bluuebunny/crossref_metadata_2025 huggingface dataset:
Environmental Impacts on the Hubble Space Telescope
Authors: Facey Terence A.
Published: February 2023

The Hubble Space Telescope represents the largest single advance in astronomical instrumentation since the Hale 5 metre telescope at Mt Palomar. Its extreme sensitivity and resolution, however, are susceptible to degradation from a number of environmental effects. This is particularly true for observations in the ultra-violet spectrum.
Materials for Space Optics
Authors: Pierce Bruce
Published: February 2023

Summary not available.
Infrared heterodyne spectroscopy of planetary atmospheres
Authors: Mumma Michael J.
Published: February 2023

It is well recognized that important information on the kinetics (winds) and on the microphysics occurring in planetary atmospheres is contained in intensity profiles of individual atomic and molecular spectral lines. In some cases, unique information is revealed by observing at Doppler-limited spectral resolution, such as the discovery of a naturally occurring CO2 laser near 75-km altitude on Mars. Other examples include the discovery of the failure of local thermodynamic equilibrium in the first 15 km above the surface of Mars, discovery of strong nonthermal emission from Venus, measurement of Venusian winds from Doppler-limited spectroscopy, the measurement of strong emission cores in C2H6 lines on Jupiter, and the measurement of dynamical heating in the polar mesosphere of Mars. All these discoveries were made with ground-based infrared heterodyne spectroscopy, a convenient technique for observing fully resolved line profiles.
Application of new technology to low vision
Authors: Woo George C.
Published: February 2023

A number of technological advances in low vision have been made in the last twenty years. The first part of this presentation deals with diagnostic methodology in low vision. From Sloan's letters for measurement of visual acuity, various logarithmic acuity charts have been derived for the assessment of distance visual acuity. Recent studies on low-vision patients also emphasize the importance of measuring visual acuity with low contrast charts. Some of these charts are discussed. In terms of retinal acuities, the optical principles of instruments including the retinometer, the visometer, and the potential acuity meter are reviewed. The clinical use of these instruments is covered. In addition to spatial frequency thresholds, measurement of contrast sensitivity provides another way in which low-vision patients’ vision can be assessed readily. Subtle changes of vision can be monitored by this technique. Illustrated clinical examples are given. The second part deals with optical treatment for low-vision problems. For example, the use of optical filters and prisms for certain low-vision patients is described. Some optoelectronic sensory aids are available at our Centre for Sight Enhancement. A description of one or two systems employing various optical and electronic components is given.
Thin layer equivalence for absorbing films
Authors: Southwell William H.
Published: February 2023

It is well known from the Herpin equivalent layer concept that a layer of Index n and thickness t is equivalent to a symmetrical three-layer combination at a given wavelength. Recently, it has been shown that for very thin films (t << λ) two layers are sufficient for equivalence. This thin-film equivalence principle allows the construction of layers of arbitrary index from a given high- and low-index pair of materials. Thick layers of arbitrary index may also be constructed with this technique by simply dividing it into many thin layers. We have investigated the question of equivalence for absorbing layers. We have found that for very thin layers, three layers (not necessarily symmetric) are sufficient for equivalence to a film of arbitrary t, n, and k. Again, since thick layers may be divided into thin layers, this generalized equivalence principle may be applied for layers of any thickness. This means that any layer of arbitrary gradient index and gradient extinction may be constructed from thin layer stacks of three materials.
Bistability and mode-mode competition in a homogeneously broadened CO2 laser
Authors: Tredicce J. R. , Poggi A. , Puccioni G. P. , Lippi G. L. , Arecchi F. T. , Gadomski W.
Published: February 2023

Unstable and bistable behavior has been predicted recently in multimode homogeneously broadened lasers as a function of the detuning between the cavity and the atomic frequencies. As an example of a device for which most required physical conditions for the appearance of this instability are satisfied, we have analyzed the behavior of a low-pressure (10–20 Torr) CO2 laser. The operating parameters (relaxation rates for the population inversion, 104s−1, and for the polarization, 108s−1) restrict the accessible range of theoretically expected phenomena to a stable intensity output without evidence of stable self-pulsing. However, mode–mode competition is responsible for bistability in both the intensity and the operating frequency on varying the detuning parameter. This behavior is confirmed by additional observations of the transient that accompanies the jump between the two stable branches. We have also studied the effect of varying the cavity losses and discovered bistability also in the vicinity of the threshold for laser action. This kind of behavior is not predicted by the plane wave Maxwell-Bloch equations but can be explained in terms of a radial gain profile. Both effects—mode–mode competition and transverse—lead to a variety of bistable behaviors depending on gas pressure and discharge current.
Theory of parametric instability in stimulated Raman scattering
Authors: Lin J. T.
Published: February 2023

Parametric instability induced by the medium saturation in stimulated Raman scattering is investigated theoretically via a generalized detuning (1) where ω
p,s,o
are the frequency of the pump, Stokes, and phonon,

ϕ
˙

p
s

is the phase modulation, and the last term is the nonlinear correction of the highly excited anharmonic molecule with an amplitude Q.The steady-state gain and hence the Stokes efficiency, in the presence of the anharmonic term, are governed by a cubic equation of |Q|2which is to be solved from the Bloch and Maxwell equations including the pump depletion. Numerical results are shown for the transition diagram of Stokes efficiency vs input pump intensity at various system conditions at the steady-state. For the transient regime, with pulse duration shorter than the dephasing time, we analyze the temporal profiles of the Stokes and the depleted pump based on a transformed equation which combines Bloch and Maxwell equation as follows: (2) where Tis a nonlinear time, G
s
is the steady-state gain, l0is the input pump intensity, and Uis the real part of the phonon amplitude Q.For an input pulse intensity given by sech2(t/t
p
), Eq. (2) is solved numerically to study the transient pulse profiles in the presence of pump depletion and medium saturation.
Performance of the Spacelab 3 holographic system
Authors: Owen Robert B. , Kroes R. L.
Published: February 2023

The recent Spacelab 3 mission utilized a holographic system to study triglycine sulfate (TGS) crystals produced by low-temperature solution growth. The experiment is of twofold interest to the optics community, since not only did it use an elaborate holographic system, but it gave insight into the growth properties of TGS, a very interesting optical material. A holographic system was chosen to allow optical techniques which were difficult to apply in orbit to be used after the flight by analyzing the holographic reconstructed images. The holograms show 3-D images of the growing crystal and interferometric data on solution temperature and concentration profiles. They are being analyzed by schlieren, shadowgraph, interferometric, and microscopic techniques. Preliminary results are presented. TGS is of interest as an optical material because of its use as a room-temperature infrared thermal detector, with important applications in astronomy, earth observation, environmental analysis, and the military. However, actual performance falls short of its potential, apparently due to common crystallographic defects which may be caused by gravity-driven convection. Convection was eliminated during the flight. It is hoped that the experimenter can understand, control, and model those aspects of the growth process which lead to high-quality single crystals.
Alignment of the Diffuse Infrared Background Experiment optics module
Authors: Magner Thomas J.
Published: February 2023

The Diffuse Infrared Background Experiment is a ten-band filter photometer on the NASA Cosmic Background Explorer. The entire telescope will operate at 2 K. Extragalactic infrared radiation and diffuse galactic radiation in the 1–300-μm wavelength range will be measured. Polarization measurements will also be made for the 1–3.5-μm range. The Diffuse Infrared Background Experiment is a well-baffled unobscured off-axis Gregorian telescope with multiple stops to provide a high level of rejection of both scattered and diffracted radiation. Additional optics are used so that each of three detector assemblies and a tuning fork chopper share a pupil image. The optics consist of an off-axis parabolic mirror, three off-axis elliptical mirrors, a general asphere, a fold flat, and a reflective chopper mirror. A breadboard optics module was constructed and used as a test bed to determine optical alignment procedures for the flight unit, to measure cryo-induced misalignments of the optical system, and to measure cryo-induced misalignments due to cryogenic vibration. Methods used to assemble the breadboard optics module and results of the environmental testing are reported in this paper.
Picosecond laser excitation of Rydberg quantum beats
Authors: Parker Jonathan , Stroud Carlos R.
Published: February 2023

A series of calculations are presented showing the response of an atom to a picosecond laser pulse that simultaneously excites a number of Rydberg states. A coherent electron wave packet is formed. The packet may disperse and reform repeatedly as its center moves along a classical orbit. The repeated acceleration and deceleration of the wave packet as it moves around the orbit leads to a corresponding variation in the radiation rate of the atom. The result is a complicated pattern of multilevel quantum beats. Examples are shown for various excitation frequencies and pulse durations. Experimental implications are discussed.
Space Telescope optical telescope assembly thermal control system
Authors: Bettini Ronald G.
Published: February 2023

The precise on-orbit stability requirements, the need to limit the thermal control system power and weight, and the ten-year life requirement of the optical telescope assembly (OTA) of the Space Telescope required the development of a thermal control system that maintained precise temperature control with a minimum of power and weight and that accomplished this with a high reliability. The achievement of these goals required a significant analytical effort: the development of new thermal control hardware and installation techniques and thermal vacuum testing that verified our approaches and techniques. This paper presents a summary of the thermal control system that Perkin- Elmer developed that maintains the OTA thermal stability with a minimum of power and weight, with the reliability required to meet a ten-year life.
Laser interferometric studies of laser-induced surface heating and deformation
Authors: Lee Wing-Kee , Davis Christopher C.
Published: February 2023

A He-Ne laser-illuminated Mach-Zehnder interferometer has been used to study the time-resolved surface heating and deformation of various solid materials caused by irradiation with the second harmonic (530 nm) of a pulsed Nd: YAG laser. Both thin and thick metal and semiconductor samples have been studied. For thick samples the thermal stress caused by rapid absorption of laser energy leads to local surface expansion that produces a phase chirp of a He–Ne beam reflected from the deformed surface. For thin samples additional surface deformations result from stress-induced mechanical vibration of the sample. For thin samples the deformation of either the irradiated (front) surface or the back surface can be observed. Interferometric detection of the induced phase chirp, for small phase chirps, leads to a linearly related output signal. The signals for both thick and thin samples can be understood quantitatively on the basis of theories that include thermal expansion of the samples and classical resonant mechanical oscillation of two-edge-clamped thin plates. Quantitative measurements of both surface excursion and temperature rise have been made at laser energies substantially below the damage threshold. Extrapolation of our data yields a melting fluence for silicon of 0.42 J/cm2.
Scattering of light by a single-layered sphere in the limit of a tiny core
Authors: Bhandari Ramesh
Published: February 2023

Scattering of light by a single-layered sphere is investigated in the limit of a tiny core. It is shown that the first-order correction to Mie scattering due to the presence of the core is a modified Rayleigh term determined by an incident wave which is the internal field of a homogeneous sphere with the parameters of the shell. Assuming the shell is nonabsorbing, the absorption cross section for the composite particle is calculated and applied to the case of absorption of visible light (λ = 0.5 μm) by a water droplet containing a tiny graphitic carbon (soot) core. Results for absorption cross section per unit volume of soot vs radius of the water droplet predict oscillations which may be identified with resonances in the internal field of the nonabsorbing water droplet, corresponding to the electric dipole mode (n = 1). The mean value in the region of oscillations is around 23 m2/cm3 which is to be compared with a maximum value of 13 m2/cm3 in a polydispersion of carbon particles in air.
Human bisection performance scales to the cortical magnification factor
Authors: Yap Yen L. , Levi Dennis M. , Klein Stanley A.
Published: February 2023

Recent estimates of the cortical magnification factor suggest that the area of the cortex devoted to the fovea is considerably higher than previously estimated. Hyperacuity is thought to reflect cortical processing and for Vernier acuity, foveal and peripheral performance has been shown to differ only in terms of the area of cortex devoted to the task (Levi and Klein, 1984). Performance on a different spatial discrimination task, 3-dot bisection, was measured in the fovea and inferior peripheral field at eccentricities of 2.5°, 5°, and 10° of two subjects using a rating scale signal detection paradigm with feedback. By scaling the stimulus size in proportion to recent estimates of the cortical magnification factor at each eccentricity, the functions of s/s over a wide range of separations of reference dots were shown to remain constant in cortical units from 0° to 10°. Further experiments comparing performance for horizontal, vertical, and oblique orientations of the stimulus in different meridians of the visual field revealed performance to be more dependent on the orientation than the location of a stimulus at a given eccentricity. Specifically, position discrimination was better for tangentially than radially oriented stimuli.
Spectral dynamics of Eu3+-doped glasses under high-power picosecond-pulse excitation
Authors: Quarles Gregory J. , Powell Richard C.
Published: February 2023

Time-resolved fluorescence spectra and lifetimes of Eu3+-doped glasses were studied after picosecond-pulse excitation with the three harmonics of a Nd:YAG laser. The emission spectra were monitored between 300 and 900 nm and the observed bands were identified with transitions from the well known 5D0,1,2 levels as well as with transitions from the 5D3 level, higher metastable states of the 4f configuration, and the 5d level. The properties of these metastable states (lifetimes, quantum efficiencies, and branching ratios) were determined and the dynamics of their pumping and decay were studied. Excitation power dependence measurements were used to identify two-photon absorption processes, and excitation pulse width dependence measurements were used to determine the importance of real intermediate states in these processes. Cross sections for these processes were determined from the time-resolved spectroscopy data. The results are compared for different fluoride and oxide glass hosts.
Special-angle-of-incidence ellipsometry for uniaxial crystals. 2: Positive crystals
Authors: Elshazly-Zaghloul M.
Published: February 2023

We discuss how to optically characterize a positive uniaxial crystal using a novel ellipsometric technique.1 We detect the largest angle of incidence at which a linearly polarized laser beam is reflected linearly polarized. The ellipsometer is composed of only a polarizer and an analyzer. At the detected angle of incidence we measure the s reflectance, perpendicular to the plane of incidence. Using the measured angle of incidence and reflectance we determine the ordinary (No) and extraordinary (Ne) refractive indices using very simple expressions. We conclude with an error analysis showing the very high accuracy of the method.
Phase-resolved resonance scattering and emission in iodine vapor
Authors: Mitra P. , Genack A. Z.
Published: February 2023

We address the distinction between resonance Raman scattering and fluorescence as the excitation source is continuously tuned through resonance. The experiments are performed in iodine vapor using a cw laser, whose intensity is electrooptically modulated in the 0.1-50-MHz frequency range. A lock-in amplifier is used to detect both the in-phase and out-of-phase response of the emission. The modulated signal is found to be the sum of two components. One component varies with angular modulation frequency ω, as (1 + ω2τ2)-1/2, where τ is the lifetime of the excited state. The other is found to be flat within the range of modulation frequency used in the experiment. Since the results of the modulation experiment are the Fourier transform of the response to pulsed excitation, the first component corresponds to exponential decay with the fluorescence lifetime and the second corresponds to a prompt response. A density matrix calculation shows that the prompt response would be absent if the absorption were independent of laser frequency. It exists as a result of the finite inhomogeneous linewidth and the laser detuning from the center of the transition. The amplitude of the delayed and prompt components is a function of laser frequency. This gives a full description of the dynamical response to the emission to linear excitation as the laser is tuned continuously through resonance. The response of the sample to nonlinear excitation is also discussed.
Q-branch spectral line shapes of D2 in foreign gases
Authors: Hurst W. S. , Rosasco G. J.
Published: February 2023

The collisional Dicke narrowing and broadening of spectral lines with foreign gas perturbers has been studied by measuring the third-order nonlinear susceptibility of isolated Q-branch (0-1) D2 lines. Perturber gas mass has been varied by employing dilute (5%) binary mixtures of D2 in H2, He, N2, or Ar, and densities at 296 K were varied from 0.25 to 5.7 amagat. We have used these data to test the validity of soft and hard collision models for describing the spectral line shape and the linewidth density dependence. At high densities, the data are well described by Lorentzian line shapes and a Dicke diffusion expression for the density dependence of the lindwidth. At lower densities, the line shape functions were fit to the data while fixing both the pressure broadening parameters to their high density values and the narrowing parameters to the values predicted from diffusion theory. For the light perturbing gases (H2, He), only the soft collision model fit the line shape and gave agreement with the observed linewidth. For the heavy perturber gases (N2, Ar), neither model described the line shape or the linewidth dependence, the disagreement being greater for Ar.
Los Alamos Fourier transform spectrometer
Authors: Palmer Byron A.
Published: February 2023

The Los Alamos Fourier transform spectrometer is a folded Michelson interferometer using cat's-eye reflectors for the moving mirrors. The maximum path difference is 5 m which gives a resolution of 0.001 cm−1. The interferometer is capable of obtaining spectra from 200 to 20,000 nm with the appropriate optics and detectors. Acquisition time for one scan is 2-6 min depending on resolution and spectral region. The servo control of the interferometer uses a Zeeman split He-Ne laser in a phase lock loop operating at 1.5 MHz. The servo is capable of position accuracies of 0.3 nm and can acquire an interferogram with any reasonable free spectral range that is desired. The A/D converter is an effective 22-bit floating point converter connected to an array processor. The A/D converter control has self-calibration to ensure linearity over the full range. The array processor corrects for any errors in the A/D converter as determined by the calibration and then digitally filters the data to remove noise outside the bandpass of interest. The servo control and the A/D converter are operated by separate 68,000 microprocessors.
Femtojoule optical switching in InGaAsP laser amplifiers
Authors: Sharfin W. F. , Dagenais Marie
Published: February 2023

Semiconductor laser amplifiers are hybrid nonlinear optical devices which offer the advantages of extremely low optical switching energies, low total energy consumption, high gain, and wavelength compatibility with diode laser sources. We have demonstrated optical switching in a Fabry-Perot amplifier. The switch-on and switch-off occur in less than a nanosecond, with optical input powers of about a microwatt. This corresponds to <7000 photons input to the device. Optical gain has been measured in excess of 20 dB. The observed switching results from a change in the index of refraction of the order of 10−4. The index change arises from a decrease in carrier concentration resulting from stimulated recombination. For a given change in the refractive index, the phase shift in a nonlinear etalon is proportional to the cavity length. In a passive device, long cavity lengths are precluded by absorptive losses. In the active device discussed here, a long cavity results in greater gain and low switching power.
Detection of features at specified and random locations on noisy images
Authors: Judy Philip F. , Swensson Richard G.
Published: February 2023

Observers detected cylindrical features superimposed at known (prespecified) or unknown (random) locations within uniform circular areas (pedestals) on noisy computed-tomographic images. The experimental conditions varied the feature's contrast and size (3.0, 7.0, and 16.1 mm in diameter) for large (63 mm) pedestals, and varied the pedestal’s size from 9.8 to 63 mm for a fixed (7.0 mm) feature. As the pedestal increased in size, the feature’s detectability (measured by ROC analysis) increased to a constant level for all six observers, whether the feature’s location was known or random. There was no decrease in detectability for randomly located features, although the ratio of pedestal-to-feature areas increased by more than a factor of 10. Independent of the feature’s size, its detectability was predictable from the signal-to-noise ratio (SNR), as calculated for its matched filter at a known location. Detectability was proportional to the SNR when features were presented in specified locations. Larger values of SNR (higher feature contrast) were required to achieve comparable levels of detectability when the features were randomly located, but the required increase in the SNR did not depend on the relative areas of pedestal and feature. These data suggest that observers’ detection of features in random locations is relatively more efficient than the detection of known-location features.
Gaussian derivative model of spatial vision
Authors: Young Richard A
Published: February 2023

A new mathematical description of visual receptive fields in the striate cortex is proposed. The hypothesis is advanced that receptive field line­weighting profiles along the axis of maximum response are describable as Gaussian derivative functions. Such functions are a close approximation to the optimum functions theoretically possible for the detection and precise localization of visual stimuli in the presence of noise. The shapes of the spatial frequency sensitivity tuning curves of fifty-five monkey cortical cells were well characterized by a single Gaussian directional derivative, most often the first through fourth derivative, with corresponding half-amplitude bandwidths in the range of 2.6-1.2 octaves. The receptive field shapes of cat and monkey cells in the spatial domain, as measured, with bar stimuli, were also well described by a single Gaussian derivative term. Gaussian derivatives generally described, better than Gabor functions, (1) the locations of the zero crossings of receptive field profiles in the spatial domain; (2) the shape of cell’s spatial frequency tuning curve, at the low and high frequency extremes; and (3) the symmetry properties of fields in the spatial domain as a function of their independently measured bandwidths. A new neural model for the formation of receptive fields described how simple differences of offset Gaussians (DOOGs) with identical standard deviations, such as are found in the monkey X-cell pathway, can easily give rise to Gaussian derivativelike functions of any order.
Test for dynamical behavior underlying amplified spontaneous emission fluctuations
Authors: Das B. , Abraham Neal B. , Albano A. M. , De Guzman G. , Tarroja M. F. H. , Gioggia R. S.
Published: February 2023

Amplified spontaneous emission (ASE) signals have been analyzed using an algorithm which computes the dimension of the underlying dynamical attractor if it exists. Experimental time series were obtained by digitizing the detected output of a linearly polarized component of a heavily saturated, homogeneously broadened Xe-He (3.51-μm) discharge tube. The autocorrelation time, τ, of the ASE signal was ~20 ns in accord with Fourier transform limits. The time between two consecutive data points was changed from ~0.02τ to ~0.5τ. There was an apparent dimension of low value for short interpoint time intervals which is likely due to a combination of the transient autocorrelations and the limited data record (1023 pts.). For longer time intervals no dimension could be found, a result similar to that for random noise. We conclude that the signals show no evidence of a dynamical cause for the fluctuations or, if it exists, the dimension of the underlying attractor was not discernible (at least greater than eight) even when the analysis was carried out in reconstructed phase spaces of dimensions up to twenty. This type of noisy behavior contrasts sharply with the low dimensional chaotic output of the unstable lasers even though they may have similar power spectra.
Remote measurements of aerosol back-scattering with a 0.2-J CO2 airborne lidar
Authors: Itabe Toshikazu , Ishizu Mitsuo , Aruga Tadashi , Igarashi Takashi , Asai Kazuhiro
Published: February 2023

An airborne DIAL system with two-color CO2 lasers has been developed for remote sensing of 3-D ozone distribution in the lower troposphere. It is an active nadir-directed system, designed to use tropospheric aerosols as the distributed radar target. A twin-engine Aero-Commander was selected to carry the system. The transmitter of the DIAL is composed of two mini TEA CO2 lasers and a telescope. Typical output energy of the laser with a SiC ceramic preionizer is 200 mJ. The receiving telescope has an almost diffraction-limited primary mirror with a diameter of 300 mm and an f/No. of 2 to collect photons efficiently. The signal is detected with a 1-X 1-mm HgCdTe detector by means of direct detection. For the first step of our DIAL system development we built an airborne one-color CO2 lidar and made flight tests of the lidar to detect tropospheric aerosol backscattering at 10.6-μm wavelength. Flight tests were successfully conducted in February 1985 over the Tokyo area at an altitude of 5000 ft(1.7 km). Results of the flight test showed that height profiles of receiving power corrected by a range-squared over ocean were more variable than those over land. We discuss more details of the flight test.
Continuous-wave laser cleaning of historic monuments and buildings
Authors: Masterson Hugh , Johnson Kristina M. , Bradley Daniel J.
Published: February 2023

Current mechanical and chemical techniques for the conservation and cleaning of stone, although successful in many applications, are not always kind to underlying surfaces. This is a major consideration when cleaning delicate artwork. These techniques are often abrasive, caustic, onerous, and time-consuming. Many surfaces can be cleaned by laser treatment. Previous laser cleaning techniques involved Q-switched pulsed lasers. The use of cw lasers has been neglected for this application. Pulsed lasers divest encrustations by vaporization. The underlying surfaces can be damaged if also subjected to these high-power densities. This is almost inevitable unless peak output powers from Q-switched lasers are accurately controlled. In this paper, a novel two-stage technique using a cw mode-locked Nd:YAG laser (1.06 μm) is presented for removing gypsum encrustations. In the first stage, gypsum is dehydrated by cw laser irradiation. This anhydrite gypsum is then easily removed by brushing. The growth of the anhydrite area is theoretically and quantitatively investigated as a function of laser intensities and exposure times. Optimum laser scanning speed and the maximum volume of encrustation removal per day are determined from these data. A comparison is made with pulsed laser cleaning systems.
Resonance ionization of sputtered atoms: detecting one atom in a billion on a surface
Authors: Calaway W. F. , Pellin M. J. , Young C. E. , Gruen D. M.
Published: February 2023

Development of methods capable of quantitatively detecting low levels of impurities or dopants on surfaces is a formidable task. Instruments for this purpose must be extremely sensitive since the total number of surface atoms is quite low and yet must also be able to distinguish surface atoms from the much larger number of atoms in the bulk. Surface analysis by resonance ionization of sputtered atoms (SARISA) is a trace analysis technique which meets these criteria. Employing SARISA, determination of Fe and Ti concentrations on Si and Mo substrates has been performed. These experiments yield detection limits of 30 ppb with the removal of less than a monolayer of material. At present the detection limit of the SARISA apparatus is fixed by noise due to nonresonance ionization of other sputtered elements. This problem and other noise sources are discussed in light of the potential of SARISA to achieve sensitivities below 1 ppb.
Application of resonance ionization mass spectrometry: survey of the lanthanide elements in the region 430-455-nm
Authors: Young J. P. , Donohue D. L. , Smith D. H.
Published: February 2023

A study of the application of resonance ionization mass spectrometry (RIMS) to the lanthanide elements, except promethium, has been initiated. The spectral range for this investigation has been generally 430-455 nm. The lanthanide atoms are generated at a thermal source and are excited and ionized by a single- or two-color process using a N2-pumped laser and/or one or two dye lasers of broad bandwidth, 1 cm–1. The purpose of the survey is severalfold: to evaluate analytically useful RIMS transitions, to gain further understanding of possible resonant optical mechanisms that can generate ions, and to gain experience in spectral interpretation that can be applied to a broad study of the heavier actinides. Several types of optical process have been identified. Many of the RIMS transitions can be assigned to single-color, resonant, two- or three-photon transitions. Other optical mechanisms for generating ions are also observed, however, such as two-photon processes to a bound state, two-photon transitions to an autoionizing level, etc. At least some of the transitions seen in europium and previously assigned to a possible hybrid resonant effect are due to two-photon transitions to apparently new levels. The implications of these results to RIMS are discussed.
Two-photon laser-induced fluorescence detection of atomic oxygen
Authors: Havrilla G. J. , Choi K.-J.
Published: February 2023

Oxygen atoms have been detected by several techniques including spontaneous Raman scattering, coherent anti-Stokes Raman spectroscopy, intracavity dye laser spectroscopy, multiphoton ionization, and two-photon laser-induced fluorescence. Of these techniques, two-photon laser-induced fluorescence has received the most attention. Using this technique, a number of investigators have detected oxygen atoms in a variety of flames and discharges. The primary advantages of laser-induced fluorescence are the high spatial resolution and high sensitivity that can be attained. This is particularly important for combustion and plasma diagnostics where low atom concentration profiles could provide information concerning fundamental processes.
Use of nonrotational aspherical surfaces in optical systems
Authors: Baker James G.
Published: February 2023

From the time of the Herschelian telescope, optical scientists have recognized that use can sometimes be made of decentered, nonrotational optical surfaces to achieve limited advantages and often practical convenience. Enough background is given to clarify recent applications of generalized nonrotational surfaces to permit convenient focusing and power changes in small cameras. In particular, attention is given to design controls that permit utilization of deformed surfaces over increased apertures and fields of view. Advances in the state of the art are discussed and attention given to limitations presently encountered.
Inverse methods for multiple scattering problems
Authors: McCormick Norman J.
Published: February 2023

The objective of these inverse methods is to estimate the coefficients of a Legendre expansion of the angular single-scattering function from angular moments of external measurements of the ingoing and outgoing angular radiance. Two distinct methods based on the radiative transfer equation have been developed for non-normally illuminated slab geometry targets: a formally exact method that requires the solution of an upper triangular system of equations linear in the unknown coefficients, and an approximate method that requires the solution of a set of uncoupled equations. The first method requires angular moments over both the azimuthal and polar angles of both slab surfaces and is ill-conditioned with respect to simulated measurement errors. One way of circumventing the ill-conditioning is to reduce the number of unknowns by seeking only the coefficients for a model scattering law; example calculations illustrate the estimation of the two coefficients for the Henyey-Greenstein model. The second method, which requires only backscattered azimuthal moments following a pulsed irradiation, is surprisingly accurate, even to simulated measurement errors, but only the single scattering albedo, the asymmetry factor, and perhaps the second-order Legendre moment can be determined.The objective of these inverse methods is to estimate the coefficients of a Legendre expansion of the angular single-scattering function from angular moments of external measurements of the ingoing and outgoing angular radiance. Two distinct methods based on the radiative transfer equation have been developed for non-normally illuminated slab geometry targets: a formally exact method that requires the solution of an upper triangular system of equations linear in the unknown coefficients, and an approximate method that requires the solution of a set of uncoupled equations. The first method requires angular moments over both the azimuthal and polar angles of both slab surfaces and is ill-conditioned with respect to simulated measurement errors. One way of circumventing the ill-conditioning is to reduce the number of unknowns by seeking only the coefficients for a model scattering law; example calculations illustrate the estimation of the two coefficients for the Henyey-Greenstein model. The second method, which requires only backscattered azimuthal moments following a pulsed irradiation, is surprisingly accurate, even to simulated measurement errors, but only the single scattering albedo, the asymmetry factor, and perhaps the second-order Legendre moment can be determined.
Infrared emission computed tomography
Authors: Devaney A. J.
Published: February 2023

The problem of deducing the temperature profile of a weakly inhomogeneous, incoherent radiating object from external field measurements is addressed within the framework of classical second-order scalar coherence theory. Within this framework it is shown that the problem can be cast into an inverse radiometric problem using the concepts of generalized radiometry first introduced by Adrian Walther and subsequently extended and developed by Emil Wolf. The inverse radiometric problem is shown to be solvable by the reconstruction algorithms of diffraction tomography. Diffraction tomography is the generalization of conventional (x-ray) tomography to applications where wave (propagation) effects are dominant. In the usual applications of diffraction tomography an object is illuminated by an external wave and the resulting scattered wave is measured. In the problem under consideration here the object is not illuminated by an external wave. Rather the measured wave is emitted as a result of the temperature profile of the object. For this reason we have called the method propagation emission tomography. The presentation includes computer simulations of propagation emission tomography together with a discussion of practical applications of the method.
Inverse scattering for dielectric media
Authors: Jaggard D. L. , Schultz K. , Kim Y. , Frangos P. V.
Published: February 2023

Several techniques have recently been developed for imaging 1-D and 2-D dielectric objects using frequency domain scattering data. Here we examine these techiques which include both perturbational schemes and exact reconstructions. For 1-D configurations we use a recently derived integral equation by Balanis and a nonlinear renormalization technique developed by us to reconstruct lossless dielectric profiles. The methods are validated by an experiment using a swept frequency microwave source and by simulation. These techniques appear robust with respect to imprecise data. For 2-D configurations, Fourier transform and backprojection methods are used to implement linear, perturbational methods of reconstruction. Again, swept frequency microwave measurements and simulations are used to validate the results for multiply connected dielectric objects. More exact schemes are now under consideration for the higher dimensional case.
Scale-invariant pattern recognition using a nonsymmetrical Fourier correlator
Authors: Szoplik Tomasz , Arsenault Henri H.
Published: February 2023

A new method for shift- and scale-invariant pattern recognition is based on a modification of the classical matched filtering technique. The nonsymmetrical Fourier spectrum of an input scene matches a filter made from the symmetrical FT of a target. The scale of the nonsymmetrical spectrum of a scene changes with the angle in the Fourier plane. Therefore a prototype filter can match the spectrum of an object having a different size in some direction. To reduce the cross-correlation noise, wedge masks are placed in the Fourier plane of a correlator. A scale search is possible by rotating the wedge masks. In the first variant of the system, a common VanderLugt filter is used and a simple threshold detection of the correlation signals is made in the output plane. In the second, a few circular harmonic filters of a target are used successively and a discrimination decision is made in feature space. Computer experiments were carried out for both variants.
Retinal receptive fields and eccentricity
Authors: Lennie Peter
Published: February 2023

In animals like cat and monkey, which have a specialized central area in the retina, the distribution of photoreceptors and the organization of their connections to the brain change greatly as one moves from the central to the peripheral retina. This is reflected in several properties of retinal ganglion cells whose axons form the optic nerve. The density of cells is highest in the central area and, despite the fact that the smallest receptive fields are found there, the overlap of receptive fields is generally greatest. Increasing eccentricity leads to reduced density of cells, larger receptive fields, and some changes in the temporal characteristics of their responses. The interpretation of these observations is made more complicated by the fact that in both species several distinct classes of ganglion cell have been identified and these differ in their distributions on the retina. The purpose of the talk is to characterize the general changes in properties of retinal ganglion cells that occur as one moves from the central to the peripheral retina and to compare the representations of the image transmitted by the different classes of cell.
Changes in acuity and spatial summation with retinal locus
Authors: Smith Robert A. , Cass Peter
Published: February 2023

We used stimuli consisting of two parallel, briefly flashed lines to measure two different aspects of spatial vision. In the first experiment, we determined the luminance threshold for the two-line stimulus as a function of line separation. From these data we determined the area of spatial summation. Using the same stimulus, at 3× threshold, we measured acuity as the separation required to resolve the two lines. In the fovea, the spatial extent of these two measures is comparable, suggesting that both may be tapping the same underlying spatial mechanism. When the experiments are repeated outside the fovea, however, the two measures diverge grossly. At 7° eccentricity, acuity has fallen by about a log unit, while spatial summation decreases little or not at all. It is difficult to devise a plausible model in which spatial summation (as defined here) and acuity reflect the same underlying process. We consider ways to correlate these findings with retinal physiology.
Sampling of spatial information in central and peripheral vision
Authors: Levi Dennis M. , Klein Stanley A.
Published: February 2023

Human observers can bisect a space with an accuracy which far exceeds the retinal grain. How spatial information is sampled to provide such hyperacuity thresholds has been of interest since Hering’s (1899) proposal that local signs are averaged along the length of the lines. We investigated this question in central and peripheral vision of human observers by measuring bisection thresholds for stimuli comprised of discrete samples, each ~1′ long. The number of samples and the intersample spacing were systematically varied. The results show that (1) the critical variable is not the total length of the pattern (i.e., length of the samples plus interspaces) but rather the number of samples; (2) central and peripheral vision differ qualitatively in their sampling characteristics. In central vision, only a small number of samples (5) are needed to provide optimum performance; increasing the number of samples from 1 to 5 results in only a slight improvement in bisection thresholds. The periphery, on the other hand, requires more samples for optimal performance, and thresholds improve in proportion to the square root of the number of samples. The data of strabismic amblyopes show the same

n

behavior as the normal periphery. The results suggest that in strabismic amblyopia, and in the normal periphery, spatial information is undersampled.
Comparison of perceived spatial frequency in the periphery and fovea
Authors: Davis Elizabeth T. , Yager Dean , Jones Barri J.
Published: February 2023

Shifts in perceived spatial frequency as a function of contrast obtained at 0° and 8° eccentricity of the visual field show that the direction of the shifts may not be constant throughout the range of frequencies tested. The perceived frequency of a grating viewed in the periphery, however, always appears to be of higher frequency than one viewed in the fovea. A multiple-channel model which incorporates retinal inhomogeneity may account for these results. Factors such as (1) receptive field size, (2) perceptual spatial frequency labels attached to the ouputs of mechanisms, (3) relative sensitivity of peripheral mechanisms compared with foveal mechanisms, and (4) relative steepness and nonlinearity of contrast transfer functions following the output of peripheral mechanisms compared with foveal mechanisms, can all influence the appearance of visual patterns. Shifts predicted by larger receptive field sizes in the periphery are consistent with the data whereas those predicted by lower spatial frequencies of perceptual labels in the periphery are not. (The other two factors have only a small effect.)
Nth-order autocorrelation functions and peripheral phase discrimination
Authors: Klein Stanley A. , Tyler Christopher W.
Published: February 2023

A pair of repetitive textures with the same Fourier spectra can be discriminated based on the relative phases of the components. We have found that for some pairs of textures phase discrimination is easy while for other pairs phase discrimination is impossible. A scheme for classifying textures based on autocorrelation functions greater than second order is able to account for these results. The autocorrelation scheme allows one to generate patterns with statistical constraints of any order, in one and two dimensions. We show that without scrutiny by foveal attention, discrimination fails at about the level of fourth-order constraints. This autocorrelation analysis also can account for why certain phases are easier to discriminate than others. For example, Rentschler and Treutwein1 showed that in the periphery the threshold phase ϕ for discriminating cos(fx) + cos(3fx + ϕ) vs cos(fx) + cos(3fx − ϕ) is much larger than the phase threshold of sin(fx) + sin(3fx + ϕ) vs sin(fx) + sin(3fx − ϕ). The autocorrelation analysis is in agreement with this result. The autocorrelation approach may provide a general metric for phase discrimination of repetitive textures in peripheral vision.
Broadband atmospheric dispersion corrector using three materials
Authors: Eisenberg Shai , Shu Ker-Li
Published: February 2023

The design goal for an atmospheric dispersion corrector is to find a set of prisms to cancel the atmospheric dispersion over a broad spectrum. Existing designs1 using two prisms are limited by the transmittance of most materials at wavelengths under 0.37 µm. Given three prism materials (a,b,c), a relation between the apex angles of the prisms (θ
a
, θ
b
,θ
c
) is obtained from the constraint of zero net deviation at the center wavelength λo: where the refractivity N
j
is related to the index of refraction, n
j
, by N
j
(λ) = n
j
(λ) − 1.
Poor man’s telescope
Authors: Shafer David
Published: February 2023

Large telescopes are very expensive, partly because of the cost of making and testing highly aspheric mirrors. A large fast-speed parabola or hyperbola may have 100 wavelengths of deformation relative to the best-fit sphere. Smooth surfaces are hard to achieve on steep aspherics, and null test optics can be quite complex and expensive.