bluuebunny/crossref_metadata_2025 huggingface dataset:
Fourier plane image processing using acousto-optic cells: a space-bandwidth analysis
Authors: Athale R.A. , Raj K. , Prather D.W. , Mait J. N.
Published: February 2023

Acousto-optic (AO) cells have been used to implement Fourier plane filtering in coherent optical processing systems. AO cells have large time-bandwidth products (>1000) and high frame rates (>10 kHz). The optical input to the AO cell at the Fourier plane consists of several plane waves travelling at different angles. The Bragg matching condition limits the input field of view of the AO cell in the Fourier plane. However, the finite acoustic wave vector spread, optical birefringence, and acoustic beam steering have been used to overcome this limitation. In this paper the relation between the SBW product of an image that can be processed by the AO cell and its time-bandwidth product is derived and experimentally verified. The AO cell in the Fourier plane is suitable for image morphology, and it is shown that the time-bandwidth product requirement for this application is independent of the size of the structuring element, enabling a comparatively large space-bandwidth input to be processed.
Turn-on transient statistics and dynamics in a multimode, short-cavity dye laser
Authors: Hodges S.E. , Munroe M. , Adkison D. , Gadomski W. , Raymer M.G.
Published: February 2023

The statistics of turn-on delay times for a longitudinal mode and the total intensity from a multimode, standing-wave, short-cavity dye laser are measured and compared with numerical simulations of a multimode theory of laser dynamics. The effects of coherent-wave mixing, the number of modes included in the simulation, and the frequency of the mode relative to the emission maximum on the delay-time statistics at various stages of the turn-on are discussed. Differences between the measurements and the theory for the average and standard deviation of the turn-on time are due to transitory modes that decay as a result of frequency-dependent losses and gain. In the system measured, the frequency dependence of the losses is principally due to a weak etalon formed by the gain medium. Associated with this phenomenon is a kink in the time evolution of the mode intensity that represents a transition in the dynamics from domination by independent growth of all modes to domination by competition between modes with differing net gains. This unequal competition increases the average and standard deviation of the mode turn-on time.
The role of optical amplifiers in video distribution systems
Authors: Joyce G. R. , Olshansky R.
Published: February 2023

Optical amplifiers are central to the increased use of fiber optics for video distribution. Conventional cable systems use an amplitude modulation format requiring highly linear DFB lasers of 50 dB CNR and -60 dBc of nonlinear distortion. Such lasers are of limited power, yielding an 8-10 dB optical power budget. However, erbium doped fiber power amplifiers (pumped by powerful 1480 nm and 980 nm diode lasers) improve this budget to better than 45 dB. Hence the role of fiber can be extended from feeder plant overlays to fiber-to-the-curb distribution systems. In digital video distribution systems the required 20 dB CNR allows the use of in-line fiber amplifiers. The optical power budget for a 16-QAM, 100 subcarrier, 400 video channel system increases from 25 dB to over 100 dB, allowing fiber-to-the-curb distribution for thousands of subscribers.
Adaptive optics for in-orbit aberration correction
Authors: Lawrence George N. , Scholl Marija S.
Published: February 2023

In the great space observatories (the Hubble, the SIRTF), a large-diameter telescope is used to gather the light and deliver it to several instruments. When the telescope entrance pupil is imaged on the secondary mirror of the imaging camera, the aberrations of these two components can be corrected. An adaptive component may be used for the secondary mirror of the high resolution imaging camera to correct the aberrations on the telescope primary mirror for varying amounts of symmetrical (spherical) and asymmetrical (astigmatism) aberration. The Hubble space telescope and the wide-field planetary camera optical system with a single adaptive component will be modeled by using glad to show the feasibility of the adaptive optics to in-orbit aberration correction.
Gain compression and temperature dependence of bistable InGaAsP 1.3 µm laser diodes
Authors: Barbosa Felipe Rudge , Caumo José R.
Published: February 2023

Bistable semiconductor laser diodes (BSLDs) have been investigated. Because they are Fabry-Perot oscillators, they can act as optical switches and amplifiers. In pulsed operation, duty cycle and temperature are shown to be equivalent parameters: critical bistability current for 10 kHz/10 µs pulses at 15°C is exactly the same as for 10 kHz/40 µs pulses at 10°C. Signal laser and BSLD spectra were investigated at different temperatures and injection currents by allowing tuning over 10 nm, the BSLD gain width. Hysteresis cycle width and bistability thresholds can be varied widely in the limited temperature range of 10°-30°C. This fact, combined with spectral tuning by temperature, provides an extremely versatile device. Amplification of 10 dB was obtained for -5 dBm signals (or less), and gain compression was observed for signals above 0 dBm, with saturation at +4 dBm.
Improved performance in ring diode lasers by controlled reflection feedback
Authors: Hohimer J.P. , Hadley G.R. , Craft D.C. , Vawter G.A.
Published: February 2023

We show that back reflection from the cleaved output waveguide termination in single-output Y-junction ring lasers has a deleterious effect on the light output by promoting lasing in the non-output-coupled direction. This effect is minimized by tilting the output waveguide about the ring axis by an angle θ. Devices (150-µm radius × 4-µm waveguide) with tilt angles θ = 0°, 5°, and 10° were fabricated. Tilting the laser by 10° increases the cw output power tenfold. Control of the reflection feedback to promote unidirectional lasing is also shown for dual-output ring lasers having separately contacted waveguide extensions that can be biased to control the reflection feedback or to act as photodetectors. Increasing the reflection feedback at one ring output alters the direction of ring lasing and affects the other ring output. Such controlled feedback will allow the development of unidirectional ring lasers.
Semiconductor lasers with regrown-lens-train unstable resonators
Authors: Paxton Alan H. , Schaus Christian F. , Srinivasan Swaminathan T.
Published: February 2023

We previously reported on the performance of wide-stripe semiconductor lasers with etched and regrown lens trains.1 Here, the theory and design rationale are presented. The modes are well approximated by the modes of a continuous unstable resonator with the index of refraction n = n0 + n2x2, where n2 is selected so that n is the index of refraction averaged over the longitudinal coordinate z. The radius of curvature of the wave fronts is essentially constant: R = 1 /η = (n0/2n2)1/2. The round-trip magnification is M = exp(2ηL), where L is the length of the laser. The efficiency and threshold current are derived as functions of η. We will describe a computer code that calculates the effective refractive index for various transverse structures. Measured properties of the modes are compared with the theory.
Applications of laser cooling and trapping to fundamental physics
Authors: Wieman C. , Cornell E. , Stephens M.
Published: February 2023

We are attempting to produce an atomic vapor that is so cold that the de Broglie wavelength is larger than the interparticle spacing. This is the condition needed to obtain Bose-Einstein condensation of a noninteracting gas. Our approach is to optically trap and cool atomic cesium and then load it into a purely magnetic trap for further cooling. In the course of this work we have investigated a number of magnetic traps and very low temperature collisions that are relevant to the success of this approach. In other work we are developing optical trapping techniques for the efficient collection of radioactive alkali isotopes. This work is aimed at measuring parity violation in these isotopes and thereby stringently testing the standard model of elementary particle physics. We have studied how to optimize the capture efficiency of atoms in an atomic vapor. We are currently developing cells that will allow the atoms to bounce off the walls until they are captured in the optical trap. The efficiency of this capture scheme will be discussed.
Stereopsis and the discrimination of rigidity
Authors: Stine William Wren , McMickell Montie
Published: February 2023

Isometric projections of three-dimensional, rigidly rotating polyhedra appear to deform under certain circumstances (Green, 1961, JEP). Relative to those that appear to be rigid, rigidly rotating polyhedra that appear to deform are more difficult to discriminate from ones that actually deform during rotation (Sparrow and Stine, 1990, ARVO). When a rigidly rotating polyhedron appears to deform, the introduction of retinal disparity can result in the perception of rigidity (Sparrow and Stine, 1987a, ARVO). We used polyhedra that were configured either to appear nonrigid or to appear rigid while rigidly rotating (see Sparrow and Stine, 1987b, 1988, OSA). These two classes of stimuli were then presented, one at a time, rotating rigidly (noise trials) or rotating with real deformations (signal + noise trials). Sensitivity to real deformations was less for polyhedra that were more likely to appear to deform than for those that were more likely to appear rigid (replicating Sparrow and Stine, 1990). Adding disparity to a stereo pair of polyhedra that appear to deform can increase sensitivity to real deformations. However, one stereo-blind subject showed no increase in sensitivity with disparity. Disparity allows the subject to see the rigidity of the polyhedron and then discriminate deforming from non-deforming stimuli.
Font “pop out” in text images
Authors: Klitz T.S. , Mansfield J. S. , Legge G. E.
Published: February 2023

What is the role of font information in reading? Words printed in a bold or italic font “pop out” from a page of text, suggesting that fonts are involved in global text page analysis. We have investigated the perceptual distinctiveness of different pairs of fonts. Text stimuli (subtending 17° × 13°) were rendered entirely with a single font or with a 6.5° × 6.5° target region in a different font from the remaining text. In each trial, the subject indicated whether the stimulus contained a target region. The decision reaction time was recorded. Every pairwise combination of AvantGarde, Bookman, Courier, Helvetica, Helvetica-Narrow, New Century Schoolbook, Palatino, and Times was tested. All seven subjects showed the same pattern of reaction times for detecting targets in each font combination. Further, the font pairs that gave the fastest reaction times also “popped out” in a second experiment in which the text was blurred (so that letter recognition was impossible). These results suggest that font analysis is a fast, global process that may use spatial frequencies lower than those critical for letter recognition.
Experiments on multiphoton pulsed holography in photorefractive crystals
Authors: Hafiz A. , Magnusson R.
Published: February 2023

Several samples of photorefractive crystals were used to study pulsed recording of holograms with application of the single-photon and two-photon techniques. A Q-switched Nd:YAG laser with 5 ns pulses was used. The single-photon holographic recording technique was applied to study the rise and decay times of the holograms as well as the lifetime as a function of cw readout with and without preconditioning (single-beam laser pulses, heat, and dc electric field) and strong white light source illumination. The two-photon recording technique was employed to study the phenomenon of optical fixing, the sensitivity of the recording medium, and the enhancement of the diffraction efficiency. Up to 32 single- and two-photon holograms were recorded in one spot in the photorefractive crystal. Definite enhancement of the efficiency by using the two-photon recording technique was found. The lifetime of the holograms was studied as a function of readout time up to 200 h. The holograms were found to decay even with the use of the two-photon recording technique. Diffraction efficiency measurements are also presented for und oped lithium niobate crystals as a function of input recording energies of the fundamental 532 nm recording beams and the 1064 nm bias beam.
Polarization and size dependence of third-order nonlinearities of metallic quantum dots embedded in a glass matrix
Authors: Yang Li , Becker Klaus , Brown Stanley W. , Haglund Richard F.
Published: February 2023

Au and Cu ions implanted in Corning 7940 glass and fused silica form metallic nanoclusters exhibiting a large third-order optical nonlinearity. The sign and magnitude of all components of χ(3) were measured for linearly and circularly polarized picosecond laser pulses at wavelengths near the surface plasmon resonance, by using both Z-scan and degenerate four wave mixing techniques. The data show that clusters over ~30 Å diameter retain bulk crystalline structure with a cubic class m3m symmetry. For smaller clusters χ(3) has isotropic symmetry. The nonlinear index of refraction is size dependent for clusters with crystalline structure; for the smaller clusters, the size dependence is not so apparent. Detailed analysis of the results shows that the main contribution to χ(3) arises from hot electrons and interband transitions.
Bistability and chaos in a Nd:YLF laser with cavity feedback
Authors: Zhu Jianqiang , Chen Shaohe , Deng Ximing
Published: February 2023

Chaotic behavior has been studied in recent years. Numerical results and experimental findings in semiconductor lasers with frequency selective feedback caused chaotic emission. In our single longitudinal mode Nd:YLF laser system, we use a Fabry-Perot interferometer to select the frequency, and another Fabry-Perot interferometer is situated between the facet of the active medium and output mirror. Therefore the resonator is a compound cavity. We advance the mathematical model based on internal feedback, phase modulation, and frequency chirping. Numerical simulation indicates that the output intensity is bistable. Furthermore, modulating the feedback parameters causes chaos. In our experiment, we observe the bistability and instability of the intensity output. By reducing feedback, we obtain stable output.
Super-Gaussian output from a cw-CO2 laser by using a graded phase mirror resonator
Authors: Van Neste R. , Lachance R. L. , Paré C. , Belanger P.-A.
Published: February 2023

We have mirror for a resonator having a specified output. 1,2 We have shown that certain optical resonators can have a fundamental mode of a stable type with a large beam waist and, at the same time, higher-order modes with large losses. The design of highly discriminating laser resonators is thus possible. We now present some experimental results for such a custom output laser device. The performances of two resonators have been compared. The graded-phase feedback mirrors are differently designed in order to provide two different super-Gaussian output beams with the following amplitude profiles: exp[−(r/2.5)2] and exp[−(r/3.2)6], where r is the transverse circular coordinate measured in millimeters. The first mirror is of course spherical, and the resonator is semiconfocal. The gain medium is a cw-CO2 circular discharge section of 18 mm of diameter. The maximum monomode power output for the conventional spherical resonator is 5 W. With the graded-phase mirror, increases of monomode power output of 25% have been measured. These observations are in close agreement with theoretical calculations of the efficiency of these resonators, taking into account the saturation. Beam profiles in the near field and far field have been measured and are presented.
Bandwidth effects on Brillouin enhanced four-wave mixing
Authors: Kuo Y. S. , McIver J. K.
Published: February 2023

Brillouin enhanced four-wave mixing (BEFWM) is a judicious combination of SBS and FWM processes. Very high phase conjugate reflectivity (>106) has been reported. Various conditions have been presented that lead to these high reflectivities, but all those discussions are based on a single mode laser. Here we report the experimental results of BEFWM with a multimode laser. The laser mode spacing is 0.15 GHz, which is larger than the linewidth of the acoustic phonon (0.1 GHz), so we can neglect the gratings that are not resonant with the acoustic frequency. We observed that the phase conjugate reflectivity is smaller for the multimode pump. Assume there is no coupling between modes through BEFWM and each mode interacts with the nonlinear medium independently. It has been shown that the reflectivity will decrease as the input pump power decreases. Thus the reflectivity of a single mode pump is higher than the resultant reflectivity from a multimode pump. Further examination of the temporal profiles of the probe and phase conjugate pulses in the multimode case shows that the pulse modulation depth is decreased in the phase conjugate pulse.
Two-photon absorption from the real Gaussian field
Authors: Elliott Daniel S. , Chen Ce
Published: February 2023

We have measured absorption spectra for Doppler-free two-photon absorption from a laser field characterized by strong amplitude fluctuations. This field, known as the real Gaussian field, is generated by randomly modulating the amplitude of the output of a cw stabilized dye laser. The absorption rate from this field is enhanced over that from a field whose intensity is nonvarying and of the same average value. When the laser bandwidth is very large, the absorption spectrum is limited, not by the laser width, but by the width of the atomic resonance. Our measurements are in excellent agreement with calculated spectra.
Femtosecond solitary wave
Authors: Potasek M. J. , Fang J. M.
Published: February 2023

We obtained, by using the Painleve method, the bright solitary wave solution to an extended nonlinear Schrodinger equation, which models the propagation of ultrashort pulses, and found that a quadruple clad fiber is needed to propagate this solitary wave. The intensity of this solitary wave depends on the ratio of the third-order derivative of the propagation constant (β3) and various higher order nonlinear (shock) terms coefficients. Since the higher order nonlinear coefficients are positive in optical fibers, we conclude that a negative β3 is needed for this solitary wave and only a quadruple clad fiber is possible. And in addition, we required the wavelength to be >1.45 μm. This is in contrast to the soliton in the nonlinear Schrödinger equation, where a negative β2, (group velocity dispersion) is needed. We also used a Gaussian approximation to evaluate the higher order nonlinear coefficients. The calculation indicated that these coefficients can be comparable to the other nonlinear terms (e.g., self phase modulation) when the pulse width is as short as 10 fs. These results may affect very high data rate systems.
Reflection from dephased index and gain gratings
Authors: Cardimona D. A. , Sharma M. P. , Kovanis Vassilios , Gavrielides A.
Published: February 2023

Modern crystal-growing techniques allow nearly any imaginable heterostructure to be grown. We are interested here in a periodic Bragg reflector in which there exists both an index-of-refraction grating as well as a gain grating. Unlike in past studies, however, we will investigate the effects due to any phase shift that might exist between these two gratings. For example, we can let the index n(z) and the gain g(z) be harmonic functions of z, as n(z) = n + n1cos2β0z and g(z) =g + g1cos(2β0z + ϕ), with ϕ being the phase difference between the functions. We then proceed with a normal coupled-wave analysis to calculate the reflection coefficient as a function of the detuning between the incident field frequency and the grating frequencies for various phase differences.
Ultrasensitive detection of single DNA molecules
Authors: Castro Alonso , Fairfield Frederic , Shera Brooks
Published: February 2023

We report on the detection of single lambda DNA molecules in flowing TBE buffer. DNA molecules at 10−14 M bound the fluorescent dye ethidium bromide at 10−10 M and were detected by using our recently developed technique for single molecule detection. This technique involves repetitive excitation of individual fluorophores with a frequency-doubled Nd:YAG laser, fluorescence detection with a microchannel-plate photo-multiplier based time-correlated single-photon counter, and signal processing with time-gated discrimination electronics. This detection takes 50 ms in a sample volume of 3.5 pL through which the DNA molecules pass at a rate of about 1 per second. The fluorescence lifetime of ethidium bromide increases from 1 to 24 ns when it becomes intercalated in DNA. To ensure that only DNA molecules were detected, we set a time window from 5 to 10 ns after the arrival of the laser pulse, thus rejecting both prompt scattering and fluorescence from free EtdBr molecules. The present method is at least 1000 times as sensitive as current flow cytometry methods. Quantitation of the fluorescence intensity will allow us to determine the lengths of individual DNA molecules, which can lead to the development of separation and size sorting techniques that are much faster than present methods.
Strong photosensitive phase gratings in optical fibers
Authors: Mizrahi Victor , Sipe John E.
Published: February 2023

With the ability to directly write phase gratings whose peak refractive index modulation exceeds 10−3 in the cores of optical fibers, interesting effects are observed. These refractive index modulations begin to approach the core-cladding index difference of the fiber. We present data taken on the wavelength dependent transmission, as well as reflection, of such strong fiber gratings. A comparison is made with calculations based on solving the coupled wave equations, which take into account possible coupling to radiation modes. It is found that the slowly varying (in space) contribution to the refractive index is essential in order to account for the detailed structure that is observed.
Optical parallel-access read/write shared memory based on photorefractive crystals
Authors: Li Kuang-Yu , Jenkins B. Keith , Waterson Clare
Published: February 2023

A shared memory computer model comprises a set of processing elements, an interconnection network, and a shared memory that consists of a set of memory modules. In this model, each processing element has random access to any memory module (MM), and by means of memory interleaving several MMs can be addressed at the same time. Thus high bandwidth data transfer to and from memory is provided. We propose a novel optical implementation of a shared memory that uses a single photorefractive crystal and can be used as the set of MMs in a shared memory computer. A complete instruction set for its memory access consists of four operations, i.e., read, write, erase, and refresh. In this implementation, two arrays of coherent but mutually incoherent sources are used and permit incoherent/coherent double angular multiplexing of data in the crystal. For selective erase (utilizing a row-controllable π-phase shift plate) or refresh, both source arrays are used simultaneously and, together with a nonlinear feedback arrangement utilizing a spatial light modulator, permit regeneration of the stored signal levels. These source arrays also permit any of the four instructions to be applied to any MM, independent of (and simultaneously with) instructions to other MMs. Details of the system design and preliminary experimental results are presented.
Computer generated holography for digital storage using sparse data words: capacity and error tolerance
Authors: Neifeld Mark A.
Published: February 2023

Fourier transform holography offers potential benefits for the storage of digital data, including high speed retrieval, reduced alignment constraints, and a high degree of media defect tolerance. Computer generated holography (CGH) provides a means through which holographic storage may be realized by using binary media such as conventional optical disks and tape. The encoding cost for such a scheme as measured by the area overhead η
A
, the ratio of the number of hologram pixels to the number of information bits however, is quite high as compared with other methods of error correction encoding. When encoding a binary data word of length N that contains M ones and N – M zeros, we expect that for a fixed encoding cost, the reconstruction quality will decrease as M approaches N. This intuitive notion is verified in simulation. In this paper we will investigate the use of sparse data words (i.e., M « N) for holographic storage. It is found that encoding with a set of sparse words is preferred, from the perspectives of capacity and error tolerance, to other methods of improving reconstruction quality (e.g., increasing the superpixel size in Lee CGH). Sparse data words will also be investigated for other algorithms, such as direct binary search. Simulation results will be compared with optical reconstructions in order to characterize the effects of system imperfections, and other methods that provide some respite from the large capacity cost of CGH will also be presented.
Thermally stable polyimide nonlinear optical materials and waveguide devices
Authors: Van Eck T. E. , Girton D. G. , Valley J. F. , Culbert D. L. , Ermer S. , Stiller M. A. , Ticknor A. J. , Lipscomb G. F. , Lytel R.
Published: February 2023

Highly integrated optical interconnect networks offer performance gains in electronic systems, but to be used by system manufacturers, the optical technology must be stable at the high temperatures experienced by electronic systems during operation and assembly. To address this requirement, we have developed polyimide-based guest/host materials that have good electro-optic performance and are stable at high temperatures. One promising material consists of Hitachi LQ-2200 as the polyimide host and the laser dye DCM as the guest. This material has been used to fabricate integrated optic devices on silicon substrates, spin-coating the polyimide waveguide layers, defining channel waveguides by photobleaching, and poling at fields as high as 250 V/μm.
Doppleron-catalyzed Bragg resonances in atom optics
Authors: Glasgow S. , Meystre P. , Wilkens N.
Published: February 2023

Effective atomic beam splitters providing large scattering angles are central to atom optics and atom interferometry. Their most common optical realization relies on first-order Bragg scattering, which generates a splitting of the atomic wave function in momentum space. For typical atomic beam velocities of the order of 100 m/s, 2ħk produces very small scattering angles. Higher-order Bragg scattering is of questionable practicality, because of the need for atom–field interaction times that scale exponentially with the scattering order. Attempts at solving this problem include the introduction of multiple laser beams, the use of three-level transition schemes, and the application of velocity-tuned, or Doppleron, resonances. We present a novel scheme that uses a Doppleron resonance as a catalyst to speed up a high-order Bragg resonance by orders of magnitude. This effect occurs when the atom–field frequency detuning is such that the Bragg resonance and the Doppleron resonance become degenerate. Alternatively, in the band-theoretical description of the near-resonant Kapitza–Dirac effect, the Doppleron resonance is required to occur either at the center or at the boundary of the first Brillouin zone.
Nonexponential and non-ohmic thermal erasure of χ(2) gratings in borosilicate glass
Authors: Driscoll T. J. , Lawandy N. M.
Published: February 2023

The mechanism by which a semipermanent effective χ(2) is encoded in centrosymmetric glass materials has remained a mystery for nearly a decade. It has been determined that the observed high conversion efficiencies result from a permanent, quasi-phase matching χ(2) grating established by a χ(3) mediated interaction with a frozen-in alternating dc field. We conducted thermal erasure studies of χ(2) gratings optically encoded in bulk samples of a high-barium low-alkali borosilicate glass (SK5, Schott Corp.) to determine the energy of trap sites responsible for the large fields (106 V/m). Q-switched mode-locked pulses at 1.064 μm and 532 nm were used to create effective χ(2) values of ~10–16 V/m in 1 cm thick samples. The thermal erasure rate of the χ(2) gratings, heated at 510,530,540, and 556 K, were dependent upon the initial grating amplitude indicative of a non-ohmic relaxation. In addition, the thermal decay of the gratings proved to be nonexponential and led to a value of a 1.9 ± 0.2 eV activation energy for the process at short times. Since only trace amounts of alkali metal ions are in the glass, the decay of the internal fields is likely to be due to electrons and or holes rather than ion migration. The nonexponential erasure behavior is addressed in terms of a dispersive transport mechanism for the thermally activated carriers.
Hue and saturation matching of the Bezold-Brucke phenomenon: the effect of equiluminant surrounds
Authors: Smith Vivianne C. , Pokorny Joel
Published: February 2023

In the majority of studies of the Bezold–Brucke phenomenon, the observers have matched spectral stimuli of disparate luminance in hue by a wavelength adjustment. We used an asymmetric matching technique to match stimuli of disparate luminance in hue and saturation. We used a PIXAR imaging system to generate 28 equiluminant (110 effective td) colors on a Sony monitor. Two rectangular stimuli (1.3° × 2°) were presented, one to each eye, in a haploscope. One stimulus was reduced in luminance by placing a 1-log-unit filter before one eye. The observer adjusted the hue and saturation of the brighter stimulus until the two patches looked chromatically identical, although of different brightness (as if a mesh curtain obscured the dimmer side). One match per color was repeated on three separate days. The entire experiment was performed with a dark surround and with an equiluminant surround. With a dark surround, the matched colors were set redder or greener, consistent with the Bezold–Brucke phenomenon for spectral colors. Additionally the saturation was reduced for reds and greens. With an equiluminant surround, only desaturation was required.
Optoelectronically implemented three-layer neural network for pattern recognition
Authors: Mu Guogang , Sun Ying , Zhang Yanxin , Yang Xiangping
Published: February 2023

A three-layer optoelectronic neural network for recognizing multiplex 3-D objects from arbitrary perspective views is demonstrated. Every kind of object is transformed into its feature codes and then classified by an associative memory of the codes. The experimental system is composed of two stages of different neural networks. The first network is implemented optically, and a bank of SDF filters are used as the interconnection weights. The optical system performs a hetero-association that encodes the projective images into a set of codes. Four kinds of aircraft are chosen as the examples, and 252 training images, which are obtained from different perspective views, are selected for each object. The four kinds of aircraft include airliner, fighter, bomber, and rocket. The experimental results show that the system can recognize correctly most of the projective images, including those outside the training set and partially hidden.
Parametric modeling of lenslet-array optical interconnections
Authors: Wiley D. J. , Glaser I. , Jenkins B. K. , Sawchuk A. A.
Published: February 2023

We describe a parametric model for simulation of an experimental lenslet-array processor. The model parameters succintly quantify the performance of the optical system and are estimated from experimental data. The parametric model specifically examines nonuniformity, nonlinearity, local (physically adjacent) element cross talk, global (not physically adjacent) element cross talk, and time-variation of output. The parameters can be set to yield ideal performance or can approximate the experimental optical system. Characterization data from a previously described experimental lenslet-array optical neural network was used in an analytical and numerical best-fit estimation of the parameters. In particular, we consider the results of an optical interconnection as an overdetermined linear system of equations, with the model parameters serving as unknowns. A linear least-squares numerical procedure then yields minimum-error estimates of the parameters of the model. The errors of the model and the validity of underlying assumptions are examined. Additional techniques of optical processor characterization are described. Suggestions for improving the accuracy and increasing the level of detail of the model follow. Generalization of the model to other optical systems is proposed.
Optical oversampled analog-to-digital conversion
Authors: Shoop Barry L. , Goodman Joseph W.
Published: February 2023

Previously,1 we introduced a new method of optical analog-to-digital conversion based on oversampling and error diffusion coding that offers the potential to extend resolution and conversion rates beyond that currently possible with other electronic or optical converters. In this new approach, the analog input signal is first optically sampled at a rate much greater than the Nyquist frequency and is then quantized by a modulator that incorporates one-bit quantizers and linear filters in a negative feedback architecture for the purpose of reducing in-band quantization noise. The output of the modulator is subsequently processed by a digital decimation filter, which removes the out-of-band noise and generates a high resolution digital approximation to the analog input signal at the signal's Nyquist rate. In this paper, we present experimental results from the first demonstration of an optical first-order noninterferometric modulator and discuss both spatial and temporal extensions of this optical error diffusion technique to multidimensional applications.
Thermal lensing in end-pumped laser rods when pumped by dual pulse sequences
Authors: Farrukh U. O. , Clayton M. F. , Brockman P.
Published: February 2023

A temperature distribution model for solid-state laser rods has been developed. A modification was made to consider the possibility of a source with a time-dependent pulse profile. Uneven heating of a laser rod may result in a distortion or defocusing of the laser beam. The temperature distribution model based on an eigenfunction expansion scheme was used in estimating thermal lensing in laser rods.1 An analysis was performed, and data will be presented for temperature distribution and thermal lensing in end-pumped rods. The rods were considered to be pumped by a series of pulses with Gaussian time profiles.
Semiconductor laser gyroscope
Authors: Pulaski P. , Diels J. C.
Published: February 2023

A laser gyroscope is a rotation sensing device. As the laser is rotated the two counterpropagating pulses in the cavity develop a frequency shift between them proportional to the rotation rate. For values of the rotation rate below a certain cutoff the pulses can lock to the same frequency, making the gyroscope ineffective. This lock-in phenomenon can be caused by backscattered radiation from one pulse (off the acousto-optic modulator, diode, etc.), which is coupled into the counterpropagating pulse. This coupling falls off exponentially as a function of the distance from the backscattering element. Therefore to minimize this coupling one can design a laser for which the pulse crossings are far from the cavity elements. This can be achieved by modulating the diode at twice the cavity round-trip rate (generating two pulses in the cavity) and by simultaneously modulating the acousto-optic modulator (essentially an optical gate) at three times the cavity rate.
Stationary nonlinear optical vortices
Authors: Swartzlander G. A. , Law C. T.
Published: February 2023

Stationary nonlinear propagation has been known to exist in slab waveguides, but not in bulk media. We have discovered that a stationary dark nonlinear wave does exist, and we will present our experimental and numerical measurements. This mode occurs in defocusing type nonlinear media and appears as an optical vortex, i.e., a black spot around which the phase varies by 2π. The nonlinear Schrödinger equation accounts for this phenomenon and was actually first described by Ginzburg and Pitaevskii (1958) in the context of superfluidity.
Propagation of fundamental and second harmonic beams in square law media
Authors: Pliszka Pawel , Banerjee Partha P.
Published: February 2023

Using parallel computers, we numerically study the propagation of beams in a quadratically nonlinear medium with a square law transverse distribution of the index of refraction, as in a graded index optical fiber. A symmetrized split-step beam propagation method is used to solve the coupled differential equations in the paraxial approximation. We show that in the range of moderate intensities, a periodic solution for the fundamental beam resulting from the superposition of many linear modes is only weakly perturbed. The second harmonic transverse profile, however, is generally nonperiodic and usually exhibits a ring structure. The single-mode solution becomes generally unstable, and periodic changes of the transverse intensity profile emerge.
Quantitative laser-induced fluorescence measurements in plasmas and flames
Authors: Jeffries Jay B.
Published: February 2023

Absolute concentration measurements of trace species using laser-induced fluorescence provide a sensitive test of the chemical mechanism of reactive processes. These absolute measurements require spectroscopic data for the measured species, knowledge of the fluorescence quantum yield for the specific excited state of that species, a measurement of the gas temperature of the process, and a calibration of the sensitivity of the optical collection and detection. Demonstration measurements of LIF absolute concentrations of OH and NO in a low pressure air flame and OH in a diamond CVD plasma are described. Each of these measurements relies on a different calibration technique, and the advantages of each of these methods are discussed. Direct and indirect determinations of the quantum yield are used, and the difficulties of these measurements are considered. The care required for spatially correlated gas temperature determination is elucidated.
Analysis of flame properties using Fourier-transform (FT) spectroscopy
Authors: Barts S. A. , Faust C. M. , Sausa R. C. , Miziolek A. W.
Published: February 2023

Fourier-transform (FT) spectroscopy is used to determine the concentrations and temperature profiles of different species in 20-Torr flames. Some of the species that have been analyzed are CO in a C2H4/O2/Ar flame and NO and N2O in a H2/N2O/Ar flame. Temperature profiles are calculated by using Boltzmann rotational distributions of these species. The concentration profiles are determined by two different methods. In method one, the absolute concentrations are determined by measuring the integrated absorbance of a vibrational band. In method two, the relative concentrations are determined by measuring the intensity of the rotational line that is least sensitive to temperature change. Species such as CO are more difficult to measure since they are combustion products that diffuse throughout the chamber, resulting in absorption due to both hot and cold gases.
Fabrication of nanometer linewidth structures in Si
Authors: Chu An-Shyang , Zaidi Saleen H. , Torres A. B. , Brueck S. R. J. , Draper B. L.
Published: February 2023

Techniques for fabrication of large, uniform arrays of semiconductor structures with nanometer-scale dimensions are of great interest for investigating quantum size effects. We report on a simple technique for fabricating arrays of Si wires with transverse dimensions ≤ 10 nm. This technique takes advantage of the capabilities of optical interferometric lithography to produce very high spatial frequency gratings and the strongly directional KOH etching of Si. A <110> Si wafer is prepared with thin (50-nm) Si3N4 and standard photoresist (0.15 mm) layers. A submicrometer period grating is interferometrically exposed in the photoresist (0.2-1 mm pitch) by using a cw Ar-ion laser source (361 or 488 nm). Following resist development, the grating pattern is transferred into the Si3N4 by CF4 plasma etching. Large area patterns with ~500-1000 nm lines are readily produced. For lines aligned in the <110> direction, a 40% KOH solution provides a highly selective (500:1) wet etch that produces very high aspect ratio Si lines. The etch selectivity also serves to reduce any nonuniformities or edge roughness induced in the lithography and etching steps. At this stage, Si structures with widths of 30-100 nm and depths of 0.5- 1 mm are obtained. Finally, a controlled dry oxidation (~800°C) is used to further reduce the Si dimensions. Large areas of uniform nanometer scale structures, including Si wires isolated by SiO2 from the substrate, are produced. Photoluminescence and Raman scattering studies will be presented.
Multiphoton ionization studies of solvent effects in large molecular clusters
Authors: Zwier Timothy S. , Garrett Aaron W.
Published: February 2023

Resonant two-photon ionization time-of-flight mass spectrometric studies of the series of clusters C6H6−(H2O)
n
, C6H6−(CH3OH)
n
, and C6H6−(CH30H)
m
(H2O)
n
have been carried out via the S1←S0 transition of C6H6. Using a combination of rotational band contour analysis in the smaller clusters and vibronic level arguments in the larger clusters, we have been able to constrain the general structural features of these clusters. The comparison of the spectroscopy of C6H6−(H2O)
n
with that of C6H6(CH3OH)
n
shows strong similarities for clusters with n = 1 and n = 2 but significant differences for larger clusters. The picture of these clusters that is emerging places the solvent molecules in a hydrogen-bonded network that builds off one side of the benzene ring. Broadly classified, the structures fall into two classes involving either cyclic or chain-like hydrogen bonded clusters of solvent molecules. We argue that the differences between C6H6−(H2O)
n
and C6H6−(CH3OH)
n
clusters are a consequence of dangling O−H's in the water cluster, which are not present in the methanol cluster. Similar data on the mixed C6H6−(H2O)
m
(CH3OH)
n
clusters will also be presented.
Spectroscopy and excited state dynamics of the HNF (DNF) molecule
Authors: Dagdigian Paul J. , Chen Jing
Published: February 2023

Laser fluorescence excitation of the HNF molecule, and its isotopomer DNF, have been detected in the

A
˜

2

A
′

−

χ
˜

2

A
″

band system for the F + HN3 (DN3) reaction. This observation indicates this reaction forms HNF + N2, in addition to the well known HF + N3 products. To our knowledge this is the first report of laser fluorescence detection of this molecule, for which the ground and excited electronic states form a Renner–Teller pair with bent equilibrium internuclear geometries. The K structure of the bands is observed to become simpler with increasing bending excitation, reflecting the reduction in the highest observable K′ levels. Decay lifetimes were measured for a variety of excited levels. The decay rate was observed to increase abruptly at an energy 23,800 ± 500 cm−1 above the

HNF

(

χ
˜

)

zero-point level. This threshold is tentatively assigned to the onset of a predissociation channel. The excited state dynamics of HNF (DNF) will be compared with the dynamics of the well-studied Renner–Teller molecules HCO and HNO.
Nitrogen inversion mode in substituted anilines
Authors: Yan Shuxin , Spangler Lee H.
Published: February 2023

Jet cooled fluorescence exitation spectra for several substituted anilines are presented. The substituent effect on inversion barrier is discussed.
Cone contributions to motion detection and identification
Authors: Gegenfurtner Karl R. , Hawken Michael J.
Published: February 2023

We have measured thresholds for detection and identification of a vertically oriented sinewave grating vignetted by a two-dimensional spatial Gaussian window. The stimulus appeared as a contrast-reversing grating to the left or to the right of fixation on the horizontal meridian and then moved either towards or away from the fovea. The temporal frequencies of the contrast reversing and drifting gratings were identical. The color of the grating was modulated along different directions in color space around an equal energy white, thus leading to different input contrasts for the L- and M-cones. This allowed us to measure complete detection and identification contours in cone contrast space (Stromeyer, Eskew, Ryu, and Kronauer, ARVO 1991). Under certain spatio-temporal conditions we find that sensitivity is particularly impaired with stimuli near the L-cone null direction. Furthermore, for stimuli having both L- and M-cone contrast sensitivity was determined primarily by the L-cones.
Recent advances in photorefractive fibers
Authors: Hesselink Lambertus
Published: February 2023

In this presentation we review recent advances in growth, evaluation, and application of photorefractive fibers for optical signal processing and data storage. Optical ferroelectric fibers are attractive alternatives to bulk photorefractives, because optical energy can be confined over longer interaction lengths, and fibers of good optical quality are easier to grow than bulk crystals, at least for certain morphologies. Since the material properties and the applications for which these fibers can be used are closely related, we will discuss both topics. Wave interactions in photorefractive fibers are discussed from a theoretical viewpoint, and applications, such as beam coupling in periodically poled fibers, stimulated back scattering in c-axis SBN fibers, and data storage in a-axis SBN fibers, including consideration of cross talk for multiplexed holograms are presented. The dependence of hologram cross talk on striations and other compositional variations in fibers is considered, and ways to overcome these problems are discussed.
General analysis of dead zone effects in optical correlators
Authors: Woods C. D. , Gianino P. D.
Published: February 2023

Both analytical and computer calculations predict consistent correlator performance for devices implemented with spatial light modulators with transmissive and/or opaque dead zones. Input camera pixelation effects are discussed. Transmissive deadzone increases the noise by introducing a strong background pattern in the input plane and by allowing an input image to propagate through the filter to the correlation plane. For transmissive input plane SLM dead zone, a de block in the filter plane greatly reduces both transmitted image and speckle noise in the correlation plane. A filter reference image that is smaller than the input SLM must be used to eliminate a false correlation peak from the transparent dead-zone edge and the filter input edge.
Smart optical correlator for real-world applications
Authors: Kirsch James C. , Jones Brian K. , Thie Melissa W. , Gregory Don A.
Published: February 2023

Optical correlators have been proposed for many practical applications but have yet to make the transition from the laboratory to the real world. Two basic problems have inhibited the development of these correlators—sensitivity to target orientation and the state-of-the-art in spatial light modulator technology. The U.S. Army Missile Command has been involved in field testing optical correlators for several years. These tests reached a milestone in 1990 with the successful flight of an optical correlator guided missile against a cooperative target. The test program has not stopped with that success, however. A correlator capable of handling changes in target scale and orientation has been designed and is currently under construction. This correlator is based on LCTV spatial light modulators and a smart filtering system. The design of this correlator, its operating characteristics, and data taken by using this correlator will be discussed as part of this presentation.