bluuebunny/crossref_metadata_2025 huggingface dataset:
3-D optical memory based on stacked layer electron trapping thin films
Authors: Yang Xiangyang , Wrigley Charles , Seiderman William , Lindmayer Joseph
Published: February 2023

Transparent electron trapping (ET) thin films are optical storage media recently developed by Quantex. A 3-D erasable optical memory based on stacked ET thin film layers is presented in this paper. The page memory is written by properly imaging the page composer onto a specific layer with blue laser light at 488 nm. To read out the memory on a specific layer, a slice of a 1064 nm IR beam is guided into the ET layer from the side of the stacked layer media. The orange emission (630 nm) corresponding to the written page memory at that layer is emitted as the result of the IR stimulation. System design considerations, requirements of writing/reading energy, storage capacity, and techniques to overcome the cross talk between adjacent layers are discussed in the paper. The preliminary experimental results are also provided.
Disorder-induced InGaAsP/InP quantum well waveguides via phosphorous ion implantation
Authors: Jones K. L. , Zucker J. E. , Tell B. , Brown-Goebler K. , Joyner C. H. , Miller B. I. , Young M. G.
Published: February 2023

We demonstrate formation of buried InGaAsP/InP quantum well waveguides by means of phosphorous ion implantation and thermal annealing during regrowth. We use absorption spectra of implanted and unimplanted regions to estimate the induced index difference, which is on the order of 1 % at 1.55 μm. Calculated mode intensities are in good agreement with the observed near field intensity patterns. With this etchless implant technique, we achieve a significant reduction in propagation loss for single-mode p-i-n waveguides relative to etched semi-insulating planar buried heterostructure waveguides fabricated from the same quantum well structure. This type of band-gap engineering, with its simplicity and high yield, lends itself to the fabrication of complex integrated optoelectronic circuits. These include integrated laser/modulators and switch arrays.
High average power beta-barium borate optical parametric oscillators
Authors: Komine Hiroshi
Published: February 2023

Conversion efficiency, frequency shift, and thermal dephasing in beta-barium borate (BBO) and lithium borate (LBO) crystals have been investigated with ultraviolet lasers. A singly resonant, injection-seeded, BBO optical parametric oscillator (OPO) at 455 nm generated up to 0.55 W output when pumped by a frequency-tripled, Q-switched Nd:YAG laser with 2.3 W average power at 355 nm. Effects of thermal loading on BBO and LBO crystals were measured interferometrically by using a xenon chloride excimer laser as a UV source at 308 nm. Refractive index variations caused by UV absorption were analyzed to determine average power scaling limitations. OPO frequency shifts due to crystal heating by pump absorption were observed in BBO with a 308 nm pump laser. These results will be presented along with current progress on tunable visible OPO devices.
Working model of Alexander Graham Bell’s photophone
Authors: Hutt D. L. , Snell K. J. , Bélanger P. A.
Published: February 2023

In the year 1880, Alexander Graham Bell patented a device with which a human voice could be transmitted by using a beam of intensity modulated light. He considered this instrument, the photophone, to be his greatest invention, “…even greater than the telephone.” The original photophone used a thin silvered glass plate to reflect a beam of sunlight. The voice of someone speaking near the plate caused it to vibrate, which in turn induced slight variations in the divergence of the reflected beam. The receiver used a photoresistive detector made of pure selenium connected to a Bell telephone earpiece. Bell and his assistant managed to communicate over a distance of 240 m with their photophone. We have built a working model of the photophone that respects the principles of operation of the original device. Instead of a beam of sunlight, we use an ordinary flashlight as a source. The modulating diaphragm is virtually identical to that used by Bell. The receiver uses an inexpensive CdS detector, a cousin of Bell's selenium detector. It is easy to understand how the demonstration works, and it is fun to see how a flashlight can be used to talk to someone across the room. Although the photophone never found practical applications, it is one of the earliest examples of optical communication technology.
Transient multimode statistics in nearly single-mode semiconductor lasers
Authors: Valle A. , Colet P. , Pesquera L. , Miguel M. San
Published: February 2023

Mode partition noise in optical fiber communication systems is still causing an error rate floor, even with distributed-feedback lasers sources having a side-mode suppression ratio larger than 30 dB in stationary conditions. This phenomenon is caused by the laser turning on initially in a side mode having a different wavelength from the principal mode. The transient statistics of nearly single-mode semiconductor lasers are studied for lasers when the injected current is suddenly switched from below to above the threshold current. The side-mode excitation probability is obtained analytically and numerically for different excitation current and gain differences. In this way the probability of having a side mode larger than the main mode during the leading edge of the optical pulse (rare events) is obtained. This is analogous to an error rate in optical communication systems. We have studied in detail the rare events. For these events a linear relation is found between the value of the main mode intensity during the leading edge of the optical pulse and the logarithm of the relation between the intensities of the side and main modes both averaged over the first relaxation peak.
Pupillary response to spatial pattern versus local luminance changes
Authors: Kennish Jessica , Young Rockefeller S. L.
Published: February 2023

Because spatial information is created by luminance variations across an image, it is not always clear whether neurons at different levels in the visual system are processing spatial information, luminance information, or both. The present paper suggests that, in humans, visual neurons at the pretectal level can convey purely spatial information. Our results show unequivocally that the pupil constricts in response to sinewave gratings formed by local luminance decrements. We infer that the pupil responded to spatial pattern, not to luminance, because the luminance decrement itself would have caused the pupil to dilate, not constrict. Additionally, we infer that both transient and sustained constriction components can be elicited by such pattern stimuli. Responses to spatial pattern and to luminance, however, may not be entirely independent of each other. The pupil response to spatial pattern plus luminance increment or decrement is smaller than the sum of the response to the pattern and the response to the luminance.
Signature of near dipole-dipole interaction in a dense medium of two-level systems
Authors: Crenshaw M. E. , Scalora M. , Bowden C. M.
Published: February 2023

We performed a numerical investigation of the dynamics of the optical Bloch equations, extended for near dipole-dipole (NDD) interactions in dense collections of two-level systems. As a function of peak field strength, the inversion that remains in the medium following excitation by an ultrashort optical pulse has step-like transitions between the ground state and the excited state. The medium is left fully inverted if the peak Rabi frequency (peak field strength written in units of frequency) is equal to the NDD interaction strength. Remarkably, this result is independent of pulse area. About this point is a region of peak field strength for which the dense medium is left fully, or nearly fully, inverted. On the weak side of this region, the dense medium is left in the ground state. On the strong side of this region, the medium alternates between absorbing (ground state) and amplifying (inverted) as a function of peak field strength. This response can be used to measure the strength of the NDD interaction, for coherent optical pumping, and also constitutes a new and unique intrinsic optical switch, which, unlike optical bistability, does not have hysteresis and is independent of dissipation from incoherent effects.
VUV and UV luminescence spectra of rare earth activated ions in LiYF4 and LiLuF4 single crystals
Authors: Dubinskii M. A. , Cefalas A. C. , Sarantopoulou E.
Published: February 2023

The allowed radiative interconfigurational d-f transitions of the rare earth ions in the wide band gap dielectric crystals offers the possibility that these materials can be used for generating coherent VUV and UV radiation when they are pumped with F2 molecular lasers at 157 nm. Therefore the search for new rare earth activated wide band gap dielectric crystals for potential VUV and UV laser sources is of great importance. We report here on the laser induced fluorescence spectroscopic features of the rare earth trivalent ions of Nd, Ho, Tm, Tb, Pr, Er in LiYF4, and LiLuF4 host dielectric crystals in the VUV and UV region of the spectrum under laser pumping of these crystals with the F2 molecular laser at 157 nm.
Influence of the light interaction on the collection efficiency of a-Si :H solar cells
Authors: Minkov D.
Published: February 2023

I propose analytical expressions for the light absorption in the active layer of an a-Si:H solar cell (SC), for non-coherent light interaction in this layer, as well as for coherent interaction, considering inclined incidence of light. The contribution of the scattered light to the integral collection efficiency (ICE) of a SC with an indium-tin-oxide conductive transparent oxide contact (CTOC) or with a SnO2 CTOC is estimated. Computations about the collection efficiency of a SC are implemented for various cases of light interaction in the layers of the SC. This allows the different appearances of the collection efficiency of SCs in practice to be explained, based on the nature of light interaction in CTOC and the active layer, which is related to their surface roughness. It is possible to calculate some optical characteristics of the transparent contact or the active layer by using the collection efficiency, when the light interaction is coherent in the respective layer. The influence of an anti-reflection coating and two-layer CTOC on the collection efficiency of a SC is also investigated, as well as the thickness dependence of ICE.
Infrared spectra of atmospheric emission
Authors: Churnside J. H. , Shaw J. A.
Published: February 2023

During November of 1991, a Fourier transform infrared spectrometer was used to measure emission spectra of the sky under both clear and cloudy conditions. Spectral resolution was 1 cm−1 over the region from 500 to 2000 cm−1. These spectra were calibrated by using two blackbody cavities, one at 77 K and the other at ambient temperature. These spectra will be compared with spectra calculated by using radiosonde profiles of the atmosphere and the U.S. Air Force radiative transfer code MODTRAN.
Broad- and narrow-band cw lasers in resonance ionization mass spectrometry isotope analysis
Authors: Tissue B. , Loge G. , Olivares J. , Fearey B.
Published: February 2023

Resonance ionization mass spectrometry (RIMS) is being developed to measure 230/232Th ratios (~5:105), which are used in U-series disequilibrium dating of geological samples of the last 400,000 years. We will discuss the precision and accuracy of the ratio measurements when resonant excitation with a broad-band dye laser and a narrow-band frequency-doubled Ti:sapphire laser is used. The dye laser is evaluated with and without optogalvanic frequency locking onto a Th transition to provide better reproducibility. The relative advantages and disadvantages of the two excitation sources will be summarized, including 1) narrowband excitation yielding greater isotope selectivity versus 2) broad-band laser excitation providing higher sensitivity (simultaneous excitation of all relevant isotopes and all atoms within the Doppler profile).
One- and two-photon photoelectron angular distribution measurements in the heavy alkali metal atoms
Authors: Elliott Daniels. , Yin Yi-Yian
Published: February 2023

We have measured photoelectron angular distributions for single photon ionization of atomic rubidium and cesium and for two photon ionization of rubidium. The single-photon measurements show clear variation as a function of wavelength of the exciting laser due to the spin-orbit interaction. From these measurements we derive the Fano parameter, a measure of the relative strength of the dipole transition amplitudes from the ground state to the j = 1/2 and j = 3/2 continuum p states. These results are in excellent agreement with, and in some cases of much smaller uncertainty than, similar results obtained through measurements of the Fano effect and related polarization measurements. The two-photon measurements also vary with wavelength because of their dependence on relative cross sections and phase shifts of the p → d and p → s transitions, and the fine structure of the continuum d-state.
Higher-order interference effects in the reflection of light from random media
Authors: Nieto-Vesperinas M. , Sanchez-Gil J. A.
Published: February 2023

We study the intensity angular correlation function of coherent waves, diffusely reflected from random media in the case in which the speckle pattern does not follow the jointly Gaussian statistics and thus the factorization approximation does not hold. As a result of the breakdown of the factorization approximation, a new enhanced long range correlation appears, exhibiting two peaks due to coherent effects that are generalizations for higher statistical moments of the scattered wave function of that leading to the phenomenon of enhanced backscattering mean intensity. The samples should have small enough dimensions for this effect to be observable. Both the theory of these correlations and numerical results for s and p electromagnetic waves scattered from rough surfaces are presented.
Two-beam coupling in electromagnetically aligned shaped microparticle suspensions
Authors: Rogovin D. , Scholl J. , Shen T. P.
Published: February 2023

We study the effect of electromagnetically aligning the suspension on the frequency-dependent gain coefficient for energy transfer via NDTWM, and we find that electromagnetic alignment of the particles vastly alters the nonlinear optical characteristics of the suspension. Previous studies focused on static index gratings and predicted a number of novel effects arising from microparticle alignment that manifest themselves in optical phase conjugation. Here we focus on moving optical index gratings and find additional new phenomena that reveal themselves in the gain spectrum for energy transfer via two-beam coupling. Specifically, (1) the magnitude of the low frequency portion of the gain coefficient due to the formation of moving translational index gratings depends on the extent of particle alignment and shape, and the direction of power flow can be reversed. (2) The high frequency portion of the gain coefficient due to the presence of a moving orientational index grating exhibits similar behavior. However, the dynamics associated with reversal of power flow is somewhat different and occurs for different material and electric field parameters.
Investigation of the diffraction near field behind phase shifting half-planes with variable edge geometry
Authors: Krumbügel M. A. , Totzeck M.
Published: February 2023

The electromagnetic near field behind phase shifting half-planes (n = 1.02, thickness <2λ, distance 0.1λ-2λ) is investigated by using a modified Mach-Zehnder-interferometer for 3-cm microwaves and a small probe-antenna. Direct measurements of the diffraction fields are performed with high accuracy (amplitude 0.2%, phase 0.1°) and with high spatial resolution (<λ/30). The dielectric half-planes are approximated by parallel plates (width 36λ, height 17λ.) with wedge shaped edges, made of foamed polystyrene. They are fabricated inexpensively with high precision (thickness <λ/30, wedge angle <2°). The measured field distributions depend strongly on the wedge angle and the polarization of the incident radiation: For polarization with E-vector parallel to the edge the diffraction fringes are more pronounced than for perpendicular polarization. Behind rectangular edges the diffraction near field is symmetric, while it is strongly asymmetric behind wedge shaped edges. The measurements are confirmed by numerical calculations based on the first Born approximation for weak scattered taking into account the complex transmission of the incident wave inside the dielectric plate.
Multiple-wavelength surface profilometry for correcting phase change of reflected light
Authors: Doi Takuma , Toyoda Kauji , Tanimura Yoshihisa
Published: February 2023

Recently, the resolving power of optical surface profilometry has been improved to below 1 nm. However, the phase change of reflected light, which depends on optical constants (n,k) of a sample, can reach several tens of nanometers. When a sample has inhomogeneity of optical constants, the phase variations of reflected light cannot be ignored in interferometric surface measurement. In measurement at a single wavelength, the influence of phase change cannot be distinguished from the true profile. However, it is possible to correct this influence if the dependence of the phase change on wavelength is used to identify the sample substances. To this end, we measure the phase changes at several wavelengths. A sample consisting of two kinds of metals in the same plane is fabricated, and its surface profile is measured by interferometry. In spite of the flat surface, the virtual step height (maximum value of 33 nm) is measured at the boundary of the two adjacent metals. The measured step height corresponds to the difference in the phase changes between two metals. The measured differences in the phase changes at several wavelengths agree well with the theoretical values. On the basis of the results, multiple-wavelength surface profilometry for correcting phase change is discussed.
Toward a generalized optical radiometry: a phase-space approach
Authors: Nemes G. , Feru V. M. , Ispasoiu Gh. P.
Published: February 2023

The paper presents a new generalized radiometry that uses a few, basic phase-space (PS) concepts. In the first section the main PS concepts are introduced: the definition of different types of PS (spatial and/or temporal), the energy distribution functions on PS coordinates, the PS domains and measures, and applications of PS to characterizing sources, propagators, and receivers. The second section deals with the definition of the radiometric quantities. The main quantity is the radiant energy distribution on the six-dimensional, spatial-temporal PS, which can be interpreted as a spectral density of a generalized radiance. For defining the radiometric quantities, two different procedures are proposed: projections in PS and sections in PS. Mixed projections and sections are also possible. Existing and new radiometric quantities are obtained; the above procedures generate all possible radiometric quantities. Their properties and usefulness are matters for future studies. The symmetry of the system determines the type of PS to be used and hence the appropriate radiometric quantities. An equivalent source is defined for a real source in each type of PS. The measuring procedure is interpreted as a convolution in PS.
A phase-space point of view on optical detection
Authors: Nemes George
Published: February 2023

The paper analyzes the action of an optical detector by using general phase-space (PS) concepts. First, the main PS concepts and the PS point of view on the optical radiometry are presented. The second section defines the detector: it is a device acting as a PS filter and subsequently as a convertor. The PS filtering is achieved by its accepted energy distribution function on PS. Provided its PS acceptance value is smaller than the PS emittance value of the measured field, the coherence properties of the latter are modified by the detector. Any of the accepted input represent radiometric quantities defined by using PS concepts. The output quantities of the detector are defined similarly as distributions in respect to different PS coordinates. The third section treats the ideal, noiseless detector and the effect of the noise. Generalized PS responsivities and generalized PS detectivities are introduced as quantities characterizing detectors. A linear detector convolves the input quantity to its own PS responsivity. Examples leading to usual detector characteristics are given. The measuring procedure is interpreted as a convolution between the PS distribution function representing the source and that of the detector.
Photon dynamics of an N-level atomic system interacting with a radiation field in the thermocoherent state
Authors: Andrade Neto M. A. , Roversi J. A. , Sharma M. P.
Published: February 2023

Photon dynamics of a radiation field, prepared in the thermocoherent state and interacting with an N-level atomic system, are studied theoretically. It is observed that the phenomenon of collapse and revival has strong dependence on the number of levels the atom has. It is also observed that the collapse and revival phenomenon is very sensitive to the initial number of photons present in the system, to the coupling constants, and to the detuning.
Device engineering with a few monolayers
Authors: Terhune R. W.
Published: February 2023

Since coming to JPL four years ago, I have been concerned with space applications of focal plane array detectors and their fabrication with molecular beam epitaxy. I have chosen to talk about a fascinating part of this work, device structures with monolayer features. First, we have had notable success growing a boron δ-doped layer on the back side of silicon charge coupled devices (CCDs) provided by EG&G Reticon. This layer changes the surface potential so that the photoelectrons generated near the surface are not lost. We add a total of about 3 nm of material efficiencies out to 250 nm for these CCDs, which matched the efficiency expected when limited by the transmittance into the silicon. I will discuss the possible use of these CCDs for UV imaging in forthcoming space missions. This will include an overview of UV imaging with the Hubble Space Telescope. In the last part of the talk, I will discuss the use of thin quantum wells made with strained (4% lattice mismatched) InAs layers in GaAs. I will illustrate some of their properties in reviewing the optical luminescence and absorption properties of 1,2,3, and 4 monolayer quantum wells.
Piezobirefringence and phase matching for second harmonic generation in strained-layer superlattices
Authors: Jackson S. A.
Published: February 2023

In strained-layer superlattices (SLS's), lattice-mismatch induced strain in pseudomorphically grown structures gives rise to a preferred axis because of tetragonal distortion, making the SLS a birefringent material. As a consequence, the indices of refraction for the ordinary and the extraordinary rays are different. They vary as a function of strain. The indices of refraction may be derived from the complex dielectric constant. The imaginary part of the dielectric constant may be calculated from a knowledge of allowed energy states in the system. In the presence of strain, the energy levels change. We calculate, within a deformation potential approach, the changes in the energy levels, hence the band gap due to lattice-mismatch strain for varying compositions in the ZnSe/ZnS
x
Se1-
x
SLS system. We then use these results to calculate the imaginary part of the dielectric function for the system as a function of frequency. We use Kramers-Kronig to calculate the real part of the dielectric function, and from it no (w) and n
e
(w). Using the phase matching condition for n
o
(w) and n
e
(w), we show the resulting strain dependence of the phase matching angle.
Detecting red in white, green, blue, and yellow adaptation fields of various sizes as a function of eccentricity in man
Authors: Iivanainen Antti , Rovamo Jyrki
Published: February 2023

The thresholds of detecting red tint in white, green, blue, and yellow adaptation fields were measured as a function of stimulus size at eccentricities of 0° to 70° in the temporal visual field. Three subjects participated in the experiments (aged 26 to 52). The CIE 1931 (x,y) chromacity coordinates corresponding to the red tint perception were subtracted from the chromacity coordinates of the white, green, blue, and yellow adaptation fields, respectively, in order to obtain the threshold differences (dx, dy) in chromacity coordinates. The size of the stimulus at each eccentricity was varied without prior knowledge of magnification factor. Threshold functions for detecting red in white, blue, and yellow adaptation fields could be successfully scaled by a spatial scaling. However, the E2 values of the magnification factors differed substantially from each other. Thresholds for detecting red in the green adaptation field could not be scaled. These findings suggest that red perception is mediated by several mechanisms with different distributions across the retina.
Applications of holographic storage in lithium niobate
Authors: Mok Fai
Published: February 2023

Multiple volume holograms can be recorded in photorefractive crystals. Holograms are typically recorded by exposing the crystals to interference patterns of plane waves and signal beams. Any one of the two recording beams can be used to read the recorded holograms. Depending on the choice of the readout beam, a multiple-hologram memory can be configured either as an inner-product computer or as an imagery memory. We show experimental results of both configurations of our multiple-hologram memory. The storage capacity of a multiple-hologram memory is a function of the average diffraction efficiency/available readout energy, bandwidth of the optical system/ separation between holograms, and tolerable noise level. In an angle-multiplexed memory, utilizing fractal-space multiplexing can increase the storage bandwidth by over an order of magnitude. Angular separation between holograms and volume holographic cross-talk noise level are both minimal when the nominal included angle between plane waves and signal beams is 90°. The tradeoff of using a 90° geometry is a reduction in the average diffraction efficiency. We attempt to answer some of the questions involved in this tradeoff.
Comparison of angle and wavelength multiplexing in holographic data storage
Authors: Yariv Amnon , Rakuljic George , Leyva Victor
Published: February 2023

Traditionally, data storage in volume holograms relied on angular multiplexing. We show that wavelength (λ) multiplexing in a counterpropagation geometry offers some fundamental advantages by reducing the cross talk among information laden holograms. Some preliminary experimental results will be shown.
Electronic holography methods for imaging through tissue
Authors: Leith E. , Chen C. , Chen H. , Chen Y. , Dilworth D. , Lopez J. , Sun P.-C. , Shih M. , Valdmanis J. , Vossler G.
Published: February 2023

Several methods of electronic holography for imaging through scattering media, especially biological tissue, are described. The methods employ short pulses, noise modulated waveforms with narrow autocorrelation functions, light of reduced spatial coherence, synthetic spectrum technology, or a combination of these methods. We introduce models that predict the limitations of the various methods and describe the various limitations and the tradeoffs. The resolution vs. signal-to-noise ratio tradeoff is particularly significant. We consider combining the first-arriving-light and the confocal-scanning methods, where we employ a confocal technique that eliminates the need for scanning. We show experimental results.
Effect of boundaries in the determination of scattering and absorption constants
Authors: Gonatas C. , Leigh J. S. , Miwa M. , Schotland J.
Published: February 2023

We discuss the effect of geometry and boundary conditions in the determination of scattering and absorption constants by using methods of time resolved spectroscopy. In particular, there is a subtle difference between absorption conditions and radiation conditions, that is, in which photons are not absorbed at the surface but may pass through unhindered. These effects may not be neglected near the surface nor in backscattering type experiments, which are inherently more sensitive to the boundaries than transmission experiments. These effects are also important in imaging using diffusive wave spectroscopy, because of the sensitivity of the inferred spatial structure with respect to the observed transmission data. This is especially true when sources and detectors are not placed within the scattering medium and photons must traverse the boundaries twice.
Time characteristics of bistable DFB amplifiers for all-optical switching
Authors: Calvani R. , Calzavara M. , Caponi R.
Published: February 2023

In all-optical switching systems bistable distributed-feedback (DFB) amplifiers are being used experimentally as memory cells and signal regenerators. In this frame a single section DFB amplifier (with one AR coated facet) operating around threshold at 1549 nm is pumped by a similar laser with a carefully controlled frequency detuning. The polarization controlled pump beam is modulated by a Mach-Zehnder switch (2.5 GHz bandwidth) to avoid source frequency chirp. The measurement of a pump reference and of the beam reflected from the amplifier is performed through a fiber directional coupler inserted between the two DFB diodes. Optical bistability has been observed both in transmission and in reflection for a sinewave modulated input in the 1-200 MHz frequency range. The output square wave exhibits up and down switching times lower than 1 ns and about 2 ns, respectively. The latter figure is consistent with the carrier recombination time in InGaAsP active structures, which is the main limit to the recovery time of bistable amplifiers. Work is in progress to investigate this feature in other types of amplifiers (e.g., multisection DFBs and quantum well structures).
Fiber optic switch using ferroelectric liquid crystals
Authors: Meadows M. R. , Chase H. , Swann W.
Published: February 2023

We describe a 2 x 2 fiber optic switch that uses 50/125 pm multimode fibers and operates at 830 nm. The switch employs six polarizing beam splitter devices and switchable electro-optic, half-wave retarders made with two surface-stabilized ferroelectric liquid crystal films. The light at each of the four fibers passes through a gradient index lens that collimates the input light and focuses the output light onto the fiber's core. A beam splitter then separates the unpolarized input light into two orthogonal linearly polarized components, and the switchable retarders control the light's path inside the switch by controlling its polarization. The component beams are recombined at the output by a polarizing beam splitter. The switch exhibits cross talk of -27.6 dB in the bar state and -22.3 dB in the cross state. Insertion loss is 2.1 dB in the bar state and 3.0 dB in the cross state. These values are stable over temperature from 0° to 45°C and then monotonically degrade until the limits of operating temperatures are reached at -20° and near 62°C. The switching time is 50 ps at room temperature when driven by ±15 V. Lifetime testing to the extent of 109 cycles produces no change in characteristics. Although we did not measure it, the signal bandwidth is limited to about 6 GHz by path length differences within the switch.
Fault-tolerant switching element for the twin butterfly
Authors: Lu Dau-Tsuong , Lin Ting-Ting Y. , Lee Sing H.
Published: February 2023

We introduced the twin butterfly as a fault-tolerant low-contention multistage interconnection network at last year's annual meeting. The twin butterfly is the superposition of a randomly permuted butterfly on a regular butterfly. Fault tolerance is essential for the reliable operation of a large network, while low contention is important for its performance. In this presentation, we first consider the switching element design that will support efficient parallel testing of the twin butterfly. The compile-time testing allows computer generated holograms that will route around faulty switching elements after fabrication and overcomes system yield problems. We then show how the switching element is also designed to support off-line testing after the system is packaged. Since the modulators and detectors of the internal switching elements in a packaged system are not directly controllable and observable, off-line system testing is designed such that switching elements check each other and attempt to mask out detector failures. During reconfiguration, switching elements with modulator faults or excessive amount of detector faults will be declared faulty and removed from active operation Note that neither packet routing nor configuration requires a dedicated routing host. VHDL simulation is in progress to verify the design as well as demonstrate system operation.
15° circular field unobscured telescope with spherical mirrors
Authors: Shafer David
Published: February 2023

There is a class of optical systems used in IR target simulators that might be called "reflective eyepieces." They are collimating systems with an external pupil. Typically, the light from an IR simulated target is collimated by the reflecting system and is projected into the external pupil. This can then be matched to the pupil, usually internal, of the optical system being tested—usually an IR seeker head on a missile. What is wanted is a reflecting system (for broad spectral coverage) that is unobscured, has a large field of view, a flat image, low distortion, and good image quality. This paper describes a new design that covers a 15° diameter circular unobscured field at f/4.5 It consists of five spherical mirrors and has a spot size of 0.1 mrad over the whole field.
Physical optics analysis of the performance of a laser beam shaper
Authors: Jiang W. , Shealy D. L.
Published: February 2023

Based on geometrical optics, a two lens system has been designed to transform a Gaussian beam into a plane wave with uniform irradiance. Differential equations are solved for the shape of two aspherical lens surfaces in the two plano-aspherical lens system. First, the aspherical lens surfaces have been fit to the conic plus aspherical deformation terms by a conventional formula to define the optical surfaces. Physical optics techniques have then been used to analyze the performance of this laser beam profile reshaper. Prospects and projected performance of a prototype laser beam reshaper lens system of this type will also be presented.
Two-channel light-matter interactions in cavity QED
Authors: Puri R. R. , Wang Liwei , Eberly J. H.
Published: February 2023

We will describe several two-channel models of quantized light-matter interactions. In the context of few-mode cavity QED these models provide analogs of familiar optical processes, such as wave mixing, optical pumping, quantum beats, downconversion, and two-photon lasing, none of which have satisfactory analogs in the (one-channel) Jaynes-Cummings model and its extensions. We will mention methods for the exact solution of these models and a few elementary predictions of nonclassical character.
Quantitative IR spectroscopy of atmospheric and combustion radicals with comparison to theory
Authors: Nelson D. D. , Zahniser M. S. , Wormhoudt J.
Published: February 2023

Infrared laser absorption techniques have been employed to measure absolute transition moments for several radical species by using a variety of techniques. For the OH radical, high precision relative transition strengths have been measured with a color center laser and used to determine the OH dipole moment function. The dipole moment function provides absolute transition strengths for Δv = 1–3 transitions with v″ < 9. This information is essential for quantitative modelling of the OH Meinel night glow. The infrared band strengths for all three fundamental vibrations of the HO2 radical have been directly measured by using tunable infrared diode laser absorption. The HO2 radicals were prepared with a known column density by reacting a known quantity of F atoms with excess H2O2. These band strengths will be used to measure HO2 radical concentrations in the troposphere. Band strengths for the BF, CF2, and CH3 radicals have also been obtained using tunable diode laser absorption. These species' concentrations were quantified by by using various optical and chemical techniques. The experimental infrared transition strengths discussed above will be compared with published theoretical transition strengths obtained by using several techniques.
Resonatorless absorptive switching and self-pulsing in bulk ZnSe
Authors: St. John W.D. , Wicksted J.P.
Published: February 2023

Resonatorless absorptive switching and self-pulsing have been observed in bulk ZnSe when excited by square input pulses at 476.5 nm on a time scale from ~1 μs to >1 s. Beyond a critical intensity of ~7 kW/cm2 the material begins to switch repeatedly between a transmission of ≥60% and ≤5%. This switching and self-pulsing behavior is a local phenomenon (resonatorless). This bistable behavior is based upon band gap renormalization, band filling, and plasma screening. Through absorption there is an increase in the temperature. This results in a shifting of the band edge to longer wavelengths. This further increases the absorption. At some point the incident photons become completely absorbed and a switching to an “off” state results. At this point a relatively large number of electron-hole pairs are created. Depending on the thermal and electron-hole pair concentration dynamics, a filling of the available states eventually results and the absorption decreases. Thermal diffusion then allows for local cooling, the band gap shifts to shorter wavelengths, and a switching to the “on” state results. This modulation of the absorption continues, and one sees a sequence of pulses (self-pulsing) in the transmission.
Transit broadening and optical multi-stability
Authors: Rosenberger A.T.
Published: February 2023

If the intracavity medium of a nonlinear optical resonator consists of a beam of atoms that cross the waist of the resonator’s fundamental mode in a time less than or comparable to a spontaneous lifetime, transit broadening will contribute to the absorption linewidth. Under the same conditions, the resonator may exhibit multistability. In the simplest case, this can be understood as resulting from a variation in absorption with intracavity intensity; the absorption is minimized when a transiting atom is carried through an integral number of Rabi cycles and is maximized if the number of cycles is half-integral. This simplest model, however, assumes that (1) the transit time is much less than the lifetime; (2) the transverse mode has a Gaussian variation only in the direction of atomic motion; and (3) the atomic beam is monoenergetic. The multistability can persist even when these three simplifying assumptions are relaxed; the effects, on the input-output characteristics, of relaxing these assumptions will be reported. Possible experiments and applications will be discussed.
Hysteresis effects attributed to free-space diffraction in a passive optical system
Authors: Jones D.J. , Bandy D.K.
Published: February 2023

We investigate the time-dependent behavior of an optically thin passive medium driven by an external coherent signal and show dynamical hysteresis effects in the regimes of large and small Fresnel numbers, positive and negative detuning, and changes in the cavity quality. We attribute shifting and deformation of the bistable loop and spatial hysteresis to free-space diffraction effects that are independent of diffusive and diffractive coupling within the medium. Since radial variation of the bistable loop is not present in the parameter space explored, we suggest that free-space diffraction does not contribute to this effect and adds weight to experimental findings that evidence diffusive coupling as the dominant mechanism for radial variations of the bistable loop.
Critical-phenomenon-based optical bistability in vanadium dioxide
Authors: Rana R.S. , Nolte D.D. , Chudnovskii F.A.
Published: February 2023

Vanadium dioxide undergoes large changes in its optical properties at the metal-semiconductor thermodynamic phase transition at 68°C. The most pronounced changes occur in the infrared. By combining low power nonlinearity from the metal-semiconductor phase transition with a thin film interference filter, we demonstrate optical bistability at 1.06 μm. Highly stable bistable operation has been obtained. By biasing at the critical point, an all-optical external switching between the semiconducting and metallic states has been demonstrated. A contrast ratio of 15:1 has been achieved. The other characteristic parameters are as follows: switching energy density = 380 pJ/μm2, switching intensity ≈0.9 W/cm2, switching time ≈10 ms, and the nonlinear index of refraction ≈0.5 cm2/W. It should be stressed, however, that these numbers are only representative and not the optimum values for these parameters. An attractive feature of the vanadium dioxide is the tunability of the transition temperature and the width of the bistable region through doping and other techniques. This tunability provides control to tune the characteristic parameters, such as switching powers and switching speeds, over a wide range.
Dispersion characterization of optical materials with white light interferometry
Authors: Diddams Scott A. , Diels Jean-Claude
Published: February 2023

A simple Michelson interferometer with an inexpensive white light source (halogen lamp) can be used to completely determine the dispersion characteristics of optical materials (glass or mirror) when the material is placed in the stationary arm of the interferometer and the other arm is lengthened by means of a motor-driven screw. The Fourier transform of the digitally sampled interference pattern gives the necessary phase information, which can be used to determine the group velocity, group velocity dispersion, and even higher order terms. Simultaneous recording of a He–Ne laser passing through the same interferometer is needed to monitor the optical path.
Polychromatic target detection using a color LCTV joint-transform correlator
Authors: Yu Francis T. S. , Yang Zhaohui , Pan Kun
Published: February 2023

A polychromatic pattern recognition using a color LCTV based joint-transform correlator (JTC) is presented. This technique uses a color liquid crystal panel with a polychromatic coherent source, by which a set of color joint-transform spectra can be captured by a polychromatic CCD camera. By simply duplicating the set of color joint-transform spectra patterns on the color liquid crystal panel, a set of color correlation peaks can be attained by polychromatic illumination. One of the major features of the polychromatic detection is the exploration of the spectra content. Since a programmable color LCTV is used in the proposed system, it is easy to make the system adaptive. Moreover, the proposed polychromatic JTC offers the advantage of simplicity of operation, in which the strengthen alignment problems can be avoided. Experimental demonstrations of the proposed adaptive polychromatic JTC are provided. We have shown that the spatial content of target can indeed be detected.
Spatial frequency analysis of holographic multiplexing
Authors: Black T. D. , Larson D. A.
Published: February 2023

Spatial phase modulation using gratings, arrays, and patterns inserted into the reference beam during holographic recording can be used to multiplex numerous data fields in the same volume of a photorefractive material. We present a basically simple but general formalism for analyzing these schemes, where encoding is achieved by spatial frequency multiplexing. Spatial frequency analysis is used to evaluate and compare various approaches and configurations. The encoding elements are analyzed in the Raman-Nath diffraction regime to determine the amplitude and relative phase of their spatial frequency components. The harmonically related terms are represented as Dirac delta functions in reciprocal space (a spatial frequency representation). The propagation phase differences are determined by using a space transmission operator (a Fresnel propagator) that is a function of spatial frequency and displacement. Dirac "kets" are used as bookkeeping aids to represent the beams. Encoding elements and holograms are represented as operators. Results of the recording and reading of holograms with various encoding devices are discussed by using this formalism.
Passive pulse train generation from a frequency modulated diode laser
Authors: Menders James H. , Choi Kyunam , Korevaar Eric
Published: February 2023

By sweeping the frequency of a diode laser beam near the cesium resonance frequency, followed by propagation through a short length of cesium vapor, we obtained periodic peaks with peak-to-average ratios near 5 at pulse repetition rates up to a gigahertz. Light in the wings of a strong atomic absorption line of an alkali metal vapor encounters large group velocity dispersion. A frequency modulation in an off-resonance cw beam passing through the vapor consequently develops an amplitude modulation. For certain combinations of laser and vapor parameters, a sinusoidally frequency modulated beam can be made to develop peaks. We generated pulse trains in a frequency modulated single mode diode laser tuned to the cesium absorption line near 852 nm, which we observed by using a fast p-i-n photodiode and a sampling oscilloscope. The frequency of a diode laser was sinusoidally modulated with a sweep of about a gigahertz and a period of a few nansoseconds by introducing a small modulation into the laser pump current. We observed the formation of sharp peaks with a width of about one-tenth of the modulation period and a peak-to-background ratio of approximately 5.
A gradient-index lens system for laser beam reshaping.
Authors: Wang C. , Shealy D. L.
Published: February 2023

Gradient-index (GRIN) lenses with spherical surfaces are able to yield the equivalent aspherical effects. A refractive system that consists of one plano-concave lens and one convex-piano lens using axial gradient-index materials has been designed to transform a Gaussian beam profile into a uniform intensity distribution. The GRIN distribution in the axial direction and the vertex curvatures of two spherical surfaces are determined by using the energy conservation condition and the condition of constant optical path length, which permits an exiting plane wave. The design and analysis of this gradient-index laser beam reshaping system will be presented and compared with a similar system1 utilizing two aspherical lenses with normal index materials.
Scanning with axicon-generated beams
Authors: Marom E. , Katz J.
Published: February 2023

Axicons provide a simple way of generating diffraction-free beams. It has been pointed out that the finite size of axicons and their conical angle determine uniquely that diffraction-free region. We will show that for scanning purposes the line spread function (LSF) is of prime importance and that the long range and narrow LSF requirements are contradictory. Performance optimization of axicon-generated beams with and without circular symmetry is investigated theoretically as well as experimentally.