bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarization Imagery Obtained from the Space Shuttle
Authors: Egan Walter G. , Whitehead Victor S.
Published: February 2023

We have obtained Space Shuttle based imagery of an area of the Pacific that includes the island of Hawaii and adjacent sea and cloud areas. The imagery was obtained using two Hasselblad cameras with polarization sensing filters oriented to sense radiation polarized in mutually perpendicular directions. For the imagery obtained, the viewing plane is referenced to the principal plane defined by the solar incident and viewing directions. The range of camera acceptance angles was 40°. The phase angle to the center of the image was 142.9°, and imagery was obtained using type 2404 plus X aerographic and type 5036 Ektachrome films which were subsequently digitized at the LPL (Lunar Planetary Laboratory, NASA, Houston). Color separation in the digitized color imagery was achieved using Wratten filters for the blue, green and red. Relative photometry, and photometric differences for the mutually perpendicular polarizations are obtained permitting the absolute percent polarization to be determined.
An Approach to the Metrology for a Space-Based Interferometer
Authors: Tubbs Eldred F.
Published: February 2023

A metrology approach to be used in the control of the effects of structural deformations on the performance of a space-based astronomical interferometer has been devised. A multi-armed, image-plane interferometer with reflection optics has been assumed. It is assumed that the field of view will be small and that the science objects will be weak or extended so that blind pointing will be required. It is further assumed that the locations of the collecting apertures in the plane of the wavefront are sufficiently well determined by the spacecraft structure and do not require monitoring.
The HST Fine Guidance Sensor Transfer Function and its Impact on Telescope Alignment and Guidance
Authors: Ftaclas C. , Basedow R. , Nonnenmacher A. , Weindling F. , Story D. , Nelan E.
Published: February 2023

The Hubble Space Telescope (HST) line of sight was required to be stabilized to better than 0.007 arcseconds rms in order to realize the resolution inherent in the width of the image core. Despite the redistribution of energy resulting from the presence of spherical aberration in the primary mirror, the image core remains small although with significantly less energy than that estimated for the as-built telescope. Therefore the pointing requirement for the current state of the telescope remains unchanged and, of course, would be imposed in any case when wavefront correctors are fitted to the telescope instruments. The line of sight is stabilized by a closed loop pointing control system based on a pointing error signal generated by the HST fine guidance sensors (FGS). An overview of this system as well as a description of the FGS’s can be found in references 1-3. Each of the three FGS work in a ninety degree annular segment (called a pickle) of the HST field of view and can interferometrically lock on to a star anywhere in the pickle. Two such locks are required simultaneously in order to point the telescope to the top level requirement while the third FGS is used for astrometry1-3. The system thus has redundancy and can perform science if all three sensors are working.
Optical Calibration of the Hubble Space Telescope Fine Guidance Sensors
Authors: Abramowicz-Reed Linda , Hallock H. Louis , Jefferys William H. , Welter Gary L.
Published: February 2023

Important objectives of the Hubble Space Telescope (HST) mission are to place targets within a science instrument aperture to an accuracy of 10 milliarcseconds and to perform astrometric measurements to an accuracy of 2.7 milliarcseconds, rms. In order to achieve these goals, ground-to-orbit changes in magnification and optical distortion must be characterized for each erf the three Fine Guidance Sensors (FGS). An additional step, not presented in this paper, aligns the three FGSs to a common reference frame via the FGS-to-FGS alignment calibration. This paper identifies the sources of distortion, describes the calibration philosophy and pre-launch feasibility studies and finally, discusses on-orbit performance pertaining to the 10 milliarcsecond pointing requirement.
Acousto-Optic Tunable Filters for the Ultraviolet
Authors: Cotter Thomas M. , Duncan Donald D.
Published: February 2023

The goal of our research is to develop Acousto-Optic Tunable Filters (AOTF) that can cover a significant portion of the UV wavelengths ranging from 150300nm. Advantages of the AOTF technology are that the devices are compact, rugged, have good spectral resolution, are electrically tunable, and have modest voltage requirements. Such a tunable UV band filter will prove indispensable for UV remote sensing.
Microstructure of Metal Coatings Deposited Using Ion Beam Deposition Processes
Authors: Coulter Daniel R. , Al-Jumaily Ghanim A. , Raouf Nasrat A.
Published: February 2023

The relationship between microstructure and film properties is the most important issue in the study of thin films and their applications. Microstructure of thin films can be influenced by many factors; most significant are the deposition process conditions, and the physical properties of the coating material. We have been interested in the investigation of the relationship between optical scattering and surface microroughness and finding optimum process conditions which yield lowest optical scattering. In this paper we present the results of our investigation of the microstructure of gold films using scanning tunneling electron microscopy (STEM), scanning electron microscopy (SEM), and x-ray diffraction.
Hydration of Glass And Polishing
Authors: Doremus Robert H.
Published: February 2023

When an alkali silicate comes in contact with water, a complicated sequence of processes occurs: ion exchange, dissolution of glass, and possible structural changes in the glass surface. The rate and extent of these reactions depend most strongly on glass composition, solution conditions, especially pH, and temperature. The reactivity of glass with water is the most important property determining the rate and quality of polishing of a glass surface (Izumitani, 1979), so the rate of hydration and condition of the surface after hydration are determining factors in polishing.
Magnetic Field-Assisted Fine Finishing
Authors: Kurobe Toshiji , Imanaka Osamu
Published: February 2023

Recently, fine finishing of the materials such as semiconductor and ceramics has been needed exceedingly in the industries of electronics and precision machinary. A variety of polishing methods [1,2,3] have been hitherto developed, in such fields. A newly-developed polishing method is devised on the basis of the electro-magnetic behavior of the magnetic fluid, which has the ability to move in the magnetic field. This polishing method is named " Field-assisted Fine Finishing . The magnetic fluid is made with the suspension of fine magnetite Fe3O4 (<150 Å) into the liquid. It has been found from experiments that the new polishing method has the possibilities of flexible surface finishing and stock removal rate by varying the current to the electromagnet.
LBI Image Recovery Using Sharpness Maximization
Authors: Steer D.G. , Ito M.R. , Dewdney P.E.
Published: February 2023

In radio Long Baseline Interferometry (LBI), the image is recovered from measurements made in the aperture plane. However, two major difficulties hinder the imaging process.
Inverse Scattering Reconstructions From Incomplete Fourier Space Data
Authors: Farhat N.H.
Published: February 2023

We show that 3-D tomographic inverse scattering reconstruction of a scattering object is obtainable from data lying on a curved surface, rather than within a volume, of its accessed Fourier space as would ordinarily be required.
Signal Reconstruction from Partial Fourier Domain Information*
Authors: Oppenheim Alan V. , Lim Jae S.
Published: February 2023

There are a variety of practical problems in which only the phase or magnitude of the Fourier transform of a signal is known and it is desired to reconstruct the signal. In this talk, a number of results developed in the Digital Signal Processing Group at M.I.T. over the past several years will be described. The work discussed began initially with an exploration of the intelligibility of phase-only signals, that is ones for which the correct Fourier transform phase is combined with a constant or characteristic Fourier transform magnitude function. Motivated by the importance of Fourier transform phase in relation to Fourier transform magnitude, a theory and associated algorithms were then developed for the exact reconstruction of finite length signals from phase information alone.
Estimation of Two Closely Spaced Frequencies Buried in White Noise Using Linear Programming
Authors: Keybl Jaroslav , Eichmann George
Published: February 2023

Linear programming is used to estimate the spectrum of two sinusoids signals closely-spaced in frequency buried in deep white gaussian noise by employing a-priori knowledge of the spectrum. The method will be illustrated by a number of examples.
Restoration of Multichannel Microwave Imagery To Estimate Rainfall Rates in Hurricanes
Authors: Chin R. T. , Yeh C. L. , Olson W. S. , Weinman J. A.
Published: February 2023

Multichannel microwave radiometers on the Seasat and Nimbus 7 satellites offer a quantitative method to measure rainfall amounts over the ocean. The emissivity of the ocean surface is low and varies predictably with wind speed; it thus provides a good background for observing precipitation. The theory and initial validation of this concept was given by Wilheit et al. [1]
The Possibility Image Transform and Logical Convolution
Authors: Frieden B. Roy
Published: February 2023

It is now well-appreciated that an image represents a probability law on position for incoming photons.1,2 A recent mutation of probability theory is "possibility" theory.3 It departs from probability theory in the following basic ways: If A and B are two disjoint events, the probabilities P(A or B), P(A and B) obey while the corresponding possibilities obey Operation max (a,b) = the larger of a,b, while min (a,b) = the smaller of a,b.
Reconstruction of a Complex-Valued Field Using the Hilbert-Hankel Transform1
Authors: Wengrovitz Michael S. , Oppenheim Alan V. , Frisk George V.
Published: February 2023

A well-known property in Fourier transform theory is that causality in one domain implies real-part sufficiency in the other domain. This property is the basis for the fact that the real and imaginary parts of a signal are related via the Hilbert transform, if the spectrum of the signal is causal. In wave propagation problems involving circular symmetry, it is the circularly symmetric two-dimensional Fourier transform, or equivalently the Hankel transform, which is of central importance. Because of the circular symmetry in such problems, the condition of causality is not applicable. However, in our work we have shown that under some circumstances, it is possible to relate the real and imaginary parts of a propagating field described by a Hankel transform. In this paper, an approximate real-part sufficiency condition for the Hankel transform is developed and an algorithm for reconstructing the real (or imaginary) component from the imaginary (or real) component is applied to synthetic and experimental underwater acoustic fields.
Exploring the Irreducible Support
Authors: Brames B.J.
Published: February 2023

The phase problem confronts one with the task obtaining a function having a specified autocorrelation (or Fourier modulus) which is also consistent with a limited number of object constraints. In many case of interest it is known that the object has compact support; indeed, in two dimensions this is often sufficient to uniquely define it [1]. Nonetheless, one can usually find an autocorrelation such that some object defined on the same compact support is but one of a multitude of functions having that autocorrelation. However, if the object happens to be defined on Eisenstein's support, it has been shown that the object is always uniquely described by its autocorrelation [2]. We shall call supports of the Eisenstein-type irreducible supports. Unfortunately, variations on Eisenstein's support are the only ones to have been shown to be irreducible, and the method of proof for Eisenstein's support does not lend itself to ready generalization. Herein the irreducible support will be defined in a wider sense, and a method of testing an arbitrary convex support for irreducibility will be presented.
Image Synthesis
Authors: Saleh Bahaa E. A.
Published: February 2023

An established practice in microphotography is the introduction of deliberate distortions in the artwork in order to compensate for known distortions in the optical system. The corrections are usually based on experience gained by a process of trial and error. Image synthesis, as defined in this presentation, provides a theoretical foundation for solving this problem. The problem can be regarded as the counterpart to the usual signal/image recovery (reconstruction, or restoration. It may be called signal/image "discovery", “construction", "synthesis", or "design". The problems of image restoration and image synthesis are very similar. In both problems the imaging system is known; the output image is known, and the input is to be found. But the motive is quite different-- discovery versus recovery. One subtle difference has to do with the existence of a solution. In an image restoration problem, the measured output results from an actual, albeit unknown, input. In an image synthesis problem, on the other hand, it is possible that no input image is capable of producing the desired output image. Therefore, in image synthesis, the problem of utmost concern is that of existence of a solution. In an image restoration problem, one is usually concerned with uniqueness and recoverability.
Existence and synthesis of bipolar incoherent pointspread functions
Authors: Mait Joseph N.
Published: February 2023

In 1978 Lohmann and Rhodes [1] presented a general two-channel hybrid system for bipolar incoherent spatial filtering. The work by Lohmann and Rhodes was significant in that it presented a unified and compact analysis of such filtering. However, of equal importance is a consideration of synthesis, or design. With respect to bipolar synthesis, two issues must be addressed; one, the feasibility of the synthesis and two, the specification of the system once its feasibility has been established. It is the question of feasibility or, in mathematical terms, existence, that is addressed in this work; the issue of system specification is presented in Ref. [2].
Iterative Synthesis of Distortion Invariant Optical Correlation Filters
Authors: Schils George F. , Sweeney Donald W.
Published: February 2023

An iterative technique can be used to synthesize pattern recognition filters that are invariant to image distortions. These distortions might be position (location), rotation, scale, and perspective. The image to detect may also appear at different intensities. In this paper, we present an iterative technique based on spectral iteration in angular Fourier space for the synthesis of rotationally, translationally, and intensity invariant optical pattern recognition filters. The iterative method allows full image information to be retained while simultaneously obtaining invariance to rotation and image location. The general method presented may be extended to synthesize filters with invariances to additional distortions.
3-D Tomographic Image Reconstruction from Incomplete Cone Beam Projections
Authors: Kudo Hiroyuki , Saito Tsuneo
Published: February 2023

3-D cone beam tomographic imaging system has attracted much attentions for its rapid data acquisition and high resolution image. Some attempts for its realization have been made, but many unsolved problems concerning its image reconstruction remain. In the typical 3-D cone beam tomography, an x-ray source moves on a bounded curve surrounding an object and a 2-D projection is recorded by the planar detector at each source position. For this geometry, the following informative theorem can be proved [1,2].
Feasible Cone Beam Scanning Methods for Exact 3-D Tomographic Image Reconstruction
Authors: Kudo Hiroyuki , Saito Tsuneo
Published: February 2023

Considerable efforts have been made for visualizing 3-D structures of human organs by x-ray tomography. From the view point of the data collection time, the cone beam method with a circular source motion is promising for this purpose. However, the exact 3-D image reconstruction from the cone beam projections is a troublesome and time-consuming problem, because the solution cannot be decomposed into 2-D transaxial slices. For this difficulty, approximate reconstruction algorithms are proposed and practically used in many application areas [1,2]. Unfortunately, these algorithms suffer from the degradation of reconstructed images when the cone angle is large.
Extending the Measurement Range of Interferometers Through the Use of a Priori Information
Authors: Greivenkamp John E. , Palum Russell J.
Published: February 2023

The primary limitation of conventional phase-shifting interferometry (PSI) is its inability to measure the shapes of surfaces or wavefronts with large departures from a best-fit reference sphere. The surface must have limited asphericity. The reason for this limitation is that the current phase-shifting algorithms will correctly reconstruct the wavefront only if the change of the wavefront between adjacent measurement points is less than a half wave. This requirement arises from the need to remove the 2π phase discontinuities that result from an inverse tangent in the data reduction algorithm for PSI. These statements are equivalent to saying that the maximum permissible fringe frequency in the interferogram is the Nyquist frequency of the sensor (there must be two samples per fringe). Fringes at higher spatial frequencies are aliased by the sensor.
Reconstruction of 2-D Signals from Nonuniform Samples in Polar Coordinates
Authors: Marvasti Farokh A.
Published: February 2023

A survey of 2-D nonuniform sampling theorems is given in [1] and [2]. This correspondence is a generalization of Stark’s theorem in polar coordinates [3] based on. the work of Butzer and Hinsen [4]. Stark [3] extended the Bessel interpolation to 2-D signals in polar coordinates (r,θ), where the nonuniform samples are derived from uniform samples in θ direction and zero-crossings of the Bessel function Jn(.) in the r direction, as shown in Figure 1. Butzer et al [4] extended the Lagrange expansion for 2-D signals. They showed that if the set of nonuniform samples lie on parallel straight lines (where the lines are nonuniformly spaced as shown in Figure 2), Lagrange interpolation is possible provided that the parallel lines and the set of nonuniform samples on each line satisfy one of the sufficient conditions for a 1-D set of uniqueness. In this correspondence, we prove that Lagrange interpolation is possible in polar coordinates under a more general setup than that of [3]; i.e., the nonuniform samples are on nonuniformly spaced concentric circles (Figure 3), or alternatively, the nonuniform samples lie on radial lines (Figure 4) and the rotational distances of radial lines are nonuniformly spaced; the nonuniform samples need not be limited to zeros of Bessel functions. The interpolation formulas for the cases depicted in Figures 3 and 4 are given in the next section.
Iterative Approaches To Computer-Generated Holography*
Authors: Allebach Jan P. , Jennison Brian K. , Sweeney Donald W.
Published: February 2023

Optics is playing an increasingly important role in the sensing, processing, and transmission of information. The elements that shape the wavefront at various points are a key part of any optical system. In many cases, computer-generated holograms (CGH’s) offer major advantages over conventional refractive optical elements in terms of size, weight, and cost. Most importantly, CGH’s can perform complex waveshaping functions that are simply beyond the capabilities of conventional elements. Recently, there has been a great deal of interest in the application of VLSI circuit manufacturing technology to the fabrication of CGH’s. Alternatively, CGH’s can be implemented with spatial light modulators. These devices offer, the possibility of real-time reconfigurability, but are limited to CGH’s with much lower space-bandwidth products than can be written with the e-beam lithographic systems used in VLSI circuit fabrication. In contrast, our research has been directed toward bringing new computational approaches to bear on the CGH synthesis problem.
Self-calibration techniques in radio-astronomy
Authors: Cornwell T.J.
Published: February 2023

Self-calibration is a technique used widely in radio-interferometry for high quality imaging of complex objects in conditions where the coherence samples are corrupted by severe amplitude and phase errors. It relies upon the concept of closure phase introduced by Roger Jennison in 1958. The closure phase is an observable which is unaffected by antenna-based calibration errors. However, rather than using the closure phases directly, the simplest form of self-calibration proceeds by allowing these antenna-based errors to be determined in the imaging process. This general principle is considerably more flexible than closure phase and can be extended to many different applications.
Regularized Reconstruction of Nonnegative Images Degraded by a Point-spread Function with a Band-limited Transfer Function
Authors: Koshy Mathew , Sedat John W. , Agard David A.
Published: February 2023

In the reconstruction of images obtained from diffraction-limited optical systems such as two and three-dimensional light microscopic images, the observed image can be modeled as the convolution of the actual image with a point spread function, whose transfer function is band limited [1]. In addition, such images are contaminated by additive noise, whose signal to noise ratio we assume can be estimated. To obtain a reconstruction which contains information about the actual images in the frequency region where the optical transfer function is zero, additional constraints, such as positivity must be imposed [2].
Bispectral Analysis of the Wavelength Dependence of Laser Speckle: Application to Remote Sensing of Object Shape
Authors: Shirley L. G. , Lo P. A.
Published: February 2023

We present a bispectrum-based technique for analyzing the wavelength dependence of laser speckle intensity. This new technique retains phase information and yields high-resolution measurements of the scattering object’s range-resolved laser radar cross section.
Guidestar-Assisted Wavefront Sensor Speckle Holography: Postdetection Distortion Compensation using a Laser Guidestar Reference
Authors: Gonglewski J.D. , Dayton D.C.
Published: February 2023

The idea that a distorted signal may be corrected after detection by an independent distortion estimate has long been known.1,2 Currently, several researchers are investigating the application of this concept to obtaining high resolution images of astronomical objects through the atmosphere.3-5 In this case, both a (short-exposure) distorted image and a distortion estimate are formed simultaneously from the object's light. Thus pairs of independent image-distortion data are used to form the final image through deconvolution and averaging. We call our configuration of this setup Wavefront Sensor Speckle Holography (WSSH).5 This paper explores the addition of an artificial reference in the form of a laser guidestar to such a distortion-estimating imaging system6. This will improve distortion estimation and imaging system performance. See figure 1.
Reconstruction of Complex Transmittance Distribution from Phase-Contrast Images
Authors: Kawata Satoshi , Noda Tomoya
Published: February 2023

An optical phase-contrast microscope1 converts the phase variation of light modulated by the refractive index variation of a sample into an intensity image For transparent biological samples, this microscope is in particular useful because it can visualize the sample structure without dye staining but as the sample are alive. However, if the sample has an absorption distribution in space, the image observed with a phase-contrast microscope no longer represents the refractive-index variation of the sample. The image generated by the absorption distribution overlaps the phase-contrast image.
High Resolution Image Reconstruction from Sparse Random Arrays
Authors: Clark S E , Desandre L F
Published: February 2023

In order to overcome such limitations as resolution, receiver weight and response time associated with large heavy monolithic laser radar receivers, a significant amount of work1-5 has been performed into the potential of array based systems to provide high resolution lightweight fast receivers. In order to achieve image resolution consistent with the overall size of the array, the amplitude and phase at each point in the array must be determined. As has been demonstrated in the microwave region6,7, the problem of phase errors due to errors in detector positioning and variations in the reference wavefront that are associated with the heterodyne detection process used to determine the phase, can be overcome in an adaptive way prior to using the array for imaging.
Restoration of optical imagery with the expectation-maximization algorithm
Authors: Snyder Donald. L. , Schulz Timothy J. , Hammoud Abed M.
Published: February 2023

The expectation-maximization algorithm, as formulated in 1977 by Dempster, Laird, and Rubin [1], is a numerical procedure for computing constrained maximum-likelihood estimates of unknown parameters that influence measured data. It’s use for image restoration from quantum-limited data was first suggested by Shepp and Vardi [2] in 1982 in the context of determining concentrations of radioactive substances within the human body; applications and extensions of this method for estimating radionuclide distributions have grown enormously in the intervening years, with contributions by numerous investigators.
Resolution Improvement for In-Vivo Magnetic Resonance Spectroscopic Images
Authors: Plevritis Sylvia K. , Macovski Albert
Published: February 2023

A reconstruction algorithm was developed to improve low resolution in vivo Magnetic Resonance (MR) spectroscopic images. MR spectroscopic images show the distribution of metabolites that exist in-vivo at low concentrations. Unlike standard MR water images, MR spectroscopic images are limited to a low resolution because the low concentrations require long acquisition times. The proposed reconstruction algorithm improves the resolution of MR spectroscopic images by using features from a corresponding high resolution MR water image.
Tomographic Imaging of Vector Fields
Authors: Prince Jerry L.
Published: February 2023

In the last decade or so several papers have introduced and developed the area of tomographic imaging of vector fields. Johnson et al. [1] began the investigation by studying the imaging of flow fields using acoustic time-of-flight measurements. In this measurement, the time of flight is influenced by the component of the field in the direction of propagation, and is not influenced by the orthogonal component. This type of measurement is called a longitudinal measurement. Norton [2] concluded that longitudinal measurements allow the reconstruction of the solenoidal (divergence-free) field component, but not the irrotational (curl-free) component. He suggested using boundary measurements to reconstruct the irrotational component. Braun and Hauck [3] then discovered that a new type of tomographic measurement called the transverse measurement (sensitive to the orthogonal component of flow) allows one to reconstruct the irrotational component without boundary measurements. Prince synthesized these discoveries and extended the results to three dimensions in [4]. New algorithms for reconstruction using convolution backprojection have also been proposed in [5].
Crystallographic Heterodyne Phase Detection Technique for Highly-Sensitive Lattice-Distortion Measurements
Authors: Takeda Mitsuo , Suzuki Jun
Published: February 2023

A main topic of inverse problems in crystallography appears to have been phase recovery of diffracted fields in diffraction crystallography1,2. In this paper we deal with a problem of detecting yet another type of phase in a structure image (or a lattice fringe image) obtained by the direct observation of a crystal using a high-resolution electron microscope. The phase in our problem represents spatial distortion of lattices in a crystal rather than the phase of X-ray or electron wave fields. We note that a quasi periodic structure of atoms observed in a TEM (transmission electron microscopy) image or in a STM (scanning tunnel microscopy) image bears a close similarity to an optical interferometric fringe pattern having spatial carrier frequencies, where lattice distortion or atom displacement may be regarded as a spatial fringe shift. The interpretation of the distorted lattice image as an interferogram permits us the use of spatial heterodyne technique for highly sensitive detection of the lattice distortion, where a phase change by 2π corresponds to the displacement of an atom by a lattice constant. Based on this interpretation, we propose a crystallographic heterodyne technique for precisely determining the positions of dislocated atoms using the Fourier fringe analysis technique originally developed for optical heterodyne interferometry3,4.
A Projection-Onto-Convex-Sets Interpretation of Cross-Entropy Based Image Super-Resolution Algorithms
Authors: Nadar Mariappan S. , Sementilli Philip J. , Hunt Bobby R.
Published: February 2023

Signal recovery problems are generally posed in the form of rigid constraints (constraint sets), flexible constraints (optimization functional) or a combination thereof. Minimum cross-entropy methods1,2 belong to this third category due to an implicit rigid non-negativity constraint. An elegant approach to solving problems of the first category for convex constraint sets is the Projection Onto Convex Sets (POCS)3 technique. POCS has been limited primarily to least-squares projections, although other distance measures have been proposed.4 In this paper, minimum cross-entropy methods are interpreted as parallel cross-entropic POCS algorithms. This interpretation provides a theoretical basis for including rigid constraints in iterative super-resolution algorithms.
Coherent Wavefront Reconstruction Using Object Statistics
Authors: Arrasmith William W. , Roggemann Michael , Welsh Byron
Published: February 2023

A coherently illuminated diffuse scatterer (object) gives rise to ensemble field statistics at spatial locations in the Fraunhofer plane of the object modeled by circularly complex Gaussian random variables [ref 1]. The joint probability density function for the phase is used to determine the ensemble phase correlation function at two arbitrary spatial locations in the object’s Fraunhofer plane (the entrance pupil plane of a telescope imaging the object). The phase correlation function is used in conjunction with a minimum variance technique to obtain an optimum solution matrix mapping phase difference measurements to phase estimates at arbitrary points in the pupil. Expressions for the expected mean squared phase error are developed for the minimum variance technique and compared with conventional Least Mean Squared reconstructors. Phase estimates using the minimum variance technique and known amplitudes are used to reconstruct the image for simple targets.
An Information Theory Approach To Three Incoherent Information Processing Systems
Authors: Dowski Edward R.
Published: February 2023

Many incoherent optical/digital systems can be used for non-imaging purposes, such as passive ranging. These systems cannot effectively be analyzed or designed in terms of traditional image-forming systems. Instead, such systems should be analyzed in terms of information theory. Through mathematical modelling of the sampled image, information theory can be used to optimize a given system.
Properties and Implications of Phase Problems for Multidimensional Images
Authors: Millane R. P.
Published: February 2023

Phase retrieval is concerned with recovery of an image from measurements of the amplitude of its Fourier transform [1]. It is of considerable practical importance in areas such as microscopy, ultrasonic imaging, astronomy, and crystallography. There are a number of applications, such as in x-ray crystallography, electron microscopy, ultrasonic imaging, and geophysical imaging, where the image to be reconstructed is three-dimensional. Uniqueness properties of phase problems in higher dimensions are examined, and implications in a number of applications of x-ray crystallography are described.
Space Object Identification using a Physically Constrained Iterative Deconvolution Algorithm
Authors: Christou Julian C. , Hege E. Keith , Jefferies Stuart M. , Cheselka Matt
Published: February 2023

A physically constrained iterative deconvolution algorithm is applied to both simulated and real artificial satellite (space object) observations obtained with adaptive optical systems. The problems associated with obtaining good point spread function information is discussed and the algorithm applied also permits reconstruction of not only the object but also the corresponding point spread functions.
Astronomical Results using Physically-Constrained Iterative Deconvolution
Authors: Hege E. K. , Cheselka M. , Lloyd-Hart M. , Hinz P. , Hoffmann W.F. , Christou J.C. , Jefferies S.M.
Published: February 2023

Iterative physical deconvolution is used for point spread function (psf) calibration of a wide range of astronomical imagery obtained in visible (CCD) through near- and mid-infrared (NICMOS and MIRAC) wavelengths. Psf complications, ranging from those of uncorrected speckle images at large telescopes to those of contemporary high-performance adaptive optics, are accomodated by this algorithm which makes use of a priori physical information about the imaging system. Examples of diffraction-limited and “super-resolved” results are presented for a variety of different astronomical objects.
Linear Phase Retrieval for Wavefront Sensing
Authors: Wild Walter J.
Published: February 2023

Very high-order zonal adaptive optics systems based on measuring the subaperture tilts using a Hartmann-Shack wavefront sensor suffer from increased hardware complexity and much greater computational burdens associated with centroid estimation and reconstructing the phase in real time. There is interest in developing practical wavefront sensors using non-interferometric techniques based entirely on intensity measurements [1]. Phase retrieval for wavefront sensing can make use of one or more intensity measurements with a known phase offset between multiple images. Phase recovery techniques are generally nonlinear and iterative [2], possibly prone to stagnation regimes, and have been the limiting factor in making real time intensity based wavefront sensors a reality. Herein we demonstrate that under the assumption of small phase and phase offsets between intensity measurements that an exact expression can be derived to recover the phase if three or more images are used.
Phase retrieval from modulated intensity patterns
Authors: Páez Gonzalo , Strojnik Marija
Published: February 2023

The interferometric measurements are among the most popular methods of non- contact, non-intrusive surface and volume characterization. Figure 1 shows an interferogram [1 of 3 minimally in the phase shifting interferometry1,2 (PSI)], that has several features that are considered challenging in the phase reconstruction: it has many fringes, some closed and some open; it high intensity gradients with a non-uniform contrast; and it is defined within a circular boundary on a rectangular array. We report a novel method for the phase determination, applicable to the majority of the existing phase reconstruction techniques.
Coherence function as carrier of optical information
Authors: Lohmann Adolf W. , Mendlovic David , Shabtay Gal
Published: February 2023

A major characteristic of an optical wave is its coherence function function which is defined by: where V is the complex amplitude and the brackets stand for ensemble averaging.
Branch cut effects in optimally estimating a coherent diffracted field
Authors: Arrasmith William W.
Published: February 2023

In optical imaging systems that image coherently illuminated diffuse scattering objects, the complex field in both the object plane and the measurement plane of the object are described by a circularly complex random process1 with a spatial correlation function for the phase of the field given by2, where k
o
is the complex coherence factor3 in the measurement plane, and
x→ and
x→ are arbitrary positions in the measurement plane. The parameters γ and Ω depend solely on the complex coherence factor and so equation (1) depends only on the object’s ensemble statistics and does not model branch cut effects.
Retrieval of complex field using nonlinear optimization
Authors: Brady Gregory R. , Fienup James R.
Published: February 2023

Intensity measurements in two or more planes are used by a nonlinear optimization algorithm to retrieve the phase. The complex field (amplitude and phase) in the pupil or elsewhere is then computed by simple propagation.
Crystal growth, structural and full optical characterizations of 3-Methyl-4-methoxy-4'-nitrostilben (MMONS)
Authors: Hong Hyung-Ki , Yoon Choon Sup , Xia Tiejun , Van Stryland E. W.
Published: February 2023

Organic crystals with large second-order nonlinear optical (NLO) susceptibilities are of great interest because of their potential use of optical parametric generation.(1) In recent years second-order cascading effects in organic crystals draw much attention not only in the context of basic understandings of the nonlinear optical processes but also potential applications in optoelectronics.
High sensitivity autocorrelation using Light Emitting Diode
Authors: Voevodkin George
Published: February 2023

Pico- and femto-second pulses are becoming powerful tools in chemistry, biology, medicine, and industry. High price for auto-correlators, nonlinear crystals and their low quantum efficiency of Second Harmonic Generation in Near Infrared region have encouraged the search of alternative approaches. It has been demonstrated recently that Si and GaAsP photodiodes and CdS photoconductive cell [1] and even unbiased Light Emitting Diodes (LED) [2] can replace nonlinear crystals and photodetectors in autocorrelators for characterisation of powerful ultrashort laser pulses. Specially fabricated waveguide structures have provided much higher sensitivity due to longer length of interaction [3,4]. However, waveguide configuration suffers from low coupling efficiency into waveguide and reduction of temporal resolution due to dispersion.
Recent Progress of Semi-organic Nonlinear Optical Crystals
Authors: Jiang Min-Hua , Fang Qi , Yuan Duo-Rong , Xu Dong , Liu Ming-Guo
Published: February 2023

Although the current workhorse in the area of second-order nonlinear optical (NLO) materials is still the inorganic NLO crystals, organic NLO crystals have their own bright aspects such as the high molecular NLO coefficient and structural diversity and flexibility. In principle, there is no distinct boundary between inorganic and organic. People hoped to develop a new kind of semi-organic NLO crystals which combine the advantages of inorganic and organic materials together.
An Interferometric Profiler for Rough Surfaces
Authors: Caber Paul
Published: February 2023

Conventional optical methods of surface profiling are limited in the range of surface heights that can be accurately measured due to phase ambiguity errors on steep local slopes. Instruments that have been developed thus far to avoid the problems with local slope typically suffer from poor measurement height resolution and slow measurement speeds. Contact profilometers such as stylus-based instruments suffer from slow measurement speeds, especially when two-dimensional scans of the surface are required. Stylus tips can also scratch delicate surfaces during the course of the measurement. A new method of optical, non-contact profiling of rough surfaces is described that utilizes interferometric techniques as well as digital signal processing algorithms to produce fast, accurate, and repeatable three-dimensional surface profile measurements.
Recent Developments in Profiling Optical Surfaces
Authors: Bennett Jean M. , Elings Virgil , Kjoller Kevin
Published: February 2023

In order to better understand the fabrication of optical surfaces and be able to produce smoother, lower scatter surfaces, surface characterization needs to be extended into shorter and longer surface spatial wavelength regions. Scanning probe microscopes are now available to profile optical surfaces. Long scan profilers are also available to give profile information for distances longer than a few millimeters with sensitivities and accuracies of atomic dimensions.
Determination of Interface Roughness Using A Wavelength Scanning TIS Instrument
Authors: Ronnow D. , Bergkvist M. , Roos A. , Ribbing C-G
Published: February 2023

Optical scattering from surface micro irregularities at a specific wavelength is directly related to the RMS-roughness value of the surface1. It is usually measured by a TIS (Total Integrated Scatter) instrument. In its’ conventional application this method can only be used to investigate the front surface of opaque samples. In the case of transparent samples or samples coated with a transparent film, one must handle two scattering interfaces as well as possible interference effects in the film. The resulting light scattering cannot be described by the standard TIS equation. By combining the scalar scattering theory with the Fresnel formalism we have obtained a model which predicts the scattering from a double layer as a function of wavelength. By fitting model calculations to experimental scattering spectra with the interface roughness values as parameters we can extract the rms-roughness values of the two interfaces. The model has been described elsewhere2. Using the scattering spectra and such fitting calculations we can conveniently, and non-destructively, determine the RMS-roughness of a "hidden" interface.
Strong-Field Processes in the Ultraviolet Region
Authors: Boyer K. , Gibson G. , Jara H. , Luk T. S. , McIntyre I. A. , McPherson A. , Rosman R. , Solem J. C. , Rhodes C. K.
Published: February 2023

A laboratory means for the generation of ultrahigh energy density states of matter, corresponding approximately to 0.1 – 1.0 W/atom at solid density, appears within technological reach. This capability enables the production, in a convenient laboratory environment, of energy densities comparable to those occurring in stellar interiors. The use of this technology will permit the study of a new realm of atomic phenomena involving (1) the behavior of matter in very strong fields, (2) the properties of highly stripped ions, (3) the characteristics of dense highly non–equilibrium plasmas, (4) high–field modes of electromagnetic propagation, and (5) the possibility of a new laser–driven means for the excitation and control of nuclear reactions.
Charge-Displacement Self-Channeling as a Method for Energy Concentration
Authors: Boyer K. , Luk T. S. , Solem J. C. , Rhodes C. K.
Published: February 2023

The concentration of energy arising from charge–displacement self–channeling is discussed. Since high energy deposition rates are expected to arise from multiphoton coupling and the channel can also serve as an effective waveguide for secondary radiation, such circumstances are Ideal for generating coherent short wavelength radiation.
Stimulated Compton Backscattering and the High Intensity Kapitza-Dirac Effect*
Authors: Schumacher D. W. , Bucksbaum P. H. , Bashkansky M.
Published: February 2023

We report the scattering of low energy free electrons from an optical standing wave at intensities of 1013 to 1014W/cm2.1 This interaction is the high intensity limit of the Kapitza-Dirac effect,2 wherein electrons Bragg scatter from the standing wave "lattice". In this regime, the momentum exchanged exceeds the reciprocal lattice vector by a factor of 500 or more, and the scattering rate is compar able to the optical frequency. The electron motion is most easily analyzed by classical mechanics.
X-Ray Microscopy for the Life and Physical Sciences
Authors: Attwood D. , Vladimirsky Y. , Kern D. , Meyer-Ilse W. , Kirz J. , Rothman S. , Rarback H. , Iskander N. , McQuaid K. , Ade H. , Chang T. H. P.
Published: February 2023

Advances in x-ray microscopy coupled with the development of bright, partially coherent radiation at x-ray wavelengths, herald a new period in which scientists in diverse disciplines will use x-ray imaging and probing techniques to see ever smaller structures, write ever smaller patterns, and study physical, chemical and biological systems, not only with an elemental sensitivity, but in many cases with a sensitivity to details of bonding. The combination of x-ray microscopy and various emission spectroscopies will permit the study of surfaces, thin films and material interfaces, as well as biological samples in their natural, unaltered and hydrated state1,2.
Amplitude- and Phase-Contrast X-Ray Microscopy
Authors: Schmahl G.
Published: February 2023

X-ray photons in the wavelength range of about 0.5 - 5 nm are best suited for x-ray microscopy. In the wavelength range λ ⩾ 2.5 nm the absorption cross sections are about one order of magnitude smaller than the cross sections for electrons in the energy range in which electron microscopy is performed. These absorption cross sections for soft x-rays are appropriate for high resolution investigation of biological specimens in their natural state having a thickness of up to about 10 micrometer. Especially interesting is the wavelength range between the K absorption edges of oxygen (λ = 2.34 nm) and carbon (λ = 4.38 nm) because in this wavelength range the radiation is weakly absorbed by water but strongly absorbed by organic matter resulting in a rather good amplitude contrast of wet specimens. For many elements and wavelengths phase shift is the dominating process and not photoelectric absorption. That means that phase-contrast x-ray microscopy can be performed with the following advantages compared to x-ray microscopy modes using amplitude contrast: For wavelengths larger than the carbon k-edge, the amplitude contrast of organic material surrounded by water is very low. To the contrary, for wavelengths slightly larger than CKα the phase contrast of such an object is high. Even in the wavelength range between the K-edges of carbon and oxygen (water window) wavelengths are found for which imaging in phase contrast is better concerning contrast and dosage compared to amplitude contrast imaging. In addition, imaging with phase contrast can be extended to wavelengths of about 0.5 nm with a dosage comparable to that necessary for imaging with amplitude contrast in the water window. The last point may be of practical importance in future work because with shorter wavelengths thicker specimens can be investigated than up to now.