bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray Crystallography as a Bayesian Signal Reconstruction Problem
Authors: Doerschuk Peter C.
Published: February 2023

A new Markov random field based algorithm is proposed for signal reconstruction from Fourier transform magnitude motivated by the data reduction calculations of x-ray crystallography. The purpose of an x-ray crystallography experiment is to determine the position in three dimensional space of each atom in a molecule. The measured data are the magnitudes squared of the Fourier transform of the electron density function of a crystal of the molecule of interest and possibly also of chemical derivatives. The data reduction calculations are a signal reconstruction problem for the three dimensional electron density. In the so-called “direct” methods of interest here, the reconstruction is based on a noisy measurement of the magnitude squared of the Fourier transform of the electron density of a single crystal, that is, no chemical derivatives of the molecule are studied.
Direct Inversion of Fourier Intensities with Application in Crystallography
Authors: Harrison Robert
Published: February 2023

In crystallography it is only possible to observe the Fourier intensities in a single diffraction experiment. There are a number of experimental methods to determine the phases, and for small molecules phase probablility methods (Direct Methods) work very well. The generic problem of inverting the intensities is considered difficult. Since the autocorrelation function (the Patterson function), can be calculated directly from the observed data, and is a quadratic function of the electron density (image intensity) it should be possible to construct an optimizer which will solve the autocorrelation function and thence the crystal structure. Since it is possible to express the autocorrelation function as a perfect square in a permutation number system this is a convex (or nearly convex) optimization problem. In principle a Newton's method root finder is all that is needed, but both the relatively poor quality of even good diffraction data and the potential singularities in the root finder prevent such a simple solution. Stronger optimizers and a statistical treatment of the errors in the data lead, sometimes, to the solution of real structures.
Multi-Resolution Deconvolution
Authors: Starck J.L. , Bijaoui A.
Published: February 2023

The continuous wavelet transform of a function f(x) is [1]: where a (> 0) is a dilatation parameter and b is translation parameter. The transform is characterized by three main properties: i/ it is a linear transformation, ii/ it is unvariant under translations, iii/ it is unvariant under dilatations.
Speckle Imaging of Satellites
Authors: Fitch J. P. , Lawrence T. W. , Goodman D. M. , Johansson E. M.
Published: February 2023

We performed a series of experiments using the Air Force Maui Optical Station’s 1.6 m telescope and a bare CCD detector to capture speckle images of various satellites. The speckle images were processed with bispectral techniques for recovering image Fourier phase as well as projection onto convex sets for recovering image Fourier magnitude from the projected autocorrelation. Results of imaging point stars and binaries are shown as a baseline assessment of our technique. We have reconstructed high quality images of numerous satellites and will show reconstructions of a very familiar satellite: the Hubble Space Telescope. To our knowledge, this is the first demonstration of the use of bare CCDs for speckle imaging of relatively bright objects such as artificial satellites.
Image Recovery from Atmospherically Degraded Images with Unknown Point-Spread Functions
Authors: Schulz Timothy J.
Published: February 2023

It is well known that, whereas atmospheric turbulence severely limits the effective resolution of a long-integration image obtained by a ground-based telescope, short exposure images retain diffraction-limited information. Since this fact was first pointed out by Labeyrie1, a variety of imaging techniques have been proposed. Correlation-based techniques – Laberyie’s method1, triple-correlation2,3, Knox- Thompson4– all recover diffraction-limited information about the observed object. For each of these techniques, a phase-retrieval problem must be solved to obtain an estimate of the object. In addition, a reference point-source must be available to correct for atmospheric seeing. A brief review of these techniques is found in the book chapter by Dainty and Fienup5.
Support-Constrained Motion-Artifact Correction for Magnetic Resonance Imaging
Authors: Fienup J.R. , Van Buhler J.E.
Published: February 2023

Motion during the collection of a magnetic resonance imaging (MRI) data set causes phase errors which result in a smearing or ghosting of the image. In this paper we present a new algorithm for correcting translational motion errors. It follows the same philosophy as the gradient search approaches that we invented to determine the aberrations of the Hubble Space Telescope [1] and to correct phase errors for synthetic-aperture radar [2].
Recovering Fourier phase data from amplitude data alone in macromolecular X-ray crystallography
Authors: Subbiah S.
Published: February 2023

The ab initio phase problem is the rate-limiting step in X-ray crystallography and by extension is also a rate-limiting step in the determination of high-resolution 3-dimensional (3-D) structures of biological macromolecules. Thus it has dramatic repercussions for the emerging areas of rational drug-design and protein engineering. Simply stated, the problem is of recovering the real-space image of a biological macromolecule - represented in Cartesian 3-D coordinates-from partial Fourier information alone. Specifically, the available information in reciprocal space is that of the Fourier amplitudes; the complementary Fourier phase information is not available.
Blind Deblurring and Deconvolution
Authors: Schulz Timothy J.
Published: February 2023

Many imaging systems in use today acquire data that are related to a desired object function f(·) through the linear relationship where h(·,·; θ) is the point-spread function for the imaging system, and θ is a collection of system parameters – some or all of which may be unknown – that characterize the system and, hence, its point-spread function. In some situations, only a small number of parameters might be required for the characterization of the system, whereas in other situations, the parameters that characterize the system might be made up of the point-spread function’s point-by-point values for all x and y of interest.
High Resolution Imaging of Astronomical Objects Using Deconvolution from Wave-Front Sensing Experimental Demonstration
Authors: Dayton D. , Sandven S. , Gonglewski J. D.
Published: February 2023

It is well known that the image forming ability of an astronomical optic system is limited by distortions due to a turbulent atmosphere1. A large aperture telescope will have no more resolving power than one with a diameter equal to Fried’s rO parameter which is usually between 5 and 10 centimeters. Recently, technological development in the areas of wave-front sensing and deformable mirrors have lead to adaptive optic systems. These systems attempt to measure the atmosphere induced wave-front distortion and cancel it through the use of a deformable mirror. Due to the short correlation time of the atmosphere, they require a high bandwidth multi-input multi-output control system.
Image Reconstruction and Information
Authors: Blahut Richard
Published: February 2023

Summary not available.
Markov random fields as a priori information for image restoration
Authors: Wu Chi-hsin , Doerschuk Peter C.
Published: February 2023

Markov random fields (MRFs) [1, 2, 3, 4] provide attractive statistical models for multidimensional signals. However, unfortunately, optimal Bayesian estimators tend to require large amounts of computation. We present an approximation to a particular Bayesian estimator which requires much reduced computation and an example illustrating low-light unknown-blur imaging. See [7] for an alternative approximation based on approximating the MRF lattice by a system of trees and for an alternative cost function.
Retrieval of Physical Properties of Atmospheric Particles by Inversion via Regularization in the Limit of a Small Optical Data Set
Authors: Müller Detlef , Ansmann Albert , Wandinger Ulla , Althausen Dietrich
Published: February 2023

Atmospheric aerosols, although only a minor constituent of the earth’s atmosphere, play an important role in many atmospheric processes. Due to their appreciable influence on the earth’s radiation budget, air quality, clouds and precipitation as well as the chemistry of the troposphere and stratosphere it is necessary to gather detailed information on their optical and physical properties. A multiple-wavelength lidar as well as a Raman lidar at the Institute provide optical particle information in terms of six backscatter coefficients and two extinction coefficients in the wavelength range from 0.355 to 1.064 μm on a vertical scale. A data-evaluation algorithm that uses the method of inversion via regularization has been specifically designed to retrieve physical properties from the given optical information. The physical parameters can be described by, e.g., the particle size distributions, the mean sizes derived from it, like the effective radius, the volume, surface-area, and number concentrations as well as the complex refractive index. Due to the low amount of available a priori information on the particle properties in combination with the small number of optical information that additionally include large measurement errors the main focus had been on the retrieval of the mean values. To control the quality of the regularization under these difficult conditions the method of generalized cross-validation is used as it does not require the knowledge of the underlying measurement errors nor the knowledge of the specific shape of the particle size distributions.
Night-sky reconstructions for linear digital imaging systems
Authors: Clarkson Eric , Denny Jack , Barrett Harrison , Abbey Craig , Gallas Brandon
Published: February 2023

In tomographic and other digital imaging systems the goal is often to
reconstruct an object function from a finite amount of noisy data
generated by that function through a system operator. One way to
determine the reconstructed function is to minimize the distance
between the noiseless data vector it would generate via the system
operator, and the data vector created through the system by the real
object and noise. The former we will call the reconstructed data
vector, and the latter the actual data vector. A reasonable constraint
to place on this minimization problem is to require that the
reconstructed function be non-negative everywhere. Different measures
of distance in data space then result in different reconstruction
methods. For example, the ordinary Euclidean distance results in a
positively constrained least squares reconstruction, while the
Kulback-Leibler distance results in a Poisson maximum likelihood
reconstruction. In many cases though, if the reconstruction algorithm
is continued until it converges, the end result is a reconstructed
function that consists of many point-like structures and little else.
These are called night-sky reconstructions, and they are usually
avoided by stopping the reconstruction algorithm early or using
regularization. The expectation-maximization algorithm for Poisson
maximum likelihood reconstructions is an example of this
situation.
Inverting Real Data: The Ipswich Experience
Authors: McGahan R.V.
Published: February 2023

The Electromagnetics Technology Division of the Air Force Research Laboratory at Hanscom Air Force Base, Massachusetts has been providing measured and theoretical data to the inverse scattering/imaging community since 1995, via a FTP server. The data is obtained in the course of our work in radar phenomenology and systems analysis, wherein we conduct both theoretical and measurement programs. Since many of our results are obtained from canonical shapes and are not of a sensitive nature we realized that we could do the inverse community a service by providing researchers with real data to exercise their algorithms. We inaugurated the Ipswich data server in late 1994.
Multi-frame satellite image reconstruction using adaptive-optics compensation
Authors: Seldin John H. , Paxman Richard G. , Ellerbroek Brent L. , Riker James
Published: February 2023

The resolution achieved in space-object imaging is usually limited by
turbulence-induced aberrations, which can severely limit the
resolution in the images by an order of magnitude or more. The
1.5-meter telescope at the Air Force Research Laboratory Starfire
Optical Range (SOR) relies upon an adaptive-optics system to eliminate
in real time much of the phase aberration introduced by atmospheric
turbulence. Despite the exceptional performance of this system, the
correction is never perfect. There are several sources of residual
aberrations that degrade the imagery: imperfect wavefront sensing
(particularly in low light-level situations), the time lag between
sensing and correction (which allows for evolution of the atmosphere
and is a particular problem when slewing to track an earth-orbiting
space object), and deformable-mirror fitting errors. A post-detection
image-reconstruction capability also insures the continuing
availability of fine-resolution images, even during adaptive-optics
down time owing to routine maintenance or temporary system failure.
Therefore, post-detection reconstruction methods provide an important
complement to and backup for pre-detection correction.
Phase Retrieval with an Opacity Constraint in LAser IMaging (PROCLAIM)
Authors: Paxman R.G. , Fienup J.R. , Reiley M.F. , Thelen B.J.
Published: February 2023

PROCLAIM is an active-illumination imaging method that utilizes flood illumination of an opaque object with a frequency-tunable laser [1,2,3]. The reflected radiation at a single frequency will create a speckle pattern in the far-field. The intensity of this far-field speckle pattern is directly detected with an array of detectors and without intervening optics. Typically, the illuminating laser will step through several frequencies so that a separate cross-range speckle intensity pattern is collected for each of multiple frequencies. Properly formatted, these data correspond to the modulus squared of the Fourier transform of the object’s 3-D complex reflectivity function [4]. If the object’s Fourier phase can be retrieved, then the Fourier representation of the object will be complete and a 3-D FFT could be used to recover the object’s 3-D complex reflectivity. Thus, phase-retrieval is an integral element of the PROCLAIM imaging modality. A schematic diagram of the data-collection and processing that constitute the PROCLAIM imaging modality is presented in Fig. 1.
Image formation and signal recovery in near field optical microscopy
Authors: Kawata Satoshi
Published: February 2023

A near-field scanning optical microscope (NSOM) changes the light field on an extremely small area of the sample surface by inserting a probe tip into the near field of the sample surface. Since the probe and the sample are very near each other, much nearer than the wavelength of incident light, near-field imaging is based on multiple scattering or interaction of photons with the total system including probe and sample. The image of an NSOM is, hence, very dependent on the gap distance between probe and sample surface, polarization of light, and nanometric distribution of structure and complex dielectric constant of sample. Nevertheless, theory of image formation has not been established. Currently people are trying to learn, from the numerically simulated experiences, how the image changes by parameters. Girard and Courjon derived representing an NSOM system with a self-consistent approach.1) Novotny et al. showed the imaging characteristics of a two-dimensional NSOM system with different samples and polarizations.2)
Protein Crystallography: From X-ray diffraction spots to a three-dimensional image
Authors: Terwilliger Thomas C. , Berendzen Joel
Published: February 2023

Proteins are remarkable molecular machines that are essential for life. They can do many things ranging from the precise control of blood clotting to synthesizing complex organic compounds. Pictures of protein molecules are in high demand in biotechnology because they are important for applications such as drug discovery and for engineering enzymes for commercial use.
Fibre Optical Lasers
Authors: Hanna D.C.
Published: February 2023

Fibre lasers have been one of the most active areas of laser development over the past decade. The fibre geometry provides high gain for a modest pump power and this has been the feature most widely exploited. The later advent of fibre gratings has further enhanced the versatility of active fibre devices. Now, there is increasing interest in the high power capabilities of fibre lasers, via cladding-pumped configurations, so that fibre lasers provide competitive solutions to areas formerly regarded as the sole province of bulk lasers. These aspects and other important developments that have taken place over the last decade will be reviewed.
Q-Switching of 10W Fiber Coupled Diode Laser Pumped Nd:YAG
Authors: Zhen Guo , Shi-Yu Wang , Jian-Guo Wen , De-Fang Cai , Tao Huang , Liang Chen
Published: February 2023

Diode laser pumped solid state laser offers high reliability efficiency and compactness. These techniques have been applied to continuous wave Nd:YAG laser system. In this letter we report on the Q switching of a diode laser pumped Nd: YAG and have obtained pulses of 18ns and peak power of 5KW at repetition rates 10KHz. The maximum repetition rate that we observed were 50KHz.
Laser Remote Sensing at NASA Langley
Authors: Barnes Norman P.
Published: February 2023

NASA is utilizing solid state laser technology in remote sensing systems to monitor the health of Planet Earth. NASA’s objective is the systematic characterization of the total Earth system with special attention to possible anthropogenic changes. By studying the entire Earth over extended periods of time, it may be possible to detect threatening situations, such as the ozone hole or global warming and take reasoned measures to avoid them. A workshop, held under NASA's auspices, identified which earth variables are important to the health of the planet. Of these, about half can be monitored using laser remote sensors. Included in this subset are: aerosols, water vapor, wind velocity, ozone, and greenhouse gasses. Measuring these variables from a satellite has several advantages such as global, high resolution coverage and better high altitude sensitivity.
The Growth of High Efficiency 2.1μmCTH:YAG Laser Crystal
Authors: Wang Yongguo , Yang Xun , Wu Shucheng , Ji Tianlai , Namu Jilatu , Gui Youxi
Published: February 2023

In this paper, we reported the growth of high -efficiency, high optical quality CTH:YAG laser ciystal using Czochralski method of medium frequency induction heating from iridium crucible. The slop efficiency of CTH:YAG is up to 5%.
Passive mode-locking of cw lasers due to frequency sliding
Authors: Mikhailov V.P. , Kalashnikov V.L. , Poloyko I.G. , von der Linde D.
Published: February 2023

Rapid progress in the field of subpico- and femtosecond pulse generation has resulted in the shortest pulse duration of 7.5 fs [1]. The main mode-locking technique used here is the Kerr-lens mode-locking [2]. However, one of the distinctive feature of modern investigations is the renovation of the interest toward passive mode-locking due to saturable absorbers, in particular, multilayer quantum-well semiconductor absorbers [3, 4]. It was shown, that such absorbers are capable to provide sub-10 fs ultra-short pulse generation, in spire the absorber’s recovery time exceeds 100 fs. This result has an explanation in terms of soliton mode-locking with slow saturable absorber as a stabilizing mechanism [5]. Last time an ultra-short pulse stabilization mechanism due to spectral filter with a transmission band shifted in respect to the generation field carrier frequency (a so called sliding frequency method [6] which is used in fiber optics lines) has received a great lot of attention.
Recent Progresses on the Study of Ultrafast Optical Switching: Materials and Devices
Authors: Yuquan Shen , Qiu Ling , Jiaxing Zhang , Jianfeng Zhai , Jinhai Si , Yougui Wang , Jiang Zhao , Bingsuo Zou , Peixian Ye , Yinghua Zou , Zonggiu Xia , Ping Yuan
Published: February 2023

Optical Kerr effect(OKE) and optical bistability(OB) are the important basis for optical switching. Nitrobenzene is an organic OKE material, however, it is not convenient to handle because of its liquid form and its toxicity. Other inorganic crystals such as tantalum potassium niobate and barium titanate are good candidates to replace nitrobenzene, but they have the problem of high price. On the other hand, optical bistability with low input power and slow temporal response in organic polymer waveguide was observed by us recently from push-pull aromatic azobenzene materials1 and optical bistabilities realized in a planar quasi waveguide and a hybrid waveguide made with a polydiacetylene film have also been reported in literature2. Meanwhile, much efforts have continuously been devoted to the search for such better organic materials in thin film form: metallo phthalocyanine is one among them. However, to our knowledge, study of ultrafast optical bistability in organic polymer waveguides has not yet been reported before us. In this paper, we are going to report our recent progresses on the study of the ultrafast optical switch properties of a novel vanadium phthalocyanine, the picosecond response OKE and OB observed from its Langmuir-Blodegett film or from a planar optical waveguide. In addition, the relationship between the chemical structure and the property of ultrafast responses will also be discussed.
Development History of Laser Materials and Their Applications in China
Authors: Gan Fuxi
Published: February 2023

Since emergence of the first laser device — ruby laser, solid state lasers continue to occupy a prominent place among the different kinds of laser devices, which are widely used in industrial, medical, military and scientific fields. The laser materials are the research keystones for development of new solid state lasers. There are two kinds of solid state laser: light-pumped and electrically excited, the latter ones are semiconductor lasers. As the preparation of semiconductor laser materials — semiconductor thin films always ties with laser devices, hence, in this paper we discuss mainly the light-pumped and ion-activated solid state materials, in which the author had long been engaged.
Highly accurate dynamic modelling of optical parametric oscillators
Authors: Hansen P. L. , Buchhave P.
Published: February 2023

Accurate modelling of the transient behaviour of optical parametric oscillators (POPs) is of great importance for the understanding of many aspects of OPOs such as the build up of signal and idler fields from spontaneous parametric fluorescence, control and locking of the resonance mode, tuning and mode hopping and de-tuning due to heating effects. In this contribution we describe a numerical model, which takes into account all of the most important processes influencing the transient behaviour of an OPO. We then apply the model to two recent experimental observations: The growth of the signal and idler fields as an OPO is scanned through resonance by means of a piezoelectric mount for one of the resonators1 and the phenomenon of self-frequency locking.2,3 In both cases thermal effects due to even very small absorption losses in the nonlinear material modify the material properties of the OPO and lead to the observed complex behaviour. Comparison between the experimental data and the model data show that the model is able to account for all the observed features of the OPO output.
Light Scatter from Polysilicon Surfaces and Comparison with Surface Roughness Statistics by AFM*
Authors: Bawolek E. J. , Mohr James B. , Hirleman E. D. , Majumdar A.
Published: February 2023

Optical scatter measurements from polysilicon surfaces were performed using 632.8 nm illumination at 45 degrees and 488 nm illumination at 76.8 degrees. Scatter was recorded up to 60 degrees from the specular beam. Results are compared with surface statistics derived from Atomic Force Microscopy (AFM).
Light Scattering by Sub-Half Micron Spherical Particles on Silicon and Oxide/Silicon Surfaces*
Authors: Bawolek E. J. , Hirleman E. D.
Published: February 2023

We report angle resolved light scattering characteristics of individual polystyrene spheres on silicon and on a 91.5 nm thick film of oxide on silicon. Scattering was measured as a function of polarization using a He-Ne laser at a 45 degree incident angle.
Specification of surface finish in terms of system performance
Authors: Church E. L. , Takacs P. Z.
Published: February 2023

The man-or-woman in the street model of optical surface quality involves two features -- 'figure', which behaves according to geometrical optics, and 'finish', which is treated by diffraction optics.
Interaction of Two Optical Beams At a Symmetric Random Surface
Authors: Gu Zu-Han , Dummer R.S. , Escamilla H.M. , Mendez E. R. , Maradudin Alexei A. , Lu J.Q. , Michel T. , Nieto-Vesperinas M.
Published: February 2023

In general, the optical field scattering from a randomly rough surface can be divided into a specular or coherent component, and a diffuse or incoherent one. It is also well known that optically rough surfaces extinguish the specular component and thus produce only diffuse light. In normal circumstances, the diffuse component is a smoothly varying envelope that modulates the speckle field. However, recently it has been reported that light scattered from randomly rough surfaces with even symmetry displays a very sharp peak in the specular direction.(1-2) The width of this peak is of order 2λ/L, where L represents the length of the illuminated portion of the surface, and λ represents the wavelength of the light. It must be stressed that this peak is not due to the presence of an unscattered component, as would be the case for a weakly scattering surface; the peak is part of the diffuse component. In previous work, this effect has been termed, in reflection, specular enhancement, and in transmission, enhanced refraction. In this paper, we shall refer to this effect as the specular enhancement.
Mueller matrix description of scattering
Authors: Church E. L. , Stover J. C.
Published: February 2023

Scattering measurements of rough surfaces are usually made using linearly polarized light. There are four possibilities: ba = pp, sp, ps and ss, where a is the initial state of polarization and b is the final state. Such measurements may be adequate for determining the power spectral densities (PSDs) of smooth topographically rough surfaces, but they do not capture all of the information about the surface that can be obtained from polarimetric measurements.
Scattering of Electromagnetic Surface Waves by Rough Surfaces
Authors: Saillard M.
Published: February 2023

The localization of classical waves, like electromagnetic or acoustic ones, has been widely studied for a few years [1]. For one- or two-dimensional systems, the localization of propagating modes is theoretically predicted at any non vanishing disorder. For instance, surface plasmon polaritons (SPP), which are extended modes of flat metallic surfaces, become localized in the presence of random roughness [2,3]. Localization of SPP on rough surfaces has important contributions to surface-enhanced phenomena [2] and gives birth to the phenomenon of enhanced backscattering for shallow surfaces [3]. But it seems that no experimental confirmation exists yet [1]. To my knowledge, no direct numerical evidence of localization has neither been published, since only backscattering peaks, considered as a signature of localization, are exhibited. Thanks to the model achieved in our laboratory [4], it is now possible.
Applications of Light Scatter for Microelectronics Manufacturing
Authors: Gaspar S.M , Krukar R. H. , Bishop K.P. , Hickman K.C. , Milner L.M. , Naqvi S.S.H. , McNeil J.R.
Published: February 2023

As the level of microelectronics integration increases, device design geometries decrease. For example, current state of the art fabrication lines for high performance devices (e.g. microprocessors and DRAMs) use design geometries with critical dimensions (CDs) of 0.8 μm and smaller. Further, SEMATECH's goal for 1993 is to have CDs of 0.35 μm in production capability; goals of 0.15 μm are being discussed for the late-1990s. This trend greatly reduces processing latitude in device fabrication and thus places even greater demands on materials properties and process control. For these goals to be met, there must be more diagnostics capabilities than presently exist. Optimal characteristics for diagnostics include being noncontact, nondestructive, simple, quantitative, rapid, and capable of being implemented in-situ.
Preparing Samples for Scattering Measurements - A Cleaning Study
Authors: Brown Jeff L.
Published: February 2023

Several cleaning methods suitable for cleaning small, low scatter samples in the laboratory were compared. The motivation for this work is to determine the relative merits of various cleaning procedures for preparing samples for BRDF measurements. A procedure which consistently reduces scatter from surface contamination to a minimum is desired.
Theoretical and experimental comparison of different techniques to characterize surface roughness
Authors: Amra C. , Bruel L.
Published: February 2023

Characterization of surface roughness remains today a crucial problem, in particular in the fields of optics and mechanics. Many techniques [1] have been developed in this aim, and involve scatterometers or profilometers. However the measured roughness values may strongly vary from one technique to another, and it becomes necessary to normalize the statistical parameters that describe surface defects. In this paper we present experimental results obtained from 3 techniques that are Angle-Resolved light Scattering measurements (ARS), mechanical profilometer (Talystep) and Atomic Force Microscope (AFM). Moreover, a theoretical tool is provided for a detailed investigation of the apparatus functions relative to the light scattering and Talystep techniques.
The Use of Reflectivity Measurements in Phase Shifting Interferometry in Surface Profiles
Authors: Deck Leslie L.
Published: February 2023

Instruments utilizing Phase Shifting Interferometry (PSI) principles are used extensively in precision surface metrology when a non-contact method of surface characterization is required. PSI entails making point to point measurements of the phase difference between a test and reference beam of an interferometer. These phase differences are assumed to be produced from small height changes in the test surface. If the reference surface profile is accurately known, the calculated height differences represent deviations from the reference profile and the test surface profile can be reconstructed therefrom.
Integrating Figure and Finish Measurements with Surface Profiling Instruments
Authors: Takacs Peter Z. , Church Eugene L.
Published: February 2023

Conventional figure measurement techniques are inadequate for testing aspheres for grazing incidence applications. Conventional techniques are best suited for optical components in the shape of flats, spheres, or conical surfaces of revolution, used mainly in normal incidence applications . These optics usually have their symmetry axis coincident with the local surface normal direction. Grazing incidence optics, on the other hand, are usually cylindrical, toroidal, or ellipsoidal in shape, with the symmetry axis intersection far outside the clear aperture. Such surfaces are not axisymmetric when viewed along their surface normals. They are highly anamorphic, having vastly different curvatures in the two directions parallel and perpendicular to the symmetry axis. It is extremely challenging to test these optical components during fabrication to insure that they indeed meet the specifications for figure and finish quality. It is because of the extreme difficulties involved in developing reliable tests with conventional interferometric techniques that we decided to use profiling techniques to characterize the figure and finish of synchrotron radiation (SR) optics.
Soft X-Ray Radiation from Low Relativistic Electrons Transversing a Superlattice
Authors: Law C. T. , Kaplan A. E.
Published: February 2023

When fast electrons pass through a periodic medium, electromagnetic wave is generated (resonant transition radiation)1. The angle of emission θ with respect to the beam and wavelength λ for this radiation is related by
ϵ¯cosθ=c/v−nλ/l where
ϵ¯ is the average dielectric constant, v is the velocity of electron, n is an integer, and l is the spatial period of interfaces. We consider a system composed of many thin (≤100 Å) layers which makes it possible to drastically reduce the critical energy to a few tens Kev or lower 2,3. The use of lower energy is prevented by the scattering of electrons and absorption of X-ray photon in the material. Taking these two factors into consideration, we obtain the optimal range of electron energy E
o
(which appears to be between a few hundreds Kev and a few Mev), the total thickness of the superlattice L and maximal radiation for a given frequency ω.
Multi-Layer Optics for Short Wavelength Lasers
Authors: Barbee Troy W.
Published: February 2023

High normal incidence reflectivities have been demonstrated for multilayer optics in the soft x-ray and extreme ultraviolet spectral domains. These structures have potential for application in short wavelength laser systems. This application, particularly in the time and intensity domains, is extreme. The current status of multilayer-optic developments are reviewed and implications of the unique characteristics of short wavelength laser systems relative to application of such optics are discussed.
Stability of Multilayers for Short-Wavelength Optics*
Authors: Ziegler E. , Lepetre Y. , Schuller Ivan K. , Viccaro J. , Spiller E.
Published: February 2023

A variety of multilayer mirrors with transition metal absorber layers (W-C, WRe-C, Co-C, and Cr-C) have been fabricated and tested up to 1000 C using standard θ-2θ x-ray diffraction, Debye-Scherrer scattering and microcleavage transmission electron microscopy.
Ellipsoidal Reflector for Longitudinal Pumping of Soft X-Ray Lasers
Authors: Young J. F. , Macklin J. J. , Harris S. E.
Published: February 2023

We propose a new geometry for collecting and focusing soft x-ray radiation from a laser-produced plasma which offers collection efficiencies greater than 20% and aspect ratios of more than 50. This combination typically results in (power density) x (length) improvements of 30 relative to present transverse multiple-spot geometries. Longitudinal pumping also significantly reduces laser excitation problems associated with amplified spontaneous emission and high atomic number densities. Removal of the laser plasma target from the active medium simplifies cell design, permits spectral filtering of the pumping radiation, and may lead to improved conversion efficiency.
Physics of X-ray Generation and Related Topics Using Picosecond High Power Lasers
Authors: Kuroda Hiroto
Published: February 2023

Physics of X-ray generation and other related plasma processes such as electron acceleration, ion production and scattering of light are studied experimentally and theoretically.
Excimer Lasers Lambdameter
Authors: Pouey Michel
Published: February 2023

We describe eximer lasers cavity and high resolution lambdameters fitted whith holographic spherical gratings.
Measurement of Oscillator Strengths of Hg by Four-Wave Mixing
Authors: Smith A. V. , Alford W. J.
Published: February 2023

We have developed new techniques based on four-wave mixing for the accurate determination of oscillator strengths and applied them to measure 61S - n1,3P and 71S - n1,3P (n = 6 - 13) matrix elements of atomic Hg. For transitions from the 61S ground state, index matching conditions were used to determine refractive indicies and thus f-values, while the frequency dependence of the nonlinear susceptibility was used to deduce matrix elements for transitions involving 71S. For all measurements, two-photon resonance with the 71S state was maintained.
Zone Plates for Short Wavelength Xrays and Microelectronics
Authors: Aristov V. V. , Erko A. I.
Published: February 2023

Summary not available
Overtone Production of Soft X-Rays With Free-Electron Lasers*
Authors: Schmitt M. J. , Elliott C. J. , Lee K. , McVey B. D.
Published: February 2023

A one-dimensional free-electron laser code has been written that includes harmonic generation. In this code the electrons are driven by a spatially-averaged superposition of the fundamental and its overtones. The waves are driven by the Fourier-analyzed transverse current. The initial wave amplitude at all harmonics originates from a stochastic placement of particles. We show that when the overtones are small compared to the fundamental, a self-consistent description is not necessary, thereby reducing the computational complexity.
Optical Physics of an XUV Free-Electron Laser*
Authors: McVey B. D. , Goldstein J. C. , Lee K. , Newnam B. E.
Published: February 2023

The optical physics of an XUV free-electron laser oscillator configuration driven by an RF linac is investigated. Some of the topics discussed are optical beam quality, methods of output coupling, ring resonator configurations, and the expected optical spectrum. The tool used to investigate these physics issues is the computer code, FELEX. FELEX simulates a three-dimensional FEL oscillator configuration. The electron beam is modelled by following individual electron trajectories including deceleration by the light wave, betatron motion, and external focussing due to quadrupole coils. The electron beam parameters used in the simulations are those believed to be scalable from present RF linac experiments. The optical beam is modelled by solving the paraxial wave equation on a square grid. After interaction with the electron beam in the wiggler region, the optical beam is propagated through the resonator cavity to the wiggler entrance where the interaction with a new pulse of electrons is initiated. Initial 3-D simulations at 82nm indicate strong distortions of the optical beam from the idealized Gaussian. Further, multiple pass calculations appear necessary to accurately determine the small signal gain. Finally, the optical spectrum is investigated using a one-dimensional periodic code.
Search for X-Rays Generated by Collisionless Multiphoton Processes
Authors: Lee Peter H. Y. , Casperson Donald E. , Schappert Gottfried T.
Published: February 2023

We have conducted photon counting experiments to search for x rays which may be generated by either collisionless multiphoton induced inner-shell processes or bremsstrahlung at high laser irradiance. Using KrF light at an irradiance ~ 3 x 1017 W/cm2 on low density Xe gas targets, we detect no prompt photons which are characteristic of these processes.
Multiphoton Ionization with Femtosecond Laser Pulses
Authors: Muller H. G.
Published: February 2023

There are a number of reasons to use subpicosecond pulses in multiphoton ionization experiments. Pulses with shorter risetimes make it possible to study processes with higher rates before one runs into the problem of depletion of target atoms. Furthermore the momentum of the electron does not change between the point of ionization and the detector if the pulse expires before the electron has time to sample the spatial inhomogeneity of the light intensity. This makes it possible to identify the intensity at which an electron was formed from the energy with which it reaches the detector.
Contact Microscopy with a Soft X-Ray Laser
Authors: DiCicco D. S. , Kim D. , Rosser R. J. , Skinner C. H. , Suckewer S. , Gupta A. P. , Hirschberg J. G.
Published: February 2023

A soft X-ray laser of output energy 1-3 mJ at 18.2 nm has been used to record high resolution images of biological specimens. The contact images were recorded on photoresist which was later viewed in a scanning electron microscope. We also present a Composite Optical X-Ray Laser Microscope "COXRALM" of novel design.
X-Ray Fourier-Transform Holographic Microscope
Authors: Haddad W. S. , Cullen D. , Solem J. C. , Boyer K. , Rhodes C. K.
Published: February 2023

The properties of an x-ray Fourier-transform holographic instrument suitable for imaging hydrated biological samples are described.
First Images from the Stanford Tabletop Scanning Soft X-Ray Microscope
Authors: Trail J. A. , Byer R. L.
Published: February 2023

We have constructed a scanning soft x-ray microscope which uses a laser-produced plasma as the soft x-ray source and normal incidence multilayer coated mirrors in a Schwarzschild configuration as the focusing optics. The microscope operates at a wavelength of 140 Å, has a spatial resolution of 0.5 μm, and has a soft x-ray photon flux through the focus of 104 s-1 when operated with only 170 mW of average laser power. The microscope is compact; the complete system, including the laser, fits on a single optical table. In this paper we describe the microscope and present images of metallic microstructures.
Progress in Optical Reconstruction of Submicron X-Ray Holograms
Authors: Joyeux D. , Polack F.
Published: February 2023

We investigate the maximum resolution which can be obtained from x-ray holograms through optical reconstruction. This implies to reject paraxial approximations, i.e. to consider high numerical apertures, and to take into account the holographic aberrations. We determine first the limits to a perfectly corrected reconstruction, set by diffraction (in terms of numerical aperture and resolution). It is shown that the diffraction limit can be as good as λc/2.8, in a particular reconstruction configuration (λc: re-construction wavelength). Discussion of practical implementation suggests that λc/2.2 is reasonably feasible.
Soft X-Ray Lenses with 400 Å Outer Zone Width
Authors: Vladimirsky Y. , Kern D. , Chang T.H.P. , Meyer-Ilse W. , Guttmann P. , Greinke B. , Attwood D.
Published: February 2023

Fresnel zone plate lenses for focussing and imaging radiation in the 10-50 Å wavelength region have been fabricated with outer zone widths as small as 400 Å. The zone plates were fabricated by electron beam lithography using a high resolution vector scan system designed specifically for nanometer pattern writing. A special circular pattern generation technique, utilizing high speed polar/cartesian conversion was utilized. Field size was calibrated for squareness and orthogonality using electron beam lithography calibration marks and laser interferometry. Patterns were written in a 180-200 nm thick PMMA resist on a 30 nm gold electroplating base. The substrate was a 100 nm silicon nitride film. The pattern received a dose of 250 μC/cm2 at 25 KeV. Special patterns requiring a thick central stop region, received a doubled dose, followed by a double development/double plating technique.

A method utilizing the phenomenon of form birefringence was used for monitoring the development of the fine features. In the optical microscope with polarized light and crossed analyzer, a distinct change of the reflected intensity is observed during the final stages of development.

Text patterns imaged at 45 Å wavelength demonstrate a spatial resolution approaching 500 Å. Measurements of zone plate efficiency are also described.
High Power, Short Pulse Ultra-Violet Laser for the Development of a New X-Ray Laser
Authors: Meixler L. D. , Nam C. H. , Robinson J. , Tighe W. , Krushelnick K. , Suckewer S. , Goldhar J. , Seely J. , Feldman U.
Published: February 2023

A high power, short pulse ultra-violet laser system (Powerful Picosecond-Laser) has been developed at Princeton Plasma Physics Laboratory (PPPL) as part of experiments designed to generate shorter wavelength X-ray lasers. With the addition of pulse compression and a final KrF amplifier the laser output is expected to have reached 1/3-1/2 TW levels. The laser system, particularly the final amplifier, will be described along with some initial soft X-ray spectra from laser-target experiments, The front-end of the PP-Laser provides an output of 20-30 GW and can be focussed to intensities of ~1016 W/cm2. Experiments using this output to examine the effects of a prepulse on laser-target interaction will be described.
12.8 eV Laser in Neutral Cesium
Authors: Barty C. P. J. , King D. A. , Yin G. Y. , Hahn K. H. , Field J. E. , Young J. F. , Harris S. E.
Published: February 2023

We report the operation of a saturated 12.8 eV (96.9 nm) laser in Cs vapor that has an extrapolated small signal gain of exp(83) in a total length of 17 cm. We believe that lasing occurs from a core-excited level embedded in the continuum of the valence electron. The laser is pumped by soft x-rays from a synchronous, traveling-wave, laser-produced (2.5 J, 15 ps, 1064 nm) plasma.
Spectra of Lead, Bismuth, Thorium and Uranium Relevent To A Neodymium-Like Soft X-ray Lasing Scheme
Authors: Hodge W.L. , Filbert P.C. , Kohler D.A. , Navoda C.L. , Perez J.D. , Hagelstein P.L. , Maxon S. , Scofield J.H. , Peek J.M.
Published: February 2023

The Nd-like isoelectronic sequence (60 electrons) of high Z elements could provide the basis for a soft x-ray laser (1). Gain may be possible at approximately 70 A for the 5f-5d transition in Nd-like Uranium. The potential advantage is that a medium power Nd:glass laser (10E12 to 10E13 watts/cm2) is sufficient to create a soft x-ray laser. As a first step in this development, soft x-ray spectra from Pb, Bi, Th and U were taken. These results will be presented along with three different atomic structure computer calculations of transition energies.
Time Development of Amplification in Na XI Hα-Line at 54.19 Å
Authors: Nishimura H. , Shiraga H. , Daido H. , Tachi T. , Herman P. R. , Miura E. , Takabe H. , Yamanaka M. , Kato Y. , Tallents G. J. , Key M. H.
Published: February 2023

Temporal behavior of the Na XI Balmer-α (Hα) transition in a laser-produced. NaF plasma is experimentally investigated. The time variation of the gain value was derived from the ratio of the Hα intensities along and transverse to the x-ray laser axis. The Na XI Hα line is amplified during 100-500 psec after laser irradiation with the maximum gain of 2-4 cm−1. The experimental result is in close agreement with a model calculation using a 2-dimensional hydrodynamic code.
VUV Amplification of Neon-Like Titanium Ion
Authors: Yashiro Hidehiko , Hara Tamio , Ando Kozo , Aoyagi Yoshinobu , Dote Toshihiko , Namba Susumu
Published: February 2023

Amplified spontaneous emission of the 2p53s3P1-2p53p3D2 transition at 50.8 nm in neon-like titanium ion has been observed in a line-shaped plasma produced by focusing a long laser pulse of 5 ns on a slab target for keeping population inversion for a long time.
X-Ray Laser Research at Physics International
Authors: Deeney C. , Levine J. , Nash T. , LePell P. D. , Krishnan M.
Published: February 2023

Photopumped and recombination X-ray laser schemes are under investigation at Physics International, on the DNA/PITHON 3 TW facility. For the sodium-neon resonant photopumped scheme, DNA/PITHON is used to implode a sodium-bearing plasma, the pump, and a secondary capacitor bank is used to drive a neon gas puff Z-pinch, the lasant. The characterization of the pinched sodium plasma is reported in this paper, as are pump power measurements, which showed 65 GW in the Na X 1s2-1s2p 1P line. In earlier experiments, neon gas was imploded onto sodium-fluoride coated targets, on-axis, but insufficient sodium pump powers were obtained. However, some very interesting spectral features, which could be an indication of recombination pumping, were observed in the neon plasmas formed when neon was imploded onto aluminum targets. These results are also presented in this paper.