bluuebunny/crossref_metadata_2025 huggingface dataset:
New method of measuring inner scale and structure constant of atmospheric turbulence
Authors: Consortini Anna , Yi Sun Yi , Ping Li Zhi , Consortini Giuliano
Published: February 2023

A new method is presented to measure inner scale and structure constant of the atmospheric turbulence. The method utilizes information contained in both phase and amplitude fluctuations of laser radiation propagating through the atmosphere. More precisely, it requires the simultaneous measurements of the intensity variance at a point of a spherical wave and the transverse displacement variance of a narrow laser beam that have crossed the same turbulent path. The method, which is suitable for measurements over very short paths, is developed in the limits of geometrical optics. An experimental laboratory test is also presented.
Spectral fanning of stimulated Raman scattering
Authors: Bobbs Bradley , Warner Charles , Carman R. L.
Published: February 2023

Broadband pump and/or seed beams input to a Raman amplifier, if not exactly collinear, will yield a broadband Stokes output spectrum which is fanned or angularly dispersed. The direction of maximum gain for growth of any component of the Stokes spectrum is found from a four-wave mixing phase matching condition. The relative angle a between the high gain directions for distinct Stokes lines will be much smaller than the angle θ between pump and Stokes directions, with a ratio of where γ is the spectral separation and ωs is the Stokes frequency.
Low pump threshold cavity design for Ti:sapphire lasers
Authors: Sizer Theodore
Published: February 2023

The Ti:sapphire laser has already proved itself to be the laser of choice for near infrared cw laser applications. In a standard folded-astigmatically compensated cavity, however, the pump power threshold is as high as 4 W making a medium-to-large frame argon or lamp-pumped dye laser necessary as the pumping source. To make the Ti:sapphire laser more reliable and accessible for both laboratory and commercial applications, it will be necessary to eliminate the need for such a large pumping laser by reducing the threshold pumping power. Astigmatically compensated laser cavities allow one to balance the intracavity astigmatism by the folded focusing optics, however, the spot in the focal region can be quite large and astigmatic. To reduce the threshold power the focal spot size needs to be reduced as much as possible. For this reason we designed a linear cavity which uses intracavity lenses to focus the light and an antireflection coated Ti:sapphire rod which is slightly wedged. In this manner the spot size is reduced significantly since all the astigmatism generating components have been eliminated. The cavity has been demonstrated and the pumping threshold power was decreased by a factor of 5–800 mW compared to the folded cavity design.
Twin-fiber technique for measuring spatial coherence
Authors: Fuhr Peter L. , Anderson Betty Lise
Published: February 2023

The traditional method for measuring spatial coherence is to use Young's double slit arrangement or some similar variant. Although quick and easy, this technique has some drawbacks, particularly in replacing and realigning successive sets of apertures. A new method is described using single-mode optical fibers to sample the beam, and a γ-coupler to combine the light from the two points. As one fiber end is translated along the fiber axis (perpendicular to the wavefront), fringes are observed at the output. This method has the added advantage of being able to compare any two arbitrarily chosen points on the wavefront, and symmetry does not have to be assumed. Spatial coherence functions for several different lasers have been measured and compared with results using the classical method. Visibility is measured as a function of aperture spacing and of bias current (for laser diodes). No fringes are observed for below lasing threshold operation of laser diodes or for a light emitting diode (LED).
Design of bistable optical devices using interference filters
Authors: Sun Degui , Weng Zhaoheng , Yang Shumei , Feng Jazhang
Published: February 2023

The optical bistabilities of ZnSe and ZnS interference filters have been studied since 1977 when Karpushko and Sinitsyn reported the first experimental results. We see from papers published that (a) it is appropriate to study and compute optical bistabilities of interference filters by a Fabry-Perot resonator; (b) during the fabrication of bistable optical devices (BOD) the parameters such as incident angles, transmission power, and influence of peak position error on BOD, etc. were not studied in detail; (c) the authors could not resolve the problems of transmission peak height for large absorption materials such as ZnSe. We propose a new method of designing BODs of interference filters to study these problems precisely.
Sum frequency mixing of radiation from a laser diode with radiation from an argon-ion laser in β-BaB2O4
Authors: Sugiyama Kazuhiko , Yoda Jun , Sakurai Toshio
Published: February 2023

Tunable cw ultraviolet radiation was generated by sum frequency mixing of the radiation from a DFB-type laser diode with the radiation from an argon-ion laser in a nonlinear crystal of β-BaB2O4. The wave-lengths of the radiation generated by sum frequency mixing, of the argon-ion laser, and of the laser diode were ~370, 514.5, and 1310 nm, respectively. The crystal was cut to a length of 7 mm and θ = 29° for type-I phase matching and was held at 40 ± 1 °C to prevent surface degradation due to atmospheric water vapor. The phase matching was made by angular tuning. A preliminary result of several nanowatts of radiation at ~370 nm was obtained by the radiation of 3.2 mW from the laser diode and the radiation of 500 mW from the argon-ion laser. The generated power could be increased by improving the collimation and optimizing the focusing of the laser diode. The dependence of the input radiation power and tolerances of the crystal tuning angle and wavelength of the laser diode were measured.
Controlled generation of nanosecond optical pulses by SBS
Authors: Zhang Tong , Bickford James H. , Ghosh Roy D. N. , Rao D. V. G. L. N.
Published: February 2023

We report experiments describing controlled production of intense optical pulses of variable width in the 2-25-ns range using stimulated Brillouin scattering (SBS) both in transient as well as quasisteady state regimes. It is known that the SBS process is accompanied by a short-lived transient state before becoming stationary. Hence if the experimental conditions are so controlled that the SBS process is not allowed to develop into the stationary state, the accompanying short-lived transient state can be used to generate narrow pulses. This can be accomplished even when the phonons are short-lived relative to the pump pulses. A passively Q-switched ruby laser was used to generate pump pulses of 25-ns width with power in the megawatt range. Experiments were carried out with sample lengths of 7, 12, and 25 cm using acetone and n-hexane. For a fixed cell length L, the pump intensity was varied giving rise to corresponding variations in the exponential gain G = gIL, where g is the stationary gain coefficient and I is the pump intensity, thereby allowing the SBS process to go from stationary to nonstationary state. At pump intensities where G values forced the SBS to be nonstationary, optical pulses with peak power in the kilowatt range are produced with width about an order of magnitude shorter than pump pulse. As cell lengths are reduced, nonstationarity developed faster resulting in narrow pulses.
Effects of grating area, spatial frequency, viewing distance, eccentricity, and noise spectral density on contrast detection in spatial noise
Authors: Rovamo Jyrki , Nasanen Risto
Published: February 2023

Using computer graphics and a two-alternative forced-choice method we measured contrast detection thresholds in spatial noise as a function of spatial frequency (F). Grating area (A) decreased in inverse proportion to F2 Hence, regardless of spatial frequency, viewing distance, or eccentricity, the test gratings had a constant number of square cycles (c
2
), calculated as AF
2
. Noise was produced by adding to each pixel a random number drawn independently from an even distribution with zero mean. Thus, noise was white up to a cutoff frequency determined by the pixel density of our display. Noise spectral density decreased in direct proportion to grating area (A) and in inverse proportion to spatial frequency squared (F
2
). Hence, a change in viewing distance had the same effect on grating area and noise spectral density as a corresponding change in spatial frequency. Increasing eccentricity results in increasing cortical spatial frequency and decreasing cortical grating area. Their magnitude is determined by the cortical magnification factor and their effects can be compensated for by reducing the viewing distance (M-scaling). Thus, the effect of increasing eccentricity is similar to that of increasing viewing distance.
Coarse disparity processing does not shift fine scale processing
Authors: Rohaly Ann Marie , Wilson Hugh R.
Published: February 2023

Several stereomatching algorithms posit that processing on coarse (low spatial frequency) scales constrains processing on fine (high spatial frequency) scales by shifting the disparity range over which fine mechanisms operate. To test this hypothesis, we measured stereoacuity and stereo increment thresholds for high spatial frequency test stimuli in the presence of low spatial frequencies. If high spatial frequency mechanisms are always shifted to an optimal range for disparity processing, as proposed in the coarse-to-fine models, stereo increment thresholds for high frequencies in the presence of low frequencies should be constant, regardless of base disparity. In contrast, we find that in the presence of low spatial frequencies, increment thresholds for high spatial frequencies increase with base disparity as do increment thresholds for high frequencies alone. As a further test of whether information on coarse scales enhances processing on fine scales, diplopia thresholds were measured. In the presence of low frequencies, fusion ranges for high frequencies are severely reduced.
Measurements of atmospheric propagation at visible and UV wavelengths using a multiwavelength transmissometer
Authors: Patterson Edward M. , Duckworth Robert M. , Gillespie James B.
Published: February 2023

The attenuation of visible and near ultraviolet light by the atmosphere will exhibit a wavelength dependence. This wavelength dependence can be quite variable as a result of variation in concentrations of gaseous absorbing species and in the optical properties and concentrations of aerosol particles. There are currently relatively few horizontal path determinations of atmospheric transmittance at wavelengths shorter than 500 nm. To investigate this wavelength dependence, we have measured atmospheric transmittance for a series of visible and ultraviolet wavelengths between 200 and 550 nm in different atmospheric conditions. These measurements were made using a filter wheel transmissometer setup to measure transmission across an approximately horizontal path. As part of the measurement program, simultaneous determinations of visibility were made.
Design considerations for confined quantum state GaAs/AlGaAs solid state photomultipliers
Authors: Brennan Kevin F. , Wang Yang
Published: February 2023

Multiplication via impact ionization of secondary carriers in interband ionization avalanche photodiodes results in significant degradation of the excess noise factor and bandwidth of the device. Alternatively, solid state photomultipliers which exploit impact ionization out of confined quantum states offer ultralow noise and high speed performance since they operate as unipolar devices thereby avoiding the occurrence of secondary ionization. As a consequence, much lower noise and high speed performance is anticipated in these devices. We present calculations of the gain, dark current, and gain to dark current ratio in confined quantum state photomultipliers made from the GaAs/AlGaAs material system. Our model calculations are based on the average ionization rate calculated from the quantum mechanical transition rate assuming a drifted Maxwellian initial carrier distribution. It is found that the highest gain at lowest dark current is achieved in an asymmetric quantum well structure in which the second barrier height is half as large as the initial barrier height.
Spontaneous and stimulated emission by atoms interacting with a phase conjugate mirror
Authors: Bochove E. J. , Milonni P. W.
Published: February 2023

The properties of a phase conjugate mirror (PCM) interacting radiatively with other objects are investigated. The spontaneous emission rate of a two-level atom (TLA) is attributed to the dipole emission of the upper energy level into vacuum field modes incident on the front face of the PCM, the emission into vacuum modes transmitted from the rear port of the PCM, enhanced by a factor 1 + R (R = reflectivity), and the emission of a photon while the atom is in the lower level, accompanied by annihilation of two pump photons, weighted by a factor of R per emitted photon. These processes lead to an enhancement factor of 1 + R for the spontaneous decay rate and a steady state upper level occupation probability R/(2R + 2), both in agreement with solution of the Heisenberg equations of TLA operators.1 The momentum transfer is zero, and the steady state emission rate is A12R(R + 2)/(2R + 2) photons/s atom. The stimulated emission and absorption constants are enhanced in a similar way. Contrary to the case of a conventional mirror, the Lippman fringes are present only for coherent radiation states.
Optical probing of superconductor thin film YBa2Cu3O7−δ
Authors: Yang Yue , Xu Ziran , Zhang Xingkui
Published: February 2023

Looking for practical applications of the high Tc superconductor has become an interesting study subject. As a research project, the superconductor film has attracted wide attention because it has its own characteristics different from the bulk superconductor sample; even more important the film is the essential material used to produce electronic superconductor equipment. According to an earlier preview of uses of the microelectronic element, a large number of reseachers are working on the high Tc superconductor film.
Diode laser range sensor for co-located geostationary spacecraft
Authors: Seshamani Ramani
Published: February 2023

Diode lasers have been chosen for space missions in view of their long lifetime, low weight and volume, high electrical-to-optical conversion efficiency, and direct modulation capability. A pulsed diode laser range sensor is being developed for ranging between co-located geostationary spacecraft (INSAT series) separated on the average by distances from 35 to 75 km with a minimum separation of 5 km. The laser range sensor consists of a transmitter, a single axis scanner, a retroreflector on the target spacecraft, and an avalanche photodiode receiver. The pulsed GaAs / GaAlAs diode laser at 850-nm wavelength has a pulse optical power output of 1000 W, 30-ns pulse width, 1-kHz pulse repetition rate, and 1-mrad beam divergence. The scan field is 360° X 120°. The retroreflector has a 200-mm aperture. The receiver optics has a 200-mm diam clear aperture. The silicon avalanche photodiode detector has 10-nW noise equivalent power. The signal-to-noise ratio at 100-km range is 4. The time interval between the start and stop pulses is measured by a coarse counter with a 50-MHz clock. The fractions of clock pulses are determined by a time-to-time conversion circuit. This provides an accuracy range of 2 cm from 6 m to 1 km and 3 m at low signal-to-noise ratios, up to 100 km.
Reduction of absorption by aerosol vaporization
Authors: Krapchev Vladimir B. , Balents Leon
Published: February 2023

We have studied the vaporization of atmospheric aerosols. The theory includes the temperature dependence of the thermal conductivity of the air and the resulting nonlinear diffusion equation has been solved analytically. By using Mie scattering and the complex index of refraction for atmospheric aerosols one can find the optimum wavelength and pulse format to clear the aerosols at modest fluence levels. We find that the KrF wavelength leads to the smallest fluence. The size distribution function of the aerosols during vaporization has been calculated and from this one can find the reduction in the aerosol absorption coefficient.1 The high energy laser wavelength is chosen to minimize molecular absorption near 1 µm. To reduce further the absorption one can use a beam clearing laser at a different wavelength, but at a power level 1-2 orders of magnitude less than the HEL. Such a scenario may resolve the difficult problems related to atmospheric thermal blooming.
Nonlinearity of buried heterostructure lasers under amplitude modulation
Authors: Wang S. J. , Dutta N. K. , Piccirilli A. B.
Published: February 2023

Fiber optic systems utilizing analog modulation have become an important area of use for semiconductor lasers, ranging from wideband microwave links for satellite communication that operate at multi-GHz frequencies, to CATV applications that operate at a few hundred megahertz. Semiconductor lasers under amplitude modulation experience certain nonlinearities that will degrade the performance of these analog transmission systems. These nonlinearities include harmonic distortion and intermodulation distortion. This paper reports the measured second harmonic, third harmonic, and intermodulation distortion of buried heterostructure lasers, and compares the measured results with those obtained by the perturbation analysis of laser rate equations. We have also evaluated the nonlinearities as a function of the laser structure. The laser structures measured include the capped-mesa and the etched-mesa distributed feedback lasers, multiple quantum well lasers, and Fabry-Perot lasers. We have compared the nonlinearities of these lasers operating at different output power levels and with various optical modulation index.
Photon counting fluorimetry of low repetition rate pulsed plasmas
Authors: Parigger Christian , Davis Lloyd m.
Published: February 2023

For the ill-conditioned problem of resolving multiple exponential components from luminescence decay profiles, time correlated photon counting (TCPC) is usually chosen because it yields data over a large dynamic range and with accurately known errors, derived from Poisson photon statistics. However, as no more than one photon is collected after each excitation, TCPC requires a large number of laser pulses to achieve the required dynamic range.
Application of tunable diode lasers to airborne measurements of atmospheric gases
Authors: Sachse Glen W. , Hill G. F. , Burney L. G. , Ritter J. A. , Barrick J. D. W. , Wade L. O. , Collins J. E.
Published: February 2023

Tunable diode laser (TDL) sensors for atmospheric measurements possess many advantages including wide tunability in the infrared where most atmospheric species possess strong absorption bands; high spectral resolution which yields high specificity and sensitivity for the detection of clean air levels of trace gas species; and fast time response that is necessary for making gas flux measurements using the eddy correlation technique. A NASA Langley developed airborne TDL sensor has participated in several major atmospheric measurement programs since the late 1970s. This presentation focuses on measurements with this sensor on the NASA Electra aircraft during the Global Tropospheric Experiment (GTE) expeditions to the Amazon forest (spring 1987 wet season) during which CO measurements were made and to Alaska (summer 1988) during which simultaneous CO and CH4 measurements were made. This TDL sensor possessed a time response of ≈70 ms which was sufficient to spatially resolve the turbulent eddies which are responsible for the vertical transport of gases emitted from the earth′s surface. By correlating rapid measurements of gas concentration with vertical wind velocity data provided by a gust boom, direct measurements of gas flux were made. Data from these expeditions have quantified CO emission by the Amazon tropical forest and CH4 release over Alaskan tundra environs. Since CO and CH4 have key roles in the green-house process, flux data of these species are important for making improved estimates of global gas budgets and as inputs to atmospheric computer models.
Optical emission diagnostics of laser-induced graphite plasma for diamondlike film deposition
Authors: Chen Xiangli , Mazumder Jyoti
Published: February 2023

Motivated by recent interest in laser graphite ablation for optical-quality diamondlike carbon-film deposition, we took emission spectra from a pulsed KrF (3 x 108 W/cm2) excimer laser-induced plasma plume on the surface of bulk graphite. A 0.3 m spectrograph and an optical multichannel analyzer (OMA) were used. In the visible region the plasma emission was dominated by the D-A swan and C-A DesIandres-d'Azambuja bands of C2 and the B-X violet band of CN. No evidence of transitions attributable to C+, C, C3, or larger carbon clusters was found. From the band emission intensity, the vibrational temperatures of the radicals were calculated from the Einstein spontaneous emission coefficients with an assumed Boltzmann population distribution. The results from the different transitions of the C2 swan and CN violet bands all fell within the range of experimental error and uncertainty error in the Einstein coefficients and indicate a vibrational temperature of (13.5 ± 1.3) x 103 K for both radicals. This excellent agreement makes one believe that the species in the plasma are likely to be in local thermodynamic equilibrium. C2 radical concentration is estimated to be 1 × 1015 cm−3 on the basis of emission intensity and Boltzmann distribution at the above temperature.
Intrinsic optical bistability of metal-coated semiconductor particles
Authors: Haus J. W. , Kalyaniwalla N. , Inguva R. , Birnboim M. H.
Published: February 2023

We consider a glass having spheroidalshaped particles dispersed in the medium. The particles have a metallic shell of silver and a semiconductor core material. Investigating core materials, we study the exciton-biexciton resonance in CuCl, the bound exciton resonance in CdS, and the exciton resonance in GaAs.
Investigations of intensity fluctuations in the laser with a saturable absorber
Authors: Mortazavi Mansour , Singh Surendra
Published: February 2023

The equation of motion for the slowly varying field amplitude of the laser containing an intracavity saturable absorber (LSA) is where a is the net gain (pump parameter) and b is a saturation parameter of the laser. In our experiment the absorber saturates faster than the amplifier and the parameter b is positive. q(t) is a complex Gaussian white noise random process representing spontaneous emission noise. From Eq. (1) we obtain for the steady-state probability density of light intensity I = | E |2. From this equation various moments of light intensity can be calculated and compared with experimentally measured quantities. For b > 0 the LSA exhibits bistability and a first order phase transition occurs at a = -3b2/16. For negative values of b there is a continuous transition at a = 0. Experiments were carried out on a He—Ne laser with an intracavity Ne absorber cell. The laser was operated close to the center of the absorption line. Slow drifts of light intensity were controlled by an electronic feedback loop. The parameter b was varied by changing the current in the absorber tube. Pump parameter a was then varied by changing passive losses in the cavity by means of an adjustable knife edge. The main beam from the LSA was allowed to fall on a detector/am- plifier combination. The voltage output from the detector was digitized by a multichannel analyzer and a histogram of voltage amplitudes was built up. Since the voltage output from the detector is directly proportional to the light intensity incident on the detector, voltage histogram is a direct representative of the intensity probability distribution. From the measured histogram moments of light intensity were calculated. These results are compared with the theoretical predictions.
Optically controlled phased array technology
Authors: Hendrickson Brian M.
Published: February 2023

This paper will discuss the status of photonics technology utilized in implementing a phased array antenna system by optical means. Systems issues and applications which highlight the advantages of optics in the design and implementation of phased arrays will be discussed.
Deformable mirror-based optical beam-forming systems for phased-array radar
Authors: Zmuda H. , Toughlian E. N.
Published: February 2023

Two types of photonic processors for generating the properly phased signals for a dynamically steered phased-array antenna are presented. Both methods make use of a class of spatial light modulator known as a deformable-mirror device (DMD). These devices can be envisioned as an N × N array of mirror elements, each capable of (computer-controlled) independent motion that is typically on the order of optical wavelengths. Varying this optical path length produces a substantial rf phase shift through photomixing. Because the number of elements in a DMD can be large (each DMD element corresponds to an array element, the highly directive antenna radiation patterns necessary for radar applications can be readily achieved. It is further demonstrated that a DMD-based system can be used to synthesize a variable rf delay line. Continuously variable true time delay in the rf regime has never been previously obtained, and, as such the scheme presented represents a significant contribution to the rf/microwave community as a whole. Experimental results that demonstrate both systems' performance are presented.
Coupled-mode theory of an alignment sensor coupler
Authors: Kahn W. K. , Salama A. S.
Published: February 2023

We explicitly carry through the extension of coupled-mode theory for optical fibers in the multimode case, illustrating our results with the design of a special coupler formed of two multimode graded-index slab-guides. This coupler may find applications as a mode filter, alignment sensor, or feed component of an optical monopulse tracking radar.
Characterization and simulation of proton-exchanged integrated optical modulators with various dielectric buffer layers
Authors: Weitzman P. S. , Charczenko W. , Mickelson A. R. , Dunn J. M.
Published: February 2023

Fast and accurate numerical techniques are developed for calculating the optical depth of modulation of integrated-optical devices with various dielectric buffer layers. The matrix effective refractive-index (MERI) method is used in calculating the LiNbO3 proton-exchange single-channel optical-mode parameters. An approximate technique for calculating electrode electric field distributions as a function of various buffer layers is presented. Comparisons of computer simulations to experimental measurements performed on Mach-Zehnder modulators containing various buffer layers demonstrate that the numerical techniques are sufficiently accurate for usein computer-aided design. The errors between calculated and measured V(pi) are given for modulators with a 200 nm SiOî buffer layer and with a 200 nm ITO electrode structure. In general, given the same electrode dimensions, the use of ITO electrodes results in a significant reduction of the drive voltage required as compared to electrodes on thin (200 nm) dielectric buffer layers.
Patterns from aspherical rain and dew
Authors: Fraser Alistair B.
Published: February 2023

Spherical water drops have long been evoked to explain familiar natural optical phenomena such as the rainbow, corona, glory, and heiligenschein, but there is little in the literature to suggest that there are any such phenomena caused by aspherical water drops. Two examples of readily observable patterns will be presented: the supernumerary bows and the sylvanshine. Although in the laboratory spherical drops can cause supernumerary bows, in natural rain showers they cannot. Aspherical drops must be present for the bows to be produced. Related to the heiligenschein, the sylvanshine is a newly described phenomenon in which some dew bedecked conifers exhibit a strong backscatter. Relatively few species exhibit this striking phenomena, which, under directional lighting at night, has the appearance of a snow covered tree in the moonlight. Neither the reversible optics of the semispherical dewdrop nor the irreversible optics of the diffusely reflecting leaf are by themselves strongly backscattering; yet their combination is. Strangely, the brightness of the sylvanshine varies as the inverse distance from the light source, rather than the normal inverse distance, squared.
Inhibition of spontaneous emission by a random dielectric medium
Authors: Lawandy N. M. , Martorell Jordi
Published: February 2023

In 1946 Purcell showed that the spontaneous emission rate of an atomic system could be enhanced by placing it in a conducting cavity. Later, Kleppner showed that spontaneous emission could also be inhibited if the vacuum modes coupled to the atom were excluded by a structure. Most recently, we experimentally have shown that a periodic dielectric structure could alter the spontaneous emission by Bragg scattering of vacuum fluctuations.1 The structure used was a colloidal crystal with a face-centered cubic structure whose (111) planes were separated by optical dimensions.
Generation of macroscopic superpositions in a two-photon micromaser
Authors: Meystre Pierre , Wilkens Martin
Published: February 2023

We study the dynamics of a two-photon micromaser driven by a sequence of polarized Rydberg atoms. If cavity losses are neglected, the density matrix of the cavity mode consists of four dynamically decoupled components. Under appropriate trapping conditions, similar to those for the one-photon micromaser, it evolves to a stationary state. When the bare two-photon frequency cancels the ac Stark shift we cannot satisfy the trapping conditions for odd and even photon number states simultaneously. For specific initial conditions, where either only odd or only even number states are initially populated, we may find, however, stationary states that are pure and that can lead to macroscopic superpositions. These pure states are analogous to the cotangent and tangent states of the one-photon micromaser. When the two atomic levels are in resonance with the bare two-photon transition, trapping conditions for odd and even photon number states can be fulfilled simultaneously. Although the ac Stark shift does not allow for pure stationary states, the stationary state resembles an incoherent superposition of only two pure states, to within a relative deviation of 10-3 off purity.
Storage and stability of recall in photorefractive barium titanate
Authors: Lin F. C. , Yang T. , Leu G. , Sun D. , Fiddy M. A. , Teng Y. Y.
Published: February 2023

An information-bearing laser beam propagating in a photorefractive material, such as barium titanate, can generate its own phase-conjugated replica with high fidelity, as a result of beam fanning. We have studied the temporal stability in this self-pumped phase conjugation (SPPC) and its accompanying total-internal-reflection (TIR) ring, as a function of the laser intensity, the orientation between the c-axis of the crystal and the beam, as well as the spatial-frequency content of the beam. This is important in applications such as dynamic associative memory storage and real-time optical signal processing. The degree of stability varies with the spatial-frequency content of the incident beam. There are regimes of unstable (chaotic) behavior and regimes with relatively stable output. We have considered the use of an incoherent second beam to stabilize the SPPC and to improve the diffraction efficiency of readout from the crystal. We have also studied the trade off between the storage and recall of information in the crystal by exploiting SPPC and TIR ring patterns.
VHDL for simulation of optoelectronic computers
Authors: Kiamilev F. , Lu Dau-Tsuong , Fan J. , Esener S. , Lee S. H.
Published: February 2023

VHSIC Hardware Description Language (VHDL) is a standard language for modelling electronic hardware. To evaluate the application of VHDL to optoelectronic computers, we simulate the programmable optoelectronic multiprocessor (POEM) architecture in VHDL. POEM is an architecture in which processing elements are interconnected with reconfigurable free-space optical interconnections. We use VHDL to simulate the POEM prototype, develop the next-generation POEM system, and design and test new parallel algorithms that exploit unique features of optoelectronic technology. We discuss our experience in the application of VHDL to the modeling of optoelectronic systems.
Fan-in limitation in optics
Authors: Caulfield H. J.
Published: February 2023

Many of the unique advantages of optics stem from its almost unlimited fan-in capability. For instance, it is possible for light from 106 or more well defined regions to come together at a single optical element or even in parallel on 106 or more optical detectors, spatial light modulator pixels, etc. Is there a theoretical limit to this fan-in number?
Disparity averaging across spatial scales
Authors: Rohaly Ann Marie , Wilson Hugh R.
Published: February 2023

Previous studies on the phenomenon of disparity averaging have used random-dot stereograms or line stimuli, leaving open the question of whether disparity averaging occurs across spatial scales as well as within them. We have examined this question by performing a series of depth-matching experiments using stimuli composed of the sum of two cosine gratings of different frequency and retinal disparity. When the frequencies of the cosines are separated by 3.5 octaves or less, perceived depth is close to the average disparity of the components. Similar results are obtained when the relative orientation of the components is less than 30°. Beyond these limits in spatial frequency and orientation, averaging no longer occurs, and the components are perceived transparently in depth. Perceived depth is also contrast-dependent. As the relative contrast of the gratings is varied, perceived depth varies smoothly in the direction of the higher contrast component. These results demonstrate that disparity averaging does occur across spatial scales and that disparity-selective mechanisms are tuned for both spatial frequency and orientation.
Variable-efficiency liquid-crystal diffraction gratings
Authors: Lewis Warren H. , Indebetouw Guy
Published: February 2023

We describe the construction and performance of a diffraction grating having an efficiency that can be varied by an externally applied electrical signal. The device consists, in part, of a nematic liquid-crystal layer sandwiched between a photoresist relief grating and a glass plate. Transparent electrodes are deposited on the grating and on the plate, followed by a thin polymer layer that is rubbed along the grating's grooves to ensure a planar orientation of the liquid crystal. The diffraction efficiency of the grating for monochromatic light that is linearly polarized parallel to the director can be changed by more than an order of magnitude by varying the electrode voltage. The characteristics and performance of the device are described, and its possible application to the problem of devising reconfigurable optical interconnections is discussed.
Normal color vision, linkage analysis, and visual pigment genes
Authors: Lutze Margaret , Cox Nancy J. , Brandt Curtis R.
Published: February 2023

People with normal color vision show interobserver variation in Rayleigh and red-green photometric matches, which may indicate variations in photopigment spectral sensitivities and receptor populations, respectively. We have previously shown that this variation is consistent with single-gene determination. The X-chromosome visualpigment genes are good candidate genes for determination of variation in these color-vision traits; however, other genes may also contribute to cone development and function, which affect these measures.
More than three cone types in normal color vision?
Authors: Neitz Jay , Neitz Maureen , Jacobs Gerald H.
Published: February 2023

Normal human color vision is usually thought to be based on only three spectrally different cone types. However, two facts suggest the possibility that some color-normal males could have more than three cone pigment types: (1) Most people with normal color vision have more than two photopigment genes on each X-chromosome and (2) there appear to be genetically specified variations in spectral positions of the normal middle-wavelength-sensitive (MWS) and long-wavelength-sensitive (LWS) pigments. For example, a male might have one gene encoding an LWS pigment and two genes encoding slightly different MWS pigments. If all three different X-encoded genes were expressed in different cones, then this person would have four spectrally different cone types. How firm is the assumption that more than two of the X-encoded pigment genes can be expressed? Both analysis of the statistics of photopigment gene number among different color vision phenotypes and analysis of the arrangement of pigment genes on the X-chromosome yield insight into this aspect of photopigment gene expression. These analyses suggest that individuals with multiple pigment genes on the X-chromosome may express more than two of those genes.
Full-spectrum cone sensitivity functions for anomalous trichromats
Authors: DeMarco Paul J. , Pokorny Joel , Smith Vivanne C.
Published: February 2023

From color matching, subjects with protanomalous (PA) and deuteranomalous (DA) trichromacy appear to have three functional classes of cone photopigment, but the peak absorption of one photopigment, either the M-cone (DA) or the L-cone (PA), occurs at a different wavelength than for normal subjects. Pokorny, Smith and Katz (1973) derived absorption spectra for anomalous photopigments of 500-700 nm by using Schmidt’s (1955) anomaloscope matching data for normal subjects with anomalous trichroma.
Optical characterization of piezoelectric fields in strained-layer superlattices
Authors: Xu L. , Zhang X.-C. , Xin S. H. , Huddle C. L. , Auston D. H.
Published: February 2023

Optically induced femtosecond electromagnetic radiation from semiconductor surfaces provides a novel optical technique to characterize multilevel static electric fields within the optical-absorption length. In addition, from the analysis of the waveform of the radiated field, the orientation and strength of the piezoelectric field can be estimated with a noncontact approach. We have measured the strain-induced piezoelectric fields in several (100)- and (111)-oriented strained-layer superlattices, including type I superlattices (GaSb/AlSb and InGaAs/GaAlAs) and staggered type II superlattices (InGaSb/InAs). The results show that only (111)-oriented samples have the macroscopic piezoelectric fields. Strain-induced fields with equal amplitudes but opposite polarities between the (111) A-face and (111) B-face samples have been observed. We have compared the electromagnetic radiation from the strained-layer superlattices and thin films; extremely fast electromagnetic pulses from (111)-oriented superlattices have been observed. The quantum-well structure in the superlattices limits the pulse duration of the transient photocurrent; it is possible to generate electromagnetic radiation having a pulse duration comparable with the photocarrier transit time across the quantum well.
Enhanced VUV generation in phase matched rare gases
Authors: Xiong X. , Westbrook C. I. , Mcllrath T. J.
Published: February 2023

Third-order frequency mixing process (ωVUV = ωOUV − ωUIR) has been used to generate coherent VUV radiation between 1200 and 1220 Å. Input tunable UV radiation is obtained by summing the YAG fundamental at 1.06 μ. and the double dye laser radiation between 5400 and 5500 Å, while the fixed IR input is from the YAG. We emphasize that our experimental scheme can generate hydrogen lyman-α radiation at 1215.6 Å, and 1202.8 Å for the two-photon excitation 1s2-1s2s 1S0 in helium using a single tunable laser. The enhancement effects on and near the two-photon resonance 4p-5p [5/2]2 in krypton have been studied. Improved conversion efficiency has been observed by phase matching negatively dispersed krypton with positively dispersed xenon or argon in this region. With UV input powers of 200,120, and 100 kW, the generated VUV powers of 80, 320, 40 W have been obtained at 1202.8,1206, and 1215.6 Å. The dependence of the VUV powers on the pressures and the mixtures of the gases has provided useful information of the wavevector mismatch values of the media which we compare with calculations.
Associative memory performance of various correlation filters
Authors: Horner Joseph L.
Published: February 2023

Associative memory is an important criterion in the performance of a pattern-recognition system based on optical correlation. Through computer simulation we compare the performance of the matched filter, the phase-only filter, and the binary phase-only filter by using such measures as signal-tonoise ratio and peak-to-secondary ratio. Performance in a zero-noise background and in a cluttered noise background is included. The performance of the unit-modulus filters is generally superior.
Photorefractive adaptive filtering for noise reduction
Authors: Khoury J. , Woods C. L. , Cronin-Golomb M.
Published: February 2023

The large electro-optical coefficient of barium titanate yields strong two-beam coupling. Here we describe a nonlinear photorefractive technique to reduce noise in a signal that is embedded in additive speckle noise. This approach implements an adaptive Wiener filter, which improves the contrast ratio by a factor of eight for a binary input signal with peaks equal to the noise peak. This technique relies on thresholding the Fourier transform of the noisy signal. The Fourier transform of the signal is a diffraction pattern of high intensity relative to the noise, and two-beam coupling is used to reduce the weaker-intensity noise Fourier transform. Our experimental results shows that it is possible to enhance features that are smaller than the grain size of the noise. The mechanism of enhancement depends on the initial signal-to-noise ratio and the specific geometry of the signal. We have also used the same technique for reducing multiplicative artifact noise and defects in images.
Quantum reflection: focusing of hyrodgen atoms with a hemispheric mirror
Authors: Walraven J. T. M.
Published: February 2023

We studied the low-energy limit of atomsurface scattering and the phenomenon of quantum reflection by using hydrogen atoms and the surface of liquid helium. Measuring the specular reflectivity of a liquid-helium-covered hemispheric mirror for a beam of hydrogen atoms we obtained information on elastic and inelastic scattering phenomena. At 100 mK, reflectivities larger than 90% were achieved; this can be used to demonstrate atomic beam focusing. Approximately three-fourths of the atoms escaping from a small orifice in a cell were reflected back into the cell. The dominant inelastic processes at work here are surface absorption and direct inelastic scattering over small angles under excitation of surface ripplons (quantized capillary waves). Helium-covered surfaces maybe useful for atomic-beam manipulation of atomic hydrogen.
Large third-order nonlinearities in solutions of imidazolium-stabilized 1,2 dipoles
Authors: Campbell D. P. , Buck J.A.
Published: February 2023

A new class of organic third-order nonlinear optical materials based on imidazolium-stabilized 1,2 dipoles has been investigated. These compounds are colorless, stable, and readily prepared and have low absorption throughout the visible region to below the near infrared region.
Enhanced third-order optical nonlinear response about polaronic bands in polythiophene films
Authors: Yang Lina , Dorsinville R. , Alfano R. R. , Zamboni R. , Taliani C. , Tubino R.
Published: February 2023

In this work we will measure the third-order nonlinear susceptibility χ(3) directly inside the polaronic bands in an homologous series of polycondensed thiophene-based polymers. Direct information is provided on the possible effect of (bi)polarons on the size and picosecond dynamics of the third-order optical nonlinearity. A novel technique is used for measuring photoinduced midgap state; these gap states are photogenerated in polythiophene samples by an above-gap excitation (2.33 eV) . The nonlinearities are subsequently probed usingby below-gap (1.2eV) degenerate four-wave mixing. Enhancement of the degenerate four-wave mixing signal at 1.2 eV of more than an order of magnitude is observed when the excitation beam (2.33 eV) overlaps with three infrared-probe beams (1.2 eV). The dependence of the enhanced signal on the polarization of the pump and probe beams is studied. Enhancement of χ(3) from the photoinduced polaronic bands is compared with the enhancement of χ(3) brought about by the doping-induced polaronic bands.
Backscattering of light from perturbed gratings
Authors: Knotts M. E. , O'Donnell K. A.
Published: February 2023

Enhanced backscattering of light is reported in scattering from metallic diffraction gratings with random groove depths. The surfaces are fabricated in photoresist with a metallic overcoat and consist of evenly spaced grooves whose depths are statistically independent Gaussian variates. For several polarization states of the incident field, the Stokes parameters of the scattered light have been measured as functions of both incidence and scattering angle. Depending on the incidence and detected polarizations, some scattering measurements have diffraction orders like those found for a perfectly periodic surface, although other measurements contain purely enhanced backscattering, as found for random surfaces. These observations are discussed in terms of the Stokes matrix characterizing the scatterer. In particular, they are interpreted as being consistent with multiple-scattering and inconsistent with single-scattering theories. Extensions of this work will also address how the backscattering effects become associated with the grating orders of a perfect grating as the amount of depth fluctuation is reduced to zero.
Commercially available glass integrated optics devices
Authors: Fabricius Norbert , Grosskopf Klaus , Ross Ludwig
Published: February 2023

Glass integrated optical devices were developed in the early 1970s. However, it took nearly 20 years for products based on this technique to be introduced into the market sufficiently for them to be purchased in quantities larger than mere laboratory samples. Worldwide, fewer than 10 companies published the development of integrated optical devices in glass by ion-exchange.
Ultrashort pulse generation with additive-pulse mode-locking in solid-state lasers
Authors: Goodberlet J. , Jacobson J. , Gabetta G. , Schulz P. A. , Fan T. Y. , Fujimoto J. G.
Published: February 2023

Additive-pulse mode-locking (APM) in solid-state lasers provides an attractive and powerful approach for ultrashort-pulse generation. The APM technique uses a nonlinear external cavity that is coupled to the main laser cavity. The nonlinear external cavity may be viewed as a nonlinear Fabry-Perot, which functions as an intensity-dependent mirror for the main laser. Additive-pulse mode-locking thus resembles passive modelocking with a fast saturable absorber. However, the APM technique has the advantage that the nonlinearity or the effective cross section of the saturable absorber can be explicitly designed by adjusting the laser and external cavity parameters. Because APM can be used to achieve passive mode-locking without the need for active external modulation, it significantly reduces system cost and complexity.