bluuebunny/crossref_metadata_2025 huggingface dataset:
Aging and topography of human photoreceptors
Authors: Curcio Christine A.
Published: February 2023

Age-related decrements in acuity and contrast sensitivity are only partially explained by the combined effects of pupillary constriction and lens opacification. The notion of a neural origin for these visual deficits remains controversial. Limited quantitative data on photoreceptors in aging suggest disorganization of both rod and cone outer segments, displacement of nuclei, and outright cell loss, particularly in the fovea. The relationship of these phenomena to nonpathological changes in retinal supporting tissues which may impair transport of nutrients across the outer blood–retinal barrier is unclear. The effects of age-related point deletions in the photoreceptor mosaic on spatial sampling characteristics of the retina are unknown. Recent studies of photoreceptor distribution in human retina show that individual variability in foveal cone density is much greater than previously appreciated. The implications of this finding for aging studies are (1) sample size must take into account high variability; (2) anatomical data need to be viewed in relation to functional and clinical data from the same individual; (3) photoreceptor counts alone are probably not sufficiently sensitive to detect age-related cell loss, and some measure of mosaic disorder is likely to be more informative.
Aging and the spatiotemporal resolution of visual events
Authors: Kline Donald W. , Schieber Frank
Published: February 2023

With aging, there is a decline in the temporal resolving capacity of the visual system. Recent evidence indicates that the type and degree of the decline varies with the spatial characteristics of the target being detected, suggesting disjunctive aging of the different channels composing the visual system, (e.g., Kline and Schieber, 1981).
Quantum well self-electrooptic effect devices
Authors: Miller D. A. B.
Published: February 2023

Quantum well structures, consisting of alternate thin layers of two semiconductors (such as GaAs and GaAIAs), show an unusual electric field dependence of the optical absorption near the optical absorption edge called the quantum-confined Stark effect (QCSE).1 This effect enables large changes in optical transmission in material only microns thick for voltages of a few volts. The total energy per unit optical area required to make these changes is ~1-30 fJ/µm2, making it much more efficient than absorption saturation or gain mechanisms at room temperature.
Measurement of Gaussian beam divergence using the combined interaction with stationary and traveling phase gratings
Authors: Black T. D. , Larson D. A. , Haghighatjou T.
Published: February 2023

Enhanced optical probing of surface acoustic waves (SAW) using stationary phase gratings in proximity to the SAW was found to be sensitive to the divergence of the probing laser beam. The sensitivity of the probing technique was seen to fall off as the separation between the stationary phase grating and the traveling SAW was increased. This gradual falloff was observed to increase as a function of the probing beam’s divergence.1 This paper presents a theoretical analysis using generalized plane waves to include divergent Gaussian beams. The analysis shows the sensitivity of the technique to the probing beam divergence increases for higher frequency SAW. Experimental measurements using y-cut LiNbO3 for z propagation were made for frequencies of 17.4 and 87.2 MHz corresponding to SAW wavelengths of 200 and 40 μm, respectively. The results of these experiments are shown for both frequencies at several beam divergences. Comparison of the calculated intensities for the 0 and ±1 orders of diffraction to the experimental results confirms the essential features of the analysis of the TEM00 mode of a He-Ne laser.
Injection phase locking in continuous CO2 lasers
Authors: Bourdet G. L. , Muller R. A. , Mullot G. M. , Vinet J. Y.
Published: February 2023

Many applications require large power laser sources with high spectral and spatial mode purity in the cw regime. The injection phase locking technique, borrowed from microwave technology, seems able to solve this problem. In this process, the light emitted by a low power single-mode master oscillator is injected into a large power slave oscillator. When the injected light frequency is in the neighborhood of a frequency resonance of the slave cavity, a large amount of the injected light is stored within it. As a consequence, the slave laser gain saturates. If the saturation is strong enough to bring the gain under oscillation thresh old, the slave laser acts as a regenerative amplifier for the incoming light reaching very large amplification coefficients.
Tunable dye laser pumped by a frequency-doubled high-power cw Nd:YAG laser
Authors: Vanherzeele H. , De Vos G. , Muys P.
Published: February 2023

In the past, researchers have pointed out the advantages of using frequency-doubled Nd:YAG lasers rather than ion lasers as a pump source for tunable dye laser oscillators and amplifiers. However, operation of these systems has been restricted to either pulsed (Q-switched) or cw mode-locked regimes (or a combination of both). In this paper we present for the first time to our knowledge a nonmode-locked cw dye laser, pumped by a high-power frequency-doubled cw Nd:YAG laser. The latter is a commercially available cw laser (YAG rod: 76 × 4 mm), which has been modified for efficient intracavity frequency doubling by means of a KTP crystal. The green output beam is characterized by a nearly TEM00 profile, and a good temporal stability (both short term and long term). The dye laser has a three-mirror folded cavity design with a jet as the gain medium (rhodamine 590, in ethylene glycol). The overall characteristics of the system, such as stability, efficiency, and tunability are outlined, together with some of its potential applications (e.g., in ophthalmology). Compared with similar ion laser pumped systems, our system provides the additional advantages of increased ruggedness and reliability. It is also more user friendly and more cost-effective since it requires less maintenance, thereby reducing the shutdown time.
Effect of incident pulse width on parameters estimated with the time-dependent inverse transport method
Authors: Duracz T. , McCormick N. J.
Published: February 2023

A few low-order Legendre polynomial moments of the angle-dependent single-scattering function can be estimated from the backscattered radiance long after a Dirac delta incident pulse, according to computer simulations.1 The accuracy of these estimates is shown to be possibly reduced for a pulse fo finite width, with a greater effect for the higher-order moments. Accurate estimates are confirmed to be more difficult to obtain when random or systematic experimental errors are simulated in the backscattered radiance. Use of a curve-fitting procedure now being used to process experimental data taken to test the inverse method is shown to ameliorate the effects of noise.
Model of lidar backscatter from multilayered sea ice
Authors: Erdmann J. C. , Saint Clair J. M.
Published: February 2023

Environmental conditions make in situ measurements of the optical properties of the Arctic Ocean difficult. Remote, rapid sensing of the optical properties of sea ice is possible from under ice ROVs (remotely operated vehicles). The application of lidar techniques requires modeling of both the lidar system and sea ice. We present progress in developing such a model, which includes the time-dependent backscattered signal incorporating multiple scattering effects via a Monte Carlo technique. The sea ice optical properties are based on recent experimental and theoretical results for the scattering phase functions of the different layers in sea ice. In addition we have included the effect of layers of biota (phytoplankton) recently found to live in and under the ice during parts of the year. The Monte Carlo technique is tested against exact results of a Markov formulation we have developed for beam spread and pulse spread in a uniform medium.
Refractive index of water vapor in infrared windows
Authors: Hill Reginald J. , Lawrence Robert S.
Published: February 2023

The refractive index of water vapor for wavelengths in the infrared windows is important for laser techniques of distance measurement. Our own interest in this refractive index is the prediction of turbulence-induced scintillation in atmospheric propagation of infrared radiation. The refractive index of water vapor is calculated by line-by-line summation using the AFGL line parameters compilation. The calculation is performed at nine wavelengths between 19 and 7.8 µm, and three wavelengths near 3.4 µm. A simple formula for its dispersion and temperature dependence is given. We compare the line-by-line summation against measurements of refractive index for wavelengths near 10.6 and 3.4 µm. The calculations are in good agreement with data. The line-by-line calculation is also performed at visible wavelengths so that the infrared-resonance contribution to the refractive index in the visible may be subtracted from the empirical values thereby giving the ultraviolet-resonance contribution. The extrapolation of this UV-resonance refractive index from the visible to the infrared is shown to have an estimated uncertainty of two parts per thousand.
Hysteretic three-photon excitation of a cyclotron resonance in semiconductors
Authors: Kaplan A. E. , Ding Y. J.
Published: February 2023

In the earlier work1 the three-photon resonance at cyclotron frequency Ω
c
, in semiconductors pumped by two lasers with their frequency difference close to Ω
c
, has been predicted and observed. Here we consider the feasibility of hysteretic excitation of such a resonance in narrow-gap semiconductors which is based on the nonparabolicity of the narrow-gap semiconductor conduction band. The expected effect is analogous to three-photon hysteretic resonance of free cyclotron electrons in vacuum.2 However, this quasi-relativistic nonlinearity caused by nonparabolicity in semiconductors is much larger than that caused by free relativistic electrons, since the nonlinearity in semiconductors is scaled to the gap energy Eg, which is much smaller than rest energy of free electron m0c2. We consider an example where two different lines 10.6 and 9.4 µm of a CO2 laser used as driving radiations, with the cyclotron three-photon excitation expected at λc ≃ 83.03 µm. Assuming the momentum relaxation time to be of the order of 10−11 s, we estimate the critical intensity required to obtain a hysteretic frequency difference cyclotron excitation to be 3.4 × 104 W/cm2 for InSb; 2.2 × 105 W/cm2 for HgTe; 2.2 × 106 W/cm2 for GaAs.
Experimental studies of the nonlinear response of select liquid crystal polymers
Authors: Sullivan B. J. , Altman J. , Elizondo P. J. , Lipscomb G. F. , Lytel R.
Published: February 2023

Certain organic and molecular polymers have been shown to exhibit large, nonresonant optical nonlinearities that arise from pi-electron delocalization. Such materials offer novel features for applications in optical devices due to the intrinsic picosecond response associated with this delocalization. Side-chain liquid crystal polymers are particularly interesting, due to the potential for molecular design of desirable macroscopic properties. We report measurements of the nonlinear optical susceptibility of select side-chain polymer systems over a wide temporal and spectral range. The nature of the nonlinear optical susceptibility may be determined by degenerate four-wave mixing, using pulsed lasers and time delay between writing and readout pulses. At subpicosecond times, the electronic contribution to the susceptibility can be measured by direct determination of the conjugate reflectivity. As the pulse width is increased certain motional contributions, probably due to the rotation of large side-chain organic molecules, appear, which increases the overall conjugate reflectivity. Both electronic and motional contributions are exhibited for select materials, with extremely fast response already reported for other polymers, such as PBI. Both contributions are relatively wavelength independent, i.e., resonant. We also report on enhancements in the third-order response when the pulse length is increased to 10 ns, and the wavelength lies within the absorption tail of the LC polymer. In this regime, a thermal grating is formed in the material, which produces thermally induced degenerate four-wave mixing. This mechanism requires coherence in the two writing beams, and a delay of ~1–10 ns on readout to allow the grating to fully develop. All three contributions are described for several polymer systems.
Ewald-Oseen extinction theorem does not describe the extinction of an incident wave in a medium
Authors: Sein John J.
Published: February 2023

Contrary to prevailing belief, the Ewald-Oseen extinction theorem1 is unrelated to the physical process of extinction of an incident wave in a medium. The apparent cancellation of the incident field in the customary derivation1 of the theorem is no more than a consequence of the super position principle: within the medium the dipole field must be expressible as the sum of the total field in the medium and of the negative of the incident field. The Ewald-Oseen extinction theorem, including its generalized forms,2 belongs both in its formal structure and in its physical content in the family of relations which may be categorized, broadly speaking, with the Huygens principle.
Use of an exponential function to model the absorption of a dielectric thin film
Authors: Johnston Barbara , Carniglia Charles K.
Published: February 2023

Most of the models for absorption in a dielectric material are based on the harmonic oscillator equations, which lead to expressions for the dispersion of the extinction coefficient k which involve several parameters. For the simple interpolation of k over short-wavelength ranges, a two-parameter dispersion relationship is desirable. Several different two-parameter expressions have been used to model the variation in k for a typical zirconia film, and the best fit to the measured data was a function of the form k = a exp(bσ), where σ is the wave number given in terms of the wavelength λ by σ = 1/λ. Various other functional forms for k are presented for comparison. The exponential model is especially useful in the determination of optical constants of coating materials from spectral scans.
Individual variability in the amount of binocular summation
Authors: Cogan Alexander I. , Chan Hoover
Published: February 2023

We compared the amount of binocular summation, defined in the usual way by the monocular/binocular threshold ratio, with the threshold effect of adapting luminance. The luminance effect obeyed Weber’s law: The slope of the threshold vs intensity function was unity for monocular as well as binocular thresholds; it was the same among all eyes and observers. The amount of binocular summation was independent of adapting luminance, but it varied among the eyes of the six normal observers between a factor of 1 (no summation) and a factor of 2 (full summation). Except in one observer, monocular thresholds remained about the same when the nontest eye was occluded, as when both eyes viewed binocularly fused backgrounds of equal luminance. Global stereoscopic relief imposed on the background had no effect on thresholds or on the amount of binocular summation. No single rule common to all observers would predict binocular performance from monocular performances alone. At least two binocular channels must contribute to the net response at the increment threshold.
Model for space-varying cone placement in the fovea
Authors: Poirson Allen , Ahumada Albert
Published: February 2023

We present a model for the placement of cones in the fovea which is an extension of the model for the near foveolar region presented by Ahumada and Poirson (ARVO 1986). This model has three parameters which can vary with eccentricity: (1) the radius of the cone disk, (2) the ratio of the cone disk standard deviation to the mean radius, (3) the standard deviation of the postpacking jitter addition. The physiological data modeled are the positions of the inner cone segments of the cone mosaic from an adult primate presented by Hirsch and Miller (ARVO 1985). This model correctly tracks the decrease in cone density as eccentricity increases by simply increasing the cone radius with distance. The increase in variance of cone positions in the data, as measured by two descriptive statistics, is consistent with the predictions of the model with the second two parameters constant.
Quenching of NH(a1Δ)
Authors: Bower R. , Blauer J. A. , Jacoby M. T.
Published: February 2023

The 193-nm ArF pulsed laser photolysis of HNCO, NH, and N2H4 produced NH(a1Δ). Its lifetime was measured as a function of quenching species concentration by LIF using the a1Δ → c1π transition near 325 nm. The rate coefficients for quenching were found to be 7.5 ± 0.6 × 10−14 for N2, 2.9 ± 0.6 × 10−12 for H2, 7.3 ± 1.0 × 10−13 for HF, 6.3 ± 1.0 × 10−13 for F2, 1.62 ± 0.16 × 10−11 for HNCO, 1.10 ± 0.08 × 10−10 for NH3, 1.7 ± 0.2 × 10−10 and <10−15 for He.
Observation of stimulated emission of Na2 at 0.75-0.80 µm by UV excitation
Authors: Sun Yuezhen , Chen Zhongxian , Du Miao
Published: February 2023

We describe the first observation of stimulated emission at 0.75–0.80 µm and at 1.06–1.14 µm in sodium vapor at 580°C and 0.5-Torr buffer argon pressure by single-UV-photon or two-visible-photon pumping. For our pumping source, we used a XeCl excimer laser (EMG 101)–dye laser (FL2002), wavelengths 3375.93-Å (PTP) and 5772.8- Å (Rh6G) for single-photon and two-photon excitation with 0.16- Å linewidth and 10-nm pulse width; heating zone of the heat-pipe 25 cm.
Visualization of rf acoustic wavefront by laser correlation theory
Authors: Yang Xuan-Min , Yi Ming , Huan Zong-Hua
Published: February 2023

In recent years, the study of nonlinear acoustics, AO information processing, and AO devices has moved into the forefront of acoustics, so there is a compelling need to study the characteristics of an acoustic wavefront in a medium. In the general method, only the intensity of the image of the acoustic field can be obtained and the optical probing method is laborious and not in real time.
CO2 laser front end for the Paladin FEL
Authors: Lowenthal D. D. , Barrett D. A. , Demboski J. S.
Published: February 2023

This paper describes the design, fabrication, and testing of a turn-key CO2 laser system constructed by Spectra Technology, Inc. for the LLNL Paladin FEL. The laser forms the front end driver for the FEL experiment and must deliver >250 mJ in 50 ns at a rep rate of up to 1 Hz. In addition, the laser must operate in a single longitudinal mode and have a transverse TEM00 beam profile. The pulse-to-pulse energy must be consistent over 1-h run times and the intensity, within the 50-ns pulse, must be flat to ≲20%. The delivered laser system employs three atmospheric UV preionized discharge lasers, and a low pressure cw laser that provides the single longitudinal line lock capability, as well as an alignment tracer beam. Fifty-nanosecond pulses are sliced from the oscillator output with a CdTe switch and Brewster stack polarizers. Technical features of the laser are described which are required to meet the laser system specifications. Performance data for the completed laser are presented.
New Design of Grating Couplers with Fiber Optics for Use as Combined Power Divider and Wavelength Demultiplexer
Authors: Noll J. , Schmitt H.-J. , Dammann H.
Published: February 2023

Digital phase gratings were formerly investigated by a simple Fourier transformation to optimize their behavior, e.g., distributing the incident radiation in distinct spectral bands to specific diffraction orders or distributing the incident intensity of light into equally bright central orders.
Effect of wavelength on light scatter in the human eye
Authors: Wooten B. R. , Geri George A.
Published: February 2023

Data on the wavelength dependence of intraocular light scatter are scarce and contradictory. Using the psychophysical glare method, we have determined the equivalent luminance at the center of an annulus of 3° inner and 8° outer diameters. The equivalent luminance is 1-2% of the ring's luminance and is independent of wavelength over the range from 420 to 650 nm. These findings were confirmed on two normal, 55-year-old observers. The results rule out Rayleigh scatter as a significant contributor to intraocular scatter in the normal human eye.
Lasing in plasmas of kryptonlike ions
Authors: Valeo Ernest
Published: February 2023

A proposed technique for achieving lasing action below 10 nm is described. Inversion in a target plasma of kryptonlike ions is obtained via multiphoton absorption from a powerful picosecond laser.
Limits and implementation of optical interconnects for computers
Authors: Haugen P. R. , Husain A.
Published: February 2023

Optical interconnect technology has demonstrated technical and commercial success for long-haul and local area network communications. Migration of optical interconnects into computing systems is being driven by increasing circuit device speeds and architectural complexity needed to realize high performance computers. For present computing architectures, data and clock distribution are examples of interconnect bottlenecks where there is an immediate payoff from using optical interconnects at the small area, board-to-board and chip-to-chip level. For future systems, hardware density and speed will be enhanced by utilizing the high density potential of optical interconnects. We present potential advantages and limitations that optical interconnects exhibit for computing implementations. In addition, we discuss packaging issues (e.g., reliability, testability, and compatibility) essential for implementing optical interconnect in computing hardware environments and present results of an optical chip-to-chip demonstration.
Temperature effects on multiple-stripe phased-array GaAIAs lasers
Authors: Wang S. C. , Gacusan L Z.
Published: February 2023

The temperature dependence of threshold current and of laser emission wavelength was investigated for the gain-guided multiple-stripe phased-array GaAIAs lasers in cw operating conditions. The laser threshold current increased with temperature in a manner similar to that of conventional single-stripe GaAIAs lasers. For 10-stripe lasers, the characteristic temperature had a mean value of ~150 K, while lasers with more than 10 stripes showed a relatively lower characteristic temperature. The dependence of laser emission wavelength and mode pattern on temperature was examined at constant operating current conditions. For all lasers tested, the wavelength showed a red shift of ~0.3 nm/deg as the temperature increased. The number of longitudinal modes remained nearly unchanged, while the mode-intensity profile showed certain variations as the temperature changed. In general, the laser output was found to be fairly stable under constant-temperature operation.
Observation of eigenmodes in gain-guided diode laser arrays using injection-seeding methods
Authors: Hohimer J. P. , Hadley G. R. , Owyoung A.
Published: February 2023

We report the first experimental observation of a progression of allowed eigenmodes in a 10-element gain-guided diode laser array. By injection-seeding the array using the single-frequency output from a tunable cw dye laser, a sequence of eigenmodes of order 1–15 are selectively excited as the injected frequency is increased. Our results, in the form of observed near- and far-field intensity distributions emitted from these arrays, provide strong corroborative evidence for a model that views these devices as spatially gain-perturbed broad-area lasers whose characteristics are dominated by plane-wavelike interactions.1,2 Consistent with this picture we find that lower-order (v < 10) modes can only be excited by optically injecting the entire width of the device. In contrast, the higher-order (v ≥ 10) modes, which exhibit larger tilts in their emission phase fronts with respect to the resonator axis, are more strongly coupled across the gain stripes of the device. These are thus easily excited by injecting the proper frequency radiation into a small region (≤ 5 μm) near the center of the array. From these studies the highest-gain eigenmodes are seen to be those for which v = 10 or 11. Indeed, these modes have been observed with the device operating in free-running conditions (i.e., no injection) near threshold. Our experimental results for both the free-running and injected arrays are compared to theory.
Thermal effects on the eigenmodes of gain-guided diode laser arrays
Authors: Hadley G. R. , Hohimer J. P. , Owyoung A.
Published: February 2023

Numerical calculations of the free-running modes of a ten-stripe gain-guided diode laser array predict the existence of modes of order >10, which represents a sharp contrast to coupled-mode theory. In this paper we show that the inclusion of junction heating in our model results in a real refractive-index profile across the width of the array. This index variation results in a strong field confinement within the device, which alters the spatial distributions and relative gains of the array eigenmodes. Our calculations show that a 10° rise in the temperature of the active region (resulting in an index increase of >0.01) produces appreciable changes in the near-field intensity profiles and observable increases in the far-field emission angles for the higher-order (v ≥ 10) modes. Junction heating also decreases the spread in gain of the high-order array modes (v ≥ 10) and accounts for their observation in high-power gain-guided arrays. The inclusion of junction heating in our model will be shown to markedly improve the agreement between our numerical predictions and laboratory observations on the eigenmodes of gain-guided diode laser arrays.
Optical emission at 1.32 μm from sulfur-doped crystalline silicon
Authors: Brown T. G. , Hall Dennis G.
Published: February 2023

The radiative decay of excitons bound to isoelectronic impurities is an important physical process in crystalline semiconductors. This is particularly true in indirect band gap materials such as silicon and gallium phosphide in which the k-con-servation selection rule forbids the immediate band-to-band radiative recombination of electrons and holes. Isoelectronic bound exciton (IBE) emission from GaP was first identified in 1963,1 but IBE emission from silicon was identified for the first time only as recently as 1979.2 We report in this paper the observation and characterization of photoluminescence from sulfur-doped silicon that we tentatively identify as IBE. The emission occurs near the 1.32-μm wavelength and is a maximum near the temperature T = 80 K. We present the results of measurements of the lifetime, temperature dependence, and external efficiency.
Spectroscopic evaluation of titanium-doped crystals for visible lasers
Authors: Tyminski Jacek K. , Deshazer Larry G.
Published: February 2023

The d1 electronic configuration of Ti3+ in sapphire has the following advantages as a tunable solid state material: high gain, broad tuning range, and lack of excited state absorption. The lack of excited state absorption is inherent for the d1 configuration and promises low spectroscopic losses in other crystals doped with Ti3+. This makes Ti-doped systems very attractive as potential solid state laser media. The 300-nm range of Ti:sapphire limits its operation to the near-infrared range from 700 to 1000 nm. A desire to shift the range of the tunable solid state laser into the visible underlines our spectroscopic study of different Ti-dopant–crystalline host combinations. We conducted absorption, luminescence, and excitation measurements on different Ti-doped crystals including YAG, GSAG, YALO, and spinel. The results of our studies are compared with the spectroscopy of Ti:sapphire to identify d1 features in other hosts. The potential for developing a new titanium-based laser system is discussed.
Effects of γ-ray Irradiation on dimensional stability of Cer-Vit 101 and 142
Authors: Johnston Steve C. , Jacobs Stephen F. , Koumvakalis Nicholas
Published: February 2023

A laser interferometer was used to monitor thermally induced length changes in samples of Cer-Vit 101 and 142 between discrete temperatures in the 250–450 K range. The Cer-Vit 101 was then irradiated with a γ-ray 132Cs source for 37 days, and the Cer-Vit 142 with a 60Co source for 58 days. Both samples received a radiation dose of 105 rad which caused them to become opaque.
Isothermal dimensional stability of various metals, alloys, welded joints, and composite structures
Authors: Jacobs Stephen F. , Johnston Steve C. , Wanielista A. C. , Bass D.
Published: February 2023

Using a laser interferometric method described elsewhere,1 we report on isothermal dimensional stability of the following materials: Invar, Super Invar, Kovar, molybdenum, TZM, elkonite, Al2O3, Si3N4, SiC, copper, fused silica (quartz), TiAlV, Kovar/Kovar welds, and composite structures of Mo/SiC, Mo/Si3N4, and Mo/Invar. Measurements were made over a two-month period with samples maintained in vacuum near 60°C. Quartz and Super Invar were used for secondary length references; copper for a secondary thermal reference. Invar was found to elongate ~1 ppm/month, molybdenum varies with manufacturer as does Kovar, Kovar/Kovar spot welds and seam welds shrank ~1 ppm/month, molybdenum composite structures shrank ~1 ppm/month, TZM, TiAlV, Si3N4, Al2O3 and SiC were all stable to ~0.1 ppm/month.
Can flicker deficits depend on spectral opponency?
Authors: Eisner Alvin , Samples John R.
Published: February 2023

While studying the aging visual system for the intended purpose of understanding age-related macular degeneration, we have employed a battery of tests that has included measures of 20-Hz flicker sensitivity on chromatic backgrounds. Unexpectedly, we found that more than 10% of people older than age 70 in a large control group had profound reductions of flicker sensitivity, more than 10 standard deviations from the mean norm, for at least one of the two background conditions used to measure flicker sensitivity. These people were more likely to be taking cardiovascular medication and/or have glaucotomous optic nerve head change than people without profound reductions. However, their intraocular pressures were within normal limits at the time of testing. Following these observations, we measure chromatic adaptation flicker tvi curves of young normal subjects, using 750-ms duration test stimuli. We found that on long wave length backgrounds flicker tvi slopes became great (~5) between 4.5 and 4.7 log td at 540 nm, but were near unity at 640 nm. The steep slopes coincided with the breakdown of effective M cone isolation. The results from young people suggest that profound losses of flicker sensitivity associated with low tension glaucoma could depend on spectrally opponent saturation. Preliminary results from people with low tension glaucoma are consistent with that possibility.
Invariant responses of opponent colors mechanisms
Authors: Calkins David J.
Published: February 2023

The threshold increment spectral sensitivity for a foveally presented 0.5-s raised cosine having blurred edges exhibits a Sloan notch which coincides with the wavelength of the adapting field and is typically 0.6 log units deep on a 578-nm field of 0.10 log quanta deg−2 s−1.1 In a previous abstract2 it was reported that the long-wave side of the Sloan notch pairs of suprathreshold stimuli of different wavelengths could be found that were indiscriminable. We have repeated and extended those results. A 650-nm standard test stimulus 0.3, 0.5, or 0.7 log units above threshold was paired with a randomly selected, variable intensity light of another wavelength between 600 and 670 nm, and the observer was forced to select the standard. For two observers it was possible to obtain complete action spectra of lights that could not be distinguished from the standard at the noted units above threshold. Truncated indiscriminability spectra were also obtained on the midwave side of the Sloan notch. In all cases the indiscriminability spectra were identical in form with the threshold action spectrum. Because the Sloan notch action spectrum is manifestly cone-antagonistic, it can be concluded that the indiscriminable stimuli are rendered so not at the quantum catch level, but rather at a proximal site where the antagonistic signals converge.
Two-frequency above threshold ionization with pulses
Authors: Wang L. , Haus J. W. , Rzazewski K.
Published: February 2023

We solve a model with one bound state and two continua.1 Two lasers are used to study the above threshold ionization process. The first laser couples the electron in a bound state to a continuum state. The photons are assumed to be energetic enough to promote the electron directly into the continuum far from the threshold; this avoids complications due to the Rydberg levels and the ponderomotive shifts of the threshold. The second laser mixes the electron wavefunction between two continuum states (C—C transitions); since we avoid the rotating wave approximation, multiple transitions between these continua are allowed. We find that the ionization rate is unaffected by the C—C transitions. Our model of hydrogenic atoms allows redistribution among the continua only during the ionization process and the photoelectron spectra exhibits peak suppression; i.e., the population is not the strongest at the energy of the ionization laser.
Spatial amplification
Authors: Chang Tallis Y. , Hong John H. , Campbell Scott , Yeh Pochi
Published: February 2023

We propose and demonstrate a novel image processing technique called spatial amplification where a set of selected spatial frequency components of an incident image is coherently amplified. In this technique, an incident image is first Fourier transformed onto a photorefractive crystal where it interacts with a nonuniform pump beam to selectively enhance the energy of certain spatial frequency components via two-beam coupling,1 and is then reimaged onto an output plane. The overlap of the pump and the Fourier transformed beam inside the crystal defines the type of image processing that is performed. For example, if only the higher-order frequency components corresponding to vertical lines are amplified, the process will yield vertical edge enhancement. With this description of spatial amplification, one can readily see its similarity to the well-known technique of spatial filtering. However, because it does not remove any spatial frequency components as is common in spatial filtering techniques, there are several advantages of spatial amplification such as high energy efficiency, high dynamic range, and cascadability. In our experiments, a photorefractive BaTiO3 crystal is used as the amplifying medium. The lack of phase crosstalk between the two interacting beams is recognized as the essential part of our technique.
Intrinsic silica optical components by solgel processing
Authors: Hench Larry L.
Published: February 2023

The unique intrinsic optical properties of new alkoxide solgels derived (type V and VI) gel silica optics are compared with types I and II fused quartz optics and types III and IV synthetic fused silica optics. Type V gel silica has excellent transmission in the vacuum ultraviolet with the cutoff near theoretical, based on quantum mechanical calculations, at 159 nm. The high optical transmission extends up to 4200 nm with no OH absorption peaks in the near infrared. Other physical properties and structural characteristics of type V gel silica are similar to the highest grade fused silica but offer the important advantages of netshape casting with high accuracy. This eliminates the labor intensive grinding and polishing of many precision optical components. In addition, optical elements such as Fresnel lenses or elements with internal cavities can be made with the solgel type V silica process. Type V gel silica also has a lower coefficient of thermal expansion than traditional commercial vitreous silica optics and the lower expansion extends over a broader temperature range. It is also possible to make optically transparent gel silica with a controlled volume fraction inside of pores. This new material for optical use is called type VI gel silica. The ultraporous type VI gel silica optics can be impregnated with up to 30-40% by volume from a second phase that can be optically active organic or inorganic compounds. The type VI porous gel silica can also be used as a substrate for laser densification of waveguides.
Additive pulse mode locking
Authors: Liu L. Y. , Haus H. A. , Ippen E. P.
Published: February 2023

No summary was available at press time.
Physical description of interferential mode locking
Authors: Piche Michel , Morin Michel
Published: February 2023

Numerous experimental results1,2 have shown that the coupling of a nonlinear cavity to a mode-locked laser leads to a drastic reduction of the duration of the emitted pulses. In this paper we present a general model describing the operation of such lasers. Our model identifies the coherent superposition of the pulses propagating in the main laser cavity and in the coupled cavity as the key physical process leading to pulse narrowing; hence, the laser operation is described as interferential mode locking. We have developed a Gaussian pulse theory with simple analytical formulas valid in the weakly nonlinear regime. Numerical simulations of the evolution of the pulse intensity in a laser with a nonlinear, nondispersive fiber inserted in a coupled cavity have revealed the existence of an unstable regime at low pump level and the development of square pulses at higher pump levels.
Programmable femtosecond pulse shaping using a liquid crystal multielement phase modulator
Authors: Weiner A. M. , Leaird D. E. , Patel J. S.
Published: February 2023

High resolution shaping of femtosecond pulses can be achieved by spatial masking of optical frequency components which are spatially dispersed within a special grating and lens apparatus.1,2 Previously masking was performed with patterned amplitude and phase masks fabricated by microlithography, and this approach allowed generation of shaped ultrashort pulses ranging from square pulses to coded pseudonoise bursts. In this paper we extend the scope of our pulse shaping technique by using a programmable liquid crystal multielement modulator as a replacement for the prefabricated masks. In particular, we demonstrated pulse shaping with a nematic liquid crystal phase modulator controlled by a linear array of thirty-two individual electrodes spaced on 100-μm centers. We tested the multielement modulator by using 80-fs, 0.62-μm pulses from a CPM ring dye laser and verified that we could generate various shaped pulses, such as odd pulses2 and terahertz rate pulse trains, by adjusting the individual electrode voltages. The modulator could be reprogrammed and a new pulse shape selected with a response time of the order of 100 ms. Futhermore, we have demonstrated gray level (continuous) control of the individual phases, a degree of control not available from prefabricated phase masks.
New wide angle equation formalism for forward light propagation
Authors: Yevick David , Glasner Moses
Published: February 2023

We have recently modeled paraxial light propagation in strongly confining semiconductor rib waveguide ϒ-junctions with various rapid numerical techniques based on the Fresnel equation. The presence of large refractive index changes, however, brings into question our paraxial description of radiation modes. Accordingly, here we verify these results with a new theoretical and computational procedure.
Superresolution in the confocal scanning microscope using extended images
Authors: Young M.
Published: February 2023

Over the past several years Bertero, Pike, and co-workers have built up a theory of resolution based on singular systems analysis. This theory has led to the proposal of a new confocal scanning microscope with a significantly higher resolution than the normal type II microscope. The main new feature of this work has been the utilization of image support which is not fixed geometrically to the object support. In previous attempts to solve the problem of object reconstruction from diffraction-limited image data using an eigenfunction analysis, due to Slepian and Poliak, the extent of the image is restricted to that of the geometric magnification of the object. Clearly, as diffraction effects become increasingly significant, information about the object will fall successively outside the geometric image region. In the confocal scanning microscope, extension of the image support is equivalent to retaining off-axis image plane formation.
Optical heterodyne technique for achieving excellent image detection in highly scattering media such as biological substances and tissues
Authors: Toida Masahiro , Kondou Makoto , Inaba Humio
Published: February 2023

The fundamental advantages and virtues of the optical heterodyne technique are fairly well recognized, and its use is extensive. An optical heterodyne system is understood to be both a receiver and an antenna.1 Its antenna properties can provide not only high spatial resolution for image formation but also excellent directivity to distinguish one specific direction from another. The technique we propose utilizes the optical heterodyne method to achieve image detection in highly scattering media and also to evaluate the capability of image resolution in comparison with the conventional detection methods. The spatial distribution of light in biological tissues and substances is determined by their optical absorption and scattering characteristics. As far as we are aware, no experimental study to use the advantages of the optical heterodyne method have been reported until now for these biological measurements.
Laser incisions in surgery: pulsed vs cw cuts
Authors: Zweig A. D. , Romano V. , Frenz M. , Weber H. P. , Meierhofer B. , Muller O. M. , Mischler C.
Published: February 2023

When laser cutting tissue a coagulated layer is formed along the incision walls. We studied its extension in freshly excised animal dermis cut by identical overlapping laser pulses of 250-μs duration at a repetition rate of 4 Hz. We compare the effect of a free running 2.94-μm Er3+ laser with a penetration depth d < 1 μm and a CO2 laser with d ≈ 10 μm. If the cutting beams are focused to diameters smaller than half of a millimeter, the extensions of the resulting thermal alterations in tissue, being typically larger than 300 μm, depend more strongly on the focal geometry than on the optical penetration depth of the drilling beam. Tissue material is heated, liquefied, and partially ejected during laser cutting.
Adaptive thresholding and peak detection using a spatial light modulator halftone processor
Authors: Oh Tae-Kwan , Fisher Arthur D. , Lee John N.
Published: February 2023

A processor employing a specialized halftone screen combined with the high gamma hardclipping of a microchannel spatial light modulator (MSLM) is used to produce logarithmic transformations of image input intensities. A continuous input image is converted into a pulse width modulated binary output. The binary output is processed with a low pass filter to recover the logarithmic intensity image in a coherent optical system. Another low pass filter is used to produce a smoothed or averaged logarithmic image, which is subtracted from the original logarithmic image with an MSLM operated in its subtraction mode. The peak intensities of the resulting normalized output image are greatly enhanced. This process is a 2-D analog to a cell averaging LOG/CFAR receiver, which has been applied to radar temporal signal processing.1 To date, the observed dynamic range of hardclip threshold of a MSLM is ~100, and the dynamic range of logarithmic transform is ~10.
Spherical surface testing by laser deflectometry
Authors: Rosete-Aguilar M. , Diaz-Uribe R.
Published: February 2023

We present a method to test spherical reflecting surfaces by measuring the deflection of a reflected laser beam from the surface when it is rotated about its center of curvature. A general equation is derived to calculate in polar coordinates the radius as a function of the linear deflection of the beam at the back focal plane of a lens used to collect the reflected light. To evaluate the departures of the surface from the ideal spherical form we also consider the effect of decentering. We present the experimental setup and some results.
Two-body relative attitude control
Authors: Sommer Thomas A. , Duncan Alan L.
Published: February 2023

An experiment is being performed at LMSC to characterize the performance of a device designed to maintain to high precision the relative alignment of large-aperture optical telescopes separated by large distances. The two-body relative attitude control system (TRACS) measures and controls relative angular motions between two V-shaped Zerodur mirrors separated by 2 m. The design eliminates first-order errors due to the instability of the laser and small amplitude motions in the optical components, making it possible to measure all three relative tilts to within a microradian. This is accomplished by directly comparing the beam which samples the orientation of the Zerodur mirrors to a reference beam which carries common path errors. The measurements are derived from quadrant detector outputs which feed back through a control loop to three pizoelectric actuators that control the tilts of one Zero-dur mirror.
Egomotion without correspondence
Authors: Horn Berthold K. P.
Published: February 2023

One can recover the motion of an observer in a static environment directly from first derivatives (spatial and temporal) of image brightness, accumulated over a large part of the image. There is no need to extract features and to determine correspondences between features in successive frames. This is fortunate, since the correspondence problem in the case of motion vision is even harder than it is for binocular stereo, where matching features have to lie on corresponding epipolar lines. Motion vision—at least short-range motion vision—should be easier than binocular stereo, not harder. In the case of rigid body motion there is also no need to first estimate the optical flow, since it is so highly constrained.
Egomotion without depth estimation
Authors: Jepson Allan , Heeger David
Published: February 2023

The motion field for an observer moving through a static environment depends on the observer's translational and rotational velocities along with the distances to surface points. We show how the equations describing the motion field can be split by an exact algebraic manipulation to form three sets of equations, the first of which relates properties of the motion field to the observer's direction of translational motion alone. Therefore, to solve for the direction of translation, the depths and rotational velocity need not be known or estimated. Unlike previous surface-based techniques, we require no assumptions about the smoothness of the surface from which the optic flow measurements are taken, or that the measurements come from the same surface. Instead, we show that this procedure can provide a robust estimate for the direction of translation, given simply a sparse sampling of the optic flow from scenes that contain a significant variation in depth. Moreover, given this estimate we show how two linear equations can be found, one of which provides an overdetermined system of the rotational velocity alone, and the other contains only the relative depths. Again we show that the rotational velocity can be computed robustly, given a sparse sampling of velocities.