bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced transmission through rough surfaces with an even profile
Authors: Gu Zu-Han , Dummer Richard S. , Maradudin Alexei A. , Mendez Eugenio R.
Published: February 2023

One of the most interesting phenomena associated with the scattering of light from a randomly rough surface is that of enhanced backscattering. Enhanced backscattering refers to the presence of a well-defined peak in the angular distribution of the intensity of the incoherent component of the light scattered from such a surface. This peak occurs in the retroreflection direction. Not all of the manifestations of weak localization in the interaction of light with random metallic grating are in reflection. It was recently shown that the angular distribution of the intensity of the incoherent component of polarized light transmitted through a thin metal film in vacuum, whose illuminated surface is randomly rough and whose back surface is planar, displays a well-defined peak in the transmission direction that is directly opposite to the direction of specular reflection of the incident light (the antispecular direction).1 The enhanced transmission effect, which is manifested as a narrow peak in the angular distribution of the intensity of diffuse scattered light in the antispecular direction, has recently been investigated experimentally. This peak is an analogue of enhanced backscattering in the transmission of light through a randomly rough surface. Several surfaces were fabricated and tested, such as one-dimensional randomly rough metal and dielectric surfaces with an even profile. A fully automatic, bidirectional reflectometer was used to measure the enhanced transmission under illumination of a He-Ne laser. The results are compared with numerical calculations.
Vacuum UV Fourier-transform spectrometer
Authors: Parkinson W. H. , Thorne A. P. , Smith Peter L. , Yoshino K.
Published: February 2023

To avoid distortions in measurements of spectral-line profiles and photoabsorption cross sections, spectrographs or spectrometers that have instrument widths much narrower than the line widths must be used. For studies of the Doppler-limited, vacuum-ultraviolet (VUV) spectra of atoms and molecules at 300 K or less, this means that resolving powers of about 106 are required. The first Fourier-transform spectrometer (FTS) capable of such resolving power at wavelengths in the 220-180 nm range has been developed and demonstrated by Thorne et al.1 It was equipped with a beam splitter made from optically contacted fused quartz. We have recently modified this FTS by using a similar beam splitter made from a MgF2 crystal and have, thus, extended the low-wavelength limit for such high-resolution spectroscopy. The performance of the VUV FTS will be discussed, and applications to the VUV spectroscopy of atmospheric molecules such as O2 and NO will be presented.
Improved correlation discrimination when using a joint-transform correlator
Authors: Alam Md. Showkat-Ul , Awwal Abdul Ahad S. , Karim Mohammad A.
Published: February 2023

The joint-Fourier-transform-based correlator is capable of real-time matching and tracking operations without the fabrication of a complex filter. However, its autocorrelation peaks are relatively weak when compared to that of the de peak. Such problems are now being handled by suppressing the de peaks by means of optical disks.1,2 In this work, we propose to solve this same problem and at the same time further increase the autocorrelation peaks by carefully preprocessing the reference objects. We show that when the reference amplitude is suitably thresholded, the resulting autocorrelation peak heights significantly increase while the de peaks can be significantly suppressed. We further show that the ratio of the autocorrelation peak value to the de peak value can be increased by suitably optimizing the threshold used in the preprocessing of the reference.
Acousto-optic tunable filter for spectropolarimetry application
Authors: Chang I. C.
Published: February 2023

The acousto-optic tunable filter (AOTF) is an all-solid-state, electronically tuned optical filter that operates on the principle of acousto-optic diffraction in an anisotropic medium. The basic theory of the AOTF and its various applications have been extensively reported.1 Most of the previous studies have been directed at nonimaging systems. Recently, there has been considerable interest in using AOTF in a spectropolarimeter for remote sensing of earth and planetary resources. To meet the system requirement, a frequency-domain analysis2 was performed on the spectral polarization and imaging characteristics of the AOTF. Because of the finite geometry of the acousto-optic interaction, the AOTF suffers performance degradations. It is possible to significantly improve the filter performance through the use of apodized transducers. Several different choices of weighting functions and implementation techniques were investigated. Numerical calculations based on the new theoretical work have resulted in optimized AOTF designs with minimized degradations.
Sensitivity of a nonlinear joint-transform correlator
Authors: Javidi Bahram , Tang Qing
Published: February 2023

Theoretical and experimental studies have shown that the nonlinear joint-transform correlator (JTC) can produce reasonably good correlation performance.1,2 The nonlinear JTC uses nonlinearity at the Fourier plane to nonlinearly transform the Fourier-transform interference intensity. It has been shown that the compression type of nonlinear, joint-transform correlator provides higher peak intensity, larger peak-to-sidelobe ratio, narrower correlation width, and better cross-correlation sensitivity than does the classical correlator. In this paper, we provide an experimental investigation of nonlinear JTC sensitivity in the presence of the rotational and scaling changes of the input signal. Experiments determine the correlation peak intensity and peak-to-sidelobe ratio for various degrees of the nonlinearity at the Fourier plane. The sensitivity of the nonlinear JTC for different scaling and rotational distortion of the input image is determined for each nonlinear transformation. The experiments are performed in the presence of the input scene noise. The spatial light modulator (SLM) used at the Fourier plane is a Hughes liquid-crystal light valve operating in different degrees of the nonlinear mode, as determined by adjusting parameters such as the bias voltage, and input frequency. The nonlinear JTC tests indicate that as the severity of the nonlinear transformation of the joint power spectrum increases, the peak intensity increases, the correlation peak-to-sidelobe ratio increases, and the correlation width decreases. On the other hand, the nonlinear JTC is more sensitive to the input plane rotational and scaling changes than is with the linear JTC. The sensitivity of the nonlinear JTC depends on the severity of the nonlinear transformation that is used at the Fourier plane.
Estimation of object location in optical scattering experiments
Authors: Tsihrintzis George A. , Devaney Anthony J. , Maleki Mohammad
Published: February 2023

We consider a set of scattering experiments in which a known scattering object is embedded in some known background medium, and is interrogated with monochromatic plane wave fields. The goal of the experiments is estimate the location of the object by means of noisy measurements of the magnitude of the wave fields transmitted by the object. These measurements are taken along straight lines that are outside the object's support volume and perpendicular to the direction of propagation of the incident waves. We employ maximum-likelihood estimation to address the problem, and we compute the log-likelihood function for additive, zero-mean, white Gaussian noise. We show that an image of this likelihood function can be generated directly from the measured intensity distributions by means of a filtered backpropagation algorithm.1 This image closely approximates the exact log-likelihood function2 generated from complete data (i.e., both the magnitude and the phase of the transmitted wave fields) as long as the measurements are performed sufficiently far from the scattering object. The Cramer-Rao bound for the estimation error is computed to measure the performance of the algorithm, and a number of examples employing both synthetic and experimental data are presented.
Localized wave solutions in optical fiber waveguides
Authors: Vengsarkar A. M. , Besieris I. M. , Shaarawi A. M. , Ziolkowski R. W.
Published: February 2023

A novel bidirectional method for the synthesis of highly directional pulses and beams in free space and in complex environments (e.g., waveguides, absorbing media, and plasmas) has been proposed recently.1 Within the framework of this approach, exact solutions to the wave equation are decomposed into bidirectional, multiplicatively backward and forward, plane waves traveling along a preferred direction z, (e.g., a guide axis). By varying the free parameters associated with the bidirectional source modulation spectrum, localized slowly decaying pulses that move predominantly in the positive z direction can be synthesized. The bidirectional decomposition method has been applied to optical fibers, and the feasibility of synthesizing solutions that can propagate along such structures with only local variations has been demonstrated. Localized wave solutions corresponding to three distinct types of source modulation spectra will be discussed. Distances over which such pulses remain almost nondecaying have been found to be on the order of 1000 km. The bidirectional method of wave synthesis leads to solutions that are capable of countering the dispersive effects introduced by the guiding structure, without invoking the need for nonlinear effects, as in the case of soliton fibers. The feasibility of practical implementation of appropriate source spectra, as well as future research directions, will be discussed.
Basic parameters for Cr-, Tm-, Ho:YAG 2.1-μm lasers
Authors: Bowman S. R. , Winings M. J. , Searles S. , Feldman B. J.
Published: February 2023

Laser emission at 2.1 μm from holmium-doped YAG at liquid-nitrogen temperatures was first reported in 1965.1 Recent performance improvements at room temperature using chromium and thulium sensitization have renewed interest in the practical application of this laser material. The potential efficiency, energy storage, and atmospheric and silica fiber transmission properties of this laser, combined with its eye-safe wavelength, have encouraged research into military, medical, materials-processing, and remote-sensing applications. As an aid to the design of Cr-Tm-Ho:YAG laser systems, we have measured the basic laser parameters and spectral and thermal characteristics of a free-running, room-temperature, flashlamp-pumped Cr-Tm-Ho:YAG system. Birefringent tuning of this system revealed at least nine distinct low-threshold transitions. Simple analysis of the performance data yields the basic parameters of transition energy levels, emission, and absorption cross sections, saturation fluences, storage lifetime, and heat deposition. The dynamics of the chromium- and thulium-sensitized holmium laser are complicated and are not yet fully understood. Our progress toward understanding and modeling the temperature, concentration, and excitation dependence of the pumping efficiency and lifetime of the holmium laser system will also be reported.
Linear and second-order nonlinear-optical properties of side-chain and cross-linked polymers
Authors: Chen Y. M. , Rahman A. K. M. , Lee J. Y. , Takahashi T. , Mandal B. K. , Kumar J. , Tripathy S. K.
Published: February 2023

Polymers with polymethyl acrylate backbone and pendant nonlinear optical (NLO) side groups with azomethine linkage1 have been synthesized. The concentration of the NLO active moieties is varied by preparing copolymers in which the comonomer is methyl methacrylate. The thermal behavior of these polymers has been characterized by using differential scanning calorimetry. The linear optical properties, such as absorption and refractive index, have been measured. Thin-film slab waveguides of the polymer on glass and silicon/SiO2 substrates have been fabricated with losses less than 1 cm-1. Second-order nonlinear susceptibility (d33) of corona-poled films has been measured by second-harmonic generation from 1.06 μm laser radiation. The temporal stability of the induced second-order susceptibility has been investigated, and compared with the stability of cross-linkable2 polymer-host systems.
Ion-assisted deposition of graded-index silicon oxynitride coatings
Authors: Al-Jumaily G. A. , Gagliardi F. J. , Mizerka L. J. , Al-Jassim M. M. , Franz A.
Published: February 2023

There is an increasing interest in nitride and oxynitride coatings of silicon for optical and microelectronic applications. Silicon oxynitride has an index of refraction that can be varied between 2.1 and 1.45 by varying the oxygen-to-nitrogen ratio.1 The fabrication of graded-index optical components, such as graded index antireflection coatings and rugate filters, is an important application of this technology. The ability to tailor the index of refraction has been realized by applying of ion beams to the optical-coating deposition process. We have been able to deposit silicon oxynitride coatings with indices of refraction varying between 2.1 and 1.45. We will present results of optical, mechanical, and chemical characterizations and examples of applications for graded-index coatings in the deposition of graded-index antireflection coatings and rugate filters.
Analysis of transient diffraction efficiency of photrefractive crystal holograms
Authors: Song Q. W. , Banerjee P. P. , Liu J. J.
Published: February 2023

Starting from the differential equations of Kukhtarev et al.1, which describe the response of photorefractive materials, we apply the perturbation method to linearize these equations. Assuming two beams (one much stronger than the other) in the recording process, we estimate the dynamics of the formation of the refraction-index grating. Thereafter, with one of the beams shut off, we recalculate the decay of the grating profile. Results indicate a ringing behavior during the buildup process with a nonzero steady state for the "perturbed" refraction index. The (temporal) frequency of the oscillations and the buildup time constant depend on the applied electrical bias and the spatial period of the induced grating, as well as the physical parameters of the materials and the strengths of the illuminating fields. The decay process is also marked by oscillations, with the frequency and the decay time constant once again dependent on the above parameters. On the basis of the above information, we calculate the time dynamics of the normalized diffraction efficiency by means of the coupled-wave theory.
Conical Stokes emission in three-level systems as a coherent propagation effect
Authors: DiMarco Steven F. , Cantrell C. D. , Crenshaw M. E.
Published: February 2023

It is now known that conical emission in a two-level atomic system is a fundamental propagation effect brought about by the breakup of the exciting laser pulse into solitary waves.1 This report presents a semiclassical numerical calculation that extends this previous work by solving the optical Bloch and Maxwell equations for a three-level atomic vapor excited by laser fields of two different frequencies. The applied fields satisfy a two-photon resonance condition between the ground and final states and are slightly detuned from the intermediate state to enhance the nonlinear polarization.2 As the fields propagate, oscillations in the nonlinear polarization of the pump beam dominate the interaction and lead to the pump's breakup into solitary waves. The Stokes polarization, depending on the pump radiation, also experiences these oscillations. Because of the intensity-dependence of the refractive index, the solitary waves experience a curvature in the time-radius plane. This curvature manifests itself in the spectrum as a radial component of the wave vector at the Rabi frequency. The Stokes field, experiencing parametric breakup, displays a similar curvature. Spectral analysis reveals a radial component of the Stokes wave vector as well. This frequency-shifted off-axis radiation is identified as conical emission in the Stokes field.
Pulse reshaping and coherent sideband generation effects on multiple-photon excitation of polyatomic molecules
Authors: Garner Stephen , Cantrell C. D.
Published: February 2023

We use a semlclassical, effective-state approach to laser pulse propagation in a gas of polyatomic molecules. Our numerical model of multiple-photon excitation includes quasicontinuum transitions to calculate the effects of coherent propagation on multiple- photon absorption. The molecular model consists of a single ground state and several bands of discrete states, which are successively connected by means of electric-dipole transitions.1 This model correctly simulates some of the major characteristics of multiple- photon absorption, such as power threshold, fluence-dependent absorption, and complete population inversion at large fluences. As the pulse propagates, the Rabi oscillations induced in the lower-level states are encoded onto the pulse and create a series of peaks and troughs similar to those found in pulse propagation in two-level systems.2 Another coherent propagation effect that can change the excitation process is coherent sideband generation. Temporal distortions and the generation of new frequencies result in changes in the population distribution among the states, as well as changes in the total population transferred to the quasicontinuum. The effective increase in total population transfer by propagation effects is offset by the decrease in fluence. The resulting transfer of energy from the pulse to the molecule depends strongly on the initial characteristics of the pulse.
Standing magnetostatic wave modulator for optical communication
Authors: Butler John C. , Fisher Arthur D. , Kramer John J. , Lee John N.
Published: February 2023

Progress has been made on a guided-wave magneto-optical modulator that is needed for a proposed communication network. The proposed modulator will perturb the optical carrier to create both upshifted and downshifted components. The system, which is described elsewhere,1 can employ a standing forward volume magnetostatic wave (FVMSW) to generate the microwave subcarriers needed to multiplex analog and/or digital signals. Separate experiments demonstrated the collinear and antico'ilinear interaction of FVMSW and guided light in an yttrium-iron-garnet thin film at frequencies in the C-band. The collinear and anticollinear interaction passbands had some frequency overlap, which indicates that k-vector matching for multiple diffractions is possible. Prisms were used to couple the light in and out of the planar waveguide. The theory of standing FVMSW-optical interaction will be presented for both collinear and transverse device configurations, using various rare- earth iron-garnet films. Phase-matching conditions, FVMSW attenuation, and harmonic generation will also be discussed.
Critical flicker frequency to red targets on yellow backgrounds at different luminance levels across the temporal visual field of man
Authors: Raninen Antti , Iivanainen Antti , Rovamo Jyrki
Published: February 2023

When the number of ganglion cells stimulated at various retinal locations are kept constant by M-scaling deep-red targets on deep red backgrounds, then log CFF = 0.19 log F + 1.3, where F is luminous flux collected by ganglion-cell receptive-field centers and is calculated by multiplying photopic retinal illuminance by Ricco's area at each eccentricity. Thus, the Ferry–Porter law for red stimuli can be generalized across the visual field by replacing stimulus luminance by F (cf.1). Although red targets stimulated predominantly cones, rod intrusion was possible. Therefore, in the present study we measured CFF to red targets on yellow backgrounds as a function of eccentricity and retinal illuminance. Temporal modulation visible to cones was 30%. However, scotopic temporal modulation was only 1%, which is never visible to rods.2 We found that log CFF = 0.27 log F + 1.1 (r2 = 0.95). The slope is steeper than in our earlier study (see above) because as retinal illuminance decreased CFF to red targets on yellow backgrounds became progressively lower than CFF to red targets on red backgrounds. Thus, the contribution of rods to CFF increases with decreasing retinal illuminance, even for deep-red targets and backgrounds. Moreover, the Ferry–Porter law can be generalized across the visual field, even when flicker is made invisible to rods by using red targets on yellow backgrounds.
Design of codirectionally coupled waveguide filters using the Gel’fand–Levitan–Marchenko inverse-scattering technique
Authors: Winick Kim Allen
Published: February 2023

The power transfer between waveguides in a codirectional coupler depends on the interaction length, the coupling coefficient, and the wavelength.1 Since power transfer is wavelength dependent, these devices act as filters or switches. The filter response can be controlled by varying the coupling coefficient along the propagation direction. Since the coupling coefficient increases exponentially with waveguide separation, this variation may be realized by tapering the spacing between the guides. The filtering action of waveguide directional couplers is modeled by the following pair of first-order coupled mode equations.
Nonlinear-optical waveguides: on the figure of merit
Authors: El-Halafawy F. Z. , Abou-El-Enein A. A. , Saleh A. A.
Published: February 2023

A newly introduced term, "figure of merit" is designed, cast, and employed to both qualititively and quantititively investigate the propagation problems in nonlinear optical waveguides made of either AlGaAs or SiO2+GeO2. Three basic parameters are handled in such a design, namely, the optical confinement factor, the maximum bit rate, and the power-pulse-width square product.1,2 Dimensionless analysis is applied and the problem is investigated under wide ranges of sources, detectors, and waveguides. The dispersion characteristics of the guide are evaluated based on Sellmeier equations, which are employed along with the spectral loss characteristics to calculate the system bit-rate. The figure of merit and each controlling parameter possess monotonic correlations with either positive or negative correlation coefficients. Four dimensionless ratios affect the figure of merit: (1) the bit-rate and the bandwidth, (2) the bit-rate and its ultimate value, (3) the confinement factor, and (4) the power–pulse-width square product and Planck's constant.
The determination of thermal properties of dielectric coatings by means of photothermal surface displacement technique
Authors: Welsch E.
Published: February 2023

Pulsed-laser-induced damage of optical thin films, in general are initiated by the absorption of laser radiation within the film bulk or at the interfaces between the film layers itself or the substrate. In the nanosecond pulse region, a heat flow analysis demonstrates the importance of thermophysical parameters of both the thin film host and the substrate. Especially, the thermal conductivity often shows, caused by thin film micro-structure, a deviating behavior, of instance anisotropy and compared to the bulk extremely low values.1-3 We demonstrate the ingluence of thermal properties on the measurement of extremely low thin film absorption as well as their measurement by the help of the photothermal surface displacement technique.4,5 The experimental technique should be advantageously, because the measurement can be performed completely contactless, nondestructively and spatially high-resolved.
Equiluminance and minimal motion
Authors: Stromeyer Charles F. , Eskew Rhea T. , Kronauer Richard E.
Published: February 2023

Cavanagh et al.1, claim that the equiluminant point can be assessed by adjusting the luminance contrast of a counterphase, flickering chromatic grating to produce "minimal motion" when this grating is paired with a counterphase luminance grating in spatial–temporal quadrature phase. The contours of direction-identification thresholds in L′=ΔL/L, M′=ΔM/M cone space, measured with a 1 cpd moving grating on a 3500 td yellow field, show that luminance and spectrally opponent motion mechanisms are not orthogonal at velocities above 2°/s (2 Hz): a luminance grating (yellow-on-yellow) also stimulates the spectrally opponent motion mechanism, which becomes L-cone-dominated at these frequencies. Quadrature experiments show that the luminance and spectrally opponent mechanisms jointly contribute to motion when stimulated simultaneously. Thus, for the minimal-motion technique to assess the equiluminant point, it is necessary that the "luminance" pedestal grating be not simply a yellow-on-yellow variation, but rather it must be a vector in L′,M′ space that is parallel to the detection contour of the spectrally opponent motion. Such a vector does not stimulate the latter mechanism and does not contribute to "minimal motion." Thus, it is unlikely that the minimal-motion phenomenon determines equiluminance much above 2 Hz.
Appearance and chromaticity of white as a function of retinal illuminance
Authors: Sternheim Charles E. , Drum Bruce
Published: February 2023

The color-temperature range perceived as absolute white increases with retinal illuminance.1 This implies that the achromatic response of the visual system grows more rapidly than the chromatic response. We studied how the appearance and chromaticity of white changes with retinal illuminance by scaling the achromatic, yellow, and blue sensation components for test lights between 2985 and 9000 K at 0.33, 2.18, and 4.10 log trolands (log td). The foveal test field was 7° of visual angle and was unlimited in duration. After the sensation stabilized (2–5 s) the subject assigned a percentage value to each of the response categories. The total response always equaled 100%. Whenever 100% was assigned to the white category, the subject was forced to choose either yellow or blue. At 4.10 log td both observers showed similar "best whites" (5310 and 4881 K) and a narrow transition zone (1050 and 1450 K) from one chromatic-response category to the other. The relative amounts of yellow, blue, and white were also similar for the full range of color temperatures. One observer maintained a similar "best white" and transition zone at all retinal illuminances, whereas for the second observer the "best white" fell to lower color temperatures, and the transition zone broadened with decreasing illuminance. At 9000 K the percentage of blue was maximal at the intermediate illuminance level, and a similar response pattern was found at 2985 K for yellow. The loss of saturation from 2.18 log td to 4.10 log td is consistent with the results of Hurvich and Jameson and reinforces the notion that the achromatic response increases more rapidly in this range than the chromatic response. Our data suggest that the opposite is true at lower illuminances.
Discrimination between a smooth and jagged temporal edge
Authors: Cogan Alexander I.
Published: February 2023

When field luminance rises or falls quickly, the temporal course of the change must be difficult, if not impossible, for perception to follow. This proposition is formally rooted in the well-known studies of two-pulse interactions at threshold; it is supported by a study by Crawford that deals with spatially coextensive, suprathreshold luminance changes.1 The present experiment measured direction-reversal thresholds and assessed observers' sensitivities to a sharp alteration in the temporal course of a luminance change. Luminance was incremented or decremented uniformly over the entire extent of the field (7.5° diameter). The magnitude of change was constant at 75 cd/m2 (50% of base luminance). The rate of change was maximum with the steepest ramp (time: 6.6 ms), and it was at minimum with the shallowest ramp (time: 280 ms). The test stimulus was a "zigzag" produced by a ramp disfigured by a step in the opposite direction to that of the ramp; the step always occurred at the half-height of the ramp. by means of a 2AFC stair-case procedure, the magnitude of the step was varied until the observer could discriminate between a smooth ramp and a zigzag (about 79% correct rate): (1) With ramp time 20 ms or less, the mean magnitude of the reversal at threshold was 78.5 cd/m2. (2) As ramp time became longer than 40 ms, reversal thresholds quickly fell, to a minimum of 6 cd/m2. (3) Thresholds were usually sign-dependent (lower with negative-going ramps) but not with either the steepest or the shallowest ramp. Apparently, linear systems analysis can account for some, but not all, of these results.
New results in nonlinear matched filtering
Authors: Ersoy O. K. , Yoon Y. , Zimmerman D.
Published: February 2023

Nonlinear matched filters (NMFs) involve the transformation of the signal spectrum and the filter transfer function through pointwise nonlinearities before they are multiplied in the transform domain. Experimental and theoretical results indicate that NMFs have considerable potential to achieve high powers of discrimination and resolution, as well as large signal-to-noise ratios.1,2 A statistical analysis in the two-class recognition indicates that the performance coefficient of the NMF is at least four times as large as the performance coefficient of the classical matched filter. In terms of resolving nearby signals, there seems to be no limit to the achievable resolution. In this paper, the most recent theoretical and experimental results in nonlinear matched filtering are discussed.
Nonlinearities and interferences in multilayer thin films
Authors: Bovard Bertrand C.
Published: February 2023

Investigations of the behavior of multilayers made of nonlinear materials have usually been restricted to structures designed for their low-power performances.1 Fabry-Perot filters, narrow-band mirrors, and Fibonacci filters have been investigated, but in all cases their optical properties are only distorted at high power and do not converge toward any chosen sets of properties. Designing multilayers that meet specific spectral requirements at both low and high powers is more attractive and would open up a tremendous range of applications. A few steps have been made in this direction, and a technique has been devised that leads to linear and nonlinear refractive index profiles. I will present the basic idea behind this technique and illustrate its use. I have designed a filter that exhibits some specific properties at both low and high powers. I will use simulation to illustrate the path followed by the filter's optical properties as it goes from the low-power to the high-power state.
Theory of phase-conjugate oscillator applied to a phase-conjugate resonator
Authors: Lee Wun-Shung , Chi Sien , Saxena Ragini , Yeh Pochi
Published: February 2023

Optical resonators containing a phaseconjugate mirror (PCM) have been a subject of great interest, especially for cases in which the PCM is employed as an end mirror of a resonator cavity for intracavity aberration correction.1 Recent theoretical analysis indicates that the insertion of a PCM inside a ring-laser cavity results in a reduction of the lock-in threshold and reduces the imbalance between the amplitudes of the oppositely directed travelling waves.2 We have developed a general theory for nondegenerate oscillations in a phase-conjugate oscillator (PCO) that consists of a Fabry-Perot cavity with a PCM as an intracavity element. The PCM is a nonlinear transparent medium pumped by a pair of counterpropagating laser beams of the same frequency and intensity. Phase conjugation with gain is possible for an injected signal of a slightly different frequency by nearly degenerate four-wave mixing (NDFWM). The linear absorption/gain in the medium is also taken into account. In this presentation, we apply the results of the general theory to a phase-conjugate resonator by equating the reflectivity of one of the conventional mirrors to zero. Analytic expressions are obtained for the two reflection coefficients and the two transmission coefficients of the injected signal, and the condition for oscillation is derived. A novel approach yields the mode spacing of such a phase-conjugate resonator.
Variational model of soliton interaction in two-mode fibers
Authors: Paré C. , Florjanczyk M. , Bélanger P. A.
Published: February 2023

All-optical switching in a nonlinear directional coupler and the evolution of the state of polarization in a nonlinear biréfringent fiber represent two important practical problems of propagation in a two-mode, nonlinear dispersive system. Both cases are described by a nonintegrable system of coupled nonlinear Schrödinger equations. On the basis of numerical simulations,1 it has already been shown that solitons present important advantages over differently shaped pulses. To improve our physical insight into the dynamics resulting from the complex interplay between nonlinearity (self- and cross-phase modulation), dispersion, and linear coupling, we have developed an approximate all-analytical model of soliton interaction. An extension of a variational method2 has been used, and the results can be recast in a suggestive potential-well picture. Besides improved estimates of optical switching powers, a symmetry-breaking instability can easily be anticipated. A detailed comparison with numerical simulations, showing a good overall agreement between exact and approximate results, will be presented.
Detection of surface acoustic waves by using traveling Bragg regime reference gratings
Authors: Larson D. A. , Black T. D. , Magnusson R.
Published: February 2023

The use of stationary Bragg-regime reference gratings to enhance the detection of weakly modulated space-time gratings produced by traveling surface acoustic waves (SAW) located at the input plane of the reference grating was analyzed by Magnusson and Black.1 Their analysis has been extended to include the use of a traveling Bragg-regime reference grating that is spatially separated from a SAW. Furthermore, experimental investigations of this double-grating interaction have been performed. When the m = 0 and either the +1 or –1 fields diffracted by the space-time grating produced by the SAW are symmetrically incident on a traveling Bragg grating of the same spatial period as the SAW, a component of the output intensities oscillates. The frequency of this oscillation is determined by the relative velocity of the two traveling gratings. In the small signal limit, in which the SAW grating is weakly modulated relative to the reference grating, the amplitude of the intensity modulation varies linearly with the modulation amplitude produced by the SAW. Results from experiments using a 100 µm SAW traveling on a LiNbO3 substrate separated from a 100 µm bulk acoustic wave traveling in a flint-glass acousto-optic modulator are in good agreement with analysis.
Optical quadratic perceptron neural network
Authors: Huynh Alex V. , Walkup John F. , Krile Thomas F.
Published: February 2023

Optical quadratic neural networks are currently being investigated because of their advantages with respect to linear neural networks.1 A quadratic neuron has previously been implemented by using a photorefractive barium titanate crystal.2 This approach has been improved and enhanced to realize a neural network that implements the perceptron learning algorithm. The input matrix, which is an encoded version of the input vector, is placed on a mask, and the interconnection matrix is computer-generated on a monochrome liquid-crystal television. By performing the four-wave mixing operation, the barium titanate crystal effectively multiplies the light fields representing the input matrix by those representing the interconnection matrix to produce an analog output. This output is then digitized by a computer, thresholded, and compared to a specified target vector. An error signal representing the difference between the target and thresholded output is generated, and the interconnection matrix is iteratively modified until convergence occurs. The characteristics of this quadratic neural network will be presented and discussed.
Temperature stability of standing-wave diffraction modulators based on piezoelectrically induced strain-optic effect
Authors: Kuti Cs.
Published: February 2023

High efficiency diffraction modulation of light by strain-optic effect of piezo-electrically induced standing acoustic waves was presented at the annual OSA meeting in Orlando last year.1 A more detailed paper on piezo-electrically induced strain-optic (PESO) diffraction modulation has been submitted to a journal on short communications. One of the reviewers has objected to our preference of PESO- modulator to the traditional standing-wave acousto-optic ones. One of the objections relates to the disadvantages of extremely low bandwidth and connecting temperature instabilities by use of high overtones, in consideration of the PESO modulator as a practical device. Meanwhile, application of a LiNbO3 PESO-modulator for mode-locking a Kr+ laser pumped Nd glass laser was carried out.2 The laser uses a commercial LiNbO3-fused silica acousto-optic (AO) mode-locker. The shortest pulse width of 7 ps could be achieved. Replacing it by the PESO diffraction modulator, we achieved pulses as short as 3.8 ps. The system worked with high stability and insertion of the modulator could be accomplished without problems arising from the usage of the commercial Bragg modulator. Recently, Irvine replaced a high quality AO-modulator for our PESO in a YiLF laser. He has achieved 17ps pulses, about one third of the 50ps pulse width obtained with the commercial modulator. In consideration of the self-stabilization mechanism observed in the experiments, a simple-model to interpret the physical processes ensuring a high degree of stabilization has been developed.
Tensor components of higher-order susceptibilities in a saturable absorber
Authors: Blouin Alain , Galarneau Pierre , Denariez-Roberge Marguerite Marie
Published: February 2023

Higher-order nonlinearities may affect the performance of optical devices based on the third-order nonlinearity and may also be important in the characterization of nonlinear materials. A geometry of n-wave mixing to selectively probe each order of the nonlinearity was first proposed by Raj et al.,1 and its behavior was analyzed by us.2 We propose a theoretical model based on a holographic approach for all orders of the nonlinearities in a saturable absorber in stationary and transient regimes. Results of the theoretical calculation for the tensor components of the susceptibilities will be presented. We have performed experiments in the picosecond regime in which we used a frequency-doubled Nd:YAG mode-locked laser. We studied the fifth- and seventh-order nonlinearities for both isotropic and anisotropic materials. We used different beam polarization configurations to separate the components of the susceptibility tensors. In conclusion, we will discuss the importance of higher-order nonlinearities for complete characterization of nonlinear materials and the possibility of some devices using these nonlinearities.
Similarity properties of optical precursors
Authors: Gagnon L.
Published: February 2023

Optical precursors determine how a wave that is initially well-defined builds up when it propagates in a dispersive medium. A rigorous uniform description can be accomplished by means of a modern asymptotic theory.1 In a first analysis, that is, for time-domain local precursors, these waves are described in the Fourier-integral representation in terms of one Bessel function (Sommerfeld precursor) and the Airy integral (Brillouin precursor).2 In this work we determine, by using an operatorial equivalence based on the dispersion relation and under the same local restriction, the evolution equations satisfied by the precursors. Because of their asymptotic nature, precursors appear naturally as self-similar solutions of these equations. The above operatorial equivalence further suggests a simple way of extending the problem to take into account a perturbative Kerr nonlinearity,ßI, where I is the intensity of the field and ß is a perturbation parameter. Although such effect is negligible in practice, it is instructive to see that the equations still remain tractable. In fact, similarity properties still exist and permit us to perform a simple perturbation scheme. Our results show that nonlinearity increases (decreases) the Sommerfeld precursor spreading for ß 0 (ß < 0) and yields a self-phase modulation of the Brillouin precursor.
Color holographic storage in LiNbO3
Authors: Yu Francis T. S. , Wu Shudong , Mayers Andy , Rajan Sumati
Published: February 2023

Some techniques have been developed for color hologram recording on photographic film. These techniques are applicable to the rainbow hologram1 and the white-light reflection hologram.2 In this paper we demonstrate the recording of color holograms in photorefractive media. The photorefractive crystal is thicker than the photographic emulsion and therefore provides a higher wavelength selectivity for the recording of color holograms. Multiple storage of color holograms is impossible in emulsion.
Soft-x-ray optics
Authors: Spiller Eberhard
Published: February 2023

This tutorial will serve as an introduction to the papers in the symposia on soft x-rays. We will explain the basic physics of imaging and dispersing devices (zone plates, multilayer structures, gratings) for x-rays in an intuitive way. Fabrication tolerances and methods together with the required metrology for the highest performance and the present state of the art will be discussed. An overview of the present and anticipated future applications will be given.
Reversible femtosecond pulse lengthening using prism pairs and a focusing element
Authors: Avramopoulos H. , Fork R. L. , Schehrer K. L.
Published: February 2023

This paper experimentally examines the use of prism pairs and focusing elements to reversibly lengthen the duration of femtosecond pulses by means of spatial dispersion of the different frequency components of an ultrashort optical pulse in a direction transverse to the direction of propagation.1 Unlike techniques based on a linear pulse chirp, this approach has the advantage of not favoring one part of the pulse spectrum over another in a nonlinear amplifier medium. The temporal lengthening described here, from the order of 50 fs to the order of 500 fs, is expected to have significant consequences because key mechanisms in amplifier media, such as spectral hole burning, have time constants of the order of 100 fs or less. The prism pairs also provide other useful features, such as a group velocity dispersion correction that can be adjusted from negative through positive values, low insertion loss, and easily adjusted spectral filtering. A comparison of the experimentally measured pulse broadening and its analytically calculated value for the experimental conditions shows good agreement between experiment and theory.2 We will also discuss amplifier designs that take advantage of this pulse lengthening technique.
Speed of the coherent component of femtosecond laser pulses propagating through random scattering media
Authors: Liu Feng , Yoo K. M. , Alfano R. R.
Published: February 2023

We measured the pulse profile and speed of femtosecond laser pulses propagating through scattering media by using a cross-correlation method. Multiple scattering in random media splits the pulse into two components: a coherent (ballistic) component and an incoherent (diffusive) component. We found the pulse profile of the coherent component to remain essentially unchanged while its speed was reduced. We found the delay in the time of arrival of the coherent component to be linearly proportional to the thickness of the media and the concentration of the scatterers. We composed the measured delay times with delay times derived from theoretical models. In one of the models coherent interference is neglected, and the increase in refractive index in the medium is purely a function of the volume fraction of the scatterers. This model underestimates the delay time. The theoretical model developed by M. Lax,1 which accounts for the coherent interference of the forward scattered waves and the effective field acting on a scatterer, describes the experimental results better than does the former model. The change in refractive index for coherent pulses appears to be described by the coherent interference of waves scattered in the forward direction with the primary wave.
Temperature-tuned optical parametric oscillation (0.9-1.3 μm) using lithium triborate crystal operated at noncritical condition
Authors: Lin J. T. , Montgomery J. L.
Published: February 2023

Lithium triborate (LBO) crystal has been recently studied for frequency doubling, tripling, and optical parametric oscillation (OPO) at room temperature.1,2 We have reported high-temperature noncritical phase matching (NCPM) frequency doubling and mixing in LBO crystal, in which the advantages of NCPM include no-walk-off, large acceptance angle, and high efficiency.3 In this paper we demonstrate what is, to our knowledge, the first experimental investigation of OPO in LBO crystal in which a tuning range of 915-1300 nm was achieved in LBO crystal by temperature tuning of 137-149°C. An OPO efficiency of 10% at the degenerate point was achieved by using an uncoated, noncritical-cut (i.e., θ = 90°, ϕ = 0°) LBO crystal with dimensions of 2 mm × 2 mm × 18.7 mm. A Quantel Nd:YAG laser, TEM00 mode, 10-ns pulse width at 1064 nm was doubled to 532 nm by a CD*A (type I) crystal. The emitted green light was down-collimated to a spot size of 1 mm and pumped an OPO resonator with the appropriate coated mirrors. The measured OPO threshold power of the pump (532 nm) was about 2 mJ at the degenerate point. We will discuss the key parameters of cavity length, temperature tuning ranges, and angular tuning curves at various temperatures (22-150°C). Results of NCPM will also be compared with those of the angle-tuned critical case (at room temperature).
Bulk photovoltaic tensor and polarization conversion in LiNbO3
Authors: Wilson Daniel W. , Glytsis Elias N. , Hartman Nile F. , Gaylord Thomas K.
Published: February 2023

Using methods that are applicable to any crystal class, the form of the third-rank bulk photovoltaic tensor for LiNbO3 is found to be composed of a symmetric part (similar to the piezoelectric tensor) and an antisymmetric part. In LiNbCO3 the antisymmetric part contains two positive elements and two negative elements, all of the same magnitude, and these are shown to lead to polarization conversion in bulk crystals and in waveguides. The polarization conversion1 is examined in terms of the propagation direction, the initial polarization direction, the electro-optic effect, and the nonlinear interaction. For propagation perpendicular to the optic axis, a space-oscillating photocurrent is produced, forming an index grating in the direction of propagation. The nonlinear coupled-wave equations that result from this grating show a unidirectional conversion to an extraordinarily polarizated output wave.2,3 For propagation parallel to the optic axis, a uniform photocurrent is produced, which can couple orthogonal polarizations by a rotation of the index ellipsoid. Experimental results for bulk LiNbO3 and Ti:LiNbO3 waveguides are presented.