bluuebunny/crossref_metadata_2025 huggingface dataset:
Hysteresis and delayed bifurcations in bistable systems
Authors: Gray George , Jung Peter , Mandel Paul , Roy Rajarshi
Published: February 2023

Bistable devices used as switches are a fundamental component of electronic and optical devices. We formulate a general dynamical theory of hysteresis and delayed bifurcations in periodically switched bistable systems. A generic model for a switched bistable system, the overdamped dynamics of a particle in a quartic double-well potential with a periodic driving force, is analyzed. The predictions of the analytic theory are tested by numerical simulation and by experiments on a bistable semiconductor laser. Excellent agreement is found in both situations. We find that the increase of the area of the hysteresis loop scales as the two-thirds power of the switching frequency. From this, we deduce a law for the increase in input power necessary to maintain repetitive switching as the driving frequency is increased.
Novel organic nonlinear optically active materials for integrated optical devices
Authors: Cox Hollace L.
Published: February 2023

DHAQ, an amine-substituted anthraqui-none, has been studied as a nonlinear, optically active (NLO) material. Theoretical studies have shown that delocalized π-elec- trons associated with the parent anthraqui- none ring system produce resonant as well as nonresonant nonlinear optical signals, both for DHAQ and other molecules belonging to this class of amine-substituted compounds. Incorporating DHAQ into a suitable host- matrix material has been studied to take advantage of the spatial polarization of the strongπ→π* electronic transitions in the parent anthraquinone ring system. A detailed model is presented of the electronic environment created for the DHAQ-host matrix composite material. The absorption spectrum for DHAQ alone has an intense "Q-band" structure (between 575 nm and 725 nm) as well as an extremely strong Sorile-band structure in the near-ultraviolet region. However, the Nπ→π
*
transitions responsible for the Q-bands and nonresonant NLO interactions are strongly perturbed by some host environments. Effects produced by a host environment on the nonresonant NLO signals produced by DHAQ in the 800-900 nm region will be presented. Suitability of various host materials for use as waveguide materials will be discussed in terms of their optical properties in the visible as well as near-infrared regions.
Optical phase-conjugate studies of organic dyes
Authors: Reddy B. R. , Venkateswarlu P. , George M. C.
Published: February 2023

We have investigated several organic dyes in an effort to identify new nonlinear-optical substances because these substances are of current scientific interest owing to their possible applications in several areas. Some of the dyes investigated are 21,71-dichlorofluorescein (DCF), rhodamine 110 (R110) and pyridin 1—all doped in boric acid host. The concentration of the dyes is 10−3-10−4 M and the thickness of the samples is ~100 µm. Degenerate four-wave mixing experiments, using multimode Argon ion laser wavelengths, have been performed on these samples to generate phase-conjugate (PC) signals. PC reflectivities are ~10−4; the largest signals are obtained for DCF. When the pump beams are vertically polarized, the generated PC signals are also observed to be vertically polarized (vector phase conjugation). Grating growth and decay times and PC reflectivities have been measured as a function of laser power and wavelength. PC signals have been detected for angular separation between probe and pump beams as large as 90°. For samples containing DCF and R110, the grating growth and decay times are in the millisecond range. For pyridin 1, grating growth time is in seconds, and the decay time is several minutes (PC signal lasted for 1 hour).
Third-order susceptibility dispersion of Mons and Dans side-chain-substituted polymers
Authors: Torruellas W. E. , Zanoni R. , Stegeman G. I. , Horsthuis W. H. G. , Mohlmann G. R.
Published: February 2023

Third-harmonic generation is used to measure the third-order susceptibility of side- chain-substituted polymers. Both the magnitude and phase ofχ(3)(3ω) are measured for a family of donor-acceptor diphenyl polyene side-chain-substituted polymers. Dimethylaminonitrostilbene (DANS) and methyloxynitrostilbene (MONS) side-chain- substituted polymer thin films are modelled by an inhomogeneously broadened two-level system. In addition to their very good linear and electro-optical properties, this class of organic polymers show χ(3)values comparable to those of fully conjugated backbone polymers. The values of the magnitude and phase of χ(3ω) have been measured at 953, 1064, 1573, and 1904 nm. The dispersion of χ(3)(3ω) for DANS and MONS side chain polymers agrees with the predictions of the two-level model. The values of the phase of χ(3)(3ω) are explained by dominant charge transfer mesomeric moments in the expression of χ(3)(3ω). The mesomeric moments obtained from our χ(3) measurements are in excellent agreement with those found in the literature.
Transparency and coherence in moving patterns
Authors: Welch Leslie
Published: February 2023

The true velocity of a straight contour moving behind an aperture cannot be determined (the aperture problem), but the true velocity of two or more contours with different orientations belonging to the same rigid object can be found. My results support the two-stage motion process proposed by Adelson and Movshon (Nature, 1982), which first extracts oriented-component motion and then combines that information to determine pattern or object velocity. A plaid pattern formed of two moving gratings is an interesting stimulus for velocity processing and coherence experiments because observers may see a rigid, coherent plaid object moving in one direction, or they may see two gratings moving different directions and sliding transparently over one another, i.e., two different solutions to the aperture problem. An observer's ability to respond to grating or plaid speed depends on whether coherence or transparency is seen; when the gratings cohere, only the plaid speed is perceptually available, and when the gratings appear transparent, only the gratingspeeds are available. The gratings must be similar to each other in contrast, spatial frequency, speed, color, and depth to be perceived as coherent. Thus, there must be a decision process based on component similarity that determines whether gratings, and presumably other oriented components, are part of the same pattern or object.
Optical flow distributions: gradient, energy, and regression methods
Authors: Simoncelli Eero P. , Adelson Edward H.
Published: February 2023

We discuss the formal relationships among several techniques for computing optical flow fields from sequences of images, and we extend those techniques to compute distributed representations of optical flow. Many computational techniques for deriving flow fields are based on the spatial and temporal derivatives of the intensity signal (i.e., the gradient). By writingspatial and temporal derivatives as quadratic combinations of spatiotemporally oriented filter outputs, traditional gradient techniques can be related to spatiotemporal energy models. Furthermore, these models can be viewed as performing a linear-regression analysis in the spatiotemporal frequency domain, thus fitting a planar surface to the signal spectrum. We discuss extensions of these techniques that compute probability distributions over the space of flow vectors. Such extensions allow the analysis of multiple motions at each spatial position (e.g., transparency) and provide a plausible model for physiological systems.
Dissociation between static and dynamic transparency
Authors: Cavanagh Patrick , Anstis Stuart
Published: February 2023

Stoner, Albright, and Ramachandran (Nature, 1990) conjecture that tacit knowledge of the physics of static transparency can influence dynamic transparency. They adjusted the luminance of intersections to make stationary crossed gratings look transparent and found that, when set in motion, the two gratings appeared to slide over each other (dynamic transparency). Conversely, gratings that did not appear transparent when stationary looked like a single plaid pattern when set in motion.
Integrated optical waveguide multiplexers for multichannel fiber-optic link
Authors: Thaniyavarn Suwat
Published: February 2023

Various types of voltage tunable Ti:LiNbO3 integrated optical waveguide multiplexers can be used to increase channel capacity of single-mode fiber-optic link.
Lorentz red shift and self-broadening of atomic potassium vapor
Authors: Maki Jeffery J. , Boyd Robert W. , Malcuit Michelle S. , Sipe John E.
Published: February 2023

The Lorentz-Lorenz equation predicts that the dispersion feature of an isolated optical resonance should have a density-dependent frequency shift toward the red end of the spectrum. We have investigated the dispersion feature experimentally by observing the frequency dependence of the Fresnel reflection (selective reflection) from the boundary between a dense atomic potassium vapor and the window of the vessel containing the vapor. We find that the selective-reflection features of both the S1/2-P1/2 (770.1 nm) and S1/2-P3/2 (766.7 nm) lines of potassium shift increasingly toward the red and broaden as the number density of the vapor is increased to 2 × 1017 atoms/cm3. We compare the results of the experiment to theoretical predictions for the selective reflection. The broadening is well described by conventional binary collision theory; however, the observed red shift of both of the lines is somewhat larger than that predicted by the Lorentz-Lorenz equation. It is possible that other mechanisms that lead to frequency shifts are occurring.
Luminescence study of ZnWO4 single crystals
Authors: Wang H. , Medina F. D. , Zhou Y. D.
Published: February 2023

Zinc tungstate (ZnWO4) has shown promise as a new scintillation material. Earlier photoluminescence studies were restricted to room temperature. In the present work, the photoluminescence from single crystals of ZnWO4 is studied in the temperature range of 20-400 K. A remarkable peak located in the infrared is reported for the first time. The zero-phonon line of this peak is located near 827 nm. The behavior of the color centers of ZnWO4 is analyzed. Based on lattice relaxation and the theory of multiphonon transitions, the spectral properties are discussed.
Phase velocity and spatial overlap of resonance modes of a sphere
Authors: Leach David H. , Acker William P. , Chang Richard K.
Published: February 2023

The internal intensity has a standing wave pattern where a sphere [with index of refraction n(ω) and size parameter ka > 1, where a is the radius and k = 2π/λ] is illuminated by a plane wave at specific wavelengths λ, which correspond to the morphology-dependent resonances (MDR's) of the sphere. The MDR's can provide high Q optical feedback for the internally generated fluorescent, Raman, and Brillouin waves. The standing-wave distribution of MDR's can be decomposed into two counterpropagating guided waves with specific phase velocity and radial distribution. We have calculated the phase velocity of the MDR's

V

n
,
l

MDR

as a function of the angular mode number n and the radial mode order l. The

V

n
,
l

MDR

→
c
/
n
(
ω
)

for MDR's with small l values because the internal intensity distribution is confined in the sphere. The

V

n
,
l

MDR

→
c

for MDR's with large l values because the internal intensity distribution extends into the surrounding air. The coherence length between the pumping wave on a MDR with n,l and the resultant wave with n′,l′ has been calculated. The effects of phase matching and spatial overlap of MDR's are demonstrated with four-wave mixing experiments.
Atom Optics
Authors: Pritchard David E.
Published: February 2023

A large-aperture liquid-He coated spherical mirror and a room-temperature bent-gold crystal have been used to focus atom beams of H and He, respectively. They are described elsewhere in this symposium. Many of the new optical elements for atoms rely on the mechanical forces of light; mirrors are one example. When atoms approach the surface of glass that has intense blue-detuned light inside, they recoil from the evanescent wave that extends several wavelengths past the surface and into the vacuum. The atoms are never close enough to the surface to be affected by its atomic attraction or its small-scale irregularities. When a highly collimated beam of sodium atoms is directed at a standing wave of light near its resonance frequency, the angular scattering pattern of the atoms exhibits the characteristics of diffraction from a short sinusoidal grating. Diffraction orders up to ~20 have been observed at high light intensities. In contrast to phase gratings made with light, material absorption gratings are amplitude gratings.
Two-particle correlation experiments with massive particles
Authors: Keith David W. , Bernstein Herbert J.
Published: February 2023

Since the first observation of two-point correlation effects in optical fields (Hanbury, Brown, and Twiss, 1957) there has been continuous theoretical and experimental interest in photon correlation. In this paper we examine the possibility of measuring similar effects involving massive particles. We first discuss the theory of correlations between noninteracting massive particles by using the formalism of second quantization. This theory is considerably simpler than that for light because we can treat particles in the strictly nonrelativistic limit. However, the theory provides a particularly interesting contrast with the photon case because we may choose particles that are either fermions or bosons. We then apply the theory to the case of beams of atoms and neutrons and consider the experimental parameters of existing beams. In particular, we consider the case of experiments with laser-cooled metastable helium.
Reconfigurable array interconnection by photorefractive correlation
Authors: Ford Joseph E. , Fainman Yeshaiahu , Lee Sing H.
Published: February 2023

The correlation matrix–tensor multiplier (CMTM) algorithm can be used to perform two-dimensional array interconnection by transmitting the input image through a phase-code mask and correlating it with a control image containing the encoded interconnection values. The control image can be manipulated (for example, by choosing an appropriate phase code or by truncating the control image to binary phase) to match the space–bandwidth product and type of the available display technology.
Lotka–Volterra dynamics in a photorefractive ring resonator
Authors: Anderson Dana Z. , Benkert Claus , Couch David , Hermanns Anno
Published: February 2023

We demonstrate a ring resonator pumped with photorefractive gain that implements two classes of Lotka–Volterra dynamics: winner-takes-all and the voter's paradox. By using two additional photorefractive crystals, we program the coupling among five modes of the resonator. One version of the system is five-fold multistable: Any one, but only one, of the five modes can oscillate at any one time. The mode is selected with an injected signal. In another version of mode coupling, the modes undergo a continuous cycle though the five modes—thus, a steady state is never reached. The coupling is achieved by placing one photorefractive medium in a Fourier plane of two copies of the resonator modes, which are formed by a beam splitter. The two copies of the modes interact again in an image plane. For winner-takes-all, every mode couples to itself in the image plane. For voter's paradox, every mode couples to its neighbor.
Band-edge surface transient diffraction
Authors: Garmire E. , Karpushko F. , Kost A. , Yang C.M.
Published: February 2023

As much as 25% self-diffraction has been observed at the surface of n-GaAs:Te when two pumps (and a weak probe) intersect with an internal angle of 0.15 rad in the Raman–Nath regime. The photoinduced gratings decayed in less than 100 ps. The diffraction efficiency was nearly independent of sample thickness (40 μm and 350 μm), and careful investigation has shown that the diffraction arose primarily at the surface and was resonant just below the band edge. It is proposed that band-bending at the surface states causes increased absorption and results in a sheet of optically induced charge. The faster diffusion of electrons relative to holes allows a transient charge separation to a distance of one diffusion length (1 μm). As a result, a space-charge field is formed (Dember field) that can cause an index change through the Franz–Keldysh effect. The resulting transient grating can cause the large observed diffraction. This new BEST effect has potential for optical-switching applications.
Effect of absorption on photorefractive two-beam coupling gain with a moving grating
Authors: Chomsky Doron , Sternklar  , Szichman Henrik , Jackel Steven
Published: February 2023

Optimum two-beam coupling gain in photorefractive semiconductors is achieved mainly by the DC field and moving grating technique. Due to the crystals' finite time response, the out of phase component of the refractive-index grating is enhanced. In this work we show that absorption, which is not negligible in these crystals (α ~ cm−1), prematurely saturates and degrades the small - signal gain along the crystal's interaction length. This is due to its' influence on the crystals' response time τ, which is approximately inversely proportional to the light intensity in the crystal, so that τ varies as τ(z) ≈ τ(o)eαz along the interaction coordinate z. A distributed time constant causes a deviation from t he optimum phase condition along the interaction length when using the moving grating technique. Our model predicts a significantly suppressed small-signal gain, which peaks at an optimum interaction length 1opτ ≈ 1/α and then degrades for larger 1. This effect can account for discrepancies between measured gain in semiconductors and previous theories. It also presents a fundamental limitation of the moving grating technique in photorefractive waveguides, which would not benefit from long interaction lengths. In this case, the AC field method would be more effective.
FJ2 Short-cavity distributed Bragg reflector laser with an integrated tapered output waveguide
Authors: Chien M. , Koren U. , Koch T. L. , Miller B. I. , Oron M. , Young M. G. , Demiguel J. L.
Published: February 2023

The use of tapered waveguides to adiabatically increase the lateral and transverse mode size of a semiconductor laser has been recently demonstrated, and improved tolerances for coupling into a single-mode fiber were reported.1 The adiabatic-mode-expansion (AME) waveguide of the previous work was part of the Fabry–Perot laser cavity.
Holographic interconnections and their applications
Authors: Wang J. M. , Sawchuk A. A.
Published: February 2023

Several holographic architectures have been proposed for implementing free-space optical interconnections. These architectures have important advantages over electronic systems and systems that use classical optical components. In addition, volume holograms, which provide high diffraction efficiency, can improve the light efficiency of the system. However, two major problems in using holograms as interconnection components are seldom considered. These are holographic distortion and the uniformity of diffraction efficiency owing to Bragg mismatch.
Single-lens stereoscopic camera
Authors: Wang John Y. A. , Adelson Edward H.
Published: February 2023

We describe a new type of range camera that performs stereoscopic measurements in both the horizontal and vertical directions but uses only a single main lens. The main lens forms an image in the usual way, but a lenticular array is placed in the image plane to break the image up into a set of "microimages." Each microimage covers several charge-coupled device elements, and different parts of this microimage correspond to light passing through different parts of the main aperture. By electronically selecting different parts of the micro-images, one can simulate the images that would be acquired by inserting various aperture stops in the main lens. In particular, one can simulate the effects of moving a small aperture stop in the horizontal and vertical directions; thus one can obtain the equivalent images that would be obtained by a small-baseline stereoscopic system. Displacements are calculated by a least-squares gradient method and are then converted to range estimates.
Smectic liquid-crystal waveguides with cylindrical geometry
Authors: Lo S. K. , Galarneau L. M. , Rogers D. J. , Flom S. R.
Published: February 2023

It has been speculated that homeotropically aligned smectic-A liquid crystals in a cylindrical configuration would prefer the Frank solution with an isotropic core, instead of the non-singular transition found in nematics. However, homeotropic alignment of the smectic-A in a cylindrical structure has never been reported. We have made liquid crystal cylindrical waveguides with low optical loss, which allows us to systematically study the physical, electro-optical and opto-optical properties in these structures. In our study of the smectic-A 8 CB (4 cyano-4′-octylbiphenyl) cylindrical waveguide, we have shown that the homeotropic alignment of the 8 CB molecular director is confined in the radial plane. The free energy diverges at the center of the waveguide to form an isotropic core satisfying the Franksolution. This result is surprising considering the large radius (75 m) of the waveguide. The alignment of the liquid crystals in the waveguide is critical in determining the index profile of the guide since the liquid crystals are highly biréfringent. Modulation of the liquid crystal alignment through electrical or optical fields would result in the modulation of the index profiles and hence the light propagation properties in the waveguides. Unique behaviors under heat treatment and interesting light propagation characteristics in the smectic and nematic liquid crystal cylindrical waveguides have been observed for the first time.
Time-resolved study of smectic A guest host system response to 488-nm pulsed excitation by means of laser speckle
Authors: Guardalben Mark J. , Wang Shen-Ge , Landry Joseph , George Nicholas
Published: February 2023

Using a pulsed, pump-probe experimental arrangement, we have investigated the speckle generated by a 100 μm path-length cell of smectic A liquid crystal of 4-cyano-4′- octylbiphenyl doped with 0.1% wt/wt dichroic dye. Upon irradiation, the guest-host system undergoes a phase transition from an initially transparent condition to a scattering state. From the statistical theory of speckle, we are seeking to establish the effective scales of turbulence in the liquid crystal, both transversely and longitudinally. A time-resolved analysis of the observed speckle during the relaxation of the system back to the ordered, homeotropic condition revealed the effective scale lengths of the liquid-crystaldye mixture in the irradiated region. Dynamic response as a function of molecular anchoring conditions was also investigated. The importance of this research to power-limiting applications will be discussed.
Cesium Atomic Resonance Filter
Authors: Batdorf Brian J. , Jacobson Mike , Macleod Angus
Published: February 2023

Atomic resonance filters (ARF) have the unique property of simultaneously being wide angle and extremely narrowband. ARFs depend on atomic excitation of a contained gas at one wavelength and the fluorescence at a longer wavelength. By sandwiching the gas between two edge filters (the input filter transmitting at and below the excitation wavelength and the output filter transmitting at and above the fluorescence wavelength) the combination has throughput only from the gas resonance.
Structural dynamics of clean and oxidized Al surfaces
Authors: Janz Siegfried , Bottomley D. , Timsit R. , van Driel H. M.
Published: February 2023

We report on experiments using optical second-harmonic (SH) generation to probe the evolution of the surface structure on clean and oxidized Al surfaces with increasing temperature. An incident beam from a synchronously pumped dye laser with a wavelength of 580 nm was used to generate SH light at the specimen surface. The SH intensity was monitored as the sample temperature was ramped from room temperature to 550°C. Above 450°C, a sharp increase in the SH signal from the oxidized Al surfaces signalled the onset of a structural transformation. Complementary studies using Auger electron spectroscopy and scanning electron microscopy indicate that this transformation involves the breaking up of the oxide film into islands of 50 nm or less in size, separated by atomically clean Al. In similar experiments on atomically clean Al surfaces, the crystalline anisotropy of the SH signal decreased with increasing temperature. A possible mechanism for this effect, which involves the evolution of steps on the surface, will be discussed.
Four-dimensional picosecond exciton capture at the interface in symmetric and asymmetric quantum wells
Authors: Takiguchi Yoshihiro , Shum Kai , Mohaidat Jihad , Morkoc H. , Alfano R. R.
Published: February 2023

Exciton dynamics at the interface have been investigated in symmetric and asymmetric GaAs quantum wells by means of four-dimensional picosecond time-resolved photoluminescence spectroscopy at different temperatures. The spectral and temporal resolutions of the system are 2.5 nm and 9.7 ps, respectively. Twenty-five periods of Al0.3Ga0.7As-GaAs-Al0.3Ga0.7As symmetric quantum wells (SQWs) and Al0.3Ga0.7As-GaAs-AlAs asymmetric quantum wells (AQWs) grown on GaAs substrates by a molecular-beam epitaxy Method were investigated. The thicknesses of the layers are 200, 50, and 200 A, respectively. The temporal profile of photoluminescence for SQWs is singleexponential, with a 260 ps decay time, whereas a two-exponential decay profile is observed for AQWs, which have a fast decay of 90 ps and slow decay of 950 ps. The fastdecay component arises from excitonic recombination in the quantum well, which is dominated by nonradiative capture at the interface between GaAs and AlAs and its alloys. These results suggest that the roughness of the interface between GaAs and AlAs has been found to produce more nonradiative pathways than that between GaAs and AlGaAs. It is also found that the bound states with a binding energy of 3.5 meV are responsible for the exciton capture process at the interface.
A High-speed Microwave Antenna Suitable for Optoelectronic Integration
Authors: Baca Loretta J. , McInerney John G.
Published: February 2023

Broadband antenna arrays are essential for applications such as radar, frequency-agile microwave communication and electronic counter-measures. Optical feeding of the individual elements of such arrays is promising for beam steering, remote positioning of the antenna with respect to the signal source or receiver, and for high-frequency operation where the inter-element spacing becomes too small for individual waveguide feeds. In this paper we describe the design, fabrication and evaluation of a compact broadband antenna on semi-insulating GaAs or similar material, which lends itself readily to array formation, and which is readily integrable with high-speed electronic and optoelectronic components for optical feeding and phase-shifting. Our design methodology has used the effective index method commonly used in optical waveguide analysis, in place of the more conventional but cumbersome method of moments. This simplification is justified by the strong confinement of the fields within the high-permittivity substrate. A slot-line antenna with a four-section Chebyshev quarter-wave impedance transformer and Marchand balun was designed and fabricated on Duroid 6010, a material chosen for its similar dielectric properties to semi-insulating GaAs. By measuring the SWR using a microwave network analyzer and sweep oscillator, and by using the antenna in receiving mode on an anechoic test range, we have demonstrated successful performance with at least 10 dB directional gain in the designed range 16-18 GHz. Possible applications of single- and multiple-element antennas of this type in hybrid optical/microwave systems will be discussed.
Laser-produced, plasma-pumped XUV molecular laser
Authors: Benerofe S. J. , Barty C. P. J. , Yin G. Y. , Gordon C. L. , Harris S. E. , Young J. F.
Published: February 2023

We have used the energetic electrons created by a laser-produced, traveling-wave plasma to pump a molecular hydrogen Werner band laser at 116 nm. Using a 400 mJ, 300 ps, 1064 nm pulse with a repetition rate of 2 Hz, we measure a gain coefficient of 1.0 cm-1 and an extrapolated total small signal gain of exp (26); the laser output exhibits saturation.
Experimental studies on the feasibility of a resonantly photopumped molybdenum laser near 600 Å
Authors: Ilcisin Kevin , Schwob J. L. , Zhang G. , Suckewer S.
Published: February 2023

Experimental studies undertaken to demonstrate a resonantly photopumped laser in molybdenum near 600 Å are presented. A two laser approach has conclusively produced enhanced fluorescence through photopumping. Experimental attempts at achieving gain will also be discussed.
Iterative phase-restoration technique using a continuous-phase SLM and a point diffraction interferometer
Authors: Tam Eddy C. , Yu Francis T. S. , Tanone LAris , Wu Shudong , Gregory Don A.
Published: February 2023

Early work with the liquid-crystal television (LCTV) in image-processing applications are mostly making use of the polarization property of the device. Even when the LCTV is used as a binary phase-only spatial light modulator, as shown by Davis et al.,1 the phase-modulation effect is actually obtained from the polarization-modulation property. However, besides the polarization-modulation property of a twisted nematic liquid crystal cell, there is also a birefringence effect inherently associated with the liquid-crystal cell.2 Therefore, it is possible for the twisted-nematic-based LCTV to operate as a phase-only spatial light modulator. We have measured this continuous phase-modulation property of an LCTV and found that a phase-modulation angle of more than 2π rad is obtained.
Optical measurement of the relative roughnesses of dielectric coatings on diffusive substrates
Authors: Lettieri Thomas R.
Published: February 2023

The surface roughness of a transparent or translucent dielectric coating can affect the optical appearance of a diffusive surface onto which the coating is applied. Because such coatings are often fragile, it would be useful to have a noncontact, optical method by which to measure their roughnesses.
Comparison of scanning tunneling microscope profiles and Talystep mechanical profiler measurements of gratings and low-scatter surfaces
Authors: Bennett Jean M. , Elson J. Merle , Archibald Philip C. , Schaub Charles L. , Garvin Hugh L. , Elings Virgil , Kjoller Kevin
Published: February 2023

Several low-scatter optical surfaces and ion-etched gratings have been profiled by using a scanning tunneling microscope (STM) or atomic force microscope (AFM) and a conventional Talystep mechanical surface profiler with a diamond stylus. Lateral resolution was not a problem with the low-scatter optical surfaces; the polished fused silica surface had about the same roughness on an atomic lateral resolution scale as it did on the macroscopic scale of the diamond stylus profiler. The ion-etched gratings had a period of 0.7 μm and a groove depth of ~2500 Å. The groove shape and depth could not be measured with the diamond-stylus profiler because the grooves were only partially resolved with a "shovel-shaped" stylus having a short radius (~0.2 μm). However, once the true shape was measured with the STM, the approximate profile that would be recorded by a diamond stylus profiler could be calculated. This calculation showed that it is not possible to guess the shape of the part of the groove that is not contacted by the diamond stylus by means of a mechanical-profiler measurement alone. Representative profiles taken with both types of instruments will be shown and compared.
Effects of spatial coherence on photorefractive two-beam coupling
Authors: Kong Honqzhi , Wu Cunkai , Cronin-Golomb Mark
Published: February 2023

Photorefractive two-beam coupling with partially coherent light is investigated both theoretically and experimentally. By applying partial-coherence theory, a spatially varying distribution function for the grating visibility is found analytically. For certain beam configurations, this function may be approximated as one-dimensional and the coupled wave equations may be established and solved numerically. When compared to the case of perfect coherence, partial coherence has two major effects on the beam coupling. One is that the effective grating length may be smaller than the crystal length as a result of the spatial-coherence limit. The second is that the visibility distribution over the grating is smaller than the constant visibility of the coherent case.
Effects of optical activity and absorption on two-wave mixing in Bi12SiO20
Authors: Webb D. J. , Solymar L.
Published: February 2023

When a Bi12SiO20 crystal is used for two-wave photorefractive amplification and a constant voltage is applied to the crystal, the gain may be considerably enhanced by detuning one of the incident beams to produce a moving grating. Simple theory shows that the gain versus detuning curve has a single maximum that depends on the total incident intensity. When crystals with lengths greater than a few millimeters are used, one must take into account the effects of optical activity and absorption, the anisotropic nature of the photorefractive effect in Bi12SiO20 causes alternating regions of high and low coupling constants as the plane of polarization of the two beams rotates through the crystal under the influence of optical activity. In the particular example where the crystal length is such that there are two regions of high coupling constant at the beginning and the end of the crystal, the average intensities within the two regions will be different because of absorption, and the optimum detuning frequencies for the two regions will also be different. This results in a double maximum in the detuning curve. Theoretical predictions of multiple peaks have been experimentally confirmed.
New investigation of the mechanism of the photorefractive effect in Ce-SBN
Authors: Xu Huai-fang , Shao Zong-Shan
Published: February 2023

The short-circuited Ce-SBN single crystal was illuminated by an extended argon laser beam with λ = 488 nm and intensity of 45-200 mw/cm2 68n of crystal can be measured by interference method without extraelectric field. Following results were obtained: 1. Δne was changed with the intensity of the illuminating beam and the value of 0.4-1.7×10-3. 2. Δn0 < Δne. 3. τ, the relaxation time of Δne was between 32 and 86 s and also changed with the intensity of the beam. 4. The moving direction of interference fringes due to laser beam illumination on the crystal was opposite to the effect of heat. 5. The Δne decreased obviously when the wavelength of the illuminating beam changed from 488 nm to 632.8 nm. 6. There were only a few effects on Δne when the polarization direction of the illuminating beam was changed. 7. No phase shift occurred in the space distribution of Δne(z) and I(z).
Polymer waveguide modulator
Authors: Chen Ray T. , Sadovnik Lev , Sun Zong J. , Robinson Daniel , Jannson Tomasz
Published: February 2023

We report the first colinear single-mode polymer waveguide modulator that can be formed on any smooth surface—including semiconductors, conductors, and insula tors—regardless of its conductivity and refractive index. The tunability of polymer film allows us to shift the guiding layer from step index profile to graded-index profile. The phase-matching condition for optical power transfer is achieved through current injection. A 34 dB extinction ratio was observed with an injection current density of ~10 μA/μm2. Unlike that of the conventional dual-channel coupler, the asymmetry of the colinear waveguide pair provides us with a much larger dynamic range of waveguide dimensions, and, thus, eases the requirements of waveguide fabrication.
High-efficiency InGaAsP/InP multiple quantum-well phase modulator for the 1.5-1.55-μm fiber band
Authors: Soole J. B. D. , Tsang H. K. , White I. H. , LeBlanc H. P. , Bhat R. , Koza M. A.
Published: February 2023

We report the design and realization of a high-performance InGaAsP/lnP multiple quantum-well waveguide phase modulator based on the quantum confined Stark effect. Use of the quaternary InGaAsP for the well material enabled a high phase-modulation efficiency to be obtained with a low intensity modulation throughout the 1.5-1.55 μm fiber band. A 180° phase modulation of TE polarized light was obtained in a 4 mm long device under 5 V bias with just 0.6 V at 1.49 μm wavelength and 0.9 V at 1.55μm wavelength. The phase shift increased quadratically with applied bias, in accordance with theory, giving a total phase shift of 1100° (TE) and 830° (TM) at 1.4 μm at 6 V, with 500° (TE) and 400° (TM) at 1.55μm. The refractive index change associated with the measured phase shift was found to have an approximate inverse-square dependence on the energy detuning from the exciton resonance. The intensity modulation associated with the phase modulation was very low. At 1.49 μm, there was just 0.7 cm-1 measured excess loss for TE light, with 1.6 cm-1 for TM light. This excess loss decreased at longer wavelengths and vanished at around 1.54 μm. No optical intensity dependence was discernible up to the maximum cavity power of 10? W/m2. Device speed was limited to −1 GHzby RC charging times.
Laser-induced fluorescence measurements of velocity in arc jet flows
Authors: Marinelli William J.
Published: February 2023

We have been working on a technique for the measurement of critical flowfield properties in arc jets using laser-induced fluorescence, which makes use of a nascent seed particle, atomic copper. The copper atoms are produced via sputtering from the arc anode. Our technique is based on Doppler-shift methods for the determination of velocity and turbulence and Doppler absorption widths for the measurement of temperature. The technique uses absorption from the ground s1/2 to the excited P1/2 state of copper at 327.5 nm. Fluorescence is observed on the P1/2 - D3/2 transition at 578 nm. We have used both CW ring dye lasers and narrow bandwith pulsed dye lasers to characterize the copper atom absorption lineshape and measure velocity in a supersonic free jet of atomic copper seeded in helium. The shift in the absorption spectra obtained with the cw ring dye laser gives the freestream flow velocity, and the Doppler width gives the velocity distribution. When probed with a frequency doubled, pulsed Nd:YAG pumped dye laser, the absorption lineshape is now determined by the laser profile, but the Doppler shift due to the flow is identical (within error limits) to the shift obtained in the cw laser measurements. The same experiments performed with the pulsed laser have now been replicated at the NASA/JSC 10 MW arc driven test facility. Doppler shift measurements have been performed in the facility as a function of specific anthalpy. An asymptotic behavior of the velocity as a function of specific anthalpy is obtained due to the increasing degree of molecular oxygen dissociation at higher anthalpies.
Tunable diode laser IR absorption diagnostics of semiconductor deposition
Authors: Wormhoudt J.
Published: February 2023

This is a program to develop and demonstrate laser diagnostics of compound semiconductor processing systems, such as the metal-organic chemical-vapor deposition (MOCVD) of III–V and II–VI materials. It focuses on tunable infrared diode-laser absorption, a technique capable of high-sensitivity quantitative measurements of absolute concentrations of both radicals and stable molecules. A long-path plasma reactor is used to generate easily detectable amounts of a wide variety of radical species in plasmas that include organoarsine compounds or methane. These latter systems have their own intrinsic interest because of their applications in diamond and hard-carbon deposition, as well as gallium arsenide etching. In addition, they contain the hydrocarbon species that are also important in MOCVD. Results to date in methane plasma observations include measurements of the methane dissociation fraction and rotational temperature and the measurement of the absolute concentrations of the decomposition products CH3, C2H4, and C2H2. The dissociation fraction is large, reaching about 0.9 at applied powers above 500 W. C2H2 and C2H4 concentrations are large, but CH3 concentrations are much smaller, on the order of 104 of the total. Plasma temperatures are low, under400 K for all conditions observed to date. Also planned are observations of arsenic hydride species, which may play a key role in suppressing carbon incorporation in MOCVD.
Optical property and application of Q-switch acetate film
Authors: Titus A. , Liu P. L. , He G. S. , Prasad P. N. , Korytko L.
Published: February 2023

Solid-state saturable absorbers are ideal for Q-switching or mode locking portable lasers. There is no need for electronic control circuits or any power consumption.
Implementation of kinoforms using a continuous-phase SLM
Authors: Tam Eddy C. , Yu Francis T. S. , Wu Shingwai , Tanone Aris , Wu Shudong , Li John X. , Gregory Don A.
Published: February 2023

Phase-only holograms, or kinoforms, have the advantage that all the incident light can be diffracted into the final image. Moreover, the space-bandwidth product requirement for displaying a kinoform is significantly lower than that of a sideband-type hologram. However, the lack of a programmable spatial-light modulator (SLM) that can provide a continuous and full range of phase modulation has limited the implementation of kinoform-to-binary phase-only holograms. Recently, we have verified that a commercially available liquid-crystal television SLM can provide the full range of phase modulation. Subsequently, we have studied the use of this device in displaying kinoforms. We have also implemented a phase-only filter in a joint-transform correlator for distortion-invariant pattern recognition to illustrate the applicability of this SLM.
Theory of diffraction and four-wave mixing by binary, optically addressed spatial light modulators
Authors: O'Callaghan M. J. , Handschy M. A. , Arnett K.
Published: February 2023

Various types of optically addressed spatial light modulators (OASLMs), which consist of a photosensor layer and a light-modulating layer, have been developed. Some of these devices have been demonstrated to be capable of performing four-wave-mixing operations, such as two-beam coupling and phase conjugation. Most of these devices produce a degree of modulation that is proportional to the incident light intensity, i.e., they produce analog modulation. There is also a class of OASLMs that are binary, i.e., the degree of modulation has one of two possible states, which depend on whether the incident light is above or below some threshold. However, because of information loss in the process of binarization, it is not obvious to what extent these devices can perform four-wave mixing. In this work we have theoretically explored the general character of light scattered by an idealized binary OASLM and have evaluated the device's capabilities for four-wave-mixing applications of two-beam coupling and phase conjugation.
Generalization of complex Snell–Descartes and Fresnel laws
Authors: Dupertuis M. A. , Proctor M. J.
Published: February 2023

Harmonic inhomogeneous plane waves (HIPW) are stationary solutions of the Max-well equations for an unbounded medium and take the following form: where k is the a complex wavevector. Since k is complex the waves may be exponentially decreasing or increasing in a direction perpendicular to the direction of propagation (in a nonabsorbing medium). Although not fully physical because they are not square intergrable, HIPW remain very useful in a number of problems as do plane waves1,2, for example the description of evanescent and surface waves and also the well known exact Sommerfield solution to the diffraction of a planewave by a conducting halfplane use HIPW.
Physical optics polarization correction of backscattering from conducting smooth surfaces
Authors: Schatzberg Alon
Published: February 2023

Polarization correction to high-frequency single-scattered fields from smoothly curved surfaces has been obtained in the past through evaluation of the next-to-leading term in the Luneburg–Kline (L–K) expansion of the scattered fields. For a backscattering situation, the correction term has been found to depend on the difference between the principal curvatures of the surface at the specular-reflection point. The above is classified as a geometrical-optics approach. For scattering surfaces that are locally cylindrically symmetric at the specular point, one would have to dig deeper into the L–K series to find the cross-polarization term—a formidable task. In such cases it pays to resort to an approach based on physical optics. The classical physical-optics solution is recognized as the leading term in the Neumann-series representation of the solution to the magnetic-field integral equation. This solution is known to be copolarized with the incident field. We derive the next term in this representation, evaluate it in the high-frequency limit, and separate the cross-polarization term from the result.
Resolution limits for incoherently averaged, photon noise-limited coherent images
Authors: Idell Paul S.
Published: February 2023

We investigate the way errors arise in coherent imaging systems and how such errors fundamentally limit the quality of the images formed. To reflect the best possible imaging performance with a photon-counting detector, we use a continuous-detection model to describe the operation of a focal-plane imaging sensor in a coherent optical-imaging configuration. By means of this detection model and the statistical properties of imaged laserspeckle patterns, we compute the signal-tonoise ratio (SNR) of the complex Fourier amplitudes of the coherent images formed under single- and multiple-exposure modes of operation. We explore physical insights provided by this SNR expression (as well as certain system design tradeoffs implied by it) and illustrate key points with the help of computer-simulated coherent imagery.
Glass waveguides—passive components and beyond
Authors: Jackel Janet Lehr
Published: February 2023

Glass has been used as the substrate for a wide range of passive, active, and nonlinear optical components. Passive functions, from beam splitting to wavelength multiplexing, have been performed in planar glass guides formed by ion-exchange or by the more recently developed silica-on-silicon technology. Although glass is typically viewed as a purely passive medium, it is possible to use glass waveguides to perform many active functions. For example, thermally induced changes in refractive index can be used to tune or switch components; response times as short as a few milliseconds are achievable. Active components can also be made by combining the glass guides with overlayers of active materials, such as liquid crystals or semiconductors. The recently demonstrated grafting of thin semiconductor layers onto glass guides has made it possible to combine the desirable qualities of glass and semiconductors. By such grafting, detectors have been integrated with glass waveguides, and the integration of sources with glass waveguides may be possible in the future. The use of rare-earth-doped glass provides another way to integrate lasers with glass waveguides. Finally, the extremely low absorption losses of glass guides makes them suitable for demonstration of nonlinear optical switching. My presentation reviews these and other uses for glass waveguides.