bluuebunny/crossref_metadata_2025 huggingface dataset:
D4WM in a mercury discharge
Authors: Richardson Wayne , Maleki L. , Bearman Greg , Garmire Elsa
Published: February 2023

The 73S1 → 63P2 (λ = 546.1-nm) transition of atomic mercury has received considerable spectroscopic attention. In this paper we examine phase conjugation reflectivities and line shapes for various pump powers on this line. The geometry is that of backward D4WM: counterpropagating pump beams and a weak probe intersect at an angle of 0.750° in a quartz mercury discharge cell. The inductively coupled rf discharge provides a density difference of 109–1011 atoms/cm3 between the levels of interest, which yields a small signal absorption α in the 0.3–3-cm−1 range. The best fit to the measured α(l) on line center is obtained using α(l) = α0/[1 + (l/l
s
)] with l
s
= 30 mW/cm2. This form of α(l) is different from what one would expect for a low pressure gas with Doppler broadening. Phase conjugation has been observed with pump powers as low as 3 mW. Spectra obtained by observing the conjugate beam as the laser frequency is scanned through resonance exhibit line broadening of 64–490 MHz depending on pump power. Additionally, line splitting is observed with increasing pump power. These splittings were 72 MHz at 134 mW of pump power. With an estimated Rabi frequency (Ω) of ~60 MHz, the predicted splitting is 3/2 Ω = 90 MHz.
Electrooptic fiber sensor
Authors: Ahmed M. Jamil
Published: February 2023

The proposed electrooptic fiber interferometer has two branches. Only one branch is made of electrooptic material, such as lithium niobate. When the device is immersed in the electromagnetic field, the velocity of light in only the electrooptic arm is affected. This produces a relative phase difference between the light propagating in the two arms. As a result, the intensity of the recombined output light is a function of the phase difference and strength of the ambient electric field. The interferometer has many advantages: it can be immersed in an electric field directly to measure it, obviating the use of metal electrodes; there is no limitation on the length1; and it can be arranged in various configurations, e.g., linear, spiral, coiled-cylindrical, etc. Other versions of the interferometer are possible. In one version the interferometer contains an optical fiber in one branch and an electrooptic waveguide in the other. The electrooptic waveguide can be titanium in diffused waveguide in lithium niobate. In another version the interferometer has optical fiber for one branch and electrooptic layer waveguide for the other, the optical fiber having been properly shaped, cut, polished, and used to couple light to the electrooptic layer waveguide. The proposed device can be used for high voltage measurement, electromagnetic field detection, modulation, temperature sensing, optical signal processing, and so on.
Multiple image reflection volume holographic optical elements
Authors: Kostuk Raymond K. , Goodman Joseph W. , Hesselink Lambertus
Published: February 2023

Microelectronic chip-to-chip interconnection necessitates channeling information from a large number of independent transmitters to a large number of receiver locations. Limitations of existing electronic interconnection techniques have prompted examination of optical methods of connection. One proposal is to use reflection-type holographic optical elements to direct modulated signals from optical sources to detectors. Obtaining multiple images from a single source requires encoding a set of gratings in the same recording medium. This can be done either sequentially (incoherently) or simultaneously (coherently). In this presentation the results of an experimental and theoretical investigation of simultaneously formed multiple image reflection volume holograms are given.
Detection of SiF radicals with multiphoton ionization spectroscopy
Authors: Hudgens Jeffrey W. , Dulcey C. S.
Published: February 2023

We have demonstrated sensitive resonance-enhanced multiphoton ionization detection (REMPI) of silicon monofluoride radicals, SiF, using light from a Nd:YAG pumped dye laser tuned between 430 and 490 nm. This SiF radical is of interest to the semiconductor industry since it is one of the products observed during chemical etching reactions at silicon surfaces. SiF radicals were generated by the reaction of fluorine atoms with silane in a low pressure flow reactor. The laser-ionized radicals were detected in a quadrupole mass spectrometer with a sensitivity of better than 1010/cm3. Two laser excitation schemes were used: (1) simultaneous two-photon absorption through C'2∏
r
← X2∏ and C″2∑+ ← X2∏
r
transitions and (2) sequential one-photon absorption through the (0,0) A2∑+ ← X2∏½ and (1,0)C″2∑+ ← A2∑+ transitions. In both schemes SiF radicals absorbed at least three photons before ionizing. An attractive feature of SiF REMPI detection is that the ion signal is concentrated exclusively into m/z 47.
Central role of thin films in nonlinear optical signal processing
Authors: Gibbs Hyatt M.
Published: February 2023

Nonlinear optical devices may change completely the character of optical signal processing and computing systems by making logic decisions and switching beam directions. This may better utilize the ability of optics to make high-speed massively parallel transformations by preprocessing the results and reducing the amount of data fed back to an electronic system. Such nonlinear devices can be classified as nonlinear waveguides and nonlinear etalons (interference filter and Fabry-Perot). Both use thin films. Both require an intensity-dependent phase change, δϕ= (2π/λ)δ(nL), of 0.1π to π, where δ (nL) is the change in optical path length. This makes the large nonlinearities of semiconductors highly attractive (δn of 10−4 to 1 cm2/kW for band-edge nonlinearities due to excitonic, band-filling, thermal, bound-exciton, etc. effects). Waveguide devices, which can use smaller nonlinearities because a high intensity is maintained over millimeter lengths, are especially applicable to optical communications and other serial processing situations. Micron-thick etalons are a natural for parallel processing of multiple beams and for imaging whole arrays of data at once. The success of thin-film nonlinear optical devices hinges not only on large nonlinear refraction but also on low background absorption and on uniformity sufficient for low-scatter guides and arrays of high-finesse etalons. Thin-film technology offers a variety of growth techniques and the opportunity for engineering desirable properties.
Deconvolution of ocular fluorophotometer data
Authors: Koester Charles J. , Smith R. Theodore , Campbell Charles J.
Published: February 2023

Following the intravenous injection of fluorescein, the concentrations of fluorescein in the ocular aqueous and vitreous are measured to determine the integrity of the blood-retinal barrier. The fluorophotometer has an effective sampling volume formed by the intersection of the excitation beam and the fluorescence detection beam. As the sampling volume is scanned through the ocular media, it produces an instrument spread function that is convolved with the actual distribution of fluorescein. Provided that the spread function can be determined, it is possible to perform a deconvolution to recover an approximation to the original distribution. Several methods of deconvolution can be utilized. Factors that affect the results include sampling interval, alignment of the data, precise knowledge of the spread function, and noise. Simulations and model data demonstrate that substantial improvement can be achieved. With patient data, the principal advantage of deconvolution is the ability to assess fluorescein concentration close to the retina, a region that is otherwise obscured by the presence of strong fluorescence in the retina itself.
Image restoration in random time-varying systems
Authors: Saleh Bahaa E. A. , Ward R. K.
Published: February 2023

The problem of restoring a constant image distorted by a system of random time-varying impulse response is discussed. The restoration is based on the observed time-varying distorted image during a finite period of time T. Three methods are considered. Restorations based on the average image is considered first. If the observation time T is finite, the system noise remains to play a role. This results in a restoration problem with object-dependent noise. Second, restoration based on the averaged spatial correlation of the image will be introduced. For finite T the result is an image restoration problem which we could not solve. Third, restoration based on a finite number of image frames will be examined in detail. We use an iterative method based on the minimum-variance unbiased estimation. When the frames are uncorrelated, we obtain the result based on using the average image as a statistic. When the frames are correlated but space–time separable, a Karhunen-Loève transformation that decorrelates the frames is used to reduce the computations. Using an example, we show how the restoration error drops as more frames are included. The higher the interframe correlation, the more reduction of restoration error is obtained by using the frame data, compared with the error of restoration based on frame averaging.
Superresolution in image construction
Authors: Saleh Bahaa E. A. , Bucklew James A.
Published: February 2023

A diffraction-limited imaging system employing a high-contrast detection system, e.g., a microlithographic system, is mathematically equivalent to a bandlimiter followed by a hardlimiter. The output of that system is a binary image. In the 1-D case it is a series of parallel lines. Is it possible to construct at the output of that system a finite number of lines of arbitrary locations and widths, even exceeding the resolution of the system (as determined by its bandwidth)? We show that if one is only interested in a region D of finite extent within which the lines lie (i.e., one disregards what the image does outside D), the answer is always affirmative.
Porosity and density measurements from Rutherford backscattering analysis (RBS)
Authors: Messerly M. J. , Macleod H. A. , Leavitt J. A. , Targove J. D.
Published: February 2023

Carbon contamination levels in the 5–15-at. % range have been observed in optical thin films deposited on graphite substrates for RBS analysis. The lack of large amounts of carbon in films grown on beryllium indicates that substrate carbon migrates along columnar boundaries and rests in the voids of films evaporated onto graphite. We originally believed that this excess carbon nullified the RBS results but have found that the stoichiometry and density of films deposited on both C and Be substrates were essentially the same. The depth profile of the carbon contamination then serves as a probe of relative film porosity without interfering with the other elemental determinations.
Influence of thin metal films on the optical scatter and related microstructure of coated surfaces
Authors: Al-Jumaily G. A. , McNally J. J. , McNeil J. R. , Bennett Jean M. , Hurt Hugh H.
Published: February 2023

Deposition of a thin (200–500-nm) metal film on a polished metal substrate changes its optical scatter characteristics.1 The light scatter due to high spatial frequency structure is reduced by as much as a factor of ten, and total integrated scatter is reduced by up to a factor of four. This effect is strongly influenced by the deposition technique employed, initial surface roughness, and film thickness. We have examined the scatter characteristics of Cu, Ag, and AI films deposited using evaporation, magnetron sputtering, and ion assisted deposition (IAD), and the scatter reduction is most apparent in the case of films deposited using IAD (300 eV Ar+). The reduction in optical scatter is presumably due to a reduction in the microstructure of the surface (i.e., a smoothing effect). However, when the samples are characterized using a profilometer (Talystep), the smoothing effect is not observed. An attempt to resolve this apparent discrepancy is discussed; a comparison of the spatial frequency bandwidths of the two measurement systems will be presented.
Zero crossings, bandwidth compression, and restoration of nonlinearly distorted bandlimited signals
Authors: Marvasti Farokh , Jain Anil
Published: February 2023

Aliased signals due to undersampling or nonbandlimited signals can be reconstructed exactly if the original signal is redundant. The necessary and sufficient conditions are found for a class of nonlinear operators ( )1/
n
for bandwidth compression. We have shown that the necessary and sufficient condition for such a compression is that the signal has nth ord. zeros. There are other nonlinear operators such as 1n(y), e
y
, y
a
, 1/y that are potentially capable of bandwidth reduction (making a nonbandlimited signal bandlimited). It is shown that any nonlinear distortion can be compensated provided that the nonlinear operation is analytic and monotonic. This fact has a potential application wherever nonlinear distortion is a problem. The signal recovery is due to the fact that the zeros of a bandlimited signal are somehow preserved in the derivative of the distorted signal. From the zeros of a bandlimited signal, one can always find the original signal within a scale factor.
Optimized binarization of sampled images and holograms
Authors: Just D. , Hauck R. , Bryngdahl Olof
Published: February 2023

Binary representations of sampled gray tone images and holograms are frequently used with success in optical information processing. Some of the binarization procedures used are based on the employment of carrier functions. Because of their passive nature, no object-dependent computations are necessary. In general these methods encounter the following handicap: to obtain a reasonable spatial resolution, a high carrier-frequency is chosen which implies a small number of sampling points with respect to the carrier period and, accordingly, a small number of representable gray levels. This trade-off can be avoided if one abandons the notion of a carrier period fixed to the underlying sampling raster. By a proper choice of carrier period and orientation with respect to the sampling raster it is possible to attain an optimization which includes a high spatial as well as high gray tone resolution.
Triangulation with expanded range of depth
Authors: Häusler G. , Maul M.
Published: February 2023

In conventional triangulation systems for 3-D sensing there is a trade-off between range of depth and resolution. We proposed a triangulation system with a large depth of field (1 m or more) and at the same time high resolution (20 μm or better). The system is essentially based on an arrangement of axicons in the illumination device and on the use of the Scheimpflug condition in the observation device. A suitable scanning-by-deflection geometry is described.
Toward visual primal sketches
Authors: Brady Michael , Yuille Alan , Asada Haruo , Ponce Jean
Published: February 2023

In his seminal paper "Early Processing of Visual Information,” David Marr introduced the primal sketch concept as a rich multiscale representation of "significant” intensity changes. The goal of building that primal sketch is, to date, unrealized. We have extended the concept to apply to significant changes in other important representations of visual information, specifically curvature changes along planar curves and surface changes in range maps. We have performed preliminary investigations of the primal sketch of intensity changes. In each case, we introduce a set of parametrized discontinuities as primitives and derive expressions for their convolutions with the first and second derivatives of a Gaussian. We derive symbolic signatures for each primitive and describe implemented algorithms that discover instances of the primitives. Applications of the resulting representations are sketched.
EUV spectroscopy using laser-generated plasma light sources
Authors: Mcilrath Thomas J.
Published: February 2023

Laser-produced plasmas have been shown to be excellent laboratory sources of continuum radiation in the XUV and soft x-ray spectral region (10-1000 Å). We present high-resolution photographic and photoelectric spectra of the continua between 40 and 500 A, comparing different target materials for cleanliness and relative intensity of the continua. Photographic spectra have been obtained on a 10.7-m grazing incidence spectrograph and a 6.67-m normal incidence spectrograph and a photoelectric spectra obtained with a 1.5-m grazing incidence spectrograph using a multichannel detector array. Spectra have been obtained using both a Nd:YAG (10-Hz) laser and a ruby (0.1-Hz) laser. The XUV output is characterized by excellent intensity stability, high intensity, and an almost line-free continuum. A comparison with other short wavelength light sources is given. The source has been used for atomic absorption spectroscopy of ground state and excited state neutral atoms and for ground state atomic ions by placing samples in a metal vapor heat pipe and using a resonant dye laser for excitation and ionization of the atomic vapor. Inner shell absorption spectra of Ca, Ca+, and other atomic systems are presented.
XUV resonant multiphoton ionization of H2
Authors: Kung A. H. , Page R. H. , Larkin R. J. , Shen Y. R. , Lee Y. T. , Gershenfeld N. A.
Published: February 2023

We have applied XUV-UV two-photon resonant multiphoton ionization (REMPI) to the detection of H2, an important homonuclear diatomic that is infrared inactive and has its electronic bands in the VUV and XUV spectral regions. The Lyman

(

B
1

Σ
u
+

)

band and the Werner (C1Π
u
) band are used as the resonant intermediate state in this study. The Werner band is found to be superior because ionization produces predominantly

H
2
+

whereas the Lyman band also produces H+ ions with variable intensities. By using the v' = 0 state of the Werner band as the intermediate, we achieved a sensitivity of 1.1 × 106 molecules/cc/quantum state. This is 2 orders of magnitude better than any techniques previously reported for H2. The ion signal is shown to be proportional to the ground state absorption when ionization from the excited state is saturated. This saturation reduces the MPI process to a linear process and simplifies calibration in the application of this technique to quantum-state-specific detection of H2. This technique will also be useful as a sensitive detector of other homonuclear diatomics such as F2, Cl2, and N2, which are of great general interest in chemistry, combustion, and semiconductor fabrication.
Inverse optoacoustic effect
Authors: Diebold G. J. , Stewart R. B. , Didascalou S.
Published: February 2023

If a spectrophone containing an infrared active gas is placed near a cold surface and the path between the two is interrupted, the periodic flow of radiation from the spectrophone causes a sound wave to be produced. Experiments were done with a 3.4- × 1.7-cm diam acoustic cell that was fitted with thallium bromoiodide windows. The cell (maintained at room temperature) viewed a liquid nitrogen Dewar whose interior was coated with soot from an acetylene flame. At a pressure of 1 atm signals were found (in increasing order) for the following gases: CO, CH4, SF6, CO2, C3H6, C2H4. The phases of the acoustic signals were π/2 relative to the modulation (but π relative to the normal optoacoustic signal). Further experiments were carried out to determine the magnitude of the acoustic signal as a function of gas concentration. As the concentration of SF6 was lowered from a mole fraction χ of 1 the signal amplitude increased, peaking at χ ≅ 0.1. The signal was linear with mole fraction for χ < 10-4. The amplitude response is not simple since, depending on wavelength, the gas is both optically thick and thin at the same time. For the optically thick part of the gas, the acoustic signal is generated in a small region near the window of the spectrophone cell.
Determination of the central position of a rotating object by laser Doppler velocimetry
Authors: Matsuda Kiyofumi , Eiju Tomoaki
Published: February 2023

Determination of the central position of rotation is an important technique. This technique is, for example, useful for the operation of a machine tool. If the height of the tool is not adjusted to the central position of rotation, the central portion of a workplace is left without being cut. Here a new method of using laser Doppler velocimetry (LDV) is proposed for this determination. The principle is based on the fact that the tangential velocity of the rotating object is proportional to the distance between a measuring point and a central position. Therefore the tangential velocity is measured by the differential LDV with a microscope and the central position is determined by finding the place where the tangential velocity becomes zero. In the experiments, the velocities at two points to each axis of the Cartesian coordinate were measured, where the separation of two points is measured in advance. By the simple calculation with measured values, the central position where the tangential velocities become zero could be determined within the accuracy of 1–2 μm.
Grating imaging and its application to displacement sensing
Authors: Hane K. , Grover C. P.
Published: February 2023

Studies relating to the imaging phenomenon due to periodic apertures include Fourier imaging, Lau effect, imaging by gratings in tandem, and the geometrical optics approach. Most of these investigations involve relatively high frequency gratings to constitute the periodic object and the imaging pupil which is usually located midway between the object and the image planes. In this paper we consider a restricted class of grating imaging of a low frequency object where the ratio of its period to that of the pupil is very high, typically of the order of 103. The images are produced in the close vicinity of the pupil at extremely high demagnifications. In the geometrical optics approach, an analogy has been drawn with the micropinhole imaging1 where each slit in the imaging pupil is considered to be the 1-D analog of the pinhole. The phenomenon has also been investigated from the standpoints of the Fresnel-Kirchhoff diffraction theory and the MTF concepts. Furthermore, the associated high magnification obtained by interchanging the conjugate planes has been employed for microdisplacement sensing with a submicron resolution. The analysis also includes the characterization of the magnified images and details of the detection technique.
Real-time electrooptic moire strain determination
Authors: Chiang Fu-Pen , Krishnamurthy R. S.
Published: February 2023

Traditionally the measurement of strain from optical methods such as the in-plane moire technique is carried out by obtaining the displacement data from a fringe pattern and subsequent differentiation. In this paper, an electrooptic method is proposed for direct measurement of strain from moire fringes on test specimens by a moving-fringe procedure. A simple, real-time strain evaluation is achieved by directly processing intensity signals to obtain phase information from the moving fringes created by grating translation. The strain value at a point is directly proportional to the phase difference between the signals from two closely spaced photodetectors in the fringe field. The specimen carries a bonded grating over which a reference grating is translated at a constant velocity. The detector output variations due to fringe movement are sent through signal conditioning units to a programmable counter interfaced with a small computer. The measured phase difference is used for direct calculation and display of strain values. Preliminary results indicate that an accuracy better than 50 microstrains is easily achieved and is largely independent of the range of strain measurement. This optical strain-gauge technique using only noncoherent light offers the advantages of quick, realtime, remote, and selectable-point strain evaluation.
Coupled modes of phased array lasers
Authors: Hardy Amos , Streifer William
Published: February 2023

A new theory describing coupled mode propagation in an array of coupled arbitrary optical waveguides is developed. The formulation unambiguously accounts for real and/or imaginary index perturbations and its solutions yield array mode (supermode) patterns and propagation constants. Several examples of coupled TE slab waveguides are evaluated and the results are shown to compare very favorably with exact solutions. The calculated propagation constants and mode patterns differ quantitatively and qualitatively from those derived from the prior theory. In particular, the array mode gains derived according to the new theory agree very well with exact solutions and predict different ordering and splitting than those derived by the prior theory. These results are illustrated by examples of real-refractive-index 10-waveguide arrays with various chirps in waveguide dimensions and locations. Near-field and far-field patterns are shown for the array modes (supermodes) generated by such lasers.
Individual spatial modes of a phase-locked injection laser array
Authors: Andrews J. R. , Paoli T. L. , Streifer William , Burnham R. D.
Published: February 2023

The oscillating spatial modes of an eleven-stripe gain-guided phase-locked AIGaAs injection laser array with a multiple quantum well active layer are observed by spectrally resolving its far-field radiation pattern. Nine distinct patterns are identified. The widening of the most intense outer lobes correlates with the shift of the wavelength of the mode to shorter wavelengths. The origin of the observed far fields is not consistent with a uniform array of emitters with equal coupling between the elements. When the array is placed in an external cavity containing a mirror, it is possible to select individual spatial modes of the compound resonator as observed in the spectrally integrated far-field patterns. A large number of patterns are observed, including the fundamental mode. Many of the far-field patterns selected with the external resonator follow the same correlation in angular separation of the outer lobes and the wavelength shift of the longitudinal modes as the native array. The external reflector induces asymmetry in the intensity distribution for many of the patterns. Operation of a phase-locked laser array in conjunction with an external resonator is shown to be a useful technique for spatial mode selection.
Injection-locking of diode-laser arrays with a stable single-mode cw dye laser
Authors: Hohimer John P. , Owyoung A. , Hadley G. Ronald
Published: February 2023

The injection of optical radiation from a master oscillator into a diode-laser array provides a means for achieving a single-lobed single-frequency output beam at power levels exceeding 100-mW cw. In our study of injection locking in diode-laser arrays, we used a single-frequency tunable cw dye laser as a master oscillator. This approach provides us with considerable control over the injection wavelength, bandwidth, intensity, and spatial profile. With a commercial ten-element diode-laser array operating at 100-mW output, we observe a single-lobed off-axis far-field beam pattern when a single element at either end of the array is injected at milliwatt power levels. In injection-locking conditions, a diode-laser linewidth of ≤2 MHz and a detuning range of several tens of gigahertz were measured. We also observe an angular scanning (1.2°) of the emission angle of the single-lobed output beam of the diode-laser array as the injection wavelength is varied over 50 GHz. This angular steering capability is of potential importance for the rapid direct pointing and scanning of diode-laser arrays.
Flash enhancement of isoluminant chromatic discrimination
Authors: Eskew Rhea T.
Published: February 2023

We have observed that when two isoluminant fields, which are juxtaposed with no dividing line between them, are adjusted from an initial match to differ slightly along a tritanopic confusion line, the initially apparent chromatic difference fades away over a brief but perceptible interval. A larger difference is required to reach a stable chromatic threshold. This effect was explored by flashing the fields simultaneously for various durations, and having the observer adjust the chromatic difference to threshold on the basis of the appearance of the fields at the end of the flash. As predicted, there is a duration-dependent enhancement of sensitivity for flashed relative to steadily viewed fields. A similar but smaller effect was found for fields differing along a deuteranopic confusion line, but no effect was found for a luminance discrimination. The time course of the enhancement is slow, peaking at between 0.2 and 0.4 s and ending by 1.6 s. Control experiments suggest that the effect does not depend on second site adaptation, and that it is dependent on the fields being juxtaposed. The observed fading of chromatic differences may be the result of a time-dependent averaging process which assigns a hue to a given region; when the fields are juxtaposed at equal luminance, the averaging process spills over into the adjacent region, reducing the apparent difference between the two fields over time.
Forming parallel fringes of variable spatial frequency
Authors: Rhodes William T. , Stroud Robert W.
Published: February 2023

We wanted to produce an array of parallel fringes of variable spatial frequency for use in signal processing experiments. Such fringes can be formed by interfering two coherent waves from orthogonally articulated galvanometer-mounted mirrors. However, because surface flatness on galvo-mounted mirrors is rarely better than one-quarter wave, it is virtually impossible to obtain, by direct interference of the waves, fringes that are straight. Holography provides a means for straightening such fringes. In holographic terms, we allowed the wave from one galvo-mirror to interfere with a holographic reconstruction of the same wave but with a slight relative tilt of the two waves. So long as aberrations are not excessive, the two aberrated but essentially identical waves interfere to produce straight fringes. Analysis and experimental results are presented.
Optical techniques for binary matrix-vector multiplication
Authors: Chandran Vinod , Krile Thomas F. , Walkup John F.
Published: February 2023

An optical technique for multiplication of binary numbers is described. A novel feature of this technique is the optical parallel generation of all carriers. The system, based on the polarization-rotation property of a liquid crystal light valve, may be space-shared to form an array of multipliers and developed into an optical matrix-vector multiplier. The system offers a better solution to the problem of propagation of carriers than the residue arithmetic approach. It has the potential of achieving high throughput rates without sacrificing noise immunity. The results of proof-of-principle experiments are discussed.
States of pairs of electrons
Authors: Rau A. R. P.
Published: February 2023

When two electrons are excited from the ground state of an atom, qualitatively new characteristics appear. This is particularly so with increasing excitation toward the ionization limit for the two-electron continuum. The increasing liberation of the electrons from the dominant central field in the atom causes greater relative importance of their mutual interaction. The independent particle picture becomes inadequate, especially for excitations in which the electrons remain comparable in their excitation. Such states are distinguished from those having disparate excitation in that, for the latter, independent particle labels for the radial motion (inner and outer electron) remain appropriate, but for the former a language that treats the two on par throughout is required. The two classes have been dubbed valley and ridge states. When viewed in joint coordinates of the pair of electrons, the potential surface of the system displays valleys in which one of the radial coordinates is small and a saddle region in which the two electrons remain comparable. Ridge states reside in the saddle, a long series having been observed for the first time in the He- system. Their description requires the use throughout of new quantum numbers characterizing the pair as a single entity. These matters and their experimental implications are discussed.
Precise frequency synthesizer scanning of a single tunable laser using electrooptic modulation techniques
Authors: Rayman M. D. , Hall J. L. , Aminoff C. G.
Published: February 2023

We have developed a new single-laser/rf sideband technique to provide accurate frequency guiding of a tunable cw dye laser. A high efficiency, broadband electrooptic modulator produces rf sidebands on a portion of the laser output. One filtered sideband is presented and locked to the resonance of a stable optical reference cavity using the output error signal to servo control the laser frequency. Thus computer-programmed changes of the rf source frequency are directly transferred onto the laser’s carrier frequency. Drifts in the cavity are measured (and corrected) when scanning the laser over an atomic resonance by periodically relocating the center of the atomic line relative to the cavity. Computer-feedforward tuning of the laser and on/off switching of the servo locks allow frequency jumping to another resonance, perhaps many reference cavity orders away. (The FSR itself can be measured very accurately with rf sideband techniques.) We measured isotope shifts and hyperfine splittings in the Hg (63P2–73S1) transition at 546.2 nm. These frequency intervals (from 850 MHz to 32 GHz) were measured with 2 × 10−3 linewidth accuracy, e.g., ~50 kHz for adjacent isotopes.
Measurement of orientation and image velocity through hierarchical processing
Authors: Fleet David J. , Jepson Allan D.
Published: February 2023

This paper concerns the first functional level of visual processing in which basic image properties are measured and made available for later interpretation. We constrain this level to be a blind process, that is, an image-independent process which involves no previous or concurrent interpretation. Interpretation is postponed until a rich description of the image, including at least orientation and velocity information, is available. The simultaneous use of such different types of visual information will facilitate most subsequent tasks. For example, in the human visual system, primitive motion and depth information contribute significantly to early form interpretation. The velocity selective mechanisms we propose correspond to short-range motion processing in the human system and require no previous spatial interpretation. By contrast, current approaches to the determination of optic flow in machine vision rely on some degree of spatial interpretation (such as contour estimation, peak finding, or more elaborate spatial analysis). Here, we show the extraction of orientation and 2-D normal velocity based on layers of explicit (bottom-up) and implicit (lateral interactions) spatiotemporal processing. The hierarchy allows a very simple and efficient construction of mechanisms that are well localized in space–time and tuned to narrow ranges of orientation and speed. The degree of specificity can be altered by varying the number of layers in the cascade and the form of processing in each layer.
Image reconstruction from partial Fresnel zone information
Authors: Rolleston Robert , George Nicholas
Published: February 2023

An iterative algorithm for reconstructing an image from partial Fresnel zone information is discussed. With the standard 4-F canonical optical processor, processing is done midway between the two lenses in the Fourier transform plane. While others have studied reconstruction from partial Fourier plane information, we have investigated methods of reconstructing an object from partial information in the Fresnel region of an optical processor. Efficient digital calculation for integrations with a Fresnel-zone type of kernel are described. Iterative algorithms for reconstructing an object from either the phase or magnitude of the Fresnel zone transform are discussed. In the case of reconstructing an image from the Fresnel zone magnitude, we obtain good images in fewer iterations at locations which are farther from the Fourier plane. Reconstructing an image from the Fresnel zone phase is fairly insensitive to this shift out of the Fourier plane. In another investigation, we start with the assumption that the object has been coded into an unknown location in the Fresnel region. We describe an iterative searching technique that locates this position; thereafter we reconstruct the image.
Generating real-time curvature contours with shearing interferometry and Talbot effect
Authors: Chiang Fu-Pen , Yu X. , Yun D. Z. , Dong B. H.
Published: February 2023

In the small deflection theory of thin plates, the bending stress is directly proportional to the curvature of the deflected plate surface. Most optical methods, such as holographic interferometry and shadow moire, give deflection contours which have to be differentiated twice to yield curvature values. Since numerical differentiation is intrinsically error prone, it is important that it be avoided whenever possible. In this paper we present a technique whereby real-time curvature fringes of a mirrored specimen surface can be obtained with a simple Ronchi grating through the use of shearing interferometry and the Talbot effect. It is done by illuminating the deflected specimen surface with a coherent beam through the grating and observing the resulting wave at a certain distance away. If the distance between the specimen surface and the observation plane is one of the Talbot distances and the resulting wave is the sum of only zeroth-order and two first-order diffraction waves, a high quality fringe pattern representing curvature contours is obtained. A sensitivity of 2 × 10−6/mm/ fringe has been achieved. Both theoretical analysis and experimental demonstration are presented.
Magnetic resonance imaging techniques for flow visualization
Authors: Helman James L. , Hesselink Lambertus
Published: February 2023

Magnetic resonance imaging techniques can be used to study fluid systems which are difficult or impossible to probe with optical methods. The problem in imaging fluid flows with magnetic resonance has been the length of time necessary to acquire an image. Recent developments in magnetic resonance imaging techniques indicate that much shorter acquisition times may be possible.
Massively parallel computation in artificial intelligence
Authors: Feldman J. A.
Published: February 2023

Massively parallel systems, with millions of simple computing units, are becoming increasingly important in artificial intelligence and computer vision. Applications of such models include local operations like convolutions, cooperative computation as in stereopsis, and perceptual organization as evidenced by ambiguous figures. Massively parallel (connectionist) models appear to be an excellent method for formalizing these problems and computationally similar ones such as the resolution of ambiguous word meanings. One particularly attractive feature of these models is their direct relation to neurobiology.
Recent developments in digital optical computing
Authors: Jenkins B. K.
Published: February 2023

Required elements in a digital optical computing (DOC) system are a nonlinearity (e.g., gates), interconnections, memory, and input/output (I/O). These may or may not be physically distinct units. The nonlinearity provides gain, regeneration of signal level, and noise reduction or elimination. I/O is required to interface with the outside world, electronic machines, or other optical machines. The nonlinearity and I/O dictate the most important limitations in DOC systems. New and improved devices are reducing the severity of these limitations. Memory may be built out of the nonlinearity and interconnections or may be separate. A hierarchy of memories may be employed; free-space propagation can function as memory; memory could be associative. The most important advantages of DOC systems are due to the interconnections and the resulting architectures that are made possible, e.g., massively interconnected processors that permit increased speed-up over their electronic counterparts. Digital optical computing systems can be characterized by the computations performed (numeric or symbolic), control structure (SIMD or MIMD, control flow, or data flow), likely instruction sets or software, speed of the logic, and by the type and location of the nonlinearity, interconnections, memory, and I/O. These issues are discussed in an overview of recent DOC systems.
Laser theory without the rotating wave approximation
Authors: Vyas Reeta , Singh Surendra
Published: February 2023

In laser theory and other branches of quantum electronics certain terms oscillating at twice the resonance frequency are dropped from the interaction Hamiltonian. The effect of these counterrotating terms on the operation of a single-mode laser is considered using the model of Scully and Lamb. It is found that these terms lead to a shift of the laser threshold and a broadening of the photon number distribution.
Extreme pressure broadening of three-photon resonances in noble gases
Authors: Ferrell W. R. , Payne M. G. , Garrett W. R.
Published: February 2023

A pressure-broadening study of three-photon and one-photon resonances was performed using counterpropagating, linearly polarized laser beams. Self-broadening, as well as the collision-induced effects due to the presence of a second noble gas, was investigated for the 6s, 6s′, 5d and 7s of xenon and the 5s′ of krypton. A multiphoton ionization scheme in a calibrated proportional counter is the basis of a new technique by which collisional processes can be investigated for high pressure regimes which have previously been inaccessible to investigation, particularly for self-broadening where the mean free path of the photons is of the order of 10−3 cm for pressures as low as 1 Torr. Using this technique, we have recorded the collision-induced widths and shifts of the resonance for pressures up to 1000 Torr. In the hundreds of torr range, asymmetric, self-broadening line shapes were observed with full widths and shifts which were greater than five times the laser bandwidth (0.002-0.005 nm).
Optical cellular logic processors
Authors: Jenkins B. K. , Sawchuk Alexander A.
Published: February 2023

A cellular logic processor (CLP) has one processing element or cell for each pixel of an image. It can implement many image processing and computer vision operations with a very high degree of parallelism. In electronics, the connections between cells are usually on a nearest-neighbor (4-neighbors or 8-neighbors) basis only. In optics, the increased interconnection flexibility may permit the construction of other topologies, such as cellular hypercubes and pyramids. These topologies can substantially reduce computation time for global tasks, e.g., summing and regional property computation, histogramming, and transforms. Incorporating some of these into the CLP architecture so that they can be implemented at the hardware level can yield the greatest speed advantage. This may result in cells that are not all identical, or in additional PEs which do not correspond to image pixels. The resulting architectures and their possible implementation with optical hardware will be discussed. This optical hardware can include volume holographic elements to maximize the number of interconnections and to take advantage of regularity in the interconnection. Volume holograms may also incorporate focal power, thereby reducing or eliminating the number of lenses needed. The holograms may be recorded optically by using an automated system under computer control, or by optically copying a computer-generated hologram, or by a combination of both methods. Resulting characteristics of the optical system are discussed.
Effect of apodization in multiaperture aberrated imaging systems
Authors: Mills James P. , Hugghins Arley J.
Published: February 2023

The effect of subaperture apodization on the amplitude impulse response has been calculated when various amounts of the third-order aberrations are present in the individual subapertures. A computer program has been developed which models a multiaperture imaging system. The model variables include size and placement of subapertures, type of apodizer, type of aberration, and choice of several canonical objects (point, two points, edge, or bar). The theoretical imaging performance of the system, in terms related to the choice of object, is reported. Depending on the intended application of the system, apodization can result in an improved image.
Soliton propagation in long fibers with periodically compensated loss
Authors: Mollenauer L. F. , Gordon J. P. , Islam M. N. , Stolen R. H.
Published: February 2023

Both experimentally and with computer simulation, we study soliton propagation in an all-optical long-distance communications system where fiber loss is periodically compensated by Raman gain. We find that the fidelity of soliton transmission is a function of the ratio L/z
0
, where L and z
0
are the amplification and soliton periods, respectively: pulse distortion shows a peak near z
0
= L/8, whereas the soliton is well preserved everywhere for z
0
≪ L/8. Finally, for z
0
≫ L/8, although not preserved everywhere, the soliton is recovered periodically with the pulse energy. We also describe optimal system design based on the exceptional pulse stability and low soliton powers to be had in the region z
0
≫ L/8. Typical amplification periods are in the 30–50-km range, pump powers are <100 mW, and for bit rates in the 10-GHz range, time average signal powers are at most a few milliwatts. The single-channel rate-length product for error rate <10−9 is ~29,000 GHz/km. Finally, we show that in the gain-compensated system with wavelength multiplexing, soliton-soliton collisions produce random modulation of individual pulse velocities. Nevertheless, multiplexing can yield rate-length products >300,000 GHz/ km.
Lidar backscatter inversion for measuring cloud droplets
Authors: Hall Freeman F. , Post Madison J. , Richter Ronald A.
Published: February 2023

The object of this investigation was to determine if it is feasible to measure cloud droplet size distributions using multiwavelength, ground-based lidars. We chose to measure first the most simple clouds, Altocumulus lenticularis, since in their laminar form they are often characterized by nearly monodisperse droplet distributions. Available for the investigation were doubled ruby and ruby, and carbon dioxide lidars with wavelengths of 0.347, 0.694, and 10.59 µm, respectively, covering well the droplet size ranges expected in the clouds. All the lidars are calibrated absolutely, so that the backscatter coefficient in units of (l/m)(l/sr) is determined. Most of the measurements made to date produce a mathematical inversion that shows a single-mode size distribution with a peak at ~4-µm droplet radius. Clouds that are more laminar in appearance show a sharper peak; clouds that appear more chaotic show a nearly flat distribution between radii of 1 and 9 µm.
Microbending losses of optical fibers embedded in composite materials
Authors: Bennett K. D. , Claus R. O.
Published: February 2023

Microbending losses produced in optical fibers which are embedded between adjacent plys of graphite/epoxy composite materials during manufacturing are considered. Such losses occur due to the periodic corrugations in the individual layers which are caused by the constituent graphite fibers.1 The geometrical arrangement of adjacent layers with respect to the embedded optical fiber sensor changes the spatial periodicity of the microbending and thus the resulting attenuation per unit length of embedded fiber. The measurements of this attenuation indicate the localized internal strain integrated along the length of the optical fiber. The simultaneous measurement of such attenuation in several fibers having different orientations with respect to the composite material structure allows the evaluation of different components of internal strain as well as interfacial boundary conditions. Potential applications in the nondestructive evaluation of composites are suggested by these results.