Showing papers on "Diffraction published in 2005"
TL;DR: In this article, the theoretical foundation of the Bessel beam is described and various experiments that make use of Bessel beams are discussed: these cover a wide range of fields including non-linear optics, where the intense central core of the bessel beam has attracted interest; short pulse non-diffracting fields; atom optics, and optical manipulation where the reconstruction properties of the beam enable new effects to be observed that cannot be seen with Gaussian beams.
Abstract: Diffraction is a cornerstone of optical physics and has implications for the design of all optical systems. The paper discusses the so-called 'non-diffracting' light field, commonly known as the Bessel beam. Approximations to such beams can be experimentally realized using a range of different means. The theoretical foundation of these beams is described and then various experiments that make use of Bessel beams are discussed: these cover a wide range of fields including non-linear optics, where the intense central core of the Bessel beam has attracted interest; short pulse non-diffracting fields; atom optics, where the narrow non-diffracting features of the Bessel beam are able to act as atomic guides and atomic confinement devices and optical manipulation, where the reconstruction properties of the beam enable new effects to be observed that cannot be seen with Gaussian beams. The intensity profile of the Bessel beam may offer routes to investigating statistical physics as well as new techniques for the...
1,173 citations
Book•
23 Dec 2005
TL;DR: Birkholz et al. as discussed by the authors proposed a line profile analysis for X-ray diffraction and showed that line profiles can be used to detect residual stress gradients in thin films.
Abstract: Preface Symbols 1 Principles of X-ray Diffraction 11 The Basic Phenomenon 12 The &theta /2&theta Scan 13 Intensity of Bragg Ref lections 14 Applications 2 Identification of Chemical Phases 21 Histogram-Based Techniques 22 Linear Attenuation Coefficient &mu 23 Determination and Interpretation of the &mu t Product 24 Analysis of Phase Mixtures 25 Amorphous Thin Films 26 Accurate Determination of Lattice Parameter 27 Applications 3 Line Profile Analysis 31 Model Functions and Peak Parameters 32 Instrumental Line Profile 33 Deconvolution by Fourier Techniques 34 Ref lection Broadening by Small Crystallite Size Only 35 Concomitant Occurrence of Size and Strain Broadening 36 Applications 4 Grazing Incidence Configurations 41 Grazing Incidence X-ray Diffraction (GIXRD) 42 Penetration Depth and Information Depth 43 Depth-Dependent Properties 44 Refractive Index for X-rays 45 Total External Ref lection and Critical Angle 46 X-ray Reflectivity (XRR) 47 Grazing Incidence Diffraction (GID) 48 Applications 5 Texture and Preferred Orientation 51 Texture Factors 52 Pole Figures 53 Measurement of Pole Figures 54 Directions, Orientations and Inverse Pole Figures 55 Fiber Textures or Layer Textures 56 Biaxial and Fully General Textures 57 Depth Dependence of Thin-Film Textures 58 Applications 6 Residual Stress Analysis (Mario Birkholz and Christoph Genzel) 61 Ceiiinnosssttuv 62 Fundamental Equation of XSA 63 Measurement of d&Psi Distributions 64 Diffraction Elastic Constants (DECs) s 1 and 1/2s 2 65 Grain Interaction Models 66 The Effect of Texture 67 Classification of Stresses 68 Effect of Residual Stress Gradients 69 Detection of Residual Stress Gradients in Thin Films 610 Applications 7 High-Resolution X-ray Diffraction (Mario Birkholz and Paul F Fewster) 71 Strain, Strain Relaxation and Composition in Epitaxial Layers 72 High-Resolution Rocking Curves 73 Mosaicity and Extinction 74 Dynamical Theory of Ewald and Extensions 75 High-Resolution Rocking Curves and Profiles from Layer Structures 76 Reciprocal Space Mapping 77 Diffuse Scattering 78 Extensions to High-Resolution Diffraction
671 citations
Book•
28 Feb 2005TL;DR: In this article, the authors discuss the development of stress measurement by diffraction and the characteristics of Neutron Strain Measurement, including extinction, texture, and multiple scattering.
Abstract: INTRODUCTION Residual Stress: Friend or Foe? Historical Development of Stress Measurement by Diffraction Special Characteristics of Neutron Strain Measurement Nature and Origin of Residual Stress Effects of Residual Stress FUNDAMENTALS OF NEUTRON DIFFRACTION Introduction Scattering and Absorption of Neutrons and X-Rays by Atoms Neutron Diffraction from Crystalline Solids Penetration of Neutron Beams Effects of Lattice Vibrations Extinction, Texture, and Multiple Scattering DIFFRACTION TECHNIQUES AND INSTRUMENT DESIGN Neutron Sources Diffractometers for Strain Measurement Neutron Detectors The Instrumental Resolution Instrument Gauge Volumes Sampled Gauge Volume and Effective Measurement Position Specialized Instruments for Strain Measurement PRACTICAL ASPECTS OF STRAIN MEASUREMENT USING NEUTRON DIFFRACTION Introduction Measurement of Diffraction Bragg Peak Profile Analyzing Bragg Peak Profiles Accuracy of Diffraction Peak Center Determination Analysis of Complete Diffraction Profiles for Strain Strain-Free Reference Reproducibility Tests INTERPRETATION AND ANALYSIS OF LATTICE STRAIN DATA Inferring Stresses from Lattice Strains Introduction to Mechanics of Crystallite Deformation Elastic Anisotropy of Single Crystals The Bulk Elastic Response of Polycrystals hkl-Specific Response in a Polycrystal Undergoing Elastic Deformation hkl-Specific Response in a Polycrystal Undergoing Plastic Deformation APPLICATIONS TO PROBLEMS IN MATERIALS SCIENCE AND ENGINEERING Introduction Welded Structures Composites and Other Multiphase Materials Plastically Deformed Components and Materials Near-Surface Stresses In Situ and Through-Process or Life Studies THE FUTURE SYMBOLS AND ABBREVIATIONS GLOSSARY APPENDICES Note on Reactor Flux Spectrum Relation between the Centroid of Sampled Gauge Volume and Translator Reading Points for Consideration When Making a Neutron Diffraction Stress Measurement Macroscopic Scattering Cross-Sections of All Elements Index
659 citations
TL;DR: The product of spatial resolutions of the ghost image and ghost diffraction experiments is shown to overcome a limit which seemed to be achievable only with entangled photons.
Abstract: High-resolution ghost image and ghost diffraction experiments are performed by using a single classical source of pseudothermal speckle light divided by a beam splitter. Passing from the image to the diffraction result solely relies on changing the optical setup in the reference arm, while leaving the object arm untouched. The product of spatial resolutions of the ghost image and ghost diffraction experiments is shown to overcome a limit which seemed to be achievable only with entangled photons.
648 citations
TL;DR: The components of the macroscopic mechanical stress tensor of a stressed thin film, coating, multilayer or the region near the surface of a bulk material can in principle be determined by X-ray diffraction as discussed by the authors.
Abstract: The components of the macroscopic mechanical stress tensor of a stressed thin film, coating, multilayer or the region near the surface of a bulk material can in principle be determined by X-ray diffraction. The various analysis methods and measurement strategies, in dependence on specimen and measurement conditions, are summarized and evaluated in this paper. First, different X-ray diffraction geometries (conventional or grazing incidence) are described. Then, the case of macroscopically elastically isotropic, untextured specimens is considered: from the simplest case of a uniaxial state of stress to the most complicated case of a triaxial state of stress. The treatment is organized according to the number of unknowns to be determined (i.e. the state of stress, principal axes known or unknown), the use of one or several values of the rotation angle φ and the tilt angle ψ of the sample, and one or multiple hkl reflections. Next, the focus is on macroscopically elastically anisotropic (e.g. textured) specimens. In this case, the use of diffraction (X-ray) elastic constants is not possible. Instead, diffraction (X-ray) stress factors have to be used. On the basis of examples, it is demonstrated that successful diffraction stress analysis is only possible if an appropriate grain-interaction model is applied.
529 citations
TL;DR: This work represents a previously uncharacterized application of x-ray diffraction microscopy to a specimen of this complexity and provides confidence in the feasibility of the ultimate goal of imaging biological specimens at 10-nm resolution in three dimensions.
Abstract: We have used the method of x-ray diffraction microscopy to image the complex-valued exit wave of an intact and unstained yeast cell. The images of the freeze-dried cell, obtained by using 750-eV x-rays from different angular orientations, portray several of the cell's major internal components to 30-nm resolution. The good agreement among the independently recovered structures demonstrates the accuracy of the imaging technique. To obtain the best possible reconstructions, we have implemented procedures for handling noisy and incomplete diffraction data, and we propose a method for determining the reconstructed resolution. This work represents a previously uncharacterized application of x-ray diffraction microscopy to a specimen of this complexity and provides confidence in the feasibility of the ultimate goal of imaging biological specimens at 10-nm resolution in three dimensions.
483 citations
TL;DR: Simulation results show that one-dimensional and two-dimensional periodical structures of 40-100 nm features can be patterned using interfering surface plasmons launched by 1D gratings, which can go far beyond the free-space diffraction limit of the light.
Abstract: A new nanophotolithography technique based on the interference of surface plasmon waves is proposed and demonstrated by using computer simulations. The wavelengths of the surface plasmon waves at metal and dielectric interfaces can reach the nanometer scale while their frequencies remain in the optical range. As a result, the resolution of this surface plasmon interference nanolithography (SPIN) can go far beyond the free-space diffraction limit of the light. Simulation results show that one-dimensional and two-dimensional periodical structures of 40−100 nm features can be patterned using interfering surface plasmons launched by 1D gratings. Detailed characteristics of SPIN such as field distribution and contrast are also investigated.
360 citations
TL;DR: In this paper, the contribution of free volume in glassy materials and metallic glasses was measured by X-ray diffraction in transmission during heating using synchrotron light, and the measured thermal expansion coefficients αth were the same as in dilatometry.
339 citations
TL;DR: In this article, a modified approach is developed that allows possible atomic distribution functions, which are consistent with the measured data to be explored, and any solution to the inversion process must be derivable from a distribution of nonoverlapping atoms or molecules as in the physical system under investigation.
Abstract: Neutron and x-ray diffraction are widely used to measure the structure of liquids and disordered solids. Using techniques such as isotope substitution or anomalous dispersion or combining neutron and x-ray data, it is sometimes possible to invert the total diffraction patterns from these materials into a set of partial structure factors, which describe the correlations between specific atom types in the material. However, even in situations where the matrix for performing this inversion appears well determined, there are significant uncertainties in the process and it is rarely possible to achieve a unique set of partial structure factors in practice. Based on the much earlier method of F. G. Edwards and J. E. Enderby [J. Phys. C 8, 3483 (1975)] and extending the reverse Monte Carlo method of McGreevy [J. Phys.: Condens. Matter 13, R877 (2001)] and others, a modified approach is developed here that allows possible atomic distribution functions, which are consistent with the measured data to be explored. The basis of the present approach is that any solution to the inversion process must be derivable from a distribution of nonoverlapping atoms or molecules as in the physical system under investigation. Solutions to the problem of inverting the measured differentialmore » cross sections to partial structure factors are then extracted assuming different levels of confidence in the data, confidence being represented by a feedback factor on a scale of 0-1. These different solutions serve to identify where ambiguities exist in the derived partial structure factors, particularly when a particular partial structure factor contributes only weakly to the total diffraction pattern. The method is illustrated using some old diffraction data on molten zinc chloride that have significant uncertainties associated with them, but that have been used extensively as the basis for a number of computer simulations of this material.« less
335 citations
TL;DR: Experimental evidence is provided for a conceptual basis that could be employed when designing high performance thermoelectric materials and dispel the decades long belief that the systems (AgSbTe2)(1-x)(PbTe)x are solid solutions.
Abstract: The nature of the thermoelectric materials Ag1-xPbmSbTem+2 or LAST-m materials (LAST for Lead Antimony Silver Tellurium) with different m values at the atomic as well as nanoscale was studied with powder/single-crystal X-ray diffraction, electron diffraction, and high-resolution transmission electron microscopy. Powder diffraction patterns of different members (m = 0, 6, 12, 18, ∞) are consistent with pure phases crystallizing in the NaCl-structure-type (Fm3m) and the proposition that the LAST family behaved as solid solutions between the PbTe and AgSbTe2 compounds. However, electron diffraction and high resolution transmission electron microscopy studies suggest the LAST phases are inhomogeneous at the nanoscale with at least two coexisting sets of well-defined phases. The minority phase which is richer in Ag and Sb is on the nanosized length scale, and it is endotaxially embedded in the majority phase which is poorer in Ag and Sb. Moreover, within each nanodomain we observe extensive long range orderin...
326 citations
TL;DR: Simulations of electron diffraction patterns for each of the known perovskite tilt systems have been performed and the conditions for the appearance of superlattice reflections arising from rotations of the octahedra are modified to take into account the effects of different tilt systems for kinematical diffraction.
Abstract: Simulations of electron diffraction patterns for each of the known perovskite tilt systems have been performed. The conditions for the appearance of superlattice reflections arising from rotations of the octahedra are modified to take into account the effects of different tilt systems for kinematical diffraction. The use of selected-area electron diffraction as a tool for perovskite structure determination is reviewed and examples are included.
TL;DR: An analytical expression for Fresnel diffraction of a plane wave by a spiral phase plate (SPP) that imparts an arbitrary-order phase singularity on the light field is deduced and the far-field intensity distribution is derived.
Abstract: We deduce and study an analytical expression for Fresnel diffraction of a plane wave by a spiral phase plate (SPP) that imparts an arbitrary-order phase singularity on the light field. Estimates for the optical vortex radius that depends on the singularity’s integer order n (also termed topological charge, or order of the dislocation) have been derived. The near-zero vortex intensity is shown to be proportional to ρ2n, where ρ is the radial coordinate. Also, an analytical expression for Fresnel diffraction of the Gaussian beam by a SPP with nth-order singularity is analyzed. The far-field intensity distribution is derived. The radius of maximal intensity is shown to depend on the singularity number. The behavior of the Gaussian beam intensity after a SPP with second-order singularity (n=2) is studied in more detail. The parameters of the light beams generated numerically with the Fresnel transform and via analytical formulas are in good agreement. In addition, the light fields with first- and second-order singularities were generated by a 32-level SPP fabricated on the resist by use of the electron-beam lithography technique.
TL;DR: In this article, a reciprocal space model was developed to describe the dependence of broadened Bragg peakwidths produced by x-ray diffraction from a dislocated epilayer.
Abstract: We develop a reciprocal-space model that describes the (hkl) dependence of the broadened Bragg peakwidths produced by x-ray diffraction from a dislocated epilayer. We compare the model to experiments and find that it accurately describes the peakwidths of 16 different Bragg reflections in the [010] zone of both GaN and AlN heterolayers. Using lattice-distortion parameters determined by fitting the model to selected reflections, we estimate threading-dislocation densities for seven different GaN and AlGaN samples and find improved agreement with transmission electron microscopy measurements.
TL;DR: Direct structural evidence of the bridged radical (CH2ICH2·) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction, is reported, revealing a change in the solvent cage geometry, heating, and thermal expansion.
Abstract: We report direct structural evidence of the bridged radical (CH2ICH2·) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction. This transient intermediate has long been hypothesized to explain stereo-chemical control in many association and/or dissociation reactions involving haloalkanes. Ultrashort optical pulses were used to dissociate an iodine atom from the haloethane molecule (C2H4I2) dissolved in methanol, and the diffraction of picosecond x-ray pulses from a synchrotron supports the following structural dynamics, with ∼0.01 angstrom spatial resolution and ∼100 picosecond time resolution: The loss of one iodine atom from C2H4I2 leads to the C-I-C triangular geometry of CH2ICH2·. This transient C2H4I then binds to an iodine atom to form a new species, the C2H4I-I isomer, which eventually decays into C2H4 + I2. Solvent dynamics were also extracted from the data, revealing a change in the solvent cage geometry, heating, and thermal expansion.
TL;DR: Fluctuation microscopy as discussed by the authors is a hybrid diffraction-imaging technique that detects medium range order in amorphous materials by examining spatial fluctuations in coherent scattering, which appear as speckle in images and diffraction patterns.
Abstract: Fluctuation microscopy is a hybrid diffraction-imaging technique that detects medium range order in amorphous materials by examining spatial fluctuations in coherent scattering. These fluctuations appear as speckle in images and diffraction patterns. The volume of material contributing to the speckle is determined by the point-spread function (the resolution) of the imaging optics and the sample thickness. The spatial periodicities being probed are related to the diffraction vector. Statistical analysis of the speckle allows the random and non-random (ordered) contributions to be discriminated. The image resolution that gives the maximum speckle contrast, as determined by the normalized variance of the image intensity, is determined by the characteristic length scale of the ordering. Because medium range ordering length scales can extend out to about the tenth coordination shell, fluctuation microscopy tends to be a low image resolution technique.This review presents the kinematical scattering theory underpinning fluctuation microscopy and a description of fluctuation electron microscopy as it has been employed in the transmission electron microscope for studying amorphous materials. Recent results using soft x-rays for studying nanoscale materials are also presented. We summarize outstanding issues and point to possible future directions for fluctuation microscopy as a technique.
Book•
17 Nov 2005
TL;DR: Powder diffraction has attracted considerable and ever growing interest in the last decades as mentioned in this paper, with the development of ever growing computer power profile fitting and pattern decomposition allowed to extract individual intensities from overlapping diffraction peaks opening the way to many other applications, especially to ab initio structure determination.
Abstract: Crystal structure analysis from powder diffraction data has attracted considerable and ever growing interest in the last decades. X-ray powder diffraction is best known for phase analysis (Hanawalt files) dating back to the 30s. In the late 60s the inherent potential of powder diffraction for crystallographic problems was realized and scientists developed methods for using powder diffraction data at first only for the refinement of crystal structures. With the development of ever growing computer power profile fitting and pattern decomposition allowed to extract individual intensities from overlapping diffraction peaks opening the way to many other applications, especially to ab initio structure determination. Powder diffraction today is used in X-ray and neutron diffraction, where it is a powerful method in neutron diffraction for the determination of magnetic structures. In the last decade the interest has dramatically improved. There is hardly any field of crystallography where the Rietveld, or full pattern method has not been tried with quantitative phase analysis the most important recent application. (orig.)
TL;DR: CMPR is written in Tcl/Tk (Ousterhout, 1994) and thus runs on nearly all modern computer platforms with a convenient graphical user interface.
Abstract: Analysis of powder diffraction data is enhanced by visualization and manipulation capabilities. The CMPR package provides tools for working with these data. CMPR is written in Tcl/Tk (Ousterhout, 1994) and thus runs on nearly all modern computer platforms with a convenient graphical user interface. Computations in CMPR may be performed within the program or by an external Fortran or C program; the distinction is usually invisible to the user. CMPR can work with many data sets simultaneously. A data set may be a diffractogram (powder pattern) or a set of diffraction peak positions.
TL;DR: This paper describes in a very easy and intelligible way, how the diffraction efficiencies of binary dielectric transmission gratings depend on the geometrical groove parameters and how a high efficiency can be obtained.
Abstract: This paper describes in a very easy and intelligible way, how the diffraction efficiencies of binary dielectric transmission gratings depend on the geometrical groove parameters and how a high efficiency can be obtained. The phenomenological explanation is based on the modal method. The mechanism of excitation of modes by the incident wave, their propagation constants and how they couple into the diffraction orders helps to understand the diffraction process of such gratings and enables a grating design without complicated numerical calculations.
TL;DR: High-energy synchrotron X-ray diffraction was used to study internal stresses in bone under in situ compressive loading of a 12-14 year old beagle fibula, and internal stresses rose proportionally with applied stress but at a higher rate, corresponding to stress concentration in the mineral of 2.8 times the stress applied.
TL;DR: In this paper, a survey of available analytical tools for X-ray Bragg diffraction can be found, along with a series of worked examples demonstrating the application of the formalism to different materials with different crystal structures and resonant ions: dysprosium borocarbide ( DyB 2 C 2 ), vanadium sesquioxide ( V 2 O 3 ), gadolinium tetraboride ( GdB 4 ), chromium sesiquioxide ( Cr 2 o 3 ), haematite and perovskite-type manganites
TL;DR: This work investigates, experimentally and theoretically, light propagation in one-dimensional waveguide arrays exhibiting a saturable self-defocusing nonlinearity and demonstrates low-intensity "discrete diffraction", and the high-intensity formation of spatial gap solitons arising from the first band of the transmission spectrum.
Abstract: We investigate, experimentally and theoretically, light propagation in one-dimensional waveguide arrays exhibiting a saturable self-defocusing nonlinearity. We demonstrate low-intensity “discrete diffraction”, and the high-intensity formation of spatial gap solitons arising from the first band of the transmission spectrum. The waveguide arrays are fabricated by titanium in-diffusion in a photorefractive copper-doped lithium niobate crystal, and the optical nonlinearity arises from the bulk photovoltaic effect.
TL;DR: Measurements showing that the resulting donut mode is free of spatial chirp are presented, and an analysis of the optical wave propagation through the authors' system based on the Kirchhoff-Fresnel diffraction integral is supported.
Abstract: We experimentally created a femtosecond optical vortex using a pair of computer-synthesized holographic gratings arranged in a 2f - 2f optical setup. We present measurements showing that the resulting donut mode is free of spatial chirp, and support this finding with an analysis of the optical wave propagation through our system based on the Kirchhoff-Fresnel diffraction integral. An interferogram confirms that our ultrashort vortex has topological charge 1, and a conservative experimental estimation of its duration is 280 fs. We used 25-fs radiation pulses (bandwidth approximately 40 nm) produced by a Ti:sapphire laser oscillator.
Book•
09 Mar 2005
TL;DR: In this paper, a review of the properties of light that are relevant for analysis of image formation in photolithography is presented, starting with Maxwell's equations and deduced the characteristics of light in this chapter.
Abstract: From the corpuscular theory in which light propagates in the form of minute particles, to the wave theory that elucidates diffraction phenomena, to the quantum theory in which both the wave and corpuscular theories are simultaneously valid, humankind's concept of light has evolved much over the last two hundred years. The principles of optical projection lithography with which we are concerned were substantially formulated before the twentieth century, prior to the general theory of relativity, which stipulates the bending of light rays by gravitational fields. By that time, Augustin Jean Fresnel (1788-1827) had laid the wave theory of light on a firm foundation, and James Clerk Maxwell's (1831-1879) conjecture that light waves are electromagnetic had been verified by Heinrich Hertz (1857-1894).
In the first three chapters of this text, we review properties of light that are relevant for analysis of image formation in photolithography. Starting with Maxwell's equations, we deduce the characteristics of light in this chapter. We shall learn that light is a transverse wave, with the electric and magnetic field vectors vibrating in a plane that is normal to its direction of propagation. When light interacts with objects whose physical dimensions are large compared with its wavelength, we can neglect the field vectors under many circumstances, and approximate Maxwell's equations by laws formulated in the language of geometry. This topic of geometrical optics is treated in Chapter 2. To describe light transmission through apertures whose dimensions are comparable to or smaller than the wavelength, however, we need to resort to diffraction theory, a subject we discuss in Chapter 3.
TL;DR: Fang et al. as discussed by the authors used a thin silver slab for superlensing and obtained an image of a 50 nm half-pitch object at λ 0/7 resolution, which is well below the diffraction limit.
Abstract: Recently, the concept of superlensing has received considerable attention for its unique ability to produce images below the diffraction limit. The theoretical study has predicted a 'superlens' made of materials with negative permittivity and/or permeability, is capable of resolving features much smaller than the working wavelength and a near-perfect image can be obtained through the restoration of lost evanescent waves (Pendry 2000 Phys. Rev. Lett. 85 3966–9). We have already demonstrated that a 60 nm half-pitch object can indeed be resolved with λ0/6 resolution with the implementation of a silver superlens with λ0 = 365 nm illumination wavelength, which is well below the diffraction limit (Fang et al 2005 Science 308 534–7). In order to further support the imaging ability of our silver superlens, a two-dimensional arbitrary object with 40 nm line width was also imaged (Fang et al 2005 Science 308 534–7). In this paper, we present experimental and theoretical investigations of optical superlensing through a thin silver slab. Experimental design and procedures as well as theoretical studies are presented in detail. In addition, a new superlens imaging result is presented which shows the image of a 50 nm half-pitch object at λ0/7 resolution.
TL;DR: In this article, the role of synchrotron radiation in the generation of coherent x-ray beams is highlighted and the requirements on the source properties are discussed, and a trial-and-error method based on the analysis of waveguiding modes within the confined geometry is discussed.
Abstract: This is a tutorial paper on the properties of partially coherent hard x-ray beams and their use in the structural analysis of condensed matter. The role of synchrotron radiation in the generation of coherent x-ray beams is highlighted and the requirements on the source properties are discussed. The technique of phase contrast imaging is briefly explained, as well as diffraction in the Fresnel and Fraunhofer regimes. The origin of speckle is elucidated and it is shown how oversampling of the diffraction pattern by at least a factor of two enables retrieval of the phases of the waves scattered from different parts of the object. This in turn allows for a direct reconstruction of the object's structure. One-dimensional objects, such as a fluid confined between two surfaces, cannot be unambiguously reconstructed by phase retrieval without additional assumptions. A trial-and-error method based on the analysis of waveguiding modes within the confined geometry is discussed.
Patent•
22 Apr 2005
TL;DR: In this article, the authors proposed a lightwave diffraction device consisting of a dielectric layer, a mirror, a semi-reflective structure, and a diffractive structure.
Abstract: Lightwave diffraction device formed of a dielectric layer (4), a mirror (12) arranged at the lower face (10) of said layer, a semireflective structure (13) arranged at the upper face (100) of said layer, and a diffractive structure (8) arranged in said layer or on its faces. The height (H) of the layer is chosen so as to substantially satisfy the resonance condition for at least one leaky mode propagating in said layer for at least one given incident wave having a determined wavelength λ and a determined incidence angle θc. Next, the diffractive structure is arranged so that there is no propagating positive diffracted order, and so that all negative orders other than the -1st propagating order have zero or a relatively small diffraction efficiency, the reflected -1st order propagating in a direction non-parallel to the incident wave. This diffraction device allows a high diffraction efficiency of up to 100% for the -1st order.
TL;DR: In this article, the role of nonlinear photoionization and avalanche ionization processes in free electron generation was investigated in fused silica irradiated by tightly focused 90 fs laser pulses at a center wavelength of 800 nm.
Abstract: Single pulse transmissivity and reflectivity of fused silica irradiated by tightly focused 90 fs laser pulses at a center wavelength of 800 nm are numerically and experimentally investigated to study the role of nonlinear photoionization and avalanche ionization processes in free electron generation. The laser beam inside fused silica is modeled with a $(2+1)$-dimensional propagation equation which considers the effects of laser beam diffraction, group velocity dispersion, self-focusing, defocusing, and absorption due to the free electrons and nonlinear photoionization of the valence electrons. Comparison of our simulation to the experimental data reveals that the avalanche ionization coefficients are much smaller than some previously reported results and that avalanche ionization is of minor importance in generating free electrons in fused silica at the laser fluence levels considered in this study.
TL;DR: Results indicate that in turbulence the beam is widened beyond its free-space diffraction values, and this diffraction eventually leads to transformation of the cosh-Gaussian beam into an oscillatory average-intensity profile with a Gaussian envelope.
Abstract: The average intensity and spreading of cosh-Gaussian laser beams in the turbulent atmosphere are examined. Our research is based principally on formulating the average-intensity profile at the receiver plane for cosh-Gaussian excitation. The limiting cases of our formulation for the average intensity are found to reduce correctly to the existing Gaussian beam wave result in turbulence and the cosh-Gaussian beam result in free space (in the absence of turbulence). The average intensity and the broadening of the cosh-Gaussian beam wave after it propagates in the turbulent atmosphere are numerically evaluated versus source size, beam displacement, link length, structure constant, and two wavelengths of 0.85 and 1.55 μm, which are most widely used in currently employed free-space-optical links. Results indicate that in turbulence the beam is widened beyond its free-space diffraction values. At the receiver plane, analogous to the case of free space, this diffraction eventually leads to transformation of the cosh-Gaussian beam into an oscillatory average-intensity profile with a Gaussian envelope.
TL;DR: It is shown both theoretically and experimentally that an electromagnetic wave can be totally absorbed by an overdense plasma when a subwavelength diffraction grating is placed in front of the plasma surface.
Abstract: We show both theoretically and experimentally that an electromagnetic wave can be totally absorbed by an overdense plasma when a subwavelength diffraction grating is placed in front of the plasma surface. The absorption is due to dissipation of surface plasma waves (plasmons polaritons) that have been resonantly excited by the evanescent component of the diffracted electromagnetic wave. The developed theoretical model allows one to determine the conditions for the total absorption.