bluuebunny/crossref_metadata_2025 huggingface dataset:
Resonance light scattering from microspheres on substrates
Authors: Lettieri Thomas R. , Marx Egon
Published: February 2023

In a recent investigation, Hill et al. show that the wavelengths of sharp structural resonances in the fluorescence emission from single dielectric microspheres resting on glass and metallic substrates are the same as those for unsupported microspheres.1 The objective in the present study was to obtain resonance light-scattering (RLS) spectra from an ensemble of nonfluorescing dielectric microspheres. The incident light from a dye laser was swept continuously through a range of wavelengths, and the intensity of the elastically scattered light at 90° was recorded as a function of wavelength. The resultant RLS spectrum was then compared to Mie-scattering computer calculations for unsupported microspheres, averaged over a diameter distribution. Three different types of substrate were used: ultrablack-coated metal; black glass; and clear glass. For polystyrene microspheres on the ultrablack-coated metal substrate, the experimental RLS spectra were in good agreement with Mie-scattering calculations for unsupported dielectric microspheres. This was true regardless of the tilt angle of the substrate relative to the incident and scattered light fields as long as the scattering angle was not changed. However, for microspheres on the black- and clear-glass substrates, the match with Mie calculations was not so good; in particular, the RLS patterns changed appreciably as the substrates were tilted. This is most likely due to the light reflected from the glass substrates which was not present with the highly absorbing ultrablack-coated metal substrate.
Extrema of the magnitude and phase of a complex function of a real variable
Authors: Azzam R.M.A.
Published: February 2023

Given a complex function F(ω) = |F(ω)| exp [jΔ(ω)] of a real argument ω, the extrema of its magnitude |F(ω)| and phase Δ(ω) as functions of ω are determined simultaneously by finding the roots of one common equation, lm[G(ω)] = 0, where G = (F'/F)
2
and F' = ∂F/∂ω. The extrema of |F| and Δ are associated with ReG ᐸ 0 and ReG ᐳ 0, respectively. This easy-to-prove theorem has a wide range of applications in optics and electrical engineering. We offer at least one example of attenuated internal reflection (AIR). In AIR the complex reflection coefficient for the p polarization R
p
(ϕ) and the ratio of complex reflection coefficients for the p and s polarizations, p(ϕ) =R
p
(ϕ)/R
s
(ϕ), are considered as functions of the angle of incidence ϕ. It is found that the same (cubic) equation1 that determines the pseudo-Brewster angle of minimum |R
p
| also determines a new angle at which the reflection phase shift δ
p
= argR
p
exhibits a minimum of its own. Likewise, the same (quartic) equation2 that determines the second Brewster angle of minimum |
ρ
| also determines angles of incidence at which the differential reflection phase shift Δ = argρ experiences a minimum and a maximum. Angular positions and magnitudes of all extrema are exactly calculated for a specific case that represents light reflection by the vacuum —Al or glass—aqueous dye solution interface.
Magnetic resonance imaging and spectroscopy in medicine
Authors: Peters T. M.
Published: February 2023

Magnetic resonance techniques were developed in the mid-1940s to analyze the structures of chemical compounds. In the last 10 years, however, the same principles have been evolved, along with advances in magnet, computer, and display technology into one of the most exciting imaging methods available in the medical field today. Magnetic resonance imaging utilizes the property that certain nuclei when placed in a magnetic field can be stimulated into a resonance condition by external radio-frequency radiation. In recovering from this disturbance, the nuclei in turn emit rf signals (whose frequencies depend on the magnetic field strength in which the nuclei are located). To image the human body, the patient is placed in a large solenoidal magnet (field strength typically 0.5-1.5 T), and the magnetic field Is coded in various ways by the application of gradient fields, causing the protons within the volume to resonate with a range of frequencies. Relating these frequencies to positions within this volume is performed by a Fourier analysis of the signal. Reconstructed images are displayed to the user as slices of the 3-D volume being imaged.
Unconventional coatings
Authors: Macleod H. Angus
Published: February 2023

No summary of this tutorial or biographical information was available at press time.
Surface plasmon resonance detection and removal of contamination from metallic film surfaces
Authors: Zhang F. S. , Wang R. H. , Macleod H. Angus , Parks Robert E. , Jacobson Michael R.
Published: February 2023

The surface plasmon resonance (SPR) phenomenon and its ability in the detection of contamination on the surface of silver films are described. This nondestructive highly sensitive technique has recently been employed to detect the deposition and removal of glass particles, power particles, and a representative vegetable oil from silver films. The cleaning experiments compared the effects of isopropoyl alcohol and acetone and considered the effects of ultrasonic cleaning on contaminant removal and surface roughness. We have concluded that the SPR technique is not very sensitive to particles in the 30-50-µm range and that these particles are easily removed by a high-pressure nitrogen gas. As for oil, the contamination can be removed efficiently by acetone; ultrasonic agitation does clean more effectively.
Digital computing utilizing optical Fredkin gates
Authors: Mirsalehi Mir M. , Shamir Joseph , Caulfield H. John
Published: February 2023

Cascadable digital processors based on 2- and 3-D optical Fredkin gate arrays are described. The 2-D structure consists of an integrated optical array of channel waveguides and a page-oriented holographic memory. The 3-D structure consists of arrays of ferroelectric liquid crystal spatial light modulators and Wollaston prisms. The Implementation of residue addition and multiplication with these processors is analyzed. Analytic expressions are derived for the required number of holograms and the number of waveguide channels in the 2-D structure and the size and number of spatial light modulators in the 3-D structure to achieve the above operations.
Digital-optical processing in bilinear transformations
Authors: Yu Francis T. S. , Lu T. , Cao M. F.
Published: February 2023

Digital optical architectures performing bilinear transformations are presented. These architectures employ the inner-product and systolic-inner-product techniques dealing in vector-matrix-vector multiplication and triple matrix multiplication. A microcomputer-based optical processing system for digital-optical computation is utilized. Programmable magnetooptic spatial light modulators (MOSLMs) are used to generate the time sequence input signals and the bilinear systolic engagement matrix. A CCD detector is in the output plane as a time integrator for the systolic processing. The proposed hybrid optical architectures offer high-data-rate and high-accuracy processing capabilities.
Electronic transitions in photon-stimulated desorption
Authors: Haglund R. F. , Barnes A. V. , Halas N. , Mendenhall M. H. , Tolk Norman H.
Published: February 2023

The discovery that neutral excited-state atoms were desorbed by UV photons with orders of magnitude greater efficiency than ions from alkali-halide surfaces has wrought a fundamental change in our approach to the study of photon-surface interactions, both with synchrotron and laser light sources. In particular, laser-surface interactions in general and laser-induced material damage in particular—once considered primarily due to the absorption of thermal energy from the incident photons—now appear to be linked to electronic interactions both at the surface and in the near-surface bulk, even for photon energies below the bulk band gap. Thus it is appropriate to consider even laser-surface interactions as generically related to the process of desorption induced by electronic transitions (DIETs), a class of energy-surface interactions triggered in exemplary fashion by photons and electrons.
Application of symmetry group theory to the perception of rotation
Authors: Kramer Patricia , Schwenzfeier Elizabeth , Growney Ronald , Shaw Robert E.
Published: February 2023

We are investigating the extent to which the perceived speed, direction, and smoothness of a rotating pattern depend on the symmetry period of the pattern (i.e., the amount of rotation required to bring the pattern into self-congruence). Subjects viewed patterns with either twofold (180°, e.g., rectangle), threefold (120°, e.g., triangle), or fourfold (90°, e.g., square) symmetry under various rates of stroboscopic illumination; rating scales were the dependent measure. Results indicate that perceived speed, direction, and smoothness of rotation depend not only on the stroboscopic sampling rate but also on the symmetry of the rotated pattern. These results correspond to predictions based on symmetry group theory.
Perception of complex shape from optic flow
Authors: Landy Michael S. , Sperling George , Perkins Mark E. , Dosher Barbara A.
Published: February 2023

In a new objective task to measure the efficacy of cues to structure from motion, one of a large lexicon of shapes defined by a multidot display is presented on each trial, and the subject attempts to identify it. The cue of changing dot density is neither necessary nor sufficient for successful performance in this task. This was shown by either eliminating the cue or presenting the cue in isolation. When the maximum dot lifetime is reduced to two frames, performance remains high, showing that it is not necessary to track identifiable points for an effective kinetic depth effect (KDE)—KDE requires optic flow. Stimulus manipulations such as dot flicker and alternation of contrast sign, which impair the computation of optic flow, impair both the KDE task performance and performance in a motion-based texture segregation task (“Where is the odd motion?”). Finally, performance on the KDE task is reduced with shorter stimulus durations, but performance is still surprisingly good when only two frames are presented.
Parallel visual search for conjunctions of form and color
Authors: Wolfe Jeremy M. , Franzel Susan L. , Cave Kyle R.
Published: February 2023

We measured reaction times (RTs) as observers searched for a target among a variable number of distractors. In searches for stimuli defined by conjunction of color and form (e.g., target: green +, distractors: red +, green ×), Treisman found that RTs increase as the number of distractors increase. Observers appear to conduct serial self-terminating searches for the target. We replicated this finding with naive observers. However, after 1000 trials of practice, RTs for two observers were independent of the number of distractors indicating that they could perform parallel searches for conjunctions. Egeth ef al1 argue that observers can simultaneously disregard all distractors along one dimension (e.g., color). Therefore, we used a triple conjunction task of form, color, and size. (Target: large green +; distractors: large green ×, large red +, small green +, small red ×.) The stimuli were chosen so that if an observer was able to disregard all the distractors of one color, the remaining stimuli would still require search for a conjunction.
Propagation properties of diffused dielectric waveguide structures: a harmonic oscillator basis set approach
Authors: Carlson Rob D. , Hawkins Raymond J.
Published: February 2023

Basis set techniques commonly used in quantum chemistry to compute the eigenvalues and eigenfunctions of the time-independent Schrodinger equation are applied to the paraxial wave equation to compute the propagation constants and the modal field distributions for dielectric waveguide structures with arbitrarily graded refractive-index profiles. A product basis of quantum mechanical harmonic oscillator eigenfunctions is used to convert the eigenvalue form of the paraxial wave equation into a matrix diagonalization problem. For a typical single (double) channel waveguide structure a basis, i.e., matrix, size of about 100 (200) is sufficient to obtain converged values for the low-order propagation constants and modal field distributions. Consequently, the propagation properties of these structures are easily studied on a VAX minicomputer. The utility of this method in diffused channel waveguide design and analysis is illustrated using examples from Ti:LiNbO3 integrated optical waveguide technology.
Spatial stochastic instabilities of nonlinear coupled modes: numerical results
Authors: Caglioti E. , Trillo S. , Wabnitz S.
Published: February 2023

Nonlinear coherent coupling between guided modes may become extremely sensitive to small changes in the input conditions.1,2 This effect has potential use in ultrafast all-optical signal processing and switching in two-mode couplers, such as fiber polarization switches1 or integrated waveguide nonlinear directional couplers. The unavoidable presence of mode-coupling imperfections, however, may lead to chaotic mode conversion that dramatically spoils the power-dependent transmission characteristics.2 Analogous stochasticity may arise whenever two intense light beams counterpropagate in an optical fiber or copropagate in two parallel linearly coupled fiber cores. Numerical integration of chaotic solutions suffers by exponential amplification of errors. However, a statistical description of the properties of a chaotic trajectory turns out to be unaffected by error propagation. Such a characterization has been obtained for the above waveguiding structures by means of different statistical estimators: among others, the maximal Lyapunov exponents (yielding the local rate of divergence of nearby trajectories) and the Grassberger-Procaccia correlation exponent (related to the fractal dimension of the chaotic domain in phase-space). We estimated stochasticity thresholds in terms of key physical parameters (e.g., critical input optical power, perturbation strength, and spatial frequency and maximal useful lengths of nonlinear switching devices.
Numerical path integration: a computationally simple approach to the propagation properties of graded-index dielectric waveguide structures
Authors: Hawkins Raymond J.
Published: February 2023

I present an improved approach to numerical path integration that expands the scope of the method I discussed recently1 and yields the propagation constants and field distributions of all the modes of a dielectric waveguide structure while retaining the ease of implementation, computational simplicity, and ability to accommodate arbitrarily graded refractive-index profiles characteristic of the previous approach. This approach follows that of Yevick and Hermansson2 in that the propagation properties are obtained by diagonalizing the propagator of the optical wave equation. It differs from their method in the manner by which the propagator is calculated: they use the propagating beam method, I use the Trotter product formula to obtain a closed form expression for the matrix elements of the propagator. The spectral properties calculable using this method are discussed, and the utility of this method in waveguide design is illustrated by calculating the propagation properties of slab waveguide structures.
Optical sectioning with the scanning slit microscope
Authors: Koester Charles J. , Khanna Shyam M.
Published: February 2023

This incident-light microscope employs an oscillating three-facet mirror to scan the image of an illuminated slit across the object plane. The light returning from this illuminated region is passed through a second slit located in the imaging system. As a result nearly all the light reaching the image plane is from a thin layer centered at the object plane. By adjusting the slit widths the optimum optical section thickness can be chosen for the particular specimen and the light source used. For studies of the inner ear of the cat, an optical section thickness of 300 μm (full width at 1/10 power) or less is chosen, so that reflections or scattering from the round window membrane are eliminated. This permits identification of anatomical details on the basilar membrane without opening the round window membrane and disturbing the environment of the structures of interest. Results of theoretical calculations of optical section thickness are given, showing how it can be varied by selection of numerical aperture of the objective and slit width.
Multiple-output trinary logic units using polarization-encoded optical shadow-casting
Authors: Karim M. A. , Awwal A. A. S.
Published: February 2023

The lensless optical shadow-casting (OSC) technique1 may be used for realizing multiple-valued logic operations to reduce both the interconnection bottleneck and the number of total logic elements. The original OSC scheme utilized only two types of input code (transparent and opaque) and was thus limited in scope; the design of binary units often involved LEDs having nonidentical output intensities. The OSC scheme was recently extended2,3 to include polarized input codes, sources, and a decoding mask. The input encoding is determined for a particular mask and a fixed source pattern (all LEDs preferably unpolarized).
Optical arithmetic computing using a linear associative memory
Authors: Eichmann George , Kostrzewski A. , Li Y.
Published: February 2023

There are a number of schemes to perform optical arithmetic computation. While there are parallel carry-free computation models that require cumbersome preprocessing and postprocessing, most digital approaches use direct binary digital computation. Such an approach is serial and requires bit-by-bit computation. Optical implementation of an inherently serial algorithm is generally undesirable. Associative memory processors are inherently parallel and, using appropriate training patterns, are nonalgorithmic. The major disadvantage of such processors is that the number of training patterns is large, leading to large, possibly unrealizable, associative memory requirements, and because the patterns are nonorthogonal and there are imperfections in the physical devices, some of the thus generated results may be in error. Using different classification and error-correcting schemes, the adverse features of an LAM are controlled.
Psychophysical evidence of higher-order color mechanisms
Authors: Krauskopf John
Published: February 2023

A number of lines of evidence reveal the operation of higher-level mechanisms in color vision. By higher-order mechanisms is meant elements beyond the second stage of most conventional models of color vision (or in physiological terms elements beyond at least the LGN). Analyses of the changes in the detectability of chromatic pulses induced by prior viewing for fields fluctuating in color reveal that such mechanisms play a role in determining visual sensitivity. While retinal processes involved in sensitivity regulation appear to be highly localized in their effects, the higher-level processes have a wider scope. For example, fluctuating conditioning stimuli have effects, not attributable to stray light, on stimuli presented to remote retinal regions. Precise measurements of simultaneous color contrast yield results which cannot be explained in terms of multiplicative or subtractive interactions in either receptoral or second-stage mechanisms and thus imply a role of higher-order mechanisms.
Evolution in the structure of a focused field
Authors: Li Yajun
Published: February 2023

We know that when a converging spherical wave is focused by an aberration-free system, the point of maximum intensity is not at the geometrical focus but lies closer to the exit pupil. It is apparent that the whole 3-D intensity distribution in the focal region is changed due to the shift of the intensity maximum from the geometrical focus to an ascertainable place in front of the exit pupil.1
Far-field pattern improvements of diode lasers with nonstandard output facets
Authors: Champagne Yves , McCarthy Nathalie , Tremblay Réal
Published: February 2023

Commercial gain-guided diode lasers usually provide far-field patterns with poor optical quality. This is due to the presence of two plane-wave output components' that are tilted with respect to the optical axis. We propose to modify the output facet properties of a diode laser to obtain an output beam with a narrow single-lobe far-field distribution. Numerical simulations have been performed to predict the effects of replacing the standard output facet by a laterally varying reflectivity facet, a spherical and a phase conjugate facet. A facet with an inverted Gaussian reflectivity profile reduces the far-field width of the wide-stripe diode laser but increases the threshold current. With a phase conjugate mirror, the beam root mean square angular width and the threshold current are, respectively, 20 and 50 % lower than with a standard facet. Spherical concave output facets give best results: the far-field width is reduced by 75 % in some configurations.
Temporal behavior of a conjugated beam by degenerate four-wave mixing in azo dyes
Authors: Mailhot Sylvain , Galarneau Pierre , Lessard Roger A. , Roberge Marguerite-Marie
Published: February 2023

Degenerate four-wave mixing (DFWM) is a simple method to achieve phase conjugation. It uses the third-order nonlinearity of the electric susceptibility to produce changes in the optical properties of materials. A dynamic grating is then induced. Such gratings might be used as fast optical memories in optical computing. Our aim is to find media with large nonlinear susceptibilities and fast response time. We report phase conjugation of 532-nm laser radiation by DFWM in dye solutions. The time dependence of the conjugated wave is investigated experimentally and compared to theoretical predictions. We have also studied the influence of the solvents, dye concentration, and pump intensity on the phase conjugated signal. The results are compared with those predicted by three nonlinear mechanisms. Thermally induced refractive-index changes, Kerr effect, and saturable absorption are considered.
Multiphoton fragmentation of CO2 at 193 nm
Authors: Turner Brian P. , Hill Wendell T.
Published: February 2023

We have investigated multiphoton fragmentation processes in CO2 as a function of pressure (10−4−100 Torr) and excitation wavelength. Subsequent to excitation by a line-narrowed (~3-cm−1) tunable (~150-cm−1) ArF* excimer laser (λ ~ 193 nm), we monitored the dispersed fluorescence along with the ion signal produced by the photofragments. Although CO2 has no strong intermediate resonances at 193 nm, our preliminary results show a strong three-photon photolysis channel leading to atomic carbon which suggests a complete breakup of the molecule. At the same time, CO2 sustains laser-induced breakdown at relatively low pressures (~7 Torr), which indicates a strong multiphoton (at least three) ionization channel as well.
Absolute value of the nonlinear susceptibility of dye solutions measured by polarization spectroscopy
Authors: Marcano Aristides O. , Aranguren L.
Published: February 2023

The absolute values of the thermal grating portion of a polarization spectroscopy signal of acetone solutions of malachite green and 1,3′-diethyl 1-2, 2 quinolythiacarbocyanine iodide (DQCI) are measured. Good agreement is obtained with the values calculated from a macroscopic description of the thermal modulation of the refractive index using a thermal susceptibility formalism. A method for measuring the resonant third-order electronic susceptibility of the dyes comparing the relative magnitude of the thermal and electronic portions of the polarization spectroscopy signal is proposed.
Spatially localized Rydberg atom wave packets
Authors: Yeazell John A. , Stroud C. R.
Published: February 2023

The quantum theory of atoms is based on a Hamiltonian which is just that of the classical Kepler theory of planetary orbits. In spite of this common foundation, the predictions of the quantum theory ordinarily do not much resemble those of the classical theory. Even in the limit of large quantum numbers the energy eigenstates of quantum theory do not look at all like the classical elliptical orbits. Recently, Parker and Stroud1 showed that it is possible to excite a Rydberg atomic wave packet localized in the radial coordinate. Also, Yeazell and Stroud2 showed that a wave packet localized in the angular coordinates can be formed. Both wave packets exhibit an evolution describable, at least in part, by classical theory. However, neither wave packet truly corresponds to a wave packet traveling in a classical elliptical orbit. We discuss the manner in which such a wave packet might be formed using a short-pulsed laser and arf dressing field. The evolution of the resulting wave packet is compared with that of its classical counterpart.
Fluorescence detection of Sr+ following Sr multiphoton Ionization
Authors: Othonos A. S. , Haugen Harold K.
Published: February 2023

The atomic beam studies of Feldmann, Welge, and co-workers,1 utilizing single-ion or electron detection, have indicated the probable importance of stepwise double ionization of Sr via Sr+ excited states. Recently, in a strong field regime (≳100 GW/cm2), Agostini and Petite2 found a broad low-energy peak which was associated with the near-energy-resonant autoionizing decay to Sr+(2P1/2,3/2).
Light emitting diode sub-Poissonian light source
Authors: Tapster P. R. , Rarity J. G. , Satchell J. S.
Published: February 2023

We drive a high-efficiency gallium arsenide light emitting diode (LED) with a low-noise current and measure the noise in the detected photocurrent from a high-quantum-efficiency silicon photodiode collecting most of the emitted light. The drive current is obtained from a resistor in series with a low-noise voltage supply. The Johnson noise in the current is much less than shot noise whenever the voltage across the resistor is large compared with 50 mV (2kT/e at room temperature). The LED converts electrons to photons directly with some efficiency η.
Numerical analysis of Gaussian beam propagation with nonlinear media
Authors: Guo Ping , Sun Yin-Guan , Shang Shi-Xuan
Published: February 2023

After passing through a nonlinear medium, a laser beam propagates in free space and transmits through an aperture in a screen; this simple device has power limiting action.1 We carried out a numerical analysis of the refraction of a laser beam by a bounded nonlinear medium and of the diffraction during the beam's subsequent free-space propagation using a 2-D Gaussian input profile. With a slowly varying envelope approximation, the Maxwell wave equation was solved using the definite difference method. Thus no thin-medium approximation is needed. Steady-state transverse profiles in the near and far fields have been calculated. We found that the results are in good qualitative agreement with those of other experiments.2
Color pattern recognition by an array of Fresnel holographic filters
Authors: Mu Guogang , Wang Zhaoqi , Chen Dongqing
Published: February 2023

We reported in a previous paper a new technique for pattern recognition using a Fresnel holographic filter (FHF).1 We now present a technique for color pattern recognition by an array of FHFs.
Multiple-Image recognition by code division multiplexed binary phase-only filters
Authors: Javidi Bahram , Farraknia F.
Published: February 2023

A multiobject shift-invariant pattern recognition system using binary phase-only correlation is presented. The system computes the binary correlation between an input pattern with a generalized set of pattern functions. This technique uses a filter which consists of a set of binary phase-only code division multiplexed functions. The available spatial light modulators (SLMs) work well in a binary phase-only mode and can be used to synthesize spatial filters of this type. Binarization also permits the recording of filters of images with larger samples on currently available binary SLMs that have a limited number of pixels.
Fabrication and characterization of a linear mode confinement modulator on GaAs
Authors: Belanger Michel , Najafi S.I. , Champagne A , Maceijko R. , Currie J. F.
Published: February 2023

The linear mode confinement modulator has been proposed and investigated on Ti:LiNbO3 waveguides.1 This modulator yielded linear modulation with high-modulation depth using a compact design. A linear mode confinement modulator is investigated using a GaAs rib waveguide. The modulator is composed of three parts. The input channel waveguide is connected to the output channel waveguide via an intermediate slab waveguide. In the latter the confinement of the optical waves is varied via an electrooptic effect to modify the transmission from input to output, thus achieving modulation.
Graphical method of ray tracing using computers
Authors: Cornejo A. , Baez J. , Camacho G. , Cardona O. , Cordero A. , Rojas F.
Published: February 2023

The traditional graphical ray tracing method has been used as an educational example,1 as well as a useful technique in some problems of lens design.2 With the use of a microcomputer or PC, this method can be revived and used for solving some particular problems of lens design in an efficient and interesting way. With adequate formulas for the computer, this method becomes a useful tool for solving the problems of finding the radius of curvature or refractive index for some special cases constrained by the lens design.
Statistical parameters for a microrough silver thin-film surface
Authors: Varnier Francoise , Rasigni G. , Rasigni M. , Mayani N. , Llebaria A.
Published: February 2023

For several years, we have been developing a new method of surface structure characterization.1 This method, based on microdensitometer analysis of shadowed surface replicas, has proved powerful, both in topography restitution and determination of statistical parameters for various surfaces such as thin evaporated films. It also proved to be particularly useful for a microroughness study. An extensive surface investigation of a silver film evaporated on a supersmooth substrate was done to explain persistent discrepancies between our results and those obtained with plasmon methods.2 We show that, in certain circumstances, it is possible to obtain values approaching those that the authors got using a plasmon method.
Thin-film growth modeling
Authors: Sargent R. B. , Macleod H. A.
Published: February 2023

Early 2-D film growth models qualitatively exhibited several effects commonly observed in conventionally deposited thin films, notably columnar microstructures. A model of this type under study at the Optical Sciences Center simulates the growth of films with dimensions as large as an optical wavelength.
Optical detection of mutagenic substances using ultraweak chemiluminescence from primary culture of rat hepatocytes
Authors: Osada K. , Okazaki S. , Kimura S. , Hishinuma K. , Mashiko S. , Kobayashi M. , Inaba H.
Published: February 2023

Very weak light emission observed in the Ames test system suggests that such chemiluminescence can be used for the detection and monitoring of mutagenic substances. To explore a new potentially practicable method of detection, we measured and examined ultraweak chemiluminescence as the response of a primary culture of rat hepatocytes to specific mutagenic and nonmutagenic substances employing a highly sensitive photon counting system that has been developed recently by our group. Hepatocytes were collected from rats (Wistar, male, 6 weeks of age) using the collagenase perfusion method and cultured for 96 h. Mutagens were added to the cells, and chemiluminescence intensity was analyzed. We found that benzo(a)pyrene, recognized as a strong mutagen, exhibited significant chemiluminescence from the hepatocytes in a dose-dependent manner for over 30 min. Substances showing no mutagenic activity, such as pyrene or triphenylene, exhibited no significant emission in the hepatocytes.
Orientation is processed in chromatic channels
Authors: Flanagan Patrick , Cavanagh Patrick , Favreau Olga Eizner
Published: February 2023

Observers adapted to 1-cycle/deg sinusoidal luminance defined (yellow/black) gratings tilted 15°CW from the vertical that alternated with 1-cycle/deg color-defined (red/green) gratings tilted 15°CCW from vertical. Subsequently viewed vertical luminance test gratings appeared tilted up to 3°CCW, while chromatic test gratings appeared tilted up to 3° in the opposite direction, demonstrating independent tilt aftereffects for color and luminance. A tilt aftereffect induced by a chromatic stimulus1 may be mediated by luminance artifacts. However, in our opposing aftereffects procedure,2 any aftereffect resulting from residual luminance differences in the chromatic stimuli will be overwhelmed by the adaptation in the opposite direction produced by the luminance stimulus itself—ensuring that the aftereffect seen on the color test is truly mediated by chromatic mechanisms. The induction of simple aftereffects (with luminance gratings or color gratings) transfers to color and luminance tests showing, as well, some overlap in luminance and color processing of orientation. These data, therefore, demonstrate that at least some color selective units in the cortex must also be selective for orientation.
Raman-resonant four-wave mixing and energy transfer
Authors: Bobbs Bradley , Warner Charles
Published: February 2023

When nonlinear four-wave mixing (FWM) is resonant with a Raman transition, it causes coupling between lightwaves separated by two Raman frequency shifts. This coupling is manifested in effects such as Raman gain suppression, higher-order Stokes generation, and coherent Raman spectroscopies (e.g., CARS). An understanding of these effects, however, has been impeded by a widespread misconception that Raman-resonant FWM does not transfer energy between the lightwaves and the medium. The equations for the photon densities at each light frequency show that, in actuality, two medium excitations are created or destroyed for each photon produced by FWM. This point may be further clarified by consideration of the driving nonlinear polarization and by comparisons with broadband Raman conversion and nonresonant FWM. The Raman gain suppression effect may be understood qualitatively in terms of destructive interference between FWM and the usual stimulated Raman process.
Effect of noise on contrast thresholds for gratings
Authors: Nasanen Risto
Published: February 2023

Contrast thresholds were measured for sinusoidal gratings at different spatial frequencies and grating areas with and without additive static spatial noise. The increase of contrast threshold produced by noise was dependent on spatial frequency and gratng area: for high spatial frequencies and small grating areas the increase of thresholds was larger than for low spatial frequencies and large grating areas.
Optical and TEM characterization of GaAs/(AI,Ga)As quantum wells and superlattices
Authors: Song J. J. , Yoon Y. S. , Jung P. S. , Fedotowsky A. , Nieh C. W. , Vreeland T.
Published: February 2023

We have employed nondestructive (optical and x-ray) as well as destructive (transmission electron microscopy) methods in characterizing molecular-beam-epitaxial GaAs/AI
x
Ga1−
x
As quantum well structures and superlattices. With photoluminescence excitation (PLE) spectroscopy, we measured optical transitions between the valence and conduction energy levels, which depend on sample parameters. With x-ray double-crystal diffraction measurements, symmetric (400), (200) rocking curves were obtained. The diffraction peak positions and their intensities also depend on the sample parameters. The MBE samples were then destroyed for transmission electron microscopy (TEM).
Transverse mode control of a pulsed Nd:YAG laser by a variable reflectivity mirror
Authors: Snell Kevin , McCarthy Nathalie , Piche Michel , Lavigne Pierre
Published: February 2023

The insertion of variable reflectivity mirrors in unstable resonators has been shown1,2 to be a solution of the detrimental effects from edge diffraction by hard apertures. We describe experimental results obtained with a pulsed low-magnification Cassegrain Nd:YAG laser using a mirror with a parabolic reflectivity profile. Such a profile was selected because it yields a fundamental mode which matches the laser medium, thus allowing an optimized extraction efficiency. The parabolic reflectivity mirror was made with a profiled layer deposited on a transparent substrate. The experimental results show a smooth near-field beam intensity distribution and a narrow single-lobe far-field pattern. Output pulses of up to 150 mJ have been obtained with a 4-mm rod.
Femtosecond laser spectroscopy studies of electronic nonlinearities in the halogen substituted benzenes
Authors: Lotshaw William T. , McMorrow Dale , Kenney-Wallace Geraldine A.
Published: February 2023

The femtosecond time-resolved optical Kerr effect (OKE) in room temperature polyatomic molecular liquids contains a wealth of information on the dynamics and structure of molecules through their nonlinear optical susceptibility.1 We present new femtosecond time-resolved results on the OKE of liquid benzene, nitrobenzene, and the series of monohalogenated benzenes (F, Cl, Br, I) which demonstrate the influence of the substituent (NO2 or halogen) on the purely electronic hyperpolarizability of these molecules.
Role of coherent coupling in the femtosecond time-resolved optical Kerr effect in simple liquids
Authors: Lotshaw William T. , McMorrow Dale , Kenney-Wallace Geraldine A.
Published: February 2023

Time-resolved pump-probe spectroscopies in the picosecond and femtosecond time domains exhibit an apparently instantaneous signal when the pump and probe laser pulses are temporally and spatially overlapped. This signal is related to the coherence properties of the laser pulses as well as to the material response. Meaningful information concerning the microscopic material response can only be extracted following a quantitative assessment of the coherence contribution to the measured signal. We present new results on this instantaneous signal via the femtosecond time-resolved optical Kerr effect in a wide variety of simple room-temperature liquids including CS2, benzene and its monohalogenated analogs, and several polyhalogenated methanes. A dramatic effect of the laser pulse width on the amplitude of the instantaneous signal (which is well described as a scalar multiple of the laser pulse intensity autocorrelation) is observed. Purely coherent contributions to this instantaneous signal are related to the electric field cross-correlation of the pump and probe pulses and have a definite symmetry in the time delay between these pulses that depends on the phase of the local oscillator in our optically heterodyned detection scheme.
Temporal and spatial beam reshaping on reflection near the Brewster angle
Authors: Fauchet P. M. , Bambha N. K. , Campbell I. H.
Published: February 2023

The amplitude and phase of the reflectivity vary strongly near the Brewster angle. Strongly focused beams or ultrashort pulses can thus undergo dramatic distortions on reflection from the surface of a solid. In particular, femtosecond pulses, which have a large bandwidth, may be reshaped after reflection from a bare surface in a way that is reminiscent of the reshaping produced after reflection from multilayer dielectric mirrors, provided that the wavelength is close to a resonance. We present calculations of the temporal reshaping of femtosecond optical pulses as a function of the pulse duration, angle of incidence, and dielectric properties of the reflector. In a related study, we calculated and measured the angular distribution of a strongly focused Gaussian beam after reflection near the Brewster angle. Here the spread in k vectors plays the role of the spread in frequency that produces the temporal reshaping observed with femtosecond pulses.
Single-shot real-time-resolved phonon dephasing measurements using phase conjugation
Authors: Delfyett Peter J. , Dorsinville R. , Alfano Robert R.
Published: February 2023

A new innovative single-shot technique to measure the dephasing rate of coherent molecular vibrations and optical phonons in liquids and solids in real time has been developed using Ramaninduced phase conjugation and streak technology. The technique uses two 30-ps pulses at 532 nm intersecting at a small angle. A third <2-ps broadband continuum pulse is directed counterpropagating to one of the 532-nm laser pulses. The signal is scattered in the phase conjugate direction and can be spectrally analyzed with a spectrometer and OMA system and temporally analyzed with a 2-ps resolution streak camera. In a single shot, the spectral output of phase conjugate signals yields the complete Raman spectrum which is phase matched over the bandwidth of the continuum, typically 2000 cm–1. The temporal response of a particular phonon or molecular vibration is obtained by placing appropriate narrowband filters in front of a streak camera to select the desired Raman frequency component.
Influence of ion-assisted deposition on structure and surface roughness of aluminum oxide
Authors: Varnier F. , Boulesteix C. , Targove J. D. , Lingg L. J. , Bovard B. G. , Macleod H. Angus
Published: February 2023

Two techniques of transmission microscopy were used to examine films of aluminum oxide made by ion-assisted deposition with a Kaufman hot cathode ion gun. The films were bombarded during their growth by oxygen ions of 500-eV energy at an ion current density of 100 μA/cm2. Substrate temperatures were nominally 100°C. The films were grown in the same pumpdown cycle with and without bombardment. The surfaces of shadowed replicas of the films were examined by a technique involving the microdensitometry of micrographs,1 and statistical parameters were derived. With ion bombardment, there appeared to be a reduction in the incidence of large nodular features but a slight increase in very fine roughness. Direct micrographs were obtained by first depositing films over carbon and then stripping them; they showed that the films were completely amorphous.
Optical properties of ThF4 films deposited using ion-assisted deposition
Authors: Al-Jumaily Ghanim A. , Yazlovitsky L. , Mooney T. , Smajkiewicz A.
Published: February 2023

Ion beam processes have been employed in different deposition techniques for the purpose of improving the optical and mechanical properties of thin films. One technique is ion-assisted deposition (IAD) which involves the bombardment of the growing film with low energy ions. In this investigation we examined the benefits of employing the IAD process on the optical properties of thorium fluoride (ThF4) films. Films of ThF4 were deposited using a resistively heated boat on fused silica and sapphire substrates. The substrates were not heated, and the deposition rate was 1 nm/s. A Kaufman ion source was used to bombard the film with 300-eV Ar ions. Conventionally deposited films adsorb moisture from the environment. This causes an increase in absorption at the water absorption band near 3 μm. Examination of IR transmission spectra at 3 μm indicated that films deposited using IAD had less absorption than those deposited with no bombardment. Samples were subjected to severe conditions of temperature and humidity for 72 h. Samples prepared using IAD showed only a slight increase in absorption, while the unbombarded sample cracked and delaminated. Spectrophotometric examination of samples showed that IAD films had a higher index of refraction than the unbombarded sample.
Ion-assisted optical coatings deposited at low temperature
Authors: Williams Forrest L. , Jacobson R. D. , McNeil J. R. , McNally J. J.
Published: February 2023

We have examined ion-assisted deposition (IAD) of thin films on substrates at reduced temperature (<150°C). Conventional deposition techniques typically require heated substrates (~300°C). The development of deposition techniques at reduced temperature is important for coating substrate materials that cannot be subjected to elevated temperature and for improving throughput. We have observed increased values of refractive index for optical thin films of Al2O3, TiO2, and Ta2O6 deposited using IAD that approach those of bulk material. In addition, optical coatings of SiO2 and MgF2 deposited with IAD have shown improved mechanical properties compared to similar films produced without IAD. We also present results from characterizing the Raman spectra and optical scatter for these films and correlate them to IAD conditions. From these results, we conclude that the application of IAD to deposition of TiO2 at low temperature promotes the growth of crystalline structure in the film with a corresponding increase in optical scatter.
Nonharmonic spectra for directive ultrashort pulses
Authors: Zucker Francis J.
Published: February 2023

Directive pulsed fields with steep rise times are remarkably nondispersive in space and time and thus invite diverse uses in optics as well as microwaves (energy transfer, target identification, clutter penetration). Recent investigations of these pulses have shown the aptness of spectral representations other than conventional time-harmonic Fourier transforms, prinicpally Heyman and Felsen’s transient plane waves1 and J. Brittingham’s "focus” wave modes.2
Implicit polarization in oblique Illumination
Authors: Batchelder J. Samuel , Goodman Douglas S.
Published: February 2023

In some applications, such as that of detecting small particles on the surface of a silicon wafer, the state of the illumination very near the surface is important. The light here is a superimposition of that arriving from the illuminator and that reflected from the surface. In general, its polarization is different from that leaving the illuminator. In the case of grazing incidence illumination, the light undergoes a 180° phase shift on reflection. Since the s-polarized light has higher reflectivity than the p-polarized light, destructive interference in s light is more complete at the surface. Thus the light here is nearly p-polarized, and submicron particles at the surface experience the light of this polarization.
Bessel series expansion of a Gaussian light beam and the distribution of energy concentration in an optical system
Authors: Li Zhengzhi , Shan Zi Juan , Zhu You Man
Published: February 2023

A method of Bessel series expansion of the Gaussian light beam—simpler than any of the other methods recently suggested in the literature—is presented, and its effectiveness for a circularly symmetric wave field is studied. In this method, the convergent speed is much faster than that of the Fourier series, and the precision is fine enough. The distribution of energy concentration of the Gaussian beam in successive Fourier-Bessel transform planes is also calculated. When the ratio between a halfwidth Gaussian beam and the diaphragm radius is 2:3, the energy concentration is optimum at the first transform plane; when the sizes of the aperture of the first transform plane and the entrance diaphragm are the same, the ratio 1:2 is optimum at the second transform plane.
Exact periodic solution in the semiclassical Jaynes-Cummings model
Authors: Kujawski Adam
Published: February 2023

In the semiclassical version of the Jaynes-Cummings1 model without the rotating-wave approximation, an exact periodic solution has been obtained and studied for some specific values of the coupling constant and the detuning. It is shown that when the atomic frequency is equal to three times the cavity frequency and the coupling constant is arbitrary, the oscillation amplitudes are maximal. The Fourier spectrum of the inversion is discrete. As is known (see, for example, Ref. 2) chaos has been found for the semiclassical Jaynes-Cummings model.
Accuracy of Fourier magnitude estimation from speckle intensity correlation
Authors: Marron Joseph C.
Published: February 2023

Following the Van Cittert-Zernike theorem, the normalized spatial correlation of the optical field in a speckle pattern is equal to the normalized Fourier transform of the intensity distribution of the object. By correlating the intensity of a speckle pattern, one can measure the magnitude of the normalized field correlation and thus the Fourier magnitude of the object.