Showing papers on "Beam (structure) published in 2004"
TL;DR: The transfer of information encoded as orbital angular momentum states of a light beam is demonstrated, which is resistant to eavesdropping and gives an experimental insight into the effects of aperturing and misalignment of the beam on the OAM measurement and demonstrates the uncertainty relationship for OAM.
Abstract: We demonstrate the transfer of information encoded as orbital angular momentum (OAM) states of a light beam. The transmitter and receiver units are based on spatial light modulators, which prepare or measure a laser beam in one of eight pure OAM states. We show that the information encoded in this way is resistant to eavesdropping in the sense that any attempt to sample the beam away from its axis will be subject to an angular restriction and a lateral offset, both of which result in inherent uncertainty in the measurement. This gives an experimental insight into the effects of aperturing and misalignment of the beam on the OAMmeasurement and demonstrates the uncertainty relationship for OAM.
2,230 citations
TL;DR: In this article, the structural response of the sandwich beam is split into three sequential steps: stage I is the one-dimensional fluid-structure interaction problem during the blast loading event, and results in a uniform velocity of the outer face sheet; during stage II the core crushes and the velocities of the faces and core become equalized by momentum sharing; stage III is the retardation phase over which the beam is brought to rest by plastic bending and stretching.
Abstract: A systematic design procedure has been developed for analyzing the blast resistance of clamped sandwich beams. The structural response of the sandwich beam is split into three sequential steps: stage I is the one-dimensional fluid-structure interaction problem during the blast loading event, and results in a uniform velocity of the outer face sheet; during stage II the core crushes and the velocities of the faces and core become equalized by momentum sharing; stage III is the retardation phase over which the beam is brought to rest by plastic bending and stretching. The third-stage analytical procedure is used to obtain the dynamic response of a clamped sandwich beam to an imposed impulse. Performance charts for a wide range of sandwich core topologies are constructed for both air and water blast, with the monolithic beam taken as the reference case. These performance charts are used to determine the optimal geometry to maximize blast resistance for a given mass of sandwich beam. For the case of water blast, an order of magnitude improvement in blast resistance is achieved by employing sandwich construction, with the diamond-celled core providing the best blast performance. However, in air blast, sandwich construction gives only a moderate gain in blast resistance compared to monolithic construction.
560 citations
TL;DR: The fundamental parameters approach to line profile fitting uses physically based models to generate the line profile shapes Fundamental parameters profile fitting (FPPF) has been used to synthesize and fit data from both parallel beam and divergent beam diffractometers as mentioned in this paper.
Abstract: The fundamental parameters approach to line profile fitting uses physically based models to generate the line profile shapes Fundamental parameters profile fitting (FPPF) has been used to synthesize and fit data from both parallel beam and divergent beam diffractometers The refined parameters are determined by the diffractometer configuration In a divergent beam diffractometer these include the angular aperture of the divergence slit, the width and axial length of the receiving slit, the angular apertures of the axial Soller slits, the length and projected width of the x-ray source, the absorption coefficient and axial length of the sample In a parallel beam system the principal parameters are the angular aperture of the equatorial analyser/Soller slits and the angular apertures of the axial Soller slits The presence of a monochromator in the beam path is normally accommodated by modifying the wavelength spectrum and/or by changing one or more of the axial divergence parameters Flat analyzer crystals have been incorporated into FPPF as a Lorentzian shaped angular acceptance function One of the intrinsic benefits of the fundamental parameters approach is its adaptability any laboratory diffractometer Good fits can normally be obtained over the whole 20 range without refinement using the known properties of the diffractometer, such as the slit sizes and diffractometer radius, and emission profile
510 citations
TL;DR: In this paper, a record peak intensity of 0.7×1022 W/cm2 was achieved by focusing a 45-TW laser beam with an f/0.6 off-axis paraboloid.
Abstract: We generated a record peak intensity of 0.7×1022 W/cm2 by focusing a 45-TW laser beam with an f/0.6 off-axis paraboloid. The aberrations of the paraboloid and the low-energy reference laser beam were measured and corrected, and a focal spot size of 0.8 µm was achieved. It is shown that the peak intensity can be increased to 1.0×1022 W/cm2 by correction of the wave front of a 45-TW beam relative to the reference beam. The phase and amplitude measurement provides for an efficient full characterization of the focal field.
350 citations
TL;DR: Experiments show the first experimental evidence of negative refraction at telecommunication wavelengths by a two-dimensional photonic crystal field by chemically assisted ion beam etching in the InP-based low-index constrast system.
Abstract: We report on the first experimental evidence of negative refraction at telecommunication wavelengths by a two-dimensional photonic crystal field. Samples were fabricated by chemically assisted ion beam etching in the InP-based low-index constrast system. Experiments of beam imaging and light collection show light focusing by the photonic crystal field. Finite-difference time-domain simulations confirm that the observed focusing is due to negative refraction in the photonic crystal area.
344 citations
TL;DR: In this article, the phase structure of an optical beam with an eil phase structure was examined after propagation through an interference-based phase-measurement technique, and it was observed that a line of alternating charge vortices is formed near the radial dislocation.
Abstract: An optical beam with an eil phase structure carries an orbital angular momentum of l per photon. For integer l values, the phase fronts of such beams form perfect helices with a single screw-phase dislocation, or vortex, on the beam axis. For non-integer l values, Berry (2004 J. Opt. A: Pure Appl. Opt. 6 259) predicts a complex-phase structure comprising many vortices at differing positions within the beam cross-section. Using a spatial light modulator we produce eil beams with varying l. We examine the phase structure of such beams after propagation through an interference-based phase-measurement technique. As predicted, we observe that for half-integer l values, a line of alternating charge vortices is formed near the radial dislocation.
338 citations
TL;DR: The experimental observation of a degaussification protocol, mapping individual femtosecond pulses of squeezed light onto non-Gaussian states by using only simple linear optical elements is described.
Abstract: We describe the observation of a "degaussification" protocol that maps individual pulses of squeezed light onto non-Gaussian states. This effect is obtained by sending a small fraction of the squeezed vacuum beam onto an avalanche photodiode, and by conditioning the single-shot homodyne detection of the remaining state upon the photon-counting events. The experimental data provide clear evidence of phase-dependent non-Gaussian statistics. This protocol is closely related to the first step of an entanglement distillation procedure for continuous variables.
336 citations
TL;DR: Interindividual comparisons of cross-sectional properties calculated from centroidal axes may be useful in terms of pattern, but are subject to high errors in Terms of absolute values.
Abstract: Long bone loading histories are commonly evaluated using a beam model by calculating cross-sectional second moments of areas (SMAs). Without in vivo strain data, SMA analyses commonly make two explicit or implicit assumptions. First, while it has long been known that axial compression superimposed on bending shifts neutral axes away from cross-sectional area centroids, most analyses assume that cross-sectional properties calculated through the area centroid approximate cross-sectional strength. Second, the orientation of maximum bending rigidity is often assumed to reflect the orientation of peak or habitual bending forces the bone experiences. These assumptions are tested in sheep in which rosette strain gauges mounted at three locations around the tibia and metatarsal midshafts measured in vivo strains during treadmill running at 1.5 m/sec. Calculated normal strain distributions confirm that the neutral axis of bending does not run through the midshaft centroid. In these animals, orientations of the principal centroidal axes around which maximum SMAs (Imax) are calculated are not in the same planes in which the bones experienced bending. Cross-sectional properties calculated using centroidal axes have substantial differences in magnitude (up to 55%) but high correlations in pattern compared to cross-sectional properties calculated around experimentally determined neutral axes. Thus interindividual comparisons of cross-sectional properties calculated from centroidal axes may be useful in terms of pattern, but are subject to high errors in terms of absolute values. In addition, cross-sectional properties do not necessarily provide reliable data on the orientations of loads to which bones are subjected.
303 citations
TL;DR: In this article, a multilevel spiral phase plate (SPP) was developed to generate an Laguerre-Gaussian beam by applying the wave surface of a spiral structure directly to a Gaussian beam for application to microscopic laser material processing.
Abstract: We investigated an Laguerre-Gaussian (LG) beam that can carry an orbital angular momentum and has a doughnut-shaped intensity pattern. We developed a multilevel spiral phase plate (SPP) that generates an LG beam by applying the wave surface of a spiral structure directly to a Gaussian beam for application to microscopic laser material processing.We experimentally demonstrate, for the first time, that it is possible to generate an LG beam with the multilevel SPP that allows the use in high intensity laser pulses.
286 citations
TL;DR: In this paper, a stochastic process for assessing the effect of spatial variability of pitting corrosion on structural reliability and fragility is developed for singly reinforced simply supported reinforced concrete (RC) beams in flexure.
276 citations
TL;DR: In this article, a form of unified theory, where a confinement factor was introduced to describe the composite action between the steel tube and filled concrete, is used in the analysis of concrete-filled hollow structural section (HSS) beams.
TL;DR: In this article, the three-point bending collapse strength of composite-polymer foam sandwich beams with composite faces and polymer foam cores has been analyzed and an indentation model for elastic faces and an elastic-plastic core has been developed.
TL;DR: In this article, the authors present the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads.
Abstract: This paper presents the results of experimental tests carried out on rectangular simply supported beams made of hooked steel fibre reinforced concrete with and without stirrups, subjected to two-point symmetrically placed vertical loads. The tests, carried out with controlled displacements, allow one to record complete load–deflection curves by means of which it is possible to deduce information on dissipative capacity and ductile behaviour up to failure. Depending on the amount of transverse reinforcement, volume fraction of fibres added in the mix and shear span, the collapse mechanism is due to predominant shear or flexure, thus showing the influence of the aforementioned structural parameters on the load carrying capacity and the post-peak behaviour of the beam. In particular, the results show that the inclusion of fibres in adequate percentage can change the brittle mode of failure characterizing shear collapse into a ductile flexural mechanism, confirming the possibility of achieving analogous performance by using reinforcing fibres instead of increasing the amount of transverse reinforcement. The ultimate values of the shear stresses recorded experimentally are compared with the corresponding values deduced by semiempirical expressions available in the literature and the correlation is satisfactory.
Patent•
22 Jun 2004
TL;DR: In this article, a particle therapy system is provided which can simply and quickly correct a beam orbit, and the correction bending amounts for causing the beam to be coincident with a predetermined orbit after the correction are determined in accordance with detected results from the first and second beam position monitors.
Abstract: A particle therapy system is provided which can simply and quickly correct a beam orbit. In a particle therapy system provided with an irradiation facility comprising a first beam transport system for receiving a beam and transporting the beam to the patient side, and an irradiation nozzle for forming an irradiation field of the beam, the particle therapy system comprises first beam position monitors for detecting a position upstream of the irradiation nozzle at which the beam passes, second beam position monitors for detecting a position downstream of the irradiation nozzle at which the charged-particle beam passes, and first and second steering magnets. Correction bending amounts for causing the beam to be coincident with a predetermined orbit after the correction are determined in accordance with detected results from the first and second beam position monitors, and first and second steering magnets are excited under control so that the determined correction bending amounts are obtained.
TL;DR: General expressions for Gauss-Laguerre beams being focused through a stratified medium are obtained and it is shown that the circularly polarised, lowest order "dark" beam is the most beneficial for STED purposes.
Abstract: This paper examines the use of Gauss-Laguerre beams in STED microscopy. These types of beams are shown to have beneficial properties that can be utilised to generate stable, high quality STED beams resulting in an aberration-resilient generation volume. In this paper we obtain general expressions for Gauss-Laguerre beams being focused through a stratified medium and describe their optimization for STED microscopy purposes. Our results show that the circularly polarised, lowest order "dark" beam is the most beneficial for STED purposes.
Patent•
09 Jun 2004
TL;DR: In this paper, an incident image displaying device for displaying at least one incident image against a scene image of a scene, where the scene image reflector is located behind the light guide, the input beam transforming element receives from the respective light guide and decouples as decoupled light beams, thereby forming a set of coupled light beams.
Abstract: Incident image displaying device for displaying at least one incident image against a scene image of a scene, the incident image displaying device including at least one light guide, at least one input beam transforming element, at least one output beam transforming element and a scene image reflector, each of the input beam transforming element and the output beam transforming element being incorporated with a respective light guide, the scene image reflector being located behind the light guide, the input beam transforming element receiving incident light beams respective of the incident image from a respective one of at least one image source, the output beam transforming element being associated with a respective input beam transforming element, the scene image reflector reflecting the scene image through at least a portion of the output beam transforming element, wherein the input beam transforming element couples the incident light beams into the respective light guide as a set of coupled light beams, the set of coupled light beams is associated with the respective input beam transforming element, wherein the output beam transforming element receives from the respective light guide and decouples as decoupled light beams, the set of coupled light beams, thereby forming a set of output decoupled images, and wherein each output decoupled image of the set of output decoupled images is representative of a sensor fused image of the incident image
TL;DR: The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles, and the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments is presented.
Abstract: Monte Carlo dosimetry calculations are essential methods in radiation therapy. To take full advantage of this tool, the beam delivery system has to be simulated in detail and the initial beam parameters have to be known accurately. The modeling of the beam delivery system itself opens various areas where Monte Carlo calculations prove extremely helpful, such as for design and commissioning of a therapy facility as well as for quality assurance verification. The gantry treatment nozzles at the Northeast Proton Therapy Center (NPTC) at Massachusetts General Hospital (MGH) were modeled in detail using the GEANT4.5.2 Monte Carlo code. For this purpose, various novel solutions for simulating irregular shaped objects in the beam path, like contoured scatterers, patient apertures or patient compensators, were found. The four-dimensional, in time and space, simulation of moving parts, such as the modulator wheel, was implemented. Further, the appropriate physics models and cross sections for proton therapy applications were defined. We present comparisons between measured data and simulations. These show that by modeling the treatment nozzle with millimeter accuracy, it is possible to reproduce measured dose distributions with an accuracy in range and modulation width, in the case of a spread-out Bragg peak (SOBP), of better than 1 mm. The excellent agreement demonstrates that the simulations can even be used to generate beam data for commissioning treatment planning systems. The Monte Carlo nozzle model was used to study mechanical optimization in terms of scattered radiation and secondary radiation in the design of the nozzles. We present simulations on the neutron background. Further, the Monte Carlo calculations supported commissioning efforts in understanding the sensitivity of beam characteristics and how these influence the dose delivered. We present the sensitivity of dose distributions in water with respect to various beam parameters and geometrical misalignments. This allows the definition of tolerances for quality assurance and the design of quality assurance procedures.
TL;DR: A three-dimensional variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF), based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector.
Abstract: A three-dimensional (3D) variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method is based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector. The experimental arrangement represents a significant generalization of regular two-dimensional (2D) scanning micro-XRF and employs a detector half-lens whose focus coincides with that of the focused incoming beam. The detection volume defined by the intersection of the exciting beam and the energy-dependent acceptance of the polycapillary optics is 100−350 μm3. Minimum detection limits are sub-ppm, and sensitivities are comparable with regular scanning XRF. Next to the reduction of in-sample single/multiple scattering, the setup provides the possibility of sample depth scans with an energy-dependent resolution of 10−35 μm in the energy range of 3−23 keV and the possibility of performing 3D-XRF analy...
TL;DR: In this paper, an analytical solution is presented to calculate the stresses in the reinforced beam under mechanical as well as thermal loads, and the solution has been extended by a numerical procedure to CFRP plates with tapered ends.
TL;DR: Monte Carlo modelling of the damage formed indicates that recoil silicon atoms contribute significantly to the damaged formed in the specimen, indicating that redeposition of milled material, enriched in gallium, can occur depending on the geometry of the mill employed.
Abstract: The damage created in silicon transmission electron microscope specimens prepared using a focused ion beam miller is assessed using cross-sections of trenches milled under different beam conditions. Side-wall damage consists of an amorphous layer formed by direct interaction with the energetic gallium ion beam; a small amount of implanted gallium is also detected. By contrast, bottom-wall damage layers are more complex and contain both amorphous films and crystalline regions that are richer in implanted gallium. More complex milling sequences show that redeposition of milled material, enriched in gallium, can occur depending on the geometry of the mill employed. The thickness of the damage layers depends strongly on beam energy, but is independent of beam current. Monte Carlo modelling of the damage formed indicates that recoil silicon atoms contribute significantly to the damaged formed in the specimen.
TL;DR: In this paper, an analytical expression for the mutual coherence function (MCF) and the scintillation index of a partially coherent lowest order Gaussian beam wave propagating through the atmosphere (based on Kolmogorov spectrum model) is developed for the pupil plane of a receiving system.
Abstract: Analytic expressions for the mutual coherence function (MCF) and the scintillation index of a partially coherent lowest order Gaussian beam wave propagating through the atmosphere (based on Kolmogorov spectrum model) are developed for the pupil plane of a receiving system. Partial coherence of the beam is modeled as a thin (complex) phase screen with Gaussian spectrum (Rytov theory and ABCD ray matrices are applied). The relation between the second- and fourth-order statistics for a beam with any degree of coherence in the atmosphere is introduced with the help of ''effective'' beam parameters, deduced from the free-space MCF. In particular, the scintillation (in weak and strong atmospheric conditions), based on these parameters, is stud- ied as a function of the diffuser's strength and that of the atmosphere. The model is applied for the calculation of the SNR and bit error rates (OOK modulation) of the communication link with diffuser at the trans- mitter and slow detection system. The improvement of bit error rates is observed in weak and strong atmospheric turbulence. In the weak re- gime, the optimal diffuser can be found. © 2004 Society of Photo-Optical Instru-
TL;DR: In this article, a small-angle X-ray scattering camera, NanoSTAR from Bruker AXS, has been modified to optimize its use for weakly scattering solution samples.
Abstract: A commercially available small-angle X-ray scattering camera, NanoSTAR from Bruker AXS, has been modified to optimize its use for weakly scattering solution samples. The original NanoSTAR is a pinhole camera with two Gobel mirrors for monochromating and making the beam parallel, and with a two-dimensional position-sensitive gas detector (HiSTAR) for data collection. The instrument has one integrated vacuum. It was constructed for position-resolved studies and thus has a small beam size at the sample position. In the present work, the instrumental configuration has been optimized by numerical calculations based on phase-space analysis and Monte Carlo simulations in order to obtain a higher flux. This has led to a setup in which the beam at the sample is larger and the collimation part of the instrument is longer, so that divergence of the beam is similar to that of the original camera. An extra pinhole is included after the Gobel mirrors to make the beam size well defined after the mirrors. The camera thus has genuine three-pinhole collimation. The use of electron-microscope pinholes minimizes parasitic scattering. At the University of Aarhus, the modified camera is installed on a powerful rotating-anode X-ray source (MacScience 6 kW Cu with a 0.3 × 0.3 mm effective source size). Measurements have been performed on a wide variety of weakly scattering samples, such as surfactant micelles, homopolymer solutions, block copolymer micelles, proteins etc. The data are routinely converted to absolute scale using the scattering from water as a primary standard. The standard configuration covers the range of scattering vectors from 0.01 to 0.35 A−1 with a flux of 1.7 × 107 photons s−1 for Cu Kα radiation at a generator power of 4.05 kW. The camera is easily converted to a high-resolution version covering 0.0037 to 0.22 A−1 with a loss of flux of about a factor of 10, as well as to a position-resolved version.
TL;DR: In this paper, the authors used ANNs to predict the ultimate shear strength of reinforced concrete (RC) beams with transverse reinforcements, and the results showed that ANNs have strong potential as a feasible tool for predicting the ultimate strength of RC beams with reinforced reinforcement within the range of input parameters considered.
TL;DR: In this paper, the authors focus on the competing collapse mechanisms for simply supported sandwich beams with composite faces and a PVC foam core subjected to three-point bending, and a failure mechanism map is constructed to reveal the dependence of the dominant collapse mechanism upon the geometry of the beam.
TL;DR: In this article, the authors reported abnormally large positive and negative lateral optical beam shifts at a metal-air interface when the surface plasmon resonance of the metal is excited and identified the optimal thickness for minimal resonant reflection as the critical thickness above which a negative beam displacement is observed.
Abstract: We report abnormally large positive and negative lateral optical beam shifts at a metal–air interface when the surface plasmon resonance of the metal is excited. The optimal thickness for minimal resonant reflection is identified as the critical thickness above which a negative beam displacement is observed. Experimental results show good agreement with theoretical predictions and the large observed bidirectional beam displacements also indicate the existence of forward and backward surface propagating waves at the surface plasmon resonance of the metal.
TL;DR: In this paper, an adjusted Iwan beam element (AIBE) is proposed for dynamic response analysis of beam structures containing joints, which consists of a combination of springs and frictional sliders that exhibits nonlinear behavior due to the stick-slip characteristic of the latter.
TL;DR: In this paper, a few-mode fiber excited by a Laguerre-Gaussian beam is used to produce light beams with radial, azimuthal, and hybrid polarization.
TL;DR: In this article, two-dimensional bright circular solitons are formed thanks to a strong static bias field, externally applied, opposite to the photovoltaic internal field, and the dynamics of the soliton formation is monitored and compared to a time-dependent numerical model.
Abstract: Photorefractive screening-photovoltaic solitons are observed in lithium niobate. Two-dimensional bright circular solitons are formed thanks to a strong static bias field, externally applied, opposite to the photovoltaic internal field. The dynamics of the soliton formation is monitored and compared to a time-dependent numerical model allowing determination of the photovoltaic field. Efficient single mode waveguides are shown to be memorized by the soliton beam for a long time.
20 Jan 2004
TL;DR: In this article, the authors present tractable mathematical models from which the practitioner can readily determine beam spreading, beam wander, spatial coherence radius (Fried's parameter), angle of arrival fluctuations, scintillation, aperture averaging effects, fade probabilities, bit error-rates, and enhanced backscatter effects, among others.
Abstract: The material in this Field Guide is a condensed version of similar material found in two textbooks: Laser Beam Propagation through Random Media (SPIE Vol. PM53) and Laser Beam Scintillation with Applications (SPIE Vol. PM99). Topics chosen for this concise presentation include a review of classical Kolmogorov turbulence theory, Gaussian-beam waves in free space, and atmospheric effects on a propagating optical wave. These atmospheric effects have great importance in a variety of applications like imaging, free space optical communications, laser radar, and remote sensing. This Guide presents tractable mathematical models from which the practitioner can readily determine beam spreading, beam wander, spatial coherence radius (Fried's parameter), angle of arrival fluctuations, scintillation, aperture averaging effects, fade probabilities, bit error-rates, and enhanced backscatter effects, among others.
Patent•
03 Mar 2004TL;DR: In this article, a particle beam therapy system consisting of a charged particle beam generator for emitting a charge particle beam, a plurality of treatment rooms provided with respective irradiation units, one first beam transport system for transporting the emitted beam toward the downstream side in the direction of beam advance, a first group of shutters provided downstream of the switching electromagnets and shutting off respective beam paths.
Abstract: A particle beam therapy system which can surely prevent a beam from being erroneously transported to a treatment room that is not an irradiation target, and can improve safety. The particle beam therapy system comprises a charged particle beam generator for emitting a charged particle beam, a plurality of treatment rooms provided with respective irradiation units, one first beam transport system for transporting the emitted beam toward the downstream side in the direction of beam advance, a plurality of second beam transport systems branched from the first beam transport system and transporting the beam to the corresponding irradiation units in the treatment rooms, a plurality of switching electromagnets for bending the beam transported through the first beam transport system to be introduced to the corresponding second beam transport systems, and a first group of shutters provided downstream of the switching electromagnets and shutting off respective beam paths.