bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Data Clustering to Optical Linewidth Measurement
Authors: Chim Stanley S. C. , Kino Gordon S.
Published: February 2023

In semiconductor manufacturing, submicrometer linewidth measurements are essential because they can be used to characterize VLSI processing steps; for example, in photolithography, the measured width is directly related to critical process parameters such as focus distances and exposure periods. Optical metrology is preferred because it is non-destructive and has a high throughput. Optical confocal microscopes1 and correlation microscopes2 are especially useful for metrology because they have better transverse and range definition than standard microscopes. However, as the dimensions of circuits shrink to below 0.5 μm (~ one wavelength of light), it is difficult to interpret the optical images obtained by these improved microscopes. Traditional measurement techniques based on thresholding the intensity of an optical image are not accurate enough for submicrometer measurements.3 We describe here a pattern recognition technique (based on data clustering) for recognizing line features which are otherwise difficult to measure.
Resolving Power and Information Theory
Authors: Viano G.A. , Scalas Enrico
Published: February 2023

In Fourier optics, imaging systems are viewed as linear systems characterized by their impulse response, also called “the point spread function”. If f is the complex amplitude transmission function characterizing an object uniformly iluminated by coherent light, then the image g formed by the system is given, in the one-dimensional case and for aberration-free systems of aperture Ω, by the following integral equation: where magnification factors are omitted and [−X, X] is the support of f. The Rayleigh resolution distance is given by R = 7π/Ω.
Parameter Estimation with Incomplete a Priori Information; Photoelectron Counts
Authors: Lading Lars , Jørgensen Thomas Martini
Published: February 2023

Photoelectron counting experiments are considered. The object of the measurement is to determine parameters defining the state of a physical system characterized by a set of parameters {αi} on the basis of an observed set of photoncount numbers {nj}. Two types of parameters are involved: those that are to be determined, {αi}p (primary), and those that have impact on the estimation but are otherwise of no interest to the object of the measurement, {αi}s (secondary). The problem can be analyzed by investigating the relations between the conditional probabilities, p({αi}p,{αi}s|{nj}) and p({αi}p|{nj};{αi}s).
Nonlinear Filtering Applied to Single-view Backpropagated Images of Strongly Scattering Objects
Authors: Morris J. B. , Fiddy M.A.
Published: February 2023

In this paper, we are concerned with characterizing the internal structure of 2D strongly scattering objects, using a single illumination direction or view and constant wavenumber k0 = 2π / λ0. The object is illuminated with the plane wave
eik0r^
i
⋅r and simulated scattered far-fields are calculated on a circular aperture in the plane of the object's cross section. A differential cepstral filter is applied to a single-view backpropagated image which relates to the product of the scattering potential and the total field. This nonlinear filter avoids the phase wrapping problems associated with homomorphic filtering, and is used to isolate the scattering potential from single-view backpropagated images.
Phase Retrieval for Icosahedral Particles
Authors: Millane R. P. , Stroud W. J.
Published: February 2023

X-ray crystallography is a technique for determining the structures of molecules [1,2]. It involves irradiating a crystalline specimen of the molecule with a monochromatic beam of x-rays and measuring the resulting diffraction pattern. The complex amplitude of the diffracted x-rays is equal to the Fourier transform of the electron density in the crystalline specimen, and only the intensity, but not the phase, of the diffracted x-rays can be measured. Reconstruction of the electron density therefore constitutes a phase problem.
Phase retrieval and time-frequency methods in the measurement of ultrasnort laser pulses
Authors: DeLong Kenneth W. , Fittinghoff David N. , Ladera Celso L. , Trebino Rick
Published: February 2023

The recovery of an optical field with respect to position when only the intensity can be measured is an important problem in image science. In this case a priori information in the form of constraints can be applied and advantage can be taken of the inherently two-dimensional nature of the problem in order to reconstruct the full complex field from the available information. A similar recovery problem also arises with temporally varying data. One such case is the measurement of the complete time-dependent intensity and phase of an ultrashort laser pulse. This problem is particularly difficult for two reasons. First, it is inherently one-dimensional, so phase-retrieval methods, so successful for the spatial problem, do not directly apply. Second, such pulses are shorter than all possible measuring devices, so even the intensity cannot be measured. Traditionally, optical scientists working with ultrashort laser pulses have had only partial diagnostics, typically the intensity autocorrelation and the spectral intensity of the pulse. These diagnostics are not enough to completely characterize the laser pulse.
Photonic band gap design based on inverse scattering techniques
Authors: Pommet Drew A. , Malley L. , Fiddy M.A.
Published: February 2023

The inverse problem is particularly important for device and application development. For non-periodic media, approximations can be made which allow estimates of the scattering permittivity distribution to be found. Our own work over the last 15 years [1,2,3] has moved from trying to interpret the most restrictive yet computationally simple of these approximations, the linearizing first Born and Rytov approximations, to the development of techniques which can be applied to both strongly scattering media as well as nonlinear (e.g. χ3) structures. We have also applied these methods to real experimental data as well as simulated cases, as such work has wide ranging uses in fields as diverse as medical and geophyiscal imaging, as well as the design of optical components. Emerging from these studies is a clearer understanding as to how the differential cepstral method (see paper by Morris et al in this volume and [4]) and distorted wave methods can be integrated in order to synthesize structures which are both strongly scattering and which have prescribed optically controllable scattering patterns. The differential cepstral filtering technique processes the function recovered by Fourier inversion of far-field scattering data, recognizing that it represents the product of the permittivity distribution and the total field within the scattering volume. This filtering method can be applied to scattering structures of arbitrarily high permittivity, in principle.
Star-Light Suppression with a rotating Rotational-Shearing Interferometer for Extra-Solar Planet Detection
Authors: Scholl Marija S.
Published: February 2023

Star light, scattered from even most smoothly polished optical surfaces, prevents detection of a faint planet light because of the enormous brightness ratio between them. Figure 1 shows two point sources: a dark (Earth-like) planet rotates slowly around a bright star. At the time of observation the planet is assumed to be on x-axis. The wavefronts originating from the star and the planet, respectively, are incident on the aperture at a distant observation plane as plane waves with the propagation vector parallel to the optical axis and tilted with the direction cosine vector (1, 0, n).
Optimizing Iterative Noise Removal and Deconvolution by Simulation
Authors: Leclere James H. , Amini Abolfazl M. , Ioup George E. , Ioup Juliette W.
Published: February 2023

Optimization of iterative noise removal and deconvolution establishes the number of iterations needed. One approach to optimization utilizes statistical analysis of numerous trials on noise-added signals. Fixing approximately the signal-to-noise ratio (SNR) for each set of trials makes possible the determination of iteration number and expected error versus SNR as well as the statistical standard deviation of these quantities. The advantage of this approach is that it allows 1) any computer-generated noise type, 2) any criterion for optimization which is calculable, and 3) the use of nonlinear constraints. Analytic approaches to optimization do not in general allow this flexibility. Since nonlinear constraints such as nonnegativity are often the key to superresolution, the ability to perform this type of optimization is quite important. Details concerning the simulations are addressed, including stopping criteria when the rate of change in the optimization measure is very slow. Although minimization of the mean squared error and absolute error have been the main criteria examined thus far in the work because of their current pervasiveness, a number of criteria, especially those related to resolution, may be more appropriate for many data types and goals.
Comparative Analysis of Image Registration Techniques in Sheared Beam Imaging
Authors: Olson David F. , Landesman Barbara T. , Pierson Robert E.
Published: February 2023

The recovered object in sheared beam imaging is an accumulated average of instantaneous "speckled" image frames. Atmospheric perturbations cause a random tilt in the phase of the return speckle pattern. This tilt induces a random translation in each reconstructed image. This random misregistration of individual frames with respect to each other degrades image quality by blurring the average resultant image.
Multiframe Blind Deconvolution for Object and PSF Recovery for Astronomical Imaging
Authors: Christou Julian C. , Hege E. Keith , Jefferies Stuart M.
Published: February 2023

Ground-based imaging of astronomical objects typically requires some form of post-processing to realize the full information content in the recorded image. The recorded image can be expressed as which is the standard expression for incoherent imaging in the absence of noise.
i(r→) is the measured target,
o(r→) is the true object distribution,
p(r→) represents the point spread function (PSF) of the optical system, and * denotes the convolution operation. Thus, when the PSF is known, inversion of this expression will yield the object distribution. However, in many cases, the PSF is either poorly determined or unknown. Thus standard deconvolution techniques cannot be applied.
Bispectral Imaging on Adaptive Optics Compensated Data
Authors: Negrete-Regagnon P. , Drummond J. , Fugate R. Q. , Gonglewski J. , Wooder N. J. , Dainty J. C.
Published: February 2023

The release of military technology in the adaptive optics (AO) and laser beacons fields [1] motivated the astronomical community to become actively involved in its implementation in astronomical sites all around the world. Unfortunately, even with the impressive gain in resolution these systems provide, high-resolution imaging from ground-based telescopes is still far from ideal. Traditional speckle interferometry techniques and post-processing data reduction are probably the only viable way to obtain approximated diffraction-limited images. This work describes the application of a posteriori processing to both AO compensated and uncompensated data and shows the improvement that can be achieved.
Massively Parallel Spatially-Variant Maximum Likelihood Image Restoration
Authors: Boden A.F. , Redding D.C.
Published: February 2023

We consider a massively parallel implementation of Richardson-Lucy or maximum likelihood restoration with a spatially-variant point spread function (PSF). Richardson-Lucy iterates involve the computation of sums of the form: where O(x'
q
) is the incident optical field estimate at discrete source location x'
q
, I(x
q
) is the measured discrete image at discrete field location x
q
, and P(x
q
, x'
q
) is the discrete PSF – the probability that a photon from source region x'
q
is incident on the detector at field region x
q
. In general P is a function of source and field coordinates, and the computational burden of Eq. 1 is intractably large.
Phase Retrieval with an Opacity Constraint
Authors: Paxman Richard G. , Fienup James R. , Seldin John H. , Marron Joseph C.
Published: February 2023

We are investigating a novel 3-D imaging modality called Phase Retrieval with an Opacity Constraint for LAser IMaging (PROCLAIM) [1]. PROCLAIM data are collected by illuminating a 3-D object with a laser and making angle-angle intensity measurements of the reflected speckle pattern in the far field. A separate angle-angle intensity measurement is made for each of several laser frequencies. Properly formatted, these data represent samples of the 3-D Fourier intensity (square of the Fourier magnitude) of the illuminated object [2]. A 3-D FFT would give the 3-D autocorrelation of the object. In order to recover a 3-D image we must apply a phase-retrieval algorithm.
Inverse problems in reflection seismology
Authors: Claerbout Jon
Published: February 2023

The international oil industry spends about $4 billion/year acquiring
reflection seismic data. A large survey collects a terabyte
(1012) of data which is computer processed to a pixel
volume of (103)3 = 109 bytes. At sea
the energy source is usually an air gun while on land, the source is
mostly buried dynamite, and sometimes, multiple trucks carrying sweep-
frequency ground vibrators. At sea, a shot is fired every 10 seconds;
echos are recorded along 6 km cables at about a thousand locations,
each channel recording a signal of about 2000 floating point values. A
typical marine survey contract whose result is shown in Figure 1,
lasts a month or more and costs upward of $10M.
Variable damping in seismic tomography based on ray coverage
Authors: Nowack Robert L.
Published: February 2023

In the seismic tomography problem, the subsurface slowness distribution is estimated from the travel-times computed along generally curved rays. For a dense and uniform set of rays, the slowness distribution will be correctly reconstructed. However, for an uneven distribution of rays, the estimated slowness distribution may be influenced by the ray configuration.
Material characterization via phaseless tomography : numerical results in phase retrieval
Authors: Pierri R. , Leone G. , Bernini R.
Published: February 2023

The diffraction tomography is a new method in which the complex
permittivity profile of an object is reconstructed using algorithms
that require the knowledge of both the amplitude and the phase of the
scattered field [1-2]. However the difficulty of
obtaining the phase of the scattered field at optical frequencies has
limited the practical applications of diffraction tomography.
Signal Recovery in the Measurement of Ultrashort Laser Pulses—Recent Progress
Authors: Trebino Rick , Krumbügel Marco A.
Published: February 2023

Because ultrashort laser pulses (as short as 10-14 seconds) are the shortest technological events ever created, their measurement remained a frustrating endeavor for many years. In order to measure an event in time, one generally requires a shorter event—which did not exist.
Regularized blind deconvolution
Authors: Lane R.G. , Johnston R. A. , Irwan R. , Connolly T.J.
Published: February 2023

Blind deconvolution is an important problem that arises in many fields of research. It is of particular relevance to imaging through turbulence where the point spread function can only be modelled statistically, and direct measurement may be difficult. We describe this problem by a noisy convolution, where f(x, y) represents the true image, h(x, y) the instantaneous atmospheric blurring, g(x, y) the noise free data and n(x, y) is the noise present on the detected image. We use to denote an estimate of these quantities and our objective is to recover both f(x, y) and h(x, y) from the observed data d(x, y).
A Method for Image Restoration and Wavefront Sensing by Using Phase Diversity
Authors: Bucci O. M. , Capozzoli A. , D’Elia G.
Published: February 2023

Cleaning the distortions of an unknown image due to an unknown
spatially invariant point spread function (PSF) is a problem of
particular interest for optical systems, like telescopes, wherein the
radiation from the object passes trough a medium in turbulent motion.
The aim of this paper is to present a stable method, based on the
approach presented in [1] for the case of coherent radiation, which is
able to estimate both the optical path disturbance (OPD) and the
unknown object from noisy and incoherent multiple images, in absence
of a reference source. The presented technique, at variance of other
existing methods, [2-3], is able to take explicitly into account the
measurement errors and noise without requiring any hypothesis on their
statistical nature. The stability of the method is ensured by
exploiting both a physical constraint on the OPD and a stabilizing
functional.
Microscope image reconstruction
Authors: Sheppard CJR
Published: February 2023

In brightfield, phase-contrast or polarization microscopy, the image can be modeled by using scattering theory. The object, consisting of spatial variations in complex refractive index, scatters components of an angular spectrum of plane waves, and the image calculated by integration over incident and scattered waves. This approach takes into account the high aperture effects, important in microscope imaging. Rigorous methods can be used to calculate the scattering by the object.1 However, these methods, in addition to being in general very computationally intensive, result in the disadvantges that it is difficult to see trends in the behaviour and usually impracticable to reconstruct the object from the image data.
Adaptive Protein Structure Refinement Using Diffraction Data
Authors: Grothe Rob
Published: February 2023

X-ray crystallography remains the primary technique for discovering the arrangement of a protein’s atoms in space. If this arrangement is given by a vector of atom positions r = (r
1
,r
2
,…,r
N
), then the resulting structure factor F(r)(S) in direction S is given by where F
a
(
i
) is the atomic scattering function of a(i) ∈ {“Carbon", “Nitrogen", “Hydrogen",…}, the atom type of the ith atom. F
a
(
i
) is the Fourier transform of ρ
a
(i), the spherical electron density for an atom of type a(i) placed at the origin.
Bayesian Image Reconstruction in X-ray Fiber Diffraction
Authors: Baskaran Shyamsunder , Millane R. P.
Published: February 2023

The structure completion problem in x-ray fiber diffraction analysis, a crystallographic method for studying polymer structures, involves reconstructing an incomplete image from a known part and experimental data in the form of the squared amplitudes of the Fourier coefficients. Formulating this as a Bayesian estimation problem allows explicit expressions for MMSE and MAP estimates to be obtained. Calculations using simulated fiber diffraction data show that the MMSE estimate out- performs current methods that correspond to certain MAP estimates.
Techniques for Signal Synthesis in Microlithography and Diffractive Optics
Authors: Saleh Bahaa E. A.
Published: February 2023

This paper is an overview of mathematical techniques for finding images whose transforms satisfy equality and/or inequality constraints. Applications include microlithography, diffractive optics, and holography.
Numerical optimization of diffractive optical elements for planar-integrated free-space optics
Authors: Testorf Markus , Fiddy Michael A.
Published: February 2023

Planar-integrated free-space optics1,2 is a promising scheme to integrate large scale optical systems into a thick transparent substrate of plane-parallel geometry. For this approach all optical elements are located on the surfaces of the substrate (Fig. 1). Light signals propagate along a folded optical axis. All elements of the entire optical system form a two dimensional structure. This makes planar-integrated optics compatible with micro-electronics and allows, for instance, the fabrication of the system as a single diffractive optical surface relief by use of standard photo-lithographic techniques.
Triple Correlation Waves
Authors: Lohmann Adolf W. , Mendlovic David , Shabtay Gal
Published: February 2023

“A wave is something that obeys the wave equation”. In the spirit of this statement, the triple correlation is indeed a wave. We will derive now this wave Then we will study the properties of triple correlation waves, and finally we will contemplate about application.
Properties of superresolution by data inversion for objects with finite support
Authors: Matson Charles L. , Tyler David W.
Published: February 2023

Several properties of superresolution achieved by data inversion for objects with finite support are given, including the biases in the Fourier domain and the spatial dependence of the increased resolution in the image.
Microchip lasers and applications*
Authors: Zayhowski J.J. , Sanchez A. , Fan T.Y.
Published: February 2023

Microchip lasers are small solid-state lasers characterized by short resonator lengths (~1 mm) and monolithic flat-flat cavities. The first feature enables solid-state lasers operating in new performance regimes while the second attribute allows inexpensive fabrication of the devices in robust packages. In the simplest of these devices, cw lasers, the laser is fabricated by polishing a wafer of gain medium with surfaces that are flat and parallel with a thickness of the desired resonator length. Resonator mirrors are deposited on the polished faces to form the cavity and then the wafer is diced. Devices with more functionality are fabricated by using two wafers to form the laser, one of which can be an electro-optic material or a saturable absorber material, that are bonded together. Frequency-modulated (>1.3-GHz modulation bandwidth) and Q-switched lasers (220-ps-long pulses with passive Q-switching) have been demonstrated using these techniques.
Diode-Pumped Passively Q-switched Nd: YLF 1.053μm Laser by Using Cr4+:YAG as a Saturable Absorber
Authors: Kim Dalwoo , Hu Wentao
Published: February 2023

Q-switching of the solid-state lasers is important because it provides short duration optical pulses required for laser ranging, nonlinear studies, medicine, and other important applications. The method chosen to switch the Q of the laser cavity greatly influences the size and complexity of the system. Passive Q-switch employing a solid-state saturable absorber is economical, simple and practical. Recently, tetravalent-chromium doped crystals such as Cr4+:YAG, Cr4+:GSGG, Cr4+:Mg2SiO4 and Cr4+:YSGG have been developed, some of them can replace conventional color-center crystals as the saturable absorbers for neodymium lasers.1-4 Unlike the F2- center in LiF crystal, Cr4+ in these crystalline hosts is formed in the specific growth process, therefore it has better long-term stability.
Recent Progress of Electro-optic Polymers for Device Applications
Authors: Jen Alex K-Y. , Hsu Ching-Fong
Published: February 2023

Electro-optic (E-O) polymers have drawn great interests in recent years because of their potential applications in photonics devices such as electro-optic modulators and switches, optical data storage and information processing1-2. Recent interests have been focused on the design and development of polymeric material systems (active and passive) with large E-O coefficients and high thermal, temporal, chemical and phtochemical stability3-8. The E-O response of a active polymer commonly arises from the electric field induced alignment of its second-order nonlinear optical (NLO) chromophore, either doped as a guest/host system or covalently bonded as a side-chain. Because of the strong interaction among the electric dipoles, the poled structure is in a meta-stable state; the poled NLO chromophores which possess large dipole moment will tend to relax back to the randomly oriented state. As a result, the stability of the poled structure strongly depends on the rigidity of the overall material system. This paper provides a brief review of the latest developments of highly efficient and thermally stable chromophores and polymers for device applications.
Comparison of pulsed laser operation of 1.5% thulium doped YAG and YLF at 2.3 μm
Authors: Sudesh V. , Piper J. A.
Published: February 2023

Tunable laser action at 2.3 μm is of great interest for chemical detection and remote sensing. A laser at this wavelength based on the 3H4 - 3H5 Tm3+ transition has been demonstrated in several garnet1-2 and fluoride hosts3-4. In this paper we report on comparison of laser performance of 1.5 atomic % Tm:YLF and 1.5 atomic % Tm:YAG laser crystals. Output energies of over 1 mJ at 5 Hz have been achieved and slope efficiencies of 18% and 14% were measured relative to absorbed pump power for the YLF and YAG crystals respectively.
Solid-state lasers for ultrashort pulse generation
Authors: Keller Ursula
Published: February 2023

Intracavity semiconductor saturable absorber mirrors (SESAMs) [1,2] provide a versatile and effective tool for simple, reliable, self-starting, passively mode-locked or Q-switched solid-states lasers, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10fs. This talk reviews the design requirements of SESAMs for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAMs provide sufficient design freedom to choose key paramaters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g. 1 μm neodymium transitions) [1].
Ti-doped sapphire with high concentration
Authors: Deng Peizhen
Published: February 2023

Solid state tunable laser crystal is a considerable well ultra-fast laser medium according to the uncertainty principle, and also an ideal high power laser amplifier medium due to its excellent thermal and mechanical properties. Thus, the laser will give widespread use in scientific field, such as spectroscopy and photo-chemistry studies, and important practical applications, such as remote sensing, pollution detecting, isotope separation, and inertia confinement fusion laser driver, etc.
High Repetition Rate LDP-SHG Nd:YAG Laser
Authors: Sheng W.D. , Li X.F. , Liu H.W. , Fang X.J. , Yao J.Q.
Published: February 2023

The second harmonic of Nd:YAG laser with short output wavelengths is interesting for applications in optical data storage and laser-printer technology. High repetition rate green laser source also can be used to high speed scanning imaging and pumping tunable laser. Intracavity doubling in diode-pumped solid state lasers seem to be a promising approach for frequency doubling. One advantage with this configuration is that the difficulties with the narrow acceptance bandwidth of the nonlinear material can be half than in external frequency doubling.
Solid State UV Laser and Its Application in Electronic Packaging
Authors: Sun Yunlong , Swenson Ed
Published: February 2023

Traditional mechanical drilling for making vias in a variety of dielectric materials, such as RF4, polimide, etc. and copper sheet are good for the via diameter greater than 200 micron.
Properties of 20-Hz eye-safe cascade Raman laser with Ba(NO3)2 crystal
Authors: Takei N. , Mori T. , Kannari F. , Yamaguchi S. , Hara H. , Krayushkin S.V.
Published: February 2023

Recently, lasers operating in the eye-safe wavelength around 1.5 μm have found increasing demand in the laser radar (LIDAR). Raman laser pumped by well established lasers such as Nd:YAG lasers is a favorable candidate with such characteristics at high repetition rate, narrow linewidth, and good beam quality.1 As the Raman conversion medium, a Ba(NO3)2 crystal has attracted much attention because of its high gain and strong mechanical properties.2 Laser output in the eye-safe wavelength region can be obtained with the Ba(NO3)2 crystal either in a first Stokes line pumped by 1.3 μm Nd:YAG laser2, or in a third Stokes line pumped by 1.06 μm Nd:YAG laser3. When the Raman crystal exhibits substantial residual absorption in the pump or Stokes wavelength, these solid-state Raman lasers require some thermal management to scale up to high average power systems such as in LIDAR. Hence, we experimentally studied the thermal characteristics of the Ba(NO3)2 cascade Raman conversion process.
Recent developments of NLO crystals in the visible and ultraviolet regions
Authors: Chen Chuangtian
Published: February 2023

With the development of all-solid state laser systems for the green, blue and even UV coherent beams, there are extensive needs for NLO crystals which can perform harmonic generation in these regions. It may be for this promotion in recent years that great efforts have been made to successfully improve optical properties and quality of the existed NLO crystals (KTP, BBO and LBO), along with development of new generation of NLO crystals, for the UV region in particular. It is of interest to note that All these research works till now are almost concentrated in the Pacific rim area.
X-Ray scattering from grazing incidence telescopes
Authors: Aschenbach Bernd
Published: February 2023

For almost 30 years grazing incidence telescopes for astronomical observations have been developed and matured to low scattering performance. A culmination point was reached with the launch of the X-ray astronomy satellite ROSAT, which is in operation since 2 years. ROSAT carries two grazing incidence telescopes covering the XUV (~50 - 750Å) and the soft X-ray (~5 - 120Å) spectral regions, separately. The Wolter type I X-ray telescope consists of 4 nested mirror pairs with a maximum aperture of 835mm and 2.4m focal length, characterized by a half energy width of <4 arcsec and extremely low scattering wings due to the superb mirror surface microroughness of <2.8Å. The point spread function, which has been measured on ground in a 130m long beam test facility prior to launch, will be compared with the performance obtained in orbit. Future grazing incidence X-ray telescopes aim at improved angular resolution, larger collecting area and broader spectral coverage. This is pursued in various projects including SAX, BBXRT, ASTRO-D, Spectrum-X, SOHO-CDS, AXAF and XMM, requiring new fabrication techniques and metrology.
Wavelength and Angular Dependence of Light Scattering From Beryllium: Comparison of Theory and Experiment
Authors: Elson J. Merle , Bennett Jean M. , Stover John C.
Published: February 2023

Beryllium optical components have been shown to have scattering characteristics considerably different from other metals such as aluminum or silver. The wavelength and angular dependence of light scattered from a beryllium surface partially overcoated with aluminum have been studied both theoretically and experimentally. The aluminum overcoating preserves the topography of the beryllium but provides different optical constants. By measuring scattering on both halves of the sample, the effects of topographic roughness and optical constants can be separated. Topographic roughness has been measured with a mechanical stylus profiler which is insensitive to the optical constants of the material. A dual-source scattering theory is used to model the surface as having both roughness and dielectric perturbations. Attention is given to both p- and s-polarization in the incident and scattered light at visible and infrared wavelengths.
High-Gain FELs for Short Wavelength
Authors: Pellegrini C.
Published: February 2023

We discuss the high gain regime of a FEL, the transition from spontaneous to stimulated emission, and its application to the production of short wavelength radiation, λ < 100nm. We will first review the different operation modes of a FEL: oscillator, self-amplified spontaneous emission and Transverse Optical Klystron. We will then discuss in more detail the self-amplified spontaneous emission , the characteristics of the radiation that can be produced in this mode and its possible advantages respect to an oscillator or a TOK.
X-Ray Optics in the USSR: X-Ray Bragg Fourier Optics
Authors: Aristov V. V. , Erko A. I.
Published: February 2023

Summary not available.
Laser-Synchrotron Studies of UV-Photon-Stimulated Desorption in Alkali Halide Crystals
Authors: Haglund Richard F. , Tolk Norman H.
Published: February 2023

Desorption Induced by Electronic Transitions (DIET) is a primary mechanism through which energy deposited by electrons and photons in the surfaces of ionic insulators is dissipated.1 Studies of Photon-Stimulated Desorption (PSD) at ultraviolet wavelengths are important from a fundamental point of view because photons deposit energy but not free charge in dielectric materials. PSD also has practical consequences in problems as diverse as optical damage in high-power lasers, non-destructive surface analysis and uv photolithography.
Review of the X-Ray Laser Program at Princeton University
Authors: Suckewer S.
Published: February 2023

The development of the soft x-ray laser program at Princeton is presented with emphasis on the recent results of measurements of stimulated emission of the C vi 182-Å line in a confined plasma column. A new approach using multiphoton excitation of confined ions is also discussed.
Soft X-Ray Pumping of Inner-Shell Excited Levels for Extreme Ultraviolet Lasers
Authors: Caro R. G. , Wisoff P. J. K. , Yin G. Y. , Walker D. J. , Sher M. H. , Barty C. P. J. , Young J. F. , Harris S. E.
Published: February 2023

When a 1.06 μm laser beam is focused onto a high-Z target at intensities of 1012 - 1014 W cm-2, a plasma is formed from which a burst of soft x-rays is emitted with a conversion efficiency in excess of 10%. This burst of x-rays can be used as an x-ray flashlamp to pump potential extreme ultraviolet (XUV) laser systems.1,2
Multi-Quantum Processes at High-Field Strength
Authors: Rhodes C. K.
Published: February 2023

Subpicosecond ultraviolet laser technology1 permits the exploration of nonlinear atomic interactions up to electric field strengths far in excess of an atomic unit
(e/ao2). Currently, peak intensities in the range of 1016 to 1017 W/cm have been produced with pulses having a duration of a few picoseconds at a wavelength of 193 nm. At this intensity, the electric field Eo is comparable to an atomic unit. Furthermore, it has been shown that technical advances in femtosecond2 ultraviolet laser technology will enable peak intensities, for coherent energy, to be produced in the range of 1020 - 1021 W/cm2. This would represent a radiation field amplitude of about 100Eo and, in terms of energy density, would be equivalent to that produced by a black-body with a temperature close to 10 keV, an environment characteristic of thermonuclear sources.
On the Theory of Multiphoton Ionization of Atoms
Authors: Szőke Abraham
Published: February 2023

A simple, "exactly solvable" atomic model will be presented that helps to discuss some of the interesting features of multiphoton ionization of atoms. The electromagnetic field is treated non-perturbatively, it can be strong. The atomic electrons are assumed to be non-interacting (Hartree model). They are bound in a harmonic oscillator potential (one- or three-dimensional). At the ionization energy, the potential is cut off and the free electron has no Coulomb attraction. The Schrodinger equation has exact analytic solutions valid in the inner or outer regions. If the field is turned on adiabatically, the exact solution can be found by matching these solutions at the boundary; both of their value and the normal derivative at all times. Thus the machine calculation reduces to repeated application of fast Fourier transforms and to the solution of linear equations (unfortunately a lot of them).
Extreme Ultraviolet Multilayer Reflectors*
Authors: Scott Marion L. , Arendt Paul N. , Cameron Bernard , Newnam Brian E. , Windt David , Cash Webster
Published: February 2023

We are investigating the design and fabrication of multilayers of various materials to be used as reflectors in the extreme ultraviolet wavelength range. The reflectance versus angle of incidence (10° to 85° from normal) has been measured for a multilayer of silver and silicon at 58.4 nm. We have discovered that contamination layers on the surface of these multilayers can cause significant degradation in their performance. Optical constants for silver from two references were quite different at this wavelength and our measurements have resolved this discrepancy in favor of one of the published values. The absorption coefficient for silicon was found to be somewhat higher than the published value at 58.4 nm. These reflectors could be utilized as polarizing components at this wavelength if the angle of incidence is approximately 40°.
High-Order Harmonics in Light Scattering by Atomic Electrons Above Threshold
Authors: Eberly J. H. , Su Q. , Javanainen J.
Published: February 2023

We report on light scattering in multiphoton ionization (MPI) computer experiments at high laser intensity. The plateau and cut-off features recently reported in laboratory experiments on high-order harmonic generation by McPherson, et al., and by Ferray, et al., are corroborated. We report scattered light spectra in four different cases and exhibit the corresponding ATI photoelectron spectra. We propose a connection between ATI and high-order harmonics.
Diffraction Contrast of a Bragg-Fresnel Lens in White and Monochromatic Radiation
Authors: Aristov V. V. , Basov Yu. A. , Frahm R. , Graeff W. , Materlik G. , Snigirev A. A.
Published: February 2023

Recent advances in the studies of x-ray diffraction phenomena and the technology of structures with elements up to hundreds of angstroms in size open up possibilities for fabrication of effective x-ray focusing elements with three-dimensional Fresnel zone structures, namely, Bragg-Fresnel lenses (BFL) [1-4]. BFL differs favourably from the Fresnel zone plate by the absence of chromatic aberrations which is due to the high spectral selectivity of Bragg reflection, Δλ/λ~10–4 ÷10–5. This enables observation of focusing [5] and image transmission [6-7] in the white spectrum of synchrotron radiation (SR).
Quantum-Mechanical Interference in Four-Wave Mixing
Authors: Chappie P. B. , Baldwin K. G. H. , Bachor H.-A.
Published: February 2023

Interference between two different quantum-mechanical pathways for 4 wave mixing in sodium vapor has been observed. The 4 wave mixing was enhanced by 2-photon resonance with the 5s state, for one pathway, and the 4d state, for the other. The phase of the interference could be varied continuously by varying laser frequencies, and constructive and destructive interference effects were studied. A model based on third-order perturbation theory gives a good description of the features observed.
Transversely Optically Pumped Ultraviolet Laser in the Range of 330-390 nm
Authors: Yu Junhua , Sun Shangwen , Cheng Yongkang , Tang Chen , Ma Zuguang
Published: February 2023

A series of six laser lines at 330-390 nm on the
B3∑x−→X3∑y− transition in sulfur dimer vapor transversely-pumped by a XeCl laser at 308.1nm was first observed and the corresponding absorption coefficient and snail signal gain coefficient were measured. The mean gain is about 0.30 cm-1.
Narrowband Tunable VUV/XUV Radiation Generated by Frequency Mixing of Pulsed and CW Laserradiation
Authors: Hilber G. , Lago A. , Wallenstein R.
Published: February 2023

Four- and six-wave mixing of pulsed and cw laser radiation in gases generates coherent radiation in the spectral region of the VUV/XUV at 60 - 200 nm.1 Recently considerable experimental progress has been achieved towards the development of powerful coherent VUV/XUV light sources based on these nonlinear optical methods.
X-Ray Laser Related Experiments and Theory at Princeton
Authors: Suckewer S.
Published: February 2023

This paper describes a new system for the development of an X-ray laser in the wavelength region from 5 nm to 1 nm utilizing a Powerful Sub-Picosecond Laser (PP-Laser) of expected peak power up to 0.5 TW in a 300 fsec pulse. Soft X-ray spectra generated by the interaction of the PP-Laser beam with different targets are presented and compared to the spectra generated by a much less intense laser beam (20-30 GW). A theoretical model for the interaction of atoms with such a strong laser EM field is also briefly discussed. The development of additional amplifiers for the recombining soft X-ray laser and the design of a cavity are presented from the point of view of applications for X-ray microscopy and microlithography. The overview ends with the presentation of recent results on the quenching of spontaneous emission radiation and its possible effect on the absolute intensity calibration of soft X-ray spectrometers.
Ne-Like Ion X-Ray Laser Experiments in Plasmas Produced by 0.53-μm and 035-μm Laser Light
Authors: Keane C. J. , Bourgade J. L. , Combis P. , London R. A. , Louis-Jacquet M. , MacGowan B. J. , Matthews D. L. , Naccache D. , Peyrusse O. , Rosen M. D. , Thiell G. , Whitten B.
Published: February 2023

Recent Ne-like ion x-ray laser experiments carried out at the Centre d'Etudes de Limeil-Valenton (CEL-V) with both 0.53-μm and 0.35-μm laser light will be described. This paper will concentrate primarily on the observation of amplification in Ne-like Sr (Z=38) in plasmas produced by 0.53-μm laser light. Small signal gains of 4.4 cm-1 and 4.0 cm-1 have been measured for the Ne-like Sr J=2-1 transitions at 164.1 and 166.5 Å, respectively. In addition, the effects of pumping the Ne-like Se laser with 0.35-μm light have been investigated. The resulting Se spectra do not differ significantly from those observed with 0.53-μm light. A brief summary of other experiments carried out at CEL-V will also be given.
X-ray holography using photoresists
Authors: Jacobsen C. , Lindaas S. , Howells M.
Published: February 2023

We have recorded 56 nm resolution Gabor holograms of biological specimens using photoresist detectors and 1.8-3.6 nm x-rays from an undulator source. With this technique, we are able to obtain high image resolution without the use of x-ray lenses; the resolution limit of the photoresist PMMA is thought to be in the 5-10 nm range. The technique also makes good use of partially coherent or multimode sources; monochromaticity requirements are eased compared to longer focal length zone-plate based scanning x-ray microscopes, and multiple spatially coherent modes can be used to record a hologram of a large field (although the image resolution will be limited by the width of one mode). Since the image is focussed in the reconstruction stage, the specimen alignment requirements are non-demanding. Judging from the survivability of photoresist exposures obtained using laser plasma x-ray sources, our current scheme may be compatible with flash exposures with x-ray lasers as they become available.
Coulomb Explosions of Molecular Iodine With Ultrashort Pulses
Authors: Beaudoin Y. , Strickland D. , Corkum P.B.
Published: February 2023

Femtosecond pulses offer the possibility of producing and studying highly transient molecular species. We report the formation of highly charged molecules that are nearly instantly produced with a nuclear separation of the uncharged precursor. We have chosen iodine since the atoms are massive, the vibrational period in the ground electronic state is low, and the equilibrium internuclear separation is large.
Calculations of High Intensity Multiphoton Ionization and Photoemission from Atoms*
Authors: Kulander K. C. , Schafer K. J. , Krause J. L.
Published: February 2023

A surprising array of effects have been observed during high-intensity, short-pulse laser excitation of atoms and molecules. To model these measurements, methods have been developed to solve the time-dependent Schrödinger equation for an atom in a time varying, classical electromagnetic field. Studies on many atomic and molecular systems have been performed over a range of intensities from the regime within which perturbative techniques are valid up to field strengths well above an atomic unit (I > 3.51x1016 W/cm2). These calculations have provided predictions for ionization rates, photoelectron energy and angular distributions and photoemission rates. The effects of ac Stark shifted and intensity broadened intermediate states on the emission processes have been investigated. At high frequency and the highest intensities atoms are found to undergo a transition to a state or states which are surprisingly stable with respect to ionization. This had been predicted using a Floquet approach which did not allow for the time variation of the pulse envelope. The time-dependent calculations, however, show that an appreciable fraction of the electronic wave function can survive the rapid rise of an intense pulse and become stabilized with a greatly reduced ionization rate. Here we present a discussion of some of the most recent results.
Harmonic Generation by an Intense Picosecond Laser in an Underdense Plasma
Authors: Umstadter D. , Liu X. , Coe J.S. , Chien C.Y. , Esarey E. , Sprangle P.
Published: February 2023

Modest power lasers interacting with a neutral gas have been observed to produce coherent harmonic radiation (up to the 61
st
harmonic) at odd multiples of the fundamental laser frequency[1]. This is a result of the laser field causing the bound electrons to oscillate in the anharmonic atomic potential. The process is limited to relatively low powers since increasing the fundamental laser power leads to ionization of the gas and to the production of unbound electrons. A very high-power laser interacting with a fully ionized plasma, however, may lead to the generation of large levels of coherent radiation at high harmonics (including even harmonics) of the incident laser frequency based on an entirely new mechanism. If the laser pulse is sufficiently intense, the plasma electron mass becomes modulated because of nonlinear relativistic effects [2]. We describe in this paper the theory and some experiments in which we observe signatures of this mechanism.
X-Ray Spectral Determination of Electron Density in Dense Laser-Excited Targets*
Authors: Luk T. S. , McPherson  , Tate D. , Boyer K. , Rhodes C. K. , Jacobs V. L. , Burkhalter P. G. , Zigler A. , Newman D. A. , Nagel D. J.
Published: February 2023

Plasmas produced by subpicosecond laser excitation of solid targets can produce bright short x-ray pulses[1] for x-ray laser pumping[2]. This type of plasma is unusual because it is hot (electron temperature in keV range), dense (near solid density) and highly non-equilibrium. It is particularly advantageous to use subpicosecond excitation to investigate this type of plasma, since expansion of the plasma can be quite small under this condition. Furthermore, it has been found that the prepulse associated with typical high-power ultraviolet laser systems does not Interfere with the subpicosecond excitation for ultraviolet transmitting solids, such as MgF2 and SiO2. This follows, since the intensity for appreciable absorption is roughly five orders of magnitude higher than the intensity associated with the laser prepulse. Also for laser radiation with wavelength of 248 nm, the critical density is 1.8 × 1022 cm−2, only a factor of 44 lower than the electron density of a completely stripped MgF2 solid target. Therefore, the laser radiation naturally interacts with a plasma of very high density. Finally, x-ray spectroscopy is particularly useful for diagnosing the conditions of the plasma for very short time intervals that are considerably outside of the range available for conventional streak-camera measurements. Since typical radiative lifetimes for kilovolt transitions are of the order of 100 fs, the emitted radiation can provide valuable information in the early hlgh-density phase of the plasma. In this experiment, we examine the dielectronic satellite from lithium-like ions in order to determine the electron density of the plasma.