scispace - formally typeset
Search or ask a question

Showing papers on "Diffraction published in 2012"


Journal ArticleDOI
08 Mar 2012-Nature
TL;DR: The method has the sensitivity to measure a 0.1 Å displacement in the oxygen bond length occurring in a time interval of ∼5 fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution.
Abstract: Molecular structures are imaged with sub-angstrom precision and exposure times of a few femtoseconds. Molecular imaging, or the determination of the positions of atoms in molecules, is an important technique in the physical, chemical and biological sciences. But going beyond mere structure determination, recent technical developments offer the tantalizing prospect of access to ultrafast snapshots of biological molecules and condensed-phase systems undergoing structural changes. One approach uses laser-ionized bursts of coherent electron wave packets to self-interrogate the parent molecular structure. Here, Blaga et al. use this laser-induced electron diffraction (LIED) method to map the structural responses of oxygen and nitrogen molecules to ionization. By measuring a 0.1-angstrom displacement in the oxygen bond length occurring in a time interval of about 5 femtoseconds, the authors establish LIED as a promising approach for imaging of gas-phase molecules with unprecedented spatio-temporal resolution. Establishing the structure of molecules and solids has always had an essential role in physics, chemistry and biology. The methods of choice are X-ray and electron diffraction, which are routinely used to determine atomic positions with sub-angstrom spatial resolution. Although both methods are currently limited to probing dynamics on timescales longer than a picosecond, the recent development of femtosecond sources of X-ray pulses and electron beams suggests that they might soon be capable of taking ultrafast snapshots of biological molecules1,2 and condensed-phase systems3,4,5,6 undergoing structural changes. The past decade has also witnessed the emergence of an alternative imaging approach based on laser-ionized bursts of coherent electron wave packets that self-interrogate the parent molecular structure7,8,9,10,11. Here we show that this phenomenon can indeed be exploited for laser-induced electron diffraction10 (LIED), to image molecular structures with sub-angstrom precision and exposure times of a few femtoseconds. We apply the method to oxygen and nitrogen molecules, which on strong-field ionization at three mid-infrared wavelengths (1.7, 2.0 and 2.3 μm) emit photoelectrons with a momentum distribution from which we extract diffraction patterns. The long wavelength is essential for achieving atomic-scale spatial resolution, and the wavelength variation is equivalent to taking snapshots at different times. We show that the method has the sensitivity to measure a 0.1 A displacement in the oxygen bond length occurring in a time interval of ∼5 fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution.

498 citations


Journal ArticleDOI
TL;DR: In this article, the authors review both theoretical and experimental advances in the recently emerged field of modulated photonic lattices and highlight a new type of modulation-induced light localization based on the defect-free surface waves.

401 citations


Journal ArticleDOI
TL;DR: NHWAVE as mentioned in this paper is a shock-capturing non-hydrostatic model for simulating wave refraction, diffraction, shoaling, breaking and landslide-generated tsunami in finite water depth.

380 citations


Journal ArticleDOI
TL;DR: In this article, a new form of low-energy transmission Kikuchi diffraction, performed in the SEM Transmission EBSD (t-EBSD) detector and software, has been proposed to capture and analyse the angular intensity variation in large-angle forward scattering of electrons in transmission.
Abstract: Summary The spatial resolution of electron diffraction within the scanning electron microscope (SEM) has progressed from channelling methods capable of measuring crystallographic characteristics from 10 μm regions to electron backscatter diffraction (EBSD) methods capable of measuring 120 nm particles Here, we report a new form of low-energy transmission Kikuchi diffraction, performed in the SEM Transmission-EBSD (t-EBSD) makes use of an EBSD detector and software to capture and analyse the angular intensity variation in large-angle forward scattering of electrons in transmission, without postspecimen coils We collected t-EBSD patterns from Fe–Co nanoparticles of diameter 10 nm and from 40 nm-thick Ni films with in-plane grain size 15 nm The patterns exhibited contrast similar to that seen in EBSD, but are formed in transmission Monte Carlo scattering simulations showed that in addition to the order of magnitude improvement in spatial resolution from isolated particles, the energy width of the scattered electrons in t-EBSD is nearly two orders of magnitude narrower than that of conventional EBSD This new low-energy transmission diffraction approach builds upon recent progress in achieving unprecedented levels of imaging resolution for materials characterization in the SEM by adding high-spatial-resolution analytical capabilities

355 citations


Journal ArticleDOI
TL;DR: An ultra-thin metamaterial constructed by an ensemble of the same type of anisotropic aperture antennas with phase discontinuity for wave front manipulation across the metammaterial enables effective wave front engineering within a subwavelength scale.
Abstract: We propose an ultra-thin metamaterial constructed by an ensemble of the same type of anisotropic aperture antennas with phase discontinuity for wave front manipulation across the metamaterial. A circularly polarized light is completely converted to the cross-polarized light which can either be bent or focused tightly near the diffraction limit. It depends on a precise control of the optical-axis profile of the antennas on a subwavelength scale, in which the rotation angle of the optical axis has a simple linear relationship to the phase discontinuity. Such an approach enables effective wave front engineering within a subwavelength scale.

320 citations


Journal ArticleDOI
TL;DR: Main features of the cell are an ultimate 90-degrees symmetrical axial opening and high stability, making the presented cell design suitable for a whole range of techniques from optical absorption to single-crystal X-ray diffraction studies, also in combination with external resistive or double-side laser heating.
Abstract: We present a new design of a universal diamond anvil cell, suitable for different kinds of experimental studies under high pressures. Main features of the cell are an ultimate 90-degrees symmetrical axial opening and high stability, making the presented cell design suitable for a whole range of techniques from optical absorption to single-crystal X-ray diffraction studies, also in combination with external resistive or double-side laser heating. Three examples of the cell applications are provided: a Brillouin scattering of neon, single-crystal X-ray diffraction of α-Cr(2)O(3), and resistivity measurements on the (Mg(0.60)Fe(0.40))(Si(0.63)Al(0.37))O(3) silicate perovskite.

258 citations


Journal ArticleDOI
TL;DR: In this article, the size and microstrain of NiO nanoparticles were calculated using Williamson-Hall plots and compared with the results obtained from the Scherrer equation, showing that the straight line obtained in the Williamson-hall plotting shows the homogeneity of the nanoparticles.

212 citations


Journal ArticleDOI
15 Feb 2012-ACS Nano
TL;DR: An optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner, and retrieving the absolute absorption cross section of light-absorbing structures is introduced.
Abstract: We introduce an optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner. Namely, the technique permits (i) mapping the temperature distribution around the source of heat, (ii) mapping the heat power density delivered by the source, and (iii) retrieving the absolute absorption cross section of light-absorbing structures. The technique is based on the measure of the thermal-induced refractive index variation of the medium surrounding the source of heat. The measurement is achieved using an association of a regular CCD camera along with a modified Hartmann diffraction grating. Such a simple association makes this technique straightforward to implement on any conventional microscope with its native broadband illumination conditions. We illustrate this technique on gold nanoparticles illuminated at their plasmonic resonance. The spatial resolution of this technique is diffraction limited, and temperature variations weaker ...

190 citations


Journal ArticleDOI
TL;DR: In this paper, a formal equivalence between generalized refraction and blazed diffraction gratings was established, and the relative merits of the two approaches were discussed, as well as the relative importance of different approaches.
Abstract: When an electromagnetic wave is obliquely incident on the interface between two homogeneous media with different refractive indices, the requirement of phase continuity across the interface generally leads to a shift in the trajectory of the wave. When a linearly position-dependent phase shift is imposed at the interface, the resulting refraction may be described using a generalized version of Snell's law. In this Letter, we establish a formal equivalence between generalized refraction and blazed diffraction gratings, further discussing the relative merits of the two approaches.

190 citations


Journal ArticleDOI
TL;DR: The generation of a new surface wave, the cosine-Gauss beam, is shown to be straightforward and highly controllable, with varying degrees of transverse confinement and directionality, by fabricating a plasmon launcher consisting of intersecting metallic gratings.
Abstract: A new surface wave is introduced, the cosine-Gauss beam, which does not diffract while it propagates in a straight line and tightly bound to the metallic surface for distances up to 80 mu m. The generation of this highly localized wave is shown to be straightforward and highly controllable, with varying degrees of transverse confinement and directionality, by fabricating a plasmon launcher consisting of intersecting metallic gratings. Cosine-Gauss beams have potential for applications in plasmonics, notably for efficient coupling to nanophotonic devices, opening up new design possibilities for next-generation optical interconnects.

185 citations


Journal ArticleDOI
TL;DR: Ab initio phasing of partially coherent diffraction patterns in three dimensions is demonstrated, while simultaneously determining the coherence properties of the illuminating wavefield.
Abstract: The wave properties of light, particularly its coherence, are responsible for interference effects, which can be exploited in powerful imaging applications. Coherent diffractive imaging relies heavily on coherence and has recently experienced rapid growth. Coherent diffractive imaging recovers an object from its diffraction pattern by computational phasing with the potential of wavelength-limited resolution. Diminished coherence results in reconstructions that suffer from artefacts or fail completely. Here we demonstrate ab initio phasing of partially coherent diffraction patterns in three dimensions, while simultaneously determining the coherence properties of the illuminating wavefield. Both the dramatic improvements in image interpretability and the three-dimensional evaluation of the coherence will have broad implications for quantitative imaging of nanostructures and wavefield characterization with X-rays and electrons.

Journal ArticleDOI
TL;DR: In this paper, an extensive measurement campaign of the diffraction at objects like edges, wedges and cylinders for frequencies of 60 and 300 GHz is presented, where different materials, realistic antennas as well as transmission through the objects are taken into account.
Abstract: Current indoor wireless communication systems are shifting from classical microwave bands towards mm wave frequencies, whereas here the 60 GHz band is of special interest. Future systems are expected to work at even higher carrier frequencies in the sub-mm band beyond 300 GHz. In indoor wave propagation channels of such systems, diffraction occurs at a multitude of objects and hence must be considered for propagation simulations. Although the relevance of diffraction has been thouroughly studied at lower frequencies, it has not yet been analyzed methodically in the mm and sub-mm wave frequency range. This paper presents an extensive measurement campaign of the diffraction at objects like edges, wedges and cylinders for frequencies of 60 and 300 GHz. Different materials, realistic antennas as well as transmission through the objects are taken into account. Theoretical approaches are validated against the measurement results. Furthermore, shadowing of rays by persons is investigated and modeled with the help of diffraction. Finally, ray tracing is applied in an office scenario in order to evaluate the impact of diffraction on mm and sub-mm wave indoor channel characteristics.

Journal ArticleDOI
TL;DR: The main physical effects of patterning are focused on, namely a reduction of reflection losses, diffraction of light in air or inside the cell, and coupling of incident radiation into quasi-guided optical modes of the structure, which is characteristic of photonic light-trapping.
Abstract: We theoretically investigate the light-trapping properties of one- and two-dimensional periodic patterns etched on the front surface of c-Si and a-Si thin film solar cells with a silver back reflector and an anti-reflection coating. For each active material and configuration, absorbance A and short-circuit current density Jsc are calculated by means of rigorous coupled wave analysis (RCWA), for different active materials thicknesses in the range of interest of thin film solar cells and in a wide range of geometrical parameters. The results are then compared with Lambertian limits to light-trapping for the case of zero absorption and for the general case of finite absorption in the active material. With a proper optimization, patterns can give substantial absorption enhancement, especially for 2D patterns and for thinner cells. The effects of the photonic patterns on light harvesting are investigated from the optical spectra of the optimized configurations. We focus on the main physical effects of patterning, namely a reduction of reflection losses (better impedance matching conditions), diffraction of light in air or inside the cell, and coupling of incident radiation into quasi-guided optical modes of the structure, which is characteristic of photonic light-trapping.

Journal ArticleDOI
TL;DR: This paper explores methods of measuring elastic strain variations in the presence of larger lattice rotations using high resolution electron backscatter diffraction and demonstrates that accurate recovery of elastic strains requires accurate knowledge of the pattern centre if this remapping algorithm is used.

Journal ArticleDOI
TL;DR: It is shown that new families of diffraction-free nonparaxial accelerating optical beams can be generated by considering the symmetries of the underlying vectorial Helmholtz equation, and fully vectorial self-similar accelerating optical wave solutions are obtained via oblate-prolate spheroidal wave functions.
Abstract: We show that new families of diffraction-free nonparaxial accelerating optical beams can be generated by considering the symmetries of the underlying vectorial Helmholtz equation. Both two-dimensional transverse electric and magnetic accelerating wave fronts are possible, capable of moving along elliptic trajectories. Experimental results corroborate these predictions when these waves are launched from either the major or minor axis of the ellipse. In addition, three-dimensional spherical nondiffracting field configurations are presented along with their evolution dynamics. Finally, fully vectorial self-similar accelerating optical wave solutions are obtained via oblate-prolate spheroidal wave functions. In all occasions, these effects are illustrated via pertinent examples.

Journal ArticleDOI
TL;DR: The results not only substantiate the potential of synchrotron-based experiments for addressing a variety of shock physics problems, but also allow us to identify the technical challenges related to image detection, x-ray source, and dynamic loading.
Abstract: The highly transient nature of shock loading and pronounced microstructure effects on dynamic materials response call for {\it in situ}, temporally and spatially resolved, x-ray-based diagnostics. Third-generation synchrotron x-ray sources are advantageous for x-ray phase contrast imaging (PCI) and diffraction under dynamic loading, due to their high photon energy, high photon fluxes, high coherency, and high pulse repetition rates. The feasibility of bulk-scale gas gun shock experiments with dynamic x-ray PCI and diffraction measurements was investigated at the beamline 32ID-B of the Advanced Photon Source. The x-ray beam characteristics, experimental setup, x-ray diagnostics, and static and dynamic test results are described. We demonstrate ultrafast, multiframe, single-pulse PCI measurements with unprecedented temporal ($<$100 ps) and spatial ($\sim$2 $\mu$m) resolutions for bulk-scale shock experiments, as well as single-pulse dynamic Laue diffraction. The results not only substantiate the potential of synchrotron-based experiments for addressing a variety of shock physics problems, but also allow us to identify the technical challenges related to image detection, x-ray source, and dynamic loading.

Journal ArticleDOI
TL;DR: In this paper, the feasibility of bulk-scale gas gun shock experiments with dynamic x-ray phase contrast imaging (PCI) and diffraction measurements was investigated at the beamline 32ID-B of the Advanced Photon Source.
Abstract: The highly transient nature of shock loading and pronounced microstructure effects on dynamic materials response call for in situ, temporally and spatially resolved, x-ray-based diagnostics. Third-generation synchrotron x-ray sources are advantageous for x-ray phase contrast imaging (PCI) and diffraction under dynamic loading, due to their high photon fluxes, high coherency, and high pulse repetition rates. The feasibility of bulk-scale gas gun shock experiments with dynamic x-ray PCI and diffraction measurements was investigated at the beamline 32ID-B of the Advanced Photon Source. The x-ray beam characteristics, experimental setup, x-ray diagnostics, and static and dynamic test results are described. We demonstrate ultrafast, multiframe, single-pulse PCI measurements with unprecedented temporal (<100 ps) and spatial (∼2 μm) resolutions for bulk-scale shock experiments, as well as single-pulse dynamic Laue diffraction. The results not only substantiate the potential of synchrotron-based experiments for addressing a variety of shock physics problems, but also allow us to identify the technical challenges related to image detection, x-ray source, and dynamic loading.

Journal ArticleDOI
TL;DR: In this article, a modified Warren-Averbach method is proposed for the analysis of the X-ray diffraction line profile based on the approximation by the Voigt function, which yields stable solutions.
Abstract: Different procedures for analysis of particle sizes by the X-ray diffraction method are compared by the example of nanoparticles of nickel and iron(3+) oxide (Fe2O3). A modified Warren-Averbach method is proposed for the analysis of the X-ray diffraction line profile based on the approximation by the Voigt function, which yields stable solutions, and the efficiency of the method is shown. The analysis within the frame-work of the Warren-Averbach method makes it possible to restore the distribution function of nanoparticles (crystallites) over true diameters, which satisfactorily correlates with electron microscopy data. The applicability of the Warren-Averbach method to the estimation of crystallite sizes by the analysis of a single diffraction line is substantiated. The range of the applicability of the Scherrer, Williamson-Hall, Warren-Averbach, and modified Warren-Averbach methods to the substructure analysis by the X-ray diffraction is determined as depending on the method of nanostructure formation.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the principle of coherent diffraction imaging, present various implementation schemes of this imaging modality, and illustrate its broad applications in materials science, nanoscience, and biology.
Abstract: For centuries, lens-based microscopy, such as optical, phase-contrast, fluorescence, confocal, and electron microscopy, has played an important role in the evolution of modern science and technology. In 1999, a novel form of microscopy, i.e., coherent diffraction imaging (also termed coherent diffraction microscopy or lensless imaging), was developed and transformed our conventional view of microscopy, in which the diffraction pattern of a noncrystalline specimen or a nanocrystal was first measured and then directly phased to obtain a high-resolution image. The well-known phase problem was solved by combining the oversampling method with iterative algorithms. In this paper, we will briefly discuss the principle of coherent diffraction imaging, present various implementation schemes of this imaging modality, and illustrate its broad applications in materials science, nanoscience, and biology. As coherent X-ray sources such as high harmonic generation and X-ray free-electron lasers are presently under rapid development worldwide, coherent diffraction imaging can potentially be applied to perform high-resolution imaging of materials/nanoscience and biological specimens at the femtosecond time scale.

Journal ArticleDOI
TL;DR: In this paper, a review of the field is provided, with a viewpoint from materials science, based on the use of highly penetrating hard X-rays from a synchrotron source and the application of tomographic reconstruction algorithms for the analysis of the diffraction data.
Abstract: Three-dimensional X-ray diffraction microscopy is a fast and nondestructive structural characterization technique aimed at studies of the individual crystalline elements (grains or subgrains) within millimetre-sized polycrystalline specimens. It is based on two principles: the use of highly penetrating hard X-rays from a synchrotron source and the application of `tomographic' reconstruction algorithms for the analysis of the diffraction data. In favourable cases, the position, morphology, phase and crystallographic orientation can be derived for up to 1000 elements simultaneously. For each grain its average strain tensor may also be derived, from which the type II stresses can be inferred. Furthermore, the dynamics of the individual elements can be monitored during typical processes such as deformation or annealing. A review of the field is provided, with a viewpoint from materials science.

Journal ArticleDOI
TL;DR: In this article, the equation of state of KCl and KBr, compressed in a helium pressure medium in a diamond-anvil cell, has been measured by x-ray diffraction in the B1 and B2 phases up to 165 GPa at 298 K.
Abstract: The equation of state of KCl and KBr, compressed in a helium pressure medium in a diamond-anvil cell, has been measured by x-ray diffraction in the B1 and B2 phases up to 165 GPa at 298 K. The P-V- ...

Journal ArticleDOI
TL;DR: The addition of on/off control of molecular emission to maintain concentrations at very low levels in each imaging frame combined with sequential imaging of sparse subsets has enabled the reconstruction of images with resolution far below the optical diffraction limit.
Abstract: In this short review, the general principles are described for obtaining microscopic images with resolution beyond the optical diffraction limit with single molecules. Although it has been known for several decades that single-molecule emitters can blink or turn on and off, in recent work the addition of on/off control of molecular emission to maintain concentrations at very low levels in each imaging frame combined with sequential imaging of sparse subsets has enabled the reconstruction of images with resolution far below the optical diffraction limit. Single-molecule active control microscopy provides a powerful window into information about nanoscale structures that was previously unavailable.

Journal ArticleDOI
20 Dec 2012-Nature
TL;DR: From the measured transmission spectra, microscopic scattering parameters are determined which allow us to show that quasi-cylindrical waves affect EOT only for high densities, when the hole spacing is roughly one wavelength.
Abstract: Results on light scattering from metal hole arrays show the relative importance of surface plasmon polaritons and quasi-cylindrical waves in extraordinary optical transmission. Over a decade ago, the 'extraordinary optical transmission' effect was discovered, in which a metal film perforated by a regular array of subwavelength holes shows unexpectedly high light transmittance at specific wavelengths. The effect was found, in part, to depend on surface plasmons, stimulating a renewed interest in plasmonics, but more recently so-called quasicylindrical waves have also been implicated. A detailed study by Frerik van Beijnum et al., involving hole arrays in metal films with varying hole density, now provides definitive quantitative evidence for the respective roles of surface plasmons and quasicylindrical waves, bringing a more complete understanding of the extraordinary optical transmission effect and opening up new possible design strategies. A metal film perforated by a regular array of subwavelength holes shows unexpectedly large transmission at particular wavelengths, a phenomenon known as the extraordinary optical transmission (EOT) of metal hole arrays1. EOT was first attributed to surface plasmon polaritons, stimulating a renewed interest in plasmonics2,3,4 and metallic surfaces with subwavelength features5,6,7. Experiments soon revealed that the field diffracted at a hole or slit is not a surface plasmon polariton mode alone8. Further theoretical analysis9 predicted that the extra contribution, from quasi-cylindrical waves10,11,12,13, also affects EOT. Here we report the experimental demonstration of the relative importance of surface plasmon polaritons and quasi-cylindrical waves in EOT by considering hole arrays of different hole densities. From the measured transmission spectra, we determine microscopic scattering parameters which allow us to show that quasi-cylindrical waves affect EOT only for high densities, when the hole spacing is roughly one wavelength. Apart from providing a deeper understanding of EOT, the determination of microscopic scattering parameters from the measurement of macroscopic optical properties paves the way to novel design strategies.

Journal ArticleDOI
TL;DR: The degeneracy parameter of the FLASH beam is estimated to be on the order of 10(10) to 10(11), which exceeds the values of this parameter at any other source in the same energy range by many orders of magnitude.
Abstract: The experimental characterization of the spatial and temporal coherence properties of the free-electron laser in Hamburg (FLASH) at a wavelength of 8.0 nm is presented. Double pinhole diffraction patterns of single femtosecond pulses focused to a size of about 10×10 μm2 were measured. A transverse coherence length of 6.2 ± 0.9 μm in the horizontal and 8.7 ± 1.0 μm in the vertical direction was determined from the most coherent pulses. Using a split and delay unit the coherence time of the pulses produced in the same operation conditions of FLASH was measured to be 1.75 ± 0.01 fs. From our experiment we estimated the degeneracy parameter of the FLASH beam to be on the order of 1010 to 1011, which exceeds the values of this parameter at any other source in the same energy range by many orders of magnitude.

Journal ArticleDOI
TL;DR: In this paper, a series solution of wave functions for 2D scattering and diffraction of plane SH (shear horizontal) waves induced by a U-shaped canyon is proposed to account for the topographic effect of such a canyon.
Abstract: The series solution of wave functions for 2D scattering and diffraction of plane SH (shear horizontal) waves induced by a U‐shaped canyon is proposed herein to account for the topographic effect of such a canyon. The wave function expansion method has been frequently employed to study the topographic effect because it can reveal the physics of the wave scattering and can test the accuracy of other methods. Through a new domain decomposition strategy, the half‐space having a U‐shaped canyon is divided into three subregions. Hence, we defined three cylindrical coordinate systems. In each coordinate system, the wave field satisfying the Helmholtz equation was represented by means of the separation of variables method, in terms of the series of both Bessel functions and Hankel functions with unknown complex coefficients. Then three wave fields are all represented in the same coordinate system using the Graf addition theorem. The unknown coefficients are solved by satisfying the continuity conditions of the auxiliary boundary and the traction‐free boundary conditions on the bottom of the canyon. To show the effects of symmetrical and nonsymmetrical U‐shaped canyons on the surface ground motion, a parametric analysis is carried out in the frequency domain. Surface and subsurface transient responses in the time domain demonstrate the phenomenon of wave propagating and scattering. It is found that a zone of amplification can obviously take place at the bottom of a U‐shaped canyon with nearly vertical walls.

Journal ArticleDOI
TL;DR: Vaterite, a polymorph of CaCO(3) was first mentioned by H. Vater in 1897, plays key roles in weathering and biomineralization processes, but occurs only in the form of nanosized crystals, unsuitable for structure determination.
Abstract: tion that is fundamental for understanding material properties. Still, a number of compounds have eluded such kinds of analysis because they are nanocrystalline, highly disordered, with strong pseudosymmetries or available only in small amounts in polyphasic or polymorphic systems. These materials are crystallographically intractable with conventional Xray or synchrotron radiation diffraction techniques. Single nanoparticles can be visualized by high-resolution transmission electron microscopy (HR-TEM) up to sub�ngstrom resolution, [2] but obtaining 3D information is still a difficult task, especially for highly beam-sensitive materials and crystal structures with long cell parameters. Electron diffraction (ED) delivers higher resolved data with a significant lower electron dose on the sample, but is biased by a substantial number of missing reflections and the occurrence of dynamic scattering that affects reflection intensities. [3] Therefore, ED is mainly used in combination with Xray powder diffraction and high-resolution electron microscopy. [4]

Journal ArticleDOI
TL;DR: In this article, the Weber wave model is introduced, which is a class of non-paraxial wave systems that propagate along parabolic trajectories while approximately preserving their shape.
Abstract: Diffraction is one of the universal phenomena of physics, and a way to overcome it has always represented a challenge for physicists. In order to control diffraction, the study of structured waves has become decisive. Here, we present a specific class of nondiffracting spatially accelerating solutions of the Maxwell equations: the Weber waves. These nonparaxial waves propagate along parabolic trajectories while approximately preserving their shape. They are expressed in an analytic closed form and naturally separate in forward and backward propagation. We show that the Weber waves are self-healing, can form periodic breather waves and have a well-defined conserved quantity: the parabolic momentum. We find that our Weber waves for moderate to large values of the parabolic momenta can be described by a modulated Airy function. Because the Weber waves are exact time-harmonic solutions of the wave equation, they have implications for many linear wave systems in nature, ranging from acoustic, electromagnetic and elastic waves to surface waves in fluids and membranes.

Journal ArticleDOI
TL;DR: In this paper, the authors used caustic beam shaping on 100 fs pulses to experimentally generate non-paraxial accelerating beams along a 60 degree circular arc, moving laterally by 14 µm over a 28 µm propagation length.
Abstract: We use caustic beam shaping on 100 fs pulses to experimentally generate non-paraxial accelerating beams along a 60 degree circular arc, moving laterally by 14 \mum over a 28 \mum propagation length. This is the highest degree of transverse acceleration reported to our knowledge. Using diffraction integral theory and numerical beam propagation simulations, we show that circular acceleration trajectories represent a unique class of non-paraxial diffraction-free beam profile which also preserves the femtosecond temporal structure in the vicinity of the caustic.

Journal ArticleDOI
TL;DR: In this article, the evolution of internal lattice strains in face-centered cubic stainless steel under uniaxial tension is studied using a recently developed full-field elasto-viscoplastic formulation based on fast Fourier transforms.

Journal ArticleDOI
01 Aug 2012-Strain
TL;DR: In this paper, the authors present the results of high-resolution strain maps of a ferritic steel cantilever sample measured at different loads by both transmission and conventional diffraction modes, as well as strains in an austenitic steel compact-tension (CT) crack sample.
Abstract: Conventional neutron radiography can be strongly enhanced by obtaining Bragg-edge information spatially correlated with the attenuation coefficient. This can now be achieved through time-of-flight techniques at pulsed neutron sources, utilising a neutron counting detector with high-spatial and high-temporal resolution. In these measurements, the positions of Bragg edges can in principle be obtained for each 55 × 55 μm2 pixel of the radiographic image. The combination of both Bragg-edge and attenuation information enables high spatial resolution studies to be carried out on material composition, phase transitions, texture variations, as well as residual strain mapping. In this article, we present the results of high-resolution strain maps of a ferritic steel cantilever sample measured at different loads by both transmission and conventional diffraction modes, as well as strains in an austenitic steel compact-tension (CT) crack sample. The proof of principle experiments performed on the ENGIN-X beamline on a bent cantilever arrangement resulting in a uni-axial stress field verified that the strain values measured in diffraction and transmission mode are in good agreement. The characteristics of the transmission mode detector as well as the measured strain maps and future possibilities of this technology are discussed.