bluuebunny/crossref_metadata_2025 huggingface dataset:
Facial recognition with peripheral viewing
Authors: Loshin David S. , Jose Randy , McGrath Meg
Published: February 2023

Low-vision patients, especially those with acuity losses associated with central field defects, often complain about the inability to recognize faces. It is important in the provision of low-vision care to be able to identify the various parameters (visual skills) involved in the facial recognition task. This investigation tried to isolate the visual parameter of peripheral viewing as it relates to the facial recognition. Normal subjects were presented photographs of faces at 15° nasal to the fovea. The subject’s task was to identify the face from a group of thirty photographs viewed foveally. The results of the study were subjects who were not familiar with the faces identified an average of 12 out of 20 (62.2% ± 3.2%) faces correctly where subjects who were familiar with the faces identified an average of 17 out of 20 (85. ± 2.4%) faces correctly. This indicates that if the low-vision patient is familiar with the face other parameters than peripheral viewing are responsible for the facial recognition problem.
Optics of the ocular telephoto system for patients with macular degeneration
Authors: Koester Charles J. , Donn Anthony
Published: February 2023

Magnifications of 2-4× can be achieved by utilizing a strong negative intraocular lens together with a positive spectacle lens.1 The advantage of this system over conventional telescopic low-vision aids is that for a given magnification the ocular telephoto system provides a significantly larger field of view. For near tasks such as reading, the system can provide greater magnification at a given working distance than can simple magnifiers or magnifying spectacle lenses. Potential problems are discussed, including IOL decentration and patient disorientation due to disparate magnifications in the two eyes. The magnification or the field of view can be simulated before surgery by using a strong negative contact lens together with a positive spectacle lens. The type of patient most likely to be helped by the ocular telephoto system has stable macular disease, substantially reduced visual acuity, difficulty utilizing conventional low-vision aids, and a strong desire to perform near tasks such as reading or computer terminal work.
Photocount statistics of broadband squeezed states
Authors: Caves Carlton M.
Published: February 2023

Consider a photodetector characterized by two bandwidths: (i) an optical bandwidth over which it has nearly unity quantum efficiency and (ii) a much smaller electronic bandwidth, the bandwidth over which it produces beats between different frequencies. Direct onto the photodetector a light beam which is the superposition of two parts: (i) an intense, nearly monochromatic carrier wave at some carrier frequency and (ii) a squeezed state with zero mean field, which is squeezed in the broadband (multimode) sense (correlation between frequencies located symmetrically above and below the carrier frequency) within some bandwidth about the carrier. The standard statements are that, if the squeezed quadrature is in phase with the carrier (amplitude-modulation squeezing), one will see sub-Poissonian photocount statistics, and if the squeezed quadrature is out of phase with the carrier (phase-modulation squeezing), one will see super-Poissonian statistics. Bandwidth considerations impact these statements in the following way: the only part of the squeezing that is relevant for decreasing or increasing the counting noise is that part that lies within an electronic bandwidth of the carrier frequency; to see the maximum decrease or increase, one must squeeze over the entire electronic bandwidth. These conclusions require modification if the carrier wave is not sufficiently intense.
Higher-order squeezing of an optical field
Authors: Hong C. K. , Mandel L.
Published: February 2023

The concept of squeezing, which generally implies that one quadrature
component of an optical field has measured fluctuations below the
vacuum limit, is generalized to higher moments of even order.
Higher-order squeezing is encountered in many of the nonlinear
processes that generate second-order squeezing. It is shown that the
field produced in degenerate parametric downconversion is squeezed to
all even orders and is intrinsically squeezed to orders 2,6,10….
Higher-order squeezing also shows up in second harmonic generation and
in resonance fluorescence from an atom. However, in those cases there
is no intrinsic squeezing beyond the second order, although a strong
second-order squeezing effect is manifest in the higher-order moments
of the field.
Thermal expansion of Polytran sodium chloride from 60 to 300 K
Authors: Browder James Steve , Ballard Stanley S.
Published: February 2023

High resolution measurements of the expansivity of Polytran NaCl were made with a three-terminal capacitance dilatometer1 in the temperature range from 60 K to room temperature. The sample, a short rod of length 1.27 cm (0.500 in.), was supplied by the Harshaw Chemical Co. Our values for the coefficients of linear thermal expansion for Polytran NaCl are compared with those for single-crystalline NaCl determined by other investigations. Also, earlier measurements on Polytran BaF2 and KCl (which were carried out in our laboratory) are reviewed.2
Three-dimensional radiative transfer in the diffusion approximation
Authors: Zardecki A. , Gerstl S. A. W. , Dekinder R. E.
Published: February 2023

A diffusion-based 3-D transport code DIF3D is employed to model the spatial distribution of radiative energy density due to a collection of volumetric, isotropic sources. The results are presented in the form of 3-D isosurface plots, which give the surfaces of constant energy density. It is shown that as the detector sensitivity decreases, the individual sources cannot be spatially distinguished, thus leading to a false target effect. A comparison of DIF3D with the discrete-ordinates finite-element code ONEDANT1 indicates that the diffusion approximation holds for a single-scattering albedo of 0.97 or higher. The significance of the optical depth and asymmetry parameters is also investigated.
Mie scattering sum rules
Authors: Box M. A. , Attard P.
Published: February 2023

Recently, Nussenzveig and Wiscombe, using complex angular momentum theory, derived an asymptotic expansion for the Mie theory extinction efficiency factor Q. From the relation between Q and the forward scattering amplitude S, plus the known analyticity properties of S (which is a complex function), we have derived the corresponding asymptotic expansion for S. If we then assume that, subject only to analyticity constraints, this result may be extended into the lower half of the complex plane, we may perform appropriate contour integrals around a semicircle of large radius. Since S has no poles in the lower half of the complex plane, we are thus able to find the value of desired integrals along the real axis–sum rules. In the case of a fixed real refractive index, we find explicit results for the three integrals: We have evaluated these integrals numerically for two different real refractive indices and found excellent agreement, indicating that the validity of our asymptotic expansion for S extends into the complex plane and also holds in the mean.
Visual acuity threshold as a function of size of the blind spot
Authors: Mizusawa Kiyoe , Sakaki Tamotsu
Published: February 2023

In our previous research it was found that the perceived apparent movement between two points across the blind spot was faster than that between two points located above the blind spot, when distance between two points was kept constant. Furthermore, a high correlation between perceived movement and the size of blind spot was obtained (r = 0.87 with p = 0.05). Thus, a larger blind spot contributed to the perception of faster apparent movement when the distance between two spots remained constant. The present research examines the effects of size of blind spot on visual acuity threshold. Eight graduate students whose size of blind spots differed from each other served as subjects. A homemade perimeter presented Vernier acuity stimuli. A 2 × 2 factorial analysis was used. The first two factors in the analysis were vertical height and horizontal width of the blind spot; the second two factors were two points across the blind spot and upper retinal two points which were 2 cm above the blind spot. The acuity thresholds were measured by the method of limits. A high correlation between visual acuity threshold and the size of blind spot was obtained (r = 0.67 with p = 0.05) with the horizontal width. However, the visual acuity threshold was not significantly influenced by the vertical height of the blind spot.
Raman line shape in semiconductor microcrystals
Authors: Campbell I. H. , Fauchet P. M.
Published: February 2023

Microcrystal sizes below 100 Å can in principle be easily measured from an analysis of the Raman-Stokes line shape. Richter et al.1 have shown that the confinement of phonons inside silicon grains of spherical shape leads to downshifting, broadening, and asymmetrization of the Raman line. In their model, phonons with finite wave vectors contribute to the line through an uncertainty principle argument. For the phonon envelope function, Richter selected a Gaussian whose magnitude is one-half at the grain boundary. We have now calculated the Stokes line for various microcrystalline semi-conductors as a function of grain size, assuming different envelope functions, and in particular that predicted by a simple theory. In silicon, we obtain significant departures from the size which can be deduced from Richter’s calculations. This may explain the often observed discrepancy between Raman and TEM results.2 In addition, we have calculated the Stokes line for various shapes, including columnar grains. These calculations are compared to measurements that we performed in various microcrystalline films having spherical or columnar grains. Finally, we discuss the influence of surface phonons, intragrain defects, and grain boundary material.
Observation of band-filling optical nonlinearity in a CdSxSe1−x doped glass
Authors: Olbright G. , Peyghambarian N. , Gibbs Hyatt M.
Published: February 2023

The origin of optical nonlinearity in a semiconductor-doped glass at room temperature is studied using a pump-probe experimental technique. Glasses doped with semiconductor crystallites which are commercially known as sharp-cut color filters provide very interesting media for nonlinear signal processing because of their rapid response time (due to short carrier diffusion time) and large optical nonlinearity.1 The output of a nitrogen laser is used to pump a tunable dye laser (pump) and a dye cell (probe continuum). The pump-induced changes in transmission of the broadband probe are recorded with a combination of a spectrometer and an optical multichannel analyzer. A 100-Å blue shift of the band edge is observed in a selenium ruby glass (100–1000-Å microcrystallites of CdS1−
x
embedded in a borosilicate glass matrix, x = 0.7–0.9) with 4 μJ of the narrow bandwidth pump tuned to 5100 Å (band edge ≃ 5200 Å). Using a high energy continuum alone (2-μJ energy), a blue shift of ≃ 175 Å is observed. The blue shift of the band edge cannot arise from a pump-induced thermal effect that would instead bring about a red shift. The band-edge blue shift is evidence for efficient band filling by injected carriers. The measurement of the nonlinear index, using an interferometric technique, is under way.
Optical beam propagation in anisotropic media
Authors: Johnson R. V. , Tanguay A. R.
Published: February 2023

Optical diffraction in media with arbitrary inhomogeneous anisotropies (including linear birefringence and/or optical activity) is characterized by pronounced polarization effects. These effects have typically been analyzed by the coupled wave formalism. An alternative analytical technique is the anisotropic optical beam propagation method (BPM) first proposed by Thylen and Yevick.1 The BPM is a highly intuitive approach to solving the light propagation equation in an optically inhomogeneous medium. The coupled wave approach is preferred for spectrally pure inhomogeneities (simple gratings), whereas the BPM is the preferred algorithm for spectrally rich inhomogeneities (image modulated gratings). The BPM replaces the distributed diffraction problem with an equivalent lumped element approximation consisting of infinitesimally thin phase and polarization modulation planes separated by optically homogeneous layers. The evolution of the light profile both in the near field and in the plane wave spectrum can be monitored as the light beam propagates through the anisotropic medium. In this paper we extend the analysis to include optical activity for modeling volume grating in materials such as bismuth silicon oxide. We also perform detailed numerical experiments to assess which classes of problem are better suited for the coupled wave formalism and which for the BPM formalism.
Analysis of polarization anomaly correction in a video-enhanced microscope
Authors: Conchello Jose A. , Hansen Eric W. , Allen Robert D.
Published: February 2023

A major limiting factor in polarized light microscopes is stray light caused by rotation of the state of polarization at oblique lens surfaces. The pupil function for such a system is a dark cross, and the point spread function resembles a four-leaf clover rather than an Airy disk.1 Reducing the numerical aperture of the condenser and/or objective avoids high obliquity surfaces but also reduces resolution. Polarization rectifiers, which introduce compensating amounts of rotation, have been difficult to produce. Recently, it has been found that operating the microscope with high compensator settings (bias retardation) and video image enhancement effectively corrects the polarization anomaly, permitting operation at full aperture with high contrast.2 This work explores the theoretical basis of the anomaly correction and investigates the fundamental limits of the method. Mathematical models developed for the pupil and point spread functions elucidate the means by which bias retardation and video enhancement restore nearly diffraction-limited performance. Images obtained from the microscope confirm the theoretical predictions. At high (quarter wave) bias retardations, the pupil function is nearly uniform, and the point spread function approaches an Airy disk, but both remain slightly asymmetric, and the phase error in the pupil displays a residual astigmatism.
Analysis of the differences between striate cell responses and their current modeling: do the differences really matter?
Authors: Hamilton David B. , Geisler Wilson S. , Albrecht Duane C.
Published: February 2023

For the most part, the modeling of visual cortical neurons has preceded complete measurement of their response characteristics. However our recent measurement of the phase transfer of striate neurons provides us the most complete description of their response to date. Our purpose in this paper is to enumerate the differences between striate cell responses and current models of these visual mechanisms. Further we describe the significance of these differences to further visual processing. Our laboratory has recently quantified striate cell response phase to drifting sinusoidal gratings. Within the linear systems framework, these measurements allow us to uniquely determine the response of cells to arbitrary visual stimuli in space and time. The phase transfer of striate cells differs from most theoretical work in two ways. First, response phase increases as a function of velocity but remains constant as a function of spatial frequency. Second, the absolute phase transfer varies from cell to cell and does not always land at the canonical phase positions often modeled in the literature. The consequences of these differences will be more fully detailed in the paper. Finally, although current theoretical work often models a Gaussian shaped response to linear increases in spatial frequency, our work indicates that the frequency response of striate cells is much better described by a Gaussian in log spatial frequency. The consequences of this have heretofore been unexplained.
Stability and time-dependent behavior of the detuned ring laser with a saturable absorber in the vicinity of multiple steady-state solutions
Authors: Chyba D. E. , Abraham Neal B. , Albano A.M.
Published: February 2023

We present an examination of the stability and time-dependent behavior of a semiclassical model of the ring laser with a saturable absorber, in the vicinity of multiple steady-state solutions. We consider particularly the case in which the cavity is tuned away from the resonance frequency of the gain medium. The model considers the absorbing and amplifying media to consist of two-level atoms. Only homogeneous spectral broadening and unidirectional propagation of the light are considered. We are able to treat the steady state with an approximate mean field solution and also with its exact longitudinal dependence. The latter is found numerically from an implicit function solution to the Maxwell-Bloch equations in the steady state. There may be as many as four steady-state solutions for a given set of parameter values. When there are four solutions, we find that three solutions are of one intensity class (high or low) and that one is of a second intensity class (low or high). When the absorbing and emitting atoms are in resonance and the cavity is tuned to their line-center frequency, two of the members of the three-solution class have the same intensity. This degeneracy is broken by detuning.
Chaotic attractors of the delay-differential ring-cavity equations
Authors: Le Berre M. , Ressayre E. , Tallet A. , Gibbs Hyatt M.
Published: February 2023

Ring-cavity delay-differential equations, first derived by Ikeda,1 are studied without any approximation. We focus on the instabilities in the limit where the delay time τR is much larger than the decay time T1. We compare the complex field amplitude solution E(t) of the infinite dimensional dynamical system with the solution E[(n + 1 )τR] = f[E(nτR)] of the 2-D mapping resulting from the adiabatic following approximation.2 Chaos of the infinite-dimensional system does not arise from a period-doubling sequence, in disagreement with the 2-D mapping scenario.3 The chaotic attractor [lmE(t
i
) vs ReE(t
i
) for many ti, in each τR and for many τR] for the 2-D mapping is a spiral. The chaotic attractors of the infinite-dimensional system are much more complex. They can be described crudely as fuzzed-out spirals which do not appear to change for τR /T1 > 5, suggesting that the Lyapunov dimension of the attractors saturates. If so, this behavior differs markedly from the linear dependence on τR /T1 found for the Mackey-Glass delay-differential equation,4 removing hope of finding a simple variation law vs τR, whatever the nonlinear flux may be.
Laser image projection using a piezoelectric scanner
Authors: Ih Charles S. , Liu W. Y. , Brown C. D.
Published: February 2023

A simple laser projection system for small images using a piezoelectric scanner is described. The image is ~50 mrad and can be controlled by a computer in real time. The 2-D image is formed by a single piezoelectric scanner. Being completely solid-state, the scanner is mechanically stable, rugged, and has a usable resolution up to 100 × 100 pixels at visible wavelengths. The image can be generated and controlled by a personal computer, thus making this system portable. Because of the small divergence of the image, this system can be incorporated into a large x-y deflection system through which the small image can be directed to any position on a large screen. The deflection system, the driving electronics, and experimental results are discussed and shown.
Experimental studies of amplified spontaneous emission in xenon
Authors: Rankin Michael B. , Bobb Lloyd C. , Davis Jon P.
Published: February 2023

We report new observations of a fast fluorescence process on 6p—6s transitions in xenon (0.01-5 Torr). A 600-ps pulse (λ~ 250 nm, Δν~ 3 GHz) from a frequency-doubled dye laser populates a single 6p state by two-photon coupling. The ensuing fluorescence (823 nm < λ < 993 nm) is collected by f/1 optics, detected by a photomultiplier or microchannel plate phototube, and displayed on an oscilloscope (1-GHz bandwidth) or digitized and recorded for statistical analysis. We previously characterized the emission process as amplified spontaneous emission (ASE) based on emission rate (> 10× spontaneous), high directionality, existence of threshold, and other time-independent characteristics.1 New time-resolved observations with the microchannel plate detector (500-ps overall rise time) showed that far above threshold the fluorescence pulses temporally reproduced the excitation pulses and occurred simultaneously. Pulses near threshold showed widths up to 3 ns and delays up to 3.5 ns. Ringing or multiple-pulse emission also occurred. When the emission was spontaneous, fluorescence energy yields showed the quadratic dependence expected of two-photon excitation and decreased monotonically when N2 was added to the xenon. ASE-dominated yields were linear in excitation energy and increased when N2 was introduced. ASE yields were smaller than predictions based on work of Raymond et al.
2
Mechanisms for these results are discussed.
Approaches to fabrication and testing of large asymmetric aspherics
Authors: Parks Robert E.
Published: February 2023

To date, virtually all large off-axis aspherics have been made using computer-controlled grinding and polishing. This method is slow and does not give altogether satisfactory results. Recently two alternative methods1,2have been proposed and one3used very successfully. In these methods the substrate mirror is warped or the lap is actively controlled to fit the desired aspheric shape. Polishing then proceeds as though one were making a sphere. The methods are complementary and the choice of method depends on the substrate stiffness and thef-ratio of the asphere. The areas of usefulness of each are treated parametrically. Other changes in the fabrication process necessitated by these new methods are also discussed. In addition, mechanical test methods for mirror surfaces far from the finished figure are covered. Conventional optical test methods work well once the aspheric is within tens of waves of the final figure. In earlier stages of fabrication a rapid assessment of the figure must be made to fairly crude tolerances. These measurements can be made with profilometers and spherometers. The utility of a Zernike polynomial representation of the required aspheric surfaces is demonstrated throughout. Insight is gained in all these processes by the use of the polynomial representation.
Polarization tracking for optical heterodyne communication
Authors: Jayaraman Vijaysekhar , Chan Vincent W. S.
Published: February 2023

The signal-to-noise ratio of an optical heterodyne receiver degrades if the signal and local oscillator optical fields are not linearly polarized along the same axis. This paper presents direct detection and heterodyne detection schemes for tracking the axis of linear polarization in the signal beam. It gives an analysis of the error performance of the polarization tracking loop when it is operating at low signal powers and in the presence of background radiation, detector dark current, and thermal noise. The analysis includes a discussion of loop optimization and loop performance in the nonlinear (large error) region. Finally, experimental results for a direct detection scheme are presented.
Wavelength dependence of the photorefractive effect in BaTiO3
Authors: Rakuljic George , Yariv Amnon
Published: February 2023

The photorefractive effect in BaTiO3 is characterized by a wide spectral response typically covering the entire visible spectrum. This result can be quantified by measuring the two-beam coupling coefficient and response time as a function of the incident wavelength. Such data were obtained for BaTiO3 over a spectral range of 400-1300 nm. In addition the variation of these parameters with grating wavelength is also presented. The most immediate result of this study was the observation of a significant near-infrared response. Therefore, many optical devices such as passive phase conjugate mirrors which utilize the photorefractive effect in BaTiO3 should be possible with near-IR sources including semiconductor lasers. The feasibility of such applications is discussed along with methods to increase the near-infrared response of BaTiO3.
Experimental and ray trace results for throat-to-throat compound parabolic concentrators
Authors: Leviton D. B. , Leitch J. W.
Published: February 2023

A compound parabolic concentrator is a nonimaging cone-shaped optic with useful angular transmission characteristics. A pair of these concentrating cones used throat-to-throat will accept light within one well-defined acceptance angle and redistribute it into another. If the first cone is fed with a diffuse source (Lambertian input), the irradiance within the cross section of the beam of light emerging from the second cone will be uniform from near the exit mouth of the second cone to infinity. Also, the beam of light will be confined to the acceptance angle of the second cone (that is, the pair operates as a beam-angle transformer). The design and fabrication of one such pair of cones and an experiment to map the irradiance pattern produced by the pair are discussed. A ray tracing program for compound parabolic concentrating cones is discussed along with a method of modeling a Lambertian source in the ray trace. Experimental results are compared with ray trace results.
Forward degenerate four-wave mixing near bound excitons in CdS
Authors: Dagenais Mario , Prise M. , Sharfin W. F.
Published: February 2023

Excitons bound to neutral donors in direct gap semiconductors are known to have remarkably large oscillator strengths (f ≠ 75). This leads to extremely fast radiative lifetime (τ ≠ 50 ps). We report here the observation of large resonant degenerate four-wave mixing signals near the l2 bound exciton in high purity (~1015/cc) CdS platelets. All the incident beams propagate in the forward direction. An electrooptically modulated cw dye laser operating single mode at 487 nm is used as the optical source. Optical pulses of 2 μs in duration are produced at a repetition rate of 10 kHz. The two incident beams responsible for generating the grating in the sample are mechanically modulated at frequencies ν1 = 1527 Hz and ν2 = 1349 Hz. Phase sensitive detection is used to detect the four-wave mixing signals at ν1 + ν2. Scattering efficiently larger than 1% for peak input power levels of ~5 mW in each beam is observed. The beam diameter on the sample is ~40 μm. Resonance enhancement of the four-wave mixing signal is observed as the laser is scanned across the bound exciton resonance. An anomalously large broadening of the four-photon signal is observed as the incident intensity is increased. The possible role of light trapping is discussed.
Investigation of a miniaturized all-fiber gyro with computerized signal evaluation
Authors: Kiesel E. , Baron K. U.
Published: February 2023

Improved electronic and optical signal-processing schemes have been made with different miniaturized all-fiber gyros at Teldix. Several well-known problems in fiber gyros with analog signal readout are discussed and suitable circumvention schemes proposed:
Computer-generated holograms with 1-D transforms
Authors: Leseberg Detlef
Published: February 2023

The use of anamorphic systems for recording holograms is well known. The two-step nature of the holographic process leads to a simplified reconstruction or allows the use of partially incoherent light. The implementation of an analogous procedure in computer holography offers modified features as well, compared to Fourier holograms. The transform differs according to direction, e.g., a 1-D Fourier transform is used in the horizontal direction and an image is formed in the vertical direction. Both steps are easily implemented numerically to calculate the hologram. Furthermore, the memory and data transfer requirements are relaxed in comparison with 2-D Fourier transforms. On the other hand, the suggested procedure makes it possible to achieve reconstructions of improved quality, for example, plane objects of 4000 × 4000 pixels or a high-speed generation of all rows in parallel. Free parameters are inherent which allow adaptations to special applications. Due to the independence of the generation steps in the two orthogonal directions, each step can be optimized. The Fourier transform can be extended to a Fresnel transform of several sectors displaced in depth, which store the image of a 3-D object with full horizontal parallax.
Detection and identification by UV laser photofragmentation
Authors: Long S. Randolph , Sausa Rosario C. , Miziolek Andrzej W.
Published: February 2023

The spectroscopic detection and identification of many molecules is hampered by the absence of absorption in readily accessible spectral regions (infrared to near ultraviolet) or, when absorption is present, by the absence of distinctive spectral features. For such molecules which have characteristic moieties, it is reasonable to consider the possibility of (1) fragmenting the species of interest by subjecting it to high intensity laser radiation and (2) taking advantage of the unique spectral signatures of the fragments to detect, and deduce the identity of, the parent. We are currently studying the utility of the ArF and KrF lasers as photolysis lasers in this technique. Laser-induced fluorescence is used as the fragment probing device. We find that focused excimer laser radiation is capable of generating photochemical activity via multiphoton absorption in molecules which have no absorption at the near-ultraviolet single-photon level. A good example of the application of this technique is the excimer laser fragmentation of organophosphonates. In addition to organic fragments, the PO radical is produced in quantities readily detectable by laser-induced fluorescence with a very distinctive spectral signature. Additional examples demonstrating the excimer laser production of spectrally distinctive photofragments are discussed.
Nd:YAG laser-induced hematoporphyrin visible fluorescence and two-photon-excited photochemical effect on malignant tumor cells
Authors: Inaba H. , Shimamoto M. , Mashiko S. , Sato S. , Kuwahara T. , Taguchi Y. , Kasai M.
Published: February 2023

A new and promising method for localization and treatment of certain forms of cancer is based on the joint action of laser irradiation and a fluorescent photosensitizer. This technique, which is customarily referred to as photoradiation therapy, is currently under development in various institutions and hospitals throughout the world. A nontoxic, photosensitizing dye with fluorescent properties, hematoporphyrin derivative, is first injected systematically. After 2–3 days this dye exhibits a higher retention in the cancerous region than in the surrounding normal tissue. Subsequent irradiation with a proper optical wavelength, mainly red light around 630 nm, results in rapid necrosis of the neoplastic tissue. However, the absorption by skin pigments for this visible light is usually larger, to a greater extent, than that of a Nd:YAG laser output at 1.064 μm. Hence spectroscopic studies including absorption and fluorescence were performed using hematoporphyrin dihydrochloride (Hp.2HCI) dissolved in PBS and ethanol solutions excited by Q-switched Nd:YAG laser output and its second harmonic beam at 532 nm. The visible fluorescence thus observed by Nd:YAG laser irradiation was attributed to the two-photon absorption, although its intensity was ∼10−4 weaker than that for second harmonic excitation. Survival rate of cultured esophagus cancer cells uptaken Hp.2HCI exhibited a linear decrease with the Nd:YAG laser irradiation time, and this two-photon excited photochemical effect was formed more appreciably for higher dye concentration.
Reflectance and transmittance of human aortal tissue in the 250-2400-nm wavelength region
Authors: Heaney J. B. , Lauder L. , Degnan J. J. , Underhill D. J. , Smith P. D. , Leon M. B. , Kruth H. S. , Bonner R. S.
Published: February 2023

Tissue specimens obtained from a normal healthy aorta and from a plaque damaged aortal portion were sliced to a thickness of ∼10 μm. They were washed thoroughly with a saline solution to remove traces of hemoglobin and had a neutral grayish-white appearance with no evident chromophores. The samples were supported between CaF2 plates while being measured. Transmittance (7) measurements were performed over the 300–2500-nm spectral region by placing the samples in the entrance port of an integrating sphere reflectometer, an arrangement that captured all the forward scattered beam. The specimens were placed next in an integrating sphere with center-mounted sample and the combined transmittance plus reflectance (T + R) of each was measured over the same wavelength range. The measured absorptance [A = 1− (T + R)] spectra of both normal tissue and tissue containing plaque revealed no discrete absorption features in the 250-700-nm region. In general, absorptance increased toward shorter wavelengths and the greatest difference between the absorptance of normal aortal tissue and plaque occurred in the 250–350-nm region. These results indicate that laser angioplasty may be improved by the use of UV lasers that operate in the 250–350-nm region and can interact more strongly with plaque than with the surrounding arterial wall.
Resting distance of the eyes and problems of near work
Authors: Owens D. Alfred
Published: February 2023

Visual problems related to near work are an old issue that has attracted renewed interest with the introduction of video display technology. A puzzling aspect of this problem, which we believe is of central importance, is the fact that some people suffer severe symptoms while others experience little or no difficulty in the same work environment. Evidence that the resting state of the eyes corresponds to an intermediate distance, which varies widely among individuals who have normal vision, suggested that problems of near work may depend on the individual’s oculomotor resting posture.
Image enhancement of fundus photographs
Authors: Mitra Sunanda , Whiteside Steven , Bagri Ravi , Krile Thomas F. , Shihab Zuhair
Published: February 2023

A novel application of digital image enhancement and restoration techniques has allowed us to detect structural changes in fundus photographs (i.e., photographs of the retina as viewed through the pupil of the eye). The visualization of the structural changes in the nerve fiber layers in the retina has been obtained by a combination of edge detection and point-to-point mapping procedures. Such a combination of optimized edge detectors has significant application in quantitative evaluation of early textural changes in the retina caused by degeneration of nerve fibers. In ocular diseases such as glaucoma, early detection of nerve fiber layer defects is a significant step forward over the existing diagnostic aids. Application of various texture models and minimum error thresholding procedures is considered for further improvement of local textural analysis of the fundus photographs.
Directional selectivity used to discriminate spatial phase at low and high background contrasts
Authors: Lawton Teri B.
Published: February 2023

A spatial phase discrimination task was used to measure our contrast sensitivity for discriminating positional differences between multifrequency components spanning a 4-octave range of spatial frequencies. Patterns having an optimal phase difference of 90° were used to activate cortical phase-sensitive units in the center of their working range. Previous studies have found that both spatial frequency and spatial extent are important when discriminating phase differences. Gabor filters characterize the rf profiles of cortical phase-sensitive units. This study investigated the gain of multifrequency backgrounds composed of high spatial frequencies having a low fundamental frequency in phase discrimination. The contrast of the background was increased from 1% to 10%. Directionally selective cues were used at all background contrasts between 1% and 5%. Only small differences in the contrast for phase discrimination were found at low background contrasts. An observer’s contrast sensitivity is a nonlinear function of the background contrast when discriminating spatial phase differences. Gabor filters are insufficient for characterizing the processing of spatial phase differences at low background contrasts. Feedback mechanisms that change the gain of these paired filters by providing directionally selective cues must also be proposed.
Variable resolution 3-D imaging sensor
Authors: Bair Max E.
Published: February 2023

A 3-D imaging sensor concept has been developed and implemented that provides a direct digital (x,y,z) readout on a pixel-by-pixel basis. The sensor uses a modulated laser source which is scanned (x,y) to form a range (z) image—range and range sensitivity are determined by the modulation phase interval and the frequency of modulation. The potential utility of this framing sensor technique has been shown for several robotic vehicle and inspection applications in which the resolution requirements (x,y,z) vary from the macro (meter) to the micro (0.1mm) scale. Functional details of the sensor concept are presented, along with specific hardware implementations for macro and micro resolution applications. Respective performance characteristics for each implementation are presented along with sample imagery.
Motion from line correspondence and trinocular stereo
Authors: Kanade Takeo
Published: February 2023

Obtaining depth information from stereopsis and obtaining motion information from image sequences are two closely related problems. This paper presents a theory for stereo and motion from images based on line correspondences. It has been known as an aperture problem where unique point correspondences in the image cannot be obtained locally except for special points such as corners. In fact, the Moravec interest operator tries to detect such points whose correspondence can be more readily determined than others. Therefore, in order to establish point correspondences, certain other global consistency constraints have been introduced, for example, minimizing overall smoothness or minimizing distortion energy.
Quantitative Fourier transform infrared photoacoustic spectroscopy
Authors: Choquet M. , Rousset G. , Bertrand Lionel G.
Published: February 2023

Using a Fourier transform spectrometer equipped with a photoacoustic cell, we have the possibility to combine the multiplex advantages of the first with the capabilities of the second. For example, this permits nondestructive analysis and spectroscopic study of optically opaque samples in the infrared region with a high signal-to-noise ratio. The photoacoustic signal depends strongly on the thermal diffusion length of the sample which, in turn, depends on the frequency modulation of the illuminating beam. In Fourier transform photoacoustic spectroscopy (FTPAS), this frequency dependence induces artificial variations of the relative amplitude bands within the spectrum. A new procedure has been developed to reduce this problem. After correcting for phase errors caused by the optical setup and detection system, the real and imaginary components of the photoacoustic signal are analyzed. Based on the MacDonald and Wetsel model for photoacoustic signal generation, we have therefore performed quantitative spectra of different samples. In this manner, we observe the dichroism of absorption of different serpentine (antigorite and chrysotile) in its raw form. Also, we study the spectrum of a thin film of indium-doped a:Si-H. These spectra demonstrate the advantages of the FTPAS in conjunction with our treatment.
Photoacoustic and photothermal material testing
Authors: Tam Andrew C.
Published: February 2023

The phenomenon of light-induced acoustic pulse generations, i.e., photoacoustic (PA) effect, and light-induced thermal wave generation, i.e., photothermal (PT) effect, can be advantageously used to monitor properties of materials. For example, extremely narrow acoustic transients can be produced by pulsed lasers in condensed matter as well as in gases. The propagation of such narrow acoustic pulses can be monitored by contact methods using transducers or by noncontact methods using optical probe beams. Acoustic velocities, dimensions, and subsurface defects can be detected. Also, Fourier transforms of the PA pulse shape at different propagation distances provide the ultrasonic absorption spectrum of the material. PA generations are frequently due to PT heating effects by optical pulses; however, PT heating can also lead to other detectable effects like refractive-index transients or infrared thermal radiation variations. This talk reviews the modern applications of PA and PT monitoring of material properties as well as basic theories and measurements of the PA pulse generation effect.
Optical-processing characteristics of a low-cost liquid crystal display device
Authors: McEwan J. A. , Fisher A. D. , Rolsma P. B. , Lee J. N.
Published: February 2023

An important component of most optical processing architectures is an electrically addressed spatial light modulator to provide the necessary electronic-optical interface for input and manipulation of information on the optical beams. A commercially available low-cost (<$150), liquid crystal TV receiver is being characterized and employed in coherent optical signal processing applications. The device employs a twisted-nematic liquid crystal modulator addressed by a 120 × 140 electrode matrix and is operated in transmission. The modulator is controlled by a microprocessor via a direct video input port. Performance parameters including dynamic-range/contrast, time response, resolution, and phase distortion are reported. The performance of this device in the input plane and the Fourier plane of coherent optical processor configurations, such as a correlator, is also being investigated. Application to more advanced optical processor architectures, for example, in the capacity of a real-time computer-generated hologram, is also discussed.
Integrated-optical synthetic aperture radar processor
Authors: Bicknell T. J. , Psaltis D. , Tanguay A. R.
Published: February 2023

Synthetic aperture radar (SAR) is a 2-D signal processing problem that normally requires a 3-D optical implementation. We describe an optical method for performing SAR imaging that can be implemented using integrated optics, which is typically configured as a planar structure. Two-dimensional signal processing is accomplished through a combination of spatial and temporal integration. The radar signal is entered into the integrated optical structure through a surface acoustic wave transducer and is first processed by spatial integration through 1-D diffraction within a uniform, planar optical waveguide. The spatially processed light is then coupled into an array of channel waveguides, which acts as a 1-D image dissector by expanding the light along the direction in which light propagates. The temporal integration takes place on a 2-D CCD detector array positioned on top of the channel waveguides. Light is selectively coupled vertically out of the waveguiding plane, with each channel waveguide illuminating a corresponding column of the CCD array through a 2-D spatially modulated transparency. Periodic transfer of the photogenerated charge on the CCD following each temporal integration period results in the formation of the focused radar image.
Noncontact dimensional measurement using a pulsed laser caliper
Authors: Lettieri Thomas R.
Published: February 2023

A pulsed laser caliper (PLC) is a device which can make noncontacting dimensional measurements on macroscopic objects using short laser pulses in a time-of-flight configuration. It can be adapted, in principle, to measure caliper dimensions of a discrete part, thickness variations across a continuous slab, or the shapes of complex contours. In operation, a laser pulse is split in two, one pulse going directly to a fast photodetector and the other reflecting off both sides of an object. The time-of-flight difference between the pulses is then measured with a counter or a sampling oscilloscope. The device is next zeroed by removing the object and again measuring the time-of-flight difference. Subtracting these two differences gives a caliper measurement of the object’s dimension. As a demonstration of the principle, a PLC consisting of a mode-locked argon laser, a high-speed photodiode, and a sampling oscilloscope was assembled and used to measure the lengths of five steel gauge blocks. The gauge blocks ranged in length from ¾ to 4 in. and were measured by the PLC to an accuracy of 0.03 in. Various sources of inaccuracy in and limitations on the PLC were determined and are discussed in the presentation.
Phase-locked semiconductor laser diode arrays
Authors: Streifer W. , Scifres Donald R. , Cross P. S. , Welch D. F. , Burnham R. D.
Published: February 2023

Phase-locked semiconductor diode laser arrays are capable of emitting light at high power in low divergence beams. Moreover, because of their small size and high electrical-to-optical conversion efficiency, these devices have many applications. The presentation begins with a review of semiconductor diode lasers and the principles of phased arrays. Various experiments relating to the lasers themselves and to their operation in external cavities are reviewed and the theory of their operation and conditions needed to favor lasing in a desired array mode (supermode) is discussed. The talk concludes with recent results concerning reliability.
Laser diode arrays for optical pumping of Nd:YAG
Authors: Krebs Danny J.
Published: February 2023

Although diode pumping of Nd:YAG lasers has been an area of active investigation for many years, developments continue to occur which show promise for a wide range of laser applications. In principle, any neodymium host laser which can be lamp pumped can also be diode pumped and generally an improvement in laser size, weight, and efficiency can be expected. In practice, diode pumping has been limited to relatively low-power Nd:YAG lasers due to cost, diode quality, and packaging constraints. Potential cost reductions in the GaAIAs wafer growth and pump array fabrication could make this technology competitive with lamp pumping for many applications requiring long life, high efficiency, and compact design.
Individually addressable monolithic arrays of AIGaAs diode lasers
Authors: Carlin Donald B.
Published: February 2023

A number of applications for high-power diode laser arrays exist, such as optical data storage, laser printing, and optical data processing, which allow enhanced operation by use of parallel, independently addressable channels. A monolithic linear array of AIGaAs diode lasers has been developed to address such applications. Pertinent considerations regarding the design, fabrication, and use of diode laser array sources include optical coupling, thermal interactions, and electrical cross talk between adjacent elements; uniformity of crystal growth; individual, independent electrical addressing of each diode; and collection and collimation of the output radiation from the laser elements. These issues are addressed, with specific examples discussed, including arrays of up to ten elements, separated by 150 µm, with each laser emitting in a fundamental spatial mode. Examples of such array based systems are shown, with particular emphasis on multichannel optical recording for high-data-rate data storage.