bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraviolet fluorescence measurements of large molecules in diffusion flames
Authors: Smyth Kermit C. , Miller J. Houston
Published: February 2023

Optical measurements in combustion environments have been very successful for detection of molecules containing two and three atoms, but no species-specific results have been reported for larger compounds. However, intermediate-size hydrocarbons as a group have been detected by laser-induced broadband fluorescence in the visible region. The observed spectra have been widely attributed to polycyclic aromatic hydrocarbons, which are thought to be important in soot formation chemistry as precursors and perhaps as building blocks. Recently, we extended these fluorescence measurements to the ultraviolet region as part of an investigation of the soot inception zone in laminar diffusion flames. Detailed concentration profiles have been determined in a methane–air flame using a variety of optical and mass spectrometric techniques. Broadband ultraviolet emission in the 300-400-nm region is observed on excitation at 282 nm. The spatial profiles of this fluorescence exhibit two distinct contributions, which show different behavior as a function of height above the burner. One contribution is located in the soot inception zone and overlaps the broadband visible fluorescence profile, whereas the second feature is unconnected with chemical growth processes and arises from a stable combustion by-product. Many candidates exist for the observed ultraviolet fluorescence including polyenes, polyynes, and the polycyclic aromatic hydrocarbons.
Oscillatory emission from the Cu-vapor laser
Authors: Rai Jagdish , Im Kiegon , Kim J. J.
Published: February 2023

Our experimental studies of the optical emission from the Cu-vapor laser indicate a breakup of laser pulse into oscillatory structures in certain conditions. We believe this phenomenon is similar to the optical ringing reported earlier.1 We attribute this breakup of the pulse to cooperative effects involved in emission from the Cu-vapor laser.2 This effect is further enhanced by propagation through the system. We earlier explained the high gain of Cu-vapor due to radiation trapping and Rabi oscillation between the 2P and 2S states.3 This analysis further shows that a large percentage of Cu atoms in the lasing medium are in the excited state (2P) most of the time. Therefore, there is a very low probability for total depletion of this level. This implies that the phenomena like gain switching and relaxation oscillation may not play a significant role in the breakup of the laser pulse. The oscillatory structures for both the 510.6-nm and 578.2-nm lines were strongly dependent on the changes in operating temperature. We observed the breakup of the pulse mainly around the temperature of 1600°C.
One-way real-time optical wave front converters
Authors: Kwong Sze-Keung , Yariv Amnon
Published: February 2023

One-way real-time distortion correction of a laser beam, which may originate from transmission through atmospheric turbulence, has been studied by optical engineers for many years. This paper presents the concept of real-time passive wave front converters (WFC) by using nonlinear two-wave mixing (2WM) and four-wave mixing (4WM) in photorefractive crystals. The 2WM-WFC is demonstrated by the unidirectional ring oscillator.1 The input distorted laser beam is used to pump the oscillation inside the ring cavity. By inserting an aperture inside the ring cavity to control the oscillating mode, a clean laser beam is obtained. A 15% conversion efficiency was measured. For the 4WM-WFCs the input distorted laser beam is phase conjugately reflected back by a passive phase conjugate mirror (PPCM).2 Then, this pair of phase conjugate beams is used to pump the laser oscillation, by means of 4WM, between a photorefractive crystal and an external mirror. A portion of the oscillating beam is coupled to the output of the device. We also demonstrate that we can use only one crystal to serve both as the PPCM and the crystal in the oscillator. The response time of these WFCs depends on the response time of the photorefractive crystals which ranges from a few seconds to microseconds. A comparison between the 2WM-WFC and the 4WM-WFC is also made.
Phase-conjugate optics and optical switching using a pulsed mode Sagnac interferometer
Authors: Li Y. , Eichmann G. , Alfano R. R.
Published: February 2023

A Sagnac interferometer, because of its fringe stability and ease of alignment, is a promising tool for pulsed mode interferometry. Unlike a Mach-Zehnder-type of pulsed interferometer, a Sagnac interferometer does not require active fringe stabilization. In this paper, nonlinear optical pulsed mode interferometry—an interferometer where one of the arms contains a nonlinear optical material—is considered. The optical source is a mode-locked pulsed picosecond Nd3+: YAG laser. Properties of this setup are analyzed. Experimental results, based on phase-conjugate nonlinear optics, are presented. Applications to picosecond optical switching are demonstrated.
Physical microstructure of evaporated titania-silica and zirconia-silica multilayer thin films
Authors: Swab P. , Klinger R. E.
Published: February 2023

Thin cross sections of titania-silica and zirconia-silica quarterwave stacks were prepared by ultramicrotomy and examined by transmission electron microscopy. Ultramicrotomy is a standard biological sample preparation technique originally developed for thin sectioning of soft tissue. In the present study, the thin films were deposited by reactive electron beam evaporation onto glass substrates at elevated temperatures. Electron-transparent cross-sectional slices were cut from these stacks and subsequently examined by transmission electron microscopy. The glassy structure of silica, the inhomogeneous crystalline morphology of zirconia, the noncrystalline anisotropy of titania, and the relationship between columnar growth and surface roughness with lateral dimensions of 3–10 nm were clearly observed. The improved resolution offered by ultramicrotomy also revealed the presence of a 2-nm thick nucleation layer in titania and a surface-smoothing effect by the silica. Thin-film microstructure analysis by ultramicrotomy offers several advantages over conventional shadow replication techniques. It provides direct imaging of the thin films in cross section, accurate thickness information, resolution not limited by a shadowing material, and image contrast which is largely independent of the specimen’s fracture mechanics. Equally important, microtomed thin sections allow direct chemical and crystalline structure analysis.
Real-time programmable image subtraction using a magnetooptic device
Authors: Yu F. T. S. , Cao M. F. , Lu X. J.
Published: February 2023

In an effort to combine the advantages of optical information processing and the flexibility of digital computers, a real-time image subtraction system has been developed. This system uses a microcomputer to control a Litton magnetooptic device and as an interface to a video camera. Since the magnetooptic device is a transmitted type spatial light modulator, it can perform real-time programmable optical signal processing. Details of the system and its performance used in image subtraction are discussed. Additionally, experimental demonstrations of the subtracted images are shown. A brief discussion of the possible use of the system in applications such as robotics vision and automated inspection is also presented.
Nonlinear transformation in human vision
Authors: Makous Walter , Williams David R. , MacLeod Donald I. A.
Published: February 2023

We have measured the form of a nonlinear transformation of retinal illuminance in the human visual system by measuring the detectability of the distortions it produces and approximating the transformation with orthogonal polynomials. Superimposing two interference fringes, of frequencies f1 and f2, produces a neural distortion product that can be more easily detected than the fringes themselves. The amplitudes of difference frequencies produced at (2f2 − f1) and (f
2
− f1) were measured separately by finding the contrast of superimposed fringes necessary to produce a threshold grating of 10 cpd. These thresholds, along with the threshold for a 10 cpd fringe, determine a set of simultaneous equations that yield the coefficients of the polynomials. As no distortion products of spatial frequency (mf2 – f1) could be detected when m > 2, we approximated the transformation with a third-order polynomial. The function that results depends somewhat on mean retinal illuminance, but it has the shape of a simple, saturating function that is more linear, and saturates more abruptly, than the function V = l/(l + s). A tenfold change of mean illumination changes the sale of intensity by slightly less than tenfold.
Beam cleanup, beam combination, and efficient energy extraction in a KrF-pumped Raman amplifier
Authors: Goldhar J. , Murray J. R.
Published: February 2023

We have demonstrated 75–85% photon conversion efficiency to a high quality Stokes pulse in a methane Raman amplifier pumped by two poor quality KrF pump pulses propagating in a lightguide. Intensity averaging and combination of poor quality pump beams in a Raman amplifier can be treated using a four-wave mixing model.1 The model explicitly shows the consequences of finite pump correlation length and illustrates the circumstances under which poor quality pump beams can be used to amplify a high quality Stokes beam without degrading its divergence. Phase-conjugate effects in a Raman amplifier are observed and described. Experimental observations2 on a double-pass methane Raman amplifier pumped by two poor quality KrF beams propagating in a lightguide demonstrate 75–85% photon conversion efficiency to the Stokes beam with a stage gain of 10–20. The Stokes beam divergence is about 2.5 times the diffraction limit and is not affected by the amplifier.
Photoacoustic and photothermal evaluation of stratified materials
Authors: Cielo P. , Rousset G. , Bertrand Lionel G.
Published: February 2023

Photoacoustic and photothermal nondestructive evaluation techniques are an emerging approach for the inspection of several materials of industrial interest. This paper focuses on stratified materials such as aluminum epoxy or graphite epoxy laminates as well as metallurgically coated materials which are widely used particularly in the aerospace industry. Such materials must be carefully inspected to detect the presence of any extended defect such as a layer-to-layer delamination which could grow under stress in service resulting in a catastrophic failure of the assembled structure. Such materials are usually inspected after manufacture by ultrasonic or radiographic techniques. Such approaches have however a number of limitations, so that alternative techniques which could be applied rapidly, noninvasively, and with access from one side only of the structure are actively searched. Optical techniques provide an attractive alternative to such methods because they require no contact with the inspected surface so that they can be deployed in hostile and remote-located environments, while being easy to scan over large surfaces.
Optical generation of random numbers: theory and experiments
Authors: Martino Anthony J. , Morris G. Michael
Published: February 2023

Simulation of physical processes and Monte Carlo solutions to numerical problems on digital computers require sources of random numbers that follow specified density functions. In our experiments, the spatial coordinates of detected photoevents are used as a fast source of true random numbers to solve numerical problems by the Monte Carlo method. The probability density function for the location of a photoevent on the detector surface is proportional to the irradiance. We have constructed an optical random number generator using a microchannel plate detector with a resistive anode. It can produce bivariate random deviates with any probability density and any correlation between the two variables. The numbers pass the standard tests for randomness and fit to the given distributions (chi-square, correlation, sequence tests). Nonuniform distributions can be obtained with no loss of speed by manipulating the irradiance distribution across the detector, e.g., by imaging a transparency onto it. In particular, we have produced uniformly distributed random numbers and normally distributed random numbers with various correlations between the variables. We have also used the optical random number generator to find approximate solutions to systems of large linear algebraic equations and approximations to the inverses of large matrices, with a maximum error of <5%.
Piecewise isoplanatic modeling of space-variant linear systems
Authors: Lin Shing-Hong , Krile Thomas F. , Walkup John F.
Published: February 2023

This paper presents a study of the piecewise isoplanatic approximation (PIA) applicable to the representation of space-variant linear systems. The approximation employed here divides the input plane into isoplanatic patches to which corresponding impulse responses are assigned. The resulting PIA output is an approximate representation of the true system output. A new measure of the degree of invariance is developed as an aid to classifying linear systems and applying the PIA model. This new measure seems to predict the relationships between the true and PIA system outputs better than the Lohmann and Paris measure.1 A comparison of both measures is described. Several examples are presented to explain the relationships between the degree of invariance and the PIA system output. With the aid of the new measure, we can find the optimal size of each isoplanatic patch in the input plane and the optimal corresponding impulse response in each patch. The relationship of the variation bandwidth to the new measure of invariance is also mentioned in supporting the validity of the new measure.
Acoustooptic signal processing using partially coherent light
Authors: Fisher D. S. , Yu F. T. S.
Published: February 2023

An investigation into acoustooptic (AO) correlation and spectrum analysis using partially coherent light is presented. The salient feature of the processing architectures is the implementation of a white-light source to reduce coherent artifact noise at the detector plane. In all information processing operations the Bragg cell is amplitude modulated to perform linear processing of light in complex amplitude. Pure sinusoidal signals with no input noise were used to drive the AO cells to isolate the effects of the multiplicative phase noise. This phase noise arises from random thickness variations and refractive-index fluctuations. Two signal-to-noise ratio (SNR) measurements are used to compare partially coherent light and laser light for the same signal processing architectures. A theoretical treatment is given to quantify the effects of the spatial and temporal coherence on these SNR measurements. Finally, the effects of the temporal and spatial coherence on the correlation peak intensity for a space-integrating and a time-integrating architecture is described. Similarly these effects are studied in the spectral estimation peak for the spectrum analyzer.
Chromatic speckle: its characteristics and applications
Authors: Wu X. P. , Shen S. Q. , Chiang Fu-Pen
Published: February 2023

It is well known that when a diffusing surface is illuminated by a coherent or quasi-monochromatic light source, a volume of random speckle is created. We examine a new phenomenon: when a diffusing surface is illuminated by a broad bandlimited or even white-light source (e.g., incandescent lamp, arc lamp, or sunlight) a field of colored speckles exists in the region near the rough surface. We refer to them as chromatic speckles. In this article we explore the statistical properties of the chromatic speckle, its 3-D size and its relationship to the roughness of the generating surface. We also explore the use of chromatic speckle to metrology. Compared with laser speckle and random pattern photography, the chromatic speckle method has many advantages. For example, it requires only a simple white-light source for recording. The chromatic specklegram can also be processed by white light resulting in low noise fringes. In addition, because of the longer axial length of the chromatic speckle the method can be applied to measuring out-of-plane as well as inplane deformations. Experimental results are presented.
Compact linear array external cavity laser
Authors: Begley D. L. , Martin D. , Vivian W. , Rice R.
Published: February 2023

External optical feedback can significantly alter the operating characteristics and output radiation properties of semiconductor diode lasers. A semiconductor injection laser operating in an external cavity is attractive for numerous applications requiring greater spectral purity, frequency stability, and smaller beam divergence than can be obtained from a solitary laser diode. A linear array of diode lasers was fabricated from a bar of five, 6-µm wide, 250-µm center spacing, single-stripe emitters. The external cavity was formed by a 0.75 pitch graded-index rod lens positioned ~1 µm from the front facet of the bar array. The rod lens transfers an image of the radiating bar facet directly from the back to the front of the rod. The external cavity is therefore formed by optical feedback from the front surface of the rod with the rod lens also performing the function of the intracavity lens element. This dual function of the graded-index rod lens enables the array laser to assume a very compact form in comparison to other external cavity configurations. It was observed that the wavelength of each diode element could be controlled through proper alignment of the external cavity. Once the diode elements were operating at the same wavelength, the array could be tuned over a 15-nm range (798-813 nm). A mutual coherence interferometer was constructed to determine qualitatively the existence of a phase locked condition. A very clear interference fringe pattern was produced. Frequency locked, mutually coherent, operation of five diode elements was achieved, with external wavelength control demonstrated.
Phase-locked laser array formed by induced filaments
Authors: Salzman J. , Larsson A. , Yariv A.
Published: February 2023

The necessary condition for a uniform index-guided phase-locked laser array to operate in the fundamental supermode is to have high gain in the regions of low refractive index and vice versa. This condition is fulfilled by a self-focused laser filament. Therefore, if filamentation could be controlled to form stripes uniformly spaced and phase locked, the expected emission would be in the fundamental supermode. Filamentation control was achieved experimentally by etching one of the mirrors of a broad area laser in a sinusoidal form. The alternating converging and diverging regions of the mirror efficiently stabilized the filament array. Since the device relies on self-focusing, it is sensitive neither to the laser length nor to the exact shape of the etched mirror. We observed emission in the fundamental supermode, with a stable near-field intensity distribution. Devices fabricated so that the filament spacing was comparable to the filament width emitted in a single lobe, nearly diffraction-limited far field. In addition to the potential applications, the device provides a powerful tool for studying self-focusing due to the nonlinear response in semiconductor lasers. As an illustration of that, measurements of the filament width and phase front curvature as a function of injection current are presented.
Color discrimination contours in a cone excitation space
Authors: Nagy Allen L. , Eskew Rhea T. , Boynton Robert M.
Published: February 2023

We have plotted several of the 1942 MacAdam ellipses1 in a normalized constant-luminance cone excitation diagram described by MacLeod and Boynton.2 In this diagram the MacAdam data become either circular or ellipse oriented at both 45° and 135°. In contrast, results we presented last year at OSA suggested that a single ellipse oriented at 135° could adequately describe color discrimination data. The simplicity of this result argues strongly for the fundamental nature of the axes in the constant-luminance chromaticity diagram. Further analysis and comparison with the experiments of MacAdam and Boynton and Kambe suggest that the recent data were obtained in conditions that minimize the effects of chromatic adaptation. This analysis suggests that, while a single ellipse may adequately describe color discrimination in some conditions, it may not be descriptive for conditions which produce significant adaptation. This analysis will be discussed with regard to the hypothesis that interactions between two fundamental mechanisms may vary with stimulus conditions and chromatic adaptation.
Chromatic discrimination in 1- and 2-month-olds with 8° test fields
Authors: Clavadetscher John E. , Ankrum Corlene , Teller Davida Y.
Published: February 2023

The chromatic discrimination ability of 1- and 2-month-old infants was examined using a forced- choice preferential looking technique. Eight degree test circles located 30° right and left of center were embedded in a 547-nm field. Each infant was tested at either 420, 450, 490, 547, or 650 nm using eleven intensity levels spaced 0.1 log unit apart. In general, 1-month-old infants failed to show evidence of the ability to make these heterochromatic discriminations over at least part of the intensity range. In contrast, 2-month-olds usually succeeded at all intensities of the heterochromatic stimulus conditions. These between-subject trends were also confirmed on a within-subject basis. Typically, infants who failed to discriminate showed a systematic U-shaped pattern of percent correct. When these dips were compared to adult brightness matches, a consistent pattern emerged. Generally, minima for 650 nm were a few tenths of a log unit higher and for short test wavelengths a few tenths of a log unit lower than the average adult brightness match. These data can be interpreted to indicate that the infants' brightness matching function differs from the adult function for these stimulus combinations.
Discriminating features and information theory
Authors: Bobick Aaron
Published: February 2023

We assume that visual recognition is accomplished by describing an object using visual features and that description is matched to some stored data base. These features must be chosen from the set of all computable properties of an image, be they direct image properties or properties of the actual object inferred from the image. What criteria should be used in selecting the features? Previous work1,2 has investigated the use of information theoretic constraints on feature selection, especially with respect to designing hierarchical classifiers. These methods attempt to maximize the entropy reduction at each decision step, where the entropy is based on the class membership probability. No consideration, however, is given to the description of the world generated by the particular features chosen. We propose that objects in the world are clustered, exhibiting high degrees of redundancy; as such, their description should reflect this structure. Therefore, the description of objects should be used as criteria for evaluating the chosen features. Specifically, the redundancy and discriminability of objects as described by the features should satisfy certain constraints derived from information theory. These constraints, expressed in terms of entropy and mutual-information measures, are motivated theoretically from the goals of a visual recognition system and empirically from cognitive science.
Comparisons of different 2-D laser beam scanners
Authors: Xiang L. Q. , Ih Charles S.
Published: February 2023

For many scanning applications, the scan line straightness, linearity, and influence of mechanical wobble and eccentricity on a scanner's performance are important. Some different 2-D scanners are compared on a common specification of a total resolution of 6.25 million pixels. According to our analyses, the polygon-mirror system offers the best straightness but is the most sensitive to mechanical wobble and eccentricity.1 Different holographic 2-D scanners are also investigated, and their performances depends strongly on design parameters and on the configurations. The scan line straightness of the grating scanner’s system is comparable with that of a polygon mirror.2 The scan line linearity of the scanner with an auxiliary reflector3 is the best one. The simplicity and therefore the expected reliability of holographic scanners may influence people to prefer holographic scanners. However many technical problems remain to be solved before holographic scanners can be widely used.
Rotation-Invariant image recognition at low light levels
Authors: Isberg Thomas A. , Morris G. Michael
Published: February 2023

It has been recently demonstrated1 that fast, reliable image recognition can be accomplished using a commercially available 2-D photon counting detector and position computing electronics. In this paper the method of circular harmonic function expansion for coherent rotation-invariant image recognition2 is extended to the case of photon-limited image recognition. Theory for rotation-invariant filtering with incoherent illumination is presented and applied to photon-limited image recognition. Low light level input images are cross correlated with the square modulus of a single circular harmonic component of a high light level reference image stored in computer memory. The mean value of the correlation signal is found to be invariant with respect to rotation of the input image. The experimental results for the correlation signals for various input images are presented. Histograms of the correlation signal are shown and compared with theoretical predictions for the probability density functions. It is demonstrated that reliable image recognition, independent of the rotational orientation of the input, is possible with as few as 5000 detected photoevents.
Microwave imaging of objects in the presence of severe clutter
Authors: Farhat Nabil H. , Shen Yuhsyen
Published: February 2023

Frequently in longwave (microwave and acoustic) imaging situations arise where the object being imaged is located in the proximity of background producing severe clutter. Examples are airborne/spaceborne downlooking radar and downlooking sonar. The aim of this paper is to demonstrate the capability of a high resolution microwave imaging system in discriminating objects of interest against such severe clutter. The approach is based on a spotlight imaging mode in which spectral, angular, and polarization diversities are utilized to access the 3-D Fourier space of a coherently illuminated microwave scene.1 A brief theoretical review of the principle is presented followed by a description of an experimental microwave imaging facility employed in collecting realistic data of a representative situation: that of a low-flying aircraft. The antennas are positioned as if they were spaceborne looking downward to the target and the ground. Only one 2-D slice of the 3-D Fourier space is obtained; hence the reconstructed image is a projective side view. The reconstructed images show clearly the ability of clutter discrimination. The polarization-enhanced microwave images obtained are comparable visually to high contrast photographs of the scene taken with flashlight illumination. Finally, a proposal for further clutter reduction by a spotlight hopping imaging mode is discussed.
Three-dimensional imaging system for robot vision
Authors: Davis Walter C.
Published: February 2023

Experimental results are given for a 3-D imaging system which accesses a wide angle field of view (FOV) but has no moving parts. The output of a 2-D array of LEDs is imaged onto the object field. The number of pixels in the field correspond to the number of LEDs in the array. The LEDs are sequentially excited with an amplitude modulated signal so that the phase of the transmitted and received signals can be compared for range information at each pixel. A single receiver channel is used which simultaneously monitors the full FOV. Processing electronics in the receiver performs bandlimiting to reduce noise, and, at each pixel, signal strength processing (brightness) for 2-D imaging, and phase processing for range.
Tomography of mildly refracting media by interferometry and perturbation analysis
Authors: Lira Ignacio , Vest Charles M.
Published: February 2023

Norton and Linzer 1 have developed an algorithm for computed tomography of refracting media. It is intended to correct to first order for bending of the probing rays due to refractive-index gradients in velocity and attenuation ultrasonic tomography. In the present work the problem and perturbation analysis have been reformulated to apply to tomography of transparent media where data are recorded by optical interferometry, including the effects of an imaging system. Accuracy and limitations of the technique are studied for both 2-D and boundary- layer phase objects. Although more limited than iterative schemes in terms of handling strong refraction, this approach is found to be very simple to apply and adequate for many measurement problems in aerodynamics and heat transfer.
Parallel algorithms and architectures
Authors: Whitehouse Harper
Published: February 2023

No summary was available at press time.
Parallel algorithms and digital optical computing architectures for numerical transforms and solutions to partial differential equations
Authors: Drabik T. , Lee S. H.
Published: February 2023

Digital optical computing offers several unique features not available from other parallel computing systems. They include massive interconnections (global or neighborhood), 2-D input and output formats, large main memory, and more degrees of freedom (e.g., polarizations in addition to intensity). The ease of interconnection and more degrees of freedom help to simplify hardware system design, whereas the 2-D input/output formats and large main memory help to simplify software development. Two classes of parallel algorithm for numerical transforms and solutions to partial differential equations are described. When they are implemented on digital optical computers, various unique features of digital optical computing are illustrated.
Why does wood look like wood?
Authors: Honig David A. , Richards W. A.
Published: February 2023

Three properties of trees produce distinctive visible characteristics of wood: the cylindrical growth rings, the vertical pores, and the radial planes that compartmentalize the tree to protect it from disease or injury. Such a model of a tree was the basis for rendering a wooden surface. With this first approximation, the growth rings will appear as elliptical contours on a planar cut, streaked by dark lines that arise from the rays, and speckled by pores. These three properties of wood capture its salient visual attributes. The particular form of the ring albedo function is not important, nor is it necessary to model the radial rays exactly. We speculate that the pattern of radial rays and elliptical rings, and possibly their intersection, allow the observer to make the inference of wood, for few other natural structures will produce this characteristic surface texture.
Seeing structure through chaos
Authors: Heeger David J. , Pentland Alexander P.
Published: February 2023

Research in motion perception has concentrated on recognizing regularities in images due to rigid motion. However, rigid motion is only one type of motion that occurs in our world. There is also elastic motion, fluid motion, and turbulent flow. Examples of turbulent flow include clouds, waves, boiling water, rustling leaves, or flags fluttering in the wind. Fully developed turbulent flow is completely chaotic and incoherent motion. Yet, it has a regular statistical structure underlying the apparent chaos. These regularities are due to the coherence of the physical process which generates turbulence. By using image data to characterize the parameters of this process we can make useful predictions and inferences: solid/fluid, viscosity, mean flow velocity. This paper develops a fractal-based model of turbulent flow, demonstrates that turbulence can be recognized visually, and suggests how the model can be used to make inferences about the flowing fluid. The model is implemented by testing for a fractal scale-invariant regularity across space and time using linear spatiotemporal bandpass filters. These filters can also be used to measure optical flow and are similar to receptive fields in the visual cortex.
Generation of fractals using the Burt pyramid
Authors: Ogden Joan M.
Published: February 2023

Fractals have been used successfully to describe complex, irregular natural forms such as clouds, coastlines, trees, and mountains, which are difficult to characterize in terms of continuous, differentiable functions.1 One of the most important properties of fractals is their self-similarity. As the spatial scale of viewing changes over many orders of magnitude, the fractal remains similar in structure and appearance. The Burt pyramid2 decomposes an image into a sum of octave width spatial frequency bands plus a low-pass filtered component. Local spatial information is also preserved. If an inherently self-similar fractal is represented in pyramid form, one would expect each spatial band to look similar to the others. Conversely, if similar patterns are entered into each spatial band of a pyramid, the sum should be a self-similar fractallike texture. We have used this technique to generate realistic looking textures including clouds, water waves, galaxies, woodgrain, and rock. The time required to synthesize a fractallike texture is much reduced over present methods, suggesting that this method may be useful for computer artwork and animation. A real-time animation sequence of clouds and waves is shown. This sequence was produced on a DeAnza image processor driven by a PDP-11/24.
Lithographic image simulations
Authors: Goodman Douglas S.
Published: February 2023

Although the physics of image formation is well known, practical questions in lithography, such as that of the depth of focus and the effects of source shape, cannot be conveniently approached by analytical methods. The interactions between the contributions to the image from the various points of the object are so complicated that computation is usually necessary to determine image irradiances. Numerous digital image simulations have appeared in the literature, but—presumably because of the computation time required—most have been of objects varying in one direction. We have performed a number of 2-D image simulations of lithographic-type objects to investigate effects of the various parameters of imaging, such as numerical aperture, defocus, aberrations, and source size and position.
Integrated fiber-optic coupler for VLSI interconnect
Authors: Prucnal Paul R. , Fossum Eric R. , Osgood Richard M.
Published: February 2023

A new optical interconnect technique is demonstrated for optical communication to a VLSI chip which is suitable for very high packing densities. This interconnect features small size (<10 µm), reproducible and accurate alignment between the optical fiber and the electronic device, and mechanically stable, high efficiency coupling. The basic idea (for a receiver structure) is to etch a hole slightly larger than a single-mode fiber core into a silicon wafer by a laser-assisted etching technique. A p-n junction is then formed on the inside of the hole and serves as a detector. As a result of the hole geometry, the fabrication process of the p-n junction requires a modification of the conventional technique used in the surface diffusion of a p-n junction. In the final stage, an optical fiber is uniformly stretched and is inserted into the hole and is affixed by means of epoxy. Here the objective is to reduce a single-mode fiber to the dimensions necessary for insertion into the hole, while preserving its guiding properties. With the fiber secured in the hole, light emanating from the end of the fiber is collected by the reverse biased junction and converted to an electrical signal. This signal can be utilized by circuitry on the surface of the wafer. In this way, the footprint of the integrated fiber-optic coupler on the chip is nearly equal to the cross-sectional area of the single-mode optical fiber core, and arrays of such interconnects can achieve very high packing densities.
Local area network with optical spread spectrum processing
Authors: Prucnal Paul R. , Santoro Mario
Published: February 2023

Asynchronous multiplexing schemes are most applicable when the traffic on the network is characterized by relatively long idle periods between the transmitted packets of data. An asynchronous system that provides random access makes the most efficient use of the channel. However, when the intensity of the traffic increases (i.e., the channel is being accessed by many users at the same time), collisions between packets become unavoidable and the throughput of the channel is greatly degraded. To alleviate this problem, spread spectrum multiplexing techniques, commonly known as code division multiple access (CDMA), can be applied. Application of CDMA requires a channel with a large bandwidth, such as an optical channel. Processing the received coded data requires a correlator. If high data rates are used, because of the bandwidth expansion of CDMA, a fast correlator must be implemented. Although for conventional systems this correlation requires sophisticated electronics, optical correlators could handle this fast processing with less complexity. Therefore, the CDMA scheme proposed here was implemented by optically correlating the incoming coded data. One set of codes that show promise for our application are prime sequences obtained from a Galois field GF(P) where P is a prime number and N = P**2. An experiment is described employing a P = 5 code sequence on a 100-Mbps fiber-optic link using 32 chips per bit. This optical CDMA system can potentially allow many more chips per bit, and therefore more users, than conventional systems.
Interferometric testing of bimetallic mirrors at 100 K
Authors: Sampler Henry
Published: February 2023

Stress-induced changes in surface figure were measured by torquing the bimetallic (electrolysis nickel on aluminum) mirror to its mount in 1 ft. -lb. increments up to 16 ft. lb., measuring the surface figure with an automatic phase measuring interferometer and fringe analysis program using photographed interferograms. The maximum stress-induced change in surface figure contributes to the measured cryogenically induced change in surface figure. The bimetallic mirror was nickel deposited with 900 µm of electrolysis nickel. Increments of 0.5 mil of nickel are ground and polished from the face of the mirror before each room temperature and 100 K interferometric test. The results show a linear relationship between the differential nickel thickness between the front and rear of the mirror and the rms surface figure of the front face of the mirror, corresponding qualitatively to a simple model’s prediction.
Preliminary characteristics of a grating crystal monochromator for use with synchrotron radiation
Authors: Rife J. C. , Hunter W. R.
Published: February 2023

The grating/crystal monochromator (GCM) consists of an initial 2° grazing angle paraboloidal mirror which collimates the synchrotron radiation from the electron beam source; a final identical paraboloidal mirror which focuses collimated monochromatic radiation to the fixed exit slit in a 1:1 image of the source; and a pair of plane diffracting elements or a mirror/diffracting element pair which monochromatize the radiation in the region of collimated light between the paraboloidal mirrors. The diffracting elements can be either crystals or gratings giving an unprecedented spectral range in one instrument from the UV to 2 keV. The two-crystallike scanning motion is ideal for an always on-blaze condition with diffraction gratings. We will report on performance tests with a plane mirror/grating pair (600 g/mm) installed in the scanning system. We present measurements of the exit slit image, the quality of which is fundamental to the resolving power of the instrument. The image quality is influenced by the source size and stability, mirror alignment, and possible mirror figuring errors. Preliminary results on spectral flux, higher-order flux, and absorption edge resolution to 100 eV are presented. Calibration and stability of the mechanical system of the GCM and the critical laser angle interferometer that encodes the orientation of the mirror/grating pair are discussed. Wavelength calibration via absorption edge spectral location is outlined.
Picosecond pulse shape manipulation in a grating pulse-compressor
Authors: Heritage J. P. , Weiner A. M. , Thurston R. N.
Published: February 2023

The temporal shape of compressed picosecond pulses may be controlled through amplitude and phase apodization of the pulse’s frequency spectrum which is spatially dispersed within a grating pulse compressor.1–2 Essentially arbitrary pulse shapes may be fabricated, subject to the limitations imposed by finite bandwidth and resolution. Our experiments are performed with pulses from a cw mode-locked Nd:YAG laser, compressed from 80 ps down to 0.9 ps, using self-phase modulation in a single-mode optical fiber and compression with a grating pair. Undesirable energy in the wings of the compressed pulses has been eliminated, with no concomitant pulse broadening, by means of a spectral windowing technique.1 Furthermore, by masking the amplitude and/or phase of the spatially dispersed frequency components within the compressor, we have synthesized a variety of pulse types, such as bursts of picosecond pulses, odd pulses, bursts of odd pulses, and square pulses.2 In this paper we describe our recent progress in the generation of novel ultrashort pulse shapes, and we discuss the application of phase and amplitude masking for picosecond code generation.
Self-Q/switched Nd:LINbO3 laser
Authors: Cordova-Plaza A. , Digonnet M. J. F.
Published: February 2023

Nd:MgO:LiNbO3 has motivated recent interest because of its reduced photorefractive damage. Quasi-cw laser action and self-frequency doubling have been reported.1 In this paper we report demonstration of self-Q-switched laser operation in this material. The active laser medium and the electrooptic Pockels cell were integrated into the same crystal rod. The laser consists of a 2- X 2- X 11.5-mm crystal in a nearly spherical 10.6-cm cavity. Prior to Q-switched operation, cw lasing at 1.093 µm was obtained by end pumping at 598 nm (Rh6G dye laser). The laser field was forced to be polarized along the crystal a axis by a thin Brewster plate Inserted inside the cavity. Applying to the crystal ~250 V (electric field along the a axis) was enough to stop cw lasing when pumping twice above threshold. In these conditions we measure a Q-switched pulse width of 500 ns and a peak power of 180 mW at~1-khlz repetition rate. Additional results are presented using much higher pumping levels. Cutting the crystal itself at Brewster angle will eliminate the need for an intracavity plate.
Chaos and cooperation in nonlinear pictorial feedback
Authors: Hausler G. , Seckmeyer G. , Weiss T.
Published: February 2023

Nonlinear feedback systems may show a principally different dynamical behavior compared with linear systems: Chaos may appear; in other words, unpredictability in any practical sense. Sometimes, however, cooperative effects can be observed. We use the term cooperative when stable patterns evolve with long-range spatial correlation. With optics, TV, and a computer we can study the dynamics of pictures running through a nonlinear feedback loop. Coupling between different pixels is introduced by convolution. The most interesting features of such pictorial feedback systems are (1) weak coupling of adjacent pixels always leads to chaos, (2) strong coupling with positive point-spread function leads to chaos, (3) strong coupling with bipolar point-spread functions leads to stable patterns with long-range spatial order, (4) stability is not destroyed by a considerable amount of noise.
Nonlinear color vision models applied to color and luminance difference thresholds
Authors: Massof Robert W.
Published: February 2023

Given two well-defined and reasonable assumptions, all nonlinear color vision models reduce to the form of a vector model under constraints imposed by conditions required for measurement of color luminance difference thresholds. The first assumption is linearization of the visual transformation equations. This assumption applies to small (threshold-level) perturbations in vision. Linearization is equivalent to saying that the linear weighting coefficients of the resultant vector model are partial derivatives of the nonlinear functions. The second assumption is that the variance in visual sensation is the same for test stimulus conditions as it is for reference stimulus conditions in a difference threshold experiment. Although this assumption is known to fail for individual observers, it is valid for the average observer if between-observer variability outweighs within-observer variability. This second assumption leads to an analytic form of the detectability index (d') that is equivalent to a vector magnitude. The present paper reports how these two assumptions formally constrain nonlinear color vision models to generate a unique set of predictions for a wide variety of color and luminance difference threshold data. An important consequence of the theory is that any nonlinear color vision model, once defined, is constrained to predict chromaticity discrimination contours, Stiles’s field sensitivity curves, threshold-vs-radiance curves, threshold-vs-wavelength functions, etc., with no additional assumptions or degrees of freedom. This constraint is illustrated for a general logarithmic color vision model.
Laser trap concept for cold potassium atoms
Authors: Stwalley William C. , Heneghan Shawn P. , Bahns John T. , Yang Kuo-Ho
Published: February 2023

We present our study on the feasibility and limitations of a purely laser trap concept, a corner cube trap, for trapping neutral K atoms. The confinement of the atoms in the two dimensions perpendicular to the laser will be provided in the cavity of a high power alexandrite laser operating in the cw TEM01*, mode (doughnut mode) tuned slightly to the blue side of the resonance line of the K atom. By reflecting the TEM01*, laser back on itself with two mirrors, one caps the ends of the cylindrical trap, resulting in a slightly weaker end plug. This trap concept employs not laser cooling, but rather counterstreaming 4He atoms which are cooled to ≲ 1.5 K, to drastically cool the K atoms to thermal energies well below the trap depth (expected to be ~10 K). We have also examined various loss mechanisms for the trapped atoms. In particular, K atoms can be lost to the trap if they are multiphoton ionized, if they are heated by absorption and emission of many photons (recoil or diffusional heating), if they simply have much higher energy than the vast majority of other atoms at 1.5 K, or if they form KHe (or KHe2, etc.). Results from these investigations will be discussed, suggesting crude lifetimes for trapped atoms of the order of 1 s.