bluuebunny/crossref_metadata_2025 huggingface dataset:
Switching-peak GaAs/AlGaAs multistack quantum well infrared detector
Authors: Grave I. , Shakouri A. , Kuze N. , Yariv A.
Published: February 2023

A novel type of intersubband GaAs/AlGaAs infrared detector for the range 6–12 μm is described. It consists of three different stacks of quantum wells, each stack designed for response at a different peak wavelength. The detector can operate in a number of modes: a) standard bound- to-continuum detector; b) wide-band intersubband detector; c) switching-peak tunable detector. All operations are controlled by the applied voltage. The device displays excellent responsivity and detectivity figures of merit. The peak-switching and tunability properties are due to the formation and readjustment of high and low electric field domains within the superlattice. Carriers in the high-field regions contribute to the photoresponse; carriers excited by the incident infrared light in the low-field domains have a large probability of being recaptured by their original quantum well, thus contributing negligibly to the photocurrent. It is shown that infrared photocurrent spectroscopy is an excellent tool to study the structure of electric field domain in doped or otherwise carrier-rich superlattices.
Lifetime characterization of n-type HgCdTe under high excess carrier density conditions
Authors: Tyan J. , Schimert T. R. , Case F.C. , Mitra P. , Claiborne L.T.
Published: February 2023

The excess carrier lifetime characterization of n-type HgCdTe under high excess carrier density conditions for both transient and steady state cases is discussed. Under low excess carrier density excitation, the excess carrier transport equations are linear and in the transient case the decay of the excess carriers is essentially exponential. At high excess carrier density excitation a departure from exponential decay is observed. An initial fast or slow decay is observed depending on initial conditions. Transient excess carrier lifetime results as measured by photoconductive decay are presented. The excess carrier density is generated by using a short (10 ns) 1.06 μm YAG laser pulse. Measurements are made over the 80–300 K temperature range. The results are compared with predictions from a three-level Shockley–Read model. In the model the three trap levels include a deep (approximately midgap) level and a compensating divalent Hg-vacancy acceptor. The donor level is assumed fully ionized. Steady state lifetime results within the framework of the model are also discussed. A drop in the steady state lifetime at high excess carrier density levels is predicted.
High-resolution spectroscopy of Th and Pa isotopes
Authors: Fearey B. L. , Tissue B. M.
Published: February 2023

Doppler-free spectroscopy has been performed on thorium and protactinium isotopes to gain a detailed understanding of the underlying physics of spectral features. Characterizing phenomena such as Lamb dips and optical pumping are important in understanding and optimizing resonance ionization mass spectrometry (RIMS) analysis. Measurement of these isotopes by RIMS is used in U-series disequilibrium dating of geological samples of the last 400,000 years. Isotope shifts and hyperfine structure of 232Th, 230Th, 229Th, 233Pa, and 231Pa are reported for several transitions. The Doppler-free spectra of Th showed an interesting effect, which was strongly dependent on laser power, in which a narrow peak replaced the usual Lamb dip. These results and a detailed analysis will be presented and discussed.
Frequency dependence of the photorefractive response with applied ac electric fields
Authors: Vachss Frederick
Published: February 2023

The process of unstationary enhancement of the photorefractive effect through the application of square-wave ac electric fields is described. By examining the charge transport equations governing the photorefractive response, we show that this response is strongly dependent upon the frequency of the applied ac field and exhibits a maximum when the period of oscillation is between the photorefractive response time, τ
p
, and the charge recombination time in the medium, t
R
. From this analysis we obtain a simple expression for the conditions for maximum response and show that the optimal oscillation period behaves as T = Const. × (τ
p
2 t
R
)1/3. These results are compared to those of earlier analyses of ac field enhancement and with experimental results in BSO.
Temperature-dependent photo induced absorption in photorefractive barium titanate
Authors: Brost George A. , Melkun Philip
Published: February 2023

The photorefractive properties of BaTiO3 are influenced by the presence of secondary centers. These are traps that are highly thermally ionized in the dark but can become populated when the crystal is illuminated with laser light. The photo-induced absorption is a signature of these traps. Two species of secondary centers are suggested by spectral and temporal characteristics of the induced absorption. The BaTiO3 sample was heated in a silicon oil bath to temperatures of up to 100°C. The dark decay rates of the photo-induced absorption had temperature dependencies of the Arrhenius form, with activation energies of 0.5 and 0.8 eV.
Photorefractive dynamics of doped bismuth silicon oxide crystals
Authors: Woods C. , Brown R. , Harris M. , Larkin J. , Armington A. , Fu T. , Khoury J.
Published: February 2023

Samples from both hydrothermal and melt growth techniques were characterized for absorption, index of refraction, and photorefractive dynamics. Doped hydrothermal samples possessed similar photorefractive properties to nominally undoped melt growth samples. BSO operates over a wide range of wavelengths, and it would be desirable to maintain the sensitivity of BSO while controlling the absorption coefficient at wavelengths into the infrared laser-diode operating region. The doped hydrothermal crystal is very transparent, having a light green color. In addition, a variety of response times may be useful in implementing optical analog devices in analogue to electronic devices. For example, heavy doping with chrome produces a dark, almost black, sample with an extremely long response time.
Measurement of diffusion time during diffraction grating formation in LiNbO3
Authors: McMillen Deanna , Lanteigne David J.
Published: February 2023

The storage of volume holograms in photorefractive crystals, such as lithium niobate, is of interest for mass storage of data and images. Grating formation in lithium niobate is usually modeled as a process of light induced diffusion of charge carriers setting up electric fields that cause variations in the index of refraction. In this work, the diffraction efficiencies of gratings were measured during and after exposure in order to determine the characteristic time scale of the diffusion. Diffusion times can be used to predict optimum grating spacings for the holograms. Applications of this work to the problems of reciprocity failure and optimizing diffraction efficiency will be discussed.
Excess spontaneous emission factor in unstable-resonator lasers
Authors: Chen Y. C. , Yao G. , Harding C. M. , Sherrick S. M. , Dalby R. J. , Waters R. G. , Largent C.
Published: February 2023

The unstable resonator belongs to the class of laser cavities that may possess excess spontaneous emission factor due to the nonorthogonal transverse modes. In this paper, we present results of an experimental study of the spontaneous emission factor in unstable-resonator semiconductor lasers. The spontaneous emission factor in an unstable-resonator laser having a convex mirror with 2-mm radius of curvature is measured to be 2 × 10−3, compared to 10−5 typical of a Fabry-Perot semiconductor laser of the same dimensions. The excess spontaneous emission factor results in multi-longitudinal-mode operation and damped relaxation oscillation. A linkage between the spontaneous emission factor, the cavity structure, and the longitudinal-mode spectra has been observed. In addition, we have observed a drastic reduction in the spontaneous emission factor, by as much as 2 orders of magnitude, due to the development of thermal wave-guiding.
Many-body effects in a semiconductor laser model
Authors: Ru P. , Moloney J. V. , Indik R. , Koch S. W.
Published: February 2023

Semiconductor lasers have been treated theoretically in the past by adopting a phenomenological approach that assumes that gain and refractive index changes vary linearly with the injected carrier density N and by introducing three ad hoc parameters to describe the material gain and refractive index changes. However, earlier bifurcation studies of the coupled mode model for multi-stripe index guided laser arrays show that the instability thresholds and consequent dynamic behavior will be a sensitive function of these three parameters. This important issue can be best resolved by appealing to a fundamental many-body theory of the interaction of light with semiconductor media. An obvious advantage of such a theory is that one can dispense entirely with ad hoc parametrization and compute the material parameters directly from first principles. We will report on a study that compares a phenomenological model extended to include transverse and longitudal effects, with parameters obtained from fitting gain and refractive index functions obtained from microscopic many-body theory and a full scale space-time evolution using a look-up table of these functions. The phenomenological approach is found to fail for weakly index guided or pure gain guided coupled laser structures.
Interferometric results from the Boeing grazing incidence ring resonator FEL
Authors: Byrd D. A. , Bender S. C. , Miller E. L. , Dowell D. H.
Published: February 2023

The Boeing HAP (High Average Power) experiment had been reconfigured throughout 1989–1990 to incorporate a grazing incidence, 133-m round-trip ring resonator. Initial spectral, mode stability, coherence length, and interferometric wave-front quality measurements have been taken. This paper reports on the optical measurement techniques and data used to characterize the resonator optical output as 2.0 to 2.5 λ OPD. Raw data-reduction methodology and analysis supporting the subtraction of effects caused by the 7× beam reducer, fold mirrors, and the radial shear interferometer itself are included. Noteworthy observations, such as the ability to overlay interferometric fringe data over the length of a macropulse (≈180 micropulses) without destroying the fringe visibility and the occurrence of centrally localized (≈30% of the diameter) disturbances of the fringe pattern are also discussed. Coherence length measurements, made by using the interferometer, showed the spectral bandwidth to be between 64 and 120 μm. Attempts to measure the micropulse-to-micropulse mode stability were made and are discussed as well.
Designing imaging systems that use coherent fiber bundles
Authors: Malone R. M. , Frogget B. C.
Published: February 2023

The use of coherent fiberoptic bundles facilitates the combining of imaging systems where complicated packaging limitations occur. Separate imaging systems can be designed independently of each other and then mated together by using coherent bundles. Several examples will be discussed. Two oscilloscopes can be lens coupled onto a two-legged coherent bundle that is mated to a TV camera for recording digitized images. Four images can be lens coupled onto a four-legged coherent bundle. The image output of this quadruplex bundle is then optically relayed onto TV cameras for recording. Microchannel plate image intensifiers can be butt coupled onto the coherent bundles if a wavelength shift is needed, if images need to be gated on at different times, or if optical gain for the recorded image is required. Optical relay designs, coherent bundle specifications, imaging resolution, distortion, and spectral responses will be discussed.
A distributed optical associative memory model
Authors: Bostel Ashley J.
Published: February 2023

If hardware implementations of neural networks are to be successful new models are required that are simpler to implement. As a first step in this direction a new associative memory model is proposed that is specifically designed for optical implementations. This memory is a modification of Kanerva’s sparse distributed memory,1 which eliminates the negative connection elements by employing sparsely coded representations on all layers. The advantages of sparse coding include improved storage capacity, small weight range, and a simplified learning rule. The implementation of the memory is illustrated by suggesting several optical architectures. The advantages and disadvantages of the model in each case are discussed.
Phase modulation for real-time kinoform generation using a liquid crystal television
Authors: Tanone Aris , Zhang Zheng , Uang Chii-Maw , Gregory Don A. , Yu Francis T.S.
Published: February 2023

Kinoform is a computer generated phase hologram that acts as a kind of Fresnel lens that changes the phase of the illuminating wave by its thickness variation. For this reason, kinoform has the advantages of high light efficiency and effective utilization of the image space but the disadvantage of tedious photographic processing during its construction. When the kinoform is displayed on a liquid crystal television (LCTV) that operates in a phase modulation mode, the thickness variations of the conventional kinoform can be replaced by the birefringent effect of the liquid crystal molecules. The technique requires a modulation depth of about 2π, which several commercially available LCTVs are unable to attain. In this paper, we will discuss an experimental technique for generating an LCTV kinoform where the modulation depth is limited by π. The major drawback of the π phase variation is that it reduces the diffraction efficiency as well as the space–bandwidth product to some degree, compared to a 2π modulation. The verification of this drawback will also be reported.
A novel temporal integration of intensity
Authors: Eckstein Miguel , Whiting James S. , Thomas James P. , Shimozaki Steven
Published: February 2023

Observers’ ability to combine intensity information over time was measured by testing accuracy in time-average intensity judgments of periodic time-varying intensity stimuli (frame sequences). The subjects’ task was to choose the highest time-average intensity stimulus (target) in a six-alternative forced-choice experiment. The intensities for each frame for each of the non-targets were assigned by randomly sampling values from a Gaussian sampling distribution (non-target sampling distribution). The same procedure was used to generate the target intensity values but by using a Gaussian sampling distribution with a higher mean than the non-target sampling distribution. Performance was measured for sequences of 4, 16, 32, and 50 frames, all displayed at 35 frames per second. For an ideal observer who perfectly integrates the intensity information, d' increases as the square root of the number of frames in the frame sequence. Our results show that the human visual system is able to integrate intensity information for a critical period, tc, of 700–900 ms. Such findings cannot be accounted for by the well studied Bloch’s Law, which has a critical period about 200–300 ms. This study suggests the existence of another temporal intensity integration mechanism distinct from the mechanism described by Bloch’s Law.
Time decay of exciton saturation in a strained InGaAs/InP MQW structure
Authors: Bradley P. J. , Calvani R. , Caponi R. , Morello G.
Published: February 2023

The effect of charge recombination, after exciton saturation, in a strained InGaAs/InP MQW sample has been analyzed. The pump-and-probe measurement is obtained through a Mach–Zehnder configuration supplied by an FCL laser mode-locked at 76 MHz and producing 8 ps (FWHM) pulses. A calibration delay is inserted in the pump branch, while a high resolution double delay line is located in the probe arm. Through the recombination beam-splitter pump and probe beams are translated and focused onto the sample, where they intersect. The two beams are linearly and orthogonally polarized to avoid the interference due to the diffraction grating formed in the sample when the pump and probe paths are balanced. Particular care has been devoted to obtaining a stable probe spot with respect to the pump on the MQW during the scanning of the double delay line. From the transmittivity curves vs. pump–probe delay, the time constant of the exciton saturation decay has been evaluated. Work is in progress to lower the time constant of the charge recombination effect exploiting two transverse electric fields applied to the structure, which should become suitable for realizing optical switching devices.
A two-layer high-content addressable optical neural network
Authors: Uang Chii-Maw , Yin Shizhuo , Yu Francis T.S.
Published: February 2023

A two-layer high-content addressable memory, based on the K-nearest neighbor and the winner take all networks, as applied to autoassociation and the heteroassociation models, is given. The architecture is an efficient neural network in which pattern classification can be obtained very easily. In this two-layer model, the total number of interconnections is Ni* M + No* M, where Ni and No are the input neurons and the output neurons respectively, and M is the number of exemplars, which is less than the conventional CAMs. Since the storage capacity can be as high as 2
Ni
, the neural network needs only one feedforward training time, such that no feedback iteration is required. Fast convergence is therefore an apparent feature, and the noise performance is better than that of the Hopfield model and the inter-pattern association (IPA) model. Since this network would converge to the nearest exemplar, it would not produce spurious outputs. Computer simulation and experimental results confirm our findings and are provided.
Optical neural network for real time face recognition
Authors: Psaltis Demetri , Li Hsin-Yu , Qiao Yong , Grot Annette
Published: February 2023

We describe a two layer optical network that is trained to recognize in real time ″Denk,″ who is a student in our group. The network is implemented with liquid crystal spatial light modulators for the neural planes and lithium niobate photorefractive crystals for the interconnections. The network has approximately 60,000 units at the input plane, 30 hidden units, and a single output unit. The network is trained with a video segment 1.5 min long, from which 180 frames were selected for learning. Specifically, each hidden unit was trained to respond to six frames. The trained network classified the rest of the training tape almost flawlessly. The system was then tested by presenting through a TV camera real time inputs of Denk and other members of our group. The system almost never mis-classifies other people as Denk and exhibits remarkable tolerance to changes in aspect, illumination, and facial expression.
Digital molecular detection in levitated microdroplets
Authors: Barnes M. B. , Ng K. , Whitten W. B. , Arnold S. , Ramsey J. M.
Published: February 2023

The detection of single fluorescent molecules in liquid phase has proven challenging because of the limited available luminescence and high background levels. The number of fluorescent photons emitted by a single molecule is limited by photolysis (≈106 for the best fluorophores) while the background signal in condensed phase is fundamentally bound by inelastic scattering from the solvent. These two constraints require the experiments to be performed in small probe volumes (≈1 pL). In our experiments the probe volume is conveniently defined by the spatial extent of a microdroplet (≈10-μm diameter). Microdroplets provide a number of advantages as a medium for single molecule detection, including their optical properties. Experimental evidence of single molecule detection and quantum electrodynamic effects in microdroplets will be presented.
Purely diffractive system that brings N wavelengths to a common real focus
Authors: Shafer David
Published: February 2023

It has been proven several times recently that a purely diffractive optical system, no matter how complex, cannot form an achromatic real image. An achromatic virtual image is possible, but not a real one. Nonetheless, there are two ways to cheat. Farn and Goodman have described in JOSA how enormous amounts of spherochromatism between two separated surfaces can be used to form a real, achromatic, perfect axial point image for nonparaxial rays. This scheme cannot work at the paraxial level. Here I will describe a different approach, which does work at the paraxial level but which is not achromatic in the conventional sense. Although it can bring an arbitrary number of wavelengths to a common real focus, by using purely diffractive elements, the focus position is never stationary with wavelength.
Multiphoton interferometry
Authors: Greenberger Daniel M.
Published: February 2023

Recent theoretical work has shown that there is an intrinsic difference in the nature of the information one can obtain from one-photon, two-photon, and multi-photon interference experiments. Using parametric down conversion, many laboratories have recently performed two-photon interference experiments. We shall discuss these and some proposals for three-photon interferometers and shall point out the kind of non-classical information one could hope to attain from such devices.
GHZ correlations of three-particle entangled states in cavity QED
Authors: Wang Liwei , Wodkiewicz K. , Eberly J. H.
Published: February 2023

We demonstrate how a new exactly soluble cavity QED model can be used to test local realism associated with three-particle entangled states, as proposed by Mermin. These states embody the correlations described by Greenberger, Horne, and Zeilinger (GHZ) and provide a stronger refutation of local hidden variable theories than is possible with Bell inequalities. It is shown that two photons distributed in the model’s four cavity modes coupled with a two-level atom can effectively produce three independent spin-1/2 particle states. We discuss preparation of the desired perfectly correlated GHZ state and a method to perform measurement on various field modes and atomic level correlations equivalent to a spin component along any direction.
Use of Bell inequalities in quantum optics and the EPR paradox
Authors: Ben-Aryeh Y.
Published: February 2023

We show that the violation of Bell inequalities in the analysis of atomic cascades may follow from additional correlations produced by the measurement process for subensembles so that it does not contradict the existence of hidden variables. The polarization measurements in atomic cascades are described by following the quantum mechanical analysis. However, the common use of the locality conditions in the proofs of Bell inequalities is criticized, and alternative formulas are suggested.
Application of Hadamard transform to fiber array sensing
Authors: Lu Cheng , Yin Shizhuo , Yu Francis T. S.
Published: February 2023

Multi-monitoring in composite structures, such as aircraft, ships, and submarines, requires array of sensing channels and detectors. It is obvious that major undertakings in procedure and system design are needed. Since multi-fiber is capable of implementing multi-channel sensings, we will propose a technique of using Hadamard transform (HT) applied to monitoring the multi-fiber sensors (MFS). The basic advantage of using the HT technique is that only a single detector is needed. We have also shown that the output signal-to-noise ratio of the proposed technique can be increased by a factor of

N

/
2

, where N is the number of sensing fibers.
Generalized Pade approximants
Authors: Yevick D. , Glasner M. , Hermansson B.
Published: February 2023

We have previously constructed a series of high-order Fresnel propagation methods based on the split-step fast Fourier transform procedure by expressing an exponential of two non-commuting operators as an alternating product of exponentials of the individual operators. Here we demonstrate that these decompositions are equally valid for the split-operator finite difference and finite element methods if the exponential operators are replaced by (1,1) Pade approximants. Such "generalized Pade approximants" can be easily generated through simple recursion formulas and implemented in a straightforward fashion. We illustrate our technique with a sixth-order calculation of light propagation through an integrated optic microlens.
Noise in optical sources and amplifiers
Authors: Teich Malvin C.
Published: February 2023

A review is presented of noise and noise reduction in light sources and optical amplifiers of current interest, including lasers, LEDs, luminescence sources, and Er3+ fiber amplifiers.
Physics of quantum-well lasers
Authors: Coleman James
Published: February 2023

Summary not available at press time.
Monolithic 2-D vertical cavity surface emitting laser OEIC
Authors: Yang Ying Jay , Dziura Thaddeus Gerard , Bardin T. , Wang S. C. , Fernandez R.
Published: February 2023

We report for the first time a monolithic integration of a GaAs vertical cavity surface emitting laser (SEL) and a MESFET.
Stable 100 fsec pulse generation from a passively mode-locked Er-fiber laser
Authors: Fermann Martin Emanuel , Andrejco Matthew J. , Stock Michelle L. , Silberberg Yaron , Weiner Andrew M.
Published: February 2023

100 fsec pulses are directly obtained from a passively modelocked Er fiber laser. The pulses are near bandwidth-limited and come in stable pulse trains.
11 femtosecond pulses from a modelocked Ti:sapphire laser
Authors: Asaki Melanie , Huang Chung-Po , Garvey Dennis M. , Zhou Jianping , Nathel Howard , Kapteyn Henry C. , Murnane Margaret Mary
Published: February 2023

Cubic dispersion in a self-modelocked Ti:sapphire laser has been reduced, allowing us to generate sub-11 femtosecond pulses, with average power of 0.6W.
Saturable absorber modelocked polarization maintaining Erbium-doped fiber laser
Authors: DeSouza E. A. , Islam Mohammed N. , Soccolich Carl E. , Pleibel W. , Stolen Roger H. , DiGiovanni D. J. , Simpson J. R.
Published: February 2023

We passively modelock an erbium-doped fiber laser (EDFL) that generates 40pJ pulses 320fs wide and that operates in a single state of polarization (polarization extinction ratio better than 18dB). The self-starting of the laser is controlled by a semiconductor saturable absorber, and the fiber acts as the gain medium with some soliton pulse shaping. We squash the fiber preform to make the fiber polarization maintaining, and we design the core size and core-cladding index difference so the fiber is single mode and near the zero dispersion wavelength in the erbium-gain band.
Sequential vs. simultaneous ionization of two-electron atoms by intense laser radiation
Authors: Blodgett-Ford Sayoko , Parker Jonathan , Clark Charles W.
Published: February 2023

Numerical integration of the Schrodinger equation for helium in a model radiation field reveals pronounced electron correlation effcts, and a threshold intensity for simultaneous ionization.
Evidence for continuous visible chemical lasing from the fast near resonant energy transfer pumping of atomic sodium
Authors: Shen Kangkang , Wang He , Gole James L.
Published: February 2023

Highly efficient energy transfer from selectively formed metastable states of S10 is used to pump sodium atom laser amplifiers at = 569, 616, and 819 nm and produce laser oscillation at 569nm.
Neodymium-doped glass channel waveguide laser containing an integrated distributed Bragg reflector
Authors: Winick Kim A. , Roman Jose E.
Published: February 2023

A rare earth-doped planner glass channel waveguide laser containing an integrated distributed Bragg reflector is reported for the first time. Single longitudinal mode operation is also demonstrated.
Coherent optical processor for inverse filtering
Authors: Riasati Vahid R. , Abushagur Mustafa A. G.
Published: February 2023

A new algorithm and system architecture for inverse filtering using a coherent iterative optical processor is presented. The algorithm theory and convergence is presented along with a computer simulation of the algorithm performance. Two optical architectures for the implementation of this algorithm are also presented. The optical implementation of this algorithm provides a method for the implementation of optical division of constants, functions of one dimension, and functions of two dimensions. Application of this processor to image restoration will be demonstrated.
Optical morphological processor with a dynamically reconfigurable structuring element
Authors: Chao Tien-Hsin
Published: February 2023

An innovative optical morphological processor with dynamic reconfigurability is introduced. This processor is able to perform basic morphological operations such as the erosion or dilation in a single pass. With the use of a binary-optic diffraction grating, the structuring element (or kernel) required for these two operations can be obtained with a reconfigurable size, depending on the processing needs. A custom built 2-D output photodetector array is utilized to perform thresholding detection and to provide a feedback path to the input spatial light modulator. Image clean-up operations, including noise and clutter removal, can be obtained through iterative combination of multiple dilation and erosion operations with high speed and full programmability. Detailed system analyses as well as experimental demonstrations of various pattern recognition applications will be presented.
High intensity laser propagation in water as a model for tissue interaction
Authors: Rogers M. E. , Roach W. P. , Mayo M. W. , Stolarski D. , Noojin G.
Published: February 2023

To understand the propagation of sub-nanosecond laser pulses operating in the visible and near infrared in tissues such as ocular components, water is used as a baseline model both theoretically and experimentally to determine the onset of optical nonlinearities such as nonlinear absorption. Preliminary data obtained from parallel experiments by using the z-scan technique in the picosecond time domain at 532 nm indicates that the nonlinear refractive indices for water and ocular media are quite close in magnitude and have the same sign. Thus, water is an excellent model for investigating subnanosecond propagation phenomena as it relates to nonlinear absorption in ocular media. We use a simplistic model reminiscent of Beer's law to describe how nonlinear absorption is mediated by the propagating field intensity. Coupled to the model, we measure linear absorption data as a function of intensity in ultrahigh purity water by using a Michelson type apparatus1 and continuous wave sources in the visible spectral region. Absorption data is tabulated, and its effect on sub-nanosecond laser pulse propagation in ocular media is discussed.
Design of optoelectonic angular position sensor
Authors: Chakraborty B.
Published: February 2023

A device for angular position sensing is fabricated with the help of a source/detector assembly and by utilizing the total internal reflection at the glass-air interface of the rotating prism. A collimated beam from a high intensity LED source is incident on the 45 prism assembly, which is rotated about the axis of the incident beam. The emergent beam is focused on to the P-I-N photodiode detector assemblies placed at different spatial angular points along the circumference of the rotating emergent beam. The prototype model of the sensor is tested in the laboratory, and the variations in pulse amplitude with the variations of photodiode-focusing optics distance are observed in the oscilloscope. The resolution of the system can be greatly enhanced for precision measurements by incorporating the focusing optics within the rotating prism assembly and by using optical fibers as light collectors. The system can also be used as precision rotating speed sensor and optical time space demultiplexer.
Picosecond time-resolved photoluminescence spectroscopy of III–V and II–VI semiconductor structures
Authors: Massa J. S. , Buller G. S. , Walker A. C.
Published: February 2023

An all-solid-state, microscope-based time-resolved photoluminescence (TRPL) system has been developed for studying excess carrier dynamics, from the picosecond to the microsecond time domains, in III-V and n-VI semiconductor structures. The system employs laser diode excitation sources and a silicon single photon avalanche diode detector, and it allows TRPL measurements in the spectral region from 430 nm to ~1 μm. By using a 780 nm excitation source, the high spatial resolution of the system (<3 μm) has facilitated the examination of GaAs/AlGaAs MQW microresonator structures fabricated by alloy mixing techniques. These structures have important applications as surface-emitting lasers and as all-optical non-linear devices based on electronic band-filling nonlinearities. For each of these, a knowledge of carrier lifetime is of fundamental importance. Effective lateral carrier confinement is demonstrated in individual square pixels of various sizes, between 2 and 50 μm, with no significant reduction in carrier lifetime. The increasing importance of "wide-gap" II-VI semiconductors for the fabrication of blue light emitting diodes and laser diodes has led to the requirement for routine TRPL measurements on these materials. The integration of a frequency-doubled laser diode source, emitting at 420 nm, has permitted TRPL measurements to be performed on both n-and p-type ZnSe of various doping densities.
A GRIN endoscope with a line-of-view prism
Authors: Prescott Rochelle
Published: February 2023

GRIN rods are now used in the manufacture of small endoscopes. A common design for the penetrating optics of these instruments is an objective with a cover glass followed by a relay of one of more periods all cemented together into a monolithic optical train. Such an endoscope has its entrance aperture within the objective, which makes it impossible to use with them the most common line-of-sight prisms. It has been discovered that these systems have an entrance tunnel with the shape of a hyperboloid of one sheet. By a variation of the length of the objective it is possible to adjust the position and scale of this tunnel. In particular, it is possible to move the hyperboloid uplight so that its waist coincides with the narrow apertures of the most common line-of-sight prism so that vignetting is eliminated or at least minimized.
Negative ion photoelectron spectroscopy of organosilicon radicals
Authors: Leopold Doreen G. , Bengali Ashfaq A.
Published: February 2023

We report laser photoelectron spectra of the

SiCH

2
−

,

SiCH

3
−

, and

SiCH

4
−

anions and their perdeuterated analogues at an instrumental resolution of 30 cm−1. These anions were prepared from tetramethylsilane by using a flowing afterglow ion source equipped with a microwave discharge cavity. The spectra yield vibrational frequencies for both the anions and the corresponding neutral molecules, and they also yield the electron affinities. These data indicate a doubly bonded silylidene structure for SiCH2 and a singly bonded methylsilylene structure for SiCH4. Both the singly bonded S–CH3 and the doubly bonded HSi=CH2 isomers are observed. These results provide new information concerning multiple bonding between silicon and carbon. In addition, they illustrate the ability of this technique to provide direct spectroscopic identification of isomers present in the flowing afterglow ion-molecule reactor.
Low frequency intensity noise characterization of an all fiber single frequency erbium ring laser
Authors: Dawson Jay W. , Sanders Steve , Park Namkyoo , Vahala Kerry J.
Published: February 2023

Erbium doped fiber ring lasers are drawing increasing interest because of their narrow linewidth, broad tunability, and inherent compatibility with optical fiber. We have recently developed such a laser that is broadly tunable (>30 nm) and stable from mode hopping for a period of time on the order of minutes in spite of having a cavity length on the order of 30 m. This is achieved through the use of tandem fiber Fabry-Perot filters. One broadband filter (30 GHz bandwidth, 30 nm free spectral range) provides tuning. The other narrowband filter (125 MHz bandwidth, 10 GHz free spectral range) provides sufficient loss difference between cavity modes to achieve a sidemode suppression greater than 50 dB. We report here on the low frequency intensity noise characteristics of this device. The relaxation oscillation frequency has been characterized as a function of laser power. It is found to vary as the square root of laser power, as expected. The relaxation oscillation frequency varies from 10 kHz to 30 kHz when the laser power is varied from 0.088 mW to 0.840 mW. Mode hopping amplitude instabilities were also investigated. When the broadband tuning element was tuned so as to give approximately equal loss to two competing modes one narrowband filter free spectral range apart, a sustained, large amplitude oscillation was observed. The oscillation has a power dependence similar to that of the relaxation oscillation frequency.
What can discrimination tasks tell us about texture perception?
Authors: Olzak Lynn A. , Thomas James P.
Published: February 2023

Several authors have proposed mechanisms in which the output of local Fourier analyzers are combined to mediate texture perception and segregation. We psychophysically investigate properties of these mechanisms in human vision by examining the ability to discriminate between texture-like patterns. We describe the relationship between performance and the contrast of Fourier elements comprising the texture patterns and examine how this relationship changes with a) the superimposition of additional components drawn from very different regions of the Fourier domain, b) the spatial extent of the pattern, and c) the type of information upon which the discrimination is based. Our findings suggest a nonlinear mechanism that combines activity rates over wide regions of both the Fourier and the spatial domains and uses preferred patterns of combination even if they are suboptimal. Regions of combination depend upon the decision task.
Investigating the dynamics of texture segregation processing by using the speed-accuracy tradeoff method
Authors: Sutter Anne , Graham Norma
Published: February 2023

We investigated the time course of texture segregation processes by using the method of cued response to obtain speed-accuracy tradeoff (SAT) functions for various psychophysical tasks and texture patterns. SAT functions were obtained by requiring subjects to respond within 200 or 300 ms after an auditory cue. The cue occurred from 0 to 750 ms after the onset of the pattern (which was 50 ms in duration). Response accuracy and reaction time were recorded. We employed several psychophysical tasks, such as discrimination between uniform texture fields and texture fields in which a rectangular patch of texture was embedded. We found that response accuracy, as a function of response signal delay, depended on the task. We also presented a variety of texture patterns, including some that have been used to investigate simple (first-order) versus complex (second-order) mechanisms. We found that the shape of the SAT function depended on the spatial characteristics of the texture patterns.
Intensive nonlinearities in perceived texture segregation
Authors: Graham Norma , Sutter Anne
Published: February 2023

Much about the perceived segregation of regions containing different textures can be explained by simple channels (linear, first-order, Fourier processes), but nonlinear processes are also needed. In addition to complex channels, an intensive nonlinearity—one dramatically compressing responses at contrasts well below 25%—is necessary to explain results of varying the sign and amount of contrast in multiple-element textures (Graham, Beck, and Sutter, 1992, Vision Research). This intensive nonlinearity might arise either from an early local nonlinearity preceding the channels or from normalization (perhaps due to intracortical inhibition) among the channels themselves. To decide between these two candidate intensive nonlinearities, we tried several approaches, including variation of the patterns' overall spatial characteristics and careful comparison of effects at different contrast levels in the two element types of a single pattern. Although deciding between the candidates has been more difficult than we had hoped, the weight of the evidence suggests that normalization at the level of the channels, rather than a local nonlinearity preceding the channels, causes the compressive effects in perceived texture segregation.
Nondegenerate two-beam coupling in anisotropic, artificial Kerr media
Authors: Kralik John C. , Malcuit Michelle S.
Published: February 2023

Anisotropic, artificial Kerr media develop large nonlinear susceptibilities under the influence of strong optical fields because of the formation of translational and reorientational gratings. When the interaction energy between the particles’ induced dipole moments and the applied field is less than the thermal energy of the host fluid, the medium is adequately described by a third- order susceptibility. However, when the interaction energy surpasses kT, higher-order terms are necessary to correctly describe this situation. We investigate this latter regime in several colloidal dispersions of titanium dioxide, whose diameters range from 100 to 300 μm. The particles possess a large intrinsic birefringence, resulting in a large reorientational nonlinearity. In addition, their average index is greatly mismatched with the host, water, so that the translational nonlinearity is also quite large. The technique we employ to investigate these samples is nondegenerate two-beam coupling with cw Ar+ and Nd:YAG lasers. The most striking feature we see is the direction of energy transfer reverses in the regime where the higher-order effects become important.
Passively mode-locked KCl:Tl laser producing femtosecond pulses near 1.55 μm
Authors: Islam M. N. , Soccolich C. E. , Mollmann K. , Gellermann W.
Published: February 2023

Using bulk InGaAsP saturable absorbers, we passively mode lock a KCl:Tl color center laser in single- and coupled-cavity configurations near 1.55 μm, which is a wavelength range important for transmission and switching in fibers and spectroscopy of erbium-doped materials. We obtain in the single-cavity configuration pulses as short as 315 fs with high amplitude stability and ~65 mW average output power. By adding a partially transmitting mirror midway in the laser, we convert the laser to a coupled-cavity configuration and obtain 1.0–1.4 ps wide pulses at somewhat reduced pulse stabilities. Since the main cavity does not incur the absorber loss, the average output power now increases up to ~350 mW. Also, the coupling between the two cavities controls the effective cross-section of the saturable absorber. We compare directly these two principally different passive mode-locking techniques in terms of differing saturable absorption requirements and influence on the laser properties (self-starting conditions, pulse properties, and output power).
A cw mode-locked chromium-doped forsterite laser generates tunable sub-100-fs pulses
Authors: Seas A. , Petricevic V. , Alfano R. R.
Published: February 2023

We report on the first successful generation, to our knowledge, of femtosecond pulses from an actively mode-locked chromium-doped forsterite laser with intracavity dispersion compensation. Mode-locked operation of the forsterite laser was achieved when an acousto-optic modulator was inserted in a basic Z-fold cavity, without prisms. A stable train of 6-ps FWHM pulses was obtained. The FWHM of the bandwidth was measured to be 1.2 nm. The pulse duration–bandwidth product Δτ
p
Δν = 1.34 indicated that the pulses were strongly chirped. To compensate for the chirp, a pair of high-dispersion Brewster prisms was inserted in the cavity. This resulted in significant reduction in pulse duration, down to 90 fs, with spectral bandwidth of the order of 19 nm, giving transform limited pulses (ΔτΔν = 0.32). Pulses as short as 60 fs FWHM were measured. The pulses were tunable over 1220–1290 nm.
Pedestal amplitude determines sensitivity
Authors: Yang Jian , Makous Walter
Published: February 2023

We used temporal forced choice to estimate threshold contrast for a test grating in the presence of a second, pedestal grating. Both gratings had the same spatial frequency, but they were either in-phase, 180° out of phase, or 90° out of phase. Mean luminance varied over 3 log units. The main finding is that luminance and pedestal contrast trade off in determining sensitivity, so that only their product, pedestal amplitude, uniquely determines sensitivity (unless pedestal contrast is close to threshold, in which case luminance has a greater effect than does pedestal contrast). This means that contrast gain control and luminance gain control have similar properties and might share the same mechanism. We also found that the relative phase of pedestal and test grating has relatively little effect and that temporal modulation of the test grating greatly decreases the effects of steady pedestals.
Optical probability density function estimation for real-time pattern classification
Authors: Goldstein Adam , Jenkins B. Keith
Published: February 2023

We present a design for the optical implementation of a Bayes classifier using the Parzen window probability density estimation technique. The system can also be configured, with simple hardware modifications, as a k-nearest-neighbor classifier. Both versions are asymptotically optimal in the limit of large training set size, in that the probability of classification error asymptotically approaches the Bayes lower limit. This system is fully optical in both the training and computation phases, with no need for off-line electronic calculations. The classifier is trained by holographically storing all available prototype patterns, which are recorded in sequence via an input spatial light modulator. A second holographic step results in a plane of frequency-multiplexed training images on which the unclassified input pattern is imaged. A resulting set of inner products (between the input and each prototype pattern), followed by optical thresholding and integration, yields an array of estimated class-conditional a posteriori probabilities. Classification is achieved with a maximum detection stage. Theoretical and practical limitations of the system will be assessed in order to determine how closely it can approximate the optimal Bayes classifier.
Optical processing of fractal images
Authors: Domash Lawrence , Ryan Vincent , Tayebati Parviz
Published: February 2023

Fractal textures occur in natural scenary or satellite images (clouds, ocean waves). However, processing of fractal image data to extract measurements such as fractal dimension is highly computation-intensive when serial digital methods are used. Massively parallel nonlinear optical processing methods are proposed to characterize fractal images in real time. A photorefractive real time image processor performing a combined convolution/correlation operation is used to measure the correlation dimension of sample fractal patterns. The optical algorithm employs an image autocorrelation performed simultaneously with an optical convolution by using a spatially multiplexed array of 9–100 discs of various radii setting a range of scales. A digital neural network in the correlation plane evaluates the maximum intensity in each light patch and computes the fractal dimension. By placing phase screens or window functions in the third port, additional fractal analyses may be accomplished, including iterated function system encoding. Double convolution involving two different images and a kernel provides scale sensitive image comparison, closely related to wavelet analysis. Real time nonlinear optical coprocessing appears useful in several different approaches to characterization of fractal imagery. Preliminary experimental results will be presented.