bluuebunny/crossref_metadata_2025 huggingface dataset:
Cooling and trapping of atoms in the presence of a colored vacuum
Authors: Mossberg T. W. , Lewenstein M. , Gauthier D. J.
Published: February 2023

The characteristics of dissipative mechanical forces acting on strongly driven atoms depend on the spontaneous decay rate of the driven transition. In previous studies,1 it has been assumed that the spontaneous decay rates arise from the coupling of the atoms to the free-space electromagnetic vacuum reservoir. Recently, it has been shown2 that new and novel physics can arise when the reservoir that mediates atomic relaxation is colored (frequency dependent) as can be accomplished by a suitably designed cavity or waveguide. We show that a two-level atom moving in an intense rest-frame-resonant standing-wave and decaying via coupling to a colored vacuum reservoir experiences a damping force (which is substantially larger than that predicted in other studies) useful in slowing the atom. This force, unlike traditional cooling forces, is effective over a dramatically wide range of atomic velocities. In fact, the force can be effective even for thermal velocity atoms if the vacuum is strongly colored.
Deceleration of atoms with a fluctuating laser field
Authors: Napolitano Reginaldo J. , Bagnato Vanderlei S.
Published: February 2023

In a recent publication1 we have analyzed the stability of the deceleration process of atoms in the Zeeman tuning technique2 by looking at the velocity profile of the atoms along the magnetic field. When the velocity [v(z)] follows the field profile [B(z)] we refer to this as adiabatic following of atoms because the absorption is adiabatically adjusted to each position so that v(z) follows B(z). This situation does not hold everywhere; in fact, at points where the absorption cannot be adiabatically adjusted the velocity ceases to follow the field interrupting the deceleration. The existence of fluctuations on the laser field produces dramatic changes on the expected behavior of the atoms during the deceleration. We have made numerical simulation and analytical investigation where v(z) is obtained for cases where the laser field has frequency and amplitude fluctuations produced by Markovian and Gaussian stochastic processes. In both cases, the deceleration is dependent on the spectral densities of the fluctuations. The process seems to be more sensitive to amplitude than to frequency fluctuation. These results are important in determining the desired characteristics of the laser source on atoms deceleration experiments.
Hydrostatic pressure changes behind chick and pigeon corneas are insufficient to account for corneal accommodation
Authors: Glasser Adrian , Howland Howard C.
Published: February 2023

Corneal accommodation accounts ~9 D of accommodation in pigeon eyes and for ~8 D of the full 15–17 D accommodative range in chicken eyes.1 The mechanisms of corneal accommodation are largely unknown. To test the role of intraocular pressure changes in corneal accommodation in chick and pigeon eyes we regulated the pressure behind excised corneas and measured the changes in corneal curvature. Curvatures of excised corneas with a hydrostatic pressure applied behind them were measured using IR keratometry. The radii of curvature of the excised corneas under hydrostatic pressure were similar to those measured in the living bird and in the intact excised eyes (six chick eyes 4.34–4.63 mm and four pigeon eyes 3.55–4.07 mm). Pressure changes regulated around physiological values2 (10–22 mmHG) resulted in small changes in corneal curvature (chicks 0.14–0.33 mm and pigeons 0.10–0.16 mm). When expressed as corneal refracting power (chicks 2.50–5.69 D and pigeons 2.36–3.20 D) the changes are insufficient to account for the full range of corneal accommodation.
Position sensing using holograms of conical waves
Authors: Leseberg Detlef
Published: February 2023

The flexibility of a holographic optical element means great potential use. Developed as a part of an optical system, its main advantage stems from its functions and combinations of them that other components cannot provide. All of these are supported by the optically reconstructed waves. Conical waves have been established as a solution of the wave equation.1 These waves focus in lines that are not parallel to the hologram plane, and they do not exhibit speckle. Several of these foci constitute a 3-D light distribution which can be used to determine the position and the orientation of homogeneous object surfaces. The inclination of the line foci converts longitudinal displacements of the surface into lateral image displacements on a position sensitive optoelectronic detector (triangulation principle). The proposed special illumination scheme allows one to build small combined illumination and detection units of large aperture. The image is converted in real time, e.g., with a CCD array. Several isolated spots result, whose coordinates determine longitudinal position and orientation of the object surface.
Optical evaluation of components for free-space digital optics
Authors: Tooley F. A. P. , McCormick F. B. , Sasian J. M. , Crisci R. J. , Morrison R. L. , Kerbis E. , Brubaker J. L.
Published: February 2023

Unique problems are present in optically interconnected symmetric-SEED array systems.1Several tools and procedures were developed to evaluate the components and systems used in experiments which demonstrated the successful cascaded operation of two 2048 pixel S-SEED arrays and a fully interconnected Banyan network. A Twyman-Green interferometer operating at 850 nm was constructed to evaluate the quality of the passive components and aid in the assembly of the custom lens used in the cascade demonstration. A radially shearing interferometer was constructed to evaluate the accumulation of wavefront distortion s the light propagates through the system and aid in the assembly of a laser pen. The interferometer, a collimation tester, and a spot size analyzer were used to correct aberrations
Modulation by symmetry-breaking of disallowed intersubband transitions
Authors: West L. C. , Roberts C. W. , Duerksen G. L. , Garcia H. , Malik R. J. , Walker J. F.
Published: February 2023

In this experiment 180-Å GaAs/AlAs quantum wells were grown with an Si concentration of 1012/cm2 δ-doped at the edge of the wells. The δ-doping created an internal electric field across the wells, breaking the reflection symmetry about the center of the well and permitting the occurrence of normally disallowed intersubband transitions between like-parity envelope states of electrons within the wells.1 The 180-Å quantum well size was chosen so that the energy of the transition between the first and third conduction subband was resonant with the light from a CO2 laser. By applying an external electric field normal to the plane of the quantum wells, modulation of the absorption of 9.7-μm light passing through the sample was observed, as the applied field augmented or counteracted the internal field. The measurements were taken at various temperatures and duty cycles to identify extraneous effects such as thermal modulation of the free-carrier absorption. The modulation was temperature and duty-cycle independent for low temperatures and duty cycles, and it showed the proper polarization dependence and magnitude as predicted by theory. This was also corroborated by spectrometer measurements of the absorption coefficient in zero external field.
Polymer based electrooptic modulators
Authors: Girton D. G. , Lipscomb G. F. , Lytel R. S.
Published: February 2023

An electrooptic (EO) polymer was used to fabricate phase modulators and Mach-Zehnder modulators on Si wafers. This glassy polymer is from a class of nonlinear, optical materials that have large EO coefficients, low dielectric constants, and small dispersion from dc to optical frequencies. The modulators were fabricated on Si wafers using conventional IC manufacturing equipment. Three polymer layers were deposited: a hard acrylate cladding layer, followed by an EO polymer from Akzo Research, by1 then another cladding layer. The waveguides were photobleached using an IC mask aligner, and microstrip electrodes were formed by gold plating. The active polymer layer was poled2 through the cladding, and waveguide end faces were prepared by cleaving. The Mach-Zehnder modulator was designed so that each arm could be modulated independently with a separate 50-Ω microstrip electrode; the modulator response was measured up to 20 GHz. Data from each type of modulator are presented. These devices illustrate that polymers offer certain advantages over standard inorganic EO materials, such as LiNbO3 and GaAs, in that multilayer integrated optical circuits can be fabricated on top of electronic substrates using processes and equipment that are largely in place for manufacturing integrated circuits.
Optical generation of frequency stable mm-wave radiation using diode laser pumped Nd:YAG lasers for visible and IR photodetector calibration
Authors: Day T. , Marsland R. A.
Published: February 2023

Many areas of research such as wide band frequency division multiplexed communication links, optical distribution of mm-waves for phased array radar, antenna remoting, and high speed photodiode characterization require optical generation of frequency stable mm-waves. Previously, a 6.33-GHz optically generated signal with a linewidth of <3 Hz was demonstrated,1 and improvements in the system have enabled sub-Hz stability to be achieved. This work utilized two diode laser pumped Nd:YAG lasers frequency locked to adjacent axial modes of a high finesse interferometer to create a frequency stable heterodyne beatnote. We have recently implemented this capability for frequency locking YAG lasers to characterize our high speed photodiodes. Two 40-mW diode laser pumped nonplanar ring oscillators were locked to successive axial modes of an interferomter that had a free spectral range of 1.00 GHz. The wavelength of the lasers was 1.06 μm, and through temperature tuning we were able to generate stable mm-wave modulation of the optical beam to 57 GHz. The optical beam was focused through a fiber into the photodetector modules and, as the modulation frequency was changed, the diodes frequency response was monitored. Several of the diodes we have developed operate in the visible spectrum however, and to characterize these units the optically generated mm-wave signal needed to be frequency doubled. In this application, the same photodiode test set could be used by placing a nonlinear doubling material (KTP) into the cavity to resonantly double the fundamental with high efficiency in a fashion similar to work done elsewhere.2 Locking of the lasers to adjacent axial modes of the cavity therefore enabled us to generate stable mm-waves in the visible and IR as well as generate modulation frequencies as high as 57×2 = 114 GHz.
Beam diameter threshold for photoinduced polarization conversion in LiNbO3:Fe
Authors: Wilson D. W. , Glytsis E. N. , Hartman N. F. , Gaylord T. K.
Published: February 2023

Photoinduced polarization conversion is a form of optical damage in LiNbO3 waveguide devices.1 In an attempt to better understand this phenomenon, we have studied the effect in bulk LiNbO3:Fe. In this work, we have observed nearly complete ordinary-to-extraordinary polarization conversion in LiNbO3:Fe for input ordinary beam diameters greater than ~200 μm and no polarization conversion for beam diameters less than ~60 μm. The extraordinary light was scattered into a wide angular distribution in a plane perpendicular to the optic axis of the crystal.2 For small beam diameters, there is no scattered light, and no energy is lost from the ordinary beam. However, as the beam diameter is increased, there is steady-state energy transfer out of the ordinary beam into two broad extraordinary peaks. Using the photovoltaic model,3,4 we have derived coupled equations that describe the polarization conversion process as a function of scattering angle and beam diameter. This model correctly describes the distribution of the scattered extraordinary light and predicts the beam diameter threshold behavior of the polarization conversion.
Spectral changes of partially coherent light incident on two apertures
Authors: Wang Ming , Foley John T.
Published: February 2023

Recently James and Wolf investigated the spectral changes produced when partially coherent light is incident on two pinholes in a Young’s interference experiment.1 For a particular class of partially coherent fields, they showed that the spectrum of the light at an on-axis observation point in the far zone can be significantly different from the spectrum at the pinholes if the latter is broadband.
Visual response and differential color thresholds from metameric matches
Authors: del Barco L. Jiménez , Jiménez J. R. , Romero J. , Hita E.
Published: February 2023

Is the response of color vision mechanisms linear and additive for stimuli with different spectral radiant power distributions? We studied this possibility by means of results obtained when differential chromaticity thresholds are determined in metameric conditions for an achromatic stimulus. Colors corresponding to stimuli with smooth spectral radiant power distributions and a wide bandwidth are matched with colors corresponding to stimuli and narrow bandwidth (very different degrees of metamerism).
Experimentally produced null Ronchi rulings
Authors: Cornejo-Rodriguez A. , Cordero-Davila A. , Cardona-Nuñez O.
Published: February 2023

For the null Ronchi test1 it is necessary to produce, with the help of a computer, the null Ronchi ruling. When using this ruling the observed pattern is a series of straight interference fringes. In the present work, instead of using a computer, a big ronchigram or screen with straight bands that covers the surface under test is used, and the null ruling is photographed on a film at a certain observing plane. Once this process is completed, the obtained null grating allows the observation of the straight interference fringes, if the same surface is used. However, if the same null ruling is used for testing some other similar surfaces, a different Ronchigram will be seen if there are errors in the tested surfaces.
Laser-induced mass selectivity in resonance ionization mass spectrometry of Os
Authors: Wunderlich R. K. , Wasserburg G. J. , Hutcheon I. D. , Black G. A.
Published: February 2023

Measurements of isotope ratios by resonance ionization mass spectrometry depend critically on knowledge of isotopic-specific effects in the laser excitation-ionization process. Reports of odd-even isotope selectivity in RIMS studies of Mo, Sn,1 and Ti have led us to investigate isotope shifts in a RIMS study of Os. We identify three sources of laser-induced mass selectivity: (i) wavelength and bandwidth effects, (ii) selection rule and polarization effects, and (iii) dynamic effects.2 (i) In the presence of optical isotope shifts and hyperfine structure the finite laser bandwidth and reproducibility of wavelength setting produce isotope shifts as a result of the incomplete overlap of the laser spectrum with the absorption maxima of the Os isotopes and their HFS components.
High-order harmonic generation and ATI
Authors: Wang L. , Haus J. W. , Rzazewski K.
Published: February 2023

We have previously developed a two-color above threshold ionization (ATI) model and used it to study the photoelectron spectra and the angular distribution of the photoelectron.1 We present calculations of the photon spectrum from recombination of the electron within the context of this model. The photon spectrum shows interesting and unexpected features that are determined by the nature of the continuum-continuum matrix element. The photon spectrum is contrasted with the photoelectron spectrum. We investigate these quantities for different ionization rates, laser pulse widths, and intensities of the redistribution laser, i.e., the laser responsible for the continuum-continuum transitions.
Generation of femtosecond pulse trains from a short cavity dye laser pumped by cw and pulsed laser
Authors: Lei Zhu
Published: February 2023

A short cavity dye laser (SCDL) as an efficient way to generate ultrashort pulses was first used by Roess.1 Recently, SCDL mixed with the saturable absorber DODCI pumped by pulsed laser had been studied theoretically and experimently.2,3 Here, it was found that under strong interactions within three bodies of laser field, DODCI and dye molecules, femtosecond pulse trains could be generated in the proper conditions.
High-power femtosecond pulse compression using spatial solitions
Authors: Reitze D. H. , Weiner A. M. , Leaird D. E.
Published: February 2023

Traditional methods of femtosecond pulse compression that use optical fiber as the bandwidth generating element are restricted in energy to a few nanojoules of compressed output owing to fiber damage thresholds. Although recent efforts1 have succeeded in compressing amplified femtosecond pulses to <20 fs while maintaining μJ energies, each is limited in application by either low repetition rate or lack of wavelength selectivity. Here we present a novel pulse compression technique that utilizes the self-trapping and stable propagation of bright 2-D spatial solitons2 in bulk nonlinear media. The self-phase modulation that accompanies soliton propagation provides sufficient bandwidth for compression, accomplished with a grating pair. Starting with 80-fs 620-nm 10-μJ pulses obtained from a colliding-pulse mode-locked ring dye laser amplified with a copper vapor laser pumped amplifier, we have achieved 19-fs 0.6-μJ pulses at a repetition rate of 8.6 kHz. Unlike alternative methods, spatial soliton pulse compression can be applied over a wide wavelength and energy range and can be used with high repetition rate amplifier systems. In addition, applications to the production of high repetition rate (>10 THz) pulse trains are discussed.
Spectral holography of shaped femtosecond waveforms
Authors: Weiner A. M. , Leaird D. E. , Reitze D. H. , Paek E. G.
Published: February 2023

Synthesis of arbitrarily shaped femtosecond optical waveforms has recently been achieved by masking the optical frequency components that are spatially dispersed within a simple grating and lens apparatus.1 The spatial mask acts as a linear filter that manipulates the phases and amplitudes of the spatially dispersed spectral components; the shaped pulse corresponds to the Fourier transform of the pattern transferred by the mask onto the spectrum. In this paper we demonstrate additional signal processing operations, such as time-reversal, correlation, and convolution, which cannot be achieved using simple linear filtering. Our demonstration relies on spectral holography within a femtosecond pulse shaping apparatus. Two input beams are incident on the holographic pulse shaper—a shaped signal beam, generated using a CPM dye laser and a second, programmable pulse shaper,2 and an unshaped 100-fsec reference beam. The interference pattern between these two beams, which are spectrally dispersed within the pulse shaping apparatus, is recorded on a thermoplastic plate. The resulting spectral hologram can be read out using an unshaped reference pulse to yield both real and time-reversed (virtual) replicas of the original signal pulse. Convolution and correlation operations are performed by using shaped pulses for readout.
Array-mode selection in nonabsorbing-mirror diode laser arrays
Authors: Thompson William E. , Cherng Chung-Pin , Osinski Mark
Published: February 2023

Nonabsorbing mirror (NAM) GaAs/AlGaAs arrays have been shown to deliver thermally limited cw output power as high as 2.4 W from a 100-μm aperture.1 Typically, these devices operate in high-order array modes with a double-lobe far field. In this paper, we show that with careful design, the NAM section can be utilized to favour single far-field lobe operation. We treat the NAM array as a composite cavity consisting of a waveguide region in which parallel single-mode waveguides are coupled through evanescent fields of guided modes and a uniform NAM section that provides further coupling between individual waveguide modes via diffraction. The eigenmodes of the waveguide section (supermodes) are calculated using the improved coupled-mode theory.2 The supermode mixing coefficients, determining the eigenmodes of the composite cavity, are obtained by evaluating the reflected image at the interface between the waveguiding and uniform sections of the device using the 3-D diffraction integral. If the phase difference between light returning from the NAM section and injected back into any particular waveguide and its nearest neighbor is an integer multiple of 2π, the in-phase supermode is reinforced. On the other hand, a small variation in the NAM-section length and/or the waveguide spacing is sufficient to dramatically change the farfield. The performance of NAM arrays, is therefore, very sensitive to details of the waveguide structure.
Size dependence of quantum Stark effect in CdSxSe1-x nanocrystals
Authors: Mei Guang , Carpenter Scott , Felton L. E. , Persans P. D.
Published: February 2023

We report experimental electromodulation results on various sized CdS
x
Se1-
x
nanocrystals doped in a glass matrix. The samples were made by heat treatment and annealing of as-received filter glass from Schott. The size of the nanocrystals can be controlled from 40 to 200Å in diameter by annealing time. Transmission electron microscopy and absorption measurements were performed to get the size and volume fraction of semiconductor nanocrystals in the sample. Raman experiments indicated that the samples are CdS0.44Se0.56 and that the composition does not change with nanocrystal size. Electromodulation experiments were performed, and two strong peaks from the quantum-confined excitons were observed.
Generalized contrast operator for texture segregation
Authors: Gorea Andrei , Papathomas Thomas V.
Published: February 2023

Texture segregation has been related to serial (attentive) vs parallel (preattentive) processes and, more recently, to low-level multiscale filtering.1,2
Real-time two-dimensional holographic imaging by an electron beam addressed spatial light modulator
Authors: Poon T.-C. , Schilling B. , Wu M. , Shinoda K. , Suzuki Y.
Published: February 2023

Real-time holographic recording using an optical heterodyne scanning technique proposed by Poon1 has recently been demonstrated, and real-time reconstruction of holograms generated by the scanning technique has also been achieved by using an electron beam addressed spatial light modulator (EBSLM).2 These experiments, however, have been limited to one-dimensional objects, such as a simple transmissive slit. In this talk, we present results of real-time two-dimensional holographic imaging. Details of the experimental set-up will also be discussed.
Four-femtosecond propagation time measurement on single photons and nonlocal cancellation of group velocity dispersion
Authors: Steinberg A. M. , Kwiat P. G. , Chiao R. Y.
Published: February 2023

In the process of spontaneous parametric down-conversion, conjugate pairs of broadband photons are emitted simultaneously from a nonlinear crystal. We use coincidence detection in a fourth-order interferometer to measure the propagation delay of one photon with respect to that of its conjugate. One photon of every pair enters each arm of the interferometer, and when the path-length difference is adjusted such that the two photons meet essentially simultaneously at the output beam splitter, a dip is observed in the coincidence rate between photon counters placed at the two output ports. In our experiment, the rms width of this dip is 15 fs. By placing various dielectric media in the path of one of the photons and then adjusting the free-space path lengths until the coincidence dip reappears, we have measured the propagation time of single photons and found it to agree with predictions based on the group velocity.1 Because of a surprising quantum-mechanical effect, group-velocity dispersion cancels out, such that the expected wave packet broadening has essentially no effect on the high time resolution of this technique.2
Thin film coatings on silicon detectors for stationary reflection properties at oblique incidence
Authors: Azzam R. M. A. , Lopez A. G.
Published: February 2023

Transparent single-layer and double-layer coatings are designed that render the reflectance (R
p
, R
s
) or ellipsometric (Ψ, Δ) parameters of a Si detector surface locally stationary with respect to small changes of the angle of incidence in the neighborhood of a given angle and at a fixed wavelength. All reflection parameters are made stationary with a triple-layer coating. Solutions are obtained, by using the Newton-Raphson method, for the refractive index and the thickness of the single layer and for the thicknesses of the constituent films of the double and triple layers whose refractive indices are preselected. These coatings are applied to reduce the sensitivity of the instrument matrix of the four-detector photopolarimeter1 with respect to small changes in the direction of arrival of the incident light beam whose Stokes parameters are to be measured.
Quantum mechanical stability of solitons
Authors: Kärtner F. X. , Haus H. A.
Published: February 2023

Solitons of the classical nonlinear Schrödinger equation are stable to noise perturbations. One may ask whether the uncertainties associated with the quantum description of a soliton could cause the soliton to become unstable and to break up. It is not difficult to derive the fact that the first order soliton disperses, so that the probability of detecting the soliton at a specified position approaches zero as the time of propagation approaches infinity. This fact does not prove or disprove breakup. It can be shown by using the formalism of Ref. 1 that the intensity correlation function of a quantum soliton is time independent.2 In this paper we describe a form of a Hanbury, Brown, and Twiss experiment that could demonstrate the stability of the fundamental soliton (in principle), and we develop expressions for the hierarchy of correlation functions measured by such an experimental setup. If the soliton breaks up, the correlation functions should show a strong dependence on the propagation time of the soliton. The calculations demonstrate that all the measurable correlation functions do not depend on the propagation time; therefore the quantum soliton is stable.
Influence of top-contact configuration on series resistance of proton-implanted vertical-cavity surface-emitting lasers
Authors: Osinski Marek , Nakwaski Wlodzimierz , Cheng Julian
Published: February 2023

Proton-implanted vertical-cavity surface-emitting lasers (VCSELs) exhibit relatively high series electrical resistances. Initially, these were attributed to the high series resistance of p-type Bragg mirrors. However, even in the case of devices with stepped,1 graded-superlattice,2 or continuously graded3 mirrors, the series resistance remains very high in comparison to that of common stripe-geometry lasers. We examine what role is played in high resistance of proton-implanted VCSELs by current spreading in the upper section of the device. Three different top-contact geometries are considered: annular, circular, and broad-area. Closed-form analytical solutions are obtained for each case. The results demonstrate that low values of series resistance can be achieved by using the broad-area contact configuration.
Producing squeezed light from conventionally pumped lasers
Authors: Savage C. M. , Stevenson A. , Ralph T. C.
Published: February 2023

It has recently been discovered that the quantum theory of the laser allows conventional lasers to produce squeezed light.1-3 The physics of this squeezing is uncomplicated and robust. It relies on the fact that a sequence of Poissonian transitions having the same total mean transition time as a single Poissonian process have less time variance than the single process. Hence the sequence of transitions has sub-Poissonian time statistics. This can be transformed into sub-Poissonian laser pumping and hence into sub-Poissonian and quadrature squeezed laser light. We will discuss how this theory can be put into practice. The effects of mode structure and inefficiences will be assessed. Candidate lasers and progress towards their experimental realization will be discussed.
Nonlinear system size quantum fluctuations in optics
Authors: Mertens C. J. , Kennedy T. A. B. , Swain S.
Published: February 2023

Quantum properties of intracavity nonlinear optical processes such as parametric oscillation and second harmonic generation are limited to a linearized analytical treatment except for certain special cases. Perfect squeezing in one quadrature and the divergence in fluctuations of the conjugate quadrature predicted at threshold in parametric oscillation are a consequence of the approximate linearized analysis. We investigate nonlinear quantum fluctuation corrections by using nonequilibrium Green’s function methods1,2 in concert with quantum master equations, to assess when these system-size effects may be observable in the laboratory.
Design of some computational building blocks by using soliton based GEO modules
Authors: Iftekharuddin K. M. , Awwal A. A. S. , Karim M. A.
Published: February 2023

Ultrafast logic gates based on soliton dragging in high bandwidth fiber system have already been shown to be possible.1 For such fiber-based logic systems, the generalized exclusive-OR (GEO) module has been identified as its natural basis.2 The fundamental building block of a GEO module consists of an exclusive-OR (XOR) gate and two AND gates. In this current work, we consider a novel approach and design a ripple carry full adder circuit by using the Boolean and connectivity complete nature of GEO module. Also we extend this technique for designing an M×N multiplier.
Psychophysical study of resolution in confocal microscopy
Authors: Kim John J. , Hansen Eric W.
Published: February 2023

Confocal scanning is an effective modality for three-dimensional microscopy because of its optical sectioning capability. However, there is a tradeoff to be made between resolution and signal-to-noise ratio (SNR) when fluorescent objects are viewed by confocal scanning. Under conditions of limited photon dose to the specimen, enlarging the confocal detector aperture admits more light and improves the SNR at the expense of resolution. Conversely, making the aperture smaller improves the depth resolution in principle, but it can also reduce SNR to the point where closely spaced elements in the object are effectively unresolvable by a human observer. We present in this paper an experimental study using psychophysical ROC analysis and the Hotelling trace criterion to evaluate resolution in this partially confocal regime. Synthetic images of objects at various confocal aperture sizes and noise levels are shown to human observers who are asked to perform a classification task requiring depth resolution. The collected responses are summarized by ROC measures. We compare these with the results of analyzing the same image sets with the Hotelling trace criterion, which has been observed to track human observer performance in certain radiological tasks.1
MOCVD-grown vertical-cavity surface-emitting laser arrays with spatially graded lasing spectra
Authors: Sze T. , Cheng J. , Hersee S. D. , McInerney J. , Sun S. Z. , Naqvi S. , Malloy K. J.
Published: February 2023

Dense wavelength-division multiplexing (WDM) is a promising approach to the improved utilization of the terahertz capacity of optical fibers for which integrated laser arrays with uniform wavelength separations are necessary. Because of its two-dimensional integrability, a surface-emitting laser array can greatly increase the number of channels that can be wavelength multiplexed. Two-dimensional VCSEL arrays with uniformly graded emission wavelengths have been achieved by using molecular beam epitaxial (MBE) growth techniques and have been used in WDM system demonstrations.1 We have shown that because of MOCVD's unique ability to continuously grade all the hetero-interfaces, it can produce VCSELs with a significantly lower series resistance and thermal dissipation, which is important to the realization of a dense VCSEL array. Here we report the first demonstration, to our knowledge, of spatial grading of MOCVD grown VCSEL emission wavelength. By using two-dimensional spatial mappings of reflectance spectra we have seen gradients of 16 nm/cm over a square centimeter area. Through tracking the positions of the cavity mode and of the reflection band and comparing them to theoretical results, the relation between wavelength shifts in the reflectance spectra and the variations in the thickness of the layers is determined. This data was used in our predictions of and comparison with the experimental lasing wavelengths of individually pumped VCSELs.
Fanning noise suppression in two wave mixing
Authors: He Q. Byron , Yeh Pochi
Published: February 2023

Photorefractive two wave mixing has many potential applications in the areas of optical image processing, optical interconnection, and optical computing. However, because of the presence of the fanning effect, the achievable two wave mixing gain and the signal to noise ratio are severely limited in those crystals with high coupling coefficients, such as BaTiO3, KNbO3, SBN, etc. It is important to reduce the fanning noise for practical applications. Several methods have been proposed.1,2 In this talk, we present a simple and effective approach to suppress the fanning noise and to increase the signal to noise ratio by introducing an incoherent erasure in the photorefractive two wave mixing amplifier. With the incoherent erasure, the achievable gain and the signal to noise ratio can be improved significantly. Results from theoretical modeling and experimental investigation in a 45°-cut BaTiO3 crystal will be presented and discussed.
Observation of a vibrational-wave-packet-induced photon echo
Authors: Dunn T. , Sweetser J. , Radzewicz C. , Walmsley I. A.
Published: February 2023

Most experiments that study the dynamics of vibrational wave packets in small molecules utilize geometries in which propagation plays little or no role.1 In contrast, we have developed an apparatus for performing time-resolved fluorescence upconversion from an extended sample of sodium dimers that are excited by a resonant short optical pump pulse, with a temporal resolution of about 70 fs.
Holographic components for integrated-optic waveguide devices
Authors: Nishihara H. , Suhara T. , Ura S.
Published: February 2023

The use of holographic components (gratings) in integrated devices is very advantageous because complex functions can be realized with a minimum number of components. Such single gratings can have various compound functions of wavefront conversion such as beam splitting, deflection, input/output coupling, focusing, and wavelength division. The grooves of these gratings are not simply straight, but curved with different curvatures and different periods. To fabricate these gratings, we have developed a specially designed EB writing system for this purpose. The system can specify 2 × 1016 computer-generated data points over a 1 mm × 1 mm area with 0.3 μm resolution. One typical example is a focusing grating coupler (FGC) for an integrated-optic disk pickup. The FGC is designed to have approximately 2,000 curved grooves over the aperture of 1 mm2 and the focal length of 2 mm at a wavelength of 0.78 μm on a glass/ SiO2/Si waveguide. Diffraction efficiency is estimated to be 60% for the optimum groove height of 35 nm. The IO disk pickup has been implemented and the fundamental functions have been experimentally confirmed. Several other grating-based waveguide devices will be discussed.
Pyroelectric detection of light beams using a phase transition in guest–host compounds
Authors: Kweon G. , Beadie G. , Lawandy N. M.
Published: February 2023

Because of their relative ease of fabrication, β-quinol clath-rates are one of the most studied among non- stoichiometric inclusion compounds. (quinol)3(CH3OH)
x
with x close to 1 has shown1 spontaneous polarization at a critical temperature near 66 K accompanying induced voltage across the sample. During the phase transition, the enclathrated methanol undergoes a sudden cooperative re-orientation during which the angle between the methanol C–O bond and the crystallographic C-axis changes discontinuously. This produces a large pyroelectric coefficient for high occupancy methanol clathrates, which suggests the possibility for a sensitive bolometer. We report on experiments where a clathrate connected by two electrical leads inside a He Dewar and held just below the transition temperature is exposed to laser radiation. By observing the voltage change, we can detect a wide range of IR and FIR wavelengths by using CO2-pumped superradiated FIR and Nd:YAG lasers. By keeping the sample size and the temperature gap small, the detector can be made very sensitive to incoming radiation.
Laser induced fluorescence spectroscopy of mercury halide radicals
Authors: Jordan Kevin J. , Lipson Robert H. , Bascal Hafed A.
Published: February 2023

The laser induced fluorescence spectrum of HgBr between 260 and 450 nm (B2Σ+ ← X2Σ+) and C2Π1/2 ← X2Σ+) has been recorded. Rotationally cold HgBr(X) was produced with both continuous and pulsed corona excited supersonic jet discharge expansions of the precursor HgBr2 in helium. Full isotopic resolution of the vibronic bandheads was observed for the B2Σ+ ← X2Σ+ transition. The preliminary vibrational numbering is in agreement with the published assignment from low resolution absorption spectra,1 and a complete vibrational analysis will yield more precise (~0.3 cm-1) spectroscopic constants for the B(2Σ+) state.
High-resolution VUV absolute photo-absorption cross sections of N2 and rare gases
Authors: Humm David C. , Asfaw Araya , Seyoum Hailemichael , Morgan H. , Fortna J. , Cleary D.
Published: February 2023

We present absolute total photoabsorption cross sections measured with the Very High Resolution Spectrometer at the SURF-II synchrotron radiation source at the National Institute of Standards and Technology, with a resolution of 9 mÅ at 835 Å in the first order. The cross sections of N2 at the wavelengths of the OΠ(2s2p4-4P2s22p3 4S) multiplet are found to be 10 Mb at 834.467 Å, 0.3 Mb at 833.332 Å, and 0.05 Mb at 832.862 Å. This new high-resolution measurement confirms the 10 Mb value, which has given rise to some still-unsolved discrepencies in interpreting atmospheric observations of the OΠ emission.1 We also measure absolute cross sections in the continua of rare gases, including the argon 3s3p6np absorption windows at 425 Å.
Resonant Voigt-effect spectra of the Rb D2 transition
Authors: Muroo Kazuyuki , Takubo Yoshitaka , Yamamoto Manabu
Published: February 2023

The resonant magneto-optic spectra of the Rb D2 transition in the Voigt configuration was measured by using a tunable, narrow-band, single-mode GaAlAs diode laser. The elliptically polarized laser beam with a small ellipticity Δα was incident upon Rb vapor in a transverse magnetic field of 0.75 T. The polarization change caused by magnetically induced optical anisotropy was analyzed with a birefringent prism placed behind the sample with a small offset angle Δθ from the perfectly crossed direction. The Voigt-effect signal had a Zeeman splitting of 50 GHz. The spectral intensity distribution of the signal, determined by the interference between the hyperfine components of 85Rb and 87Rb, was dependent on Δα, Δθ, and the number density of atoms. The theoretical prediction1 for the Voigt-effect line profiles for various Δα and Δθ agreed with the experimental result. The minimum detectable density of Rb atoms was limited by statistical fluctuations of photon counts.
State-selected photodissociation of alkali diatomics by all-optical triple resonance: nonadiabatic effects on the resulting atomic fluorescence and its polarization
Authors: Ji B. , Whang T.-J. , Wang J. X. , Wang H. , Kleiber P. D. , Sando K. M. , Stwalley W. C. , Lyyra A. M. , Yiannopoulou A.
Published: February 2023

Diatomic molecular photodissociation (e.g., B–X in K2 and NaK) samples interacting potential energy curves from small to large internuclear distances. Thermal photodissociation studies of the polarization of atomic fluorescence and atomic fine structure branching in which thousands of rovibrational levels contribute suggest nearly adiabatic behavior in K2 (Ref. 1) and strongly nonadiabatic behavior in NaK.2 Recently an all optical triple resonance (AOTR) technique has been demonstrated with which individual rovibrational levels are selectively photodissociated.3 The application of this technique to studies of alkali diatomic photodissociation will be described.
Subharmonics in photorefractive materials in the presence of an a.c. applied field
Authors: Kwak C. H. , Takacs J. , Shamonin M. S. , Solymar L.
Published: February 2023

It has been shown experimentally1 that a subharmonic beam may appear spontaneously between two pump beams without detuning either of the beams when a field varying sinusoidally or in the form of a square wave is applied across the crystal. That work has now been extended to cover the rise of the subharmonics as a function of time and their dependence under stationary conditions on the ratio between the pump intensities. The experiments were done on photorefractive bismuth silicate crystals. A simple theory is found to describe well the repetition frequency at which the subharmonics appear.
Wave amplification in photorefractive BSO with two pump beams
Authors: Erbschloe D. R. , Solymar L. , Takacs J. , Wilson T.
Published: February 2023

Energy transfer between waves in photorefractive media occurs generally in one direction only, with a coupling dependent on the imaginary part of the modulated space charge field. Ringhofer and Solymar1 have described a mechanism in which energy is transferred inward from two pump beams and in which the coupling is partially dependent on the real part of the space charge field. This talk explores qualitative features of this mechanism such as the symmetry between the internal companion orders and the two pump beams and the required frequency detuning among the four beams. Experimental studies in which one pump beam was frequency shifted off a moving mirror allowed experimental verification of this mechanism in ring and linear resonators.
Contradirectional two-beam coupling in heavily Rh-doped (and strongly absorbing) SBN:60
Authors: Vazquez R. A. , Vachss F. R. , Neurgaonkar R. R. , Ewbank M. D.
Published: February 2023

Optimizing photorefractive charge density for contradirectional two-beam coupling suggests doping photorefractive crystals with high impurity concentrations. A series of Rh-doped SBN:60 samples with Rh concentrations ranging from 0.015 to 0.20% by weight were grown and fabricated. The corresponding absorption coefficients α, extending from 0.5 to 6.2 cm−1, are a penalty for such high doping levels. These α are non-negligible when compared to the measured contradirectional two-beam-coupling coefficients Γ, which ranged from 0.8 to 13.8 cm−1. In this regime of non-negligible α, the simple analytic expressions derived by Yeh1 are no longer valid. Ja2 has provided an applicable theoretical description giving a numerical solution. We have extended Ja’s work, deriving an approximate expression for the two-beam-coupling gain g in the presence of strong α, which ranged from 0.8 to 13.8 cm−1. In this regime of non-negligible α, the simple analytic exp which is a function of α, Γ, thickness L, and incident pump-probe intensity beam ratio r
pp
. We will present g versus rpp data for six different Rh concentrations and compare that data to various theoretical predictions.
Approximations in analytic models of laser oscillators
Authors: Beausoleil Raymond G.
Published: February 2023

Rate equation analyses of laser oscillator dynamics generally include an integrodifferential equation that describes the time dependence of the intracavity photon number.1,2 This rate equation usually gives reasonable predictions for continuous-wave characteristics of low gain lasers. However, these predictions are inconsistent with Poynting’s theorem and disagree significantly with plane-wave calculations for high-gain lasers. It is often assumed that only first-order saturation effects are important2 and that the laser mode is well-collimated within the gain medium.1 I present a model of multimode laser oscillator dynamics that is consistent with both continuous-wave high-gain plane-wave analyses and rate-equation descriptions of Q-switched lasers. As an example, I describe a detailed analytic model of a continuous- wave high-gain end-pumped four-level laser, including thermal loading effects. I compute the maximum errors incurred by neglecting higher-order saturation terms and Gaussian beam expansion, and I simultaneously optimize both the output coupling and the laser mode waist.
Free-space optoelectronic neural system prototype
Authors: Krishnamoorthy Ashok V. , Yayla Gökçe , Marsden Gary C. , Esener Sadik
Published: February 2023

We have previously designed a freespace optoelectronic neural system1 based on the D-STOP architecture.2 The neural architecture minimizes the number of required light transmitters and provides full connectivity between neurons, flexible functionality neurons and synapses, low signal timing skew, and accurate electronic fan-in with dendritic processing capability. Neural signals are encoded by using a combination of pulse-width modulating optical neurons and pulse-amplitude modulating electronic synapses. The neural system prototype consists of a 16-node input layer, a four-neuron hidden layer, and a single neuron output layer. The input layer consists of a 4 × 4 array of PLZT modulators. An 8 × 8 synapse scalable prototype of the neural chip and the space-invariant optical interconnection system have been fabricated. The image of the modulator array is distributed optically to the 64 synapses of the four hidden layer neurons, which are electrically connected to the output neuron. One differencing dendrite per four synapses is used. Measured synapse and dendrite unit characteristics exhibit high linearity with low power consumption. Test results allow a 100 ns minimum pulse width for neural outputs.
Threshold characteristics of microdisk semiconductor lasers
Authors: Levi A. F. J. , Slusher R. E. , McCall S. L. , Stark J. B.
Published: February 2023

Semiconductor microdisks 2 to 5 μm in diameter composed of six 100-Å InGaAs quantum well layers separated by 100-Å InGaAsP barriers are fabricated on InP support pedestals. These disks form high-Q optical resonators for the whispering-gallery mode around the edge of the disk.1 Optical pumping results in lasing for wavelengths near 1.5 μm with emission both vertically and from the edge of the disk. Threshold pump powers are in the range from 50 to 100 μW. Near threshold the laser emission for the smaller diameter disks varies smoothly with pump power as expected for an optical resonator where the emission is restricted to only a few optical modes. The emission linewidth also varies smoothly with pump power. The measured emission characteristics allow us to model the microdisk emission by using rate equations involving the microresonator Q value and the β parameter, i.e., the ratio of the probability of emission into the lasing mode to the probability of emitting into all modes. We will report Q and β values as a function of disk radius, perfection of the disk edge, the dimensions and shape of the support structure, and the disk temperature for both cw and pulsed excitation. These low threshold microlasers may find application in large arrays and optical interconnects.