bluuebunny/crossref_metadata_2025 huggingface dataset:
Multimode branching waveguides for guided-wave optics
Authors: Kapon Eli , Thurston R. N.
Published: February 2023

Waveguide junctions are important for performing splitting and recombining of optical signals for guided-wave optics applications.1 We describe a new class of multichannel waveguide junction which is useful for a variety of guided-wave manipulations. These junctions consist of an m-mode channel waveguide that branches into m single-mode channels, each having a different refractive-index profile. It is shown that each mode of these junctions becomes localized in a different single-mode channel as the channel separation increases. Thus, for sufficiently small branching angles, the junctions can route each mode of the multimode waveguide into a different output channel. When the junctions are excited from their single-mode channels end, they can serve to excite selectively each mode of the multimode waveguide. Furthermore, when both the width and refractive index of the single-mode channels are properly varied across the junction, the mode localization scheme becomes wavelength-dependent. Hence such junctions can operate as wavelength multiplexers/demultiplexers. Finally, by dynamically varying the refractive-index steps of the junction channels, e.g., via the electrooptic effect or optical nonlinearities, the waveguide junctions can perform multiport switching, modulation, and dynamic wavelength multiplexing/demultiplexing of guided waves.
Time-dependent spectra of copper laser oscillators and amplifiers
Authors: Molander W. A.
Published: February 2023

We have examined the time-dependent spectra of copper vapor laser oscillators and amplifiers. The spectra of the two lasing lines were examined with a spectral resolution of ~0.75 GHz and a time resolution of 3 ns. The oscillator spectra were quite similar to those previously reported by a number of other authors. The main features are that the green line (511 nm) is ~6.5 GHz wide and consists of an approximately rectangular line with three peaks whose amplitudes vary in time. The yellow line (578 nm), on the other hand, is composed of one narrow peak of <2 GHz wide early in time and three narrow well-resolved peaks covering ~7 GHz later in time.
Emulation of photon antibunching and squeezing
Authors: Mertz Lawrence
Published: February 2023

The experimental evidence for squeezed states might be interpreted as resulting from photon antibunching without squeezing. Even though this Interpretation leads to no benefit for interferometric measurements the implied antibunching remains philosophically fascinating with respect to photon predictability. It also turns out that photon counting of ordinary light with integration for a preset total count as opposed to a preset time easily can emulate the evidence. A novel optical homodyne receiver based on a lenticular screen furnishes the two quadrature signal components simultaneously for either tracing phasor diagrams or bidirectional fringe counting. Because of its efficiency and simplicity this receiver should find numerous applications in coherent optical communication, laser metrology, stellar interferometry, and laser gyroscopes.
Laser beam combination using stimulated Brillouin scattering
Authors: Chandra Suresh
Published: February 2023

This paper presents new ways in which stimulated Brillouin scattering (SBS) may be used to combine the outputs of several laser amplifiers to create a single coherent beam of high average power. The SBS produces optical phase conjugation which is characterized by (a) retroreflection of the incident beam and (b) correction of the wavefront distortions. Both properties are important for combining in the most useful manner the outputs of separate amplifiers. Three approaches to beam combining are discussed: (1) time multiplexing; (2) spatial multiplexing or phased arrays; and (3) serial combining. New conceptual designs are presented for each approach. The time multiplexing approach appears best suited when high pulse repetition rates are desired. The phased array approach provides the highest energy per pulse, while the third approach is rather flexible regarding the pulse repetition rate and laser pulse energy for a given average output power.
Analysis of transient phase conjugation in photorefractive media
Authors: Papen George C. , Tataronis J. A. , Saleh B. E. A.
Published: February 2023

We explore phase conjugation of transient optical signals through the mechanism of degenerate four-wave mixing in photorefractive media. Our model is governed by Maxwell’s equations for the transient optical fields, coupled with Kukhtarev’s1 diffusion equations for the material variables, under the assumptions of slowly varying envelopes and strong undepleted sinusoidal pumps. The resulting linear partial differential equations for the wave envelopes are solved via Laplace transform techniques in time. An explicit expression for the transfer function of the conjugator is obtained, and the related impulse response function is found by performing numerically an inverse Laplace transform. The conjugate signal is then expressed as an integral expression involving the probe signal and impulse response function. The effects of material parameters, an applied steady electric field, the total pump intensity, and the asymmetry of the pumps on the stability and performance of the conjugator are assessed.
Transient optical phase conjugation in dynamic media
Authors: Tataronis J. A. , Papen George C. , Saleh B. E. A.
Published: February 2023

We explore dynamic media, such as plasmas and photorefractive materials, as generators of phase conjugated replicas of transient optical signals via four-wave mixing. The characterizing element of dynamic media is a population of free charge carriers that leads to induced charge density gratings on probe illumination. In steady-state conditions, phase conjugation in such media normally appears with smaller pump intensities than are required in Kerr media but at the expense of potentially slow response times.1
Long-term storage and phase conjugation of time-resolved multiple images
Authors: Kim M. K. , Kachru R.
Published: February 2023

We have observed long-term storage and phase conjugation of multiple images using a backward stimulated echo scheme in the 3H4—3P0 transition of Pr3+:LaF3 crystal. The input spatial images are separated by 20-ns time intervals. The temporal order of the multiple-echo images is the reverse of the input images. Each echo image is a phase-conjugate replica of the corresponding input image. The storage lasts up to 15 s. This constitutes, in principle, the first demonstration of an ultrafast holographic movie using stimulated photon echo.
Selective enhancement of higher-order grating components in phoforefractive materials
Authors: Vachss Frederick , Hesselink Lambertus
Published: February 2023

Although the existence of nonlinear holographic response in phoforefractive materials has been experimentally observed and its presence treated in some theoretical detail,1 standard holographic recording techniques have yielded higher-order grating components substantially weaker than the fundamental linear component. Using the unstationary running wave technique of Huignard and Marrakchi,2 however, we show that these higher grating harmonics may be substantially increased in strength. Furthermore, this enhancement is selective in that there are distinct criteria for the optimal amplification of each grating order. In addition to a theoretical analysis of this effect, we present experimental verification using photorefractive Bi12SiO20 crystals. By measuring the diffraction efficiency of both the fundamental and second harmonic grating components, we observed substantial enhancement of this nonlinear second-order response with respect to the fundamental.
Programmable optical interconnection using a double phase conjugate mirror
Authors: Cronin-Golomb M. , Biernacki A. M. , Kong H. , Lin C.
Published: February 2023

One of the biggest challenges confronting optical computing is the need for an interconnection scheme that accommodates extremely high speed and parallelism for optical processing techniques. A real-time holographic element is a possible means of addressing these requirements with the added advantage of programmability. This can be realized by using the bidirectional light modulating capabilities of the double phase conjugate mirror (DPCM)1 to form an interconnection mask or pattern. The DPCM employs four-wave mixing in a photorefractive crystal to achieve the exchange of spatial information between beams incident from opposite sides of the crystal that can be switched on or off to establish communication.
Real-time image addition and subtraction in photorefractive BaTiO3 using image multiplexing
Authors: Biernacki A. M.
Published: February 2023

Image addition and subtraction in real time are very useful techniques for image processing, permitting the compilation of composite images from a number of separate inputs via addition, and correction or modification of images via subtraction. The time constant associated with photorefractive materials that dictates the time required to write and erase holographic gratings can be used to integrate or accumulate image information that is written into the crystal. By multiplexing the desired number of inputs to a photorefractive device such as the double phase conjugate mirror or a two-beam coupling configuration, multiple images can be combined as the photorefractive BaTiO3 crystal integrates the information by constructive interference in the holographic gratings that are formed. Similarly, image subtraction can be achieved by introducing a π phase shift1 between multiplexed inputs to create a destructive interference condition that selectively erases image information. (Earlier information is erased by the new inputs to the crystal.)
Time-reversal fidelity
Authors: Ewbank M. D. , Vazquez R. A.
Published: February 2023

A phase conjugate Michelson interferometer (PCMI),1 where both ordinary mirrors in a standard Michelson interferometer have been replaced with phase conjugate reflectors, has been the foundation for a number of new optical device applications, including optical phase detection, image subtraction, novelty filters, and phase conjugate fiber-optic gyroscopes. Additionally, the PCMI can be employed as a new method to measure the time-reversal fidelity of a phase conjugate reflector. This paper compares the time-reversal fidelities of a number of configurations of seif-pumped phase conjugate mirrors2 constructed with photorefractive BaTiO3. The comparison includes both the qualitative phase conjugate imaging method and the quantitative approach using the PCMI. In considering the PCMI, if both phase conjugate mirrors are capable of performing true time reversal of the incident optical waves, the output port of the PCMI is a perfect null, independent of any optical path length variations in either arm of the interferometer.
Extracting 3-D curvatures from images of surfaces using a neural network
Authors: Lehky Sidney R. , Sejnowski Terrence J.
Published: February 2023

A network which extracts principal curvatures and orientations from images of simple surfaces using shading information was constructed with the backpropagation learning algorithm.1 The surfaces were elliptic paraboloids with a parabolic cross section in depth, an elliptical cross section in the fronto-parallel plane, and a Lambertian reflectance function. The network finds the principal curvatures and directions at the centers of the surfaces over a wide range of values for those parameters, independent of illumination direction and the location of the center. Input is mediated by convolving the image with a hexagonal array of input units with overlapping circularly symmetric Laplacian receptive fields. Output is represented in a distributed fashion in the joint activities of a population of units whose sensitivities are 2-D Gaussian functions in a curvature-orientation parameter space. During learning, a variety of oriented and nonoriented patterns form among the inhibitory and excitatory synaptic weights associated with the hidden units, which are located between the input units and output units in the threelayer network.
Conical emission in atomic xenon
Authors: Rankin Michael B. , Davis Jon P. , Giranda C. , Squicciarini Martin J. , Bobb Lloyd C.
Published: February 2023

Excitation of xenon near the two-photon resonance between the ground state and the 6p(1/2,0) state produces forward conical emission at a wavelength close to the 828-nm 6p(1/2,0)—6s(3/ 2,1) excited-state transition. We describe experimental features of this process as excited by 600-ps pulses of 250-nm radiation from a frequency-doubled dye laser with intensity up to 1.3 × 108 W/ cm2 in xenon at pressures of 1-20 Torr. The conical emission occurs most prominently when the driving field is a few gigahertz above the frequency at which spontaneous emission from the excited 6p state peaks. The cone angle increases with xenon pressure in the 1-10-Torr range. The dependence appears consistent with the predictions based on noncollinearly phase-matched four-wave mixing. In this interpretation, the fourth wave would be near resonance with the 146.9-nm first resonance transition of xenon and detuned to the low-frequency side. The conical emission co-exists (and may compete with) an axial stimulated process which may be either two-photon driven amplified spontaneous emission or stimulated hyper-Raman scattering. The different tuning characteristics for the two processes make the extent of their competition unclear.
Response of stimulated Raman scattering to a pulse train
Authors: Herman Bruce J. , Konopnicki Marek J.
Published: February 2023

The high pulse repetition rates (~100 MHz) of radio-frequency free-electron lasers make possible the investigation of molecular response to a rapid pulse train.1 When the molecular decay time T2 is much larger than the time between pulses T, molecular memory is carried from pulse to pulse. For stimulated Raman scattering (SRS) the memory effect can lead to an increase in the size of the Raman dipole resulting in enhanced scattering. We analyze the 1-D SRS equations in the condition that the scattering under an individual pulse occurs in the transient regime (~10 ps). We obtain a general expression for the behavior of SRS which reduces to the following long-time limits: (1) When T2 ≪ T, the SRS from each pulse in the train develops independently from the others; (2) When T2 ≫ T, the transient SRS response is equivalent to the steady-state response to a constant pump at the time-averaged pump intensity. We also perform this analysis for a medium such as the atmosphere where the density of scatterers and Raman bandwidth decrease exponentially with distance.
Induced gain and modified absorption in a strongly driven sodium vapor
Authors: Gruneisen Mark T. , MacDonald Kenneth R. , Boyd Robert W.
Published: February 2023

The results of an experimental and theoretical study of the gain (or absorption) experienced by a weak probe beam propagating through a sodium vapor in the presence of an intense pump field that is nearly resonant with the 3s→3p atomic transition are presented. In general, the probe transmission spectrum is found to be comprised of three distinct features, two of which can lead to amplification of the probe wave. The origin of these features can be traced to the modification of the atomic level structure by the ac Stark effect. The experimentally measured spectra are in good agreement with the predictions of a theoretical model based on the solution of the density-matrix equations of motion for a two-level atom and including the effects of Doppler broadening. The dependence of the induced gain on the pressure of a helium buffer gas has been measured and is found to be in good agreement with the predictions of theory. The maximum gain observed in these experiments occurs at one of the Rabi sidebands and leads to a 38-fold increase in the intensity of the probe wave.
Polarization instabilities in an isotropic nonlinear Kerr medium
Authors: Gaeta Alexander L. , Boyd Robert W.
Published: February 2023

The steady-state polarizations of fields counterpropagating in nonlinear Kerr media can exhibit complicated behavior.1 We examine the temporal behavior for the case of an isotropic nonlinear Kerr medium and show that the polarizations are temporally unstable above a certain threshold intensity, even when the input polarizations are linear and parallel to each other. This polarization configuration is known to be spatially stable and is often chosen for the two strong pump waves in phase conjugation by degenerate four-wave mixing. We find that the threshold intensity for the polarization instability is approximately the intensity at which the phase conjugate reflectivity is equal to unity. Depending on the ratio of the two input intensities, this instability just above threshold can manifest itself as an abrupt rotation of the output polarizations to a new steady-state value or as a periodic oscillation of the output polarizations. At higher intensities the polarization can evolve chaotically in time, and depending on the ratio of the transit time through the medium to the response time of the medium the output intensity can fluctuate chaotically as well.
Visible spontaneous emission by atoms in an optical resonator
Authors: Heinzen D. J. , Childs J. J. , Feld M. S.
Published: February 2023

Recently, we observed enhancement and inhibition of visible spontaneous emission by atoms in a confocal resonator.1 In these experiments, the partial emission rate of the atom into the resonator modes is modified by a factor of 1/(1 − R), where R is the mirror reflectivity. The change in the total spontaneous emission rate is proportional to the solid angle ΔΩ subtended by the mirrors; the change was small (+1.6%, −0.5%) because ΔΩ ≈ 0.04 sr was small. Currently we are conducting experiments in which atoms are placed in a concentric resonator of large solid angle ΔΩ ≈ 3.6 sr and finesse of ~10. We estimate that a 30% decrease and 300% increase should be observable in the total spontaneous emission rate, when the resonator is tuned off or on-resonance, respectively. Results of this new experiment are presented. In addition to studying spontaneous processes, one can also consider the stimulated emission which occurs when a cavity field builds up which contains more than one photon. We have formulated a model which describes both the spontaneous and stimulated emission by the atom into the cavity and clarifies the relationship between enhanced spontaneous emission and stimulated emission.
Numerical modeling of transient Raman amplification
Authors: Hilfer Godehard , Menyuk Curtis R.
Published: February 2023

To model experiments performed by Reintjes et al.,1 a numerical code has been developed that solves the Raman interaction equations: The purpose is to study the influence of transience, transverse beam structure, pump depletion, and dispersive effects on the amplification and phase modulation of diverse forms of transient Stokes and pump beams in a cross-beam geometry.
Wavefront studies in a transient Raman amplifier
Authors: Duncan M. D. , Mahon R. , Tankersley L. L. , Reintjes J.
Published: February 2023

We describe results of experiments that evaluate the ability of a transient Raman amplifier to preserve the wavefronts of both aberrated and unaberrated incident Stokes beams. The experimental measurements were made using 40-ps pulses produced by a mode-locked Nd:YAG laser doubled to 532 nm. The incident Stokes was produced in a self-generator cell filled with hydrogen gas at 25 atm. A Mach-Zehnder interferometer that had a 1-m amplifier cell in one arm was used to measure distortions in the wavefront of the Stokes beam that were introduced by the transient Raman amplifier. In addition, aberrations could be imposed onto the incident Stokes beam by using a small gas jet. Near-and far-field intensity distributions and power-in-the-bucket energy measurements were also made of the unaberrated beam. Power-in-the-bucket measurements show a very minor degradation of a good quality incident Stokes beam. Preliminary near-and far-field results indicate that a good quality Stokes beam may undergo spatial gain narrowing in unsaturated conditions and can show other spatial effects in saturated conditions. Far-field results are presented and compared with calculated results. Interferometer measurements show little distortion of weakly aberrated beams but more significant distortion for larger initial aberrations.
Use of Gaussian brackets in holographic optical design
Authors: Buralli Dale A. , Rogers John R.
Published: February 2023

The ability to factor expressions for the back focal distance and magnification of a multielement optical system in terms of the element powers and separations provides a simple means of investigating the dependence of the first-order optical properties (and their chromatic variations) on the system parameters. The Gaussian bracket expressions for the first-order properties of multielement systems consist of products and sums of the expressions for the elements rather than continued fractions. By examining the structure of the Gaussian bracket expressions for an arbitrary system, conclusions of a general nature may be formed. A rigorous proof is given that any achromatic image of a real object which is formed by an all-holographic imaging system must be virtual regardless of the number of holographic elements in the system. Also, a three-hologram imaging system is derived from the theory, and it Is shown to be the only three-element solution which is corrected for the chromatic difference of magnification and both primary and secondary longitudinal chromatic aberration. Although this solution has previously been found through other means, it was not known to be the only solution.
Weak ground glass diffusers
Authors: Greivenhamp John E. , Sharf A. H. , Thompson A. D. , Barski L. L. , Moore W. E. , Gursslin G. D.
Published: February 2023

It is often necessary to add diffusers to an optical system to improve its performance. The two primary reasons are to increase the uniformity of the illumination and increase the solid angle of the illumination or the apparent source size. This latter situation is especially important when imaging objects have surface defects. The use of diffuse illumination to hide these phase defects is sometimes called scratch suppression.
Sine-filter-cosine cascade for an optical correlator
Authors: Wang Shen-Ge , George Nicholas
Published: February 2023

A novel sine-filter-cosine correlator is described for coherent optical processing. The advantages of this system are that it uses filter masks that are real-valued and non-negative while still providing a maximum value of SNR in the output, i.e., matched filter performance. Additionally and quite importantly, this system also provides desirable control over the shape of the correlation signal. Theoretical justification is presented by calculations of the shape of the cross-correlation of two real-valued functions compared and contrasted with corresponding correlations of their even and odd parts separately.
Active method for object recognition from multiple 2-D views
Authors: Bandyopadhyay Amit
Published: February 2023

There is mounting evidence for believing that a select number of characteristic views of solid objects may serve as an adequate model for recognition tasks. This idea is examined in a constrained application domain involving machine part recognition and assembly. Methods of structural and syntactic pattern recognition are used to derive compact and efficient codes for 2-D views of geometric objects. The model data base stores information about characteristic views of objects and the visual events that lead to transition between these views. Such events denote change in relative position and orientation between sensor and object. The recognition method can be broadly described as exploratory, where data base search is conducted based on extracted 2-D features, and if necessary sensor movement is initiated to generate features leading to maximum disambiguation of the match set. The areas of investigation include syntactic representation of 2-D views, organization of hierarchical model data base, fast indexing into the data base using a hardware engine, and sensor guidance to achieve recognition with the minimum number of views.
Phase of steady-state VEP elicited with laser interference gratings in Maxwellian view: influence of spatial frequency, contrast, and reversal rate
Authors: Simon Friedemann
Published: February 2023

Steady-state VEPs were recorded and analyzed using laser interference gratings in Maxwellian view as a pattern reversal stimulus and Fourier analysis. Two groups of 51 and 36 persons served as normal subjects in this study. The object of interest was the relationship of phase to spatial frequency (2-30 cycles/deg), contrast (0.1-0.99), and pattern reversal rate (2-31 rps). The phase shows a weak increase of some 10° with decreasing contrast. It remains constant with spatial frequency until local flicker effects lead to a small increase for coarse gratings (2 cycles/deg). This phase behavior appears to be approximately constant in contrast to phase and latency results of other authors,1,2 who obtained large variations as a function of spatial frequency and contrast with VEP stimulation involving the MTF of the eye. We find constant phase both with gratings offered in isolation and with simultaneous multifrequency stimulation using superimposed laser gratings. The reversal rate was varied from 2 to 31 rps in 0.5-rps steps. The extremely linear phase relationship enables a precise latency estimation (t = 1/360 × dϕ/df). Estimated latencies correspond well with P
2
latencies. For example, estimates were 113.6 ms for a 2-cycles/deg grating, 104.9 ms for18 cycles/deg, and a value of 105.6 ms for a 30-cycles/deg grating.
Hemispheric and hemiretinal symmetry in sensitivity to spatial frequency
Authors: Church Katherine L. , Sturr Joseph F.
Published: February 2023

Evidence from studies requiring the recognition and discrimination of facial and letter stimuli suggests that the right and left cerebral hemispheres are more sensitive to low and high spatial frequencies, respectively. More direct tests requiring the detection of simple sinusoidal gratings have yielded inconclusive findings with some supporting hemispheric asymmetries and others failing to do so. These studies using sinusoidal gratings have used small n terms of 2 or 3, have not controlled eye movements, and in some cases have confounded hemiretina with hemispheric stimulation. Therefore, in the present study we investigated hemispheric and hemiretinal sensitivity to a low (0.8-cycle/deg) and a high (8.7-cycles/deg) spatial frequency grating in 8 observers. To minimize eye movements, the gratings were randomly presented for 100 ms, 1.4 deg from a central fixation in the right, left, upper, or lower visual fields. The right and left eye of each observer was tested during each of two sessions using a criterion-free spatial forced choice procedure. No evidence for asymmetric sensitivity to either spatial frequency was found between the right and left visual fields or for the nasal and temporal hemiretina.
Generation of bandlimited images from unequally spaced slices
Authors: Nashold Karen M. , Saleh B. E. A.
Published: February 2023

It is often desired to generate a 2-D bandlimited function f (x,y), which when thresholded has specified edges. This is the case, for example, in generating binary masks through diffraction-limited systems. It has been shown in the past that bandlimited images can be constructed from slices which are themselves generated using 1-D methods. No emphasis, however, was placed on where the slices should be made. If an exact solution exists, and the slices are produced at distances separated by 1/2B (B being the required bandwidth in the y direction), f(x,y) can be found by simply low pass filtering the slices. If, however, an exact solution does not exist, which is often the case in image construction, such construction only guarantees the exact zero crossings along the slices. Our results indicate that uneven sampling can improve resolution. Samples are taken closer together in a finite region where greater resolution is required and farther apart elsewhere. The desired image is then formed using interpolating functions which are determined, depending on the desired sampling locations, by properly inserting and deleting zeros in a known bandlimited function. The resulting image can thus be forced to have the desired zero crossings at more places than in regular sampling, and hence greater accuracy is achieved.
Imaging system design for reducing the complexity of postdetection processing
Authors: Matic Roy M. , Goodman Joseph W.
Published: February 2023

Assume that an image acquired from a diffraction- limited system using partially coherent illumination is processed by a linear postdetection filter having a desired transfer function. The processing performed by an imaging system followed by a linear filter can be described by a bilinear transfer function. The problem is to design an equivalent system consisting of an apodized imaging system followed by a short-length finite impulse response (FIR) filter that has a bilinear transfer function that closely approximates the bilinear transfer function of the diffraction-limited imaging system followed by the ideal linear filter. The complexity of the postdetection filter is reduced since the FIR filter is presumably easier to implement than the ideal linear filter. Alternatively, a high-order FIR implementation of the ideal linear filter can be replaced by a lower-order implementation without loss of performance. Assuming that the coherence of the illumination is fixed, the problem reduces to finding the pupil screen of the imaging system and the weights of the FIR filter that result in the best approximation to the desired bilinear transfer function. The problem is solved using nonlinear parameter optimization techniques. The design of several equivalent systems is presented.
Optical confinement of bound exciton emission in a silicon epitaxial waveguide
Authors: Brown T. G. , Bradfield Philip L. , Hall Dennis G. , Soref R. A.
Published: February 2023

The widespread use of silicon in the microelectronics arena makes the notion of using silicon for integrated optics attractive. Several authors have reported schemes for making various kinds of optical waveguide in or on crystalline silicon. One approach is the epitaxial waveguide,1 in which a heavily doped substrate exhibits a depressed refractive index due to the high density of free carriers, but the guiding layer remains lightly doped and of good optical quality. Beryllium pairs form an isoelectronic complex in crystalline silicon that can bind an exciton. At sufficiently low temperatures (T = 30 K), this bound exciton radiates efficiently in a narrow line near the wavelength λ = 1.15 μm. We report the observation of optical confinement of subband gap radiation emitted by excitons bound to beryllium pairs introduced by ion implantation and suitable annealing. Photographs and transverse image scans show clear confinement of the emitted radiation within the 15.5-μm epitaxial layer.
Optical emission from impurity-doped crystalline silicon
Authors: Bradfield Philip L. , Brown T. G. , Hall Dennis G.
Published: February 2023

Efficient luminescence from crystalline silicon (x-Si) could be an important step toward the goal of integrating optics and modern electronics. The light emitted from the recombination of an exciton bound to an isoelectronic impurity has shown promise as a possible way this goal could be achieved. The recent discovery of sulfur as an impurity which exhibits isoelectronic bound exciton (IBE) emission1 at λ = 1.32 μm has prompted the study of other chalcogens for similar behavior. We report the results of an investigation of photoluminescence (PL) from x-Si samples that contain selenium and oxygen impurities. Typically, the samples were treated in the same manner as the sulfur-doped samples in Ref. 1. Results from experiments investigating the temperature dependence of the IBE lifetime and the PL spectrum are presented and compared with similar experiments involving sulfur.
Nondestructive test method for guided-wave devices
Authors: Tateda Mitsuhiro , Tsubokawa Makoto , Shibata Nori , Kawachi Masao
Published: February 2023

A nondestructive optical path tracing method for guided-wave optical devices is proposed, which has been successfully used in evaluating guided-wave multi/demultiplexer performance for optical frequency-division-multiplexing (FDM) transmission. When a testing light is injected into one of the two input ports of a multi/demultiplexer having a Mach-Zehnder interferometer configuration, each output light from the two output ports contains two mixed components, one from the upper branch and the other from the lower branch of the interferometer. This makes waveguide parameter measurements difficult. We overcome this difficulty by utilizing the light source's coherence length finiteness. The ratios of the two mixed optical power components traveling along the two different paths can be determined by using the spatial interferometric technique with a heterodyne power detection scheme.1 The power coupling coefficients at the two branching points are thus nondestructively determined from the measured power ratios.
Second harmonic generation in dc-biased quantum wells
Authors: Yoo S. J. B. , Fejer M. M. , Harwit Alex , Byer R. L. , Harris J. S.
Published: February 2023

It has recently been shown that the dipole matrix elements between subbands in semiconductor quantum wells are extremely large.1 Third-order nonlinear susceptibilities are proportional to the fourth power of these matrix elements. Large nonlinearities have thus been predicted for these systems, in particular an intensity-dependent index of refraction suitable for use in all-optical logic elements.1 Second-order nonlinearities vanish identically in symmetric wells, suggesting the use of asymmetrically graded quantum wells for quadratic interactions.2 External bias electric fields also break the inversion symmetry, resulting in Stark shifts and large quadratic susceptibilities whose sign depends on the direction of the applied field. The magnitude of the nonlinearity depends on the carrier density, the dc bias field, and the detuning of the fundamental and second harmonic frequencies from resonances.
Resonant three-wave mixing in semiconductor structures of reduced dimensionality
Authors: Jiang M. , Burstein E. , Pinczuk A.
Published: February 2023

We are exploring resonant three-wave mixing as a spectroscopic probe of interband and intersubband excitations at semiconductor surfaces and interfaces (e.g., heterojunctions) and in quantum wells. Three-wave mixing at either a semiconductor surface or heterojunction, or in an asymmetric quantum well, involves contributions from electric field-induced optical interband and intersubband transitions and can, therefore, take place in centrosymmetric as well as noncentrosymmetric semiconductors. On the other hand, three-wave mixing in a symmetric quantum well is normally forbidden but can take place in the presence of a perpendicular electric field. Unlike Raman scattering, three-wave mixing can also be used to probe transitions between subbands that are unoccupied. We note moreover that, in the case of quantum wells, three-wave mixing can be used to probe intersubband excitations between subbands in the valence band and subbands in the conduction band and that, in the case of spatially confined levels at a semiconductor surface or a heterojunction, it can be used to probe transitions between subbands in two valence bands or two conduction bands.
Phase management in interferometric diffraction tomography with Incoherent illumination
Authors: Shentu Lian
Published: February 2023

The reconstruction of amplitude objects based on the method of grating interferometric tomography1 requires the measurement of both the contrast and phase of fringes formed in many different planes. For a relative high spatial frequency (~200-lines/mm) grating interferometric system, it appears very difficult to measure the phase difference between different fringe patterns (which in fact are the Fourier components of the object) directly. An axicon lens system has been developed to correct the random error generated by the CCD camera carrying slide that transports the camera to different planes. Also, the real phase of the Fourier component must be calculated from the measured phase of the corresponding fringe plane. The measurement error of a random nature degrades the reconstruction; the linear phase error or obliquity of the alignment process generates a permutation of the reconstruction. In addition, the window size, both for the object and the fringe pattern, must be set properly to retrieve the right phases.
Analysis of the interference fringes in a cross-grating interferometer
Authors: Cheng Yih-Shyang
Published: February 2023

The on-axis interference pattern of a cross-grating interferometer was analyzed.1 In different cases, the localized fringes can be formed with either an extended white-light source or an extended monochromatic source. If a structured source is used, the contrast of the interference fringes in a 4-beam cross-grating interferometer is similar to that in the 4-pinhole Young’s experiment with different planes along the optical axis corresponding to different pinhole separations. With a cross-gratinglike illuminating source, the fringes are localized in discrete planes. When proper spatial filterings are done, multiple images can be formed at off-axis positions with light from an extended monochromatic source. By suitably choosing 4 beams to interfere, the fringes can be formed with white light. Fringes can also be formed further downstream with different transfer functions. When many cross gratings are used in the cross-grating interferometer, the fringes are formed in a similar way. The three-cross-grating interferometer is particularly interesting because it can be either an in-line interferometer or an off-axis interferometer.
Rigidity-based approach to structure from motion
Authors: Mitiche Amar
Published: February 2023

The problem of determining structure and motion of objects in space from images is currently a topic of major interest in computer vision. Many useful applications are giving much impetus to research in this area. For example, a challenging application is the realization of a robot with autonomy of navigation. Moreover, a computational theory of vision is of interest in the study of the human visual system.
Different classes of questions in the psychophysical study of visual motion
Authors: Nakayama Ken
Published: February 2023

When studying visual motion from the vantage point of psychophysics, we can discern two broad sets of research questions. First and most common are questions regarding the encoding of retinal image velocities and the uses to which this image velocity information is put. This is the area where psychophysics and physiology have had the most success, and several examples are discussed. Second and relatively unexplored is the higher-order question as to what gives rise to the perception of motion. In this context we present evidence and demonstrations from which we draw the following conclusions: (1) the perception of motion is dictated by many cues other than image velocity, including occlusion and stereopsis; (2) the actual perception of motion is often an effect rather than a cause and can be understood in terms of the propagation of 3-D real-world constraints.
Energy conversion in nonlinear pulse propagation
Authors: Zardecki Andrew
Published: February 2023

An analysis is presented describing the interactions of atmospheric aerosols with a high-intensity laser beam propagating along an atmospheric path. For the case of moderate beam irradiances, diffusive mass transport and conductive energy transport dominate the aerosol-beam interactions. In this regime, the coupled aerosol-beam equations are solved numerically to obtain the spatiotemporal behavior of the propagating beam and of the irradiated aerosol. For higher beam irradiances, convective transport of mass, energy, and momentum away from the irradiated aerosols must be considered. Numerical examples illustrative of both regimes are given for the case of irradiated water aerosol droplets. The energy balance equation allows us to compute the conversion of the pulse energy into temperature increase, vaporization, conduction, and convection. In addition, we include the droplet radius shrinking with time, as recently discussed by Davies and Brock.1
Fabry-Perot etalons for solar corona spectral measurements
Authors: Smartt Raymond N. , Bonaccini Domenico
Published: February 2023

Fabry-Perot etalons with birefringent substrates are studied for application to the measurement of the spectral profile of faint solar corona emission lines. The method uses polarization spectral chopping by means of a photoelastic modulator that allows alternate measurements of the radiation within the bandwidth corresponding to the coronal line and orthogonally polarized radiation in a similar adjacent bandwidth. These two bands are isolated from their associated channeled spectra by an interference filter. Electronic subtraction gives the coronal signal. The line profile is obtained by successive sampling through the line. Design parameters of the etalons such as the interorder spectral interval, the spectral interval between orthogonally polarized components, the bandwidth, transmittance, and the angular characteristics are investigated for optimum performance.
Interferogram aberration analysis to very high orders
Authors: Jensen Arthur E.
Published: February 2023

Three-hundred and sixty-one Zernike circle polynomials (with radial index N and angular index M so that 0 ≤ N + M ≤ 36, 0 ≤ M ≤ N, N – M is even) have been least-squares fit to wavefront maps derived from interferograms or synthesized test data. The analysis is based on the assumption that the wavefront aperture is symmetric about the X, Y and 45° axes. This, however, covers a large and useful class of circular or noncircular apertures with circular or noncircular obstructions. The role of aperture symmetry and wavefront manipulation in the analysis is discussed along with the accuracy and convergence of the Zernike circle polynomial representation of the wavefront.
Estimators for restoration and reconstruction using a principle of minimum discriminability
Authors: Frieden B. Roy
Published: February 2023

Classical decision theory allows the user to decide optimally between two alternative signatures, H1i or H2i, given data R
i
, i = 1,…, N. The probability for making a correct decision turns out to depend solely on the forms of H1
i
(and H2
i
, and the type of noise present. Here regard H1
i
as an unknown object that it is desired to restore or reconstruct from incomplete data R
i
. Let H2
i
be a known template object that the user wants to bias an estimate of H1
i
toward. In the absence of data, H1
i
should equal H2
i
, and with any data present H1
i
should be minimally distinguishable from H2
i
. Thus H2
i
represents prior information about the shape of H1
i
and provides a medium for inserting such information. The precise sense by which H1
i
and H2
i
is to be minimally distinguishable is as follows: Even if the data were combined optimally by classical decision theory, the decision should still be minimally probable to be correct. On this basis, different estimators for H1
i
may be formed, depending on the statistics of the noise in the data. As examples, with additive Gaussian noise the estimator is least squares; with Poisson noise, the estimator is maximum cross-entropy.
Generalized electronic halftoning procedure
Authors: Just Dieter , Mrusek Ralf , Bryngdahl Olof
Published: February 2023

Electronic halftoning is frequently applied in picture and hologram coding. The result is a binary representation of 2-D information on a sampled raster. Those binarization procedures which use carrier functions or dither are simple and suitable for digital implementation. In general, a compromise between detail resolution and gray-tone reproduction is necessary. Furthermore, the performance of the halftoning process on a discrete raster causes interaction between the raster and carrier. To overcome some problems which conventional methods of this type suffer from we introduce an additional degree of freedom by allowing rational ratios between the raster and carrier period. The concept is demonstrated by a 1-D triangular-shaped carrier function.
Sldelobe-reduclng Invariant composite filters
Authors: Arsenault Henri H. , Leclerc Luc
Published: February 2023

Composite filters, which are linear combinations of matched filters, allow arbitrary correlation peaks to be obtained for any objects but are usually associated with large sidelobes. This problem Is compounded when the composite filters are composed of circular harmonic rotation-invariant filters,1 because such filters trade off the SNR for rotation invariance. One way to reduce sidelobes is to make a filter that minimizes the mean-square difference between the outputs of two filters: One Is designed to recognize a given object and to discriminate against another given object. The other Is designed to discriminate against noise. The combined filter yields good sidelobe reduction.
Optical activity in the mercurous halides
Authors: McCarthy K. A. , Gottlieb M. , Goutzou-Lis A. P. , Singh N. B.
Published: February 2023

The mercurous halide crystals (Hg2Cl2, Hg2Br2, and Hg2I2) have recently been synthesized for use in acoustooptic devices because of their several unusual and useful properties. The optical activity in these materials is large (at 0.6328 μm, 190 deg/mm for Hg2Cl2, 212 deg/mm for Hg2Br2, and 232 deg/mm for Hg2I2) for crystalline systems and thus must be considered and incorporated in the design of devices fabricated from these materials. These crystals belong to the D4
h
crystal class, and the optical activity in such crystal classes is associated with the structural arrangements of the molecules.
Pipelined number conversions using optical arithmetic/logic units
Authors: Houk Theodore L. , Falk R. Aaron
Published: February 2023

Optical crossbar arithmetic/logic units (OALUs) described by Falk et al.1 perform residue arithmetic addition and multiplication without internal carry operations. This makes residue arithmetic algorithms practical in high-speed devices. Two tasks in connecting customary weighted number arithmetic processors to residue number processors are to convert binary or decimal numbers to residue numbers and vice versa. The latter task may advantageously convert residue representation to mixed radix digits, a special form of weighted number, as an intermediate representation through an algorithm which uses residue arithmetic. The mixed radix digits themselves may be used to find sign, magnitude, and overflow conditions without further conversion to binary or decimal digits. Methods for connecting OALUs to binary, decimal, and binary-coded decimal digit signals for conversion to residue numbers and to residue number signals for conversion mixed radix digits are derived from standard algorithms. Where these algorithms involve multiplying by a constant, a simplified faster OALU based on fixed mapping may be inserted.