bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical interface message processor for fiber-optic communication networks
Authors: Song Q. Wang , Choudhary Alok , Hariri Slim , Banerjee Partha , Ranka Sanjay
Published: February 2023

Optical technology has become a significant part of communication networks. We propose an optical interface message processor (OPTIMP) that exploits high bandwidth, parallelism, multidimensional capability, and high storage density. The most time-consuming operations in communication networks, such as switching and routing, are performed in the optical domain in the proposed system. Furthermore, the OPTIMP does not suffer from optical/electrical conversion bottle-necks and can perform switching and routing in the range of gigabits/s. OPTIMP has three main functional modules: a timespace conversion module, a parallel search and routing look-up table, and an optically controlled switching module. The sourcedestination (SD) information from a message is first converted to the spatial domain. The routing table stores all SD codes and the corresponding control codes for the switching module. The SD code serves as a microprogrammed instruction (similar to that in processor designs). The routing table is searched in parallel (single step) by means of a cylindrical system, and control signals corresponding to the matched S-D row from the table are used to control the switching network. Based on the SEED array technology, the switching module can be reconfigured in gigahertz range and can provide high bandwidth. The proposed design can have significant application to high-speed communication networks as well as to high-speed interconnection networks for parallel computers.
Optoelectronic three-dimensional solid model relational data-base machine
Authors: Eichmann G. , Zhang Y. , Li Y.
Published: February 2023

Using state-of-the-art optical technologies, such as holographic three-dimensional interconnect and optical disk storage, a novel optoelectronic programmable data-base ma chine for storing, processing, and reconstructing three-dimensional solid objects is proposed. The so-called edge-based boundary model that represents a three-dimensional object by its faces and edge sequence is used as the data structure. For efficient optical storage and processing, this data structure is further decomposed into three levels: a face, an edge, and a vertex level. Each decomposed level is encoded into a set of matrices that are suitable for optical matrix processing. Various Boolean set operations, such as select, join, intersect, and project, are used.
No title available at press time
Authors: Bumham Ralph
Published: February 2023

No summary was available at press time.
Surface-emitting lasers with integrated beam deflectors
Authors: Williamson R. C.
Published: February 2023

Diode lasers with integrated beam deflectors provide emission perpendicular to a wafer surface. Special technology for forming the laser facets and the deflectors has yielded high-efficiency high-power arrays of such lasers at 0.81μm in AlGaAs/GaAs and at 1.3μm in GaInAsP/InP.
Monolithic surface-emitting devices with etched micro-mirrors
Authors: Jansen M. , Yang J. J. , Ou S. S. , Sargant M. , Mawst L. , Rozenbergs J. , Wilcox J. , Hayashida P. , Botez D.
Published: February 2023

We report on the development of surface-emitting lasers with etched micro-mirrors in both the junction-up and junction-down (emission through the substrate) configurations. Material growth, processing, and packaging techniques required to fabricate monolithic devices on a wafer scale are described in detail.
A common photonic band gap in an exactly soluble model
Authors: Leung K. M.
Published: February 2023

To gain important insights into the photonic band problem, we investigate an analytically exactly soluble model that consists of a two-dimensional periodic array of infinitely long rectangular dielectric cylinders. Our aims are (1) to have a model that exhibits a band gap that opens up in all directions in the Brillouin zone, (2) to identify some of the favorable conditions for creating sizable photonic band gaps, and (3) to set benchmarks to test numerical methods for calculating the band structures of more complicated analytically insoluble problems. We show that this model is capable of having a common gap simultaneously for the transverse-electric and transverse-magnetic waves irrespective of the direction of propagation within a two-dimensional plane. Because of the large number of free parameters in this model we have optimized only one of the parameters. We find that this gap can exist for a minimum refractive index ratio of about 3.4. We believe that by optimizing all the available parameters, a substantially lower value can be found.
New applications in x-ray technology
Authors: Freeman Richard R.
Published: February 2023

This tutorial will review the emerging technologies in soft-x-ray science and their applications, from projection lithography to sub-picosecond time-resolved scattering and holography. Special emphasis will be placed on new technologies for soft-x-ray optics.
The dielectric function of highly excited semiconductors
Authors: Yevick David , Bardyszewski Witold
Published: February 2023

We have investigated the dielectric properties of GaAs in several calculations that incorporate the effects of both temperature and subband coupling in the valence band. We find that for certain energies and moments, the dielectric function of the realistic system diverges strongly from that associated with either the one-band effective-mass model or the plasmon pole approximation. We finally applied our dielectric function model to the quasiparticle correlation energy and thus generated curves for the temperature-dependent band-gap renormalization. This quantity is critical in determining the actual emission and absorption line positions in optoelectronic devices.
Single photon interference—a reinterpretation
Authors: Chin S. L.
Published: February 2023

We use the single photon Young's doubleslit experiment as an example. The accepted result of this experiment is that a photon interferes only with itself. Some accepted concepts still remain puzzling, however. Examples include the fact that there is no energy loss when a photon's wave passes "simultaneously" through the slits, the single photon's indivisibility versus its wavefront's separability into two parts, and the sudden collapse of a broad wavefront into a photon. An alternative interpretation is proposed. Based on the quantization of a radiation field, one postulates that a vacuum (zero-point) mode can be activated, which may become an EM wave if it is energized by many photons. Thus, a photon is not independent before a measurement but is a unit of energy h "dressed" on a vacuum mode. By using the quantized field approach, one shows that a vacuum mode coherently couples to other vacuum modes by means of the interaction with the two slits. It is as though the incident mode is separated into two secondary modes, which interfere on the screen. The pattern is "invisible" because there is no energy detector to detect it. Energizing the incident vacuum mode by photons automatically leads to the energization of the "invisible" pattern by "guiding" some of the incident photons through the two slits individually and onto the screen.
Surface profiles and scatter from soft-x-ray optics
Authors: Takacs Peter Z. , Church Eugene L.
Published: February 2023

The performance of soft-x-ray optics in synchrotron beam lines and for space astronomy use requires detailed knowledge of the topological properties of their surfaces. Instrumentation now exists for the measurement of surface profiles on spherical and aspherical surfaces up to one meter in length with subnanometer height resolution and submicroradian slope resolution. Analysis of surface profile data in terms of the power spectral density function over the entire range of spatial periods—from micrometers to meters—allows one to predict the performance of the component in a unified theoretical approach encompassing both the specular image and scattered light distribution. There is no longer any need for an artificial distinction between surface figure and surface finish. We will discuss numerous examples of actual surface profile measurements on grazing incidence and normal incidence optics, and we will relate them to measured performance at x-ray wavelengths where possible.
Multilayer coated diffraction gratings
Authors: Rife J. C. , Hunter W. R.
Published: February 2023

The recent successes in producing multilayers as reflecting coatings on mirrors for the VUV and soft-x-ray regions has prompted an investigation of their applicability to diffraction gratings. If the grating is to be used at near-normal incidence, matching the coating to the grating is a simple problem. If, however, the grating is to be used at oblique incidence, the matching technique must take into consideration the fact that the grating obeys the simple Bragg law, but the coating follows the corrected Bragg law. Furthermore, even if grating and coating are properly matched for use at grazing incidence there remains the problem of contamination of the spectrum by radiation from "suborders" and longer-wavelength spectral regions, where the outermost layers of the multilayer have a high reflectance. Successful coatings have been produced for both laminar and blazed gratings. Examples will be given of the matching procedure, and calculations and measurements will be presented showing the dramatic increase in efficiency as well as the presence of longer-wavelength radiation.
Plasma-based soft-x-ray sources
Authors: Forsyth James M.
Published: February 2023

Synchrotron soft-x-ray sources have been used to ad vance the state of x-ray optics in the last two decades, particularly in the fields of microscopy and microlithography. However, the size and cost of a synchrotron installation is burdensome in many instances. Even so-called compact storage ring sources occupy substantial floor space when the beam lines are laid out and appropriate shielding is installed. Thus, there continues to be significant development of nonsynchrotron sources for microscopy and microlithography applications. In the past decade, development has shifted away from e-beam excited fluorescent sources and toward plasma sources in order to achieve the necessary high radiating efficiency.
Time-resolved fluorescence from normal and atherosclerotic arteries
Authors: Pradhan Asima , Liu C. H. , Das B. B. , Alfano R. R. , Deckelbaum L. , O'Brien K. M. , Stetz M. L. , Scott J. J.
Published: February 2023

Fluorescence lifetimes of coronary arteries with normal intima, white atherosclerotic plaque, and calcified atherosclerotic plaque were measured in the wavelength range beyond 360 nm and in the bandwidths centered on 390 nm, 450 nm, and 500 nm. The fluorescence profiles were fitted to a double exponential with a fast and a slow component. At wavelengths above 360 nm, arteries with white atherosclerotic plaque appear to have a fast component (113 31 ps) that is shorter than that of normal arteries (126 17 ps) or arteries with calcified plaque (133 35 ps). In the band centered at 390 nm, the fast components of normal arteries (148 41 ps) and arteries with white plaque (112 141 ps) are slower than that of calcified plaque arteries (81 56 ps). In the 450 nm band, both arteries with white plaque and calcified plaque arteries have fast components that are faster (x ps) than that of normal arteries. The slow component of arteries with white plaque in the 390 nm band is greater (3 0.4 ps) than that of normal arteries or arteries with calcified plaque (2.2 0.2 ps, 2.6 0.2 ps). These preliminary results indicate that arteries with white plaque, arteries with calcified plaque, and normal arteries may be distinguished from one another.
Chaotic crystals
Authors: Lawandy N. M. , Adler C. L.
Published: February 2023

Work on deterministic instabilities and chaos over the past decade has largely focused on spatiotemporal behavior. In connection with fluids and, more recently, laser dynamics, spatial structures have played an increasingly important role. In this work we show that standing light waves, which can exert periodic radiation forces on dielectric particles, can be used to produce complex structures in colloidal crystals of polystyrene spheres. The crystals are formed by a strong repulsive Debye-potential interaction in ultraclean aqueous environments having particle densities on the order of 1014/cmA Quasielastic laser-light scattering measurements show that the crystals assume a face-centered cubic lattice with a (111) plane separation of several thousand angstroms. The injection of a standing optical wave produces a second periodic potential, which in one-dimensional results in the well-studied circle mapping for the position of the nth ball: Xn + 1 = Xn + a + sin 2kxn, where a is the unperturbed lattice spacing and is proportional to light intensity. We have studied the phenomenon in two-dimensional and three-dimensional systems and will show that the light forces available from cw lasers can produce "chaotic crystals," as well as other solutions, for certain winding numbers and intensities.
Chaos of a V-channeled substrate inner-stripe semiconductor laser under opto electronic feedback
Authors: Wang X. L. , Ih C. S.
Published: February 2023

Chaotic behavior and the route to chaos in various laser systems are the subjects of intense studies in view of both their scientific interest and their potential applications. Self sustained oscillations may represent one form of a quite general complex dynamic behavior related to the appearance of optical turbulence or optical chaos. According to the properties of nonlinear dynamic systems, one would expect such pulsation to be replaced by a sequence of oscillations that culminate in deterministic chaos. In case of semiconductor lasers, the chaos has only been experimentally achieved either by an external cavity mirror reflection or by periodic modulation. We report what is, to our knowledge, the first observation of chaotic behaviors of a V-channeled substrate inner-stripe (VSIS) laser brought about by optoelectronic feedback. The laser is self-pulsating within the range of 24 GHz under dc bias. The self-pulsating rf signal was received by a high-speed photodiode, amplified, and partially fed back to the laser driver. By varying the strength of the feedback, we brought the self-pulsation into the chaotic regime. Observed spectra and accompanying waveforms show a route to chaos through various frequency combinations. Experimental results and calculations will be presented.
Spatial phase effects in pattern masking
Authors: Bowen Richard W. , Wilson Hugh R.
Published: February 2023

Masking of bandpass-test stimuli by cosine gratings is known to be selective for spatial frequency and orientation, thus indicating a cortical component the phenomenon. Here we report that within 200 ms following the onset of a cosine mask, a phase-dependent masking effect emerges: Threshold elevation for a 33 ms D6 pattern (sixth derivative of a Gaussian) is greater on a light bar (0 phase) than on a dark bar (180 phase). A plausible hypothesis is that this phase effect results from a pointwise retinal luminance-adaptation process. To test this, we compared threshold elevations on cosine masks with those produced by uniform fields at the same luminance levels as the peak and trough of the cosine mask. The bright uniform mask produced a small threshold elevation, but the dark uniform mask actually facilitated detection of the test pattern. Comparable results were obtained with both positive and negative D6 test patterns. The effect of spatial phase can therefore be explained by a mode] consisting of a pointwise retinal luminance-adaptation process, followed by a phase-independent cortical contrast-adaptation process that is orientation- and spatial-frequency selective.
Simultaneous discrimination of the spatial frequency and contrast of gratings
Authors: Greenlee Mark W. , Thomas James P.
Published: February 2023

We explored the human observer's ability to discriminate changes in the spatial frequency or contrast of Gaussian-truncated sine-wave gratings. Two gratings, differing either in their spatial frequency or in contrast, were presented in two temporal intervals. In a 4-altemative forced-choice (4-AFC) paradigm, subjects responded first by determining whether spatial frequency or contrast differed and second by determining in which interval the grating with the higher parametric value was presented. We compare these results to those found when subjects performed a simple discrimination task in which spatial frequency and contrast discrimination were measured in separate 2IFC runs. The Weber fraction (f/f, q/c) was measured as a function of pedestal contrast (0.020.32) and stimulus bandwidth (0.252.0 octaves) at photopic (270 cd/m2) luminance levels. Independent of the type of task, the Weber fraction decreased (1) with increasing stimulus contrast and (2) with decreasing stimulus bandwidth. Discrimination thresholds were a factor of two or more lower when either frequency or contrast was discriminated alone compared to when they were discriminated conjointly. An analysis of the role of suprathreshold stimulus uncertainty in these results will be presented.
How many samples are needed for precise localization?
Authors: Levi Dennis M. , Klein Stanley A. , Wang Hong
Published: February 2023

Perfect reconstruction of a sine-wave grating requires at least two samples per cycle in order to determine the amplitude and phase. We have measured vernier acuity for discretely sampled sine-wave gratings. The stimulus was a pair of abutting horizontal sine-wave gratings, and the observers' task was to judge the direction of vertical offset between the two gratings. Each horizontal sample was 0.6 ft. (18.3 cm) wide and the luminance between samples was fixed at the mean luminance. The equally spaced samples were lined up in the two gratings, but the position of the gratings was random with respect to the samples. We found that reducing the number of discrete samples comprising the gratings has two effects: (1) grating visibility is reduced, and (2) vernier thresholds increase. When the visibility of the grating is held constant (by increasing the physical contrast) as the number of samples is reduced over a wide range of grating spatial frequencies, vernier thresholds are unimpaired with four samples per cycle and are only slightly impaired with three samples. Our results suggest that the human observer acts almost like an ideal observer in spatial localization tasks.
The dependence of Vernier acuity on blur
Authors: Klein Stanley A. , Carney Thom , Levi Dennis M.
Published: February 2023

Vernier acuity is less degraded by blur than is resolution acuity. However, unlike resolution, the amount of degradation of vernier acuity depends on the contrast of the stimulus and the type of blur. We used both two-dimensional, and one-dimensional Gaussian blur. The following results were found. At low contrast, vernier acuity has a weak dependence on the type of blur and begins to be degraded at blur standard deviations as low as 1 min. At high contrast the degradation does not occur until 23 min, and in the two-dimensional case the falloff of vernier acuity with blur becomes quite steep with an exponent of 1.5. We explored the shapes of the threshold-versus-blur curves for three different strategies of fixing contrast: (1) fix the peak contrast independent of blur, (2) fix the "energy" (%min) so that the peak contrast is inversely proportional to blur, and (3) fix contrast in threshold units so that contrast increases with blur. Each of these procedures is appropriate to different situations, and each leads to different notions about how vernier acuity depends upon blur.
Vernier acuity for sinusoidal gratings: effect of the number of cycles
Authors: Gu Yuanchao , Legge Gordon E.
Published: February 2023

Efficiency, as defined by signal-detection theory, is a measure of the performance of a real observer relative to the performance of the ideal observer. Sine-wave grating detection is most efficient for patterns containing one to three cycles, suggesting receptive fields of a fairly broad spatial extent. Studies of vernier acuity, on the other hand, suggest a narrow range of spatial interaction in a direction perpendicular to the target lines. The purpose of the present study was to measure efficiency for vernier alignment as a function of the number of cycles in sinusoidal targets and to infer the spatial extent of the underlying mechanisms. We measured efficiency by obtaining vernier thresholds for Gaussian-enveloped sinusoidal targets in the presence of one-dimensional static luminance noise. The grating's width, defined as the distance between 1/e points of the Gaussian envelope, varied from 0.1 to 4 cycles. Efficiency showed the same dependence on the number of cycles for 0.5 and .2c/deg gratings. Maximum efficiencies of 70% were obtained when the Gaussian envelope width was in the range of 0.250.5 cycles. Outside this range, efficiency declined. These results indicate that the visual computation of spatial alignment can be efficient but relies on spatially narrow (and spatial-frequency broad) mechanisms.
Crossing of two ultrashort solitons in an optical fiber
Authors: Hong B. J. , Yang C. C.
Published: February 2023

Crossing may occur when two short pulses of different central frequencies are propagated in an optical fiber. In the anomalous-dispersion range, the pulse with the higher frequency propagates faster and may catch up with the one with lower frequency. During crossing, the two pulses interact through cross-phase modulation. For picosecond-range solitons, the effects of cross-phase modulation in the first-half crossing cancel those in the second-half, so that the individual solitons remain unchanged after a complete crossing. However, for femtosecond-range or ultrashort solitons, individual solitons change owing to higher-order dispersion, shock effects and Raman scattering. In particular, Raman scattering results in energy redistribution between the two solitons. The peak gain of the Raman spectrum in optical fibers is at 440/cm frequency shift, corresponding to a delay time of 75 fs in the Raman response function. Hence, when any two femtosecond-range solitons are separated by a lime period shorter than 75 fs, Raman scattering occurs. In our research, the dependence of the energy redistribution on several input parameters, such as frequency separation, temporal separation, relative phase, and relative intensity, are investigated. A modified beam-propagation method is used for numerical study.
Far-infrared Raman lasers with metallic mesh mirrors
Authors: Koppang Paul , Zhu Wen-sen , Izatt Jerald R.
Published: February 2023

Continuously tunable laser emission in the 701200 m region can be produced by pumping various isotopic species of NH3, CH3F, and CH3Cl with sufficient infrared pump power so that stimulated Raman scattering is the dominant gain mechanism. Typically, the far-infrared (FIR) medium is contained in a mirrorless, dielectric waveguide cavity with an IR transmitting window on the input end and a quartz or TPX window on the FIR output end. We have fabricated and tested metallic mesh mirrors on quartz and TPX substances in both inductive and capacitive configurations. Use of these mirrors, as well as free-standing meshes, in NH3 and CH3F FIR Raman lasers has produced a substantial increase in the output intensity and some improvement in the continuity of the spectral coverage provided by these lasers.
Transient thermal focal length in multipulse laser rods
Authors: Farrukh Usamah O. , Brackett Vincent G. , Brockman Phillip
Published: February 2023

Transient thermal focal length calculations of side-pumped Nd:YAG and Ti:sap- phire laser rods indicate an appreciable deviation from standard steady-state average-power calculations using Koechner's well-known formulation.1 When started from an inactive condition, the thermal focal length of a Nd:YAG rod (length, 7.6 cm; radius, 0.25 cm) stabilized at about 3 s. However, the steady-state calculations indicated a higher focusing power of about 15%30% at frequencies of 610 Hz. The pump pulse duration was 100 s with a 10 J input. The thermal focal length varied from 28 m at 100 ms to 4.4 m at steady state. Other examples of thermal-focal-length calculations for end-pumped configurations are provided. The present model for temperature distribution in laser rods2 can be applied to both side-pumped and end-pumped situations. The model was used to estimate the effect of surface cooling on the thermal focal length. Koechner's formulation, by comparison, is for a fixed surface temperature.
Locking range of general coupled lasers
Authors: Shakir Sami A. , Erkkila John H.
Published: February 2023

A general model for coupled lasers is established. The coupled system is characterized by two parameters: the self-feedback, S, and the mutual coupling, M. The coupled system is analyzed as one composite system and the eigenvalues of the system are calculated. We show that the frequency locking range, δVR, is given by where L is the average length of the individual resonators. M and S are calculated for mode-matched Fabry-Perot type resonators and for adjoint coupled unstable resonators. Diffraction effects are taken into account and frequency locking range is estimated for a strip unstable resonator and a three-dimensional unstable resonator.
Subnatural spontaneous emission spectra in driven atoms: the V-model
Authors: Narducci L. M. , Ru P. , Tredicce J. R. , Oppo G. L. , Scully M. O.
Published: February 2023

The coherent coupling of atomic levels under the action of driving electromagnetic fields is known to create unusual and interesting effects, such as the well-known population trapping phenomenon and subnatural line narrowing. In this paper we discuss two alternative configurations of three-level atoms, the cascade model and the inverted-V (lambda) model, in an effort to provide alternative options for experimental tests. In both cases we focus on the fluorescent emission spectrum of an atom driven by two resonant fields and on the absorption spectrum of a weak probe passing through a gas in such a driven system. Subnatural line narrowing can be obtained from the cascade system but not from the lambda system. The lambda system, however, is characterized by strong population trapping, so that it is not suitable for fluorescence studies (except out of resonance) because of its strongly reduced emission rate. The absorption spectrum of a weak probe displays gain features under high-field conditions which suggest that useful amplification of a probe or laser-like emission should be possible over appropriate frequency ranges. We give a physical interpretation of the origin of the gain and explain why that in the case of a lambda system, but not a cascade system, steady-state population inversion can be obtained between both excited states relative to the lowest state of the atom. We also discuss the effect of Doppler broadening on the predicted emission and absorption lineshapes.
Emission and absorption spectra in cascade and lambda models of driven atoms
Authors: Doss H. , Manka A. , Ru P. , Narducci L. M. , Oppo G. L. , Scully M. O.
Published: February 2023

The coherent coupling of atomic levels under the action of driving electromagnetic fields is known to create unusual and interesting effects, such as the well-known population trapping phenomenon and subnatural line narrowing. In this paper we discuss two alternative configurations of three-level atoms, the cascade model and the inverted-V (lambda) model, in an effort to provide alternative options for experimental tests. In both cases we focus on the fluorescent emission spectrum of atom driven by two resonant fields and on the absorption spectrum of a weak probe passing through a gas in such a driven system. Subnatural line narrowing can be obtained from the cascade system but not from the lambda system. The lambda system, however, is characterized by strong population trapping so that it is not suitable for fluorescence studies (except out of resonance) because of its strongly reduced emission rate. The absorption spectrum of a weak probe displays gain features under high field conditions which suggest that useful amplification of a probe or laser-like emission should be possible over appropriate frequency ranges. We give a physical interpretation of the origin of the gain and explain why that in the case of a lambda system, but not a cascade system, steady-state population inversion can be obtained between both excited states relative to the lowest state of the atom. We also discuss the effect of Doppler broadening on the predicted emission and absorption lineshapes.
Formation of Ge E’ centers in photosensitive optical fibers
Authors: Simmons Kelly D. , LaRochelle Sophie , Griscom David L. , Mizrahi Victor , Stegeman G. I.
Published: February 2023

In recent years much work has been done to determine the cause of photosensitive grating effects in germanium-doped silica fibers. Past research has suggested a link between the formation of defect centers and the occurrence of photosensitivity in these materials. For the first time, we observe a correlation between photosensitivity and the Ge E' center, characterized by a singly charged oxygen vacancy, as measured with electron-spin resonance (ESR) techniques. We irradiated a length of single-mode optical fiber (n = 0.028, c = 438 nm) with argon laser radiation in the usual manner. A grating was written in the fiber, and optical transmission and reflection data were recorded. Subsequently, the fiber end was dipped in index-matching fluid, prohibiting back reflection, and the sample was re-exposed with a high-power Ar+ laser beam for an extended time to induce sufficient defects to be detectable with ESR. Analysis of optical data at a wavelength of 488 nm showed a 50% decrease in fiber transmission after 3.5 s. ESR analysis of the same sample showed the Ge E' defect concentration more than doubled over that of an identical, but unexposed, fiber. We will discuss the significance of these results in the context of the current theory of two-photon absorption to these E' centers.
Q-switched Nd lasers for femtosecond dye laser pumping
Authors: Agnesi A. , Diels J.-C. , Di Trapani P. , Kubecek V. , Marek J. , Reali G. , Yeh C. Y.
Published: February 2023

A two-photon absorbing semiconductor inserted in the cavity of a Nd Q-switched mode-locked lasers is shown to act simultaneously as energy limiter and pulse compressor. The latter action is due to self defocusing by the carriers generated during the pulse. With a proper positioning of an intracavity aperture, maximum losses occur at the tail of the pulse, resulting in pulse compression. Extracavity measurements have shown that the compression factor can be as large as 50%. The energy limiting effect ensures optimum operation for the intracavity saturable absorber. As a result, the pulse train is stabilized and stretched out to include at least 100 pulses of nearly equal energy and duration (10 ps for the Nd:YAG laser). The reproducibility of the stabilized pulses is better than 1.5 from shot to shot. Typically, the evolution towards steady state in a fs laser requires about 100 round-trips. With an energy/pulse of 10 J, and at least 100 pulses of identical energy, the new source has unique characteristics for pumping fs dye lasers.
Double passage imaging through a random phase screen
Authors: Solomon C. J. , Mavroidis T. , Dainty J. C.
Published: February 2023

We consider imaging a deterministic object situated in the far-field of a random screen. When the object is illuminated and viewed through the same random screen, the long-exposure average intensity spectrum is shown to contain diffraction-limited information on the object Fourier modulus. This occurs because a certain fraction of the light propagating to the object and back is in phase and always gives rise to constructive interference in the image plane. The effect is physically closely related to the backscatter enhancement of light scattered by dense random media or rough surfaces.
Binary gratings for broadband infrared antireflection coatings
Authors: Moharam M. G.
Published: February 2023

Broadband, durable, damage-resistant antireflection coatings have been the subject of a great deal of interest for a variety of applications. The most promising technique for efficient broadband reduction of reflection is the step-down or "inhomogeneous film" method. Design tools are available for normal incidence. Conventional antireflection coatings are prone to damage and are not adequate because the required refractive indices of the layers are not available. Ultrahigh-frequency binary gratings have been shown to exhibit very low reflectivity. The etched grating has a durable substrate, and any refractive index can be synthesized by adjusting the duty cycle. In this work, it is shown that multilevel binary gratings exhibit broadband, low reflectivity in the IR spectrum for any angle of incidence and for both TE and TM polarizations. A design procedure is developed for oblique incidence and for TE and TM polarizations. A comparison between the antireflection properties of two- and three-level binary gratings is presented. Twodimensional binary gratings are shown to offer further reduction in reflectivity for unpolarized light.
Spatial binary multiplication by photon echoes
Authors: Manganaris D. , Kim M. K.
Published: February 2023

The phase conjugation property of backward-stimulated photon echo (BSE) has numerous potential applications in optical data storage and processing. We demonstrate mixed binary multiplication of spatially encoded bit patterns, by taking advantage of the fact that the geometry of BSE is analogous to that of conventional holography or four-wave mixing of nonlinear optics, where an object (data) and a reference (write) beams interfere to create a grating inside the medium, and another reference (read) beam is diffracted from that grating. When all three input beams contain structures, the output pattern is the convolution and correlation of the input patterns, which, with certain arrangements and interpretation, can be used for multiplication of binary numbers. The experiments were done by using a 477.8 nm transition of praseodymium ion-doped in single-crystal lanthanum trifluoride.
Space-time pulse propagation for optical computing
Authors: Marathay A. S.
Published: February 2023

Beginning with the free-space scalar wave equation, a Green's function formulation of diffraction is presented in space and time. Depending on the choice of the modified Green's function, the formulation requires specification of the field and is time derivative or specification of its space derivative in the aperture plane. Of interest in optical computing is a space-time pulse with an identifiable carrier frequency, v0. For this special case, if the logarithmic time derivative of the pulse envelope is much smaller than 2πv0, then the diffraction formula may be approximated by an integral in which the time derivative of the pulse envelope does not appear explicitly. Two examples are presented. In the first example, the pulse is assumed to have a factored form with a Gaussian spatial envelope multiplied by a Gaussian temporal envelope. The condition of validity for the approximation dictates a distance (4/π)λ0(v0/Δv)2 over which pulse factorization is maintained. Beyond this distance the spatial and temporal envelopes influence each other significantly. For a picosecond pulse the distance is about 25 cm, with λ0 = 500 nm; for a nanosecond pulse it is 106 times larger. In the second example, temporal distortion after passage through a grating is studied. For a grating of 103 lines, a narrow pulse broadens to about 3 ps. The approximate formula enables explicit calculation of the pulse's space-time structure.
An acousto-optic modulator-based analog-to-digital converter
Authors: Li Y. , Zhang Y. , Eichmann G.
Published: February 2023

Many optical signal processing and computing applications require the availability of a fast analog-to-digital (A/D) converter. As a basic building block, an electro-optic directional coupler was used for an optical A/D converter implementation. Previously we have shown that an optical theta-modulation effect could be used for an optical A/D conversion application. In this presentation, an acousto-optic theta-modulation A/D conversion architecture is proposed. An acoustooptic device is used as an optical FM modulator that maps input voltage to an output beam deflection angle. To cast the deflected optical intensity its binary format, a prefabricated intensity-coded A/D conversion mask is used. By means of a commercially available GaP acousto-optic deflector, a 1 new acousto-optic, theta-modulation A/D device in various optical signal processing and computing applications will be addressed.
Comparison of host materials for diode-pumped solid-state lasers
Authors: Caffey David P. , Hyslop Douglas A. , Utano Richard A. , Allik Thomas H.
Published: February 2023

The one micron laser performance of Neodymium-doped YLF, LYAG, YAG, GSGG, GGG, BZAG, and YSAG have been studied using diode array side pumping. The 2-D diode pump arrays fabricated by MDESC and SDL have 808 nm efficiencies of greater than 40%, total bandwidth of less than 3 nm in a 200 µs pulse, and emit at up to 1.8 kW/cm2.4, 5, 10 and 20 bar stacks of one centimeter AlGaAs laser bars were close-coupled to 6.35 mm diameter by 15 mm long laser rods to achieve maximum optical coupling efficiency. Materials were pumped from one side in a double pass configuration, and then pumped from two sides to determine scalability. Small signal gain was measured in the amplifier configuration. The array center wavelength was temperature-tuned to vary absorption efficiency and energy deposition within the rods. Spectroscopic and laser results are analyzed and compared.
Diode-pumped, electro-optically tuned, single-frequency Nd:YAG laser
Authors: Henion S. R. , Schulz P. A.
Published: February 2023

A diode-pumped Nd:YAG laser running in a single longitudinal and transverse mode tunes at a rate of 25 MHz/ns limited by the electronics. Voltage to frequency linearity tests demonstrated 1% nonlinearity for 500- MHz frequency chirp in 570 ns.
A novel coupling technique for end pumping solid-state lasers using 1-cm linear-aperture high-power laser diode bars
Authors: Lynn J. G. , Stoneman R. C. , Esterowitz L.
Published: February 2023

We present a simple and inexpensive optical system that can focus more than 80% of the output power of a laser diode bar with a 1 cm aperture into a spot smaller than 300µm in diameter for end pumping of solid-state lasers. The system uses off-the-shelf components and is particularly suitable for three- level laser systems.
Diode pumping of solid-state lasers with nonimaging optics: a theoretical study
Authors: Koshel R. John , Walmsley I. A.
Published: February 2023

We have calculated the gain distribution within a circular absorbing medium that is pumped by a large-area planar-diode array by means of a nonimaging cavity design. The nonimaging cavity directs the light to the absorber, so there is negligible loss of pump light; a uniform gain distribution is achievable over the absorber cross-section. The gain uniformity is much better than current side- pumped geometries, and this leads to a higher-quality mode in the output beam. The nonimaging pump cavity requires a single reflecting surface. Therefore, problems due to alignment of the system should be reduced, and, in addition, the design is easily scalable. This design is compared to an elliptical (imaging) pump cavity design and to current diode pumping designs. We attempt to define concentration ratio,1 or effective étendue, for a nonplanar absorber. The concentration ratio is used as a figure of merit in comparisons between various nonimaging and imaging pump cavity designs.
Design of pure phase gratings by generalized projections
Authors: Stark Henry , Catino William , LoCicero Joseph L.
Published: February 2023

We address the problem of designing pure phase gratings that generate prescribed light intensities in the far field. The method of generalized projections is used to find a solution consistent with prior constraints and available data. Although the method of generalized projections is known to occasionally converge to erroneous solutions, such solutions were not observed in this analysis. Several reconstructed light intensities are furnished and the quality of the reconstruction is discussed.
Absence of the facilitation effect in older adults
Authors: Beard Bettina L. , Ginsburg Arthur P. , Stacy Marnie L.
Published: February 2023

Considerable research has been devoted to measurements of contrast threshold in older adults. These studies have revealed significant differences between young and older observers in contrast sensitivity at high spatial frequencies. Normal age-related changes in suprathreshold contrast perception have also been reported. With a contrast discrimination paradigm, it has been found that the facilitation effect commonly reported at 0.008 standard contrast level in young observers is not present for older participants. The current investigation tested whether a facilitation in contrast discrimination ability for older adults is totally absent or is merely shifted to a higher contrast level. The subjects were 10 young and 10 older individuals. All observers had corrected visual acuity of at least 20/20 for the test distance and revealed no signs of visual pathology. Results indicate that the facilitation effect is entirely absent in this sample of older observers. The results are discussed in terms of existing theories of the facilitation effect, incorporating the effects of added noise and slower temporal processing in the visual systems of older adults.
How do saccades aid visual pattern recognition?
Authors: He Peiyuan
Published: February 2023

It has been shown that saccades play an important role in visual tasks, but they do not simply improve resolution of the display. To understand their role, I studied not only the way in which texture perception benefits from saccades, but also the patterns of saccades that are most beneficial. The displays (55) consisted of 1515 randomly oriented T's and L's. The T's formed a random polygonal shape (target) in the central 24 of the display. Eye movements were recorded while subjects estimated both the size and the shape of the target and were under instructions to (1) SCAN the display with saccades or (2) maintain the line of sight in the center without saccades (STAY). The results are as follows: (1) SCAN performance improved with increasing display duration; (2) STAY performance did not improve with increasing display duration longer than 2 s; (3) scanning improved performance for 5 s durations; (4) scanning improved the ability to detect texture patterns; (5) retinal image transients, created by flickering (2 Hz) or jumping (0.5 Hz, 15 ft. [4.57 m] peak-to-peak amplitude) the display, improved performance somewhat for size discrimination but not for shape discrimination; (6) boundary scanning was more beneficial for discrimination than other scanning patterns.
Detection of vertical and circular gratings in noise
Authors: Näsänen Risto , Rovamo Jyrki , Osmoviita Kari
Published: February 2023

Contrast-detection thresholds were measured for vertical and circular cosine gratings with and without two-dimensional static noise by means of a two-alternative forced-choice method. The stimuli were produced on a high-resolution computer monitor with computer graphics. The increase in the contrast energy thresholds produced by noise was equal for circular and vertical gratings for all spatial frequencies and grating areas studied. The increase in energy threshold was a single function of relative grating area and was independent of spatial frequency. The relative grating area is described by the number of square-cycles which is given by Af2 where A is the grating area and f is the spatial frequency. Noise produced the same increase in energy threshold between 1 and 64 square-cycles. Above 64 square-cycles the increase in energy threshold became progressively larger. The results show that stimuli with highly different spectral properties are equally detectable: A change in stimulus orientation bandwidth (from vertical to circular gratings) does not affect the detection performance of vision. Moreover, the detection performance of vision is independent of relative spatial-frequency bandwidth (inversely proportional to relative stimulus size) over a broad range. These results support the view that in vision signals are not detected by detectors with fixed filtering properties but that the visual system adaptively uses knowledge about the properties of the stimulus.
The illusory effect of a one-dimensional sinusoidal grating on the shape of the circular two-dimensional Gaussian window
Authors: Osmoviita Kari , Rovamo Jyrki
Published: February 2023

When the contrast of a clearly suprathreshold, one-dimensional, sinusoidal grating was weighted with a circular, two-dimensional Gaussian window, the shape of the grating was found to be elliptical: It was flattened in the direction of grating bars. We studied this shape illusion by measuring how much the spatial dimensions of the Gaussian window along or across the bars had to be adjusted in order to make the perceived shape circular. Our experiments showed that the grating appeared circular when the diameter of the two-dimensional Gaussian window along the bars was about 1.25 times the diameter across the bars. The illusion was found to be independent of spatial frequency, grating area, and viewing distance. Neither was it affected by peripheral viewing at eccentricities over the 020 tested. The magnitude of the illusion was the same for horizontal, vertical, and oblique gratings and in monocular and binocular vision. However, the illusion disappeared when the number of grating bars was small or the grating contrast was near the threshold.
The phenomenon of shadow stereopsis: basis and applications
Authors: Puerta Antonio Medina
Published: February 2023

Shadow stereopsis is defined as the psychophysical phenomenon by which stereoscopic depth is perceived on the basis of shadows alone. It is impossible to judge the stereoscopic role of shadows by observing natural images because shadows are cast, and located, by edges that are themselves powerful stimuli for stereoscopic depth. Edges and shadows are inseparable. We isolate the role of shadows in stereo vision by means of a special technique that allows us to take stereo pictures in which all disparities, except those arising from shadows, are removed. These special stereo pairs (shadowgrams) present the same monocular view to each eye but preserve shadows as they would be seen by each eye in a natural, stereoscopic situation. The importance of shadows in stereo vision can be judged by observation of the presented shadowgrams. Shadows are a robust and powerful cue for depth perception. The same technique used to demonstrate the phenomenon of shadow stereopsis can be used to acquire anaglyph shadowgrams with a single camera and a very simple set-up consisting of a pair of light sources of complementary colors. We show many shadowgrams taken this way to corroborate the phenomenon and to demonstrate the potential of the technique.