bluuebunny/crossref_metadata_2025 huggingface dataset:
Detection efficiency comparison between VanderLugt and joint transform correlators
Authors: Yu Francis T. S. , Song Qiwang , Lu Xiaojin , Gregory Don A.
Published: February 2023

An optical correlator plays a major role in optical information processing and computing. As the technology progresses, various schemes for optical correlation have been proposed. Basically, almost all these schemes can be classified into either VanderLugt or joint transform types. We discuss the peak intensity performance of the VanderLugt correlator (VLC) and the joint transform correlator (JTC). The analysis is carried out with the same illumination and optimum spatial filters. Objects embedded in random noise and multiple input objects are considered. For the case of simple input objects (i.e., correlation with the reference image), the JTC offers a higher correlation peak intensity than the VLC. For the case of objects embedded in random noise, the correlation intensity of the JTC monotonically decreases as a function of noise, whereas the peak intensity of the VLC is independent of noise. For multiobject cases, the correlation intensity of the JTC is inversely proportional to N, and the correlation intensity is unchanged.
Synthetic discriminant function-based nonlinear correlator
Authors: Javidi Bahram , Odeh Souheil F. , Kuo Chungjung
Published: February 2023

A synthetic discriminant function-based nonlinear image correlator is presented. This pattern recognition system is capable of storing a large number of reference patterns in the spatial domain. The synthetic discriminant function is synthesized for a training set of images and is displayed at one side of the input plane. The input scene is displayed at the other side of the input plane. Thus the correlation between the input image and the reference patterns stored by the synthetic discriminant function is produced by nonlinear joint transform optical correlation.
Optical image series subtractor using two liquid crystal light values
Authors: Ransom P. L. , Airth-Kindree W. A. , Schmitz B. D. , Lawrence D. P.
Published: February 2023

The detection of differences between optical images is an important processing operation with applications in medicine, meteorology, robotics, earth resonance studies, and other fields. In each, optical subtraction is used to suppress areas of commonality between images, thereby highlighting the differences. Many methods have been employed to perform optical image subtraction. Most of these are reviewed by Ebersole.1 Since the publication of Ebersole’s review, real-time optical image subtraction using liquid crystal light valves (LCLVs) has been demonstrated.2,3 These LCLV subtractors do not require phase matching fluids, and they can subtract time-varying images taken, for example, from a video terminal.
Semiconductor laser theory with many-body effects
Authors: Koch Stephan W. , Haug Hartmut , Sargent Murray
Published: February 2023

A theory of a semiconductor laser is developed that includes the many-body effects due to Coulomb interactions. The theory is valid for both 3-D bulk semiconductors as well as quasi-2-D quantum well structures. We emphasize plasma density-dependent band gap renormalization, broadening due to intraband scattering, and electron–hole Coulomb enhancement. The very short intraband scattering relaxation time allows us to eliminate the interband polarization adiabatically and to introduce a hydrodynamic description of the intraband kinetics. From this general formulation a diffusion equation for the carrier density is derived. The resulting diffusion coefficient decreases with carrier density and laser intensity due to the reduction of the electron drift. We use our theory in the problem of laser gain, index, and side mode instabilities. We show that near the laser operating point, our many-body theory can be approximated by a simple rate equation formalism. However, in contrast to the usual rate-equation theory, the semiconductor rate constants are functions of temperature, tuning, and carrier density.
Single-mode model of surface-emitting DFB and DBR semiconductor lasers
Authors: Dzilira Thaddeus G. , Wang S. C.
Published: February 2023

The surface-emitting semiconductor laser1-3 is expected to be a key component in future optoelectronic and optical signal processing applications. Several designs are under development including electrically excited and photopumped lasers. The requirement of a surface-emitting geometry imposes important constraints on laser design, which must be considered to achieve an efficient emitter. For example, the method of extracting the laser beam must accommodate that part of the structure providing electrical excitation. Also, a model that calculates laser properties only at threshold is clearly not adequate. We have developed a transfer equation model of short cavity DFB and DBR surface-emitting lasers in which the resonator is defined by multilayer quarter-wavelength semiconductor structures providing distributed feedback. These lasers naturally lend themselves to a description in which the forward and backward waves are propagated from layer to layer by a set of equations detailing the gain and loss due to the material and the feedback and radiation loss due to the Bragg grating. We apply this method to calculate power output, longitudinal modes, and axial intensity profiles for several laser types. In particular, we show that the forward to backward power ratio can depend on mode number as well as pumping level.
Novel integrated-optics modulator for optical communications
Authors: Kissa Karl , Wang X. L. , Ih Charles S. , Hunsperger R. G.
Published: February 2023

An integrated-optics standing-wave surface-acoustic-wave modulator (SWSAWM) for optical communications is being investigated. This novel modulation method, which has been described previously,1 was used to upconvert a color TV video signal to TV channel 4 by generating a 70-MHz subcarrier with a Ti-LiNbθ3 modulator. Prisms were used to couple light in and out of the waveguide. A photodetector placed at one of the diffracted beams received the upconverted signal. An ordinary TV receiver recovered the original video signal. Picture quality was good. The phase of the acoustooptically generated subcarrier could be changed by changing the phase relationship between the rf signals driving the two inter-digital transducers. The standing wave nature of the modulator was also demonstrated by the frequency dependence of the diffracted optical power. Nonlinearities in surface acoustic wave generation and/or acoustooptic diffraction caused sub-carrier distortion on high diffraction efficiencies. This effect is being examined theoretically and experimentally to determine its influence on system performance. Subcarrier generation at higher frequencies (600 MHz and above) is also being explored.
Use of edge light emitting diodes in signal coherence multiplexing
Authors: Houk Theodore L. , Falk R. Aaron , Huggins Raymond W.
Published: February 2023

An edge light emitting diode (ELED) emission spectrum is near Gaussian at 820-nm center wavelength with 33-nm FWHM, promising a short coherence length within the range of feasible titanium indiffused lithium niobate (Ti:LiNbO3) integrated optics unequal arm Mach-Zehnder interferometer (IOMZ) optical path differences. Interferometric ELED coherence measurements were made in a tilted mirror Michelson interferometer. Fringes were viewed with a near-IR video camera and digital imaging frame store connected to a computer. This apparatus measured all the quantities needed to compute the coherence function (Born and Wolf), which fits a Gaussian function of 6.4-μm standard deviation (SD) and peak value 0.78. We observed interference fringes in the output light of the second of two Michelson interferometers in series whenever any two of the four possible optical path lengths were equal within 3 SDs, 20 μm. These fringes are the reconstructed signal for coherence multiplexing. Proton exchange applied to one side of a symmetric Ti:LiNbO3 IOMZ can form a 2000-μm optical path difference via changes in the substrate refractive index. From such MZs, we propose to form coherence multiplexing systems of up to ten parallel channels. ELED power attenuated by system Y-junctions, background, and detector noise imposes this channel limit.
Free space optical pulse position modulation communication with laser diode transmitter and avalanche photodiode receiver
Authors: Sun X. , Davidson Frederic
Published: February 2023

A direct detection optical communication system for use in an intersatellite link was constructed with an AIGaAs laser diode (Hitach-HL8314E, λ = 833.4 nm) as the transmitter and an avalanche photodiode (RCA C30902S) as the photodetector. The system used Q = 4 pulse position modulation (PPM) signaling and operated at 25 Mbits/s. The PPM slot clock at the receiver was recovered by using a transition detector followed by a phase lock loop (PLL). The PPM word clock was recovered by using a second PLL whose input consisted of back- to-back PPM pulse pairs contained in the received random PPM pulse sequences. A special PLL circuit was devised to phase lock further the word clock with the slot clock. The use of the recovered slot and word clocks at the receiver resulted in no penalty in receiver sensitivity compared to a receiver that used common transmitter/receiver clocks. The measurements of the received bit error probabilities vs detected photons per information bit agreed well with the theoretical computation results. The system achieved a bit error probability of 10−6 at <60 detected photons per information bit (−63.5 dBm). The receiver was capable of acquiring and maintaining slot and word synchronization for received signal levels of >15 photons per information bit.
Spectral saturation and its prediction
Authors: Fuld Kenneth
Published: February 2023

The saturation of spectral lights was measured in the following two ways: with a standard color-naming procedure, in which subjects reported the percent whiteness perceived in a given stimulus, and with a heterochromatic saturation matching technique, generally analogous to heterochromatic brightness matching. Both methods yielded similar results. For each subject, chromatic valence and spectral sensitivity functions were also determined. Heterochromatic flicker photometry and heterochromatic brightness matching were used for the latter. Predictions of each subject’s saturation data were made on the basis of the individual’s chromatic valence and spectral sensitivity functions within the framework of opponent colors theory. No reliable difference was found between heterochromatic flicker photometry and heterochromatic brightness matching as predictors of saturation. Although the theoretically and empirically derived saturation functions were qualitatively similar, it was generally found to be the case that the ratio of saturation of shortwave to longwave lights is less than that predicted by theory.
Contribution of chromatic channels to brightness: effects of retinal Illuminance
Authors: Yaguchi Hirohisa , Komatsu Koichi , Miyake Yoichi , Kubo Souichi
Published: February 2023

Spectral luminous efficiency functions were measured by direct heterochromatic brightness matching and flicker photometry at the retinal illuminance levels, 1, 10, 100, and 1000 trolands with a 2° visual field. For all four subjects, as the retinal illuminance increases, the luminous efficiency curves for heterochromatic brightness matching broaden, but those for flicker photometry do not. It is understood through recent investigations that the sensitivity rises in short- and long- wavelength regions for heterochromatic brightness matching are consequences of the chromatic channels’ contribution to the brightness. From the present results, it is suggested that the contribution of the chromatic channels to the brightness increases as the retinal illuminance increases. Development of a model that makes quantitative predictions of the experimental results is in progress.
Photon antibunching in optical bistability
Authors: Brecha R. J. , Xiao Min , Kimble H. J.
Published: February 2023

While the problem of photon antibunching in optical bistability has been the subject of numerous theoretical investigations, there appears to be no general result in the literature that includes a complete specification of the dependence of antibunching on the system parameters. Motivated by the importance of such a result to experimental observation of this effect, we present a treatment that includes the parametric dependences on cavity and atomic detunings, cooperativity parameter, nonradiative (collisional) damping, and the ratio of cavity and atomic damping rates. We also attempt to analyze the contribution of fourth-order correlations of the fluctuating fields, which have been neglected in previous treatments. Although the antibunching initially increases with decreasing system size due to the approximate scaling of quantum fluctuations as the inverse of the saturation photon number ns, higher-order fluctuations begin playing an increasingly important role at values of ns ⪝ 1. We show that the linearized theory itself does not necessarily break down for arbitrarily small values of ns (as previously suggested), but that photon antibunching is lost in this limit, thus placing restrictions on the design of an experiment.
Ranging and velocimetry signal generation in a backscatter-modulated laser diode
Authors: De Groot P. J. , Gallatin Gregg M. , Macomber S. H.
Published: February 2023

A compact self-aligning laser radar has been constructed for coherent ranging and velocimetry using a laser diode modulated by feedback from light scattered from a diffusing target. The phenomenology of beat-signal generation in the device is discussed from both experimental and theoretical points of view. The ac-coupled modulation waveform is asymmetric (similar to a sawtooth) and different for the two propagation directions of the light leaving the diode. A theoretical model, based on the mode structure of a three-mirror Fabry-Perot cavity, is shown to describe the signal generation in these experiments, to account for the sawtooth waveform, and to predict the modulation depth of the waveform. Possible applications and extensions of this technology are briefly discussed.
Real-time deconvolution of signals using a liquid crystal light valve
Authors: Reeve C. D. , Bryant F. D.
Published: February 2023

Given a signal s(t), which is the convolution of a known signal f(f) with an unknown signal g(f), there is often the need to extract g(f). It is easily shown that in the frequency domain the Fourier transform of g(f) may be obtained by dividing the cross-spectral density of s(t) and f(f) by the power spectral density of f(t). Results are presented of experiments designed to obtain both the cross-spectral density and power spectral density optically using acoustooptic systems and, using a liquid crystal light valve as a programmable mask in the Fourier plane, to achieve the deconvolution of the signals in real time. Using digitally generated input signals, the results are compared to theory. The degree of success is found to be limited by the spatial resolution and dynamic range of the light valve.
Self-synchronizing pulse-interval technique for optical routing control in a photonic switch
Authors: Perrier Philippe A. , Prucnal Paul R.
Published: February 2023

The speed of future photonic switches will be limited by the device switching speed and by the processing speed of the routing controller. A data flow bottleneck will occur at the controller if routing decisions are executed electronically. This bottleneck can be eliminated if optical processing is used.’ If, in conjunction, self-routing is used, the propagation delay of data through a photonic switching network can be substantially reduced.
Weak dispersive effects in Raman amplification
Authors: Warner Charles , Bobbs Bradley
Published: February 2023

Linear medium dispersion can reduce the stimulated Raman scattering gain for a broadband laser. This increases the Raman cell length required for Stokes frequency conversion and also limits the ultimate conversion efficiency achievable in a long cell. Modeling of these effects, particularly the latter one, must account for depletion of the pump laser intensity as it is converted. Inclusion of depletion effects into previous undepleted pump modeling efforts may be accomplished using a perturbation technique for weak dispersion. Numerical results for a 351-nm laser in 3.5 atm of hydrogen with a 1-nm bandwidth show that a fourth-order perturbation calculation is adequate to predict a conversion efficiency 9% below the quantum limit. The efficiency is found to decrease approximately quadratically with increasing bandwidth for bandwidths up to ~2.3 nm. An equivalent dispersion formulation may be used to extend these results to include the effects of a small angular misalignment between the pump and Stokes seed beams.
Double phase-conjugate oscillators
Authors: McMichael Ian , Beckwith Paul , Yeh Pochi
Published: February 2023

When two phase-conjugate mirrors with gain are placed near each other, an oscillation will build up between them. This is called a double phase-conjugate oscillator (DPCO). DPCOs have many interesting physical properties that can be used to make sensors. For example, the frequencies of the counterpropagating oscillations in a linear DPCO are independent of the reciprocal optical path length of the resonator and dependent on the nonreciprocal optical path length. This is the exact opposite of linear oscillators using conventional mirrors (i.e., lasers). Since inertial effects produce nonreciprocal phase shifts, the DPCOs can be used to sense motion. In fact, the DPCO is the only oscillator that is known to be capable of measuring translation. Although conventional optics can be used to make rotation sensing oscillators (i.e., ring laser gyros), these devices cannot use solid-state gain media due to gain competition, and they suffer from the problem of frequency locking. These problems do not exist in phase-conjugate oscillators.
Picosecond nonlinear optical response in polymers using four-wave mixing techniques
Authors: Dorsinville R. , Yang Lina , Alfano R. R. , Tubino R. , Destri S. , Taliani C.
Published: February 2023

The magnitude and response time of the third-order nonlinear coefficient were measured in dilute solutions of polyacetylene and thin polythiophene films using four-wave mixing techniques. In soluble polyacetylene the relatively large (> 10−9 esu) and fast (<20-ps) response, comparable to results in solid samples, seems to indicate that interchain interactions do not play a significant role in the nonlinear response. In polythiophene and its derivatives, one of the largest values of the nonlinear optical coefficient (> 10−8 esu, <20 ps) was measured within the absorption band.
Perception of unsaturated colors at various visual field locations in man
Authors: Iivanainen Antti , Rovamo Jyrki
Published: February 2023

We studied how much blue, green, or red light had to be subtracted from or added to white (CIE 1931 chromaticity coordinates x = 0.35 and y = 0.35) to obtain veridical hue perception (blue, green, red, or their complementary colors) at various eccentricities in the temporal visual field. The smallest increment/decrement necessary for veridical hue perception was expressed as a linear distance from the white in chromaticity coordinates. When the stimulus had the same retinal size at all eccentricities, in the discrimination threshold (linear distance in chromaticity coordinates) increased toward the periphery of the visual field. However, when the stimulus was M-scaled by magnifying it with increasing eccentricity in inverse proportion to the density distribution of ganglion-cell receptive fields across the human retina,1 the discrimination threshold became independent of visual field location.
Statistics of waiting times in the photodetection of squeezed light
Authors: Vyas Reeta , Singh Surendra
Published: February 2023

The theory of photoelectric detection is used to calculate the waiting time distributions for squeezed light. Analytic expressions for the conditional and unconditional waiting time distributions for squeezed light have been derived in the large photon number limit. Both pure squeezed and squeezed coherent states have been considered, and the results are compared with those for the other states of light.
Time averaged quantities in the Jaynes-Cummings model
Authors: Cresser J. D. , Hillery Mark
Published: February 2023

The Jaynes-Cummings model is one of the most basic systems in quantum optics. It is exactly soluble but the quantities of interest are given by infinite oscillating series which cannot be summed. This leads to problems if one wants to learn about the long-time behavior of the system. On the other hand, the time averages of those quantities can be computed exactly. Infinite time averages give information about behavior which persists for all time. We examine the time averages of the squeezing and the variance of the photon number of the field. We also use time averages to gain information about the inversion. For example, one finds that the fraction of time which the inversion spends far from its mean value decreases as the amplitude of the initial field increases. The importance of periodic behavior in the inversion also decreases as the initial amplitude increases. Finally we examine how long the system must be observed for time averages of quantities to approach their infinite time limits.
Photon correlations and spectra in the bimodal regime of single-atom cavity-enhanced absorption
Authors: Alsing P. , Carmichael Howard J. , Rice Perry R.
Published: February 2023

We recently reported that the transmitted light from a driven optical cavity containing a single-atom absorber shows strong nonclassical features.1 Also, Savage and Carmichael2 have shown that this single-atom system can be operated in a regime in which the transmitted light has a bimodal photon-counting distribution; as the saturation photon number is increased this bimodality develops into a single-atom version of absorptive optical bistability. We present results for the degree of second-order coherence and the spectrum of the transmitted light in the operating regime at the onset of bimodality. In this regime we can study the onset of low frequency behavior associated with transitions between the local states defined by the peaks of the bimodal distribution. Our results are calculated numerically, using a supercomputer to solve matrix element equations derived in the Fock-state basis. Our numerical approach also allows us to extend our analytical study of nonclassical effects in single-atom cavity-enhanced absorption. Our analytical results are restricted either to the bad-cavity limit1 or to weak driving fields outside this limit. We can now study how the nonclassical effects identified in these analytical calculations are changed by using finite driving fields outside the bad-cavity limit.
Steady-state population Inversion via quantized fields
Authors: Savage C. M. , Lindberg M.
Published: February 2023

Placing an optical cavity around a two-level atom modifies the electromagnetic vacuum to which it couples. Effects such as inhibited and enhanced spontaneous emission are known to result. Recently one of us predicted a new nonclassical effect of vacuum engineering.1 A two-level transition may be laser driven into an inverted steady state. Semiclassical theory forbids this fully quantum mechanical result. Unlike squeezing and antibunching, this inversion is not a property of the linearized quantum fluctuations. We present numerical and analytical results which clarify the physics of the inversion. The maximum inversion possible is determined. We attempt to identify obstacles to the experimental realization of steady-state inversion. Multiple atoms and multiple cavity modes do not destroy the effect. A significant difficulty appears to be localizing the atoms at the cavity beamwaist until they reach steady state. The inversion may be observed via fluorescence changes as the cavity is blocked and unblocked or via the presence of a fluoresence maximum as a function of the driving field intensity.
Low-energy optical communication inside digital processors: quantum detectors, sources, and modulators as efficient Impedance converters
Authors: Miller David A. B.
Published: February 2023

There is debate on the comparative usefulness of optical (or optoelectronic) and electronic devices in digital processors. Here I point out one feature of optics not so far stressed, optical detectors, sources, and modulators, because they can be quantum devices and can operate as efficient impedance transformers, which can reduce the energy required to communicate information between logic devices. Because of noise and threshold uniformity, room-temperature electronic logic levels are ~1 V. Because electromagnetic propagation is practically low impedance, large dissipations result in irreversible electrical communication of logic-level signals (e.g., 20 pJ for a 1-V, 1-ns pulse on a 50-Ω line). Optical quantum detectors, sources, and modulators can, however, effectively impedance match small (high-impedance) electronic devices to this propagation. For example, a photodiode giving one electron per absorbed photon and operating into high impedance can generate ~1 V with ~1 nW of light, although there is only ~600-μV classical voltage in such a beam. A similar argument works in reverse for ideal quantum emitters or modulators, generating or modulating one photon per electron of current. Properly integrated, semiconductor photodetectors and quantum well modulators (or possibly low-threshold lasers) could actually reduce energy for all except the shortest intrachip interconnects.
Tunable lasers
Authors: Moulton Peter F.
Published: February 2023

Tunable lasers are routinely used in scientific investigations and are now finding application in areas such as medicine and remote sensing. The tutorial covers the basic physics of tunable laser media as well as elements of laser technology specific to tunable systems. Included as subject matter are dye, color-center, solid-state, and parametric-oscillator devices. The use of optical components such as prisms, gratings, birefringent filters, and etalons as tuning elements is also discussed. The factors determining operating linewidth of both pulsed and cw lasers are considered with techniques for obtaining narrow laser linewidths.
Ultrahigh resolution UV and VUV laser source
Authors: Kung Andrew H. , Cromwell E. , Trickl T. , Lee Y. T.
Published: February 2023

Recent advances in high-power injection-seeded lasers, pulse amplified dye lasers, and four-wave mixing technologies make possible the development of high-power, broadly tunable, and ultranarrow sources in the UV, VUV, and XUV regions. By combining the latest technological advances in these areas we have developed a near-transform-limited laser source that tunes from 74 to 1000 nm with peak powers of >150 MW in the visible and >30 MW in the ultraviolet and has more than 1012 photons/s in the VUV-XUV region. The bandwidth in the XUV below 100 nm is mea sured to be 210 MHz. The spectral brightness of 1.5 × 1017 photons/s/0.1 % bandwidth of this tabletop laser source is several orders of magnitude higher than the best sources available today.
Real-time 3-D incoherent processing
Authors: Poon Ting-Chung , Park Jinwoo
Published: February 2023

An acoustooptic two-pupil heterodyne scanning system has been proposed to overcome the constraints in a conventional incoherent optical systems.1,2 We investigate the defocusing image effect on the optical transfer function (OTF) of the two-pupil system. We first show that the OTF of the defocused system can be expressed by the cross ambiguity of the two pupil functions. Next, we take two offset pupil functions both having Gaussian shape and obtain the OTF of the defocused system. It is shown that the OTF in this particular case is a bandpass filtering function. As the defocusing distance increases, the center spatial frequency corresponding to the OTF peak value moves from the high-frequency range to the low-frequency range. Experimental results are presented. Finally, we discuss the system's potential use in 3-D processing.
Joint transformation correlation implementation of the circular harmonic expansion for pattern recognition
Authors: Yu Francis T. S. , Li Xiaoyang , Tam Eddy , Gregory Don A.
Published: February 2023

A real-value implementation of circular harmonic expansion by a joint transformation correlation scheme to achieve rotation-invariant pattern recognition is presented. Both the real and imaginary parts of one component of the circular harmonic expansion of a template are used as reference functions. Based on the measurements of the two peaks of the correlation between input object and the two reference functions, rotation-invariant patten recognition is achieved. The rotation angle of the input object with respect to the template is recovered. By using a ¼ waveplate, the rotation invariance based on only one correlation peak is obtained while sacrificing shift invariance. The proper circular harmonic expansion center plays an important role in the circular harmonic expansion-based rotation-invariant pattern recognition. An efficient and effective way of finding the proper center is discussed. The ability of the reference functions to discriminate the object which contains the template from other objects is analyzed. Experimental results are included.
More curious features of nonlinear pulse propagation in single-mode optical fibers
Authors: Tomlinson W. J.
Published: February 2023

Among the curiosities of nonlinear pulse propagation in single-mode optical fibers are optical solitons—pulses with the appropriate intensity and shape so that the self-phase modulation resulting from the intensity-dependent refractive index of the fiber exactly compensates for the effects of its group velocity dispersion (GVD), and the pulse propagates with a constant shape and intensity. Bright solitons, which exist for anomalous GVD, have been studied for some time, but only recently has it been possible to observe dark solitons, which exist for normal GVD. Dark solitons, short depressions or holes in the intensity of a background signal, have the curious feature that they are odd or antisymmetric pulses. When, as in recent experiments, the background is a pulse only a few times wider than the dark pulse, the background will evolve rapidly, decreasing in intensity and developing a frequency chirp. We show that, even with such a rapidly evolving background, dark pulses have the curious feature that they can propagateas dark solitons, adapting adiabatically to the changing background.
Berry’s topological phases in optical interferometry
Authors: Nathel H. , Chiao Raymond Y. , Antaramian A. , Ganga K. M. , Jiao H. , Wilkinson S. R. , Garrison J. C.
Published: February 2023

We study two types of topological phases, i.e., Aharonov-Bohm phases, by means of optical interferometry. The first arises from a cycle of redirections of the photon spin and is closely related to the Aharonov-Anandan phase. The second arises from a cycle of polarization changes on the Poincare sphere and was discovered by Pancharatnam. Both of these phases, and their combined effects, have been investigated by a nonplanar Mach-Zehnder interferometer. The signs of the fringe shifts arising from these topological effects have been determined and agree with theory.
Tunable Fabry-Perot interferometer using liquid crystals
Authors: Bonaccini D. , Smartt Raymond N.
Published: February 2023

A liquid crystal Fabry-Perot etalon (LCFPI), in which tuning is achieved via the electrooptic effect, is described. The design is applicable to measurements of the solar emission corona, which requires precise subtraction of the scattered light component from the faint emission signal of the coronal lines. For this, spectral chopping is used, in which the signal from one polarization Fabry-Perot channel positioned in the continuum of the spectrum is subtracted electronically from the tunable orthogonally polarized channel via a polarization modulator. The particular use that we require from the filter established the class of LC material to be used and requires special care in the preparation of the substrates. Applications in the IR are possible preserving the full tunability of the filter with low voltages and low powers. The basic design properties of the LCFPI are discussed, and analysis is performed of its thermal sensitivity, transmittance, and stability.
Resonantly enhanced multiphoton ionization in strong laser fields
Authors: Perry M. D. , Landen O. L. , Szoke A.
Published: February 2023

The effect of intermediate multiphoton resonances on the threshold and above-threshold ionization probability of rare gas atoms in intense visible and UV laser fields is illustrated with ion and photoelectron spectra. Substructure observable in the electron energy distribution resulting from multiphoton ionization with ultrashort pulses is observed and attributed to intermediate states being shifted into resonance as first described by Freeman et al. Resonant enhancement remains significant at intensities in excess of 1013 W/cm2. Measurement of the ac Stark shifts and photoionization rates of members of the 4p54d and 4p54d′ manifolds of krypton are presented along with measurements of the multiphoton Rabi rate between the ground and excited states. Measurements of multiphoton ionization cross sections are presented for krypton and xenon and compared with recent perturbative and nonperturbative calculations.
Nature of variations in normal color matches
Authors: Neitz Jay , Jacobs Gerald H.
Published: February 2023

Although there is a considerable body of evidence from color matching to suggest that there are reliable variations in the spectral positioning of the M and L cone pigments among normal trichromats, both the magnitude of the variation and its distributional nature are still matters of concern. Earlier we found discrete variation in color matching among normals and interpreted that result as indicating a discrete variation in the spectra of the underlying cone pigments. Recently, Jordan and Mollon (ARVO, 1988) reported on a color matching experiment in which they attempted to check our result. They failed to find discrete variation in color matching. Since their experiment differed from ours in several procedural details, we ran a new experiment incorporating these differences. The results again reveal discrete variations in color matching among color normals. We also obtained two different color matches from each of sixty subjects. Comparisons of the matches allow one to eliminate the possibility that the differences between groups of normals arise from mechanisms other than variations in the spectra of the cone pigments.
Sources of shared variance in Rayleigh and photometric matches
Authors: Pokorny Joel , Smith Vivianne C. , Lutze Margaret B.
Published: February 2023

Studies of Rayleigh matches and heterochromatic flicker photometry (HFP) have noted a small but significant correlation. An observer who is red-sensitive to HFP is likely to show a red-shifted Rayleigh match. Furthermore, Lutze1 demonstrated that major gene activity accounts for interobserver variability in both Rayleigh matches and heterochromatic modulation photometry (HMP).
Algebraic analysis of parvocellular color-opponent ON-OFF interactions
Authors: Martinez-Uriegas Eugenio
Published: February 2023

The adopted assumptions are as follows: (1) At each point on the retina there are at least four concurrent receptive fields of parvocellular color-opponent geniculate units, two ON-center OFF-surround units (subtypes +R – G, +G – R) and two OFF-center ON-surround units (subtypes –R + G, –G + R). (2) All units receive excitatory E and inhibitory I inputs. Both E and I are expressable as the product of a spectral and spatiotemporal function, implying that spectral and spatiotemporal sensitivities are separable. Spatial and temporal sensitivities are not assumed to be separable. (3) Concurrent geniculate units interact by pairs on first-stage cortical cells adding or subtracting their signals. The analysis shows the chromatic and spatiotemporal implications of the proposed interactions.
OKN isoluminance points and equivalent achromatic contrasts in infants and color-normal and abnormal adults
Authors: Teller Davida Y. , Lindsey Delwin T.
Published: February 2023

Nine-week-old infants, color-normal adults, and red-green color-deficient adults were tested with an Anstis/Cavanagh OKN paradigm. 50 × 50°, 0.5-c/d, 50-townsend (TD) red-green (R/G), and yellow-black (Y/Bk) gratings were moved in opposite directions on a color video screen. An observer judged whether OKN occurred in the R/G or the Y/Bk direction (R/G OKN vs Y/Bk OKN). The R/G ratio was varied to find the OKN isoluminance point, and the Y/Bk contrast was varied to find the equivalent achromatic contrast. Extensive within-subject data were collected. In all cases, the direction of OKN was consistent and readily measured, and transitions from R/G to Y/Bk OKN were sharp. At Y/Bk contrast = 0, R/G OKN occurred in all subjects at all relative luminance values. For all groups of subjects, Y/Bk contrasts of ~15% allowed Y/Bk OKN to predominate over a confined range of R/G ratios. The isoluminance points differed systematically among groups; surprisingly, the equivalent achromatic contrasts (EACs) did not. Thus, at least in the present conditions, OKN isoluminance points are more useful than are EACs incharacteizing color vision deficiencies.
Back-Action Evasion Using Parametric Downconversion
Authors: La Porta A. , Slusher R. E. , Yurke B.
Published: February 2023

The uncertainty principle in general requires that "back-action" noise is introduced into an optical field after it has been measured, so that the precision of subsequent measurements is progressively reduced. However, it has been shown that one quadrature component of the field can be measured without changing its quantum state; i.e. a quantum nondemolition, or more precisely, a back-action evasion measurement can be performed.
Constraints on Passive Coherence Filtering of Imaging Systems Due to Properties of the Impulse Response
Authors: Sica L.
Published: February 2023

To find the output intensity of an imaging system due to a spatially coherent source of narrow spectral bandwidth, the amplitude impulse response is integrated over the source, and the modulus of the result is then squared. For imaging of an incoherent source with the same spectral content, the modulus of the amplitude impulse response is squared and then integrated over the source. A system for which the coherent image intensity is zero while the incoherent intensity is unaffected is defined to be a coherence filter. The realizability of such a system is constrained by the above-mentioned properties of impulse responses. It follows from the definitions that a zero response to an unresolved coherent source located somewhere in a finite field implies a zero response to an incoherent source in the same field. Further, if a coherent source is resolved, and the impulse response of the system is space-invariant with finite support, it is shown that a coherence filter is unrealizable. However, a heuristic example suggests the possibility of approximate coherence filtering over a limited field, for a space-variant impulse response. Perfect global coherence filtering is impossible to realize however.
Crystal-Orientation Dependence of the Energy Exchange in BSO Crystals
Authors: Kukhtarev N. , Rouede D. , Khitrova G. , Gibbs H. M.
Published: February 2023

We observe and explain a strong dependence of energy exchange on the orientaion of the crystal. Experiments are performed with a 1.8-mm BSO crystal of holographic cut (001, 110,

1

1
¯

0

). The crystal is mounted such that it can be rotated around the [110] axis by 360°. Two equal-intensity (≃10mW/cm2) beams a and b are incident onto the (110) plane, each with an angle of 35° to the normal. The angle for maximum energy exchange is often different from the values 0° or 90° usually used. For linear polarization the angularly dependent curves have four maxima and four minima. To explain such behavior we solve two-dimensional amplitude equations where G is optical activity, r is an electro-optic factor proportional to r14, ΔE is the space-charge field, and ϕ is the angle of the light grating relative to the [110] axis. Analytical solutions that include optical activity and both anisotropic and isotropic diffraction agree well with linearly polarized curves (four cases: both along [001], both along [110], left along [001] and right ±45° to [001]) of energy exchange versus crystal rotation angle. However, for circular polarization the data follow the theoretically expected sinϕ dependence, but exhibit dips at 90° and 270° that are not fully understood. Anisotropy in the diffusion field might explain this discrepancy.
Coherent Microwave Spectroscopy Using Picosecond Optoelectronic Integrated Antennas
Authors: Pastol Y. , Arjavalingam G. , Halbout J.-M. , Kopcsay G.V.
Published: February 2023

We describe a new broadband microwave spectroscopy technique based on the transient radiation from optoelectronically pulsed integrated antennas. We use exponentially tapered coplanar stripline antennas fabricated on silicon-on sapphire substrates [1]. The coherent microwave transient spectroscopy (COMITS) experiment consists of a transmitter and a receiver with the sample to be characterized located between them. Optical pulses of 2.5 ps duration at 532 nm wavelength are used to excite the transmitter and to photoconductively sample the received voltage signal. With no sample between the two antennas, a typical waveform consists of a 7 ps wide central peak with two negative peaks separated by 17 ps. The amplitude spectrum of the received signal, obtained by Fourier transforming the temporal data, has components extending up to 150 GHz and tends to zero at low frequencies. For a standard COMITS measurement two recordings are taken with and without the sample. The amplitude and phase of the transmission function of the sample are derived by comparing the Fourier transforms of the two sets of temporal data. We use samples of well known and predictable behaviour to characterize the experimental set-up. For instance, the measured amplitude and phase for Fabry-Perot interferometers display the expected spectral dependence determined by the plate separation. Measurements of the loss and dispersion properties of materials were also performed with the spectroscopy apparatus, and results obtained for fused silica over the 10-125 GHz band will be presented.
Multiple Quantum Well Passive Modelocking of NaCl Color Center Laser
Authors: Sunderman E.R. , Islam M.N. , Bar-Joseph I.
Published: February 2023

We have produced 260 fsec pulses by passively modelocking a NaCl color center laser using multiple quantum well (MQW) saturable absorbers. This femtosecond source is a simple, single cavity, tunable, all-solid-state laser with ~2.3kW peak power. The experimental configuration consists of a NaCl cavity as described in [1] plus two 50mm lenses and a MQW sample. Our shortest pulses are obtained with an AR-coated, proton bombarded (to reduce the recombination time) sample containing 60 periods of 200Å InGaAs wells between 100 Å InAlAs barriers. We obtain pedestal-free 260fsec pulses with a bandwidth of ~ l.5THz (δνδτ = 0.39, which lies between the values for a secant hyperbolic and Gaussian pulse). By rotating a 1mm thick quartz birefringent plate, we can tune the wavelength for passive modelocking by ~40nm. Furthermore, we tuned the passive modelocking between 1.59 and 1.7μm using MQW’s with different well sizes. For each MQW, we find the optimal modelocking wavelength to be about 50nm below the heavy hole exciton peak.
High CW conversion efficiency in a strained InGaAs/AlGaAs quantum well laser (λ = 930nm)
Authors: Bour D. P. , Evans G. A. , Gilbert D. B.
Published: February 2023

A strained InGaAs/AlGaAs quantum well laser with a front-end power conversion efficiency exceeding 33%, and available output power greater than 1 Watt, is demonstrated. The laser structure is grown by atmospheric pressure organometallic vapor phase epitaxy, and consists of a graded index separate confinement heterostructure (GRIN SCH) with a 70Å In0.2Ga0.8As strained quantum well active region. The lasing wavelength of 930nm is in good agreement with that expected from quantum well thickness and composition. The longest attainable wavelength is dictated by the tradeoff between InAs alloy content and sub-critical quantum well thickness; we have fabricated devices up to λ = 1.08μm. Threshold currents of strained quantum well lasers are as low as those in unstrained lasers. In fact, they may be lower, a result of some beneficial effects of biaxial compression, and the possibility of higher confinement factors. Despite this, quantum efficiencies are somewhat reduced; the best we have observed is ηe = 58.4%. This may be due to the increased importance of nonradiative processes in the low-bandgap InGaAs. With the exception of lower quantum efficiencies, these devices behave much like unstrained GaAs quantum well lasers. For example, in the short-cavity regime, where average losses are high, threshold currents are increased while characteristic temperatures decrease.
Fluorescence Studies of Laser Vaporized Aluminum: Evidence for a 3πu Ground State of Aluminum Dimer.
Authors: Cai M. F. , Dzugan T. P. , Bondybey V. E.
Published: February 2023

Aluminum is an element of considerable importance in chemistry and technology. Simple aluminum containing molecules, including Al2 dimer were therefore extensively studied, both experimentally1-3 and theoretically.4-8 While some theoretical studies and a previous gas phase study suggested a ground state of 3∑g symmetry, and some matrix studies claimed a 1∑ ground state, other theoretical works predicted an X 3πu ground state.
k-Ratio improvement by a sharp p-n junction
Authors: Choa F. S. , Liu P. L.
Published: February 2023

A large difference in the ionization rates for electrons and holes is essential for a low-noise avalanche photodiode (APD). Enhancement of electron impact ionization in a heterojunction superlattice has been experimentally demonstrated since 1982. However, the trapped carriers in heterostructures can occasionally contribute to impact ionization, and charging or discharging delay, therefore, degrades the originally expected performance. We propose to use a sharp p-n junction to improve the k-ratio. Such a scheme can be applied to both the heterojunction and homojunction and is free of the miscibility problem and trapping effect. The length of the sharp p-n junction is much shorter than its carrier energy relaxation mean free path. Impact ionization happens in the region right after the junction. Because the carrier distribution function is a nonlinear function of energy, an equal amount of injection level from the junction affects electrons and holes differently when their ionization thresholds are different. Calculations based on a lucky-drift model1 show that the k-ratio improvement increases with the height of the injection level and becomes extremely significant when the level approaches the lower one of the thresholds.
Concept for a solid-state imaging photon counter
Authors: Mertz Lawrence
Published: February 2023

Consider a crosspoint array of thyristors. Initially all are off, and then one thyristor is turned on to give conduction from one row to one column. A peripheral array of diodes serves to encode just which row and column are conducting. The power may then be interrupted briefly to reset the thyristors. It is proposed that the thyristors be designed as avalanche photothyristors and that the device be moderately cooled and operated somewhat over the avalanche breakdown voltage as recommended by Ekstrom1 for activation by individual photons. The result of obtaining photon positions is an imaging photon counter that should have three basic advantages over a CCD at extremely low light levels: lower background because of no readout noise; higher pictorial speed because of no raster scanning; and preservation of temporal sequence information for a posteriori dynamic image processing.