bluuebunny/crossref_metadata_2025 huggingface dataset:
Programming a digital optical cellular image processor
Authors: Huang Kung-Shiuh , Jenkins B. K. , Sawchuk A. A.
Published: February 2023

A single-instruction machine is generally considered to be impractical in electronics because it may lead to excessively complex programs. In digital optical cellular image processors (DOCIPs), the single-instruction machine is well suited to the system architecture. The reason for this is that the optical parallelism and global interconnection capabilities of DOCIP also contribute to parallel optical control signal flow. We show that two DOCIP architectures, DOCIP array and DOCIP hypercube, have a simple organization, low cell complexity, and (with external memory) the ability to simulate random access machines and Turing machines. Both of them have a simple control structure: (1) a single instruction that includes fetch, execute, store, and pipelines the three fundamental operations of binary image algebra1; (2) a single control level that has only one higher control level for interpretation between program and data. The DOCIP array, a nearest-neighbor connected cellular array, has an extremely simple organization due to its O(1) interconnectivity. The DOCIP hypercube increases the interconnectivity to O(log N) and combines features of conventional cellular logic and conventional hypercube architectures for 2-D computational cells. The programming and instruction set of the DOCIP array and the DOCIP hypercube are illustrated and compared.
Spectroscopy of ionic clusters
Authors: Kung C.-Y. , Kennedy Richard A. , Dolson David A. , Miller Terry A.
Published: February 2023

Ions can be created in seeded supersonic free jets by crossing the expansion with a high-energy short-wavelength laser. Examples include non-resonant ionization of aromatic molecules by excimer lasers and resonantly enhanced multiphoton ionization of small molecules by a tunable dye laser. If the ions are created sufficiently close to the nozzle, they are clustered by neutral atoms and molecules. Ionic clusters have been studied by laser-induced fluorescence and time-of-flight mass spectrometry.
Do size-tuned mechanisms help discount the illumination?
Authors: Thomas James P. , Gille Jennifer L.
Published: February 2023

The luminance pattern presented to the eye is the product of separate patterns of illumination and object reflectance. In many situations, the viewer is at least moderately successful in factoring this product into its components and separately perceiving the pattern of illumination and the pattern of object reflectance. Approximate lightness constancy is one aspect of this ability. One necessary condition is that illumination and reflectance have different spatial distributions, and this fact suggests that size-tuned mechanisms may play an important role. The nature of any such role is complicated by the fact that, in the space domain, the illumination and reflectance patterns are multiplied. Consequently, in the frequency domain, where the selectivities of tuned mechanisms are most conveniently defined, the spectra of the illumination and reflectance patterns are convolved with one another.
Visible and infrared continua in gases
Authors: Corkum P. B. , Rolland Claude
Published: February 2023

This paper describes the onset of self-focusing as well as the spectral and spatial properties of an ultrashort pulse that has passed through a self-focused region.
Gas-phase supercontinuum generation with a 160-fs excimer amplifier system
Authors: Glownia J. H. , Misewich J. , Sorokin P. P.
Published: February 2023

In recent papers we have described apparatus capable of simultaneously generating both intense subpicosecond UV (308-248.5-nm) excitation pulses and subpicosecond continua for probing photoexcited molecules via broadband absorption spectroscopy. Both UV (450-230-nm) and IR (2.2-2.7-μm) continua have thus far been produced through the focusing of 160-fs, 308-nm pulses into various gaseous media. A method of upconverting the IR continuum to the visible for ease of detection has also been demonstrated. We first describe these developments and then discuss the results of a time-resolved experiment using some of this new apparatus. This particular experiment combines subpicosecond 248.5-nm excitation with subpjcosecond IR continuum probing to measure the

B
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internal conversion rate in 1,4-diazabicyclo[2.2.2]octane (DABCO) vapor.
Continuum spectroscopy using optical pulses of 6-fs duration
Authors: Fork R. L. , Brito Cruz C. H. , Becker P. C. , Shank C. V.
Published: February 2023

A principal problem in obtaining optical pulses with bandwidths approximating that of the visible spectrum and durations approaching the transform limit has been the uncompensated cubic phase distortion of pulses compressed by grating pairs. We describe the use of combined prism and grating sequences to compensate not only the quadratic, but also the cubic, phase distortion of optical pulses frequency broadened in an optical fiber. We obtain pulses of 6-fs duration which can be used on a routine basis for time-resolved spectroscopy. We have used these pulses to study the dynamics of spectral hole burning in organic dye molecules and in semiconductor materials. Examples are given of recent work on molecules, such as cresyl violet and Nile blue, and on semi-conductor materials, such as GaAs. We have also used these 6-fs pulses to examine the optical Stark effect in organic dye molecules such as rhodamine B and rhodamine 6G. We obtain, in particular, direct observations of the dynamic shift of the rhodamine B absorption spectrum on a femtosecond time scale. We also use the intensity dependence of these shifts as an alternate means of measuring the molecular dipole moment.
Self-phase modulation and spectral broadening of ultrashort pulses in a nonlinear medium
Authors: Yang Guozhen , Shen Y. R.
Published: February 2023

Self-phase modulation of light in a nonlinear medium is a well-known phenomenon resulting from the intensity dependence of refractive indices. Its occurrence in space leads to self-focusing or defocusing, while its occurrence in time yields spectral broadening. With ultrashort laser pulses, the spectral broadening can be so strong as to form a continuum extending from IR to near UV. Such a broadening has been used extensively as a continuum source in the studies of ultrafast phenomena, but its basic understanding is not yet complete.
Diffraction of light in a cascade linear system: general transfer function
Authors: Lakshminarayanan Vasudevan , Calvo Maria Luisa
Published: February 2023

We present a systematic procedure for calculating the general transfer function of a cascaded linear optical system working under the Fresnel regime. The validity of neglecting the quadratic phase factors is also discussed. For the case of inhomogeneous optical devices with Gaussian profiles, explicit expressions for the transfer functions are calculated through specific Gaussian integrals.
Guided waves for the characterization of multilayer coatings
Authors: Flory F. , Hu Y. , Pelletier E.
Published: February 2023

Starting with the equations of guided waves in a quarterwave multilayer stack (mirror or Fabry-Perot filter), we can calculate the synchronous angles associated with the different TE and TM modes. A comparison to experimental results allows an accurate characterization of the stack. A good approach to this study is to consider the classical case of two alternate materials and, by assuming that layers are rigorously quarterwave, to first determine refractive indices of the two materials. These values can be obtained with good accuracy by a conjoined use of the available TE and TM modes. A more extensive analysis can be made by studying an electric-field distribution for the different modes. In some cases, this can lead to a selective study of some particular layers of the stack. With some examples, we show how this can display anomalies in the stack structure. We find, particularly, that the refractive index of a layer depends on its position in the stack. The influence of the errors on the thicknesses of the layers can be distinguished from those due to index variations.
Molecular dynamics of laser-induced desorption
Authors: Tully John C.
Published: February 2023

Molecular dynamics techniques have been developed to simulate accurately laser-induced chemistry at surfaces with the full complexity of multidimensional interactions. Equations of motion are integrated explicitly for a slab of about fifty atoms with additional adsorbate molecules. Stochastic boundary conditions incorporate energy flow to the remaining bulk atoms and permit transient heating effects to be included correctly. Infrared laser excitation is described by an applied oscillatory external force that drives the dipole moment of the system. The simultations reveal directly the extent of disequilibrium achieved by short-pulse laser excitation. Predictions are made of situations where selective (nonthermal) desorption may be possible.
Saccadic suppression of energy-based motion
Authors: Shioiri Satoshi , Cavanagh Patrick
Published: February 2023

Previous studies have shown that small displacements that are easily detected in normal viewing become invisible if they occur during a saccade. However, it is not clear what process is suppressed during a saccade; energy-based (short-range) motion, form-based (long-range) motion, and perception of position change can all contribute to the displacement detection. We measured motion detection during a saccade using a random-dot stimulus presented within a stationary frame. This stimulus has no identifiable form whose displacement can be noticed either directly or by activation of the form-based motion process. Therefore, the impression of motion produced by the displacement of this stimulus must be mediated by the energy-based motion process alone. Saccadic suppression was found for the stimuli when they were displaced a small distance (less than Dmax) either in spatial coordinates or in retinal coordinates. This result implies that the energy-based motion process is suppressed during the saccade, and since this process is able to signal motion for stimuli with ISIs longer than the duration of saccades in our experiment (mean of 60 ms), it appears to be suppressed across the saccade as well.
Monte Carlo evaluation of the propagation properties of single-mode dielectric waveguides
Authors: Troudet Terry , Hawkins Raymond J.
Published: February 2023

A Monte Carlo path integral approach to the treatment of propagation problems in integrated optics is presented. Unlike the many methods that work very well for slab waveguides but require orders of magnitude more computer time for channel waveguides, Monte Carlo simulation requires a comparatively modest increase (typically a factor of 2-4) in computer time to treat a channel waveguide to the same degree of accuracy as a slab. We have used Monte Carlo simulation to obtain the propagation constants of the fundamental and first-order modes of a number of dielectric waveguide structures. Excellent agreement has been found in 1-D and 2-D with the fundamental mode propagation constants of the analytically soluble refractive-index profiles involving 1/cosh2. For realistic air/Ti:LiNbO3 diffused waveguides, excellent predictions are obtained for the propagation constant of the fundamental mode. The Monte Carlo evaluation of the first-order mode requires more time, and predictions are obtained with a fair degree of accuracy. These preliminary results are very encouraging for future use of Monte Carlo techniques to describe the optical characteristics of waveguide structures with arbitrary refractive-index profiles.
Optimized excitation of surface plasmons in metal films
Authors: Kou F. Y. , Tamir T.
Published: February 2023

When exciting surface plasmon waves along thin metal films by means of a light beam, the procedure often used is to adjust the incidence parameters to minimize the reflected field. Such incidence conditions are assumed to maximize the power coupled into the plasmon field, but they imply that the incoming flux is matched to a complex zero of the reflectance function. However, maximum intensity is achieved for the plasmon field if the incident flux is matched to a complex pole of the reflectance function rather than to a complex zero. This general conclusion agrees with recently reported results1 for plasmons in iron films. We found that the difference between the incidence angles for the two (zero or pole) situations can be substantial; this difference is strongly dependent on the configuration used to support the plasmon wave, and, in each geometry, it is generally larger for metals with greater damping loss.
Surface plasmon coupling in highly asymmetric corrugated thin silver films
Authors: Gruhlke R. W. , Hall Dennis G.
Published: February 2023

Surface plasmon cross-coupling has been reported recently1 as a radiative-decay mechanism for molecules near a corrugated thin metal film. To demonstrate this, corrugated photoresist-silver air samples having the same silver film thickness, but different grating periods were fabricated. Since the cross-coupling process is wavelength-dependent, coupling between surface plasmons at opposite sides of the silver film was demonstrated to occur at different wavelengths for samples having different grating periods. In the present experiments, samples having the same grating period but different silver thicknesses were made. The wavelength at which cross-coupling occurs was observed to shift 40 nm toward longer wavelengths as the silver film thickness is decreased. To determine the origin of this shift, the dispersion curve of the silver-photoresist interface surface plasmon was measured and was found to shift toward a larger wave number as the silver film thickness was decreased.
Optical characterization of gas etching processes
Authors: Palik E. D. , Glembocki O. J. , McMarr P.
Published: February 2023

We use optical emission to study chemically assisted ion-beam etching. Ar-ion and Cl2-gas beams are used separately and together to etch Al and Si. The atomic and electronic optical emission is measured with a multichannel analyzer spectroscopic system. The relationship between optical emission and etch rate is examined. We observe surface roughening caused by Ar sputtering of Al which is minimized by the addition of small amounts of O2 to the etching chamber. This is ascribed to the smoothing out of ion-channeling effects by the amorphous oxide which grows on the surface and is itself sputtered off.1 O2 pressure determines the oxidation rate, while Ar pressure determines the sputter rate. As these two processes compete, the intensity of neutral Al (398.3 nm) varies, depending on whether the Ar ions are sputtering Al from Ai or Al2O3. Similar results are obtained for neutral Si (288.1 nm) for Si and SiO2. The addition of the Cl2 beam begins to alter the emission characteristics, since in addition to sputtering we expect chemical etching to form volatile Al and Si chlorides.
Characterization of gold/electrolyte interface by spectroscopic ellipsometry
Authors: Kim S. Y. , Vedam K.
Published: February 2023

In situ spectroscopic ellipsometric measurements have been carried out on a gold electrode in an electrolyte under a dc electric field. An intermediate layer which begins to form just above the threshold potential of the oxidation of gold has been detected and characterized in terms of its optical properties and thickness. It is confirmed with the aid of computer simulation that the effect of the redistribution of the ions in liquid and the electrons in gold electrode on the ellipsometric parameters Δ and ψ has a minimal effect compared with the experimental results. Even though the intermediate layer at the S/L interface revealed some properties which are characteristics of metals, a simple model based on the modulation of gold under a dc electric field turned out to be unable to explain quantitatively the experimentally observed changes of δΔ and δψ.
Cortical mechanisms of color vision
Authors: Lennie Peter
Published: February 2023

In macaque monkey three distinct pathways relay information from the lateral geniculate nucleus (LGN) to the striate cortex. Two parvocellular pathways contain neurons with chromatically opponent receptive fields: one receives opposed inputs from R cones and G cones; the other receives inputs from B cones opposed by some combined signal from R and G cones. A distinctive feature of the R–G neurons (much the largest group in the LGN) is that they respond well to chromatic patterns of low spatial frequency and achromatic patterns of high spatial frequency. Magnocellular neurons receive inputs from all three classes of cone.
Stability analysis of actively mode-locked lasers
Authors: Morin M. , Piche Michel , Tremblay Real
Published: February 2023

AM mode-locking is very sensitive to the loss modulation frequency. The laser emits trains of mode-locked pulses when the duration of a round trip through the cavity is matched to the period of the modulator. However, very little detuning from the optimum frequency results in instabilities and relaxation oscillations. A stability analysis has been conducted within the framework of the Kuizenga-Siegman model.1 According to this model, the stationary field created by the mode-locking process is a chirpless Gaussian pulse whose spectrum is centered on the peak of the homogeneous line. The pulse duration can be analytically predicted in terms of the laser parameters. The stability of this equilibrium solution was evaluated analytically as well as numerically regarding the shown that the correlation bandwidth obtained by pumping rate was assumed, and inversion decay was taken into account. Contrary to what has been done until now,2 our work considers the effects of nonzero chirp and carrier frequency perturbations on the process. It is shown that these can make the chirpless solution unstable for positive detuning. A stable solution with a sizable chirp has also been obtained.
Supermode theory of coupled unstable resonators
Authors: Shakir Sami A. , Erkkila John H.
Published: February 2023

Laser coupling is one method for developing high-brightness output from individual laser modules. To achieve good quality, high-brightness power extraction from an array of coupled lasers, the outcoupled beams should be mutually coherent and ideally equal in amplitude and in phase at the far field. An important practical consideration in the operation of an array is that the peak far-field intensity should be insensitive to fluctuations in the resonator lengths and the length of the coupling paths. For multimode systems, these requirements should be satisfied for all the lasing modes of the system.
Phase-locking of 2-D laser arrays by diffractional coupling
Authors: Piche Michel , Cantin Daniel , Man George Heck
Published: February 2023

Phase-locking of semiconductor laser arrays can be achieved1 through evanescent wave coupling or Y junctions. More recently,2 a hollow bore ridge waveguide geometry has been used for phase-locking of CO2 lasers. We study the mode structure developed by 2-D laser arrays where phase-locking results from diffractional coupling. Three types of configuration are investigated: rectangular arrays of plane-parallel resonators with circular apertures; concentric arrays of resonators with circular apertures; and arrays of concentric curved surfaces of identical area.
Diffraction by truncated-Gaussian apertures: an experimental study
Authors: Horng Jing Shyang , Li Yajun
Published: February 2023

Rotating film processes are used to produce the apodization Gaussian filters of the Gaussian Fresnel G = 0.5, 1, and 5. The focal shift theory as presented in Ref. 1 has been verified by using these filters in different beam-truncation conditions. Results, presented in intensity charts and photographs, are compared to theoretical predictions along the axis and in various planes parallel to the geometrical focal plane. Encircled energy is also measured by placing circular pinholes of different radii in front of the detector which is centered on the axis. The results are similar to those reported in Ref. 2. The principal maximum value of the encircled energy is not found in the geometrical focal plane; its position changes abruptly when the radius of the pinhole is varied.
Pseudospin approach to the dynamics and squeezing of SU(2) and SU(1,1) coherent states
Authors: Aravind P. K.
Published: February 2023

The semiclassical Dicke model and the ideal parametric amplifier are described by Hamiltonians linear in the SU(2) and SU( 1,1) group generators, respectively. We use the usual pseudospin vector as well as its SU(1,1) analog1 to give a unified description of the dynamics of the coherent states in these models. The pseudospin dynamics is governed by a precession (or pseudoprecession) equation, hence simple geometrical arguments can be used to infer the evolution of the coherent state parameters. To study fluctuations and squeezing we introduce a correlation tensor which is a higher-order generalization of the pseudospin vector. The correlation tensor obeys a generalized precession equation which can be factored into scalar, vector, and quadrupole parts and solved exactly by application of the Cayley-Hamilton theorem. Our approach to the calculation of squeezing and fluctuations provides an alternative to the more traditional approach employing disentangling theorems. It also provides an attractive and closely parallel geometrical description of coherent state evolution and squeezing in the two models.
Modulation instability in an extended nonlinear Schrodinger equation
Authors: Potasek M. J.
Published: February 2023

Modulation instability is investigated in an extended nonlinear Schrodinger equation. This effect results in the instability of an initially cw optical beam. Here the effects of modulation instability in an optical fiber are investigated. The instability manifests itself through the appearance of new frequencies in the spectrum which give rise to a periodic temporal behavior of the optical beam. Besides the first-order dispersion and intensity-dependent index of refraction, higher-order dispersion terms, the time variation of the intensity of the slowly varying envelope of the electromagnetic field and retardation effects are considered. It is found that higher-order odd dispersion terms do not influence the frequency of the modulation instability. The time derivative of the intensity of the optical beam can restrict the parameters over which modulation instability occurs. Furthermore, the nonlinear retardation effect significantly alters the modulation instability.
Acceleration of electrons by the ponderomotive force of a CO2 laser
Authors: Xiong W. , Yergeau F. , Chin S. L. , Lavigne Pierre
Published: February 2023

In a vacuum chamber pumped down to 1 × 10−8 Torr, Xe gas was leaked at a rate so that the Xe pressure inside the vacuum chamber was 1 × 10−6 Torr. An intense 1-ns CO2 laser was used to ionize the gas. The ejected electrons were detected with a retarding potential energy spectrometer. On the energy spectrum there are two peaks. One starts at a few electron volts and centers around 50 eV. The other starts at 230 and centers around 350 eV. Referring to the saturation intensity measured by Yergeau et al.1 the peak at 350 eV can be explained with the acceleration of electrons created in the ionization of Xe by the ponderomotive force. The low-energy peak at 50 eV was attributed to a similar acceleration process of electrons created in the ionization of some impurities. This speculation was confirmed by repeating the same experiment with Xe of higher purity.
Ion-assisted deposition of Al2O3 thin films
Authors: Targove J. D. , Messerly M. J. , Macleod H. A.
Published: February 2023

Aluminum oxide films have been deposited by ion-assisted deposition. The films were electron beam evaporated at a chamber temperature of 100°C with argon and/or oxygen ion bombardment. The optical constants of these films have been measured in the visible and UV: the refractive index of the films has been increased by the bombardment (to 1.70 at 350 nm), while the extinction coefficients are essentially unchanged (2 × 10−4 at 350 nm). Infrared transmittance measurements in the 3-μm water band show that even an unbombarded Al2O3 film with low refractive index (1.61 at 350 nm) contains virtually no water, indicating a very high packing density. We confirmed this result by observing no air-to-vacuum shift for the same film in a specially equipped spectrophotometer. All the Al2O3 films deposited in this experiment clearly approach unity packing density whether bombarded or not.
From perimeter chart to retina: projection in a schematic eye
Authors: Dagnelie Gislin , Massof Robert W.
Published: February 2023

Several transformations play a role if one wants to relate the metric of visual field defects to that of the underlying retinal abnormality: (1) Most perimeters currently used present stimuli inside a half-spherical bowl with the tested eye in the center and map the visual field in planar polar coordinates, leading to a planimetric distortion. (2) Ray tracing instead of paraxial geometric optics needs to be used to relate extraocular and intraocular light paths. (3) Although the retina is reasonably well represented by a sphere, the center of this sphere does not coincide with that of the perimeter bowl. If perimetry charts are used to estimate areas of diseased retina, or the position of a lesion, these transformations should be taken into account. This has been recognized: Drasdo and Fowler1 mapped the optical and geometric properties of the schematic eye, and Kirkham and Meyer2 described the transformation from perimeter to planar chart. Overall relationships of eccentricities and areas in field chart and retina are shown. Tables can be derived that limit the inaccuracy of most measurements in real eyes to less than a few percent.
Test of a vector model for the combined effect of color and luminance contrast in figure-ground segregation
Authors: Sternheim Charles E. , Penn Richard P.
Published: February 2023

A single border between two adjacent colored fields of light of equal luminance becomes more visible when luminance contrast is introduced and is less likely to fade on steady fixation. Measurements of the visibility of a border of this kind are consistent with a model that combines chromatic contrast and luminance contrast as orthogonal vectors.1 In the experiments described here a test of this model was performed using a stimulus pattern that consisted of a thin rectangular figure centered on a larger rectangular ground.
Real-time joint transform image correlation by partially coherent readout Illumination
Authors: Javidi Bahram
Published: February 2023

A real-time joint Fourier transform image correlator that uses partially coherent readout illumination to perform signal detection in complex amplitude is described. The interference between the Fourier transforms of input images is obtained by coherent light. However, the correlation signal is produced by partially coherent illumination which is used to read out the Fourier transforms' interference intensity from the output of the spatial light modulator (liquid crystal image transducer). The advantage of this technique is the reduction in the spatial phase variations in the output wavefront of the image transducer. Such nonuniformities may arise from nonflatness and mismatch of various output layers in some devices that can degrade the performance of the correlator.
Model for pulse amplification by a gaseous laser amplifier
Authors: Boley C. D. , Warner B. E.
Published: February 2023

We have developed a computational model for pulse amplification by a pulsed electric discharge laser amplifier. We applied the model to the copper vapor system, for which the oscillator has previously been modeled on a 0-D level1 and a 1-D level.2 The laser intensity transport equations are set up on a ray and differenced with respect to the longitudinal coordinate. Amplified spontaneous emission is handled similarly. Rate equations for the atomic levels are set up in each longitudinal cell. The motion of the atoms is negligible on the nanosecond time scales of interest. The entire system of equations is advanced in time by a standard mathematical package. Working with a selection of input pulse shapes and energies, we obtained predictions for the amplified signal as a function of time.
Uses of ultrashort pulses and measurement techniques in laser medicine
Authors: Fujimoto J. G.
Published: February 2023

Recent developments in the generation of ultrashort laser pulses, including advances in picosecond and femtosecond laser generation and measurement techniques, permit the investigation of a wide variety of laser medical phenomena. Ultrashort pulse durations allow not only the measurement of transient phenomena but also enable the investigation of laser tissue interaction at extremely high peak laser intensities. We describe studies of laser tissue interaction using high-intensity femtosecond laser pulses. Studies of femtosecond laser injury in the rabbit retina are discussed. The retina provides a well-studied model system for the investigation of laser tissue effects. In contrast to longer pulse durations, the femtosecond pulses permit the investigation of tissue effects at intensities in excess of 1011 W/cm2 with reduced thermal or acoustic effects. Injury thresholds and mechanisms are discussed. As an example of nonlinear laser tissue interaction, we describe the use of high-intensity femtosecond pulses for producing ablation of the cornea. These results demonstrate ablation in a system which is nominally transparent to the laser wavelength. In addition, we discuss applications of time-resolved measurement techniques for the investigation of laser medical and laser tissue interaction. As an example, we describe optical ranging using femtosecond pulses. This technique has been demonstrated for measuring the epidermal structure of human skin as well as the anterior eye and corneal profile alterations produced by laser ablation. Finally, the use of time-resolved spectroscopic measurement techniques and applications to the measurement of transient excited state dynamics and photophysical processes are discussed.
Infrared laser ablation of tissue
Authors: Walsh Joseph T. , Hruza George J. , Flotte Thomas J. , Anderson R. Rox , Deutsch Thomas F.
Published: February 2023

Precise removal of soft tissues and bone is often necessary in surgery. Clinical cw CO2 lasers are ineffective in cutting bone, yet efficiently ablate soft tissue. However, there is typically a 300–1000-jum zone of thermal damage left at the cut edge which impedes healing. A simple model predicts that short pulses of strongly absorbed laser radiation should efficiently ablate tissue and minimize residual damage. Studies were performed on guinea pig skin with pulsed CO2 lasers (λ = 10.6 μm), the residual damage could be minimized to 50 μm when the pulse duration was less than the calculated thermal relaxation time for a layer one optical absorption length thick. At the peak of the water absorption curve, 2.9 μm, tissue absorbs 10 times more strongly than at 10.6 μm, and even less residual damage is possible; 100-ns Q-switched Er:YAG laser pulses (λ = 2.9 μm) ablated both soft tissues and bone; the zone of thermal damage was 5-10 μm. To compare healing, lesions were created in epilated guinea pig skin with Er:YAG and CO2 lasers and a scalpel. Er:YAG laser wounds and scalpel wounds healed quickly and with the same minimal scarring, CO2 laser wounds healed slowly with more scarring.
Picosecond and femtosecond pulse generation near 1000 nm from a frequency-doubled Nd:YAG-pumped cw dye laser
Authors: Dawson Martin D. , Boggess Thomas F. , Smirl Arthur L.
Published: February 2023

Efficient cw dye laser operation has recently been achieved from 875 to 1084 nm by pumping two new styryl derivatives—dyes Styryl 13 (S13) and Styryl 14 (S14)—with an Ar-ion laser.1 We report synchronous mode-locking of an S14-based dye laser medium in a simple prism-tuned linear cavity. This allowed the generation of picosecond (~2-ps) pulses to 1030 nm when pumped by a frequency-doubled mode-locked cw Nd:YAG laser. This is believed to be the first report of green-pumped synchronously mode-locked cw dye laser operation beyond 1 μm. The identification of suitable polymethine cyanine dye saturable absorbers has allowed hybrid synchronously pumped passive mode-locking of the dye laser. For this we used the full dispersion-compensated linear cavity arrangement with which 55-280-fs pulses have been generated in the 560-840-nm range.2 Pulses as short as 228 and 263 fs were produced in this manner in previously uncovered spectral regions near 975 and 900 nm, respectively. These pulses should provide immediate use in, for example, investigations of the photorefractive effect in GaAs on a picosecond and subpicosecond time scale.
Femtosecond dynamics of charged solitons in trans-polyacetylene
Authors: Rothberg L. , Jedju T. M. , Etemad S. , Baker G. L. , Townsend P. D.
Published: February 2023

Recently, directly photogenerated charged solitons as predicted by Su and Schrieffer have been observed.1 Here we report studies of their formation and decay dynamics using transient absorption with 0.35-ps pulses. Above band gap (2.1 eV) radiation creates intrachain electron–hole pairs which degenerate into charged soliton pairs. These are probed using synchronized pulses tunable from 2.5 to 5.5 μm which are generated by mixing amplified femtosecond pulses with white light continuum generated in water.2 The charged soliton pairs are shown to recombine geminately in ~0.5 ps with power-law decay dynamics characteristic of 1-D diffusion. At high pump fluences, saturation of the charged soliton absorption can be attributed to a volume filling mechanism. Varying the probe wavelength allows us to observe femtosecond spectral relaxation of the charged solitons and to interpret this in terms of conformational relaxation. Work on oriented Durham trans-polyacetylene has enabled us to probe the dynamics following interchain electron-hole pair creation as well.
Subpicosecond pulse evolution within a cavity-dumped hybrid mode-locked dye laser
Authors: Davis Lloyd M.
Published: February 2023

The evolution of the intracavity pulse after cavity dumping a subpicosecond synchronously pumped hybrid mode-locked dye laser was experimentally studied by measuring the spectra of individual intracavity pulses after an increasing number of round trips using a nanosecond gateable optical multichannel analyzer. The contribution of amplified spontaneous emission was inferred by comparing the spectra with those of the UV obtained by frequency doubling the pulses. Spontaneous emission has been predicted1 to be essential for the continued operation of synchronously pumped lasers with cavity lengths detuned longer than the pump laser. These experiments show the change in the proportion of spontaneous emission with increasing round trips and the dependence on the detuning and pump power. The pulse-to-pulse reproducibility of the output also depends on operating parameters and is demonstrated by collecting spectra of individual pulses. Methods of obtaining the pulse intensity vs time from the spectral intensity are reviewed. When the time-averaged autocorrelation function has exponential sides considerable pulse-to-pulse fluctuations are observed, whereas more repeatable pulses are obtained with the laser operating just above threshold and with a Gaussian-shaped autocorrelation function.
Electron-beam deposition system for soft x-ray multilayer synthesis
Authors: Hayden Cindy J. , Smith D. J.
Published: February 2023

Electron-beam evaporation of multilayers for the soft x-ray region has had extensive support by the work of Spiller.1 Many of these principles have been incorporated in a uniquely designed deposition chamber at the University of Rochester. The deposition rate and thickness control are measured in situ by a soft x-ray reflectivity monitor and a quartz crystal oscillator. Substrate positioning and photon detection are stepper motor controlled through one axis of rotation. This enables the reflectometer to be fine-tuned during deposition as well as provide postdeposition evaluation. A modified Henke tube with various targets serves as the characteristic line source for the reflectometer. Filters and a single-channel analyzer suppress unwanted signals. The system is designed to monitor optically multilayer periods in excess of 20 Å.
Ion-assisted deposition of thermally evaporated Ag films
Authors: Hwangbo C. K. , Lingg L. J. , Lehan J. P. , Targove J. D. , Jacobson Michael R. , Macleod H. Angus , Makous J. L.
Published: February 2023

Optical constants of thin Ag films (~50 nm thick) deposited by thermal evaporation on prisms were measured at 632.8 nm by the attenuated total reflection method. The effects of Ar-ion energy and current on the refractive index and extinction coefficient of IAD Ag films are presented. Their electrical resistivity, measured with a four-point probe, is also discussed. Finally, the results of humidity tests are described.
Finite element method for solving the Fredholm-II equation with continuous kernels and its use in laser physics
Authors: Zhang Guozhu , Wu Baishi
Published: February 2023

This paper puts forward the finite element method for solving the Fredholm-II equation with continuous kernels. The numerical results of low-order modes obtained by applying this method to the practical problems of optical resonators with infinite strip plane mirrors, inclined strip plane mirrors, and circular mirrors are the same as those obtained using Fox and Li's method.1 By using this method, we obtained some unpublished field distributions and diffraction loss curves of many high-order modes.
Spectral modulation by controlled source correlations
Authors: Gamliel Avshalom , Wolf Emil
Published: February 2023

It has recently been shown that correlations between source fluctuations throughout the source region can lead to frequency shifts of spectral lines.1,2 We consider the more general problem of modifying the spectrum of the emitted radiation by making a suitable choice of the degree of spatial coherence of the source. To illustrate the potential of this method we consider a simple configuration of two small sources emitting light with identical spectra. We demonstrate that some source correlations can generate multiple spectral lines from a single spectral line of either a Gaussian or Lorentzian profile. Spectral line-shape parameters such as width, amplitude, center frequency, and functional form can also be controlled.
Light scattering by Gaussian rough surfaces
Authors: Dainty J. C. , Friberg A. T. , Kim M.-J.
Published: February 2023

We present an experimental study of electromagnetic wave scattering from rough surfaces. The height profiles of the surfaces approximate a Gaussian process with a Gaussian autocorrelation function and are characterized by two parameters, the Rayleigh parameter R = 4πσ
h
/λ and the correlation scale a = 2πξ/λ, where σ
h
is the rms surface height and ξ is the 1/e correlation length. Three classes of surface are studied at two different wavelengths, 0.63 and 10.6 μm. The first class has low slopes (R/a << 1) and long correlation lengths (a >> 1). The second also has low slopes but short correlation lengths (a ≈ 1). The third class has high slopes (R/a ≈ 1) and shows the phenomenon of enhanced backscattering.1 Comparisons with theory are made where possible.
Raman study of lattice modes in the high-temperature superconductor Y-Ba-Cu-O
Authors: Rosen H. , Macfarlane R. M. , Seki H. , Engler E. M. , Strand T. S.
Published: February 2023

Raman spectra of high-temperature superconducting materials comprised of Y-Ba-Cu-O compounds are reported. These spectra show numerous lattice modes which are attributed to both the superconducting phase YBa2Cu3O7 and also impurity phases of BaCuO2 and Y2BaCuO5. Ten Raman active modes are observed in the superconducting material with frequencies of 153, 217, 291, 309, 335, 441, 493, 507, 601, and 640 cm–1. The temperature dependence of these spectra has been measured, and the 337-cn–1 mode shows anomalous behavior. Above T
c
it increases in frequency on cooling, but below T
c
its frequency shift changes sign as the mode begins to soften. This very interesting anomaly may suggest the possibility of larger changes in the phonon spectra occurring at nonzero wave vectors. Raman spectroscopy has been shown to be a sensitive probe of both the structure of the superconducting phase and of impurity phases in the material.
Principal-component analysis of human cone spectra
Authors: Young Richard A.
Published: February 2023

Principal-component analysis was used to find an optimum set of orthonormal basis vectors that could span the chromatic space of cone spectra in the human eye. The Smith and Pokorny cone spectra1 were used, weighted by the percentages of the various cone pigment types in the monkey fovea and raised to the 1/3 power to account for response compression. The eigenvectors of these cone spectra were then orthogonally rotated into the macaque monkey lateral geniculate nucleus (LGN) eigenvectors2 using the optimum least-squares rotation matrix. The second (biphasic) vector had to be reflected as well as rotated. The correlations of the rotated human cone vectors with the monkey LGN vectors were 0.98, 0.99, and 0.92, indicating close correspondence between the principal axes of human cones and monkey LGN cells. Indeed, since all relative distances and angles between points in a space are preserved by an orthogonal rotation, it can be concluded that human tricone chromatic space and monkey LGN cell chromatic space are formally congruent.
Generalization of the acoustooptic time-and-space integrating architecture for real-time SAR processing
Authors: Haney Michael W. , Psaltis Demetri
Published: February 2023

The time-and-space integrating acoustooptic architecture for real-time synthetic aperture radar (SAR) processing was described previously.1 Techniques have recently been outlined which extend the applicability of this approach to SAR data collection geometries in which a high degree of flexibility is needed.2 We detail these hybrid techniques with particular emphasis on spotlight mode geometry. Electronic programmability empowers the hybrid architecture to compensate on-the-fly for the anomalous effects of range walk, range/azimuth coupling, and spurious or programmed changes in the parameters of the radar/target geometry. Interpolation of the focused image data occurs in the optical domain, thereby maintaining high resolution without a large power-hungry electronic processor. The features of this approach suggest that it is well matched to those real-time programmable SAR processing applications in which size and power are severely constrained.
Array illuminator based on the phase contrast method
Authors: Schwider Johannes
Published: February 2023

An array illuminator is proposed using a phase grating in the entrance plane. The grating is illuminated uniformly and converted into the amplitude image with the help of a phase contrast setup. The conversion is brought about by a proper choice of the grating phase structure in combination with a suitable phase shift of the zero-order diffraction in the phase contrast setup. The result is a light distribution of bright areas surrounded by darkness. Since the phase grating is periodic, only one elementary cell of this grating need be considered to get the necessary condition for the phase delays in the grating and phase platelet. The compression ratio p defined as the quotient of the bright area to the cell area is limited to 1 > p ⩾ 1/4 due to the underlying two-beam interference phenomenon. Cancellation in the dark surrounding is total only in this compression range. If the total cancellation in the dark area is given up, arbitrary compression ratios can be attained although the energy concentration is limited to a factor of ~5.
Color appearance in central and peripheral retina
Authors: Abramov Israel , Gordon James
Published: February 2023

Cone and ganglion cell densities fall rapidly with eccentricity from the fovea. But the decline is not symmetrical: cell densities decrease more rapidly on the temporal retina. We examined the implications of this spatial organization for color vision. Spectral lights were presented along the horizontal meridian from 40° nasal to 40° temporal. Several stimulus sizes were used to identify the minimal size for best color vision at each retinal locus. Color vision was assessed by means of hue and saturation scaling. Multidimensional scaling was then used to derive uniform appearance diagrams from the data. These diagrams illustrate the color spaces associated with each size-location combination; we also derived discrimination functions from them. As expected from retinal anatomy, peripheral stimuli had to be progressively enlarged to maintain a full range of saturated hues; this enlargement had to be greater in temporal retina to produce comparable sensations to those from the corresponding nasal locations. Small stimuli produced restricted color spaces akin to those of tritanlike deficits. Variations in cone destiny alone cannot account for the changes in color vision across the visual field.
Review of the LLNL soft x-ray laser program
Authors: Trebes J. , Barbee T. , Brown S. , Albrecht-Buehler G. , Campbell M. , Ceglio N. , Eder D. , Gaines D. , Hawryluk A. , Keane C. , London R. , MacGowan B. , Matthews D. , Maxon S. , Pinkel D.
Published: February 2023

A review of the Lawrence Livermore National Laboratory's soft x-ray laser program at the Nova laser facility is presented. The long-term goal of this program is to develop and utilize a fully coherent gigawatt power level sub-44-Å laser.
What is new in soft x-ray lasers at Princeton?
Authors: Suckewer S.
Published: February 2023

A short review is given of recent progress in soft x-ray development in a magnetically confined recombining plasma column. We also present the experimental arrangement, performance testing, and the first experimental results from a powerful picosecond laser system.
Guided waves on highly nonlinear substrates
Authors: Wood Van E. , Kenan Richard P.
Published: February 2023

Analytical descriptions are presented of properties of TE guided modes of a linear planar wave-guiding layer on a thick nonlinear substrate characterized by a dielectric permittivity containing terms quartic as well as quadratic in the magnitude of the electric field of the propagating optical wave. Conditions for and characteristics of interface guided modes are also presented. Both initially focusing and initially defocusing situations are considered. Useful dimensionless parameters for compactly presenting the power-dependent mode spectra are described. These results, which generalize those in Ref. 1, have several applications including (1) providing an analytical description of the first stages of departure from nonlinearity in saturable media, (2) modeling situations in which free carriers produced by two-photon absorption contribute to the optical susceptibility, and (3) determining the range of validity of commonly used approximations for TM modes on Kerrlike nonlinear substrates.
Model of a nonlinear directional coupler in GaAs
Authors: Gibbons Wayne M. , Sarid Dror
Published: February 2023

In recent years, much attention has been given to the all-optical nonlinear directional coupler (NLDC), where the transfer of optical power between two coupled channel waveguides is controlled by the power carried in the modes. One should use a physically realistic model for the nonlinearities of the waveguide material when designing optimized NLDCs. Previous designs assumed a Kerr nonlinearity in the core or cladding of the NLDC channel waveguides. In most Kerr media, high optical densities are required to control the output of the NLDC. However, semiconductor materials with resonant electronic nonlinearities exhibit the highest known nonthermal optical nonlinearities and show promise for all-optical device fabrication.