bluuebunny/crossref_metadata_2025 huggingface dataset:
Hadamard Transforms with Ferroelectric-Liquid-Crystal-over-Silicon Spatial Light Modulators
Authors: Gourlay J. , McOwan P. , Vass D.G. , Underwood I. , Worboys M.
Published: February 2023

The ability to perform image processing tasks requires computationally intensive two dimensional matrix handling with particular emphasis on transformations1.
Optically Driven Optically Addressed Spatial Light Modulator.
Authors: Reardon Janine V. , Gregory Don A.
Published: February 2023

Organic based materials have been developed that can record an intensity distribution in the form of an amplitude or a phase distribution and can be written and read multiple tirnes(1.,2. ,3.,4.,5.). These materials show great promise as SLM modulation media. Although the chemistry of these organic materials is fairly well understood, the process of inducing anisotropy in these materials by photons, the method by which information is stored by these materials, has not yet been the subject of careful examination. The aim of this paper is to present an investigation of these materials and construct a model for these systems. This model will be used to experimentally modify properties of these materials, such as response time, contrast, and resolution.
Electrically and Optically Addressable Spatial Light Modulators Based on n-i-p-i Doping Superlattices
Authors: Döhler G.H. , Kiesel P. , Kneissl M. , Linder N. , Gulden K.H. , Riel P. , Wu X. , Smith J.S.
Published: February 2023

In this paper three different versions of n-i-p-i based spatial light modulators will be discussed: 1) optically addressed modulators, based on the large non-linear absorption changes, 2) electrically addressed modulators with largely improved performance characteristics, and 3) optically addressed "smart modulators", consisting of a combination of fast detectors with gain with electro-optical modulators.
Wedged Liquid Crystal Beam Steering Device
Authors: Searcy Paul , Hahn Tami , Wang Li , Moddel Garret , Wootton John , Waldman Gary , Holder Dave
Published: February 2023

Liquid crystals have long been investigated for non-mechanical beam steering devices. Previous work has approached beam steering by using an electrically addressed cell with multiple electrodes arranged in stripes. By creating a series of steps in the index of refraction profile, the beam experiences an effective wedge and is steered in a particular direction [1]. The discrete nature of the steps creates a substantial amount of scattering which can be reduced by the addition of a resistive region between electrodes to interpolate neighboring voltages [2]. Another method of beam steering is to create a voltage drop along one electrode which produces continuous phase profiles [3]. The steering angle is limited by the product of the change in index and thickness of the cell divided by the length of the cell. This creates a trade-off between switching speed and steering angle since the nematic relaxation time is proportional to the thickness squared.
Spatial Light Modulation at Photon-Counting Light Levels
Authors: Hunt J. H. , Holmes R. B.
Published: February 2023

Recently, there has been a great deal of interest in the use of avalanche photodiodes (APD) for spatial light modulation.1,2,3 We report improved performance of our all-optical spatial light modulation with an avalanche photodiode. Modulation is performed with the APD operating as an asymmetric Fizeau interferometer with refractive index modulated by optically-initiated, avalanche-induced heating. Modulation of 80 % is achieved with optically optimized APDs. We demonstrate multiple-pixel operation, as well as free-carrier induced modulation.
Electroholographic Spatial Light Modulators
Authors: Agranat Aharon J.
Published: February 2023

We present a new generic architecture for spatial light modulators (SLM), based on the concept of electroholography (EH). The pixel of the EH-SLM is a minute prestored volume hologram, the diffraction efficiency of which is controlled by a locally applied electric field.
Characterization of the optical quality and modulating properties of a PLZT modulator through Mueller matrix imaging polarimetry
Authors: Pezzaniti J. Larry , Sornsin Elizabeth A. , Chipman Russell A. , Mansoorian B.
Published: February 2023

The Physics Department at the University of Alabama in Huntsville (UAH) in collaboration with the Electrical and Computer Engineering Department of University of California, San Diego (UCSD) has applied Mueller matrix imaging polarimetry[1] to quantifying the polarization modulating properties of PLZT spatial light modulators. The purpose of this study was to evaluate the optical quality of a wire-bonded transmissive PLZT (9/65/35) modulator array, the uniformity of modulation across pixels, and the cross-talk between adjacent pixels.
Liquid Crystal Device Performance Degradation through Selective Adsorption of Ions by Alignment Layers
Authors: Perlmutter Stephen H. , Doroski David , Moddel Garret
Published: February 2023

We have found selective adsorption to be responsible for the observed increase in liquid crystal ion populations as test cells are driven. Increasing ion populations correlated well with evidence of increased shielding of an applied voltage. A number of different alignment layers were compared for their tendency toward selective absorption. To investigate the interaction between ions and the alignment layers, in addition to liquid crystals a number of alcane liquids with known ionic components were used in test cells. A computer-implemented simulation of ion behavior was developed and used to verify our interpretations of our experimental results.
Providing Optical I/O to Electronic Logic Circuits with Multiple Quantum - Well (MQW) Diodes (Invited)
Authors: Chirovsky Leo M. F.
Published: February 2023

The introductory paragraph to the Call for Papers for this Spatial Light Modulators (SLM's) Topical Meeting contains a very cogent definition of SLM's. In the context of that definition, the topic of this talk falls into the category of "highly integrated semiconductor ’smart’ SLM's which spatially modify the intensity of a two-dimensional light distribution under the time-varying control of another spatial optical intensity distribution". The general purpose of these SLM's is to enable the construction of information processing systems which take advantage of the massive parallelism possible with free-space optical interconnects for very high data throughputs. The SLM's take the form of optoelectronic chips, which generate pixellated, parallel, synchronous, monochromatic, digital optical data streams. These chips usually also receive similar optical data streams, although the inputs do not need to be either digital, or pixellated or monochromatic or quite as synchronous. The circuitry on these chips can contain purely electronic components such as transistors , resistors, diodes, etc., but very importantly, need only one type of optoelectronic component - the p-i(MQW)-n diode, since it performs both Optical to Electrical (O/E) signal conversions and E/O conversions.
Switchable optical kinoforms, complex modulation holograms with twisted nematic liquid crystal television
Authors: Neto Yunlong Sheng Luiz Gonçalves , Roberge Danny
Published: February 2023

Twisted nematic liquid crystal cell provides continuous phase modulation [1]. In this paper we explore this interesting property for implementation of switchable holograms and correlation filters.
Realizing optical logic with a smart pixel spatial light modulator
Authors: Kane Jonathan S. , Kincaid Thomas G.
Published: February 2023

Amethod of realizing optical logic has been realized experimentally with the design and construction of a ferroelectric liquid crystal spatial light modulator. The different logic functions realized, OR, AND, NOR, NAND and XOR will be discussed.
Field-of-view Limitations of Phased Telescope Arrays
Authors: Harvey James E.
Published: February 2023

The optical performance of phased telescope arrays used for imaging applications is degraded by various design, manufacturing, and operational errors. However, even if diffraction-limited performance is achieved on-axis, there are both fundamental and practical limitations to off-axis performance which will severely limit the useful field-of-view of such systems. Two separate and distinct mechanisms that degrade off-axis performance are pupil mapping errors encountered in the beam combining process and the field curvature of the individual telescopes making up the array. The pupil mapping errors are operational errors which have been discussed in some detail elsewhere. Field curvature of traditional telescopes is a rather benign aberration which doesn't really degrade the image of a point source but rather displaces it axially by an amount proportional to the square of the field angle. However, in phased telescope arrays, the field curvature of the individual telescopes result in relative phase errors and relative tilt errors between the various subapertures which severely degrades the image quality of off-axis object points in addition to producing a traditional field curvature for the array. This paper deals specifically with the off-axis image degradation due to the field curvature of the independent telescopes and how it varies with the subaperture configuration and the telescope design parameters. Two very interesting results of these parametric studies are that the off-axis image quality of phased telescope arrays is a very strong function of subaperture size requiring the field curvature of the individual telescopes to be very well corrected for subaperture diameters greater than 1 meter and that the sensitivity of image quality to residual field curvature is highly dependent upon the subaperture configuration. Circular configurations of subapertures (located at constant radial positions) are far less sensitive to field curvature than other configurations. Quantative results of parametric studies will be presented.
Preliminary Optical Design for a Laser Gravitational Wave Antenna in Space
Authors: Bender P. L. , Faller J. E. , Hall J. L. , Hills D. , Stebbins R.
Published: February 2023

Summary not available.
The Role of Imaging Optical Interferometry Using Arrays of Spacecraft
Authors: Stachnik Robert V.
Published: February 2023

A number of authors have suggested employing arrays of spacecraft for high spatial resolution optical aperture synthesis. This approach to imaging interferometry is in contrast to use of a monolithic structure to define the interferometer's optical geometry. The attractiveness of the multiple spacecraft approach stems from the possibility of achieving exceptionally high spatial resolution and of easily reconfiguring the array.
Ultra-Sensitive Infrared and Visible Photon Detector
Authors: Bharat R.
Published: February 2023

The Solid State Photomultiplier (SSPM) is a photon detector based on impurity band conduction (IBC) in semiconductors. The high internal gain (over 50,000) in the device and its fast response (rise time less than 10 ns) combine to permit the detection of single photons over a wide spectrum. The SSPM is a two-terminal device that can operate continuously with a dc bias, yielding an output current pulse for each detected photon. Quantum efficiencies of over 5036 have already been achieved at wavelengths of 0.45 and 20 micrometers using arsenic-doped silicon (Si:As) for the IBC region; even higher values are possible, not only through the addition of anti-reflection coatings but also by the design of device structures optimized for specific wavelength ranges. Currently available Si:As SSPMs operate best at temperatures between 6 and 10K. Pulse count rate densities in excess of 109 per cm2−s have been achieved when an SSPM of typical size (10−4 to 10−2 cm2) is used in conjunction with suitable readout electronics. As the amplitude of the output pulses is large compared to the noise of the readout electronics and the pulse height distribution is quite tight, processing of the output signals can be handled rather conveniently by digital computers without the need for analog-to-digital converters.
Diffraction Gratings for Space Astronomy
Authors: Bach Bernhard W.
Published: February 2023

Present and future space astronomy missions require new manufacturing techniques to fabricate efficient gratings. The major requirements of high throughput and low scatter are still high on the list of priorities for these special optics, but there are new concerns and design goals to challenge the grating manufacturer.
Telescope Array Performance in the Optical Limit
Authors: Watson Maj Steven M. , Mills James P.
Published: February 2023

Many astrophysical observations require large diameter space borne optics. Because of the limited space and weight requirements for boost into orbit and manufacturing limitations, large diamteter optics pose a problem. Multi-aperture optical systems may provide a solution. This theoretical analysis examined many multi-aperture systems (Figure 1) and determined that multi-aperture systems composed of 19, 37, 61, and 91 apertures could provide impulse responses (displayed in Figure 2) which were superior to that of a single large optic of an equivalent diameter. The multi-aperture systems were superior in the sense that the secondary lobe irradiance maxima of these systems was less than 0.0175, the secondary lobe irradiance of the single large aperture. In all cases, the central lobe widths of the impulse responses were equal to that of the single large aperture of equivalent diameter. The addition of obstructions which covered the central portion of each aperture (to simulate a Cassegrain telescope system) caused the secondary lobe irradiance maxima to be reduced further for the 19 and 19 (rotated) aperture systems. Figure 3 displays the results of this analysis. For obscured and unobscured cases, the 19 (rotated) aperture system exhibited the lowest side lobes.
A Four Telescope Wide Field of View Phased Array
Authors: De Hainaut C. R. , Hentz K. P. , Weaver L. D. , Gonglewski J. D.
Published: February 2023

A phased array telescope is an array of optical telescopes whose images are coherently combined so as to achieve the resolution of a single but much larger telescope. Design of a wide field of view phased array imaging system is considerably more difficult than phased array beam transmission telescopes such as PHASAR,1 which has no field of view. In addition to maintaining optical phase to a fraction of a wavelength on the optic axis, an imaging telescope must accurately control phase and align the images from all telescopes to within a fraction of a resolution element over the whole field of view simultaneously. This requires lateral pupil geometry3 that is extremely close to the ideal.
Geometrical Ray-Tracing Calculations for a Space-Borne, Single-Aperture Astrometric Telescope Facility
Authors: Buffington A. , Mendoza E.
Published: February 2023

A 1.5 m telescope in space could achieve unprecedented differential astrometric precision, using essentially present-day technology. A Ronchi ruling in the prime focal plane moves over the images, and photoelectric detectors view the modulated starlight to determine angles between the target and reference stars within a 5 arcminute radius. A 10 microarcsecond precision can be achieved, after about an hour s integration time, for 13th magnitude targets. Such a telescope, operating over 20 years, could detect planets around nearby stars, and make major contributions to other stellar and galactic problems (Levy et al. 1986, 1987).
The Dynamic Components of a Phased Array Imaging System
Authors: Marker D. K. , Duneman D. C.
Published: February 2023

The phased array telescope imager or Multipurpose Multiple Telescope Testbed (MMTT) contains several important dynamic components. These components are used to maintain the critical optical geometries required to coherently combine multiple telescope apertures. Here we describe the dynamic components that manipulate the optical geometry. A more complete optical and controls description can be found in the references. The experiment contains two dynamic systems. One is used to maintain beam tilt, beam piston, and pupil geometry while the other allows the sensor system to examine the entire field of view.
Evolution of Ground and Space based Optical Systems during the Past 30 Years
Authors: Meinel Aden B. , Meinel Marjorie P.
Published: February 2023

The challenge today seems to be shifting from the question of technological feasibility to one of affordability. The demands of terrestrial and space astronomers continue to grow as new exciting results are obtained from their explorations. For two decades no major advances in telescope size have occurred, the main activity being to exploit the 4-meter class telescopes and see how the Soviet 6-meter system performs. In the space arena A pent-up demand for a dozen astronomical telescopes larger than any now in operation has evolved during the past decade, but funding realities have been such that only one is actually under construction, the 10-m keck segmented mirror telescope. The European Southern Observatory countries have now announced a governmental commitment to build a 16-meter system consisting of four 8-meter telescopes. The world optical industry has developed capabilities that will permit 8-meter class optical telescopes that in turn promise significant advances in scientific capabilities, but few observatories appear to be able to afford them. There thus is a maximum effort to achieve major cost reductions to bring this new class into affordability.
Large Deployable Reflector
Authors: Swanson Paul
Published: February 2023

The Large Deployable Reflector (LDR) will be a 20 meter diameter, orbiting, reflecting telescope used to observe astronomical sources at wavelengths between 50 and 1000 urn. It must operate in space because the Earth's atmosphere is largely opaque in this spectral region. Because of its tremendous scientific potential, LDR was recommended by the Astronomy Survey Committee of the National Academy of Sciences as one of four major, national programs for the 1980's. It now appears that LDR will not be launched until near the turn of the century.
HST Primary Mirror Characterization
Authors: Furey L. , Dubos T. , Hansen D. , Samuels-Schwartz J.
Published: February 2023

The presence of spherical aberration in the Hubble Space Telescope (HST) was announced by NASA on June 21, 1990. Investigation teams were commissioned by NASA to determine the cause of the aberration and then to quantify the amount of aberration in the telescope. This information is critical for the design of future replacement instruments. The Hubble Independent Optics Review Panel (HIORP), a team chaired by Dr. Duncan Moore, coordinated the investigation of the on-orbit data received from the telescope. Different methods of analyzing the images were used including phase retrieval algorithms.
On Orbit Hubble Space Telescope Phase Retrieval
Authors: Lyon Richard G. , Miller Peter E. , Grusczak Anthony
Published: February 2023

After launch it became readily apparent that there were large unexplained aberrations present in the Hubble Space Telescope. Phase Retrieval was the method used to determine that the source of error was spherical aberration. Phase retrieval was used to measure the magnitude of the spherical aberration from on-orbit flight data and to help determine the description for the corrective optics of next generation instruments. To date this is the first time that phase retrieval has been used on orbit.
Design of Wide Field Planetary Camera 2 for Hubble Space Telescope
Authors: Page Norman A. , McGuire James P.
Published: February 2023

The design of the Wide Field Planetary Camera 2 to correct the large spherical aberration error in the Hubble Space Telescope is discussed.
HST Science Recovered by COSTAR
Authors: Ford Holland
Published: February 2023

Corrective optics space telescope axial replacement (COSTAR) will restore the scientific performance of the Fair Object Camera, the Faint Object Spectrograph, and the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope. The scientific programs that will be recovered by COSTAR are described.
Vacuum ultraviolet performance of a Wolter Type II telescope: theoretical and experimental results
Authors: Wright Geraldine A. , Leviton Douglas B. , Fleetwood Charles M.
Published: February 2023

Researchers at Goddard Space Flight Center have been developing fabrication and testing techniques for glancing incidence mirrors for many years.1,2 We have also been developing analytical tools to predict performance of such mirrors from their measured surface data.3 The ability to predict imaging from surface metrology would allow us to set error budgets on the surface quality of glancing incidence mirrors to obtain any imaging requirement requested. Efforts have been ongoing to verify our imaging calculations by comparison with actual imaging tests. We have succeeded in verifying our calculations by comparing predictions of the imaging of the SERTS-C4 Wolter type II telescope with actual imaging tests at 1236 Å.
Ground-Based Multipurpose 1.5m Telescope System for Space Optics
Authors: Aruga T. , Itabe T. , Hiromoto N. , Takami H. , Aoki T. , Toyoda M. , Kunimori H. , Smith W.S. , Kimbrell J.E. , Duggins D.F.
Published: February 2023

A new optical system with a 1.5 m diameter telescope for multiple studies was designed and has been under construction for three years at CRL. Now the construction is almost complete and it is in the phase of operation. In this paper, we will introduce the outline of the new optical system for space optics and report several important results of preliminary experiments.
OSI: Orbiting Stellar Interferometer for Astrometry and Imaging
Authors: Colavita M. M. , Shao M. , Rayman M. D. , Short K. L.
Published: February 2023

OSI, Orbiting Stellar Interferometer, is a concept for a space interferometer mission with both astrometric and imaging goals: 10 μarc sec astrometric accuracy for 16th mag objects in 100 sec of integration time and for 20th mag objects in 1 h, and 5 mas resolution aperture synthesis imaging. The instrument consists of 6 siderostats arranged as 3 co-linear interferometers on a single structure; two interferometers are used for attitude control, and the third for science observations. Delay lines are used for path- length equalization, allowing a large field of view. Available baselines range from 1 to 20 m, with ~50 cm clear apertures. High astrometric precision is obtained with a laser metrology system which monitors the instrument baselines, i.e., the siderostat positions, as well as the delay-line positions. Mission and flight system studies resulted in an implementation which would use an Atlas HAS for insertion into a 900 km sun- synchronous orbit. The total spacecraft mass was ~3600 kg (including contingencies), and the structure would fold in order to fit within a standard launch shroud. Some of the science possible with OSI includes the astrometric detection of planets and the high resolution imaging of Seyfert II narrow-line regions.
Recent Developments in Structural Composite Mirror Technology for Space Telescopes
Authors: Freeland Robert E.
Published: February 2023

Lightweight, low-cost, high-precision mirrors are needed to accommodate a number of near-term and far-term submillimeter, space-based astronomical telescopes. These telescopes range in size from 3 to 20 meters, and possibly larger. They will utilize mirrors from 1 to 2 meters in size with surface precision from 1 to 3 μm rms while operating in a thermal environment somewhere between 100 and 200°K. Examples of such potential missions would include the Submillimeter Imager and Line Survey (SMILS) and the Large Deployable Reflector (LDR).
Optical challenges for the detection of extra-solar planets
Authors: Meinel Aden B. , Meinel Marjorie P.
Published: February 2023

The next great goal for space exploration and discoveries is the discovery and characterization of planet systems about other stars. Spacecraft have visited all the planets of the Solar System except Pluto. The final step, a flyby or rendezvous with this interesting double planet is now being given serious consideration. What's next? Do some other stars have planets? And if so, are they like our Solar System planets? Are there any like the Earth?
Emissive Reference Spheres as Absolute Calibration Sources for an Orbiting LWIR Sensor*
Authors: Kintner Eric C.
Published: February 2023

An orbiting LWIR sensor may be calibrated by deploying emissive reference spheres at known temperatures into its field of view. Observations of stars made with a sensor calibrated in this way offer an independent means for calibrating the irradiances of standard stars. The planning for such a calibration experiment will be discussed.
Long Duration Orbital Effects on Optical Coating Materials
Authors: Herzig Howard , Toft Albert R. , Fleetwood Charles M.
Published: February 2023

Concern about the ability of thin film coatings used for reflective optical elements to withstand the orbital space environment has led to a series of Shuttle-based experiments known as the Evaluation of Oxygen Interaction with Materials (EOIM), the last mission of which was flown in 1983. During the following year, the opportunity to evaluate long-term effects on these coatings presented itself with the deployment of the Long Duration Exposure Facility (LDEF), with an intended duration of one year. Due to changes in Shuttle schedule priorities, however, it was almost six years before the spacecraft was retrieved.
The Michelson Doppler Imager for SoHO
Authors: Title Alan , Tarbell Ted , Rosenberg Bill
Published: February 2023

The Michelson Doppler Imager is an instrument for doing helioseismology from Lagrangian point between the Earth and Sun. It is a full sun imager that includes 12 cm refractor, a high speed image stabilization system, a narrowband filter system (Ni 6768 angstroms), and a 1024 × 1024 CCD detector. One hundred milliangstrom spectral analysis is provided by a combination of dielectric filters, a fixed Lyot filter, and a pair of tunable solid Michelson interferometers.
Effects of Various Polishing Conditions on the Surface Finish of Materials
Authors: Ahmed Wase U.
Published: February 2023

The principle aim of polishing is to produce a specular reflective surface which is free of damage and artifacts. This is generally accomplished by three distinct polishing process: 1. Abrasive Polishing where abrasive particles are employed to abrade the surface 2. Chemical Polishing where dissolution of a surface is involved and is accomplished by chemical means. Semiconductors such as Ga As for example is polished using Bromine-Methanol as a chemical polishing medium. 3. Chemical Mechanical Polishing is a combination of the two process where a surface is oxidized by chemical means and then removed by abrasive action. Semiconductors and some metals are often polished using this method.
Progressive Mechanical and Chemical Polishing
Authors: Kasai Toshio , Kobayashi Akira
Published: February 2023

The reproducible preparation of mirror-like, damage-free and optically flat surfaces is crucial to the fabrication of high performance semiconductor or optical devices. Therefore, various polishing methods have been proposed and successed for finishing a brittle or a metallic material surface.
The Relaxation of Deformed Si and Al Surfaces
Authors: Lawrence John E. , Barnes Lloyd L.
Published: February 2023

The deformation and relaxation properties of silicon and aluminum surfaces have been studied. A procedure for recycling rejected aluminum rigid memory discs has evolved from the acquired understanding.
Analysis of Subsurface Layers and Spots and the Reactivity of Glass Components
Authors: Bach H.
Published: February 2023

Surface analysis and the response of optical properties of uncoated and coated glass surfaces to changes of polishing conditions allow to reveal reaction kinetics changes.
Surface Finishing of Optical Components for Carbon Dioxide Laser
Authors: Kawata Koichi , Hashidate Yuji , Miyata Takeo , Ono Takuhiro
Published: February 2023

This paper presents a result achieved for surface finishing of optical components for high-power carbon dioxide laser up to 20KW. The materials used for mirror are molybdenum and tungsten, and for window, beamsplitter and lense are zinc selenide and potassium cloride. The finished surfaces are evaluated for reflectance, damage threshold and absorption using 500W CW carbon dioxide laser. The results are compared with damaged layer generated by surface finishing.
The Phase Problem of X-Ray Crystallography from the Viewpoint of Signal Recovery
Authors: Bricogne Gerard
Published: February 2023

The diffraction of X-rays by crystals was discovered in 1912 by Laue who proposed a theory of the phenomenon based on its analogy with optical diffraction by gratings. It is most easily understood from the standpoint of Fourier analysis, in which language it was reformulated shortly afterwards. The electron density in a crystal is periodic, and may therefore be conceived as a superposition of plane waves whose wave vectors belong to a "reciprocal lattice" dual to the crystal lattice. The contribution of each wave, or system of fringes, is described by a complex Fourier coefficient, whose amplitude gives the strength of this system of fringes, and whose phase determines the position of the fringes relative to some fixed origin. If all the amplitudes and phases of these waves are known, it is possible to obtain a picture of the electron distribution in the crystal by superposing them; that is, by a simple Fourier synthesis.
Phase Synchronization of Distorted Imaging Antenna Arrays
Authors: Steinberg Bernard D.
Published: February 2023

Diffraction-limited performance of an imaging system is often unattainable without some feedback-controlled compensation built into the image-forming process. Dielectric-constant perturbations due to atmospheric turbulence distort the phasefront of the optical radiation field. Muller and Buffington have discovered a class of integrals of the image intensity which, when maximized by adjustments of a compensating lens or mirror, reduce the error in the image to zero, except for an unknown shift in the optical axis [1]. This is a remarkable theorem. Its success depends upon the spatial incoherence of optical sources. Another approach, due to Gerchberg and Saxton [2], utilizes known properties of the class of expected signals, their autocorrelations or their Fourier transforms. It introduces considerable heuristics into the iterative Fourier transformation process. After each successive transformation, portions of the image or its Fourier transform are retained and portions deleted. Retention or deletion is based on a priori scene information and the physics of the process. Ref. [3] and [4] apply [2] to the optical problem.
Incorporation of Prior Constraints in Tomographic Reconstructions from Coded Images
Authors: Paxman Richard G. , Gindi Gene R. , Barrett Harrison H.
Published: February 2023

The study of coded-aperture imaging has usually centered on the restoration of planar objects from planar coded images. The concept has been generalized to the problem of restoring a 3-dimensional object from a planar coded image. These two tasks are illustrated in Figure 1.
Signal Reconstruction From Fourier Transform Amplitude*
Authors: Van Hove Patrick L. , Lim Jae S. , Oppenheim Alan V.
Published: February 2023

In a variety of contexts, it is desirable to reconstruct a sequence from partial Fourier domain information. As a consequence, considerable attention has been paid to, and some significant results have been developed in, this area. For example, it has been established [1,2] that under very mild restrictions a finite extent one-dimensional (1-D) or multi-dimensional (M-D) sequence is uniquely specified to within a scale factor by its Fourier transform (FT) phase, and algorithms for implementing the reconstruction have been developed. It is well known that in contrast, the FT magnitude does not uniquely specify a 1-D sequence. Even for M-D sequences, the FT magnitude specifies a sequence only to within a translation and a central symmetry [2], and reconstruction algorithms developed so far have been successful [2] for only a very restricted class of M-D sequences.
Frequency Domain Optimal Inverse Convolution Filtering of Noisy Data
Authors: Chittineni C. B.
Published: February 2023

In many physical experiments, the observations r(m,n) can be represented as the convolution of a model p(m,n) with a source function s(m,n) subject to additive noise e(m,n). The ultimate goal of deconvolution schemes1,2 is to recover both the model and the source function using observations and all other available information. Let d(m,n) = p(m,n) * s(m,n). The signal-to-noise ratio α is defined as α = Σ Σ d2(m,n)/Σ Σ e2(m,n).
Optimal Iterative Image Reconstruction with Incomplete and Approximate Data
Authors: Gassmann J.
Published: February 2023

For the determination and improvement of phases in X-ray analysis a procedure called "phase correction" or "density modification" has been developed1,2). It is applicable to all types of images when the spectral density is known. It has been applied to various structure determinations of small molecules3), resolution extension of macro molecules4), phase improvement in a virus structure5) and reduction of the effect of missing projection data in electron microscopy.
Reconstruction of Objects from Coded Images by Simulated Annealing
Authors: Smith Warren E. , Barrett Harrison H. , Paxman Richard G.
Published: February 2023

Coded apertures are useful for imaging sources of x rays and gamma rays in nuclear medicine, x-ray astronomy, laser fusion studies, and nuclear reactor safety research. While conventional apertures such as a pinhole or multibore collimator provide only two-dimensional (2D) projections of a three-dimensional (3D) source, coded apertures give some information about the 3D structure of the source. The easiest way to see this is by considering a point source some finite distance from the aperture plane. The coded image in this case is merely an enlarged shadow of the aperture transmission function. This shadow contains all the necessary information to fully characterize the source. The scale of the shadow gives the longitudinal coordinate of the point (i.e., its distance from the aperture plane), and the lateral position of the shadow on the detector is simply related to the lateral position of the point in a plane parallel to the aperture. The strength of the source is related to the number of recorded photons in the coded image. Thus the shadow uniquely determines the 3D location of the source and its strength if we know a priori that it is a point source. Of course, we are usually interested in more complicated sources, and the central problem of coded-aperture imaging may be stated as follows: Given one or more 2D coded images and possibly some a priori information about the source, estimate the 3D distribution of the source.
A Model-Based Restoration Procedure For Small, Low-Resolution Optical Images
Authors: Saghri John A. , Tescher Andrew G.
Published: February 2023

Compensation of image degradations caused by inaccuracies in the optics or sensing mechanism, transmission error, or reflection from spurious objects is commonly referred to as image restoration. Restoration techniques require at least limited information about the degradation phenomenon (e.g., point spread function, characteristics of the noise and the sensing mechanism). These techniques are often based on classical one-dimensional signal processing. An efficient restoration method should use the maximum amount of a priori information about the object.
Practical Interpolation of 2-D Surfaces Using the Gerchberg Algorithm
Authors: Carlotto Mark J. , Tom Victor T.
Published: February 2023

The interpolation of 2-D wind and hydrographic surfaces is accomplished using the Gerchberg algorithm. Special emphasis is given to algorithm implementation on an array processor.
The Use of Singular Systems in Inverse Problems in Signal Processing
Authors: Pike E R , Bertero M , de Mol C
Published: February 2023

In a number of experiments in various scientific fields a common method for determining certain characteristics of a physical sample is to observe the interaction between the sample and the radiation emitted by a known source. One or several detectors measure space and/or time variations of the scattered radiation, as scattering amplitudes, field fluctuations, absorption coefficients and so on. The output of the detectors can be digitized and the final result of the experiment is a set of (real or complex) numbers
{gn}nN=1 stored in a computer. The interpretation of the data requires the solution of a mathematical problem, ie the restoration of the unknown characteristic of the sample from the set of numbers gn.
Stability Conditions in Image Reconstruction: a New Regularization Principle
Authors: Lannes A. , Casanove M. J. , Roques S.
Published: February 2023

Owing to systematic and noise-type errors, theinverse problems ofImage Reconstruction prove to be unstable (see for instance [1]). To cope with these ill-conditioned situations, we therefore have to develop appropriateregularizationmethods. The problem is to choose aregularization principleensuring thestabilityof the restoration procedures. Intuitively, it is clear that we have to find a compromise betweenresolutionandrobustness.It is therefore natural to devise a stabilization principle involving the notion of resolution explicitly. As specified at the end of this paper, this is not the case, in particular, for the regularization principle introduced by Tihonov. In other respects, it must be possible to select the stabilization parameters before setting the reconstruction process in motion. In this context, we have devised and implemented a new method for Partial Deconvolution with Support Constraint. The aim of this communication is to give a survey of the corresponding interactive procedure. For clarity we restrict ourselves to the special case of Band-Limited Extrapolation [1]; the generalization to Partial Deconvolution is straightforward.
Suppressing Sidelobe Artifacts in Microwave Images of Undersampled Radiation Fields
Authors: Subbaram Harish M. , Steinberg Bernard D.
Published: February 2023

Microwave images of coherent targets obtained by using thinned random arrays will contain huge sidelobe artifacts. We present a method for suppressing these artifacts.
Direct Pulse Recording for Reconstruction of Bistatic Synthetic Aperture Radar Images
Authors: Gabriel Andrew K. , Goldstein Richard M.
Published: February 2023

An imaging experiment was performed utilizing a synthetic aperture radar tansmitter on the space shuttle and a receiver on an airplane. Because of this "bistatic" geometry, focusing is considerably more difficult than in a conventional monastatic SAR. Because the transmitter and receiver are moving relative to each other, the phase history of any target in the scene depends on its location in both the along-track (azimuth) and the cross-track (range) directions, and focusing thus depends on location in the image. As a result, the image must be generated from a collection of separately focused sub-images.
Error Lower Bound for Phase Retrieval
Authors: Cederquist J.N.
Published: February 2023

In phase retrieval problems, it is desired to estimate the phase of the Fourier transform of an object given measurements of the modulus (square root of intensity) of the Fourier transform. This is equivalent to estimating the object itself because of the Fourier transform relationship. Several iterative Fourier transform algorithms have had great success in making such object estimates from Fourier magnitude data and object constraint information [1,2]. However, other than through empirical results [3], it has not been known how the error in the object estimate depends on measurement noise, constraint information, and other parameters describing the problem.
Correction of motion blur in CCD color endoscope images
Authors: Badiqué E. , Ohyama N. , Yachida M. , Honda T. , Tsujiuchi J.
Published: February 2023

Color CCD endoscopes with sequential three color illuminations have the advantage of a high resolution but are sensitive to object motion. A digital method for the restoration of color-shifted images is proposed. Restored images are suitable for further image processing such as color emphasis and structure enhancement.
Use of Fourier Domain Real Plane-Zeros in Phase Retrieval
Authors: Wackerman Christopher C. , Yagle Andrew E.
Published: February 2023

Throughout a large number of disciplines, including astronomy, wave-front sensing and x-ray crystallography, there exists a class of problems referred to as the phase retrieval problem; given the modulus |F(u,v)| of the Fourier transform of an object f(x,y) and some constraints about the form of f(x,y), reconstruct f(x,y). Several solutions to this problem have been proposed, but our research has concentrated on the iterative Fourier transform algorithm (IFTA) [1,2] which has the advantages of being robust under noisy conditions and not computationally burdensome. An area of difficulty for the IFTA however is that the algorithm often stagnates at a reconstruction with stripe like noise, especially for real, non-negative objects [3]. This paper will present research that we have done to address this problem by using information about locations in the Fourier plane where F(u,v) is identically zero, what we will call Fourier domain real-plane zeros (RPZ's). Two new algorithms will be presented: one corrects a stripe stagnation problem from only a single reconstruction; the other modifies the IFTA to allow it to use locations of RPZ's as an additional constraint and prevents stripe stagnation from occurring altogether.
Local Criteria : A Unified Approach to Locally Adaptive Linear and Rank Filters
Authors: Yaroslavsky L.P.
Published: February 2023

During the last several years a lot of new linear and nonlinear rank algorithms for signal and picture processing have been proposed [1-13]. The linear ones have been derived from one or another statistical model of the signal to be processed. The rank ones have been substantiated from different positions and without any rather general notion of optimality. The aim of this paper is to introduce a new family of criteria of processing quality as a basis for unified approach to synthesis of optimal linear and rank filters for signal and picture processing.
Synthesis of a Holographic Beamformer Using a Separability Constraint
Authors: Eismann M.T. , Tai A.M. , Cederquist J.N.
Published: February 2023

In applications such as laser radar, active coherent imaging (possibly using phase retrieval), and optical data processing, it is often desired to uniformly illuminate a rectangular area that is in the far-field of the source. When using a laser with a Gaussian (TEMoo) intensity distribution as a source, an optical device is required to modify the near-field complex amplitude distribution of the beam such that its phase and intensity become uniform upon propagation to the far-field. We investigated the use of a holographic system to efficiently redistribute the beam energy into a near-field sinc(x) sinc(y) complex amplitude distribution. This holographic system was synthesized using the Gerchberg-Saxton algorithm.
Signal Processing in Higher Dimensions
Authors: Lohmann Adolf W.
Published: February 2023

Suppose the signal is u(t). Two examples of representations in artifical and/or higher dimensions are the autocorrelation: and the (auto-)triple correlation: Isn't it masochistic to deal with these indirect representations of the signal instead of with the signal u(t) itself? The triple correlation is an example of artificial increase of dimensionality. The signal u(t) is ID, the triple correlation u3(t1,t2) is 2D.
Reconstruction of Objects Viewed through Turbulence Using the Triple Correlation
Authors: Dainty J C , Northcott M J , Ayers G R
Published: February 2023

Since the invention in 1970 by Labeyrie1 of the technique of stellar speckle interferometry, there have been many attempts to extend it to produce diffraction-limited images through turbulence. In speckle interferometry, short exposure (≈10ms) images i(x) are recorded through a narrowband filter (≈10nm) and an estimate is made of the average energy spectrum <|I(u)|2> of the image, where I(u) is the Fourier transform of i(x).
Proposal And Analysis Of Aberration-Free Array Imaging Using Phase Conjugation
Authors: Ikeda Osamu
Published: February 2023

In this article, a signal-processing method is proposed to achieve diffraction-limited imaging of objects present in an aberrating medium. An array optical system is needed to acquire the data; some adaptive optics systems or optical fiber systems may be applicable for this purpose. The data are then processed in a computer, following the physical concept of repeated transmission of phase-conjugated wave, to find out the wave sharply focusing at a single point on the object. A mathematical analysis of the method does not guarantee the generation of such a sharp focal beam. Studies by computer simulation, however, show that this method works fairly well except for a few exceptional cases of object.
On a Remarkable Property of Phase-Closure Imaging: Generalized Inverse via Backprojection Mechanisms
Authors: Lannes A.
Published: February 2023

The phase-restoration procedure, which is a key element in solving the inverse problems of aperture synthesis, can be decomposed into two main stages. The first one is characterizing the space of solutions resulting from the phase-closure data; the second amounts to localizing the final solution in this space by taking into account additional constraints. Although these problems are closely imbricated, as revealed by the hybrid approaches [1], it is essential to examine them separately to clarify the analysis. This should help in defining the optimal method to be implemented in each particular situation. All the elements presented in this paper appear in the general framework of what may be called spectral extrapolation in phase-closure imaging. As shown in Refs. [2-4], the compromise to be found between resolution and robustness requires a good understanding of the inverse problems encountered in this field. In this paper, we simply propose a new formulation of the algebraic properties of phase-closure imaging, and outline some algorithmic implications concerning the first stage of the phase-restoration procedure.
Superresolution in confocal scanning microscopy: Theory of the incoherent case
Authors: Bertero M , Boccacci P , Defrise M , De Mol C , Pike E R
Published: February 2023

In 1982 Bertero and Pike [1] showed that superresolution was possible in microscopy by recording the image over a larger area than the geometric one and subsequent inversion of the data by, for example, a singular system analysis. In a series of papers following, these authors and others have considered a number of special cases, both analytically and numerically. In this paper we investigate the incoherent case, which applies to confocal scanning fluorescence microscopy, in 1-D. Numerical studies have already given a clear indication of the form of the results for the case of an infinite recorded image, indicating a transfer function of the curious form shown in figure 1.
Phase Retrieval Approaches Applied to the Hubble Space Telescope
Authors: Fienup J.R.
Published: February 2023

Soon after launch it was discovered that the Hubble Space Telescope suffers from a large amount of spherical aberration which blurs the images it produces and reduces their contrast. It is important to very accurately determine those aberrations (phase errors) in order to (1) design correction optics which, when installed in the telescope, will compensate for the aberration, (2) compute point-spread functions (PSFs) which can be used to deblur the degraded images received until the correction optics are installed, and (3) align the secondary mirror of the Optical Telescope Assembly (OTA—the main telescope).