bluuebunny/crossref_metadata_2025 huggingface dataset:
High Contrast Spatial Light Modulator Using Stark Effect Tuning and Heterostructure Acoustic Charge Transport (HACT) Pixel Addressing
Authors: Jain F. , Cheung S.K. , LaComb R. , Grudkowski T. , Sacks R. , Cullen D.
Published: February 2023

The demonstration of optical modulation by Miller et. al. [1] using the Stark effect in multiple quantum wells (MQWs) has resulted in a variety of device structures[2] based upon changes in absorption, index of refraction, and polarization.
Optical Data Processing With Bacteriorhodopsin And Its Genetically Modified Variants
Authors: Bräuchle C. , Hampp N. , Oesterhelt D.
Published: February 2023

BR from Halobacterium halobium [1] is embedded as a twodimensional crystallin lattice of BR-trimers in the lipid bilayer of the cell membrane.
Epitaxial Liftoff Integration of a GaAs Multiple Quantum Well Modulator Array onto Si VLSI for Optical Signal Processing
Authors: Chang W. , Ranganathan R. , Arbet-Engels V. , Yablonovitch E. , Hansen M. , Fan C. , Esener S.C. , Efron Uzi
Published: February 2023

The need for increased processing speed in advanced computing systems is straining the limits of purely electronic systems. Opto-electronic systems may represent the future form of implementation of high throughput data processing systems. The components that are selected for Opto-Electronic data processing systems have to meet the requirements of both high speed and low power dissipation. GaAs/AlGaAs Multiple Quantum Well (MQW) Spatial Light Modulators (SLM) exhibit low switching power and very high speed. Moreover, they operate at voltages which are compatible with Si VLSI technology1. These make them attractive in high density optical information processing systems such as optical correlators. Thin film integration between Si integrated circuits and MQW modulators can be done by Epitaxial Lift-Off (ELO) technique. A major advantage of ELO is that Si circuitry and GaAs MQW modulators can be optimized individually and then integrated together resulting in improved yield and performance.
Liquid crystal over silicon spatial light modulators: emphasis on design for applications
Authors: McKnight Douglas J. , Serati Steve A. , Johnson Kristina M. , Schuck Miller H.
Published: February 2023

Liquid crystal on silicon spatial light modulators are made by placing a thin layer of liquid crystal directly on top of a silicon chip. For a recent review of this technology see, for example, reference [1]. We have constructed a 256 by 256 binary spatial light modulator (SLM) for an optical correlator application which uses a chiral smectic C (SmC*) ferroelectric liquid crystal as the light modulating layer [2]. This device is currently the subject of our planarization experiments. We have also made a 128 by 128 analog SLM and in this summary we present some early results from this device
16x16 SLM with Silicon CMOS Drivers and III-V Modulators
Authors: Hansen Mark , Shih David , Fan Chi , Esener Sadik , Chang Wei , Yablonovitch Eli , Efron Uzi
Published: February 2023

Hybrid integration of III-V based optical devices, such as modulators, LEDs, and lasers, with silicon VLSI technology promises cost effective solutions to many optoelectronic challenges. It combines the low cost, high density, and high yield of silicon circuitry with the unique optical properties of III-V devices. Flip-chip bonding is a mature and commercial technology. It provides a means of reliable, rapid integration of these two types of devices.1
High yield, low cost Fabry-Perot modulators utilizing correctable partial anti-reflection coatings
Authors: Goossen K.W. , Cunningham J.E. , Jan W.Y. , Centanni J.
Published: February 2023

Many systems are contemplated that use surface-normal multiple quantum well (MQW) modulators to imprint data on optical beams. These include "smart pixel" digital processors,1 as well as image processors that employ spatial light modulators. These modulators are typically pi( MQW)-n diodes, grown by techniques such as Molecular Beam Epitaxy (MBE), wherein an integral multilayer mirror is produced underneath the MQW. By reverse biasing the diode the MQW’s absorption is modified and hence the reflectivity of the device is modulated. In simple designs a perfect anti-reflection coating is placed on the surface so multiple reflections do not occur within the modulator. This has the advantage that no strict control of the overall thickness of the device is required.
Compensation of Thickness Variations in a Fabry-Perot Modulator Array using a Self Tuned Fabry-Perot Structure
Authors: Harvey Phil , Esener Sadik
Published: February 2023

Many optical modulators achieve improved performance when used in a Fabry-Perot (FP) configuration[1-3]. This is due to the increased interaction of the light with the modulator active material. A conventional FP modulator consists of an active layer (electrooptic, electroabsorptive, or optically active material) acting as a cavity sandwiched between two dielectric or metal mirrors. To increase the interaction in the cavity, higher reflectance mirrors are required resulting in higher finesse cavities[4]. However, as the finesse increases, the cavity thickness tolerance decreases. This proves to be a serious practical limitation when building large size and/or large arrays of FP modulators (e.g. wafer size). Only when fabrication techniques that create materials one monolayer at a time are used does it become possible to build uniform FP modulator arrays.
Ferroelectric liquid-crystal optically addressed spatial light modulators for binary phase holograms
Authors: O’Brien D.C. , Moddel Garret
Published: February 2023

Ferroelectric liquid crystal spatial light modulators have a robust binary (0 and π) phase modulation scheme [1], which can potentially be both polarisation independent and lossless using an optimised device [2]. This is ideally suited to displaying binary phase computer generated holograms (CGHs) [3], combining holographic elements with programmability.
Future Directions in "Smart" Quantum Well Spatial Light Modulators and Processing Arrays
Authors: Miller David A. B.
Published: February 2023

Quantum well modulators and photodetectors are one attractive option for large scale integration of arrays of optical inputs and outputs in information processing systems. Optics is fundamentally attractive because it offers basic physical advantages in interconnections, and may allow novel architectures of information processing systems not well-suited to electronics alone. In the past, large arrays of quantum well devices have been used in experimental systems, and more recently technologies have emerged that have allowed "smart" arrays incorporating electronics both for added functional complexity and reduced optical energy requirements. The FET-SEED technology, for example, has integrated GaAs field effect transistors with quantum well modulators and detectors for high speed circuits with sophisticated functions, and has already been used to fabricate multi-project wafers for experimental use by a broad range of users.
Solid-State Laser Technology: Tunable Sources for Emerging Aerospace Applications
Authors: Allario F. , Barnes N. P. , Jalink A.
Published: February 2023

Tunable, solid-state laser sources are rapidly emerging technologies, providing continuous coverage of the electromagnetic spectrum (EM) from the ultra-violet through the far infrared. These sources provide obvious advantages for remote sensing experiments from space platforms by providing high electrical-to-optical conversion efficiencies, long lifetimes, reduced weight and volume. Several space and aircraft systems are currently under development for experiments to improve understanding of the chemistry and dynamics of the terrestrial atmosphere, using solid-state laser sources. 1Flight experiments are currently planned in the late 80’s and early 90's. Three laser facilities are planned by the National Aeronautics and Space Administration (NASA), for the Space Station, Earth Observing System (Eos). Under NASA's Civil Space Technology Initiative (CSTI), technology in tunable solid-state laser sources is being developed; initially the focus was 6000 to 1000 nm. This range of the EM spectrum is adequately covered by titanium-doped sapphire, pumped in the green by Nd:based materials.
Photometric Nonlinearity of the Faint Object Camera
Authors: Giaretta D. , Greenfield P. , Heaps C.
Published: February 2023

The Faint Object Camera (FOC) of the Hubble Space Telescope builds up an image by counting individual photons. The detector consists of a three-stage image intensifier coupled to a television camera. The video signal from the television camera is processed by a video processing unit (VPU) which attempts to locate the center of the amplified event in order to increment the appropriate memory location. At low light levels essentially all the events are counted, but at higher rates an increasing number are missed by confusion with overlapping events, or by rejection of a cluster of photons as being an ion event.
Coronagraphic Methods for Direct Imaging of Extra-Solar Planets
Authors: Terrile Richard J.
Published: February 2023

The goal of directly detecting the presence of planets around the nearby stars is one of great scientific interest and extreme difficulty. At visible wavelengths a Jupiter-sized planet around a nearby star 5 parsecs away is about one billion times fainter than the parent star and only 1 arcsec away. To extract such a small signal out of the background of scattered and diffracted light from the central star requires extraordinarily smooth optics at mid-spatial frequencies with instrumentation designed to reduce diffracted light.
Effects of Coatings on the Optical Scatter and Related Roughness of Coated Surfaces
Authors: Al-Jumaily Ghanim A. , McNeil John R.
Published: February 2023

The effects of coatings on the optical scatter and surface microroughness have been investigated by many authors recently. In previous publications [1-3] we have presented experimental results which indicate that coated surfaces, under certain conditions, may be smoother than the bare substrate. For example, it was reported that coating a polished copper (Cu) surface with a thin, 0.1 to 1 um, Cu film caused a significant reduction optical scatter and related surface microroughness. Different factors such as film thickness, deposition conditions, and the microroughness of the substrate, determined the magnitude of surface smoothing. In this report we present experimental results that illustrate the role of deposition mechanism and substrate morphology in the smoothing of coated surfaces. A model for the smoothing process will be presented.
Fabrication and Performance Prediction of the AXAF Technology Mirror Assembly
Authors: Reid P. B. , Babish R. , Berman J. , Gordon T. , Sarnik A. , Waluschka E. , Glenn P.
Published: February 2023

Recent advances in fabrication of the AXAF Technology Mirror Assembly are discussed. Performance of the telescope with the measured mirror surface figure is also presented.
Absolute Extreme-Ultraviolet Solar Spectral Irradiance Monitor
Authors: Smith Peter L. , Parkinson W. H. , Kühne Michael , Huber Martin C. E. , Kock Manfred
Published: February 2023

Reliable, long-term, radiometric calibration of space-based instruments for the study of extreme-ultraviolet (EUV) radiation, nominally 10 to 120 nm, has not been achieved in the past (Neupert 1986). Solar EUV observations have depended upon periodic recalibrations with rocket-borne instruments, but the data have been subject to adjustments and, as a consequence, criticisms (Lean 1987). Other astrophysical studies at EUV wavelengths have frequently used white dwarfs as standards, but the observed spectra are model-dependent. EUV radiometric fidelity requires in-orbit irradiance standards that can be used to monitor changes in the detection sensitivity of sun-observing and astronomical EUV spectrometers.
Scattering from Diffraction Gratings in the Extreme Ultraviolet
Authors: Edelstein Jerry
Published: February 2023

Characterization of the scattering behavior of diffraction gratings is critical for the design of spectrometers with good background rejection. The ability to compare grating scatter performance is essential as new grating manufacturing techniques are developed. Historically, scattering from diffraction gratings has been described in a plethora of functional schemes. These schemes are typically specific to the particular instrument or mounting in use, and they may not be used for ready comparison among gratings made by different processes or for analyzing a given grating used in various mountings.
The Evaluation of Photoelectrochemically Etched Gratings in GaAs
Authors: Leviton Douglas B. , Carrabba Michael M.
Published: February 2023

The GSFC Diffraction Grating Evaluation Facility has recently been used to evaluate several sets of echelle gratings in crystalline GaAs fabricated at EIC Laboratories under a small business innovative research contract. New technology echelle gratings will be required to achieve science goals for future space missions such as Space Telescope Imaging Spectrograph. The amount of scattered light in the plane of dispersion of these gratings was measured for orders on blaze. Also, the distribution of energy into the gratings’ zero orders and orders around blaze was measured for determinations of relative groove efficiency and blaze angle. Although substrate quality would not always permit quantitative evaluation of image quality, images were examined qualitatively to locate problem areas in the grating fabrication process and to assess progress in the technology of photoelectrochemically etched gratings. Preliminary results indicate that the GaAs gratings are obviously blazed at or near angles predicted by theoretical considerations relating to crystallography and to the measured stoichiometry during the photoelectrochemical etching process.
Fiber-Linked Optical Array of Telescopes (FLOAT)
Authors: Connes P.
Published: February 2023

We will describe the space version of our FLOAT proposal. This will be an array of telescopes connected by equal-length single-mode fibers to a mixing station, where the images will be synthesized. The main advantage, compared to all-mirror proposals, is a large simplification of the adjustment problem; the main limitation is exclsuion of far UV. A first step will be a similar array built on a ground-based radiotelescope.
The Space Infrared Telescope Facility (SIRTF)
Authors: Fazio G. G.
Published: February 2023

In 1983 the Infrared Astronomical Satellite (IRAS) radically changed our view of the infrared sky. IRAS carried out an all-sky survey in four broad wavelength bands between 8 and 120μm, detecting about 250,000 sources. This survey detected new comets and dust bands in our solar system, discovered protostars and possible proto-planetary disks around near-by stars, generated detailed images of the entire galactic plane, and discovered extremely luminous infrared galaxies. The Space Infrared Telescope Facility (SIRTF) was designed to provide an enormous gain in our ability to explore in greater depth the infrared sky as revealed by IRAS, and to explore some of the most fundamental questions about the origin, evolution, and ultimate fate of the Universe.
A Triple Fabry-Perot Spectrometer for the Far Infrared
Authors: Pickett Herbert M.
Published: February 2023

A Far Infrared Limb Observing Spectrometer (FILOS) is being developed for observations of OH and other upper atmospheric species. It uses three Fabry-Perot etalons in series to obtain resolution of 1 part in 100,000 at a wavelength of 100 microns. The largest of the three etalons is placed between the telescope and the atmosphere and has dimensions of 10 cm. The smaller two etalons are cooled to 4 K and function to filter out a single order of the large Fabry-Perot resonator. A Triple Fabry-Perot spectrometer is a very simple and effective way of obtaining high resolution spectra of atmospheric emission. Versions are being developed for balloon observations and are being proposed as part of the Earth Observing System for the Polar Orbiting Platform or for the Manned Space Station. Current methods of fabrication and testing the etalons will be described, along with measured and projected performance.
An Artificial Neural Network for Phase Recovery from HST Stellar Images
Authors: Sandler David G. , Barrett Todd K.
Published: February 2023

During the last two years, we have developed and refined a novel approach to estimate phase distortion across an optical beam directly from focused images of starlight. The method, applicable to real-time atmospheric compensation of large telescopes using guide stars, relies on a nonlinear neural network processor to determine the phase from two distorted point spread functions, one at the exact focus of the telescope and one intentionally out of focus. Real-time phase retrieval is possible because the network is trained using simulated data to recognize and predict the near-field phase from the characteristic shapes and features of far-field images.
Evolution of the Wide Field/Planetary Camera for Hubble Space Telescope
Authors: Vaughan Arthur H.
Published: February 2023

Early design considerations and other factors that led to the adopted optical configuration of the first generation Wide Field/Planetary Camera flown on the HST are reviewed in the context of requirements for a second generation instrument.
Advanced Fabrication Method for Corrective Telescope Optics
Authors: Gunnarsson G. H. , Hull-Allen C. G. , Engelbrecht O.
Published: February 2023

Corrective optics for aberrated telescope systems are a relatively inexpensive way to improve image performance. Both refractive and reflective corrective components may be used. Work is currently being performed on the fabrication of the Corrective Optics Space Telescope Axial Replacement, COSTAR, program. This paper discusses the fabrication methods used to produce the non-spherical COSTAR optics. The overall fabrication strategy is presented first followed by a detailed discussion on the polishing approaches. Finally, metrology results and convergence data of the polishing process are presented.
Optical System for the On-Orbit Calibration of the Wide Field/Planetary Camera
Authors: Smith S. T.
Published: February 2023

In order to perform photometric measurements of astronomical objects with the Wide Field/Planetary Camera (WF/PC), the relative pixel-to-pixel response as a function of wavelength must be calibrated for each of the eight WF/PC CCDs. The current on-orbit camera does this by taking streak flats, which are obtained by pointing the entire Hubble Space Telescope at the Pacific Ocean. The operational costs in performing calibrations in this manner are considerable. Therefore, an in-flight calibration system is being added to the Wide Field/Planetary Camera II. This system will provide uniform illumination across each of the eight CCD detectors in the Camera for a wavelength range of 122 nm to 1100 nm.
On Orbit Performance of the Hubble Space Telescope Fine Guidance System Operating in the Coarse Track Mode
Authors: Whittlesey Richard A.
Published: February 2023

The Hubble Space Telescope (HST) Fine Guidance System (FGS) was designed and demonstrated to provide a robust Coarse Track capability with a pointing accuracy of .02 arc second rms when tracking a Mv 14.5 star. Orbital data indicates that tracking performance varies from .02 to .065 arc second (Bely and Liu). Two HST hardware characteristics are identified as contributing to the higher than expected pointing errors. High jitter levels are induced by Solar Array Assembly mechanical shocks during and following day/night orbital transitions. Reduced signal to noise performance occurs in the Coarse Track control loop because of the spherically aberrated images from the telescope optics. A Computer simulation has been developed to investigate the operation of the Coarse Track mode performance and to determine if performance can be enhanced by modification of up-link control variables.
Cryogenic Performance of the Space Infrared Telescope Facility Prototype Secondary Mirror Assembly
Authors: Stier Mark T. , Doyle John C. , Duffy Michael A. , Gottschalck Kenneth S. , Gullapalli Sarma N. , Neuner Jeffrey W.
Published: February 2023

The Space Infrared Telescope Facility (SIRTF), planned for an early 21st century launch, is the fourth of NASA's Great Observatories. It contains a 1-meter class Ritchey-Chretien telescope, all of whose components will be cryogenically cooled to superfluid helium temperatures. Achievement of diffraction-limited performance at wavelengths as short as 3 μm will likely require realignment of the secondary mirror following launch. Efficient use of SIRTF's limited cryogenic lifetime (5 years, with a sensitivity of 1 month/mW) requires a means for tilting the secondary mirror to rapidly relocate the telescope's line of sight and to map small regions of the sky. Furthermore, at the longest SIRTF wavelengths (200-1200 μm) the emission from the cooled telescope will be significant, thereby requiring the use of periodic tilt oscillations of the secondary mirror to modulate the signal.
Progress in optical testing of prototype mirrors for JPL’s Precision Segmented Reflector (PSR) Program.
Authors: Hochberg Eric B.
Published: February 2023

jpl's Precision Segmented Reflector (PSR) program is developing enabling technologies for large space telescopes employing segmented optics, and in particular, lightweight, thermally-stable mirrors. NASA astrophysics missions1 operating at sub-millimeter wavelengths serve as the primary focus for this technology development program which began in 1987.
Mechanism of Float Polishing
Authors: Namba Yoshiharu
Published: February 2023

Introduction The float polishing has been widely used to make the gap opposed surfaces of VCR (Video Cassette Recorder) heads in Japan since 1978 [1], because the method can obtain the super smooth and extremely flat surfaces [2] on Mn-Zn ferrite single crystals with good edge geometry [3] and no damaged layer [2]. Nowadays, millions of the heads are manufactured per month using this technology. It is very easy to control the flatness of a lap in the float polishing, so that this is the most suitable method for automation of polishing in high quality.
Mechanism of Mechanochemical Polishing
Authors: Imanaka Osamu , Yasunaga Nobuo
Published: February 2023

Polishing techniques which produce geometrically accurate surface without damage and strain are required for most inorganic materials used for electronics. In general, these materials are mechanically polished with fine hard abrasives. The present "Mechanochemical Polishing" developed by the authors (1) is ideal for this request, because very flat and damageless mirror surface can be easily obtained by using this technique, which can be carried out in the same way as conventional mechanical polishing methods. The main distinction of this method is to use powders which are mechanically softer than the materials to be polished and chemically reactable with them. As the soft powders neither mechanicallyindent nor scratch the material surface, smooth and scratch-free surface of hard materials can be obtained, even if powders of large grain sizes and relativelly rigid polishers are used.
An Algorithm for Incomplete Range of Views Reconstruction
Authors: Tuy Heang K.
Published: February 2023

To reconstruct a cross-section of a 3D object, most algorithms require knowledge of the projection data in a full range of views [1]. In some practical situations [2, 3], reconstruction from an incomplete range of views is inevitable although it is not desirable from a mathematical point of view. Objects to be reconstructed are of compact support. Their Fourier transforms can be extended to an entire function of exponential growth (band-limited function). Consequently, there is a unique solution to the incomplete range of views reconstruction problem. On the other hand, the problem is an ill-posed problem. For example, it has been indicated [4] that the spectrum of the singular values of the Radon transform for limited range of views is split up into_two parts. One part consists of singular values near one, and the other part consists of singular values near zero. The recovery of small singular values is necessary for a process to reconstruct objects with good quality. This, however, exacerbates instability in the process, i.e., a small error in the projection data might lead to an undesirable large difference in reconstructed images. Making use of a priori information on image and projection data is being examined to reduce this instability.
Localization From Projections Based on Detection and Estimation of Objects*
Authors: Rossi David J. , Willsky Alan S.
Published: February 2023

The problem of reconstructing a two-dimensional (2D) function from its ID projections arises, typically in the context of cross-sectional imaging, in a diversity of disciplines [1-3]. In this problem, a 2D function f(x) is estimated from samples of its Radon, transform (line integral measurements) where
θ_=(cosθ sinθ)¢. The major emphasis of research and applications in this area has been on producing accurate, high-resolution cross-sectional images (requiring a large number of high signal-to-noise ratio (SNR) measurements taken over a wide viewing angle [4,5]) which in practice are post-processed, perhaps by humans, to remove artifacts and extract the information of interest about the cross-section. For example, in nondestructive testing applications [3], reconstructed images are post-processed to determine whether flaws or defects are present within a homogeneous medium; in oceanographic applications, reconstructed images are post-processed to determine where within the cross section an oceanographic cold-core ring is located [2]. Such post-processing is effectively the utilization of a priori information about the medium being measured to enhance and extract specific pieces of information.
Analysis of Time-Sequential Sampling with a Spatially Hexagonal Lattice
Authors: Cramblitt Robert M. , Allebach Jan P.
Published: February 2023

Hexagonal sampling of 2-D signals has been considered a useful alternative to rectangular systems. Mersereau [1] analyzed hexagonal sampling and showed that when images are circularly or elliptically bandlimited the sampling density can be 13.6% less than that required for a rectangular sampling system. Murphy and Gallagher [2] studied hexagonal sampling in the context of optical systems. Here we investigate spatially hexagonal sampling of spatiotemporal signals. Since obtaining samples at every point in space at the same time instant is impractical for many applications, we constrain the sampling to be time-sequential. We examine the performance of various sampling patterns as we sample below the temporal Nyquist rate, and we compare their performance with that of the corresponding rectangular case that was analyzed previously [3].
Image Registration; The Undersampled Case
Authors: Barry P. E. , Klop M. , Hulsmann J. D.
Published: February 2023

The registration of a multi-frame sequence of images has been a classic problem in image processing whose solution has found wide application in such diverse areas as astronomy, earth resource analysis, electron microscopy, computed-aided medical imaging, military surveillance and photo-reconnaissance. In the most general sense, precise image registration allows such subsequent processing as signal-to-noise improvement, pattern enhancement and characterization, and the automated detection of spatio-temporally varying patterns, to be carried out at a level that would be impossible if the image sequence were not accurately registered.
Speckle Interferometry: One-Dimensional Image Reconstruction from Zeros of Complex Spectrum
Authors: Bruck Yuri M. , Sodin Leonid G.
Published: February 2023

The method suggested by Labeyrie [1] allows reconstruction of the Fourier spectrum modulus to be performed for images scattered by a random atmosphere. Ultimately one is able to determine the autocorrelation function of the image, yet not the image itself.
Retrieval and Synthesis Problems in Optics - An Overview
Authors: Baltes H. P.
Published: February 2023

Motivations for studying inverse optical problems in the Central Laboratory of the Landis & Gyr Corporation are the encoding of information in diffracting or scattering structures tailored to purpose, the reading of such information using optical sources and detectors, and the retrieval of structural information in the presence of random scatterers (such as a rough surface), with emphasis on the automatic optical checking of identity or authenticity. One example of a product based on such procedures is the PHONOCARD currently being manufactured by Sodeco-Saia, a company of the Landis & Gyr group. The PHONOCARD is a pay telephone operated by pre-paid cards (see Fig. 1) with optically stored value units, whose authenticity is checked by an optical reading system.
Detection of Line Spectra and Point Sources
Authors: Papoulis A.
Published: February 2023

The problem of detecting an object consisting of point sources in a noisy environment in terms of a single sample of a diffraction limited image is considered. The proposed method in its simplest form can be phrased as follows.
Spectrum extrapolation on a finite band
Authors: Gori F. , Wabnitz S.
Published: February 2023

The iterative method of Gerchberg (GM) for extrapolating the whole spectrum of a finite support object1 has been analyzed and generalized by several authors2-14. In principle, during each iteration of the GM an infinite band of frequencies should be handled. At first sight, it seems that the (obvious) existence of a cut-off frequency in any practical implementation of the GM should simply allow the spectrum extrapolation to be achieved only below such a frequency. This is not the case, as we shall presently show, in that the extrapolated spectrum obtained by this method up to the cut-off frequency does not coincide with the true spectrum. In this paper we present a modified version of the GM that allows to obtain a spectrum extrapolation on a finite band of frequencies. This is of use both to limit the storage and computation time requirements and to reduce the sensitivity to high frequency noise.
Electromagnetic image reconstruction techniques in inhomogeneous media satisfying the Born-Rytov approximation
Authors: Boerner Wolfgang-M.
Published: February 2023

The basis for developing projection tomographic reconstruction algorithms has been the assumption of straight-line ray-path propagation. But, in the case in which propagation occurs within discretely inhomogeneous media at wavelengths of the order of the size of the scatterer, phenomena such as refraction, reflection and diffraction can no longer be neglected and a straight-line projection tomographic approach fails. This is especially evident when a large difference in refractive index occurs, such as that encountered with dm-to-mm-wave propagation in inhomogeneous atmospheric media, representing hydrometeorite distributions, the marine ocean boundary layer, the ground surface underburden, or bone and soft layers within soft tissue. An exact solution for the general vector scattering case which strictly requires a polarimetric radiative transfer approach is not available, and in this research, the assumption is made that the media are weakly diffracting so that the Born and Rytov approximations are valid. Based on this assumption, various diffraction imaging methods were developed most recently, and we are basing our studies on Devaney's back-propagation tomographic approach which was developed upon the scalar wave theory. It is the main objective of this research to extend this work to the realm of electromagnetic vector wave theory for the improved diffraction-corrected imaging of radar targets embedded in clutter within the dm-to-mm-wavelength region of the electromagnetic spectrum.
Spectral Extrapolation of Constrained Signals
Authors: Mammone R. J.
Published: February 2023

There are many applications where it is desirable to restore the high frequency components of a signal, for example, in radar and sonar, greater range accuracy can be obtained by spectral extrapolation, In imaging systems, the restoration of an image will provide increased resolution, The ability to restore the fine details of an image is of obvious value in such diverse fields as astronomy, electron microscopy, satelite survailance, medical image processing, remote sensing, and in image data compression applications.
Matched Image Formation and Restoration System*
Authors: Cathey W. Thomas , Frieden B. Roy , Rhodes William T. , Rushforth Craig K.
Published: February 2023

In the past, attempts to increase the resolution of images by modification of the imaging system or by image enhancement techniques have been two separate fields of endeavor. Research on imaging systems concentrated on resolution increase by use of such approaches as special phase masks, the rearrangement of the spatial bandwidth of a system, and trades of temporal bandwidth for spatial bandwidth [1-7]. The image restoration techniques have concentrated on spectral extrapolation using maximum entropy, Bayes’ theorem, Gerchberg's algorithm, or some other iterative approach [8-12].
Image Restoration by the Method of Projections onto Convex Sets
Authors: Stark H. , Sezan I.M.
Published: February 2023

In this paper we use the method of projections onto convex sets (POCS) to restore an image for which only partial knowledge of the Fourier transform is available. A spectacular improvement over the Gerchberg-Papoulis restoration is observed when the number of iterations is small.
Stable, non-iterative, object reconstruction from incomplete data using prior knowledge
Authors: Darling A.M. , Hall T.J. , Fiddy M.A.
Published: February 2023

The non-uniqueness and instability of object reconstruction from incomplete data can only be resolved by a priori constraints restricting the set of admissible solutions. A successful approach is to choose the object consistent with the data and of minimum norm in a weighted Hilbert space [1,2]. The weight is chosen to reflect our prior knowledge of the solution. The algorithm involves the solution of a set of linear equations with Toeplitz structure which can be efficiently solved in a finite number of steps by the Levinson recursion [3]. We show the equivalence between this method and Miller regularisation [4,5] for ill-posed problems. Experimental results demonstrating the effectiveness of the method are shown in the presentation [see also ref. 2].
An Iterative Deconvolution Algorithm with Exponential Convergence
Authors: Morris C.E. , Richards M. A. , Hayes M.H.
Published: February 2023

Iterative deconvolution is an established technique for recovering the input sequence of a linear shift-invariant system given the output sequence and some knowledge about the distorting system [1]. Since the standard approach to iterative deconvolution has a linear convergence rate, some authors have proposed techniques such as gradient search methods [2,3] and kernel splitting [4] to increase the rate of convergence. These methods, however, are either computationally expensive or do not achieve a substantial gain in convergence rate. In this paper we describe an accelerated iterative algorithm that requires slightly more computational time or memory storage than the standard approach while achieving a favorable exponential rate of convergence.
Phase Retrieval in Imaging
Authors: Ferwerda Hedzer A.
Published: February 2023

In this review an overview will be given of the state-of-the-art in phase retrieval (PR). PR occurs in many different areas of signal processing: - in imaging, where the image only yields the modulus of the wavefunction in the image plane, while for the reconstruction of the object we also need its phase - in speckle interferometry where we obtain the modulus of the Fourier transform of the object wavefunction, while its phase cannot be determined - in interferometry where often only the modulus of the coherence function of the source can be determined.
Phase Retrieval: Algorithm Improvements, Uniqueness, and Complex Objects
Authors: Fienup J.R.
Published: February 2023

Since the first topical meeting on Signal Recovery and Synthesis [1], significant new developments have taken place in phase retrieval. Some of these are discussed in other papers in the Digest for this meeting, Signal Recovery and Synthesis II. In this paper we review recent developments in phase retrieval and image reconstruction that revolve around around the use of the iterative Fourier transform algorithm [2-4].
Phase Diversity
Authors: Gonsalves Robert A.
Published: February 2023

Phase diversity [1] implies that an image is measured through two or more phase "channels". The primary channel uses an adaptive optical system which attempts to remove phase distortions. The secondary channel introduces phase diversity by adding a known phase aberration to the adaptive optical system. In the simplest form of phase diversity the image plane is displaced, which introduces a quadratic phase into the optical path. The two outputs might be recorded simultaneously by using two focal planes; or they might be recorded sequentially, in which case the time lapse must be small enough that the primary channel's state is unchanged for the second measurement.
Recognition of 3-D Objects from Partial View Data
Authors: Wu Ronald , Stark Henry
Published: February 2023

We consider a problem that occurs in machine vision research, namely, how to determine the class membership of an object when only partial view data about it is available. For example, suppose that a machine vision system must determine whether a physical (i.e., a three-dimensional) object belongs to class A or class B and only 90 degree view data is available. How should the data be organized into a useful feature vector? What rule should be used to determine class—membership? One way to proceed is via image recovery i.e., the restoration of missing view data using any of the several extrapolation algorithms known to the image recovery community. However if only class membership is desired, is image recovery really needed? First we note that if the partial view data is insufficient i.e, it contains no information that is not common to both classes, then image recovery will not work (now for that matter will anything else!). Second, assuming that the data is sufficient i.e., that it contains at least some data characteristic of only one class, image recovery may not be the answer for two reasons: 1) the recovery process is most-often ill-posed, thereby introducing possibly too much noise for subsequent discrimination; and 2) regularization may induce sufficient smoothing to destroy what little class-differentiability may exist in the partial data. Thus we concentrate on information recovery rather than image recovery. We are therefore led to the following problem statement: given partial view data of a 3-D object known to belong to one of M well-defined classes, what operation (linear or non-linear) will enhance the discriminating value of the data? The algorithm we have derived is based on the ful1-view algorithm described below.
Two dimensional image restoration using Linear Programming
Authors: Mammone R.J. , Rothacker R.J.
Published: February 2023

In this paper we address the issues involved in implementing the Linear Programming (LP) method of image restoration in two dimensions. A modified pivot strategy is introduced in order to reduce the number of iterations. This approach is necessary due to the number of arithmetic operations required per iteration for two dimensional data. We shall also discuss the effects of additive noise, such as that due to quantization. The effects of noise on the performance of restorations with both separable and nonseparable degradations will be presented. The performance of the LP approach has previously been seen to show a preference for sparse images C13, i.e. images with many zero valued pixels. This preference is also found in the two dimensional case. The error in the LP restored image is shown to be less for sparse images than it is for dense images with the same signal-to-noise ratio (SNR). Linear Programming, despite its name, is nonlinear. That is, the LP solution of the sum of two images is not necessarily the sum of the two solutions obtained for each image separately. The LP method also allows for inequality as well as equality constraints to be imposed on the solution. The advantage in performance of the constrained nonlinear approach taken here over linear non-constrained methods is also demonstrated. This is accompli shed by illustrating the pseudo-inverse solution for each LP restoration. The pseudo-inverse method represents the optimal non-constrained linear restoration.
The Phase Problem of X-Ray Crystallography
Authors: Hauptman Herbert
Published: February 2023

The electron density function ρ(r) in a crystal, a function of the position vector r, is a triply periodic function of r and may therefore be represented by means of the triple Fourier Series where V is the volume of the fundamental parallelepiped and the three components of the vector H range over all the integers.
Phase Retrieval Using Ayers/Dainty Deconvolution
Authors: Seldin J.H. , Fienup J.R.
Published: February 2023

An iterative algorithm developed by Ayers and Dainty [1] for the blind deconvolution of two functions is applied to the problem of phase retrieval. Because its structure closely resembles that of the Error Reduction (ER) algorithm commonly used for phase retrieval [2-4], the performance of the Ayers/Dainty (AD) algorithm is compared with that of ER. Both of these algorithms are compared to the faster hybrid input-output (HIO) algorithm [2-4] for the cases of real, nonnegative objects with known and unknown support using Fourier intensity data with different levels of additive Gaussian noise.
Direct Phase Estimation from Phase Differences Using Fast Elliptic PDE Solvers
Authors: Ghiglia Dennis C. , Romero Louis A.
Published: February 2023

Obtaining robust phase estimates from phase differences is a problem common to severed areas of importance to the optics and signal processing community. Specific areas of application include speckle imaging and interferometry, adaptive optics, compensated imaging, and coherent imaging such as synthetic-aperture radar. The purpose of this paper is to relate the equations describing the phase estimation problem to the general form of elliptic partial differential equations, and illustrate results of reconstructions on large M by N grids using existing, published, and readily available Fortran subroutines.
Optical Tomography by Confocal Fluorescence Microscope
Authors: Nakamura O. , Kawata S. , Minami S.
Published: February 2023

In the past few years, microscope tomography has been intensively studied.1-5 Agard and Sedat restored the 3-D structure of biological cells from the focus series images given by a conventional epi-fluorescence microscope, by inverting the 3-D optical transfer function of the system.1 However, since the 3-D OTF of an epi-fluorescence microscope is angularly band-limited,6 the 3-D spatial frequency components only within the angular band can be restored in their method. As a result, the longitudinal resolution in the restored 3-D structure is not at all satisfactory.
L-Shape Array for Estimating 2-D directions of Mu 11ip1e-Wave Arrival
Authors: Hua Yingbo , Sarkar Tapan K.
Published: February 2023

For high resolution wave direction finding, much attention has been recently paid on linear arrays which are used to extract 1-D directions of wave arrival. The techniques based on linear (1-D) arrays can be used to extract 2-D directions of wave arrival if two linear arrays oriented to different directions are used and if an additional pairing process is employed. However, we believe that for the 2-D direction estimation, more efficient techniques should be explored based on 2-D arrays.
On Deterministic Convergence of Iterations of Relaxed Projection Operators
Authors: Youla Dante C.
Published: February 2023

In our talk we describe a conceptually simple model for system identification that involves unrestricted iterations of nonexpansive operators drawn from either a finite or infinite pool.
Properties and Computational Implications of Zero-Sheets
Authors: Bates R.H.T. , Quek B.K.
Published: February 2023

The spectrum (i.e. Fourier transform) of a K-dimensional compact (i.e. of finite amplitude and size) image is characterised (up to an arbitrary complex constant) by its zero-sheet, which is the (2K-2)-dimensional surface whereon the spectrum vanishes in 2K-dimensional complex Fourier space (constructed by generalising each real Fourier coordinate to a complex variable) [1].
Using Phase Retrieval to Determine the Intensity and Phase of an Ultrashort Laser Pulse
Authors: Trebino Rick , Kane Daniel J.
Published: February 2023

We have solved the long-standing problem of measuring the full electric
field, E(t), of a single ultrashort laser pulse by reducing it to a
two-dimensional phase-retrieval problem.
Aspects of the Phase Problem for Periodic Images
Authors: Millane R. P.
Published: February 2023

Phase problems for periodic images, such as occur in x-ray crystallography, do not generally have unique solutions. The effect of a priori information on constraining the solution to such problems is examined.
Approximating Fourier Phase Values Using Zero Locations
Authors: Wackerman Christopher C. , Yagle Andrew E.
Published: February 2023

The existence of linear zeros in the Fourier domain (locations where the real part and the imaginary part of the Fourier transform are simultaneously zero and both go through the zero linearly) has a tremendous impact on the value of the Fourier phase throughout the frequency plane. Branch cuts in the wrapped Fourier phase (curves along which the phase abruptly changes from −π to π) provide most of the visual information when examining an image of the phase values, and they must stop and start at linear zeros.
Imaging Correlography Using an Inverse Synthetic Aperture
Authors: Rider Douglas B. , Voelz David G. , Gonglewski John D. , Bush Keith A.
Published: February 2023

Imaging correlography is a technique for recovering images of coherently illuminated objects from pupil plane measurements of the backscattered laser-speckle intensity.1 In this paper, we describe the implementation of the imaging correlography technique using a one-dimensional (linear) receiver array. Two-dimensional images are reconstructed from intensity data that is collected and processed in the form of an inverse synthetic aperture. The synthetic aperture is produced by the motion of the object (with respect to the receiver) which causes the backscattered intensity pattern to “sweep” across the linear array.
Superresolution in Confocal Scanning Microscopy: The Two-Dimensional Incoherent Case
Authors: Bertero M , Boccacci P , Davies R E , Grochmalicki J , Pike E R , Walker J G
Published: February 2023

In a series of recent papers [1-4] we have proposed an approach to achieving superresolution in confocal scanning microscopy based on a singular system approach to the inverse problem. In this approach the Fredholm equation of the first kind which describes the imaging system is solved by finding its singular-value spectrum and its "object" and "image" singular functions. These functions provide complete orthonormal basis sets for the description of object and image which have the desirable feature of minimum "representational entropy". The inversion is performed by finding the coefficients of the singular function expansion up to an index determined by the level of noise in the image and the singular value spectrum. We have recently described an all optical technique to perform these operations which involves designing an optical mask to place in the image plane of the system (apodisation in the pupil plane is not suitable for incoherent light imaging). The mask function for five terms in the series is shown in Fig 1 [3]. The transfer function for this mask is shown by the heavy line in Fig 3.