bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Wrapping in Phase Retrieval Caused by Camera Noise
Authors: Daw Glen H. , Smith Richard C.
Published: February 2023

Phase wrapping in phase retrieval recovered wavefronts has been observed. The wavefronts used to generate the images used in the phase retrieval algorithm were very nearly flat, as confirmed by Strehl analysis of the images. Noise in the normally dark part of the image was the cause of the the phase wrapping. A modification to the phase retrieval image plane constraints allowed for recovery of the wavefront without the need to perform a phase unwrapping step. With this method reproducibility of better than 97 % was achieved.
Mediation of Ill-posedness in Multiparameter Inverse Scattering
Authors: Johnson Steven A. , Borup David T. , Wiskin James W. , Berggren Michael J.
Published: February 2023

It is advantageous to formulate the Inverse Scattering problem as a nonlinear integro-differential equation. However, intrinsic to the nature of these inverse problems is their potential for ill-posedness. We review our experience in overcoming ill-posedness of inverse scattering problems and some of the theoretical and practical results we have achieved in our pursuit of numerically efficient and robust algorithms, i.e. fast algorithms that also mediate the ill-posed nature of some inverse problems. This is commensurate with the stated goal of the Center for Inverse Problems, Imaging, and Tomography, which is the development of imaging algorithms that produce quantitative maps of material parameters. The incident (electromagnetic or acoustic) energy is diffracting in the cases we study, so that standard Computed Tomographic (CT) algorithms are inadequate for the kind of resolution required for quantitative maps. The need to solve the wave equation exactly, dramatically increases the complexity of the inversion problem.
Coherent Laser Radar and Array Imaging
Authors: Anderson Richard , Boger James K. , Voelz David
Published: February 2023

In the research laboratory the imaging of a target on a detector array using heterodyne detection techniques1 was performed. The targets were both transmissive and reflective and good results were obtained for both types of targets. Figure 1 is a sketch of a typical experimental set up for a reflective target. A motorized precision rotatable mount held the target so motion was possible. The half waveplate in the local oscillator arm rotated this field's plane of polarization by 90° so only the field components in the plane of the page would interfere also the polarizer before the detector selected this state of polarization. Both the frequencies of the L0 and signal beams were shifted by acousto-optic modulators. A 64×64 element array of the camera was used to record the intensity pattern. The target was moved using a stepping motor so at each sampling interval the target was at rest and the data at each element of the camera was sampled 10 times so the intermediate frequency waveform was recovered. In a given sampling period at least 10 or more different samplings were taken. This number is small but was limited by the camera and electronics. The camera frame speed was slow which restricted the intermediate frequency of the heterodyne signal to be no higher than 10 Hz.
Use of Additional Constraint Terms in Maximum A Posteriori Super Resolution
Authors: West Karen F. , Granrath Douglas J. , Lersch James R.
Published: February 2023

Super resolution algorithms derived by maximum a posteriori (MAP) estimation have been successfully applied to images of stars and other compact objects on dark backgrounds. One such algorithm, derived under the assumptions of positivity and Poisson statistics is [1] where the corresponding imaging equation is and ∗ denotes convolution, h(x) = imaging system point spread function (psf), f(x) = object, g(x) = image, and fn(x) = current estimate of object.
Experimental study for parallelization of simulated annealing applied to tomographic reconstruction of binary images
Authors: Garnero Line , Lalanne Philippe
Published: February 2023

In the early 80's, Smith and Barrett [1] have introduced Simulated Annealing techniques (SA) in the domain of tomographic image reconstruction. Since, this technique has been tested in various domains of Medical Imaging [2]-[3]. The main advantage of SA is to theoritically converge to the global minimum of a cost or energy function. In reconstruction imaging, this cost function contains two terms : one term which represents the mean squared error between the measured and estimated data, and another term, which acts as regulazrization and translates a priori information. In another approach, Geman and Geman have showed that SA converges to the Maximum A Posteriori solution in a bayesian estimation [4].
A Proposal of Generalized Analytic Reconstruction from Discrete Samples (GARDS)
Authors: Ohyama Nagaaki , Barrett Harrison H.
Published: February 2023

In both image reconstruction and restoration fields many methods have been reported or proposed so far, and they contribute a lot to the research development. Although these image processing techniques deal with continuous objects and start with discretely sampled data, there has not been developed a complete model which can well represent a continuous-discrete relation. This continuous-discrete relation means that the object space is defined as continuous, while the observation space is discrete. So, we call this relation a C-D mapping in this paper. Using this expression, it can said that conventional methods developed in image processing fields are essentially based on either C-C or D-D mapping.
Two Numerical Methods of Image Reconstruction in Diffusion Tomography
Authors: Gutman Semion , Klibanov Michael V. , Song Hua
Published: February 2023

We consider Inverse Scattering Problem (ISP) for the Diffusion Equation (1) The ISP consists in determination of either of coefficients D(x) or a(x) given function u(x,t)|∂-Ω = φ(x,t), where ∂ Ω is a boundary of a bounded domain Ω ⊂ ℝn.
Symmetry as a priori information: low-resolution reconstruction of viral structure from solution x-ray scattering data
Authors: Zheng Yibin , Doerschuk Peter C. , Johnson John E.
Published: February 2023

The so-called “small spherical viruses” are viruses with a shell of protein (the so-called “capsid”) surrounding an inner core of nucleic acid. The capsid is “crystalline” in the sense that it is constructed from many repetitions of the same polypeptides and the entire capsid is invariant under the rotational symmetries of the icosahedron. The icosahedron, as shown in Figure 1, is constructed from 20 equilateral triangles and has 60 rotational symmetries: a 5-fold axis where 5 triangles meet, a 3-fold axis through the center of each triangle, and a 2-fold axis at the midpoint of each edge between two triangles. For the viruses discussed in this paper, the outer radius of the capsid is about 140Å.
Fine-Resolution Multispectral Imaging Using Wavelength Diversity
Authors: Thelen Brian J. , Reiley Michael F. , Paxman Richard G.
Published: February 2023

Often the state or calibration of a measurement system is not known perfectly. The general concept of measurement diversity is the attempt to jointly estimate the state of the system and the object of the measurement by making multiple measurements while perturbing the state of the system in a known fashion. Phase diversity [1] is a well established example of measurement diversity. In phase diversity, the unknown phase aberrations and fine-resolution image are estimated from an in-focus and an intentionally defocused image. In this case the imaging system is perturbed by introducing a quadratic defocus term in the phase aberration.
Solar Imaging by Blind Deconvolution of Segments from Multiple frames
Authors: Miura Noriaki , Baba Naoshi , Tsumuraya Fumiaki , Sakurai Takashi
Published: February 2023

A short-exposure solar image observed on the ground is given as the convolution of a solar surface structure and an instantaneous point-spread-function (PSF) of an atmosphere-telescope system 1. Thus, one can hardly observe finer structure on the solar surface than a seeing-disk size. The iterative blind deconvolution (BD) proposed by Ayers and Dainty 2 is a powerful tool for recovering the solar image atmospherically degraded. We have proposed two BD methods based on the iterative BD methods, multiframe BD 3 and segment-image BD 4. The former method consists of the application of the iterative BD method to several frames observed at different times. In the latter method, the iterative BD method is applied to images segmented from a single frame. In this paper, we present a BD method using images segmented from multiple frames, referred to as a segmented-multiframe BD (SMBD) method, which is a fusion of the previous two methods.
Image reconstruction and isoplanatic patch measurements with phase diversity in day and night-time astronomy
Authors: Acton D. S. , Soltau D.
Published: February 2023

Phase diversity techniques use the information in the 3-D volume near the focal plane to measure the optical wavefront errors present in an imaging system. Usually, the "focal volume" is sampled by recording an image at the best focus and an additional image taken slightly out of focus. Since phase diversity techniques do not require a point source, they are well suited for making wavefront measurements from extended objects. Once the wavefront errors are determined, the OTF associated with the optical aberrations can be deconvolved from both the focused and the defocused images to make a more accurate estimation of the object.
High temporal resolution laser radar tomography for long range target identification
Authors: Dierking M. , Heitkamp F. , Barnes L.
Published: February 2023

The Air Force Electro Optics Division is pursuing advanced laser target identification technologies under its Enhanced Recognition and Sensing Ladar (ERASER) program. Long range, eyesafe target identification is of central importance in many regional operations. Building on advancements in laser sources, detectors1 and signal processing, direct detection ladar can provide ID well beyond the range of conventional imaging sensors. High temporal resolution laser radar can produce range resolved (ID) scattering profiles, which are unique to each aircraft relatively independent of target range2,3. This allows a variety of ID techniques to be applied at ranges well beyond the resolution limits of comparably sized imaging apertures. The ID profiles can be applied to automatic target recognition systems for classification and identification. However, in-class variation as well as large numbers of unclassified targets may limit these techniques. In this paper, we investigate the use of tomographic reconstruction to enhance long range identification. The reconstruction is based on compilations of ID signatures obtained at various angles due to relative target sensor motion. We describe the ladar system used to measure the ID returns of an F-4 aircraft. Based on the measured capabilities of the ERASER ladar, we use the IRMA computer model to generate sets of data consistent with the measured ladar data. Finally, we utilize the filtered back-projection method to investigate the reconstruction model data for both the ideal and limited-data cases.
Resolution improvement using sampling diversity
Authors: Granrath Douglas J.
Published: February 2023

Sampling diversity occurs under certain circumstances during multiple-frame imaging of a common object. When an undersampled sensor takes images without repeating the locations of the samples on the object, sampling diversity will occur. The undersampling causes the local phenomenon of aliasing, and small local differences between frames can be seen upon close inspection. Small object features near the sampling limit can exhibit radical changes and may even vanish if at Nyquist. The multiple frames can be combined with a Projection Onto Convex Sets (POCS) approach [1], resulting in significant resolution improvement. Under the assumption of linear transformation of coordinates, we discuss an algorithm that computes the result in FFT-time using the Fast Fractional Fourier Transform [2].
Convergent, recursive phase reconstruction with synthetic interferograms
Authors: Páez Gonzalo , Strojnik Marija
Published: February 2023

In most phase reconstruction algorithms1-6, two generalized intensity functions Ic(x,y) and Is(x,y), shown in Fig. 1, are obtained after some initial processing steps, independently of the specific experimental technique used to obtain the modulated intensity patterns. Generalized intensity with the background intensity subtracted is coded in the levels of gray.
Visualization of turbulence and motion-blur removal in wide-area imaging through the atmosphere
Authors: Fraser Donald , Thorpe Glen , Lambert Andrew
Published: February 2023

We explore the feasibility of a new technique for visualization of the effects of turbulence in clear air [1]-[2], [4]-[5], based on some earlier ideas [10]. Sequences of short exposure images of a scene, such as the surface of the moon or a horizontally imaged scene on the earth, are captured using a 0.4 m diameter optical telescope. The field of view, typically 100 arc secs across, is wide compared to that of most astronomical observations [6]-[8], so that the main effect observed is a random “wobbling” within each image. With an exposure time of between 5 and 10 ms, the atmospheric wobble is “frozen” to provide a sequence of randomly warped images. The point spread function (PSF) for each image, due to the atmosphere and telescope, approximates a position-dependent randomly-displaced delta function (if we temporarily ignore instantaneous speckle and instrument blurring).
Algorithms for the Phase Retrieval Problem: an automatic Way to Overcome Stagnation
Authors: Cohen Nir , De Pierro Alvaro R. , Salvador Clarice Favaretto
Published: February 2023

This work is concerned with the Phase Retrieval (PR) problem [3]. In its general formulation, the PR problem consists of retrieving the Fourier phase for a signal f whose Fourier transform F is known only in magnitude. In the applications, some additional information on f is available, e.g. the magnitude |f|. We shall be interested in the 2-D case where the additional information is the nonnegativity of f and the autocorrelation support. Iterative algorithms are commonly used to solve this problem [4]. Whereas these algorithms are the most successful in the applications, they do not enjoy ensured convergence, and often do not converge to a solution. Quite often they wind up either oscillating between two non-solutions, or converging very slowly towards a non- solution. In [2] a geometric characterization of the solution set is presented as well as experimental results suggesting an automatic way to avoid stagnation in the context of the retrieval algorithms mentioned above. For concreteness, let us consider the Error Reduction (ER) method. We observe that oscillations for the ER always occur between one fixed toroid [2] and the nonnegative orthant. The point x′ of stagnation on the toroid is external to the (convex) orthant. It is reasonable, as a means to avoid stagnation, to move from x′ to the point x” on the toroid which is “antipodal” to x′, thereby (roughly speaking) overrelaxing the operation of (convex) projection onto the orthant. More precisely, let c be the center of the toroid in question. It has been observed before [2] that c is in the positive orthant. We set x” = 2c − x′. We then use x” as an initial value for the ER algorithm. To summarize, we propose the following method : suppose that the algorithm stagnated in an image g
k
, that has a projection
g
k
′ onto the toroids set; then we get a new initial estimate for the algorithm by setting
g
o
=−g
k
′+2c with c representing the center of the toroid. This new starting point automatically satisfies the Fourier magnitude constraints, but not necessarily the positivity constraint, unless it happens to be a solution. In principle, the new initial point may lead to a renewed stagnation. However, in practice the phase retrieval improves considerably from one stagnation to another, leading to a good approximate solution. We have performed numerous experiments, using the ER algorithm with this stagnation breaker, and in all the cases it was not necessary to repeat the stagnation breaker more than twice per example. One advantage of the suggested method is that it is automatic, i.e. there is no need to identify on-line the stagnation type. A typical experiment using our new method is shown below. Two overrelaxations were necessary in this case, in order to obtain an acceptable approximation to the solution. The starting image that begins the process was taken random. Figure 1 is the image to be retrieved, Figure 2, the result after 100 iterations of ER.
Phase retrieval in the Fresnel transform system : A recursive algorithm
Authors: Cong Wen-Xiang , Chen Nan-Xian , Gu Ben-Yuan
Published: February 2023

Phase retrieval problem is the recovering of the lost phase information of an optical field. Usually the directly measurable quantity in an optical system is the intensity of the image or diffractive pattern. Consequently, substantial information available encoded in the phase is lost. In order to reconstruct the image, one needs both the amplitude and phase information. Therefore, it is important to reconstruct the image from the intensity measurements only.1 Various algorithms for the phase retrieval have already been proposed, including the iterative algorithms,2-5 the direct methods,6,7 and so on.8-10
Applications of extended depth of focus technology to light microscope systems
Authors: Bradburn Sara , Cathey W. Thomas , Dowski Edward R.
Published: February 2023

Previous research has demonstrated the success of using a cubic phase mask in optical systems to perform wavefront coding which, along with digital post-processing can extend the depth of focus of standard optical imaging systems [1, 2]. Experimental images have demonstrated an increase of six to eight times the depth of focus of standard systems when using the extended depth of focus technology. This technology is now being extended to high magnification or light microscope systems. Several challenges have arisen due to the special nature of light microscope systems but extended depth of focus (EDF) technology is still found to be useful in such systems.
Output Characteristics of Diode-Laser Side-Pumped Solid-State Laser
Authors: Ning Jiping , Tang Shengshu , Xong Ying , Chang Zhiwu , Yao Jianquan
Published: February 2023

Pump rate density and cavity photon density are spatial distribution functions. For multi-mode laser classified rate-equations are: When system is stable
∂ΔN(x,y,z)∂t=0, ∂Si∂t=0 (2) formula is stable equation satisfied for m transverse modes.
Research on the high stable DPSSL
Authors: He Bin , Yan Pin , Wu Keying , Zhao Changming , Wei Guanghui
Published: February 2023

In many fields such as the inertia controlled fusion (ICF), the stabilization of the laser power sometimes plays an important role in the whole system. We choose the LiNbO3 crystal as the light attenuator to stabilize the laser power. By using the successive approach method, the stabilization of the LD pumped Nd:YLF laser improves from 2~3%/h to less than 0.5%/h.
High - Efficiency Laser Diode Arrays Pumped Nd: YAG Laser
Authors: Fu Rulian , Zhang Lingqian , Wang Guangjun , Wang Zhaoqi , Ba EnXu , Mu Guoguang , Hu Xinhua
Published: February 2023

With the development of high-power LD arrays, there is a resurgence of interest in DPSSL. But a practical problem is that the output beams of LD have a large divergent angle, generally θ11 equal to 10° and θ⊥ equal to 40° or so. This caused a high loss of pumping power. Meanwhile one of the main obstruct in LD arrays end-pumped architecture is that the laser beams which emitted from unit bar can’t be focused as a single beam by imaging system, i.e. the light field distribution at the focal plane of the focusing system is inhomogeneous and the laser beam doesn’t match the cavity mode. This restricted the pumped efficiency and 1.06 μm laser beams quality. The coupling methods Currently adopted include: aspheric lens series[1], gradient refractive index lens[2], optical fiber[3] and “close” coupling[4]. But all kinds of these coupling systems have some defeats: low transfer efficiency; bad quality of laser beam and restraining the number of unit bars of LD arrays. Lens duct is a kind of good coupling system[5,6,7], we adopted it in our experiment to improve the total conversion translate efficiency and beam quality.
High-Power Nd:YAG Laser Beam Delivery by Optical Fiber
Authors: Wang X.L. , Zhang R. , Yao J.Q.
Published: February 2023

The advantages of using fiber beam delivery for high-power Nd:YAG lasers were well known. In many cases, high-power YAG laser was one kind of multimode laser, its beam quality was evaluated by beam parameter product ω θ . At a given output power, the laser beam parameter product was a constant, which is only related to laser resonator structure.
Study of the electro-optic polymer films with improved properties
Authors: Xu Dong , Guo Shiyi , Zhang Guanghui , Yuan Dourong , Bing Yonghong , Jiang Minhua , Ren Quan
Published: February 2023

Electro-optic polymer films are interesting materials for their potential application in electro-optic switch and modulator, and significant progress in device design has been reported recently. Among many interesting properties, the major attraction of electro-optic polymer materials is their large electro-optic coefficients. Furthermore, as reported before, one of the important requirements in photonic device fabrication is the stability of the electro-optic response of the poled polymer materials. The intrinsic low dielectric constant, ease of processing into thin film, and compatibility with microelectronic process are the other major advantages of the organic polymer materials. Doped polymer films with high glass transition temperature Tg are promising in this respect.
Polymer Optoelectronics
Authors: Peyghambarian Nasser
Published: February 2023

The recent advances in photorefractive polymers and electroluminescent polymers are discussed. We have achieved more than 3% electroluminescent efficiency and more than 24,000 cd/m2 in cw mode from our electroluminescent polymers and nearly 100% diffraction efficiency in photorefractive polymers.
3 μm Er:Cr:YSGG-laser with a SBS phase conjugating mirror
Authors: Eichler H.J. , Liu B. , Sperlich O.
Published: February 2023

Erbium lasers with wavelengths around 3 μm can be widely used in medical applications due to water absorption maximum at 3 μm. Also collagen, the main part of organic bone materials, has a higher absorption in this wavelength range than at the 10.6 μm wavelength of CO2 laser, almost by a factor of 4 [1], This allows cleaner cuts with smaller destruction of adjacent tissues. But a higher power with good beam quality of laser radiation in this wavelength range is also very important to reach good surgically results.
Solid-State Lasers Advance Optical Fiber Communications
Authors: Li Tingye
Published: February 2023

Solid-state lasers play a key role in optical fiber communications. Directly modulated semiconductor lasers have been used ubiquitously as transmitters in lightwave communication systems. As the output power and modulation speed of these lasers improve, so do the repeater spacing and transmission capacity. Lightwave transmission systems that operate at 2.5 Gb/s with repeater spacings of 40 km or more have been commercially available since 1991. These traditional systems operate in a single wavelength (channel) per fiber at either 1.3- or 1.5-μm wavelength, and employ optoelectronic regenerators as repeaters. For such systems, upgrading networks to higher capacity requires developing higher-speed multiplexers and repeaters, and thus obsoleting existing repeater equipment.
Solid State Lasers: From Laboratory to Applications
Authors: Moulton Peter F.
Published: February 2023

Solid state lasers, because of their high power output per unit volume and inherently rugged nature have always been desirable for a number of uses outside of the laboratory. The Nd:YAG laser, pumped by cw arc lamps or pulsed flashlamps, has for a number of years been the most widely employed solid state system and has found wide use in scientific, industrial and military applications. With the development of new laser crystals, high-power semiconductor lasers and new or improved nonlinear materials the lamp-pumped Nd:YAG laser is becoming just one of many useful solid state systems. We consider several examples of the newest types of solid state laser systems, some of which combine a variety of new or improved technologies.
Growth and Characterization of Laser and Nonlinear Optical Crystals for Solid State Laser Applications
Authors: Fukuda Tsuguo , Terada Yasuko , Shimamura Kiyoshi , Imai Katsuhiro , Imaeda Minoru
Published: February 2023

Many investigations on the optoelectronic materials have been carried out by numerous research groups. However, only a few crystals such as LiNbO3, LiTaO3 and Nd:Y3Al5O12 have been successfully used in industrial applications. Recently, the development of new laser and nonlinear optical crystals has become a focus of considerable interest because of the progress of optoelectronics technologies. We have carried out the investigations focusing on the development of new optoelectronic and photonic materials, using advanced crystal growth techniques. Here, our research and progress in development of optoelectronic materials are introduced to propose one meritorious trend.
Solid-state Laser and Its Applications in China
Authors: Sui-Sheng Mei
Published: February 2023

The first laser of China was built at Changchun Institute of Optics and Fine Mechanics, Academia Sinica, in September 1961. It was ruby laser also ,but the design was a little different from the laser invented by T.H.Maiman in May 1960. It applied spherical mirror instead of cylindrical one and straight tube flash lamp instead of spiral one.
Laser Frequency Conversion Technology and Application
Authors: Yao Jian-quan
Published: February 2023

I. Past of Nonlinear Optical Frequency Conversion Technology

• Material: KTP, ADP, LiNbO3(MgO:LiNbO3), LiIO3, BNN.

• Technology: SHG, THG, OPO.

• Application:

– SHG ( and THG) of Nd:YAG Laser

– Visible and near-infrared.
Study of Yellow Laser Source by Optical Parametric Oscillation and Sum Frequency Mixing
Authors: Xiao X.H. , Yao J.Q. , Shi X.C. , Wang J. , Du S.R. , Wang P.
Published: February 2023

The recently developed Raman excitation plus laser-induced electronic fluorescence (RELIEF) method of tagging oxygen molecules provides a powerful tool for studying turbulent structure in high-speed air flows. The advantage comparing with other flow diagnosis methods is that a nonintrusive, instantaneous structure of high-sped flow can be obtained by this new technique. For this method, it is necessary to pump oxygen molecules up to vibrational exciting states by two simultaneously pulsed high-power lasers whose frequencies differ by the vibrational frequency of oxygen(1555cm-1). The wavelengths of the two lasers are 532nm and 580nm, respectively, which are usually chosen as pump source for tagging oxygen molecules. In our experiment, nonlinear optical frequency conversion technology has been applied to generate 580nm coherent radiation.
Power scaling of solid state lasers over 100 W with fiber phase conjugators
Authors: Eichler H.J. , Haase A. , Kunde J. , Liu B. , Mehl O.
Published: February 2023

The beam quality of high average power solid-state lasers can be significantly improved using phase conjugation based on stimulated Brillouin scattering (SBS) [1] in cells with a simple focusing geometry. The relatively high SBS threshold of several 10 kW in such cells, however, limits applications e.g. in continuously pumped laser systems. The SBS-materials used up to now are toxic liquids or gases under high pressure.
Quasi-Phasematching, a New Approach for Material Engineering
Authors: Fejer M. M.
Published: February 2023

Materials with periodically-patterned nonlinear susceptibilities offer qualitative improvement in nonlinear frequency conversion devices. Methods for patterning ferroelectric materials, generation of UV, visible and tunable IR radiation, ultrafast QPM nonlinear optics are discussed.
Study Of New Nonlinear Crystal -CsLiB6O10
Authors: Xiurong Zhang , shuunxin Zhang , yao Chai
Published: February 2023

Along with extensive application of solid ultraviolet laser, specially the nuclear fusion device go up for request more and more high. For example: large size, high quality, high resist damage and high convesion efficienty. to now, there are some shortcoming of the nonlinear crystals-BBO,LBO,KTP KDP ect, as small size, lowe resist damage and long growth period ect They are not satisfing above request So, it is necessary that research new nonlinear crystals continuously. The new UV NLO crystal-CsLiB6O10 (CLBO) have been reported by Y. Mori et al in 1995 (Japan). The advantages of CLBO crystal are large size, high resist damage, sort growth period and slight hygroscopic and very good NLO properties. We report on growth and the UV, NLO properties and application of CLBO cyrstal and compared with other borate crystals.
Enhanced Long Range Correlations of Light Reflected from Random Rough Surfaces
Authors: Nieto-Vesperinas M. , Sanchez-Gil J.A.
Published: February 2023

Intensity angular correlations of Light diffusely reflected from random rough surfaces in the case in which the speckle pattern does not follow a Gaussian second order statistics are studied. A new effect is found which constitutes a generalization of the enhanced backscattering and is due to time reversal symmetry.
Exact calculations of surface impedance for periodic rough surfaces
Authors: Brudny Vera L.
Published: February 2023

The concept of surface impedance has been widely used in electromagnetic theory of scattering. For a 2D scattering problem the impedance Z(x) on a surface ∑ can be defined as (1) where E║ and H║ represent the components of the electric and magnetic fields tangential to surface ∑, x is a coordinate on the surface and
n^ the unit vector normal to it. If Z(x) is known, eq. (1) can be used as a boundary condition exactly equivalent to Maxwell’s, but since it is defined in terms of the fields this knowledge requires the complete solution of the scattering problem.
Surface Measurements and Frequency Analysis
Authors: Bristow Thomas C.
Published: February 2023

The measurement of surface roughness is typically an important parameter for describing the quality of fine finished parts. Examples include measurements of finely polished flat and curved optics, computer hard disks, semiconductor wafers and optical disks. Most often an RMS or RA roughness value is reported for the part, typically by the high spatial information. Other surface information can also be of interest, including mid-spatial roughness and figure information. Three basic surface profiles are generally used to define the surface, including total profile, waviness and roughness. A different approach is to examine the spatial information on the surface by using the power spectrum or the autocovariance function. Both of these functions can be calculated over any user selected spatial frequency region.
Perturbation Theory of the Enhanced Backscattering of Light From Weakly Rough Random Metal Surfaces
Authors: Maradudin A. A.
Published: February 2023

The enhanced backscattering of light from a small rms height, small rms slope, one-dimensional randomly rough surface of a metal was first predicted on the basis of an infinite-order perturbation calculation that used the techniques of many-body theory and employed the concepts of weak localization theory. In this paper we present an elementary calculation of the contribution to the mean differential reflection coefficient from the incoherent component of the scattered light that is based on the first few terms in the expansion of this function in powers of the surface profile function. We show that this approach accounts not only for enhanced backscattering but gives the correct order of magnitude of the effect predicted by infinite-order perturbation theory.
Experimental Measurements of Enhanced Backscattering and Related Effects from Randomly Rough Surfaces
Authors: Dainty J C
Published: February 2023

Light scattering from randomly rough surfaces of relatively low root-mean-square (rms) slope and long correlation length (> λ) is well-understood, at least for moderate angles of incidence, in terms of physical optics (Kirchhoff) theory. However, until the past five years, there has been little experimental or theoretical work carried out on surfaces with a large rms slope for which multiple scattering occurs. One consequence of strong multiple scattering is the presence of an enhanced backscatter peak: this peak has a similar origin to that observed from strongly multiple scattering volume media, such as white paint, and analogous effects are observed in the propagation of light through turbulence in "double pass" geometries.
"Ultrasonic Measurements of Surface Roughness"
Authors: Blessing G.V. , Boudreaux J.C. , Eitzen D.G. , Slotwinski J.A.
Published: February 2023

We describe the use of pulsed ultrasound at MHz carrier frequencies to reflect and scatter from rough surfaces in an analogous way that light is used, comparing the results to stylus data. A principal application is to the manufacturing environment for on-line real-time sensor feedback and process control.
Self-Amplified Undulator Radiation in High Gain Free Electron Lasers
Authors: Kim Kwang-Je
Published: February 2023

We discuss the transition from simple undulator radiation to more fully developed coherent radiation of high gain free electron lasers. In a simple undulator the radiation from different electrons add incoherently. For a long undulator and a high brightness electron beam, the cumulative effect of the radiation-beam interaction leads to development of regions of periodic density variation in the electron beam, resulting in an exponential amplification of the radiation intensity. The amplification eventually stops because the induced momentum spread counteracts the effects of electron correlation. A high gain free electron laser operating in a bypass of a 1 GeV, high brightness electron storage ring is based on this principle, and can potentially generate tens of megawatts of partially coherent power at wavelengths shorter than 1000Å.
Experiments to Characterize Undulator Radiation
Authors: Sasaki Taizo
Published: February 2023

Optical properties of undulator radiation are unique in many respects. Great enhancement in brightness and nearly perfect linear polarization on axis of mean electron trajectory, a series of quasimonochromatic odd harmonic components, axial symmetry of spectral distribution, tunabilities provided through variable field parameters, observing angles, or electron energies, and partial coherence are features to be distinguished from the synchrotron radiation from the dipole.
Soft X-Ray Interferometry and Holography
Authors: Kikuta Seishi , Aoki Sadao
Published: February 2023

Developments in the fundamental optics for soft X-ray interferometry and holography are reviewed. To improve the quality of interference fringes it is essential to develop the soft X-ray sources, optical components and recording films. In this study soft X-ray radiation emitted from the undulator arranged in the 2.5 GeV Photon Factory ring was used, as well as radiation from the microfocus X-ray Generator. The coherence properties of undulator radiation were examined by the interference technique. Owing to the recent development of microfabrication technology, soft X-ray optical components such as Fresnel zone plates, transmission gratings, grazing incidence mirrors and multilayers are available for collimating, focussing, splitting or monochromatizing soft X-ray radiation. These components provides various possibilities for the optical system of interferometric and holographic experiments. As recording films, PMMA and inorganic resists with a high spatial resolution, as well as conventional films, are useful. The interferometric and holographic patterns were recorded by adopting several fundamental optical geometries such as the Lloyd's mirror arrangement, the Gabor in-line geometry and the Fourier transform geometry. The holograms with fringes several hundred Ångstrom wide were observed. Finally the prospects for further development are discussed.
X-Ray Imaging Experiments by Zone Plates Using Undulator Radiation at the BL-2B Line of Photon Factory
Authors: Aritome H. , Nagata K. , Mikuni A. , Maezawa H. , Sasaki T. , Namba S.
Published: February 2023

A zone plate, a focusing element that operates using diffraction, is of particular interest for focusing soft x-rays and a key element of an x-ray microscope.
Proposal for a Femtosecond X-ray Light Source
Authors: Falcone R W. , Murnane M.
Published: February 2023

Laser plasma x-ray sources have traditionally been produced by focussing laser pulses with a duration greater than 10 picoseconds onto solid metal targets1. At these pulse lengths, the intense laser light generates an expanding coronal plasma above the surface. A gradient in plasma density is produced and the laser light is primarily absorbed at the so called critical surface where the plasma frequency equals the optical frequency. High intensity short wavelength radiation is emitted from the hot, dense plasma through various microscopic processes including line emission, bremsstralung and recombination radiation.
Mechanisms of Multiphoton Excitation and Ionization of Multielectron Atoms
Authors: Lambropoulos P.
Published: February 2023

The excitation and ionization of bound electrons under strong (1012 W/cm2 and above) laser pulses is an inherently time-dependent process. Although under certain conditions a transition probability averaged over the pulse may be meaningful, in general events during the evolution of the pulse must be followed in detail because total decay (ionization) of various species (atoms and ions) is apt to occur. As a result, at different stages of the pulse, processes of different order may appear.
Multifacet Metal Mirror Design for Extreme-Ultraviolet Applications*
Authors: Newnam Brian E. , Scott Marion L. , Arendt Paul N.
Published: February 2023

The future operation of broadly tunable free-electron laser (FEL) oscillators below 100 nm is very dependent on the development of resonator end mirrors with reflectance greater than 50 per cent. We have determined that a multifaceted mirror configuration of a few metal films, e.g., Al, Si, Rh, and Ag, offers the potential of achieving large values (≥50 per cent) of XUV retroreflectance. Even larger net reflectance values are possible for 90° beam-turning mirrors. These make use of the principle of quasi-total external reflectance for incidence angles larger than the critical angle (≥60°) and with S-plane polarization. Only when the optical constants n and k both are sufficiently less than unity is there a large increase over a single, normal-incidence reflection.
Multiphoton Ionization for the Production of X-Ray Laser Plasmas
Authors: Corkum P. B. , Burnett N. H.
Published: February 2023

In the long wavelength (or high intensity) limit, above threshold ionization (ATI) is primarily the result of the interaction of a newly freed electron with the laser field. A classical model of ATI predicts that the energy of a newly released electron can be controlled by varying the laser wavelength and polarization. Similar predictions are made by Keldysh-style theories. Measurements, performed using both linearly and circularly polarized picosecond 10 μm pulses, confirm these conclusions.

Cold, high-Z plasmas for recombination XUV lasers can be produced by multiphoton ionization with linearly polarized visible or UV radiation. Hot electrons, potentially suitable for electron-pumping of ionization-phase XUV lasers can be produced using longer wavelength or circularly polarized light.
Investigations of Multiphoton Excitation and Ionization in a Short Range Potential
Authors: Susskind S. M. , Cowley S. C. , Valeo E. J.
Published: February 2023

We introduce an approach to the study of excitation and ionization for a system containing a model confining potential consisting of a set of δ-functions. In particular, analytical and numerical results are presented for the multiphoton ionization rate, under strong field conditions, of an electron confined by a δ-function potential.
Soft X-Ray Spectroscopy of Laser-Produced Plasma
Authors: Chen Shi-sheng , Xu Zhi-zhan , Zhang Zheng-quan
Published: February 2023

Laser-produced plasmas emit intense X radiation primarily at sub-KeV
Photon energies. Spectra in the sub-KeV region were measured with a
pinhole transmission grating and grazing incidence spectrographs
respectively. The transmission grating spectrometer with two pinholes
of 25 μm and 50 μm in diameter is consisted of
free-standing gold bars (1000 Lines/mm, bar thickness 0.45 pm). The
wavelength resolution achieved in the spectrometer was 10Å.
The grazing incidence spectrograph is composed of a toroidal mirror
and a concave grating. It is designed to cover the spectral range of
10~450 Å in the first difraction order. The angles of
incidence on both mirror and grating are 87~87.5° in order to
maintain good efficiency down to 20 Å. The spectrograph of
998.8 mm radius and 2400 grooves/mm, the brazing angle being
2°.
The production of long coherence-length hard x-rays using nuclear Bragg scattering of synchrotron radiation
Authors: Siddons D. P.
Published: February 2023

Recently, several experimenters have successfully observed nuclear Bragg scattering from crystals containing 57Fe. By coherently exciting the 14.4keV resonance at the Bragg condition, almost pure beams of extremely monochromatic radiation can be generated. Although the intensities observed are so far quite low, the brightness produced by these techniques exceeds that available from radioactive sources. Instrumental improvements will soon make possible interesting new experiments. Several properties of the nuclear Bragg reflection process are interesting in themselves. These include the observation of beating in the time domain among hyperfine split resonance lines, and polarization mixing produced by scattering from oriented circularly polarized oscillators. Some speculations on the potential applications of this new source of long coherence-length radiation will be presented.
Studies of Hot, Solid Materials Produced by an Ultrashort Pulse Laser
Authors: Milchberg H. M. , Freeman R. R.
Published: February 2023

A series of ultrashort pulse laser-solid interaction experiments have been performed using copper and aluminum which illustrate charge transport properties of these strongly heated materials at near-solid density. In aluminum, as a Drude metal at the laser wavelength, the transport is seen to be strongly dominated by collisions with the appearance of a minimum mean free path. In copper, band absorption of the laser light is seen to be a strong process even at ~ 50 eV temperatures.

In the context of using ultra-short pulse laser-produced plasmas as a source of ultrashort pulse soft X-rays, evidence is presented that heat loss mechanisms in these hot solids may not be sufficiently rapid to result in subpicosecond soft X-ray bursts.
Calculation and Design of Ni-Like W Soft X-Ray Lasers†
Authors: Maxon S. , Dalhed S. , Hagelstein P. , MacGowan B. , London R. , Rosen M.
Published: February 2023

Gain on 0-1 transitions has now been demonstrated in Ni-like Eu1,2 and Yb3 using targets between 60 and 100 μg/cm2. The intensities of the input laser were 7×1013 W/cm2 (Eu) and 1.4×1014 W/cm2 (Yb). The measured gain coefficient on the 71Å (Eu) and the 50.3Å line (Yb) was 1 cm−1. Using a modified version of the Lagrangian hydrodynamics code LASNEX together with the kinetics code XRASER, the calculated gains are in reasonable agreement with experiment.2
Multiterawatt Excimer Laser System
Authors: Watanabe S. , Endoh A. , Watanabe M. , Sarukura N.
Published: February 2023

A peak power of 4 TW has been obtained in KrF with an output energy of 1.5 J in 390 fs from an electron-beam-pumped amplifier with an active cross section of 320 cm2. The amplified spontaneous emission was as low as 1.8% in energy. The pulse width was measured by the newly-developed third-order autocorrelation technique based on the XeF C-A transition. An initial pulse width of 210 fs was increased to 390 fs through amplifiers. The process of the pulse width broadening was investigated in detail through dummy optics, the thickness of which coinsides with the entire system. The broadening was attributed mainly to the linear dispersion of thick optics for near-transform-limited input pulses. Nonlinear absorption and self-phase modulation were not significant in the output window of a 25-cm-thick CaF2 at an intensity of 13 GW/cm2.
High Efficiency, Scalable, 130 nm Coherent Source by Four-Wave Mixing in Hg Vapor
Authors: Muller C. H. , Hamilton C. E. , Lowenthal D. D. , Smith A. V.
Published: February 2023

Coherent vacuum ultraviolet (VUV) pulses with energy 1.1 mJ, 3 ns pulse length (1.3 MW cm-2 unfocused), and measured bandwidth <0.1 cm-1 have been achieved using four-wave sum-frequency mixing in mercury vapor. High energy conversion efficiencies of 5 percent have been demonstrated in a collimated beam geometry over 1 meter interaction lengths. The 130 nm radiation is tunable over 2.5 cm-1. The experimental facility assembled to produce this efficient VUV laser source will be described, and comparison between experimental measurements and theory are provided.
Observations of High Density Plasmas Produced with a Picosecond High Power KrF Laser
Authors: Willi O. , Kiehn G. , Edwards J. , Barrow V. , Smith R.
Published: February 2023

The interaction of a single picosecond, high power KrF laser pulse with solid targets has been studied using time integrated and time resolved x-ray spectroscopy. Fully ionized aluminum plasmas with temperatures of about 400 eV and densities well above 1023 cm-3 were observed when the ASE prepulse was less than 10-5.
Current Prospects for Free-Electron Lasers in the Extreme Ultraviolet*
Authors: Newnam Brian E.
Published: February 2023

In the last few years, free-electron laser (FEL) oscillators and amplifiers have produced coherent radiation over a broad spectral range extending from 463 nm in the visible to millimeter wavelengths as summarized graphically in Fig. 1. These successful demonstrations have encouraged a number of research centers to boldly consider extension of this electron-accelerator-based technology to the extreme ultraviolet (XUV) below 100 nm where no powerful, tunable, coherent-radiation source presently exists. Here, the peak- and average-power output of FEL oscillators and amplifiers should surpass the capabilities of any existing, continuously tunable photon sources by many orders of magnitude.
Targets for Efficient Femtosecond-Time-Scale X-Ray Generation
Authors: Kmetec J. D. , Harris S. E.
Published: February 2023

High power femtosecond lasers can be used to generate bright x-ray sources. The choice of element for the laser-produced-plasma target strongly affects the nature of the emitted x-rays. Combining low Z and high Z elements results in the brightest femtosecond x-ray radiators. Examples of lithium and tin combinations yielding 3.6 Ǻ x-rays with up to several percent conversion efficiencies are given.
Gain Guided X-Ray Beams
Authors: Fill Ernst E.
Published: February 2023

It is shown that with gain and index profiles of typical x-ray laser experiments the x-ray beam is guided by the gain profile rather than defocussed by the refractive index distribution. An arbitrary beam generated within the medium or injected into the medium is quickly transformed into a ’matching’ beam, propagating without change. The effective gain of the matching beam is somewhat, lower than the gain at the maximum of the gain distribution.

If the gain distribution exhibits a small curvature in direction of beam propagation the effective gain is dramatically reduced.