversal photon localization will be given on the basis of our results. These are apparently the first to be concerned with such a fundamental topological problem. This one is found to involve, in a new manner, relativistic retardation effects as well as a new EPR-type experimental configuration. Experimental results on the process of field interference by the partially interacting microlasers1,2 will also be reported. This topic raises (and our results answer) additional questions regarding the quantum structure of light. The QED theory of the interference process will also be given with reference to our results.
Extended-lifetime holograms for image processing in bismuth silicon oxide
Authors: Bashaw M. C. , Ma T.-P. , Barker R. C. , Mroczkowski S. , Dube R. R.
Published: February 2023

Extended-lifetime holograms are observed in photorefractive bismuth silicon oxide (BSO) at 785 nm. In the crystal, light beams from a diode laser (~500 μW/cm2) create an index grating with a period of 10 μm. An electric field ~5 kV/cm is optionally applied in the direction of the grating 110 for hologram formation by either diffusion or drift of charge carriers. Different formation procedures lead to different decay processes of the grating. In the first case, the hologram is written with the applied field for 70 s and, upon uniform illumination in the applied field, decays normally, with a time constant ~15 s. In another, the hologram is written without the applied field for 640 s and decays less simply: The initial diffusion grating is extremely weak for this period; however, upon uniform illumination in the applied field, the hologram quickly strengthens to the level of the previous case ~15 s, and then decays more slowly ~2000 s. Two-level electron–hole transport1 can explain these effects: using one level, electrons establish quick-response gratings; using the other, holes establish complementary extended-lifetime gratings. Vainos et al.2 have multiplexed short-lived photorefractive with long-lived photochromic holograms in BSO, leading to many image processing techniques. Multiplexing the normal and extended-lifetime holograms described here may yield similar techniques.
Unidirectional ring resonator using undoped GaAs
Authors: Cheng Li-Jen , Liu Duncan T. H. , Chua Peter L.
Published: February 2023

This paper reports experimental results on a self-starting unidirectional ring resonator using a photorefractive undoped GaAs crystal as the amplification medium. Two types of ring configurations, triangular and rectangular, were investigated. The oscillation occurred only in the small portion of the crystal near the cathode under a dc voltage, which can provide a uniform, amplified phase-conjugate beam in a four-wave mixing in the same GaAs crystal. The cross-section of the resonating beam in the rectangular configuration was considerably larger than that in the triangular one. The coupling efficiency in the resonator as a function of external-pump beam intensity under different applied dc voltages was measured. The maximum observed value was about 40% of the external-pump beam intensity, which was about twice of that in Cr-doped GaAs reported by Rajbenbach et al.1 The oscillation can occur with the external-pump beam intensity as low as 1 mW/cm2. The coupling efficiency became saturated at high intensities.
Retroreflector arrays to implement cross over interconnections between arrays of SEED logic gates
Authors: Tooley F. A. P. , Cloonan T. J. , McCormick F. B.
Published: February 2023

Issues arising from the use of retroreflector arrays to implement the crossover interconnect in multistage switching networks will be presented. Several authors have adopted this technique.1-4 This paper will discuss its advantages and some of its limitations and drawbacks. In particular, the precision to which it is necessary to fabricate the arrays will be explained. The discussion will provide details on the use of one type of retroreflector array—the prismatic mirror array1,4—in the implementation of part of a network. This network uses prism arrays of different periods to interconnect 16 × 8 arrays of symmetric SEEDs operating as logic gates.
Optimal implementation of arbitrary Boolean functions using space-variant optics
Authors: Louri Ahmed , Post Arthur D.
Published: February 2023

Although there have been many proposals for digital optical computing using spatially invariant interconnections,1 these systems have not provided truly general-purpose computing architectures. We have been examining a simple space-variant system that is capable of implementing any Boolean function and uses only as many gates as are required by an electronic implementation. We will show that this system has significant advantages over any spatially invariant system so far proposed, and that because our system can implement arbitrarily complex functions efficiently, control can be optical. This allows either SIMD or MIMD computations to be performed, potentially simultaneously.
Optimization in the design of photonic integrated devices
Authors: Gobbi E. F. , Houde-Walter S. N.
Published: February 2023

The current trend in integrated optics and optoelectronics is toward more complicated structures. Multilayer structures are used to satisfy a number of requirements that often compete with one another, making it difficult to design the best device without the aid of an optimization routine. Optimization requires that the complex propagation constants for a particular structure be found without user input. This is accomplished by using an adapted version of the Lorentzian function generation as found in Ramadas et al.1 This method is valid for finding both bound and leaky modes of an arbitrary, multilayer structure. The optical-field profiles are calculated by using the thin-film field-transfer matrix theory for planar, multilayer waveguides. The Nelder–Mead simplex method is then employed to find the optimum solution as defined by the device-dependent merit function. Degrees of freedom include layer thicknesses, index of the layers, and layer placement. The results of a program that can quickly find the optimum solution to formidable, analytical design problems will be presented.
Guided-mode resonance properties of dielectric strip gratings
Authors: Wang S. S. , Magnusson R.
Published: February 2023

To account for the detailed properties of diffraction gratings, an exact electromagnetic model is necessary. We have recently used such a model, the rigorous coupled-wave theory, to study the guided-mode resonance properties of planar dielectric-layer diffraction gratings.1 Earlier related work was done by Hessel and Oliner.2 In this paper, the guided-mode resonances of strip gratings with rectangular grating shape placed on arbitrary substrates are treated. To observe the resonances, the strip grating must have an average permittivity larger than that of the cover region and the substrate (waveguide-like structure). If the permittivities composing the adjacent half-periods of the grating have similar magnitudes, the homogeneous waveguide eigenvalue equation may be used to predict the resonance locations. If this difference is large, as it often is in practice, numerical calculations must be used to obtain the resonance behavior. Calculated results for both cases are presented in this paper, and the resonance properties of bulk and surface-relief gratings are compared.
Fundamental limits of VLSI liquid-crystal spatial light modulators
Authors: Jared David A. , Johnson Kristina M.
Published: February 2023

A new class of spatial light modulator based on very-large-scale integration (VLSI) semiconductor/liquid-crystal technology has been developed. Devices in this class consist of a liquid-crystal modulator atop an active semiconductor backplane.1,2 The liquid-crystal modulator may consist of combinations of photodetectors, analog/digital electronics, and metal pads on the semiconductor backplane. The liquid-crystal material is sandwiched between the semiconductor backplane and a sheet of glass coated with a transparent conductor. Optically or electronically addressed devices can be, fabricated depending upon the design of the semiconductor backplane. In this manner, it is possible to design special-purpose, well-integrated spatial light modulators that perform specific functions in optoelectronic computing architectures.
Multiscale optical flow computations for real-time tracking
Authors: Camus Ted , Bulthoff Heinrich
Published: February 2023

Most current optical flow algorithms are not suited for practical implementations, such as tracking, because they either require massively parallel supercomputers, specialized hardware, or up to several hours of computing time on a scientific workstation. A recent optical flow algorithm1 has been shown to be robust and noise-resistant, but until now it could only run in anything close to real-time on a massively parallel computer (such as a Connection Machine). We describe a modified algorithm that uses a pyramid architecture that is fast enough to power a real-time tracking system and requires only a conventional workstation. Three main techniques are employed. The first is a simple but powerful abstraction mechanism, based on a pyramid architecture, that can quickly extract the information from an optical flow field, which is necessary for real-time tracking. The second technique uses this abstraction mechanism to control focused fine-scale optical flow processing, and it results in a detailed optical flow field at a fraction of the normal cost. Third, by a controlled image-sampling rate, real objects can be tracked over a wide range of velocities.
Information properties of Fourier-Mellin image descriptors
Authors: Li Yajun , Yu Francis T. S.
Published: February 2023

The Fourier-Mellin image descriptors (FMDs) are invariant to both a scale and a rotation change in the input image. The FMDs can be calculated by using a computer, but the computational load is heavy.1 In this paper, we have proposed a method for calculating the accurate values of the FMDs of binary patterns constructed by rectangular pixels. This method was successfully applied to the calculation of the FMDs of all the alphanumeric characters that are more complicated patterns than squares, square frames, and rectangles. The results clearly show the information properties of the FMDs, some do not provide enough information for discrimination between characters and others just emphasize the same parts. It is known1,2 that the values of the high-order FMDs are dominated by the outer portion of a visual pattern and that the radial information from the central portion is suppressed. A suggestion has been made to reduce the unbalance in information extraction.
Heterodyne profilometer for measuring the roughness of cylindrical surfaces
Authors: Shukla R. P. , Perera G. M. , Venkateswarlu P. , Georqe M. C.
Published: February 2023

Sommargren1 devised a method for measuring the roughness of optically plane surfaces. Interferometric techniques for optical alignment2 of the sample in the Sommargren profilometer were presented by us earlier. However, this profilometer is not suitable for measuring the roughness of curved surfaces. Our present paper describes a heterodyne profilometer for measuring the roughness of cylindrical surfaces. It is based on a Twyman-Green heterodyne profilometer and uses a polarizing cube as the beam splitter and Zeeman split laser as the light source. Two collinear, orthogonal linearly polarized beams with a frequency difference of 1.5 MHz are separated by a polarizing cube at right angles to each other. A light beam of one frequency is focused on the cylindrical surface under test, while a beam of another frequency is focused on a reference-plane mirror. The reflected beams interfere at the detector to produce a beat-frequency signal. For measuring roughness, the cylindrical surface is displaced in small steps precisely parallel to its axis, and the phase of the beat frequency signal is measured as a function of displacement. Variation of the phase with the displacement provides the surface profile.
Diffraction of metastable helium atoms by a transmission grating
Authors: Carnal O. , Faulstich A. , Mlynek J.
Published: February 2023

We have measured the diffraction of metastable helium atoms by a transmission grating with a period of 500 nm. The atomic beam is derived from a supersonic nozzle by adiabatic gas expansion with a velocity ratio v/Δv 20; with the nozzle cooled to liquid nitrogen temperature, the corresponding de Broglie wave length of the helium atoms is 1.08 Å. We have observed diffraction peaks up to the third order with a good signal-to-noise ratio. The position and the height of the different orders are in satisfactory agreement with the measured grating shape and the mean velocity in the atomic beam. As was pointed out previously, such transmission gratings offer one way to realize an atom-wave interferometer.1 In this context, our results demonstrate that an efficient diffraction can also be obtained with excited-state atoms: Here the use of metastable rare-gas atoms is of special interest because they are easy to handle and can be detected on almost zero background. As an alternative to the use of transmission gratings in matter-wave interferometry, we also discuss a simple double-slit arrangement that may provide another approach to the study of atomic interference phenomena.
Characteristics of low-spatial-frequency photorefractive gratings recorded by projection processes
Authors: Larson D. A. , Black T. D. , Magnusson R. , Hafiz A.
Published: February 2023

The use of contact- and optical-projection techniques for recording low-spatial-frequency Raman-Nath-regime phase gratings in LiNbO3 has been characterized.1 By using the contact method, gratings have been recorded with periods ranging 50-200 μm that produced as many as 40 diffracted orders when probed by a low-power He—Ne laser. An optical-projection technique using unit magnification has also been used to produce phase gratings of similar periods. Both processes made use of the bulk photovoltaic effect as the primary transport mechanism. Diffraction efficiencies on the order of 20% in the first diffraction order were achieved by means of these techniques. General descriptions of the experimental arrangements used for projection recording will be presented.
Systematic study of the effects of rhodium doping on the photorefractive properties of strontium barium niobate
Authors: Vazquez R. A. , Ewbank M. D. , Neurgaonkar R. R.
Published: February 2023

Photorefractive strontium barium niobate (SrxBa1-xNb2O6) (SBN), is an attractive material for photorefractive applications because of its large Γ33 electro-optic coefficient. Although SBN crystals with various dopants have been studied,1-3 a systematic study of the effects of increasing dopant concentration on the photorefractive properties of SBN has not been done.
Temporal modulation effects on the noise properties of optical linear algebra processors
Authors: Batsell S. G. , Walkup John F. , Krile Thomas F.
Published: February 2023

Previous research has been conducted on noise and its effect on accuracy in optical linear algebra processors by assuming tempo rally unmodulated light.1,2 In this paper, we explore the effects of temporal modulation of the light at the source and/or at the spatial light modulator on the standard deviation of the system output voltage. We begin with a theoretical analysis for a number of temporal waveforms (squarewave, ramp, etc.) and consider individually the effects at the light source and at the spatial light modulator. We then present results from experimental measurements. Finally, we discuss the effect of temporal modulation on computational accuracy.
Design considerations for 2×2 optoelectronic bypass/exchange switches
Authors: Cheng L. , Govindarajan M. , Forrest S. R. , Sawchuk A. A.
Published: February 2023

Multistage networks are widely used in parallel signal-processing systems for interconnection, sorting, and computing.1 In such a network, each stage is composed of a fixed connection pattern and an array of 2 × 2 bypass/exchange switch modules. The inherent parallelism and potentially low crosstalk of optics can be fully utilized for the fixed connections at each stage. However, a light-efficient and easily controlled optical switch module is difficult to build. A more promising system uses optics for the fixed connections and optoelectronic technology for the switching.
Characterization of deformable-mirror spatial light modulators
Authors: Strozewski K. J. , Wetsel G. C. , McBride S. E. , Cantrell C. D. , Boysel R. M. , Florence J. M.
Published: February 2023

The deformable mirror, a monolithically integrated, silicon-based array of individually electronically addressable micromechanical mirror elements that move by means of electrostatic deflection, is an important class of spatial light modulator (SLM). A particularly promising version of this type of SLM is the deformable-mirror device (DMD).1 A sensitive, fast, high-resolution, and calibratable method of DMD element characterization uses optical-beam deflection (OBD) to measure surface displacement,2 which is well-suited to the characterization of whole-pixel motion and the imaging of pixel surface displacement with a spatial resolution of a few microns. Calibration of displacement, probebeam position, measurement of the deflection signal, and construction of amplitude and phase images are accomplished under computer control. Experimental results will be presented and compared with nonlinear theoretical models of the DMD.
Real-time edge enhancement using a hybrid amorphous silicon/ferroelectric liquid-crystal device
Authors: Mao Chongchang , Johnson Kristina M.
Published: February 2023

Image-edge enhancement has been demonstrated with photorefractive crystals and optically addressed spatial light modulators (OASLMs) with nematic liquid crystals.1,2 These methods used devices that operate with 10–100 ms response times. We report analysis and experimental results of the edge enhancement of images by means of an amorphous silicon/ferroelectric liquid-crystal OASLM.
Current-voltage characteristics and space-charge effects in semiconductor electron-wave filter/emitters
Authors: Glytsis Elias N. , Gaylord Thomas K. , Brennan Kevin F.
Published: February 2023

Starting from fundamental principles, the quantitative analogies between electron waves in semiconductors and electromagnetic waves in dielectrics have been developed.1 A voltage-biased semiconductor superlattice structure that can serve simultaneously as an electron filter and a tunable emitter has recently been proposed.2 The current-voltage (I–V) and transmission characteristics of these structures are analyzed by means of a nonself-consistent (NSC) and a self-consistent (SC) calculation. For the NSC calculation, only the Schrodinger equation is solved, but for the SC calculation both the Schrodinger and Poisson equations are solved iteratively.3 The approach of Esaki et al4. is used for the computation of the I–V characteristics. It is shown that for low-to-medium Fermi energies, the effect of the space-charge on the filter/emitteroperation is small and results in a shift of the I–V and transmission characteristics toward higher bias voltages. Examples of Ga1-xAlxAs filter/emitters are presented. Resonant filter/emitters with a current peak-to-valley ratio of ~50, as well as nonresonant devices, are analyzed. Charge-density distributions are presented. Superlattice electron filters/emitters can be used as high-speed switches and oscillators and as monoenergetic emitters in electroluminescent devices and photodetectors.
Analysis of diffraction from wavelength-sized surface-relief slots
Authors: Qu D. N. , Burge R. E. , Yuan X.
Published: February 2023

Diffraction from wavelength-size surface-relief structures has considerable physical importance and many practical applications. One relevant treatment of this problem has shown that the apparent sizes of the obstacles are different from their real geometrical sizes.1 In this paper we will present a further experimental and numerical analysis of diffraction of electromagnetic waves from near-wavelength-size and subwavelength-size surface-relief slots. The fabrication procedure, which involves plotting photographic masks and contact printing them onto a photoresist, will be outlined. By rigorously evaluating the complex value of the surface current nearby, the amplitude and the shape of the wave front can be obtained. The far-field intensity is obtained by taking into account the output wave front just above the surface. The results to be explained include the effects of incident angle, slot width and depth, finite conductivity and complex permittivity of the material, and the polarization states. The experimental results for various cases will be compared with one another and with numerical results.
Femtosecond transition-state absorption spectroscopy of atoms produced by photodissociation of gas-phase molecules
Authors: Glownia J. H. , Misewich J. A. , Walkup R. E. , Sorokin P. P.
Published: February 2023

Femtosecond transient absorption spectroscopy of transition states has recently been applied to the study of both Tl-halide1 and Bi22 gas-phase photodissocation. In our approach a femtosecond UV pump source excites a molecule to a repulsive electronic state, V0(R). After a variable delay, a femtosecond probe pulse is applied. In this case, the probe pulse is an ~10000 cm–1 wide white-light continuum pulse, and the photofragments are detected by means of broadband absorption spectroscopy. A complete spectrum corresponding to a given pump-probe delay is thus recorded in a single shot. Changes that are observed in the absorption spectrum as a function of the pump-probe delay provide information about variations δω (R) in the separation between the potential curves, V0(R) and V1(R), involved in the probe transition occurring as the interatomic spacing, R, is varied. These time-dependent absorption spectra form the data base for this approach to real-time transition-state spectroscopy.
Femtosecond nonlinear-optical response of quantum wells in strong magnetic fields
Authors: Stark J. B. , Knox W. H. , Chemla D. S.
Published: February 2023

The near-band-edge nonlinear optical response of semiconductors is dominated by exciton-exciton interactions and anarmonicities in the exciton-photon and exciton-phonon couplings. These mechanisms depend critically on dimensionality, as is demonstrated by nonlinear optical studies of quantum wells.1 A magnetic field applied perpendicularly to a quantum well confines the electronic states within the plane of the layer, so that confinement is obtained along all three directions. For large magnetic fields the magnetic confinement length can be made smaller than the excitonic Bohr radius. The quasi-two-dimensional states of the quantum wells can thereby be continuously tuned to quasi-zero dimensions without introducing additional material inhomogeneities. The first effect of such confinement is a change of the optical nonlinearities associated with many-body interactions. These changes are manifested in altered oscillator strengths, altered transition energies, and broadened electronic resonances. The second effect is a modification of particle-particle scattering. Changes in these interactions affect the kinetics of relaxation by modifying the scattering channels available to a nonthermally excited system. We use femtosecond nonlinear optical techniques to measure the manybody and kinetic response of magnetically confined electronic states as the quasi-two-dimensional states are continuously tuned to quasi-zero dimensions.
Determination of stimulated emission cross sections for Er-doped glass
Authors: Quimby R. S. , Miniscalco W. J.
Published: February 2023

Despite the high level of activity in the area of Er-doped fiber lasers and amplifiers, questions still remain regarding the values of the absorption and stimulated-emission cross sections. The disagreement between experimental and calculated values arises from a breakdown in the conventional Einstein A and B coefficient analysis when the necessary assumptions of uniform Stark-level occupations or equal transition strengths are not satisfied. By means of experimentally measured absorption and emission cross sections, we verified that the more general theory of McCumber1 successfully relates cross sections for the 4I13/2 ↔ 4I15/2 transitions. In McCumber's analysis, the emission and absorption cross sections at a given wavelength are connected by a known wavelength-dependent factor and an unknown wavelength-independent factor. Close agreement was found between the shapes of the experimental emission cross-section spectra and those calculated from the absorption cross section. To generate absolute cross sections, we developed an empirical procedure using measured linewidths to calculate the wavelength-independent factor. This technique is accurate to 15% for most glasses and, with few exceptions, is significantly better than an Einstein A/B analysis. In this way one may determine either the absorption or emission cross section if only the other is known.