Scheme for Low Energy Beam Transport with a Non-Neutralized Section
Energy Technology Data Exchange (ETDEWEB)
Shemyakin, A. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Prost, L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
2015-04-23
A typical Low Energy Beam Transport (LEBT) design relies on dynamics with nearly complete beam space charge neutralization over the entire length of the LEBT. This paper argues that, for a beam with modest perveance and uniform current density distribution when generated at the source, a downstream portion of the LEBT can be un-neutralized without significant emittance growth.
Bidirectional beam propagation method
Kaczmarski, P.; Lagasse, P. E.
1988-05-01
A bidirectional extension of the beam propagation method (BPM) to optical waveguides with a longitudinal discontinuity is presented. The algorithm is verified by computing a reflection of the TE(0) mode from a semiconductor laser facet. The bidirectional BPM is applicable to other configurations such as totally reflecting waveguide mirrors, an abruption transition in a waveguide, or a waveguide with many discontinuities generating multiple reflections. The method can also be adapted to TM polarization.
Diagnostics for the ATA beam propagation experiments
Energy Technology Data Exchange (ETDEWEB)
Fessenden, T.J.; Atchison, W.L.; Barletta, W.A.
1981-11-01
This report contains a discussion of the diagnostics required for the beam propagation experiment to be done with the ATA accelerator. Included are a list of the diagnostics needed; a description of the ATA experimental environment; the status of beam diagnostics available at Livermore including recent developments, and a prioritized list of accelerator and propagation diagnostics under consideration or in various stages of development.
Wave Beam Propagation Through Density Fluctuations
Balakin, A. A.; Bertelli, N.; Westerhof, E.
2011-01-01
Perturbations induced by edge density fluctuations on electron cyclotron wave beams propagating in fusion plasmas are studied by means of a quasi-optical code. The effects of such fluctuations are illustrated here by showing the beam propagation in the case of single harmonic perturbations to the wa
Generalized rectangular finite difference beam propagation method.
Sujecki, Slawomir
2008-08-10
A method is proposed that allows for significant improvement of the numerical efficiency of the standard finite difference beam propagation algorithm. The advantages of the proposed method derive from the fact that it allows for an arbitrary selection of the preferred direction of propagation. It is demonstrated that such flexibility is particularly useful when studying the properties of obliquely propagating optical beams. The results obtained show that the proposed method achieves the same level of accuracy as the standard finite difference beam propagation method but with lower order Padé approximations and a coarser finite difference mesh.
Laser beam propagation generation and propagation of customized light
Forbes, Andrew
2014-01-01
""The text is easy to read and is accompanied by beautiful illustrations. It is an excellent book for anyone working in laser beam propagation and an asset for any library.""-Optics & Photonics News, July 2014
Electromagnetic beam propagation in nonlinear media
Institute of Scientific and Technical Information of China (English)
V.V.Semak; M.N.Shneider
2015-01-01
We deduce a complete wave propagation equation that includes inhomogeneity of the dielectric constant and present this propagation equation in compact vector form. Although similar equations are known in narrow fields such as radio wave propagation in the ionosphere and electromagnetic and acoustic wave propagation in stratified media, we develop here a novel approach of using such equations in the modeling of laser beam propagation in nonlinear media. Our approach satisfies the correspondence principle since in the limit of zero-length wavelength it reduces from physical to geometrical optics.
Beam-propagation method - Analysis and assessment
van Roey, J.; van der Donk, J.; Lagasse, P. E.
1981-07-01
A method for the calculation of the propagation of a light beam through an inhomogeneous medium is presented. A theoretical analysis of this beam-propagation method is given, and a set of conditions necessary for the accurate application of the method is derived. The method is illustrated by the study of a number of integrated-optic structures, such as thin-film waveguides and gratings.
Negative propagation effect in nonparaxial Airy beams.
Vaveliuk, Pablo; Martinez-Matos, Oscar
2012-11-19
Negative propagation is an unusual effect concerning the local sign change in the Poynting vector components of an optical beam under free propagation. We report this effect for finite-energy Airy beams in a subwavelength nonparaxial regime. This effect is due to a coupling process between propagating and evanescent plane waves forming the beam in the spectral domain and it is demonstrated for a single TE or TM mode. This is contrary to what happens for vector Bessel beams and vector X-waves, for which a complex superposition of TE and TM modes is mandatory. We also show that evanescent waves cannot contribute to the energy flux density by themselves such that a pure evanescent Airy beam is not physically realizable. The break of the shape-preserving and diffraction-free properties of Airy beams in a nonparaxial regime is exclusively caused by the propagating waves. The negative propagation effect in subwavelength nonparaxial Airy beams opens new capabilities in optical traps and tweezers, optical detection of invisibility cloacks and selective on-chip manipulation of nanoparticles.
Nonparaxial Propagation of Vectorial Elliptical Gaussian Beams
Directory of Open Access Journals (Sweden)
Wang Xun
2016-01-01
Full Text Available Based on the vectorial Rayleigh-Sommerfeld diffraction integral formulae, analytical expressions for a vectorial elliptical Gaussian beam’s nonparaxial propagating in free space are derived and used to investigate target beam’s propagation properties. As a special case of nonparaxial propagation, the target beam’s paraxial propagation has also been examined. The relationship of vectorial elliptical Gaussian beam’s intensity distribution and nonparaxial effect with elliptic coefficient α and waist width related parameter fω has been analyzed. Results show that no matter what value of elliptic coefficient α is, when parameter fω is large, nonparaxial conclusions of elliptical Gaussian beam should be adopted; while parameter fω is small, the paraxial approximation of elliptical Gaussian beam is effective. In addition, the peak intensity value of elliptical Gaussian beam decreases with increasing the propagation distance whether parameter fω is large or small, and the larger the elliptic coefficient α is, the faster the peak intensity value decreases. These characteristics of vectorial elliptical Gaussian beam might find applications in modern optics.
Vertical laser beam propagation through the troposphere
Minott, P. O.; Bufton, J. L.; Schaefer, W. H.; Grolemund, D. A.
1974-01-01
The characteristics of the earth's atmosphere and its effects upon laser beams was investigated in a series of balloon borne, optical propagation experiments. These experiments were designed to simulate the space to ground laser link. An experiment to determine the amplitude fluctuation, commonly called scintillation, caused by the atmosphere was described.
Laser beam shaping profiles and propagation.
Shealy, David L; Hoffnagle, John A
2006-07-20
We consider four families of functions--the super-Gaussian, flattened Gaussian, Fermi-Dirac, and super-Lorentzian--that have been used to describe flattened irradiance profiles. We determine the shape and width parameters of the different distributions, when each flattened profile has the same radius and slope of the irradiance at its half-height point, and then we evaluate the implicit functional relationship between the shape and width parameters for matched profiles, which provides a quantitative way to compare profiles described by different families of functions. We conclude from an analysis of each profile with matched parameters using Kirchhoff-Fresnel diffraction theory and M2 analysis that the diffraction patterns as they propagate differ by small amounts, which may not be distinguished experimentally. Thus, beam shaping optics is designed to produce either of these four flattened output irradiance distributions with matched parameters will yield similar irradiance distributions as the beam propagates.
Laser beam propagation in atmospheric turbulence
Murty, S. S. R.
1979-01-01
The optical effects of atmospheric turbulence on the propagation of low power laser beams are reviewed in this paper. The optical effects are produced by the temperature fluctuations which result in fluctuations of the refractive index of air. The commonly-used models of index-of-refraction fluctuations are presented. Laser beams experience fluctuations of beam size, beam position, and intensity distribution within the beam due to refractive turbulence. Some of the observed effects are qualitatively explained by treating the turbulent atmosphere as a collection of moving gaseous lenses of various sizes. Analytical results and experimental verifications of the variance, covariance and probability distribution of intensity fluctuations in weak turbulence are presented. For stronger turbulence, a saturation of the optical scintillations is observed. The saturation of scintillations involves a progressive break-up of the beam into multiple patches; the beam loses some of its lateral coherence. Heterodyne systems operating in a turbulent atmosphere experience a loss of heterodyne signal due to the destruction of coherence.
Definition and measurement of the beam propagation factor M2 for chromatic laser beams
Institute of Scientific and Technical Information of China (English)
Tao Fang; Xin Ye; Jinfu Niu; Jianqiu Xu
2006-01-01
The concept of the beam propagation factor M2 is extended for chromatic laser beams. The definition of the beam propagation factor can be generalized with the weighted effective wavelength. Using the new definition of factor M2, the propagation of chromatic beams can be analyzed by the beam propagation factor M2 as same as that of monochromatic beams. A simple method to measure the chromatic beam factor M2 is demonstrated. The chromatic factor M2 is found invariable while the laser beam propagates through the dispersion-free ABCD system.
EXACT ANALYSIS OF WAVE PROPAGATION IN AN INFINITE RECTANGULAR BEAM
Institute of Scientific and Technical Information of China (English)
孙卫明; 杨光松; 李东旭
2004-01-01
The Fourier series method was extended for the exact analysis of wave propagation in an infinite rectangular beam. Initially, by solving the three-dimensional elastodynamic equations a general analytic solution was derived for wave motion within the beam. And then for the beam with stress-free boundaries, the propagation characteristics of elastic waves were presented. This accurate wave propagation model lays a solid foundation of simultaneous control of coupled waves in the beam.
Safe Laser Beam Propagation for Interplanetary Links
Wilson, Keith E.
2011-01-01
Ground-to-space laser uplinks to Earth–orbiting satellites and deep space probes serve both as a beacon and an uplink command channel for deep space probes and Earth-orbiting satellites. An acquisition and tracking point design to support a high bandwidth downlink from a 20-cm optical terminal on an orbiting Mars spacecraft typically calls for 2.5 kW of 1030-nm uplink optical power in 40 micro-radians divergent beams.2 The NOHD (nominal ocular hazard distance) of the 1030nm uplink is in excess of 2E5 km, approximately half the distance to the moon. Recognizing the possible threat of high power laser uplinks to the flying public and to sensitive Earth-orbiting satellites, JPL developed a three-tiered system at its Optical Communications Telescope Laboratory (OCTL) to ensure safe laser beam propagation through navigational and near-Earth space.
Hollow Gaussian Schell-model beam and its propagation
Wang, Li-Gang
2007-01-01
In this paper, we present a new model, hollow Gaussian-Schell model beams (HGSMBs), to describe the practical dark hollow beams. An analytical propagation formula for HGSMBs passing through a paraxial first-order optical system is derived based on the theory of coherence. Based on the derived formula, an application example showing the influence of spatial coherence on the propagation of beams is illustrated. It is found that the beam propagating properties of HGSMBs will be greatly affected by their spatial coherence. Our model provides a very convenient way for analyzing the propagation properties of partially coherent dark hollow beams.
Nonparaxial propagation of phase-flipped Gaussian beams
Institute of Scientific and Technical Information of China (English)
Gao Zeng-Hui; Lü Bai-Da
2008-01-01
This paper derives the closed-form expressions for nonparaxial phase flipped Gaussian (PFG) beams propagating in free space, through a knife edge and an aperture, which enable us to study nonparaxial propagation properties of PFG beams and to compare nonparaxial results with paraxial ones. It is found that the f parameter, offsetting distance of the knife edge and truncation parameter affect the nonparaxial beam propagation properties. Only under certain conditions the paraxial approximation is applicable. The results are illustrated by numerical examples.
Positron Beam Propagation in a Meter Long Plasma Channel
Energy Technology Data Exchange (ETDEWEB)
Marsh, K.A.; Blue, B.E.; Clayton, C.E.; Joshi, C.; Mori, W.B.; /UCLA; Decker, F.-J.; Hogan, M.J.; Iverson, R.; O' Connell, C.; Raimondi, P.; Siemann, Robert H.; Walz, D.; /SLAC; Katsouleas, T.C.; Muggli, P.; /Southern California U.
2008-03-17
Recent experiments and simulations have shown that positron beams propagating in plasmas can be focused and also create wakes with large accelerating gradients. For similar parameters, the wakes driven by positron beams are somewhat smaller compared to the case of an electron beam. Simulations have shown that the wake amplitude can be increased if the positron beam is propagated in a hollow plasma channel (Ref. 1). This paper, compares experimentally, the propagation and beam dynamics of a positron beam in a meter scale homogeneous plasma, to a positron beam hollow channel plasma. The results show that positron beams in hollow channels are less prone to distortions and deflections. Hollow channels were observed to guide the positron beam onto the channel axis. Beam energy loss was also observed implying the formation of a large wake amplitude. The experiments were carried out as part of the E-162 plasma wakefield experiments at SLAC.
Propagation of ion beams through a tenuous magnetized plasma
Energy Technology Data Exchange (ETDEWEB)
Chrien, E.F.; Valeo, E.J.; Kulsrud, R.M.; Oberman, C.R.
1985-10-01
When an ion beam is propagated through a plasma, the question of charge neutralization is critical to its propagation. We consider such a problem where the plasma is magnetized with magnetic field perpendicular to the beam. The plasma-number density and beam-number density are assumed comparable. We reduce the problem to a two-dimensional model, which we solve. The solution suggests that it should be possible to attain charge neutralization if the beam density is properly varied along itself.
Beam Propagation Factor and Generation of Cosh-squared-Gaussian Beams
Institute of Scientific and Technical Information of China (English)
ZHU Kaicheng; TANG Huiqin; ZHU Zhenhe
2001-01-01
A new light beam termed as a cosh-squared-Gaussian beam (ChSGB) which may be one of solutions of the paraxial wave equation for propagation in complex optical systems has been introduced. Their beam propagation factor (M2-factor) is derived and schemes to generate this light beams are proposed.
A Schrdinger formulation research for light beam propagation
Institute of Scientific and Technical Information of China (English)
刘承宜; 郭弘; 胡巍; 邓锡铭
2000-01-01
The wave equation of light beam propagation was written in the form of an axial-coordinate-dependent Schrodinger equation, and the expectation value of a dynamical variable, the trial function of variational approach and the ABCD law were discussed by use of quantum mechanics approach. In view of the evolution equations of expectation values of dynamical variables in the framework of quantum mechanics, the definition of a potential function representing the beam propagation stability and its universal formula with the quality factor, the universal formula of beam width and curvature radius for a paraxial beam and cylindrically symmetric non-paraxial beam, the general formula of second derivative of beam width with respect to the axial coordinate of beam for a paraxial beam, and the general criteria of the conservation of beam quality factor and the existence of a potential well of a potential function for a paraxial beam, were given or derived, respectively. Starting with the same trial function, the co
Theoretical tools for atom-laser-beam propagation
Riou, Jean-Félix; Le Coq, Yann; Impens, François; Guerin, William; Bordé, Christian,; Aspect, Alain; Bouyer, Philippe
2008-01-01
We present a theoretical model for the propagation of non self-interacting atom laser beams. We start from a general propagation integral equation, and we use the same approximations as in photon optics to derive tools to calculate the atom laser beam propagation. We discuss the approximations that allow to reduce the general equation whether to a Fresnel-Kirchhoff integral calculated by using the stationary phase method, or to the eikonal. Within the paraxial approximation, we also introduce...
Propagation of Gaussian Beams through Active GRIN Materials
Energy Technology Data Exchange (ETDEWEB)
Gomez-Varela, A I; Flores-Arias, M T; Bao-Varela, C; Gomez-Reino, C [Grupo de ' Microoptica y Optica GRIN' , Unidad asociada al Instituto de Ciencias de Materiales de Aragon, ICMA/CSIC, Zaragoza, Espana y Escuela de Optica y OptometrIa, Campus Sur s/n, Universidade de Santiago, E15782 Santiago de Compostela (Spain); De la Fuente, X, E-mail: maite.flores@usc.es [Instituto de Ciencia de Materiales de Aragon (Universidad de Zaragoza-CSIC), Maria de Luna 3, E50018 Zaragoza (Spain)
2011-01-01
We discussed light propagation through an active GRIN material that exhibits loss or gain. Effects of gain or loss in GRIN materials can be phenomenologically taken into account by using a complex refractive index in the wave equation. This work examines the implication of using a complex refractive index on light propagation in an active GRIN material illuminated by a non-uniform monochromatic wave described by a Gaussian beam. We analyze how a Gaussian beam is propagated through the active material in order to characterize it by the beam parameters and the transverse irradiance distribution.
The Propagation Characteristics of the Electron Beam with Initial Modulation
Institute of Scientific and Technical Information of China (English)
Zhang Jun(张军); Zhong Huihuang(钟辉煌)
2003-01-01
The propagation characteristics of the beam under various initial conditions are investigated by means of PIC method. The influences of density modulation and velocity modulation on the propagation characteristics are discussed and compared. The results reveal that by changing the amplitude of the two kinds of modulations and the phase difference between them, the distribution property of the first harmonic of the current density can be adapted along the beam propagating path, which is a feasible method to enhance the beam-wave interaction efficiency in Cerenkov HPM devices.
Mean intensity of vortex Bessel beams propagating in turbulent atmosphere.
Lukin, Igor P
2014-05-20
Transformation of vortex Bessel beams during propagation in turbulent atmosphere is theoretically analyzed. Deforming influence of the random inhomogeneity of the turbulent medium on propagation of diffraction-free beams leads to disappearance of their invariant properties. In the given research, features of evolution of the spatial structure of distribution of mean intensity of vortex Bessel beams in turbulent atmosphere are analyzed. A quantitative criterion of possibility of carrying over of a dark central domain by vortex Bessel beams in a turbulent atmosphere is derived. The analysis of the behavior of several physical parameters of mean-level optical radiation shows that the shape stability of a vortex Bessel beam increases with the topological charge of this beam during its propagation in a turbulent atmosphere.
Propagation of ultrashort pulsed beams in dispersive media
Institute of Scientific and Technical Information of China (English)
刘志军; 吕百达
2003-01-01
Starting from the Rayleigh diffraction integral, the propagation equation of ultrashort pulsed beams in dispersive media is derived without making the paraxial approximation and slowly varying envelope approximation (SVEA). The spatiotemporal properties of ultrashort pulsed beams in dispersive media, such as spectrum redshifting, narrowing and pulse distortion are illustrated with pulsed Gaussian beams. It is stressed that the "antibeam" behaviour of ultrashort pulsed beams can be avoided, if a suitable truncation function is chosen.
Scintillation Reduction for Laser Beams Propagating Through Turbulent Atmosphere
Berman, G P; Torous, S V
2010-01-01
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams, including the optical vortices, propagating in turbulent atmospheres. The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. These studies were performed for different dimensions of the detector, distances of propagation, and strengths of the atmospheric turbulence. Methods for significantly reducing the scintillation index are described. These methods utilize averaging of the signal at the detector over a set of partially coherent beams (PCBs). It is demonstrated that the most effective approach is using a set of PCBs with definite initial directions of propagation relative to the z-axis. This approach results in a significant compensation of the beam wandering which in many cases is the main contributor to the SI. A novel method is to generate the PCBs by combining two lase...
Propagation dynamics of vortices in Helico-Conical optical beams
Bareza, Nestor
2015-01-01
We present the dynamics of optical vortices (OVs) that came from the propagation of helico-conical optical beam. This dynamics is investigated numerically by tracking the OVs at several distances using rigorous scalar diffraction theory. To ensure that our numerical calculations are correct, we compare the intensity profiles and their corresponding interferograms taken at different propagation distances between simulations and experiments. We observe that the peripheral isopolar vortices transport radially inward, toward the optical axis along the transverse spatial space as the beam propagates. When the beam has a central vortex, these vortices have significant induced angular rates of motion about the optical axis. These propagation dynamics of vortices influence the internal energy flow and the wave profile reconstruction of the beam, which can be important when deciding their applications.
Laser beam propagation in non-linearly absorbing media
CSIR Research Space (South Africa)
Forbes, A
2006-08-01
Full Text Available Many analytical techniques exist to explore the propagation of certain laser beams in free space, or in a linearly absorbing medium. When the medium is nonlinearly absorbing the propagation must be described by an iterative process using the well...
Unified formalism for TE and TM beam propagators
Poladian, Leon; Ladouceur, Francois J.
1998-07-01
The unification of transverse electric (TE) and transverse magnetic (TM) beam propagation algorithms is made possible through a transformation which converts the wave equation for TM fields in planar waveguides into a form identical to the corresponding TE wave equation. The transformation can be applied to any smoothly varying waveguide. This transformation can be made independently of any paraxial or other approximations. Thus, any TE propagation algorithm can also be applied immediately to TM fields without additional approximations. This includes the classical fast Fourier transform beam propagator, which has not previously been applied successfully to TM propagation. We also specifically develop a Finite Difference Beam Propagation Method that applies to both TE and TM propagation in 1D (planar) geometry. Previous implementations for the TM case involve an approximation that in certain circumstances leads to severe errors (including the totally unphysical occurrence of field amplification). This is the first TM propagator which exactly conserves power. We also investigate the role of the reference background wavenumber (or index) and clarify its role as it is dynamically adapted. The algorithms proposed are easily adaptable to wide-angle beam propagators and to modern transparent boundary conditions. The extension of these ideas to rapidly varying structures (such as Bragg gratings) is also briefly discussed.
Efficient interface conditions for the finite difference beam propagation method
Hoekstra, Hugo; Krijnen, Gijsbertus J.M.; Lambeck, Paul
1992-01-01
It is shown that by adapting the refractive indexes in the vicinity of interfaces, the 2-D beam propagation method based on the finite-difference (FDBPM) scheme can be made much more effective. This holds especially for TM modes propagating in structures with high-index contrasts, such as surface
Wave Propagation in an Ion Beam-Plasma System
DEFF Research Database (Denmark)
Jensen, T. D.; Michelsen, Poul; Juul Rasmussen, Jens
1979-01-01
The spatial evolution of a velocity- or density-modulated ion beam is calculated for stable and unstable ion beam plasma systems, using the linearized Vlasov-Poisson equations. The propagation properties are found to be strongly dependent on the form of modulation. In the case of velocity...
Characteristic of laser diode beam propagation through a collimating lens.
Xu, Qiang; Han, Yiping; Cui, Zhiwei
2010-01-20
A mathematical model of a laser diode beam propagating through a collimating lens is presented. Wave propagation beyond the paraxial approximation is studied. The phase delay of the laser diode wave in passing through the lens is analyzed in detail. The propagation optical field after the lens is obtained from the diffraction integral by the stationary phase method. The model is employed to predict the light intensity at various beam cross sections, and the computed intensity distributions are in a good agreement with the corresponding measurements.
Beams Propagation Modelled by Bi-filters
Lacaze, Bernard
2010-01-01
In acoustic, ultrasonic or electromagnetic propagation, crossed media are often modelled by linear filters with complex gains in accordance with the Beer-Lambert law. This paper addresses the problem of propagation in media where polarization has to be taken into account. Because waves are now bi-dimensional, an unique filter is not sufficient to represent the effects of the medium. We propose a model which uses four linear invariant filters, which allows to take into account exchanges betwee...
Multiple-beam Propagation in an Anderson Localized Optical Fiber
Karbasi, Salman; Mafi, Arash
2012-01-01
We investigate the simultaneous propagation of multiple beams in a disordered Anderson localized optical fiber. The profiles of each beam fall off exponentially, enabling multiple channels at high-density. We examine the influence of fiber bends on the movement of the beam positions, which we refer to as drift. We investigate the extent of the drift of localized beams induced by macro-bending and show that it is possible to design Anderson localized optical fibers which can be used for practical beam-multiplexing applications.
Gamma-beam propagation in the anisotropic medium
Maisheev, V A
2000-01-01
Propagation of gamma-beam in the anisotropic medium is considered. The simpliest example of such a medium of the general type is a combination of the two linearly polarized monochromatic laser waves with different frequencies (dichromatic wave). The optical properties of this combination are described with the use of the permittivity tensor. The refractive indices and polarization characteristics of normal electromagnetic waves propagating in the anisotropic medium are found. The relations, describing variations of gamma-beam intensity and Stokes parameters as functions of propagation length are obtained. The influence of laser wave intensity on the propagation process are calculated. The gamma-beam intensity losses in the dichromatic wave depend on the initial circular polarization of gamma-quanta. This effect is also applied to the single crystals, which are oriented in some regions of coherent pair production. In principle, the single crystal sensitivity to a circular polarization can be used for determina...
Propagation of Airy Gaussian vortex beams in uniaxial crystals
Weihao, Yu; Ruihuang, Zhao; Fu, Deng; Jiayao, Huang; Chidao, Chen; Xiangbo, Yang; Yanping, Zhao; Dongmei, Deng
2016-04-01
The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374108, 11374107, 10904041, and 11547212), the Foundation of Cultivating Outstanding Young Scholars of Guangdong Province, China, the CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, the National Training Program of Innovation and Entrepreneurship for Undergraduates (Grant No. 2015093), and the Science and Technology Projects of Guangdong Province, China (Grant No. 2013B031800011).
A Highly Adjustable Helical Beam: Design and Propagation Characteristic
Wen, Yuanhui; Yu, Siyuan
2016-01-01
Light fields with extraordinary propagation behaviours such as nondiffracting and self-bending are useful in optical delivery for energy, information, and even objects. A kind of helical beams is constructed here based on the caustic method. With appropriate design, the main lobe of these helical beams can be both well-confined and almost nondiffracting while moving along a helix with its radius, period, the number of rotations and main lobes highly adjustable. In addition, the main lobe contains almost half of the optical power and the peak intensity fluctuates below 15% during propagation. These promising characteristics may enable a variety of potential applications based on these beams.
Instability versus equilibrium propagation of a laser beam in plasma.
Lushnikov, Pavel M; Rose, Harvey A
2004-06-25
We obtain, for the first time, an analytic theory of the forward stimulated Brillouin scattering instability of a spatially and temporally incoherent laser beam that controls the transition between statistical equilibrium and nonequilibrium (unstable) self-focusing regimes of beam propagation. The stability boundary may be used as a comprehensive guide for inertial confinement fusion designs. Well into the stable regime, an analytic expression for the angular diffusion coefficient is obtained, which provides an essential correction to a geometric optic approximation for beam propagation.
Generation and propagation of radially polarized beams in optical fibers
DEFF Research Database (Denmark)
Ramachandran, Siddharth; Kristensen, P; Yan, M F
2009-01-01
Beams with polarization singularities have attracted immense recent attention in a wide array of scientific and technological disciplines. We demonstrate a class of optical fibers in which these beams can be generated and propagated over long lengths with unprecedented stability, even in the pres......Beams with polarization singularities have attracted immense recent attention in a wide array of scientific and technological disciplines. We demonstrate a class of optical fibers in which these beams can be generated and propagated over long lengths with unprecedented stability, even...... in the presence of strong bend perturbations. This opens the door to exploiting nonlinear fiber optics to manipulate such beams. This fiber also possesses the intriguingly counterintuitive property of being polarization maintaining despite being strictly cylindrically symmetric, a prospect hitherto considered...... infeasible with optical fibers. (C) 2009 Optical Society of America....
Scintillation reduction for laser beams propagating through turbulent atmosphere
Energy Technology Data Exchange (ETDEWEB)
Berman, G P; Gorshkov, V N [Theoretical Division, T-4 and CNLS MS B213, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Torous, S V, E-mail: gpb@lanl.gov [National Technical University of Ukraine ' KPI' , 37 Peremogy Avenue, Building 7, Kiev-56, 03056 (Ukraine)
2011-03-14
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams, including the optical vortices, propagating in turbulent atmospheres. The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analysed. These studies were performed for different dimensions of the detector, distances of propagation, and strengths of the atmospheric turbulence. Methods for significantly reducing the SI are described. These methods utilize averaging of the signal at the detector over a set of partially coherent beams (PCBs). It is demonstrated that the most effective approach is using a set of PCBs with definite initial directions of propagation relative to the z-axis. This approach results in a significant compensation of the beam wandering which in many cases is the main contributor to the SI. A novel method is to generate the PCBs by combining two laser beams-Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the effective suppression of the SI does not require high-frequency modulators. This result is important for achieving gigabit data rates in long-distance laser communication through turbulent atmospheres.
Beaconless operation for optimal laser beam propagation through turbulent atmosphere
Khizhnyak, Anatoliy; Markov, Vladimir
2016-09-01
Corruption of the wavefront, beam wondering and power density degradation at the receiving end are the effects typically observed at laser beam propagation through turbulent atmosphere. Compensation of these effects can be achieved if the reciprocal conditions for the propagating wave are satisfied along the propagation range. Practical realization of these conditions requires placing a localized beacon at the receiving end of the range and high-performance adaptive optics system (AOS). The key condition for an effective performance of AOS is a high value of the reciprocal component in the outgoing wave, since only this component is getting compensated after propagating turbulence perturbed path. The nonreciprocal components that is present in the wave directed toward the target is caused by three factors (detailed in this paper) that determine the partial restoration of the structure of the beacon beam. Thus solution of a complex problem of focusing the laser beam propagating through turbulent media can be achieved for the share of the outgoing wave that has a reciprocal component. This paper examines the ways and means that can be used in achieving the stated goal of effective laser power delivery on the distant image-resolved object.
Analysis of laser beam propagation in a turbulent atmosphere
Clarke, R. H.
1985-09-01
The beam propagation method, based on the parabolic approximation to the wave equation, is used in conjunction with Papoulis' redefinition for optical fields of Woodward's ambiguity function. A simple derivation is given of Tatarskii's formula for the lateral coherence function, and hence the mean intensity profile, of a laser beam propagating through a turbulent atmosphere. Statistics of the received signal and the effects of spatial nonstationarity of the turbulence can also be deduced using this technique, as can the effects of very large-scale variations in refractive index and receiver directivity.
Self-healing in scaled propagation invariant beams
Arrizón, Victor; Mellado-Villaseñor, Gabriel; Chávez-Cerda, Sabino
2015-01-01
We analyze and demonstrate, numerically and experimentally, the self-healing effect in scaled propagation invariant beams, subject to opaque obstructions.We introduce the signal to noise intensity ratio, a semi-analytical figure of merit, explicitly dependent on the features of the beams and the obstructions applied to them. The effect is quantitatively evaluated employing the Root Mean Square deviation and the similarity function.
Instability Versus Equilibrium Propagation of Laser Beam in Plasma
Lushnikov, Pavel M.; Rose, Harvey A.
2003-01-01
We obtain, for the first time, an analytic theory of the forward stimulated Brillouin scattering instability of a spatially and temporally incoherent laser beam, that controls the transition between statistical equilibrium and non-equilibrium (unstable) self-focusing regimes of beam propagation. The stability boundary may be used as a comprehensive guide for inertial confinement fusion designs. Well into the stable regime, an analytic expression for the angular diffusion coefficient is obtain...
Spatial-temporal dynamics of broadband terahertz Bessel beam propagation
Semenova, V. A.; Kulya, M. S.; Bespalov, V. G.
2016-08-01
The unique properties of narrowband and broadband terahertz Bessel beams have led to a number of their applications in different fields, for example, for the depth of focusing and resolution enhancement in terahertz imaging. However, broadband terahertz Bessel beams can probably be also used for the diffraction minimization in the short-range broadband terahertz communications. For this purpose, the study of spatial-temporal dynamics of the broadband terahertz Bessel beams is needed. Here we present a simulation-based study of the propagating in non-dispersive medium broadband Bessel beams generated by a conical axicon lens. The algorithm based on scalar diffraction theory was used to obtain the spatial amplitude and phase distributions of the Bessel beam in the frequency range from 0.1 to 3 THz at the distances 10-200 mm from the axicon. Bessel beam field is studied for the different spectral components of the initial pulse. The simulation results show that for the given parameters of the axicon lens one can obtain the Gauss-Bessel beam generation in the spectral range from 0.1 to 3 THz. The length of non-diffraction propagation for a different spectral components was measured, and it was shown that for all spectral components of the initial pulse this length is about 130 mm.
Modeling beam propagation and frequency conversion for the beamlet laser
Energy Technology Data Exchange (ETDEWEB)
Auerbach, J.M.
1996-06-01
The development of the Beamlet laser has involved extensive and detailed modeling of laser performance and beam propagation to: (1) predict the performance limits of the laser, (2) select system configurations with higher performance, (3) analyze experiments and provide guidance for subsequent laser shots, and (4) design optical components and establish component manufacturing specifications. In contrast to modeling efforts of previous laser systems such as Nova, those for Beamlet include as much measured optical characterization data as possible. This article concentrates on modeling of beam propagation in the Beamlet laser system, including the frequency converter, and compares modeling predictions with experimental results for several Beamlet shots. It briefly describes the workstation-based propagation and frequency conversion codes used to accomplish modeling of the Beamlet.
Propagation of electromagnetic stochastic beams in anisotropic turbulence.
Yao, Min; Toselli, Italo; Korotkova, Olga
2014-12-29
The effects of anisotropic, non-Kolmogorov turbulence on propagating stochastic electromagnetic beam-like fields are discussed for the first time. The atmosphere of interest can be found above the boundary layer, at high (more than 2 km above the ground) altitudes where the energy distribution among the turbulent eddies might not satisfy the classic assumption represented by the famous 11/3 Kolmogorov's power law, and the anisotropy in the direction orthogonal to the Earth surface is possibly present. Our analysis focuses on the classic electromagnetic Gaussian Schell-model beams but can either be readily reduced to scalar and/or coherent beams or generalized to other beam classes. In particular, we explore the effects of the anisotropic parameter on the spectral density, the spectral degree of coherence and on the spectral degree of polarization of the beam.
Pérez, Darío G; Funes, Gustavo
2012-12-03
Under the Geometrics Optics approximation is possible to estimate the covariance between the displacements of two thin beams after they have propagated through a turbulent medium. Previous works have concentrated in long propagation distances to provide models for the wandering statistics. These models are useful when the separation between beams is smaller than the propagation path-regardless of the characteristics scales of the turbulence. In this work we give a complete model for these covariances, behavior introducing absolute limits to the validity of former approximations. Moreover, these generalizations are established for non-Kolmogorov atmospheric models.
Vibration and wave propagation characteristics of multisegmented elastic beams
Nayfeh, Adnan H.; Hawwa, Muhammad A.
1990-01-01
Closed form analytical solutions are derived for the vibration and wave propagation of multisegmented elastic beams. Each segment is modeled as a Timoshenko beam with possible inclusion of material viscosity, elastic foundation and axial forces. Solutions are obtained by using transfer matrix methods. According to these methods formal solutions are first constructed which relate the deflection, slope, moment and shear force of one end of the individual segment to those of the other. By satisfying appropriate continuity conditions at segment junctions, a global 4x4 matrix results which relates the deflection, slope, moment and shear force of one end of the beam to those of the other. If any boundary conditions are subsequently invoked on the ends of the beam one gets the appropriate characteristic equation for the natural frequencies. Furthermore, by invoking appropriate periodicity conditions the dispersion relation for a periodic system is obtained. A variety of numerical examples are included.
Beam propagation in Cu +-Na + ion exchange channel waveguides
Energy Technology Data Exchange (ETDEWEB)
Villegas Vicencio, L. J.; Khomenko, A. V.; Salazar, D.; Marquez, H. [Centro de Investigacion Cientifica y de Educacion Superior de Ensenada, Baja California (Mexico); Porte, H. [Universite de Franche-Comte, UFR des Sciences et Techniques, Besancon, Cedex (France)
2001-06-01
We employ the fast Fourier transform beam propagation method to simulate the propagation of light in graded index channel waveguides, these have been obtained by solid state diffusion of copper ions in soda-lime glass substrates. Longitudinal propagation has been simulated, the input light beam has a gaussian profile. Two cases have been analyzed, in the first, the Gaussian beam is collinear center to center with respect to waveguide; in the second, a small lateral offset and angular tilt have been introduced. Modal beating and bending effects have been founded. We have proven the validity of our numerical results in detailed comparison with experimental data. [Spanish] Se ha empleado el metodo de propagacion de haces por la transformada rapida de Fourier para simular la propagacion de la luz en guias de onda de indice de gradiente. Estas han sido fabricadas por difusion de iones de cobre en estado solido en substratos de vidrios sodicos-calcicos. Se han simulado dos casos, el primero, el perfil de luz de entrada, que es gaussiano, es colineal centro a centro respecto al centro de la guia de ondas: el segundo, se ha dado un pequeno corrimiento lateral y una inclinacion angular. Como consecuencia de los casos anteriores se ha observado efectos de batimiento modal. Los resultados de la simulacion se han validado con resultados experimentales.
Role of beam propagation in Goos-Hänchen and Imbert-Fedorov shifts.
Aiello, A; Woerdman, J P
2008-07-01
We derive the polarization-dependent displacements parallel and perpendicular to the plane of incidence for a Gaussian light beam reflected from a planar interface, taking into account the propagation of the beam. Using a classical-optics formalism we show that beam propagation may greatly affect both Goos-Hänchen and Imbert-Fedorov shifts when the incident beam is focused.
Energy Technology Data Exchange (ETDEWEB)
Lagasse, P.E.; Baets, R.
1987-12-01
The advantages and disadvantages of various propagating beam methods (BPMs) used in the solution of electromagnetic and acoustical problems are considered. The basic assumptions and approximations which are necessary for the derivation of the BPM algorithm are discussed with respect to applications to acoustics and optics and linear and nonlinear materials. Particular attention is given to the case of passive waveguiding structures and the role that BPM can play in the analysis of nonlinear structures such as semiconductor lasers. 28 references.
Lagasse, P. E.; Baets, R.
1987-12-01
The advantages and disadvantages of various propagating beam methods (BPMs) used in the solution of electromagnetic and acoustical problems are considered. The basic assumptions and approximations which are necessary for the derivation of the BPM algorithm are discussed with respect to applications to acoustics and optics and linear and nonlinear materials. Particular attention is given to the case of passive waveguiding structures and the role that BPM can play in the analysis of nonlinear structures such as semiconductor lasers.
Beam propagation factors and kurtosis parameters of a Lorentz-Gauss vortex beam.
Zhou, Guoquan
2014-06-01
Based on the second-order and the higher-order moments, analytical expressions for the beam propagation factors of a Lorentz-Gauss vortex beam with l=1 have been derived, and analytical propagation expressions for the kurtosis parameters of a Lorentz-Gauss vortex beam with l=1 through a paraxial and real ABCD optical system have also been presented. The M² factor is determined by the parameters a and b and decreases with increasing the parameter a or b. The M² factor is validated to be larger than 2. The kurtosis parameters depend on the diffraction-free ranges of the Lorentz part, the parameters a and b, and the ratio A/B. The kurtosis parameters of a Lorentz-Gauss vortex beam propagating in free space are demonstrated in different reference planes. In the far field, the kurtosis parameter K decreases with increasing one of the parameters a and b. Upon propagation, the kurtosis parameter K first decreases, then increases, and finally tends to a saturated value. In any case, the kurtosis parameter K is larger than 2. This research is beneficial to optical trapping, guiding, and manipulation of microscopic particles and atoms using Lorentz-Gauss vortex beams.
Beam wander of Gaussian-Schell model beams propagating through oceanic turbulence
Wu, Yuqian; Zhang, Yixin; Li, Ye; Hu, Zhengda
2016-07-01
For Gaussian-Schell model beams propagating in the isotropic turbulent ocean, theoretical expression of beam wander is derived based on the extended Huygens-Fresnel principle. The spatial coherence radius of spherical waves propagating in the paraxial channel of turbulent ocean including inner scale is also developed. Our results show that the beam wander decreases with the increasing rate of dissipation of kinetic energy per unit mass of fluid ɛ, but it increases as the increasing of the dissipation rate of temperature variance χt and the relative strength of temperature and salinity fluctuations ϖ. The salinity fluctuation has greater influence on the beam wander than that of temperature fluctuations. The model can be evaluated submarine-to-submarine/ship optical wireless communication performance.
Tao, Rumao; Si, Lei; Ma, Yanxing; Zhou, Pu; Liu, Zejin
2012-08-10
The propagation properties of coherently combined truncated laser beam arrays with beam distortions through non-Kolmogorov turbulence are studied in detail both analytically and numerically. The analytical expressions for the average intensity and the beam width of coherently combined truncated laser beam arrays with beam distortions propagating through turbulence are derived based on the combination of statistical optics methods and the extended Huygens-Fresnel principle. The effect of beam distortions, such as amplitude modulation and phase fluctuation, is studied by numerical examples. The numerical results reveal that phase fluctuations have significant influence on the spreading of coherently combined truncated laser beam arrays in non-Kolmogorov turbulence, and the effects of the phase fluctuations can be negligible as long as the phase fluctuations are controlled under a certain level, i.e., a>0.05 for the situation considered in the paper. Furthermore, large phase fluctuations can convert the beam distribution rapidly to a Gaussian form, vary the spreading, weaken the optimum truncation effects, and suppress the dependence of spreading on the parameters of the non-Kolmogorov turbulence.
Propagation of a Laguerre-Gaussian correlated Schell-model beam in strongly nonlocal nonlinear media
Qiu, Yunli; Chen, Zhaoxi; He, Yingji
2017-04-01
Analytical expressions for the cross-spectral density function and the second-order moments of the Wigner distribution function of a Laguerre-Gaussian correlated Schell-model (LGCSM) beam propagating in strongly nonlocal nonlinear media are derived. The propagation properties, such as beam irradiance, beam width, the spectral degree of coherence and the propagation factor of a LGCSM beam inside the media are investigated in detail. The effect of the beam parameters and the input power on the evolution properties of a LGCSM is illustrated numerically. It is found that the beam width varies periodically or keeps invariant for a certain proper input power. And both the beam irradiance and the spectral degree of coherence of the LGCSM beam change periodically with the propagation distance for the arbitrary input power which however has no influence on the propagation factor. The coherent length and the mode order mainly affect the evolution speed of the LGCSM beam in strongly nonlocal nonlinear media.
Influence of propagation in digital wireless beam, microwave links
Bursztejn, J.
1984-10-01
Methods are presented for determining the parameters which permit the prediction of the quality of tropospheric scattering and line of sight microwave links. Wireless beam, microwave links with tropospheric scattering are considered based on experiments for determining the coherence band which is the essential parameter for digital transmission by tropospheric scattering. The effects of propagation difficulties in line of sight links are discussed with focus on depolarization and selective fading. Experimental results are given which permit calculating the sensitivity of equipment and predicting the quality of the links.
Real-time reconfigurable counter-propagating beam-traps
DEFF Research Database (Denmark)
Tauro, Sandeep; Bañas, Andrew Rafael; Palima, Darwin;
2010-01-01
We present a versatile technique that enhances the axial stability and range in counter-propagating (CP) beam-geometry optical traps. It is based on computer vision to track objects in unison with software implementation of feedback to stabilize particles. In this paper, we experimentally...... which simulates biosamples. By working on differences rather than absolute values, this feedback based technique makes CPtrapping nullify many of the commonly encountered pertubations such as fluctuations in the laser power, vibrations due to mechanical instabilities and other distortions emphasizing...
Gouesbet, Gérard; Lock, James A.
2016-07-01
When dealing with light scattering and propagation of an electromagnetic beam, there are essentially two kinds of expansions which have been used to describe the incident beam (i) a discrete expansion involving beam shape coefficients and (ii) a continuous expansion in terms of an angular spectrum of plane waves. In this paper, we demonstrate that the angular spectrum decomposition readily leads to two important consequences, (i) laser light beams travel in free space with an effective velocity that is smaller than the speed of light c, and (ii) the optical theorem does not hold for arbitrary shaped beams, both in the case of electromagnetic waves and scalar waves, e.g. quantum and acoustical waves.
Propagation of Bessel beams from a dielectric to a conducting medium.
Mugnai, D
2011-06-10
Recently, the use of Bessel beams in evaluating the possibility of using them for a new generation of ground penetrating radar systems has been considered. Therefore, an analysis of the propagation of Bessel beams in conducting media is worthwhile. We present here an analysis of this type. Specifically, for normal incidence we analyze the propagation of a Bessel beam coming from a perfect dielectric and impinging on a conducting medium, i.e., the propagation of a Bessel beam generated by refracted inhomogeneous waves. The remarkable and unexpected result is that the incident Bessel beam does not change its shape even when propagating in the conducting medium.
Numerical simulation of broadband vortex terahertz beams propagation
Semenova, V. A.; Kulya, M. S.; Bespalov, V. G.
2016-08-01
Orbital angular momentum (OAM) represents new informational degree of freedom for data encoding and multiplexing in fiber and free-space communications. OAM-carrying beams (also called vortex beams) were successfully used to increase the capacity of optical, millimetre-wave and radio frequency communication systems. However, the investigation of the OAM potential for the new generation high-speed terahertz communications is also of interest due to the unlimited demand of higher capacity in telecommunications. Here we present a simulation-based study of the propagating in non-dispersive medium broadband terahertz vortex beams generated by a spiral phase plate (SPP). The algorithm based on scalar diffraction theory was used to obtain the spatial amplitude and phase distributions of the vortex beam in the frequency range from 0.1 to 3 THz at the distances 20-80 mm from the SPP. The simulation results show that the amplitude and phase distributions without unwanted modulation are presented in the wavelengths ranges with centres on the wavelengths which are multiple to the SPP optical thickness. This fact may allow to create the high-capacity near-field communication link which combines OAM and wavelength-division multiplexing.
Alternative modes for optical trapping and manipulation using counter-propagating shaped beams
DEFF Research Database (Denmark)
Palima, Darwin; Lindballe, T.B.; Kristensen, M.V.;
2011-01-01
-propagating shaped-beam traps that depart from the conventional geometry based on symmetric, coaxial counter-propagating beams. We show that projecting shaped beams with separation distances previously considered axially unstable can, in fact, enhance the axial and transverse trapping stiffnesses. We also show...
Oblique non-neutral solitary Alfven modes in weakly nonlinear pair plasmas
Energy Technology Data Exchange (ETDEWEB)
Verheest, Frank [Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B-9000 Gent (Belgium); School of Physics, Howard College Campus, University of KwaZulu-Natal, Durban 4041 (South Africa); Lakhina, G S [Indian Institute of Geomagnetism, New Panvel, Navi Mumbai 410218 (India); Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-0011 (Japan)
2005-04-01
The equal charge-to-mass ratio for both species in pair plasmas induces a decoupling of the linear eigenmodes between waves that are charge neutral or non-neutral, also at oblique propagation with respect to a static magnetic field. While the charge-neutral linear modes have been studied in greater detail, including their weakly and strongly nonlinear counterparts, the non-neutral mode has received less attention. Here the nonlinear evolution of a solitary non-neutral mode at oblique propagation is investigated in an electron-positron plasma. Employing the framework of reductive perturbation analysis, a modified Korteweg-de Vries equation (with cubic nonlinearity) for the lowest-order wave magnetic field is obtained. In the linear approximation, the non-neutral mode has its magnetic component orthogonal to the plane spanned by the directions of wave propagation and of the static magnetic field. The linear polarization is not maintained at higher orders. The results may be relevant to the microstructure in pulsar radiation or to the subpulses.
Alternative modes for optical trapping and manipulation using counter-propagating shaped beams
DEFF Research Database (Denmark)
Palima, Darwin; Lindballe, T.B.; Kristensen, M.V.
2011-01-01
Counter-propagating beams have enabled the first stable three-dimensional optical trapping of microparticles and this procedure has been enhanced and developed over the years to achieve independent and interactive manipulation of multiple particles. In this work, we analyse counter-propagating sh......Counter-propagating beams have enabled the first stable three-dimensional optical trapping of microparticles and this procedure has been enhanced and developed over the years to achieve independent and interactive manipulation of multiple particles. In this work, we analyse counter......-propagating shaped-beam traps that depart from the conventional geometry based on symmetric, coaxial counter-propagating beams. We show that projecting shaped beams with separation distances previously considered axially unstable can, in fact, enhance the axial and transverse trapping stiffnesses. We also show...... for optical trapping and manipulation using patterned counter-propagating beams, which still remains to be fully tapped....
A Modeling and Data Analysis of Laser Beam Propagation in the Maritime Domain
2015-05-18
A TRIDENT SCHOLAR PROJECT REPORT NO. 433 A Modeling and Data Analysis of Laser Beam Propagation in the Maritime Domain by...433 (2015) A MODELING AND DATA ANALYSIS OF LASER BEAM PROPAGATION IN THE MARITIME DOMAIN by Midshipman 1/C Benjamin C. Etringer United States Naval...2. REPORT TYPE 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE A Modeling and Data Analysis of Laser Beam Propagation in the Maritime
Laser Beam Propagation Through Inhomogeneous Media with Shock-Like Profiles: Modeling and Computing
Adamovsky, Grigory; Ida, Nathan
1997-01-01
Wave propagation in inhomogeneous media has been studied for such diverse applications as propagation of radiowaves in atmosphere, light propagation through thin films and in inhomogeneous waveguides, flow visualization, and others. In recent years an increased interest has been developed in wave propagation through shocks in supersonic flows. Results of experiments conducted in the past few years has shown such interesting phenomena as a laser beam splitting and spreading. The paper describes a model constructed to propagate a laser beam through shock-like inhomogeneous media. Numerical techniques are presented to compute the beam through such media. The results of computation are presented, discussed, and compared with experimental data.
Aksenov, V. P.; Dudorov, V. V.; Kolosov, V. V.
2016-09-01
We suggest a technique for generation of optical vortex beams with a variable orbital angular momentum based on a fiber laser array. The technique uses the phase control of each single subbeam. Requirements for the number of subbeams and the spatial arrangement for the vortex beam generation are determined. The propagation dynamics of a vortex beam synthesized is compared with that of a continuous Laguerre-Gaussian beam in free space and in a turbulent atmosphere. Spectral properties of a beam synthesized, which is represented as a superposition of different azimuth modes, are determined during its free-space propagation. It is shown that energy and statistical parameters coincide for synthesized and continuous vortex beams when propagating through a turbulent medium. Probability density functions of the beam intensity fluctuations are well approximated to a gamma distribution in the cases where the scintillation index is lower than unity independently of the beam type and observation point position relative to the propagation axis.
Institute of Scientific and Technical Information of China (English)
戈迪; 蔡阳健; 林强
2005-01-01
By use of a tensor method, the transform formulae for the beam coherence-polarization matrix of the partially polarized Gaussian Schell-model (GSM) beams through aligned and misaligned optical systems are derived. As an example, the propagation properties of the partially polarized GSM beam passing through a misaligned thin lens are illustrated numerically and discussed in detail. The derived formulae provide a convenient way to study the propagation properties of the partially polarized GSM beams through aligned and misaligned optical systems.
Propagation Effect of Hollow Gaussian Beams Passing through a Misaligned Optical System
Institute of Scientific and Technical Information of China (English)
ZHAO Cheng-Liang; WANG Li-Gang; LU Xuan-Hui; WANG Yu-Zhu
2006-01-01
@@ A generalized formula of hollow Gaussian beams through the first-order misaligned ABCD systems is derived by using the generalized diffraction integral formula. It is shown that the hollow Gaussian beam passing through the misaligned system becomes a decentred hollow Gaussian beam. The propagation properties of the output beam are investigated when it propagates through a simple misaligned lens system. These results provide a powerful theoretical tool for applications of optical traps.
Cyclotron waves in a non-neutral plasma column
Energy Technology Data Exchange (ETDEWEB)
Dubin, Daniel H. E. [Department of Physics, University of California at San Diego, La Jolla, California 92093 (United States)
2013-04-15
A kinetic theory of linear electrostatic plasma waves with frequencies near the cyclotron frequency {Omega}{sub c{sub s}} of a given plasma species s is developed for a multispecies non-neutral plasma column with general radial density and electric field profiles. Terms in the perturbed distribution function up to O(1/{Omega}{sub c{sub s}{sup 2}}) are kept, as are the effects of finite cyclotron radius r{sub c} up to O(r{sub c}{sup 2}). At this order, the equilibrium distribution is not Maxwellian if the plasma temperature or rotation frequency is not uniform. For r{sub c}{yields}0, the theory reproduces cold-fluid theory and predicts surface cyclotron waves propagating azimuthally. For finite r{sub c}, the wave equation predicts that the surface wave couples to radially and azimuthally propagating Bernstein waves, at locations where the wave frequency equals the local upper hybrid frequency. The equation also predicts a second set of Bernstein waves that do not couple to the surface wave, and therefore have no effect on the external potential. The wave equation is solved both numerically and analytically in the WKB approximation, and analytic dispersion relations for the waves are obtained. The theory predicts that both types of Bernstein wave are damped at resonances, which are locations where the Doppler-shifted wave frequency matches the local cyclotron frequency as seen in the rotating frame.
The analysis of optical wave beams propagation in lens systems
Kazakov, I.; Mosentsov, S.; Moskaletz, O.
2016-08-01
In this paper some aspects of the formation and propagation of optical wave beams in lens systems were considered. As an example, the two-lens optical information processing system was considered. Analysis of the two-lens optical circuit has been made with a systems approach perspective. As part of the radio-optical analogies had been applied certain provisions of the theory of dynamical systems to the spatial optical system. The lens system is represented as a simple series-connected optical elements with known spatial impulse response. General impulse response of such a system has been received, as well as consider some special cases of the impulse response. The question of the relationship between the parameters and the size of the input aperture lenses for undistorted transmission of the optical signal has been considered. Analysis of the energy loss resulting from the finite aperture of the lens. It's based on an assessment of the fraction of radiation that propagates beyond the lens. Analysis showed that the energy losses depend explicitly on the following parameters: radiation wavelength, distance between input aperture and lens, and ratio of the input aperture and lens aperture. With the computer help simulation the dependence of losses was shown on the above parameters
Zhang, Yalin; Ma, Donglin; Yuan, Xiuhua; Zhou, Zeyu
2016-11-10
In this paper, the aperture averaged scintillation, mean signal-to-noise ratio (SNR), and average bit error rate (BER) for both flat-topped vortex hollow beams and Bessel beams propagating in a turbulent atmosphere are evaluated. Investigations are also made illustrating the variation of aperture averaged scintillation, mean SNR, and average BER against the beam type, propagation distance, and size of the receiver aperture. Compared with the flat-topped vortex hollow beams, the Bessel beams have a smaller aperture averaged scintillation, higher mean SNR, and lower average BER when the receiver aperture is relatively small under the same conditions.
Propagation of a cosh-Gaussian beam through an optical system in turbulent atmosphere.
Chu, Xiuxiang
2007-12-24
The propagation of a cosh-Gaussian beam through an arbitrary ABCD optical system in turbulent atmosphere has been investigated. The analytical expressions for the average intensity at any receiver plane are obtained. As an elementary example, the average intensity and its radius at the image plane of a cosh-Gaussian beam through a thin lens are studied. To show the effects of a lens on the average intensity and the intensity radius of the laser beam in turbulent atmosphere, the properties of a collimated cosh-Gaussian beam and a focused cosh-Gaussian beam for direct propagation in turbulent atmosphere are studied and numerically calculated. The average intensity profiles of a cosh-Gaussian beam through a lens can have a shape similar to that of the initial beam for a longer propagation distance than that of a collimated cosh-Gaussian beam for direct propagation. With the increment in the propagation distance, the average intensity radius at the image plane of a cosh-Gaussian beam through a thin lens will be smaller than that at the focal plane of a focused cosh-Gaussian beam for direct propagation. Meanwhile, the intensity distributions at the image plane of a cosh-Gaussian beam through a lens with different w(0) and Omega(0) are also studied.
An exact solution to paraxial propagation of laser beams in longitudinal inhomogeneous plasmas
Institute of Scientific and Technical Information of China (English)
Zhou Bing-Ju; Huang Zheng; Liu Ming-Wei; Liu Xiao-Juan
2007-01-01
An exact, general solution for laser beams propagating in longitudinally inhomogeneous plasmas is obtained in the form of the diffraction integral. The Gaussian beam and the Hermite-Gaussian beam are taken for example. In the case of an increasing plasma density along the propagation distance, natural diffraction of the Gaussian beam is retarded. This retardance has a less effect on the central part of the Hermite-Gaussian beam while a considerable rise of the power in bucket (PIB) occurs in the surrounding part of the beam.
Dou, Lingyu; Ji, Xiaoling; Li, Peiyun
2012-04-09
The model of partially coherent annular beams with linear non-uniformity field profile in the x direction is set up. The analytic expressions for the average intensity and the centre of gravity of partially coherent annular beams with decentered field propagating through atmospheric turbulence along a slant path are derived. The propagation equation governing the position of the intensity maximum is also given. It is found that the beam non-uniformity is amended gradually as the propagation distance and the strength of turbulence increase. The centre of beam gravity is independent of both the propagation distance and the turbulence. However, the position of the intensity maximum changes versus the propagation distance and the turbulence, and is farthest away from the propagation z-axis at a certain propagation distance. When the propagation distance is large enough, the position of the intensity maximum reaches an asymptotic value which increases with decreasing the zenith angle and is largest for the free space case. When the propagation distance is large enough, the position of the intensity maximum is not on the propagation z-axis, and is nearer to the propagation z-axis than the centre of beam gravity. On the other hand, changes in the intensity maximum in the far field are also examined in this paper.
Propagation of Airy beams from right-handed material to left-handed material
Institute of Scientific and Technical Information of China (English)
Lin Hui-Chuan; Pu Ji-Xiong
2012-01-01
Based on the ABCD matrix formalism,the propagation property of an Airy beam from right-handed material(RHM)to left-handed material(LHM)is investigated.The result shows that when the Airy beam propagates in the LHM,the intensity self-bending due to its propagation in the RHM can be compensated.In particular,if the propagation distance in the RHM is equal to that in the LHM and the refractive index of the LHM is nL=-1,the transverse intensity distribution of the Airy beam can return to its original state.
Underlying conservation and stability laws in nonlinear propagation of axicon-generated Bessel beams
Porras, Miguel A; Losada, Juan Carlos
2015-01-01
In light filamentation induced by axicon-generated, powerful Bessel beams, the spatial propagation dynamics in the nonlinear medium determines the geometry of the filament channel and hence its potential applications. We show that the observed steady and unsteady Bessel beam propagation regimes can be understood in a unified way from the existence of an attractor and its stability properties. The attractor is identified as the nonlinear unbalanced Bessel beam (NL-UBB) whose inward H\\"ankel beam amplitude equals the amplitude of the linear Bessel beam that the axicon would generate in linear propagation. A simple analytical formula that determines de NL-UBB attractor is given. Steady or unsteady propagation depends on whether the attracting NL-UBB has a small, exponentially growing, unstable mode. In case of unsteady propagation, periodic, quasi-periodic or chaotic dynamics after the axicon reproduces similar dynamics after the development of the small unstable mode into the large perturbation regime.
Mossoulina, O. A.; Kirilenko, M. S.; Khonina, S. N.
2016-08-01
We use radial Fractional Fourier transform to model vortex laser beams propagation in optical waveguides with parabolic dependence of the refractive index. To overcome calculation difficulties at distances proportional to a quarter of the period we use varied calculation step. Numerical results for vortex modes superposition propagation in a parabolic optical fiber show that the transverse beam structure can be changed significantly during the propagation. To provide stable transverse distribution input scale modes should be in accordance with fiber parameters.
Propagation dynamics of a light beam in fractional Schr\\"odinger equation
Zhang, Yiqi; Belić, Milivoj R; Zhong, Weiping; Zhang, Yanpeng; Xiao, Min
2015-01-01
Dynamics of wavepackets in fractional Schrodinger equation is still an open problem. The difficulty stems from the fact that the fractional Laplacian derivative is essentially a nonlocal operator. We investigate analytically and numerically the propagation of optical beams in fractional Schr\\"odinger equation with a harmonic potential. We find that the propagation of one- and two-dimensional (1D, 2D) input chirped Gaussian beams is not harmonic. In 1D, the beam propagates along a zigzag trajectory in the real space, which corresponds to a modulated anharmonic oscillation in the momentum space. In 2D, the input Gaussian beam evolves into a breathing ring structure in both real and momentum spaces, which forms a filamented funnel-like aperiodic structure. The beams remain localized in propagation, but with increasing distance display increasingly irregular behavior, unless both the linear chirp and the transverse displacement of the incident beam are zero.
Propagation of a general-type beam through a truncated fractional Fourier transform optical system.
Zhao, Chengliang; Cai, Yangjian
2010-03-01
Paraxial propagation of a general-type beam through a truncated fractional Fourier transform (FRT) optical system is investigated. Analytical formulas for the electric field and effective beam width of a general-type beam in the FRT plane are derived based on the Collins formula. Our formulas can be used to study the propagation of a variety of laser beams--such as Gaussian, cos-Gaussian, cosh-Gaussian, sine-Gaussian, sinh-Gaussian, flat-topped, Hermite-cosh-Gaussian, Hermite-sine-Gaussian, higher-order annular Gaussian, Hermite-sinh-Gaussian and Hermite-cos-Gaussian beams--through a FRT optical system with or without truncation. The propagation properties of a Hermite-cos-Gaussian beam passing through a rectangularly truncated FRT optical system are studied as a numerical example. Our results clearly show that the truncated FRT optical system provides a convenient way for laser beam shaping.
Propagation of an Airy-Gaussian beam in defected photonic lattices
Shi, Zhiwei; Zhu, Xing; Li, Yang; Li, Huagang
2016-01-01
We investigate numerically that a finite Airy-Gaussian (AiG) beam varies its trajectory and shape in the defected photonic lattices. The propagation properties and beam self-bending are controlled with modulation depth and period of the photonic lattices, positive and negative defects, beam distribution factor and nonlinearity change. For positive defects, the pseudo-period oscillation and localization of the AiG beam may be formed under a certain condition, while the beam is diffused for negative defects. Moreover, the solitons may appear during the propagation process when the self-focusing nonlinearity is introduced.
A Schr(o)idinger formulation research for light beam propagation
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The wave equation of light beam propagation was written in the form of an axial-coordinate-dependent Schrdinger equation, and the expectation value of a dynamical variable, the trial function of variational approach and the ABCD law were discussed by use of quantum mechanics approach. In view of the evolution equations of expectation values of dynamical variables in the framework of quantum mechanics, the definition of a potential function representing the beam propagation stability and its universal formula with the quality factor, the universal formula of beam width and curvature radius for a paraxial beam and cylindrically symmetric non-paraxial beam, the general formula of second derivative of beam width with respect to the axial coordinate of beam for a paraxial beam, and the general criteria of the conservation of beam quality factor and the existence of a potential well of a potential function for a paraxial beam, were given or derived, respectively. Starting with the same trial function, the comparative research of our formulation with variational approach was done, which gave some further insight into the physical nature of a beam propagation parameters. The ABCD law of non-paraxial beam was discussed in terms of the definition of the non-paraxial expectation value of a dynamical variable for the first time. The applications to the media of constant second derivative of beam width with respect to the axial coordinate of a beam, square law media and the media of constant refractive index in the momentum representation were discussed, respectively.
Aksenov, Valerii P; Kolosov, Valeriy V; Pogutsa, Cheslav E
2014-06-10
The propagation of laser beams having orbital angular momenta (OAM) in the turbulent atmosphere is studied numerically. The variance of random wandering of these beams is investigated with the use of the Monte Carlo technique. It is found that, among various types of vortex laser beams, such as the Laguerre-Gaussian (LG) beam, modified Bessel-Gaussian beam, and hypergeometric Gaussian beam, having identical initial effective radii and OAM, the LG beam occupying the largest effective volume in space is the most stable one.
Institute of Scientific and Technical Information of China (English)
Li Ya-Qing; Wu Zhen-Sen
2012-01-01
On the basis of the extended Huygens Fresnel principle and the model of the refractive-index structure constant in the atmospheric turbulence proposed by the International Telecommunication Union-Radio Communication Sector,the characteristics of the partially coherent Gaussian Schell-model(GSM)beams propagating in slanted atmospheric turbulence are studied.Using the cross-spectral density function(CSDF),we derive the expressions for the effective beam radius,the spreading angle,and the average intersity.The variance of the angle-of-arrival fluctuation and the wander effect of the GSM beam in the turbulence are calculated numerically.The influences of the coherence degree,the propagation distance,the propagation height,and the waist radius on the propagation characteristics of the partially coherent beams are discussed and compared with those of the fully coherent Gaussian beams.
Charnotskii, Mikhail; Baker, Gary J.
2011-06-01
Asymptotic theory of the finite beam scintillations (Charnotskii, WRM, 1994, JOSA A, 2010) provides an exhaustive description of the dependence of the beam scintillation index on the propagation conditions, beam size and focusing. However the complexity of the asymptotic configuration makes it difficult to apply these results for the practical calculations of the scintillation index (SI). We propose an estimation technique and demonstrate some examples of the calculations of the scintillation index dependence on the propagation path length, initial beam size, wavelength and turbulence strength for the beam geometries and propagation scenarios that are typical for applications. We suggest simple analytic bridging approximations that connect the specific asymptotes with the accuracy sufficient for the engineering estimates. Proposed technique covers propagation of the wide, narrow, collimated and focused beams under the weak and strong scintillation conditions. Direct numeric simulation of the beam waves propagation through turbulence expediently complements the asymptotic theory being most efficient when the governing scales difference is not very large. We performed numerical simulations of the beam wave propagation through turbulence for conditions that partially overlap with the major parameter space domains of the asymptotic theory. The results of the numeric simulation are used to confirm the asymptotic theory and estimate the accuracy of the bridging approximations.
Modeling laser beam diffraction and propagation by the mode-expansion method.
Snyder, James J
2007-08-01
In the mode-expansion method for modeling propagation of a diffracted beam, the beam at the aperture can be expanded as a weighted set of orthogonal modes. The parameters of the expansion modes are chosen to maximize the weighting coefficient of the lowest-order mode. As the beam propagates, its field distribution can be reconstructed from the set of weighting coefficients and the Gouy phase of the lowest-order mode. We have developed a simple procedure to implement the mode-expansion method for propagation through an arbitrary ABCD matrix, and we have demonstrated that it is accurate in comparison with direct calculations of diffraction integrals and much faster.
Berreman approach to electromagnetic wave and beam propagation in anisotropic metamaterials
Gnawali, Rudra; Banerjee, Partha
2016-09-01
The Berreman matrix method is used to analyze the polarization and propagation of electromagnetic waves and beams in anisotropic metamaterials. The metamaterial, comprising a multilayer structure of alternating metal and dielectric layers, is modeled as an effective anisotropic medium. The Maxwell's equations for electromagnetic propagation are then represented as a set of coupled differential equations using the Berreman matrix. These coupled equations are then solved analytically and cross checked numerically using MATLAB® for plane wave propagation. The analysis can be extended to Gaussian beam propagation through such anisotropic metamaterials using the angular plane wave spectral approach.
Propagation properties of hollow sinh-Gaussian beams in quadratic-index medium
Zou, Defeng; Li, Xiaohui; Pang, Xingxing; Zheng, Hairong; Ge, Yanqi
2017-10-01
Based on the Collins integral formula, the analytical expression for a hollow sinh-Gaussian (HsG) beam propagating through the quadratic-index medium is derived. The propagation properties of a single HsG beam and their interactions have been studied in detail with numerical examples. The results show that inhomogeneity can support self-repeating intensity distributions of HsG beams. With high-ordered beam order n, HsG beams could maintain their initial dark hollow distributions for a longer distance. In addition, interference fringes appear at the interactional region. The central intensity is a prominent peak for two in-phase beams, which is zero for two out-of phase beams. By tuning the initial beam phase shift, the distribution of the fringes can be controlled.
Wu, Yuqian; Zhang, Yixin; Zhu, Yun
2016-08-01
We studied Gaussian beams with three different partially coherent models, including the Gaussian-Schell model (GSM), Laguerre-Gaussian Schell model (LGSM), and Bessel-Gaussian Schell model (BGSM), propagating through oceanic turbulence. The expressions of average intensity, beam spreading, and beam wander for GSM, LGSM, and BGSM beams in the paraxial channel are derived. We make a contrast for the three models in numerical simulations and find that the GSM beam has smaller spreading than the others, and the LGSM beam needs longer propagation distance to transform into a well-like profile of average intensity than the BGSM beam in the same conditions. The salinity fluctuation has a greater contribution to the wander of LGSM and BGSM beams than that of the temperature fluctuation. Our results can be helpful in the design of an optical wireless communication link operating in oceanic environment.
Zhang, Yiqi; Liu, Xing; Belić, Milivoj R; Zhong, Weiping; Wen, Feng; Zhang, Yanpeng
2015-08-15
We analytically and numerically investigate an anharmonic propagation of two-dimensional beams in a harmonic potential. We pick noncentrosymmetric beams of common interest that carry orbital angular momentum. The examples studied include superposed Bessel-Gauss (BG), Laguerre-Gauss (LG), and circular Airy (CA) beams. For the BG beams, periodic inversion, phase transition, and rotation with periodic angular velocity are demonstrated during propagation. For the LG and CA beams, periodic inversion and variable rotation are still there but not the phase transition. On the whole, the "center of mass" and the orbital angular momentum of a beam exhibit harmonic motion, but the motion of the beam intensity distribution in detail is subject to external and internal torques and forces, causing it to be anharmonic. Our results are applicable to other superpositions of finite circularly asymmetric beams.
The damped oscillating propagation of the compensating self-accelerating beams
Liu, Wei-Wei; Yu, Pan-Pan; Wang, Hao-wei; Wang, Zi-qiang; Li, Yin-Mei
2016-01-01
We report a new form of compensating accelerating beam generated by amplitude modulation of the symmetric Airy beam (SAB) caustics with an exponential apodization mask. Our numerical study manifests that the compensating beam is with one main-lobe beam structure and can maintain the mean-intensity invariant both in the free space and loss media. Specially, the beam inherits the beamlets structure from the SAB and owns a novel damped oscillating propagation property. We also conduct a comparative study of its propagation property with that of the Airy beam theoretically. And by altering the signs of 2D masks, the main lobe of the compensating beam can be modulated to orientate in four different quadrants flexibly. The proposed compensating accelerating beam is anticipated to get special applications in particle manipulation or plasmas regions.
Propagation of a radial phased-locked Lorentz beam array in turbulent atmosphere.
Zhou, Guoquan
2011-11-21
A radial phased-locked (PL) Lorentz beam array provides an appropriate theoretical model to describe a coherent diode laser array, which is an efficient radiation source for high-power beaming use. The propagation of a radial PL Lorentz beam array in turbulent atmosphere is investigated. Based on the extended Huygens-Fresnel integral and some mathematical techniques, analytical formulae for the average intensity and the effective beam size of a radial PL Lorentz beam array are derived in turbulent atmosphere. The average intensity distribution and the spreading properties of a radial PL Lorentz beam array in turbulent atmosphere are numerically calculated. The influences of the beam parameters and the structure constant of the atmospheric turbulence on the propagation of a radial PL Lorentz beam array in turbulent atmosphere are discussed in detail.
The research of propagation characteristic and formation of double half-Gaussian hollow beams
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
A new kind of hollow beams, double half-Gaussian hollow beams,was put forward. With the help of the Collins formula, the analytical equation of propagation and transformation of the hollow laser beams in free space was deduced. The simulation shows that the intensity exhibits the three-dimensional trap distribution in the near-field, while the double half-Gaussian hollow beams turn into solid laser beams when propagating a certain distance, which shows the characteristics of self-focus. The double half-Gaussian hollow beams were obtained by means of the dual-reflecting splitting optical system. The intensity of the vertical loop in different distances was tested, which shows that the analytical equation of propagation and transformation is in agreement with the result.
The research of propagation characteristic and formation of double half-Gaussian hollow beams
Institute of Scientific and Technical Information of China (English)
DONG Yuan; ZHANG XiHe; NING GuoBin; JIN GuangYong; LIANG Wei; L（U） YanFei; ZHANG Kai
2009-01-01
A new kind of hollow beams, double half-Gaussian hollow beams, was put forward. With the help of the Collins formula, the analytical equation of propagation and transformation of the hollow laser beams in free space was deduced. The simulation shows that the intensity exhibits the three-dimensional trap distribution in the near-field, while the double half-Gaussian hollow beams turn into solid laser beams when propagating a certain distance, which shows the characteristics of self-focus. The double half-Gaussian hollow beams were obtained by means of the dual-reflecting splitting optical system. The intensity of the vertical loop in different distances was tested, which shows that the analytical equation of propagation and transformation is in agreement with the result.
DEFF Research Database (Denmark)
Baltser, Jana; Bergbäck Knudsen, Erik; Vickery, Anette
2011-01-01
of X-ray beamline designs for particular user experiments. In this work we used the newly developed McXtrace ray-tracing package and the SRW wave-optics code to simulate the beam propagation of X-ray undulator radiation through such a "transfocator" as implemented at ID- 11 at ESRF. By applying two...
Propagation of high-power partially coherent fibre laser beams in a real environment
Institute of Scientific and Technical Information of China (English)
Tao Ru-Mao; Si Lei; Ma Yan-Xing; Zou Yong-Chao; Zhou Pu
2011-01-01
The propagation performance of high-power partially coherent fibre laser beams in a real environment is investigated and the theoretical model of a high-power fibre laser propagating in a real environment is established. The influence of a collimating system and thermal blooming is considered together with atmospheric turbulence and mechanical jitter. The laser energy concentration of partially coherent beams in the far field is calculated and analysed based on the theoretical model. It is shown that the propagation performance of partially coherent beams depends on the collimating system,atmospheric turbulence,mechanical jitter and thermal blooming. The propagation performance of partially coherent beams and fully coherent beams is studied and the results show that partially coherent beams are less sensitive to the influence of thermal blooming,which results in that the energy degeneration for partially coherent beams is only 50%a of that for fully coherent beams. Both partially coherent beams and fully coherent beams become less sensitive to thermal blooming when the average structural constant of the refraction index fluctuations increases to 1.7x10-14 m-2/3. The investigation presents a reference for applications of a high-power fibre laser system.
Zhi, Dong; Tao, Rumao; Zhou, Pu; Ma, Yanxing; Wu, Wuming; Wang, Xiaolin; Si, Lei
2017-03-01
A new ring Airy Gaussian (RAiG) vortex beam generation method by coherent combination of Gaussian beam array has been proposed. To validate the feasibility of this method, the propagation properties of the RAiG vortex beam and the coherent combining beam in vacuum have been studied and analyzed. From the comparisons of the intensity distributions and phase patterns along the propagation path, we can conclude that the coherent combining beam has the same properties as those of the ideal RAiG vortex beam. So this method can be used to obtain RAiG vortex beam in practice. Then the general analytical expression of the root-mean-square (RMS) beam width of the RAiG vortex beam, which is appropriately generated by coherent combining method, through anisotropic non-Kolmogorov turbulence has been derived. The influence of anisotropic turbulence on RMS beam width of the generated RAiG vortex beam has been numerically calculated. This generation method has good appropriation to the ideal RAiG vortex beam and is very useful for deriving the analytical expression of propagation properties through a random media. The conclusions are useful in practical applications, such as laser communication and remote sensing systems.
Extension of filament propagation in water with Bessel-Gaussian beams
Directory of Open Access Journals (Sweden)
G. Kaya
2016-03-01
Full Text Available We experimentally studied intense femtosecond pulse filamentation and propagation in water for Bessel-Gaussian beams with different numbers of radial modal lobes. The transverse modes of the incident Bessel-Gaussian beam were created from a Gaussian beam of a Ti:sapphire laser system by using computer generated hologram techniques. We found that filament propagation length increased with increasing number of lobes under the conditions of the same peak intensity, pulse duration, and the size of the central peak of the incident beam, suggesting that the radial modal lobes may serve as an energy reservoir for the filaments formed by the central intensity peak.
Propagation property of the non-paraxial vector Lissajous singularity beams in free space
Chen, Haitao; Gao, Zenghui
2016-12-01
The analytic expressions for the free-space propagation of paraxial and non-paraxial vector Lissajous singularity beams are derived, and used to compare the propagation property of a Lissajous singularity carried by paraxial and non-paraxial vector beams in free space. It is found that the creation of a single Lissajous singularity, the creation and annihilation of pairs Lissajous singularities may take place for the both cases. However, after the annihilation of a pair of singularities, no Lissajous singularities appear in the output field for non-paraxial vector Lissajous singularity beams, which is different from the paraxial vector Lissajous singularity beams.
Propagation of Coherent Gaussian Schell-Model Beam Array in a Misaligned Optical System
Institute of Scientific and Technical Information of China (English)
ZHOU Pu; WANG Xiao-Lin; MA Yan-Xing; MA Hao-Tong; XU Xiao-Jun; LIU Ze-Jin
2011-01-01
@@ Based on a generalized Collins formula,the analytical formula for the propagation property of coherent Gaussian Schell-rnodel(GSM) beam array through a misaligned optical system is derived.As numerical examples,the propagation of a coherent GSM beam array in a typical misaligned optical system with a thin lens is evaluated.The influence of different misalignment parameters is calculated and the normalized-intensity distribution is graphically illustrated.%Based on a generalized Collins formula, the analytical formula for the propagation property of coherent Gaussian Schell-model (GSM) beam array through a misaligned optical system is derived. As numerical examples, the propagation of a coherent GSM beam array in a typical misaligned optical system with a thin lens is evaluated.The influence of different misalignment parameters is calculated and the normalized-intensity distribution is graphically illustrated.
DEFF Research Database (Denmark)
Bertelli, N.; Balakin, A.A.; Westerhof, E.
2010-01-01
A numerical analysis of the electron cyclotron (EC) wave beam propagation in the presence of edge density fluctuations by means of a quasi-optical code [Balakin A. A. et al, Nucl. Fusion 48 (2008) 065003] is presented. The effects of the density fluctuations on the wave beam propagation...... are estimated in a vacuum beam propagation between the edge density layer and the EC resonance absorption layer. Consequences on the EC beam propagation are investigated by using a simplified model in which the density fluctuations are described by a single harmonic oscillation. In addition, quasi......-optical calculations are shown by using edge density fluctuations as calculated by two-dimensional interchange turbulence simulations and validated with the experimental data [O. E. Garcia et al, Nucl. Fusion 47 (2007) 667]...
Estimation of propagation losses for infrared laser beam in turbulent atmosphere
Zaponov, A. E.; Sakharov, M. V.
2016-11-01
In present work, the radiation propagation in atmosphere from laser source to the receiver is considered by taking into account deviations of optical beam due to turbulence. The photon flux density on the receiver has been evaluated.
Quantitative study on propagation and healing of Airy beams under experimental conditions.
Zhuang, Fei; Zhu, Ziyi; Margiewicz, Jessica; Shi, Zhimin
2015-03-01
We investigate the propagation and healing of Airy beams in two dimensions that are obtainable under practical experimental conditions. We introduce an intensity similarity factor to quantitatively describe how an Airy beam retains its original shape. Based on such a figure of merit, we define a shape-retaining distance to quantify how far an Airy beam can keep the shape of its main lobe upon propagation and a healing distance to quantify how soon an initially partially blocked Airy beam can restore its main lobe profile. We perform an analysis on how these two distances scale with experimental parameters. We further use an interference picture to interpret the healing phenomenon of an Airy beam. Our work can serve as a guideline for quantitative performance analysis for applications of Airy beams and can be extended to other special beams in a straightforward fashion.
Propagation of Gaussian beams family through a Kerr-type left-handed metamaterial
Institute of Scientific and Technical Information of China (English)
A. Keshavarz; M. Naseri
2015-01-01
In this paper the propagation of elegant Hermite-cosh-Gaussian, elegant Laguerre Gaussian, and Bessel Gaussian beams through a Kerr left-handed metamaterial (LHM) slab have been studied. A split-step Fourier method is used to investigate the propagation of laser beams through this media. Numerical simulation shows that Gaussian beams have different focusing behaviors in a Kerr LHM slab with positive or negative nonlinearity. Beam focusing happens in slabs with positive nonlinearity and not in slabs with negative nonlinearity;however, negative nonlinearity is required for a Kerr LHM slab to act like a lens. Additionally, the focusing properties of beams can be controlled by controlling the thickness of the slab or the input power of the incident beam. A multilayer structure is also proposed to have beam focusing by thinner slabs and passing longer distances.
Hermite-cosine-Gaussian laser beam and its propagation characteristics in turbulent atmosphere.
Eyyuboğlu, Halil Tanyer
2005-08-01
Hermite-cosine-Gaussian (HcosG) laser beams are studied. The source plane intensity of the HcosG beam is introduced and its dependence on the source parameters is examined. By application of the Fresnel diffraction integral, the average receiver intensity of HcosG beam is formulated for the case of propagation in turbulent atmosphere. The average receiver intensity is seen to reduce appropriately to various special cases. When traveling in turbulence, the HcosG beam initially experiences the merging of neighboring beam lobes, and then a TEM-type cosh-Gaussian beam is formed, temporarily leading to a plain cosh-Gaussian beam. Eventually a pure Gaussian beam results. The numerical evaluation of the normalized beam size along the propagation axis at selected mode indices indicates that relative spreading of higher-order HcosG beam modes is less than that of the lower-order counterparts. Consequently, it is possible at some propagation distances to capture more power by using higher-mode-indexed HcosG beams.
Comparison between Bessel and Gaussian beam propagation for in-depth optogenetic stimulation
Tejeda, Hector; Li, Ting; Mohanty, Samarendra
2013-03-01
Optogenetics technology has opened new landscapes for neuroscience research. Due to its non-diffracting and selfhealing nature, Bessel beam has potential to improve in-depth optogenetic stimulation. A detailed understanding of Bessel beam propagation, as well as its superiority over commonly used Gaussian beam, is essential for delivery and control of light irradiation for optogenetics and other light stimulation approaches. We developed an algorithm for modeling Bessel beam propagation and then compared both beam propagations in two-layered mice brain under variance of multiple variables (i.e., wavelength, numerical aperture, and beam size). These simulations show that Bessel beam is significantly advantageous over Gaussian beam for in-depth optogenetic stimulation, leading to development of lessinvasive probes. While experimental measurements using single-photon Bessel-Gauss beam generated by axicon-tip fiber did not show improved stimulation-depth, near-infrared Bessel beam generated using free-space optics and an axicon led to better penetration than near-infrared Gaussian beam.
Fahrbach, Florian O.; Rohrbach, Alexander
2012-01-01
Laser beams that can self-reconstruct their initial beam profile even in the presence of massive phase perturbations are able to propagate deeper into inhomogeneous media. This ability has crucial advantages for light sheet-based microscopy in thick media, such as cell clusters, embryos, skin or brain tissue or plants, as well as scattering synthetic materials. A ring system around the central intensity maximum of a Bessel beam enables its self-reconstruction, but at the same time illuminates out-of-focus regions and deteriorates image contrast. Here we present a detection method that minimizes the negative effect of the ring system. The beam's propagation stability along one straight line enables the use of a confocal line principle, resulting in a significant increase in image contrast. The axial resolution could be improved by nearly 100% relative to the standard light-sheet techniques using scanned Gaussian beams, while demonstrating self-reconstruction also for high propagation depths.
Vectorial beam propagation simulation of a novel polarization conversion waveguide structure
Li, Daoping; van Brug, Hedser H.; Frankena, Hans J.; van der Tol, Jos J.; Pedersen, Jorgen W.
1995-02-01
The vectorial beam propagation method has successfully been applied to a passive polarization converting waveguide structure. A complete polarization conversion has been simulated. The propagating fields are calculated and the power attenuation is evaluated. The influence of structural changes of the device on the polarization conversion is investigated.
Nonparaxial propagation of Lorentz-Gauss beams in uniaxial crystal orthogonal to the optical axis.
Wang, Xun; Liu, Zhirong; Zhao, Daomu
2014-04-01
Analytical expressions for the three components of nonparaxial propagation of a polarized Lorentz-Gauss beam in uniaxial crystal orthogonal to the optical axis are derived and used to investigate its propagation properties in uniaxial crystal. The influences of the initial beam parameters and the parameters of the uniaxial crystal on the evolution of the beam-intensity distribution in the uniaxial crystal are examined in detail. Results show that the statistical properties of a nonparaxial Lorentz-Gauss beam in a uniaxial crystal orthogonal to the optical axis are closely determined by the initial beam's parameters and the parameters of the crystal: the beam waist sizes-w(0), w(0x), and w(0y)-not only affect the size and shape of the beam profile in uniaxial crystal but also determine the nonparaxial effect of a Lorentz-Gauss beam; the beam profile of a Lorentz-Gauss beam in uniaxial crystal is elongated in the x or y direction, which is determined by the ratio of the extraordinary refractive index to the ordinary refractive index; with increasing deviation of the ratio from unity, the extension of the beam profile augments. The results indicate that uniaxial crystal provides an effective and convenient method for modulating the Lorentz-Gauss beams. Our results may be valuable in some fields, such as optical trapping and nonlinear optics, where a light beam with a special profile and polarization is required.
Wu, Yuqian; Zhang, Yixin; Wang, Qiu; Hu, Zhengda
2016-11-01
For Gaussian beams with three different partially coherent models, including Gaussian-Schell model (GSM), Laguerre-Gaussian Schell-model (LGSM) and Bessel-Gaussian Schell-model (BGSM) beams propagating through a biological turbulent tissue, the expression of the spatial coherence radius of a spherical wave propagating in a turbulent biological tissue, and the average intensity and beam spreading for GSM, LGSM and BGSM beams are derived based on the fractal model of power spectrum of refractive-index variations in biological tissue. Effects of partially coherent model and parameters of biological turbulence on such beams are studied in numerical simulations. Our results reveal that the spreading of GSM beams is smaller than LGSM and BGSM beams on the same conditions, and the beam with larger source coherence width has smaller beam spreading than that with smaller coherence width. The results are useful for any applications involved light beam propagation through tissues, especially the cases where the average intensity and spreading properties of the light should be taken into account to evaluate the system performance and investigations in the structures of biological tissue.
Propagation of a laser beam in a plasma
Chapman, J. M.; Kevorkian, J.; Steinhauer, L. C.; Vagners, J.
1975-01-01
This paper shows that for a nonabsorbing medium with a prescribed index of refraction, the effects of beam stability, line focusing, and beam distortion can be predicted from simple ray optics. When the paraxial approximation is used, diffraction effects are examined for Gaussian, Lorentzian, and square beams. Most importantly, it is shown that for a Gaussian beam, diffraction effects can be included simply by adding imaginary solutions to the paraxial ray equations. Also presented are several procedures to extend the paraxial approximation so that the solution will have a domain of validity of greater extent.
Institute of Scientific and Technical Information of China (English)
Jixiong Pu
2006-01-01
@@ The propagation of polychromatic electromagnetic Gaussian Schell-model (EGSM) beams in free space is investigated. It is shown that the spectral degree of polarization, spectral degree of coherence, and normalized spectrum change generally on propagation. The conditions of keeping the spectral invariance and keeping polarization invariance for the polychromatic EGSM beams are derived respectively. The results indicate that the constraints on the parameters of EGSM source to keep polarization invariance on propagation are more rigorous than those to keep invariance of the normalized spectrum.
Wave beam propagation in a weakly inhomogeneous isotropic medium: paraxial approximation and beyond
Energy Technology Data Exchange (ETDEWEB)
Bornatici, M [INFM, Physics Department ' A. Volta' , University of Pavia, I-27100 Pavia (Italy); Maj, O [INFM, Physics Department, University of Milan, I-20133 Milan (Italy)
2003-05-01
The various methods put forward for the description of paraxial wave beams propagating in weakly inhomogeneous media are shown to be equivalent to each other. This issue is discussed in terms of a comparative analysis with respect to the complex eikonal-based solution relevant to the propagation of a Gaussian wave beam in a lens-like isotropic medium (such a solution being readily extendible to the propagation in a plasma slab). The accuracy of the paraxial solution thus considered is assessed numerically in comparison with the corresponding exact solution of the Helmholtz equation.
A finite element beam propagation method for simulation of liquid crystal devices.
Vanbrabant, Pieter J M; Beeckman, Jeroen; Neyts, Kristiaan; James, Richard; Fernandez, F Anibal
2009-06-22
An efficient full-vectorial finite element beam propagation method is presented that uses higher order vector elements to calculate the wide angle propagation of an optical field through inhomogeneous, anisotropic optical materials such as liquid crystals. The full dielectric permittivity tensor is considered in solving Maxwell's equations. The wide applicability of the method is illustrated with different examples: the propagation of a laser beam in a uniaxial medium, the tunability of a directional coupler based on liquid crystals and the near-field diffraction of a plane wave in a structure containing micrometer scale variations in the transverse refractive index, similar to the pixels of a spatial light modulator.
Generation and propagation of a sine-azimuthal wavefront modulated Gaussian beam.
Lao, Guanming; Zhang, Zhaohui; Luo, Meilan; Zhao, Daomu
2016-07-21
We introduce a method for modulating the Gaussian beam by means of sine-azimuthal wavefront and carry out the experimental generation. The analytical propagation formula of such a beam passing through a paraxial ABCD optical system is derived, by which the intensity properties of the sine-azimuthal wavefront modulated Gaussian (SWMG) beam are examined both theoretically and experimentally. Both of the experimental and theoretical results show that the SWMG beam goes through the process from beam splitting to a Gaussian-like profile, which is closely determined by the phase factor and the propagation distance. Appropriate phase factor and short distance are helpful for the splitting of beam. However, in the cases of large phase factor and focal plane, the intensity distributions tend to take a Gaussian form. Such unique features may be of importance in particle trapping and medical applications.
Propagation of Gaussian beams in the presence of gain and loss
Graefe, Eva-Maria; Schubert, Roman
2016-01-01
We consider the propagation of Gaussian beams in a waveguide with gain and loss in the paraxial approximation governed by the Schr\\"odinger equation. We derive equations of motion for the beam in the semiclassical limit that are valid when the waveguide profile is locally well approximated by quadratic functions. For Hermitian systems, without any loss or gain, these dynamics are given by Hamilton's equations for the center of the beam and its conjugate momentum. Adding gain and/or loss to the waveguide introduces a non-Hermitian component, causing the width of the Gaussian beam to play an important role in its propagation. Here we show how the width affects the motion of the beam and how this may be used to filter Gaussian beams located at the same initial position based on their width.
The complex Jacobi iterative method for three-dimensional wide-angle beam propagation.
Le, Khai Q; Godoy-Rubio, R; Bienstman, Peter; Hadley, G Ronald
2008-10-13
A new complex Jacobi iterative technique adapted for the solution of three-dimensional (3D) wide-angle (WA) beam propagation is presented. The beam propagation equation for analysis of optical propagation in waveguide structures is based on a novel modified Padé(1,1) approximant operator, which gives evanescent waves the desired damping. The resulting approach allows more accurate approximations to the true Helmholtz equation than the standard Padé approximant operators. Furthermore, a performance comparison of the traditional direct matrix inversion and this new iterative technique for WA-beam propagation method is reported. It is shown that complex Jacobi iteration is faster and better-suited for large problems or structures than direct matrix inversion.
Selective propagation and beam splitting of surface plasmons on metallic nanodisk chains.
Hu, Yuhui; Zhao, Di; Wang, Zhenghan; Chen, Fei; Xiong, Xiang; Peng, Ruwen; Wang, Mu
2017-05-01
Manipulating the propagation of surface plasmons (SPs) on a nanoscale is a fundamental issue of nanophotonics. By using focused electron beam, SPs can be excited with high spatial accuracy. Here we report on the propagation of SPs on a chain of gold nanodisks with cathodoluminescence (CL) spectroscopy. Experimental evidence for the propagation of SPs excited by the focused electron beam is demonstrated. The wavelength of the transmitted SPs depends on the geometrical parameters of the nanodisk chain. Furthermore, we design and fabricate a beam splitter, which selectively transmits SPs of certain wavelengths to a specific direction. By scanning the sample surface point by point and collecting the CL spectra, we obtain the spectral mapping and identify that the chain of the smaller nanodisks can efficiently transport SPs at shorter wavelengths. This Letter provides a unique approach to manipulate in-plane propagation of SPs.
Chen, Chunyi; Yang, Huamin; Lou, Yan; Tong, Shoufeng
2011-08-01
Novel analytical expressions for the cross-spectral density function of a Gaussian Schell-model pulsed (GSMP) beam propagating through atmospheric turbulence are derived. Based on the cross-spectral density function, the average spectral density and the spectral degree of coherence of a GSMP beam in atmospheric turbulence are in turn examined. The dependence of the spectral degree of coherence on the turbulence strength measured by the atmospheric spatial coherence length is calculated numerically and analyzed in depth. The results obtained are useful for applications involving spatially and spectrally partially coherent pulsed beams propagating through atmospheric turbulence.
Reciprocity breaking during nonlinear propagation of adapted beams through random media.
Palastro, J P; Peñano, J; Nelson, W; DiComo, G; Helle, M; Johnson, L A; Hafizi, B
2016-08-22
Adaptive optics (AO) systems rely on the principle of reciprocity, or symmetry with respect to the interchange of point sources and receivers. These systems use the light received from a low power emitter on or near a target to compensate phase aberrations acquired by a laser beam during linear propagation through random media. If, however, the laser beam propagates nonlinearly, reciprocity is broken, potentially undermining AO correction. Here we examine the consequences of this breakdown, providing the first analysis of AO applied to high peak power laser beams. While discussed for general random and nonlinear media, we consider specific examples of Kerr-nonlinear, turbulent atmosphere.
Propagation of specular and anti-specular Gaussian Schell-model beams in oceanic turbulence
Zhou, Zhaotao; Guo, Mengwen; Zhao, Daomu
2017-01-01
On the basis of the extended Huygens-Fresnel principle and the unified theory of coherence and polarization of light, we investigate the propagation properties of the specular and anti-specular Gaussian Schell-model (GSM) beams through oceanic turbulence. It is shown that the specularity of specular GSM beams and the anti-specularity of anti-specular GSM beams are destroyed on propagation in oceanic turbulence. The spectral density and the spectral degree of coherence are also studied in detail. The results may be helpful for underwater communication.
Propagation of the Lissajous singularity dipole emergent from non-paraxial polychromatic beams
Haitao, Chen; Gao, Zenghui; Wang, Wanqing
2017-06-01
The propagation of the Lissajous singularity dipole (LSD) emergent from the non-paraxial polychromatic beams is studied. It is found that the handedness reversal of Lissajous singularities, the change in the shape of Lissajous figures, as well as the creation and annihilation of the LSD may take place by varying the propagation distance, off-axis parameter, wavelength, or amplitude factor. Comparing with the LSD emergent from paraxial polychromatic beams, the output field of non-paraxial polychromatic beams is more complicated, which results in some richer dynamic behaviors of Lissajous singularities, such as more Lissajous singularities and no vanishing of a single Lissajous singularity at the plane z>0.
Chen, Yu-Jen; Lin, Yu-Sung; Jiang, I-Min; Tsai, Ming-Shan
2008-03-17
This study investigates the optical nonlinearity of beam propagation in homogeneously aligned nematic liquid crystal (NLC) cells at a temperature close to the nematic-isotropic temperature (TNI). The undulate propagation mode with convergent and divergent loops appearing alternately is reported and the thermally enhanced optical reorientation nonlinearity at the focus is described. The optically induced phase transition exists along the pump beam direction. With the application of the conscopic technique, the arrangements of LC at the focus are proposed in this study. Results of this study demonstrate that the evolution of the LC configuration was affected by the pump beam based on the analysis of conoscopic patterns.
Institute of Scientific and Technical Information of China (English)
刘承宜; 郭弘; 胡巍
2002-01-01
The Helmhotz equation of light beam propagating through a medium of complex refractive index is reduced to the axial-coordinate-dependent Schr?dinger equation of complex potential. The new bra vector, the new expectation value of a dynamical variable and the extended Heisenberg picture are defined by the inverse of the evolution operator instead of its Hermitian adjoint, and the complex beam propagation parameters defined in terms of the new expectation value, the complex ABCD law and the ABCD formulation of the Huygens' integral are discussed in terms of quantum mechanics. It is shown that the evolution equations of the complex beam propagation parameters are the same as those of the beam propagation parameters of beam propagating through a medium of real refractive index. The research on an optical system of the conservative complex beam quality factor shows that the complex ABCD law holds, the evolution of its coordinate operator and the momentum operator is linear, and the Huygens' integral is of the ABCD formulation.
Propagation of a laser beam in a time-varying waveguide. [plasma heating for controlled fusion
Chapman, J. M.; Kevorkian, J.
1978-01-01
The propagation of an axisymmetric laser beam in a plasma column having a radially parabolic electron density distribution is reported. For the case of an axially uniform waveguide it is found that the basic characteristics of alternating focusing and defocusing beams are maintained. However, the intensity distribution is changed at the foci and outer-beam regions. The features of paraxial beam propagation are discussed with reference to axially varying waveguides. Laser plasma coupling is considered noting the case where laser heating produces a density distribution radially parabolic near the axis and the energy absorbed over the focal length of the plasma is small. It is found that: (1) beam-propagation stability is governed by the relative magnitude of the density fluctuations existing in the axial variation of the waveguides due to laser heating, and (2) for beam propagation in a time-varying waveguide, the global instability of the propagation is a function of the initial fluctuation growth rate as compared to the initial time rate of change in the radial curvature of the waveguide.
Review of intense-ion-beam propagation with a view toward measuring ion energy
Energy Technology Data Exchange (ETDEWEB)
Garcia, M.
1982-08-25
The subject of this review is intense ion beam propagation and the possibilities of measuring time dependent ion energy in the beam. Propagation effects discussed include charge separation, charge and current autoneutralization, electron thermalization and current neutralization decay. The interaction of a plasma beam with material obstacles, like collimators, and with transverse magnetic fields is also described. Depending on beam energy, density and pulse length, these interactions can include material ablation with plasmadynamic flow and undeflected propagation across transverse magnetic fields by a polarization drift. On the basis of this review I conclude that three diagnostics: a single floating potential probe, net current probes (Faraday cups) and a Rutherford scattering spectrometer appear capable of giving prompt, time dependent ion energy measurements.
Off-axial elliptical cosine-Gaussian beams and their propagation properties
Institute of Scientific and Technical Information of China (English)
Lu Zhang-De
2007-01-01
In this paper, a new kind of light beam called off-axial elliptical cosine-Gaussian beam (ECosGBs) is denned by using the tensor method. An analytical propagation expression for the ECosGBs passing through axially nonsymmetrical optical systems is derived by using vector integration. The intensity distributions of ECosGBs on the input plane, on the output plane with the equivalent Presnel number being equal to 0.1 and on the focal plane are respectively illustrated for the propagation properties. The results indicate that an ECosGB is eventually transformed into an elliptical cosh-Gaussian beam. In other words, ECosGBs and cosh-Gaussian beams act in a reciprocal manner after propagation.
Slant path average intensity of finite optical beam propagating in turbulent atmosphere
Institute of Scientific and Technical Information of China (English)
Yixin Zhang; Gaogang Wang
2006-01-01
The average intensity of finite laser beam propagating through turbulent atmosphere is calculated from the extended Huygens Fresnel principle. Formulas are presented for the slant path average intensity from an arbitrarily truncated Gaussian beam. The new expressions are derived from the modified von Karman spectrum for refractive-index fluctuations, quadratic approximation of the structure function,and Gaussian approximation for the product of Gaussian function and Bessel function. It is shown that the form of average intensity is not a Gaussian function but a polynomial of the power of the binomial function, Gaussian function, and the incomplete gamma function. The results also show that the mean irradiance of a finite optical beam propagating in slant path turbulent atmosphere not only depends on the effective beam radius at the transmitting aperture plane, propagation distance, and long-term lateral coherence length of spherical wave, but also on the radius of emit aperture.
Evolution of branch points for a laser beam propagating through an uplink turbulent atmosphere.
Ge, Xiao-Lu; Liu, Xuan; Guo, Cheng-Shan
2014-03-24
Evolution of branch points in the distorted optical field is studied when a laser beam propagates through turbulent atmosphere along an uplink path. Two categories of propagation events are mainly explored for the same propagation height: fixed wavelength with change of the turbulence strength and fixed turbulence strength with change of the wavelength. It is shown that, when the beam propagates to a certain height, the density of the branch-points reaches its maximum and such a height changes with the turbulence strength but nearly remains constant with different wavelengths. The relationship between the density of branch-points and the Rytov number is also given. A fitted formula describing the relationship between the density of branch-points and propagation height with different turbulence strength and wavelength is found out. Interestingly, this formula is very similar to the formula used for describing the Blackbody radiation in physics. The results obtained may be helpful for atmospheric optics, astronomy and optical communication.
Active Signal Propagation and Imaging Using Vortex Beams
2014-08-01
power tolerance (~500W/cm2). As shown in Fig. 1 a horizontally polarized continuous wave Gaussian beam (Coherent: Verdi-V18, 532 nm, 0-20 W) is expanded ...rectangular quart cell (1cm x 10 cm x 10cm). Various TM conditions are simulated inside the cell by diluting deionized water with polystyrene spheres...polarized Gaussian beam from a Helium-Neon laser cavity (633nm, ~5mW) is expanded and collimated to a beam waist of ~5mm and converted into an OV baring
Analytical Model for Fictitious Crack Propagation in Concrete Beams
DEFF Research Database (Denmark)
Ulfkjær, J. P.; Krenk, Steen; Brincker, Rune
1995-01-01
An analytical model for load-displacement curves of concrete beams is presented. The load-displacement curve is obtained by combining two simple models. The fracture is modeled by a fictitious crack in an elastic layer around the midsection of the beam. Outside the elastic layer the deformations ...... starts to grow correspond to the same bending moment. Closed-form solutions for the maximum size of the fracture zone and the minimum slope on the load-displacement curve are given.......An analytical model for load-displacement curves of concrete beams is presented. The load-displacement curve is obtained by combining two simple models. The fracture is modeled by a fictitious crack in an elastic layer around the midsection of the beam. Outside the elastic layer the deformations...
Propagation characteristics of Bessel beams generated by continuous, incoherent light sources.
Altıngöz, Ceren; Yalızay, Berna; Akturk, Selcuk
2015-08-01
We investigate the propagation behavior of Bessel beams generated by incoherent, continuous light sources. We perform experiments with narrowband and broadband light emitting diodes, and, for comparison, with a laser diode. We observe that the formation of Bessel beams is affected minimally by temporal coherence, while spatial coherence determines the longitudinal evolution of the beam profile. With spatially incoherent beams, the fringe contrast is comparable to the coherent case at the beginning of the Bessel zone, while it completely fades away by propagation, turning into a cylindrical light pipe. Our results show that beam shaping methods can be extended to cases of limited spatial coherence, paving the way for potential new uses and applications of such sources.
Propagation of obstructed Bessel and Bessel–Gauss beams
CSIR Research Space (South Africa)
Litvin, IA
2008-08-01
Full Text Available . and Dholakia K., “Wavelength dependent propagation and reconstruction of white light Bessel beams”, J. Opt. A: Pure Appl. Opt., 8, 477, (2006) 10. Anguiano-Morales M., Mendez-Otero M. and Iturbe-Castillo D., “Conical dynamics of Bessel beams”, Opt. Eng., 46...
Scintillation reduction using multi-beam propagating technique in atmospheric WOCDMA system
Institute of Scientific and Technical Information of China (English)
Yaqin Zhao; Danli Xu; Xin Zhong
2011-01-01
Wireless optical code division multiple access (WOCDMA) combines code division multiple access (CDMA) with wireless-optic communications.It can not only reserve the advantage of CDMA technology in radio frequency (RF) communication,but also use huge bandwidth and have simple network protocol,random access,and other characteristics.%We propose employing multi-beam propagating technology to mitigate the influence of atmospheric scintillation to the wireless optical code division multiple access (WOCDMA) system and then deduce the bit error rate (BER) formulas of systems in weak and strong scintillations, respectively. According to simulation experiment results, multi-beam propagation can improve the system performance very well compared with single-beam propagating technique. Moreover, the more beams we use, the better the performance we get. When the received optical power is -30 dBm, the BER of the system employing four beams is 5 and 1 dB lower than that of using single-beam propagating technique in weak and strong scintillations, respectively.
Dynamics of the off axis intense beam propagation in a spiral inflector
Goswami, A.; Sing Babu, P.; Pandit, V. S.
2017-01-01
In this paper the dynamics of space charge dominated beam in a spiral inflector is discussed by developing equations of motion for centroid and beam envelope for the off axis beam propagation. Evolution of the beam centroid and beam envelope is studied as a function of the beam current for various input beam parameters. The transmission of beam through the inflector is also estimated as a function of the beam current for an on axis and off axis beam by tracking a large number of particles. Simulation studies show that shift of the centroid from the axis at the inflector entrance affects the centroid location at the exit of the inflector and causes reduction in the beam transmission. The centroid shift at the entrance in the horizontal plane (h plane) is more critical as it affects the centroid shift in the vertical plane (u plane) by a large amount near the inflector exit where the available aperture is small. The beam transmission is found to reduce with increase in the centroid shift as well as with the beam current.
Pulse propagation in a two-pass optical amplifier with arbitrary laser beams overlap
Directory of Open Access Journals (Sweden)
AH Farahbod
2011-09-01
Full Text Available An analytical model for two-pass optical amplifier with arbitrary beams overlap has been developed which generalized the classical theory of Frantz-Nodvik for single pass amplifier. The effect of counterpropagating beams on gain and output energy fluence included in the model. Moreover, the appropriate limiting relations for two special cases of weak input signal and saturation state of the amplifier gain have been derived. The results indicate that for complete beams overlap, the gain and output energy have the least values. The model predictions are consistent with experimental observations and exact analytical model for two-pass amplifier when beam propagation paths are coincided.
Institute of Scientific and Technical Information of China (English)
He Xue-Mei; L(u) Bai-Da
2011-01-01
The propagation properties of partially coherent Hermite-Gaussian beams through non-Kolmogorov atmospheric turbulence are studied. The effects of non-Kolmogorov turbulence and beam nonparaxiality on the average intensity evolution and the beam-width spreading are stressed. It is found that the evolution of the average intensity distribution and the beam-width spreading depends on the generalized exponent factor,namely,on the non-Kolmogorov turbulence strength for the paraxial case. For the non-paraxial case the effect of the turbulence is negligible,while the beamwidth spreading becomes very large. The analytical results are illustrated numerically and interpreted physically.
Analytical Model for Fictitious Crack Propagation in Concrete Beams
DEFF Research Database (Denmark)
Ulfkjær, J. P.; Krenk, S.; Brincker, Rune
-displacement curve where the fictitious crack starts to develope, and the point where the real crack starts to grow will always correspond to the same bending moment. Closed from solutions for the maximum size of the fracture zone and the minimum slope on the load-displacement curve is given. The latter result......An analytical model for load-displacement curves of unreinforced notched and un-notched concrete beams is presented. The load displacement-curve is obtained by combining two simple models. The fracture is modelled by a fictitious crack in an elastic layer around the mid-section of the beam. Outside...
Propagation-dependent beam profile distortion associated with the Goos-Hanchen shift.
Wan, Yuhang; Zheng, Zheng; Zhu, Jinsong
2009-11-09
The propagation-dependent profile distortion of the reflected beam is studied via deriving the theoretical model of the optical field distribution in both the near and far field. It is shown that strong and fast-varying beam distortions can occur along the propagation path, compared to the profile on the reflecting surface. Numerical simulations for the case of a typical SPR configuration with a sharp angular response curve reveal that, when the phase distribution in the angular range covered by the input beam becomes nonlinear, previous theories based on the linear phase approximation fail to predict the Goos-Hanchen shift and its propagation-dependent variations precisely. Our study could shed light on more accurate modeling of the Goos-Hanchen effect's impact on the relevant photonic devices and measurement applications.
Institute of Scientific and Technical Information of China (English)
Cheng Ke; Liu Pu-Sheng; Lü Bai-Da
2008-01-01
Taking two Laguerre-Gauasian beams with topological charge l=±1 as an example,this paper studies the composite optical vortices formed by two noncollinear Laguerre-Gaussian beams with different phases,amplitudes,waist widths,off-axis distances,and their propagation in flee space. It is shown by detailed numerical illustrative examples that the number and location of composite vortices at the waist plane are variable by varying the relative phase β,amplitude ratio η,waist width ratio ξ,or off-axis distance ratio μ.The net topological charge lnet is not always equal to the sum lsum of charges of the two component beams.The motion,creation and annihilation of composite vortices take place in the free-space propagation,and the net charge during the propagation remains unchanged and equals to the net charge at the waist plane.
Scintillation analysis of truncated Bessel beams via numerical turbulence propagation simulation.
Eyyuboğlu, Halil T; Voelz, David; Xiao, Xifeng
2013-11-20
Scintillation aspects of truncated Bessel beams propagated through atmospheric turbulence are investigated using a numerical wave optics random phase screen simulation method. On-axis, aperture averaged scintillation and scintillation relative to a classical Gaussian beam of equal source power and scintillation per unit received power are evaluated. It is found that in almost all circumstances studied, the zeroth-order Bessel beam will deliver the lowest scintillation. Low aperture averaged scintillation levels are also observed for the fourth-order Bessel beam truncated by a narrower source window. When assessed relative to the scintillation of a Gaussian beam of equal source power, Bessel beams generally have less scintillation, particularly at small receiver aperture sizes and small beam orders. Upon including in this relative performance measure the criteria of per unit received power, this advantageous position of Bessel beams mostly disappears, but zeroth- and first-order Bessel beams continue to offer some advantage for relatively smaller aperture sizes, larger source powers, larger source plane dimensions, and intermediate propagation lengths.
Sheikh, Mumtaz; Riza, Nabeel A
2010-06-01
To the best of our knowledge, we propose the first motion-free laser beam propagation analyzer with a hybrid design using a digital micromirror device (DMD) and a liquid electronically controlled variable focus lens (ECVFL). Unlike prior analyzers that require profiling the beam at multiple locations along the light propagation axis, the proposed analyzer profiles the beam at the same plane for multiple values of the ECVFL focal length, thus eliminating beam profiler assembly motion. In addition to measuring standard Gaussian beam parameters, the analyzer can also be used to measure the M(2) beam propagation parameter of a multimode beam. Proof-of-concept beam parameter measurements with the proposed analyzer are successfully conducted for a 633 nm laser beam. Given the all-digital nature of the DMD-based profiling and all-analog motion-free nature of the ECVFL beam focus control, the proposed analyzer versus prior art promises better repeatability, speed, and reliability.
Accurate finite difference beam propagation method for complex integrated optical structures
DEFF Research Database (Denmark)
Rasmussen, Thomas; Povlsen, Jørn Hedegaard; Bjarklev, Anders Overgaard
1993-01-01
A simple and effective finite-difference beam propagation method in a z-varying nonuniform mesh is developed. The accuracy and computation time for this method are compared with a standard finite-difference method for both the 3-D and 2-D versions......A simple and effective finite-difference beam propagation method in a z-varying nonuniform mesh is developed. The accuracy and computation time for this method are compared with a standard finite-difference method for both the 3-D and 2-D versions...
Mao, Haidan; Du, Xinyue; Chen, Linfei; Zhao, Daomu
2011-06-01
On the basis of the fact that a hard-edged aperture function can be expressed as finite matrices with different weighting coefficients, we obtain the analytical formula for the propagation of the broadband gaussian Schell-model (BGSM) beam through the apertured fractional Fourier transformation (AFrFT) system. It is shown by numerical examples that the intensity distribution in the plane of a small fractional order is obviously influenced by the bandwidth when the BGSM beams propagate through the AFrFT system. Further extensions are also pointed out.
Vectorial Nonparaxial Four-Petal Gaussian Beams and Their Propagation in Free Space
Institute of Scientific and Technical Information of China (English)
GAO Zeng-Hui; L(U) Bai-Da
2006-01-01
@@ The vectorial nonparaxial four-petal Gaussian beam (FPGB) is introduced. The closed-form propagation expressions for the free-space propagation of FPGBs are derived and their more general applicable advantages are illustrated analytically and numerically. Some special interesting cases, in particular the paraxial one, are discussed. It is found that the parameter f = 1/kw0 with the k being the wave number and w0 being the waist width plays a crucial role in determining the nonparaxiallity of FPGBs. For small values of the f parameter the paraxial approximation is allowable. In the nonparaxial regime the beam order n additionally affects the vectorial and nonparaxial behaviour of FPGBs.
Reciprocity breaking during nonlinear propagation of adapted beams through random media
Palastro, J P; Nelson, W; DiComo, G; Johnson, L A; Helle, M H; Hafizi, B
2016-01-01
Adaptive optics (AO) systems rely on the principle of reciprocity, or symmetry with respect to the interchange of point sources and receivers. These systems use the light received from a low power emitter on or near a target to compensate profile aberrations acquired by a laser beam during linear propagation through random media. If, however, the laser beam propagates nonlinearly, reciprocity is broken, potentially undermining AO correction. Here we examine the consequences of this breakdown. While discussed for general random and nonlinear media, we consider specific examples of Kerr-nonlinear, turbulent atmosphere.
Indian Academy of Sciences (India)
Saini R S; Tyagi Y; Ghodke A D; Puntambekar T A
2016-04-01
In this paper, we present the results of transverse beam emittance and twiss parameter measurement of an electron beam, delivered by a 20 MeV microtron which is used as a pre-injector system for a booster synchrotron in the Indus Accelerator Facility at RRCAT Indore. Based on these measured beam parameters, beam optics of a transport line was optimized and its results are alsodiscussed in this paper. This beam transport line is used to transport the electron beam from the 20MeV microtron to the booster synchrotron. The booster synchrotron works as a main injector for Indus-1 and Indus-2 synchrotron radiation facilities. To optimize the beam optics of a transport linefor proper beam transmission through the line as well as to match the beam twiss parameters at the beam injection point of another accelerator, it is necessary to know the transverse beam emittance and twiss parameters of the beam coming from the first one. A MATLAB-based GUI program has been developed to calculate the beam emittance and twiss parameters, using quadrupole scanmethod. The measured parameters have been used for beam transport line optimization and twiss parameters matching at booster injection point. After this optimization, an enhancement of ∼50% beam current has been observed in the booster synchrotron.
Robustness of bipartite Gaussian entangled beams propagating in lossy channels
Barbosa, F A S; de Faria, A J; Cassemiro, K N; Villar, A S; Nussenzveig, P; Martinelli, M; 10.1038/nphoton.2010.222
2010-01-01
Subtle quantum properties offer exciting new prospects in optical communications. Quantum entanglement enables the secure exchange of cryptographic keys and the distribution of quantum information by teleportation. Entangled bright beams of light attract increasing interest for such tasks, since they enable the employment of well-established classical communications techniques. However, quantum resources are fragile and undergo decoherence by interaction with the environment. The unavoidable losses in the communication channel can lead to a complete destruction of useful quantum properties -- the so-called "entanglement sudden death". We investigate the precise conditions under which this phenomenon takes place for the simplest case of two light beams and demonstrate how to produce states which are robust against losses. Our study sheds new light on the intriguing properties of quantum entanglement and how they may be tamed for future applications.
Effect of oceanic turbulence on the propagation of cosine-Gaussian-correlated Schell-model beams
Ding, Chaoliang; Liao, Lamei; Wang, Haixia; Zhang, Yongtao; Pan, Liuzhan
2015-03-01
On the basis of the extended Huygens-Fresnel principle, the analytic expression for the cross-spectral density function of the cosine-Gaussian-correlated Schell-model (CGSM) beams propagating in oceanic turbulence is derived and used to investigate the spectral density and spectral degree of coherence of CGSM beams. The dependence of the spectral density and spectral degree of coherence of CGSM beams on the oceanic turbulence parameters including temperature-salinity balance parameter ω, mean square temperature dissipation rate χT and energy dissipation rate per unit mass ɛ is stressed and illustrated numerically. It is shown that oceanic turbulence plays an important role in the evolution of spectral density and spectral degree of coherence of CGSM beams upon propagation.
Scintillation reduction for combined Gaussian-vortex beam propagating through turbulent atmosphere
Energy Technology Data Exchange (ETDEWEB)
Berman, Gennady P [Los Alamos National Laboratory; Gorshkov, V. N. [NATL' TECH. UNIV. OF UA; Torous, S. V. [NATL' TECH. UNIV. OF UA
2010-12-14
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams (PCBs), including the optical vortices, propagating in turbulent atmospheres, The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. A method for significantly reducing the SI, by averaging the signal at the detector over a set of PCBs, is described, This novel method is to generate the PCBs by combining two laser beams - Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the SI is effectively suppressed without any high-frequency modulators.
Scintillation reduction for combined Gaussian-vortex beam propagating through turbulent atmosphere
Berman, G P; Torous, S V
2011-01-01
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams (PCBs), including the optical vortices, propagating in turbulent atmospheres. The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. A method for significantly reducing the SI, by averaging the signal at the detector over a set of PCBs, is described. This novel method is to generate the PCBs by combining two laser beams - Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the SI is effectively suppressed without any high-frequency modulators.
A study of nondiffracting Lommel beams propagating in a medium containing spherical scatterers
Belafhal, A.; Ez-zariy, L.; Hricha, Z.
2016-11-01
By means of the expansion of the nondiffracting beams on plane waves with help of the Whittaker integral, an exact analytical expression of the far-field form function of the scattering of the acoustic and optical nondiffracting Lommel beams propagating in a medium containing spherical particles, considered as rigid and single spheres, is investigated in this work. The form function of the scattering of the high order Bessel beam by a rigid and isolated sphere is deduced, from our finding, as a special case. The effects of the wave number-sphere radius product (ka) , the polar angle (φ) , the propagation half-cone angle (β) and the scattering angle (θ) on the far-field form function of the scattered wave have been analyzed and discussed numerically. The numerical results show that the illumination of a rigid sphere by Lommel beams produces asymmetrical scattering.
Propagation dynamics of finite-energy Airy beams in nonlocal nonlinear media
Wu, Zhen-Kun; Li, Peng; Gu, Yu-Zong
2017-10-01
We investigate periodic inversion and phase transition of normal and displaced finite-energy Airy beams propagating in nonlocal nonlinear media with the split-step Fourier method. Numerical simulation results show that parameters such as the degree of nonlocality and amplitude have profound effects on the intensity distribution of the period of an Airy beam. Nonlocal nonlinear media will reduce into a harmonic potential if the nonlocality is strong enough, which results in the beam fluctuating in an approximately cosine mode. The beam profile changes from an Airy profile to a Gaussian one at a critical point, and during propagation the process repeats to form an unusual oscillation. We also briefly discus the two-dimensional case, being equivalent to a product of two one-dimensional cases.
Scintillation reduction for combined Gaussian-vortex beam propagating through turbulent atmosphere
Energy Technology Data Exchange (ETDEWEB)
Berman, Gennady P [Los Alamos National Laboratory; Gorshkov, V. N. [NATL' TECH. UNIV. OF UA; Torous, S. V. [NATL' TECH. UNIV. OF UA
2010-12-14
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams (PCBs), including the optical vortices, propagating in turbulent atmospheres, The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. A method for significantly reducing the SI, by averaging the signal at the detector over a set of PCBs, is described, This novel method is to generate the PCBs by combining two laser beams - Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the SI is effectively suppressed without any high-frequency modulators.
Propagation of Plasma Generated by Intense Pulsed Ion Beam Irradiation
Institute of Scientific and Technical Information of China (English)
WU Di; GONG Ye; LIU Jin-Yuan; WANG Xiao-Gang; LIU Yue; MA Teng-Cai
2006-01-01
@@ Taking the calculation results based on the established two-dimensional ablation model of the intense-pulsed-ion-beam (IPIB) irradiation process as initial conditions, we build a two-dimensional hydrodynamic ejection model of plasma produced by an IPIB-irradiated metal titanium target into ambient gas. We obtain the conclusions that shock waves generate when the background pressure is around 133 mTorr and also obtain the plume splitting phenomenon that has been observed in the experiments.
Propagation of Polarization Modulated Beams Through a Turbulent Atmosphere
2014-11-24
1012) range. The polarization is thus a convolution of the electric field at previous times with the time- dependent susceptibility. In the case of a...by the following: (a) Commence with () and cos(), separately , and delay each constituent beam by /2, separately , to...3.1, above). A example of continuation of the analysis procedure. Probability density measures were calculated based on a normal kernel function for
Suo, Qiangbo; Han, Yiping; Cui, Zhiwei
2017-09-01
Based on the extended Huygens-Fresnel integral, the analytical expressions for the Wigner distribution function (WDF) and kurtosis parameter of partially coherent flat-topped vortex (PCFTV) beams propagating through atmospheric turbulence and free space are derived. The WDF and kurtosis parameter of PCFTV beams through turbulent atmosphere are discussed with numerical examples. The numerical results show that the beam quality depends on the structure constants, the inner scale turbulence, the outer scale turbulence, the spatial correlation length, the wave length and the beam order. PCFTV beams are less affected by turbulence than partially flat-topped coherent (PCFT) beams under the same conditions, and will be useful in free-space optical communications.
COUNTER PROPAGATION OF ELECTRON AND CO2 LASER BEAMS IN A PLASMA CHANNEL.
Energy Technology Data Exchange (ETDEWEB)
HIROSE,T.; POGORELSKY,I.V.; BEN ZVI,I.; YAKIMENKO,V.; KUSCHE,K.; SIDDONS,P.; KUMITA,T.; KAMIYA,Y.; ZIGLER,A.; GREENBERG,B.; ET AL
2002-11-12
A high-energy CO{sub 2} laser is channeled in a capillary discharge. Occurrence of guiding conditions at a relatively low plasma density (<10{sup 18} cm{sup -3}) is confirmed by MHD simulations. Divergence of relativistic electron beam changes depending on the plasma density. Counter-propagation of the electron and laser beams inside the plasma channel results in intense x-ray generation.
Propagation of partially coherent flat-topped beams through a turbulent atmosphere.
Dan, Youquan; Zhang, Bin; Pan, Pingping
2008-09-01
Based on the modified beam model for flat-topped beams and the Schell model for partially coherent light, an expression for partially coherent flat-topped (PCFT) beams has been proposed. The propagation characteristics of PCFT beams with circular symmetry through a turbulent atmosphere have been studied. By using the generalized Huygens-Fresnel integral and Fourier transform method, the expressions for the cross-spectral density function and the average intensity have been given and the analytical expression for the root-mean-square width has been derived. The effects of the beam order, the spatial coherence, and the turbulent parameter on the intensity distributions and beam spreading have been discussed in detail. Our results show that the on-axis intensity of the beams decreases with increasing turbulence and decreasing coherence of the source, whereas the on-axis intensity of the beams in the far field decreases slightly with increasing beam order. The relative spreading of PCFT beams is smaller for beams with a higher order, a lower degree of global coherence of the source, a larger inner scale, and a smaller outer scale of the turbulence.
Xiao, Xifeng; Voelz, David G; Toselli, Italo; Korotkova, Olga
2016-05-20
Experimental and theoretical work has shown that atmospheric turbulence can exhibit "non-Kolmogorov" behavior including anisotropy and modifications of the classically accepted spatial power spectral slope, -11/3. In typical horizontal scenarios, atmospheric anisotropy implies that the variations in the refractive index are more spatially correlated in both horizontal directions than in the vertical. In this work, we extend Gaussian beam theory for propagation through Kolmogorov turbulence to the case of anisotropic turbulence along the horizontal direction. We also study the effects of different spatial power spectral slopes on the beam propagation. A description is developed for the average beam intensity profile, and the results for a range of scenarios are demonstrated for the first time with a wave optics simulation and a spatial light modulator-based laboratory benchtop counterpart. The theoretical, simulation, and benchtop intensity profiles show good agreement and illustrate that an elliptically shaped beam profile can develop upon propagation. For stronger turbulent fluctuation regimes and larger anisotropies, the theory predicts a slightly more elliptical form of the beam than is generated by the simulation or benchtop setup. The theory also predicts that without an outer scale limit, the beam width becomes unbounded as the power spectral slope index α approaches a maximum value of 4. This behavior is not seen in the simulation or benchtop results because the numerical phase screens used for these studies do not model the unbounded wavefront tilt component implied in the analytic theory.
Model for Atmospheric Propagation of Spatially Combined Laser Beams
2016-09-01
AGENCY USE ONLY (Leave Blank) 2. REPORT DATE Sept 2016 3. REPORT TYPE AND DATES COVERED Master’s Thesis 12-01-2015 to 09-23-2016 4. TITLE AND SUBTITLE...the thesis starts with an overview of DE weapons and end with the dierent types of available laser sources. In Chapter 3, the thesis discussed... fluoride to produce a 4 µm laser and was integrated with the SeaLite Beam director for operational testing. Due to MIRACL’s wavelength, it was prone to
Yesayan, G L
2001-01-01
The equations for the width and curvature radius of the wave front for a Gaussian beam of light propagating along the axis of the longitudinally inhomogeneous graded index waveguide with gain and losses in the presence of third-order nonlinearity are obtained. By means of numerical calculations it is shown that in such waveguides the mode of stabilization of the beam width is possible, when the absorption of radiation on the edges of the beam compensates its spreading caused by the longitudinal inhomogeneity and nonlinearity of the waveguide
On the accuracy of the finite difference method for applications in beam propagating techniques
Hoekstra, Hugo; Krijnen, Gijsbertus J.M.; Lambeck, Paul
1992-01-01
In this paper it is shown that the inaccuracy in the beam propagation method based on the finite difference scheme, introduced by the use of the slowly varying envelope approximation, can be overcome in an effective way. By the introduction of a perturbation expansion the accuracy can be improved as
Cylindrical Beam Propagation Modelling of Perturbed Whispering-Gallery Mode Microcavities
Shirazi, Mohammad Amin Cheraghi; Vincent, Serge; Lu, Tao
2013-01-01
We simulate light propagation in perturbed whispering-gallery mode microcavities using a two-dimensional finite-difference beam prop- agation method in a cylindrical coordinate system. Optical properties of whispering-gallery microcavities perturbed by polystyrene nanobeads are investigated through this formulation. The light perturbation as well as quality factor degradation arising from cavity ellipticity are also studied.
2010-03-01
describe turbulence effects on optical beam propagation. [6] Toselli et al summarized recent experimental results that did not agree with analytical...Tennekes, H. and J. L. Lumley. A First Course in Turbulence. MIT Press, Cambridge, MA, First edition, 1972. [18] Toselli , Italo, Larry C. Andrews
Energy Technology Data Exchange (ETDEWEB)
Ronald C. Davidson; Igor Kaganovich; Edward A. Startsev
2004-04-09
Properties of the multi-species electromagnetic Weibel and electrostatic two-stream instabilities are investigated for an intense ion beam propagating through background plasma. Assuming that the background plasma electrons provide complete charge and current neutralization, detailed linear stability properties are calculated within the framework of a macroscopic cold-fluid model for a wide range of system parameters.
Propagation of an Airy-Gaussian-Vortex beam in a chiral medium
Hua, Sen; Liu, Youwen; Zhang, Huijie; Tang, Liangzun; Feng, Yunxcai
2017-04-01
Based on the Huygens diffraction integral, the analytical expressions of electric field distribution of the Airy-Gaussian-Vortex (AiGV) beam in a chiral medium are derived, and its propagation properties are investigated. With increasing the value of chiral parameter γ, the parabolic deflection of the LCP light increases and the RCP light decreases respectively. For the first-order AiGV beam with only one positive or negative optical vortex (OV), a half-moon-shaped intensity profile can be observed because of overlap of the OV and the Airy main lobe, and then the main lobe will be reconstructed and the vortex could be recovered after the overlap position. The intensity distribution of AiGV beam, the deflection trajectories of central positions of Airy beam and OV under different competing parameters between Gaussian and Airy terms have been studied. Furthermore, for the second-order counterrotating AiGV beam with positive and negative vortexes, it could be considered the superposition of two first-order AiGV beams with respective positive and negative vortexes. Two vortexes can regenerate during propagation and the intensity distribution the AiGV beam in the far zone can be controlled by adjusting the coordinates of two vortexes.
Propagation of whistler waves driven by fine structured ion beams in the magnetotail
Burinskaya, T.; Schriver, D.; Ashour-Abdalla, M.
1994-01-01
In a previous paper, which examined the propagation of low-frequency whistler waves generated by ion beams in the Earth's plasma sheet boundary layer (PSBL), it was found that whistler waves driven in the PSBL are focused toward the central plasma sheet due to the global magnetotail inhomogeneities; this finding may help explain the observations of magnetic noise bursts in the tail (Burinskaya et al., 1993). In this paper the same phenomenon is examined, but this time a much more realistic model is used for the ion beam in the PSBL. While the PSBL has been modeled as a solid, homogeneous ion beams with a width of one Earth radius, observations and theoretical considerations have shown that PSBL ion beams actually have a decreasing velocity profile toward the plasma sheet and that the density of the beams within the PSBL can vary locally. We consider again the propagation and generation of electromagnetic waves but in the presence of fine structured ion beams in the PSBL. Our results show that whistler waves, generated quasi-parallel to the background magnetic field, can be trapped locally within small spatial regions where the ion beam density is enhanced compared to the density of the adjacent PSBL region. Wave spectra and nonlinear saturation mechanisms are discussed.
Directory of Open Access Journals (Sweden)
Edward A. Startsev
2010-06-01
Full Text Available The transverse dynamics of an intense charged particle beam propagating through a periodic quadrupole focusing lattice is described by the nonlinear Vlasov-Maxwell system of equations, where the propagation distances play the role of time. To determine matched-beam quasiequilibrium distribution functions, one needs to determine a dynamical invariant for the beam particles moving in the combined applied and self-generated fields. In this paper, a perturbative Hamiltonian transformation method is developed which is an expansion in the particle’s vacuum phase advance ϵ[over ¯]∼σ_{v}/2π, treated as a small parameter, which is used to transform away the fast particle orbit oscillations and obtain the average Hamiltonian accurate to order ϵ[over ¯]^{3}. The average Hamiltonian is an approximate invariant of the original system, and can be used to determine self-consistent beam quasiequilibrium solutions that are matched to the focusing channel. The equation determining the average self-field potential is derived for general boundary conditions by taking into account the average contribution of the charges induced on the boundary. It is shown for a cylindrical conducting boundary that the average self-field potential acquires an octupole component, which results in the average motion of some beam particles being nonintegrable and their trajectories chaotic. This chaotic behavior of the beam particles may significantly change the nature of the Landau damping (or growth of collective excitations supported by an intense charged particle beam.
Tie, B.; Tian, B. Y.; Aubry, D.
2013-12-01
The elastic wave propagation phenomena in two-dimensional periodic beam lattices are studied by using the Bloch wave transform. The numerical modeling is applied to the hexagonal and the rectangular beam lattices, in which, both the in-plane (with respect to the lattice plane) and out-of-plane waves are considered. The dispersion relations are obtained by calculating the Bloch eigenfrequencies and eigenmodes. The frequency bandgaps are observed and the influence of the elastic and geometric properties of the primitive cell on the bandgaps is studied. By analyzing the phase and the group velocities of the Bloch wave modes, the anisotropic behaviors and the dispersive characteristics of the hexagonal beam lattice with respect to the wave propagation are highlighted in high frequency domains. One important result presented herein is the comparison between the first Bloch wave modes to the membrane and bending/transverse shear wave modes of the classical equivalent homogenized orthotropic plate model of the hexagonal beam lattice. It is shown that, in low frequency ranges, the homogenized plate model can correctly represent both the in-plane and out-of-plane dynamic behaviors of the beam lattice, its frequency validity domain can be precisely evaluated thanks to the Bloch modal analysis. As another important and original result, we have highlighted the existence of the retropropagating Bloch wave modes with a negative group velocity, and of the corresponding "retro-propagating" frequency bands.
Stress wave propagation in a composite beam subjected to transverse impact.
Energy Technology Data Exchange (ETDEWEB)
Lu, Wei-Yang; Song, Bo; Jin, Huiqing
2010-08-01
Composite materials, particularly fiber reinforced plastic composites, have been extensively utilized in many military and industrial applications. As an important structural component in these applications, the composites are often subjected to external impact loading. It is desirable to understand the mechanical response of the composites under impact loading for performance evaluation in the applications. Even though many material models for the composites have been developed, experimental investigation is still needed to validate and verify the models. It is essential to investigate the intrinsic material response. However, it becomes more applicable to determine the structural response of composites, such as a composite beam. The composites are usually subjected to out-of-plane loading in applications. When a composite beam is subjected to a sudden transverse impact, two different kinds of stress waves, longitudinal and transverse waves, are generated and propagate in the beam. The longitudinal stress wave propagates through the thickness direction; whereas, the propagation of the transverse stress wave is in-plane directions. The longitudinal stress wave speed is usually considered as a material constant determined by the material density and Young's modulus, regardless of the loading rate. By contrast, the transverse wave speed is related to structural parameters. In ballistic mechanics, the transverse wave plays a key role to absorb external impact energy [1]. The faster the transverse wave speed, the more impact energy dissipated. Since the transverse wave speed is not a material constant, it is not possible to be calculated from stress-wave theory. One can place several transducers to track the transverse wave propagation. An alternative but more efficient method is to apply digital image correlation (DIC) to visualize the transverse wave propagation. In this study, we applied three-pointbending (TPB) technique to Kolsky compression bar to facilitate
Zhang, Lifu; Li, Chuxin; Zhong, Haizhe; Xu, Changwen; Lei, Dajun; Li, Ying; Fan, Dianyuan
2016-06-27
We have investigated the propagation dynamics of super-Gaussian optical beams in fractional Schrödinger equation. We have identified the difference between the propagation dynamics of super-Gaussian beams and that of Gaussian beams. We show that, the linear propagation dynamics of the super-Gaussian beams with order m > 1 undergo an initial compression phase before they split into two sub-beams. The sub-beams with saddle shape separate each other and their interval increases linearly with propagation distance. In the nonlinear regime, the super-Gaussian beams evolve to become a single soliton, breathing soliton or soliton pair depending on the order of super-Gaussian beams, nonlinearity, as well as the Lévy index. In two dimensions, the linear evolution of super-Gaussian beams is similar to that for one dimension case, but the initial compression of the input super-Gaussian beams and the diffraction of the splitting beams are much stronger than that for one dimension case. While the nonlinear propagation of the super-Gaussian beams becomes much more unstable compared with that for the case of one dimension. Our results show the nonlinear effects can be tuned by varying the Lévy index in the fractional Schrödinger equation for a fixed input power.
Studies of beam propagation characteristics on apertured fractional Fourier transforming systems
Institute of Scientific and Technical Information of China (English)
Hongjie Liu(刘红婕); Daomu Zhao(赵道木); Haidan Mao(毛海丹); Shaomin Wang(王绍民); Feng Jing(景峰); Qihua Zhu(朱启华); Xiaofeng Wei(魏晓峰); Xiaomin Zhang(张小民)
2004-01-01
Based on the principle that a rectangular function can be expanded into a sum of complex Gaussian functions with finite numbers, propagation characteristics of a Gaussian beam or a plane wave passing through apertured fractional Fourier transforming systems are analyzed and corresponding analytical formulae are obtained. Analytical formulae in different fractional orders are numerically simulated and compared with the diffraction integral formulae, the applicable range and exactness of analytical formulae are confirmed.It is shown that the calculating speed of using the obtained approximate analytical formulae, is several hundred times faster than that of using diffraction integral directly. Meanwhile, by using analytical formulae the effect of different aperture sizes on Gaussian beam propagation characteristics is numerically simulated, it is shown that the diffraction effect can be neglected when the aperture size is 5 times larger than the beam waist size.
Shu, Hong; Mokhov, Sergiy; Zeldovich, Boris Ya; Bass, Michael
2009-01-01
A further extension of the iteration method for beam propagation calculation is presented that can be applied for volume Bragg gratings (VBGs) with extremely large grating strength. A reformulation of the beam propagation formulation is presented for analyzing the reflection of a laser beam by a deformed VBG. These methods will be shown to be very accurate and efficient. A VBG with generic z-dependent distortion has been analyzed using these methods.
Yin, Suqin; Zhang, Bin; Dan, Youquan
2011-06-01
When high-power annular laser beams produced by the unstable resonator pass through the volume Bragg grating (VBG), absorption of light in the VBG will induce a temperature increment, resulting in changes in surface distortion. Considering that the surface distortion of the grating induces index and period differences, the scalar wave equations for the annular laser beams propagating in the VBG have been solved numerically and iteratively using finite-difference and sparse matrix methods. The variation in intensity distributions, the total power reflection coefficient, and the power in the bucket (PIB) for the annular laser beams passing through the reflection VBG with deformation have been analyzed quantitatively. It can be shown that the surface distortion of the VBG and the beam orders of the annular beams affect evidently the intensity distributions, the power reflection coefficient, and the PIB of the output beam. The peak intensity decreases as the deformation of the VBG increases. The total power reflection efficiency decreases significantly with the increase in deformations of the VBG. The PIB of the output beam decreases as the obscuration ratio β and the deformation of the VBG increase. For the given obscuration ratio β, the influence of deformation of reflection VBG on the PIB of the annular beams is more sensitive with increase in distortion of the VBG and decrease in beam order.
A Modified Beam Propagation Method Based on the Galerkin Method with Hermite-Gauss Basis Functions
Institute of Scientific and Technical Information of China (English)
Xiao Jinbiao; Liu Xu; Cai Chun; Fan Hehong; Sun Xiaohan
2006-01-01
A beam propagation method based on the Galerkin method with Hermite-Gauss basis functions for studying optical field propagation in weakly guiding dielectric structures is described. The selected basis functions naturally satisfy the required boundary conditions at infinity so that the boundary truncation is avoided. The paraxial propagation equation is converted into a set of first-order ordinary differential equations,which are solved by means of standard numerical library routines. Besides, the calculation is efficient due to its small resulted matrix. The evolution of the injected field and its normalized power along the propagation distance in an asymmetric slab waveguide and directional coupler are presented, and the solutions are good agreement with those obtained by finite difference BPM, which tests the validity of the present approach.
Study of Gaussian and Bessel beam propagation using a new analytic approach
Dartora, C. A.; Nobrega, K. Z.
2012-03-01
The main feature of Bessel beams realized in practice is their ability to resist diffractive effects over distances exceeding the usual diffraction length. The theory and experimental demonstration of such waves can be traced back to the seminal work of Durnin and co-workers already in 1987. Despite that fact, to the best of our knowledge, the study of propagation of apertured Bessel beams found no solution in closed analytic form and it often leads to the numerical evaluation of diffraction integrals, which can be very awkward. In the context of paraxial optics, wave propagation in lossless media is described by an equation similar to the non-relativistic Schrödinger equation of quantum mechanics, but replacing the time t in quantum mechanics by the longitudinal coordinate z. Thus, the same mathematical methods can be employed in both cases. Using Bessel functions of the first kind as basis functions in a Hilbert space, here we present a new approach where it is possible to expand the optical wave field in a series, allowing to obtain analytic expressions for the propagation of any given initial field distribution. To demonstrate the robustness of the method two cases were taken into account: Gaussian and zeroth-order Bessel beam propagation.
Propagation of the off-axis superposition of partially coherent beams through atmospheric turbulence
Institute of Scientific and Technical Information of China (English)
Zhang En-Tao; Ji Xiao-Ling; Lü Bai-Da
2009-01-01
The propagation properties of the off-axis superposition of partially coherent beams through atmospheric tur-bulence and their beam quality in terms of the mean-squared beam width w(z) and the power in the bucket (PIB)are studied in detail, where the effects of partial coherence, off-axis beam superposition and atmospheric turbulence are considered. The analytical expressions for the intensity, the beam width and the PIB are derived, and illustrative examples are given numerically. It is shown that the maximum intensity/max and the PIB decrease and ω(z) increases as the refraction index structure constant C2n increases. Therefore, the turbulence results in a degradation of the beam quality. However, the resulting partially coherent beam with a smaller value of spatial correlation parameter γ and larger values of separate distance Xd and beam number M is less affected by the turbulence than that with a larger value of γ and smaller values of xd and M. The main results obtained in this paper are explained physically.
Dispersion and stability analysis for a finite difference beam propagation method.
de-Oliva-Rubio, J; Molina-Fernández, I; Godoy-Rubio, R
2008-06-09
Applying continuous and discrete transformation techniques, new analytical expressions to calculate dispersion and stability of a Runge- Kutta Finite Difference Beam Propagation Method (RK-FDBPM) are obtained. These expressions give immediate insight about the discretization errors introduced by the numerical method in the plane-wave spectrum domain. From these expressions a novel strategy to adequately set the mesh steps sizes of the RK-FDBPM is presented. Assessment of the method is performed by studying the propagation in several linear and nonlinear photonic devices for different spatial discretizations.
Beam-displacement ray-mode theory of sound propagation in shallow water
Institute of Scientific and Technical Information of China (English)
张仁和; 李风华
1999-01-01
A normal mode method for propagation modeling in common horizontally stratified shallow water, which is called beam-displacement ray-mode (BDRM) theory, is introduced. The peculiarity of this method is that the boundary effects on the sound field can be expressed by the equivalent boundary reflection coefficient, so BDRM theory can be extended to elastic bottom easily. Theoretical calculations of shallow-water sound field show that BDRM has high accuracy and fast speed. The pulse propagation in shallow water is also calculated by BDRM, and the calculated waveforms are in good agreement with the measured waveforms.
Srisungsitthisunti, Pornsak; Ersoy, Okan K; Xu, Xianfan
2009-01-01
Light diffraction by volume Fresnel zone plates (VFZPs) is simulated by the Hankel transform beam propagation method (Hankel BPM). The method utilizes circularly symmetric geometry and small step propagation to calculate the diffracted wave fields by VFZP layers. It is shown that fast and accurate diffraction results can be obtained with the Hankel BPM. The results show an excellent agreement with the scalar diffraction theory and the experimental results. The numerical method allows more comprehensive studies of the VFZP parameters to achieve higher diffraction efficiency.
Role of Density Profiles for the Nonlinear Propagation of Intense Laser Beam through Plasma Channel
Directory of Open Access Journals (Sweden)
Sonu Sen
2014-01-01
Full Text Available In this work role of density profiles for the nonlinear propagation of intense laser beam through plasma channel is analyzed. By employing the expression for the dielectric function of different density profile plasma, a differential equation for beamwidth parameter is derived under WKB and paraxial approximation. The laser induces modifications of the dielectric function through nonlinearities. It is found that density profiles play vital role in laser-plasma interaction studies. To have numerical appreciation of the results the propagation equation for plasma is solved using the fourth order Runge-Kutta method for the initial plane wave front of the beam, using boundary conditions. The spot size of the laser beam decreases as the beam penetrates into the plasma and significantly adds self-focusing in plasma. This causes the laser beam to become more focused by reduction of diffraction effect, which is an important phenomenon in inertial confinement fusion and also for the understanding of self-focusing of laser pulses. Numerical computations are presented and discussed in the form of graphs for typical parameters of laser-plasma interaction.
EXPERIMENTAL STUDY ON CRACK CURVING PROPAGATION IN BENDING BEAMS UNDER IMPULSIVE LOAD
Institute of Scientific and Technical Information of China (English)
Fang Jing; Yao Xuefeng; Xiong Chunyang
2000-01-01
Dynamic fracture behaviour of crack curving in bent beams has been investigated.In order to understand the propagation mechanism of such cracks under impact,an experimental method is used that combines dynamic photoelasticity with dynamic caustics to study the interaction of the flexural waves and the crack.From the state change of the transient stresses in polymer specimen,the curving fracture in the impulsively loaded beams is analyzed.The dynamic responses of crack tips are evaluated by the stress intensity factors for the cracks running in varying curvature paths under bending stress wave.
Green frequency-doubled laser-beam propagation in high-temperature hohlraum plasmas.
Niemann, C; Berger, R L; Divol, L; Froula, D H; Jones, O; Kirkwood, R K; Meezan, N; Moody, J D; Ross, J; Sorce, C; Suter, L J; Glenzer, S H
2008-02-01
We demonstrate propagation and small backscatter losses of a frequency-doubled (2omega) laser beam interacting with inertial confinement fusion hohlraum plasmas. The electron temperature of 3.3 keV, approximately a factor of 2 higher than achieved in previous experiments with open geometry targets, approaches plasma conditions of high-fusion yield hohlraums. In this new temperature regime, we measure 2omega laser-beam transmission approaching 80% with simultaneous backscattering losses of less than 10%. These findings suggest that good laser coupling into fusion hohlraums using 2omega light is possible.
Hanson, Frank; Lasher, Mark
2010-06-01
We characterize and compare the effects of turbulence on underwater laser propagation with theory. Measurements of the coupling efficiency of the focused beam into a single-mode fiber are reported. A simple tip-tilt control system, based on the position of the image centroid in the focal plane, was shown to maintain good coupling efficiency for a beam radius equal to the transverse coherence length, r(0). These results are relevant to high bandwidth communication technology that requires good spatial mode quality.
Propagation of a beam halo in accelerator test facility 2 at KEK
Institute of Scientific and Technical Information of China (English)
BAI Sha; P.Bambade; GAO Jie
2013-01-01
The beam halo is a major issue for interaction region (IR) backgrounds at many colliders,for example,future linear colliders,B factories,and also it is an important problem at ATF2.In this paper,we report on the halo propagation along the ATF2 beam line with realistic apertures,the nonlinear optics influence on the increasing number of halo particles input is analyzed,and the transmitted halo particles distribution just before the last BPM is then described,the results from which will benefit the Compton recoil electrons measurement.
Propagation of flat-topped multi-Gaussian beams through a double-lens system with apertures.
Gao, Yanqi; Zhu, Baoqiang; Liu, Daizhong; Lin, Zunqi
2009-07-20
A general model for different apertures and flat-topped laser beams based on the multi-Gaussian function is developed. The general analytical expression for the propagation of a flat-topped beam through a general double-lens system with apertures is derived using the above model. Then, the propagation characteristics of the flat-topped beam through a spatial filter are investigated by using a simplified analytical expression. Based on the Fluence beam contrast and the Fill factor, the influences of a pinhole size on the propagation of the flat-topped multi-Gaussian beam (FMGB) through the spatial filter are illustrated. An analytical expression for the propagation of the FMGB through the spatial filter with a misaligned pinhole is presented, and the influences of the pinhole offset are evaluated.
Propagation of multi-Gaussian Schell-model vortex beams in isotropic random media.
Tang, Miaomiao; Zhao, Daomu
2015-12-14
The effect of isotropic and homogeneous random media on propagation characteristics of recently introduced multi-Gaussian Schell-model (MGSM) vortex beams is investigated. The analytical formula for the cross-spectral density function of such a beam propagating in random turbulent media is derived and used to explore the evolution of the spectral density, the degree of coherence and the turbulence-induced spreading. An example illustrates the fact that, at sufficiently large distance from the source, the source correlations modulation of the spectral distribution in free space is shown to be suppressed by the uniformly correlated turbulence. The impacts, arising from the index M, the correlation width of the source and the properties of the medium on such characteristics are analyzed in depth.
Network Non-neutrality Debate: An Economic Analysis
Altman, Eitan; Xu, Yuedong
2010-01-01
This paper studies the economic utilities and the quality of service (QoS) in a two-sided non-neutral market where Internet service providers (ISPs) charge content providers (CPs) for the content delivery. We propose new models on a two-sided market which involves a CP, an ISP, end users and advertisers. The CP may have either the subscription revenue model (charging end users) or the advertisement revenue model (charging advertisers). We formulate the interactions between the ISP and the CP as a noncooperative game problem for the former and an optimization problem for the latter. Our analysis shows that the revenue model of the CP plays a significant role in a non-neutral Internet. With the subscription model, both the ISP and the CP receive better (or worse) utilities as well as QoS in the presence of side payment at the same time. However, with the advertisement model, the side payment impedes the CP from investing on its contents.
Modeling and measurement of angle-beam wave propagation in a scatterer-free plate
Dawson, Alexander J.; Michaels, Jennifer E.; Michaels, Thomas E.
2017-02-01
Wavefield imaging has been shown to be a powerful tool for improving the understanding and characterization of wave propagation and scattering in plates. The complete measurement of surface displacement over a 2-D grid provided by wavefield imaging has the potential to serve as a useful means of validating ultrasonic models. Here, a preliminary study of ultrasonic angle-beam wave propagation in a scatterer-free plate using a combination of wavefield measurements and 2-D finite element models is described. Both wavefield imaging and finite element analysis are used to study the propagation of waves at a refracted angle of 56.8° propagating in a 6.35 mm thick aluminum plate. Wavefield imaging is performed using a laser vibrometer mounted on an XYZ scanning stage, which is programmed to move point-to-point on a rectilinear grid to acquire waveform data. The commercial finite element software package, PZFlex, which is specifically designed to handle large, complex ultrasonic problems, is used to create a 2-D cross-sectional model of the transducer and plate. For model validation, vertical surface displacements from both the wavefield measurements and the PZFlex finite element model are compared and found to be in excellent agreement. The validated PZFlex model is then used to explain the mechanism of Rayleigh wave generation by the angle-beam wedge. Since the wavefield measurements are restricted to the specimen surface, the cross-sectional PZFlex model is able to provide insights the wavefield data cannot. This study illustrates how information obtained from ultrasonic experiments and modeling results can be combined to improve understanding of angle-beam wave generation and propagation.
Role of Density Profiles for the Nonlinear Propagation of Intense Laser Beam through Plasma Channel
Sonu Sen; Meenu Asthana Varshney; Dinesh Varshney
2014-01-01
In this work role of density profiles for the nonlinear propagation of intense laser beam through plasma channel is analyzed. By employing the expression for the dielectric function of different density profile plasma, a differential equation for beamwidth parameter is derived under WKB and paraxial approximation. The laser induces modifications of the dielectric function through nonlinearities. It is found that density profiles play vital role in laser-plasma interaction studies. To have num...
The characteristics of an intense laser beam propagating in a corrugated plasma channel
Tian, Jian-Min; Tang, Rong-An; Hong, Xue-Ren; Yang, Yang; Wang, Li; Zhou, Wei-Jun; Xue, Ju-Kui
2016-12-01
The propagation of an intense laser beam in a corrugated plasma channel is investigated. By using the source-dependent expansion technique, an evolution equation of the laser spot size is derived. The behaviors including aperiodic oscillation, resonance, beat-like wave, and periodic oscillation with multipeak are found and analyzed. The formula for the instantaneous wave numbers of these oscillations is obtained. These theoretical findings are confirmed by the final numerical simulation.
Wang, Fei; Toselli, Italo; Korotkova, Olga
2016-02-10
An optical system consisting of a laser source and two independent consecutive phase-only spatial light modulators (SLMs) is shown to accurately simulate a generated random beam (first SLM) after interaction with a stationary random medium (second SLM). To illustrate the range of possibilities, a recently introduced class of random optical frames is examined on propagation in free space and several weak turbulent channels with Kolmogorov and non-Kolmogorov statistics.
Stimulated Raman Scattering and Nonlinear Focusing of High-Power Laser Beams Propagating in Water
Hafizi, B; Penano, J R; Gordon, D F; Jones, T G; Helle, M H; Kaganovich, D
2015-01-01
The physical processes associated with propagation of a high-power (power > critical power for self-focusing) laser beam in water include nonlinear focusing, stimulated Raman scattering (SRS), optical breakdown and plasma formation. The interplay between nonlinear focusing and SRS is analyzed for cases where a significant portion of the pump power is channeled into the Stokes wave. Propagation simulations and an analytical model demonstrate that the Stokes wave can re-focus the pump wave after the power in the latter falls below the critical power. It is shown that this novel focusing mechanism is distinct from cross-phase focusing. While discussed here in the context of propagation in water, the gain-focusing phenomenon is general to any medium supporting nonlinear focusing and stimulated forward Raman scattering.
(3+1)-dimensional nonlinear propagation equation for ultrashort pulsed beam in left-handed material
Institute of Scientific and Technical Information of China (English)
Hu Yong-Hua; Fu Xi-Quan; Wen Shuang-Chun; Su Wen-Hua; Fan Dian-Yuan
2006-01-01
In this paper a comprehensive framework for treating the nonlinear propagation of ultrashort pulse in metamaterial with dispersive dielectric susceptibility and magnetic permeability is presented. Under the slowly-evolving-wave approximation, a generalized (3+1)-dimensional wave equation first order in the propagation coordinate and suitable for both right-handed material (RHM) and left-handed material (LHM) is derived. By the commonly used Drude dispersive model for LHM, a (3+1)-dimensional nonlinear Schr(o)dinger equation describing ultrashort pulsed beam propagation in LHM is obtained, and its difference from that for conventional RHM is discussed. Particularly, the self-steeping effect of ultrashort pulse is found to be anomalous in LHM.
Institute of Scientific and Technical Information of China (English)
GUO; Hong
2001-01-01
［1］Sacks, R. A., The PROP 92 Fourier Beam Propagation Code, UCRL-LR-105821-96-4.［2］Williams, W. H., Modeling of Self-Focusing Experiments by Beam Propagation Codes, UCRL-LR-105821-96-1.［3］User guide for FRESNEL software.［4］Hunt, J. H., Renard, P. A., Simmons, W. W., Improved performance of fusion lasers using the imaging properties of multiple spatial filters, Appl. Opt., 1977, 16: 779.［5］Deng Ximing, Guo Hong, Cao Qing, Invariant integral and statistical equations for the paraxial beam propagation in free space, Science in China (in Chinese) Ser. A, 1997, 27(1): 64.［6］Goodman, J. W., Introduction to Fourier Optics, New York: McGraw-Hill, 1968.［7］Born, M., Wolf, E., Principles of Optics, New York: Pergamon Press, 1975.［8］Siegman, A. E., Lasers, New York: Mill Valley CA, 1986.［9］Fan Dianyuan, Fresnel number of complex system, Optica Sinica (in Chinese), 1983, 3(4): 319.［10］L
Xu, Yonggen; Li, Yude; Dan, Youquan; Du, Quan; Wang, Shijian
2016-07-01
The Wigner distribution function (WDF) has been used to study the propagation properties of partially coherent Laguerre Gaussian (PCLG) beams through atmospheric turbulence. Based on the extended Huygens-Fresnel principle, an analytical formula of the propagation matrixes in terms of the second-order moments of the WDF for PCLG Beams in the receiving plane is derived. And then the analytical formulae for the curvature radii of PCLG Beams propagating in turbulence are given by the second-order moments of the WDF. The numerical results indicate that the curvature radius of PCLG Beams changes more rapidly in turbulence than that in the free space. The influence of the transverse coherence width and the beam waist width on the curvature radius of PCLG Beams is obvious, while the laser wavelength and the inner scale of turbulence have a slight effect. The study results may be useful for remote sensing and free space optical communications.
Aksenov, V. P.; Dudorov, V. V.; Kolosov, V. V.
2016-08-01
Using a numerical simulation, we investigate the possibility of synthesising vortex laser beams with a variable orbital angular momentum by a hexagonal array of fibre lasers under a phase control of individual subapertures of the array. We report the requirements to the parameters of the device generating a vortex beam (number and size of subapertures, as well as their mutual arrangement). The propagation dynamics of synthesised vortex beams is compared with that of conventional Laguerre-Gaussian beams in free space and in a turbulent atmosphere. The spectral properties of the synthesised beam, represented as a superposition of different azimuthal modes, are determined during its propagation in free space. The energy and statistical parameters of the synthesised and Laguerre-Gaussian vortex beams are shown to coincide with increasing propagation distance in a turbulent medium.
Pulsed electron beam propagation in gases under pressure of 6.6 kPa in drift tube
Kholodnaya, G. E.; Sazonov, R. V.; Ponomarev, D. V.; Remnev, G. E.; Poloskov, A. V.
2017-02-01
This paper presents the results of an investigation of pulsed electron beam transport propagated in a drift tube filled with different gases (He, H2, N2, Ar, SF6, and CO2). The total pressure in the drift tube was 6.6 kPa. The experiments were carried out using a TEA-500 pulsed electron accelerator. The electron beam was propagated in the drift tube composed of two sections equipped with reverse current shunts. Under a pressure of 6.6 kPa, the maximum value of the electron beam charge closed on the walls of the drift tube was recorded when the beam was propagated in hydrogen and carbon dioxide. The minimum value of the electron beam charge closed on the walls of the drift tube was recorded for sulfur hexafluoride. The visualization of the pulsed electron beam energy losses onto the walls of the drift chamber was carried out using radiation-sensitive film.
Wang, Li; Hong, Xue-Ren; Sun, Jian-An; Tang, Rong-An; Yang, Yang; Zhou, Wei-Jun; Tian, Jian-Min; Duan, Wen-Shan
2017-07-01
The propagation of q-Gaussian laser beam in a preformed plasma channel is investigated by means of the variational method. A differential equation for the spot size has been obtained by including the effects of relativistic self-focusing, ponderomotive self-channeling and preformed channel focusing. The propagation behaviors and their corresponding physical conditions are identified. The comparison of the propagation between q-Gaussian and Gaussian laser beams is done by theoretical and numerical analysis. It is shown that, in the same channel, the focusing power of q-Gaussian laser beam is lower than that of Gaussian laser beam, i.e., the q-Gaussian laser beam is easier to focus than Gaussian laser beam.
Ion injection optimization for a linear Paul trap to study intense beam propagation
Directory of Open Access Journals (Sweden)
Moses Chung
2007-01-01
Full Text Available The Paul Trap Simulator Experiment (PTSX is a linear Paul trap whose purpose is to simulate the nonlinear transverse dynamics of intense charged particle beam propagation in periodic-focusing quadrupole magnetic transport systems. Externally created cesium ions are injected and trapped in the long central electrodes of the PTSX device. In order to have well-matched one-component plasma equilibria for various beam physics experiments, it is important to optimize the ion injection. From the experimental studies reported in this paper, it is found that the injection process can be optimized by minimizing the beam mismatch between the source and the focusing lattice, and by minimizing the number of particles present in the vicinity of the injection electrodes when the injection electrodes are switched from the fully oscillating voltage waveform to their static trapping voltage.
Propagation and interaction of cos-Gaussian beams in photorefractive crystals
Jiang, Qichang; Su, Yanli; Nie, Hexian; Ma, Ziwei; Li, Yonghong
2017-07-01
Investigate numerically the propagation and interaction of cos-Gaussian beams in a biased photorefractive crystal by the finite difference method. The results show that the single cos-Gaussian beam can evolve into Y-type breathing solitons when the self-focusing nonlinearity is small, and the soliton properties can be controlled by adjusting the nonlinear parameter or cos modulation parameter. The distance between two components of Y-type breathing solitons will decrease with increasing the nonlinear parameter or decreasing the cos modulation parameter. The breathing soliton with two weak sidebands can form when the self-focusing nonlinearity is big. Moreover, two internal components of two cos-Gaussian beams have obvious interaction but two outside components have tiny interaction.
Ideal laser-beam propagation through high-temperature ignition Hohlraum plasmas.
Froula, D H; Divol, L; Meezan, N B; Dixit, S; Moody, J D; Neumayer, P; Pollock, B B; Ross, J S; Glenzer, S H
2007-02-23
We demonstrate that a blue (3omega, 351 nm) laser beam with an intensity of 2 x 10(15) W cm(-2) propagates nearly within the original beam cone through a millimeter scale, T(e)=3.5 keV high density (n(e)=5 x 10(20) cm(-3)) plasma. The beam produced less than 1% total backscatter at these high temperatures and densities; the resulting transmission is greater than 90%. Scaling of the electron temperature in the plasma shows that the plasma becomes transparent for uniform electron temperatures above 3 keV. These results are consistent with linear theory thresholds for both filamentation and backscatter instabilities inferred from detailed hydrodynamic simulations. This provides a strong justification for current inertial confinement fusion designs to remain below these thresholds.
Quantification of optical turbulence in the ocean and its effects on beam propagation.
Nootz, Gero; Jarosz, Ewa; Dalgleish, Fraser R; Hou, Weilin
2016-11-01
The influence of optically active turbulence on the propagation of laser beams is investigated in clear ocean water over a path length of 8.75 m. The measurement apparatus is described and the effects of optical turbulence on the laser beam are presented. The index of refraction structure constant is extracted from the beam deflection and the results are compared to independently made measures of the turbulence strength (Cn2) by a vertical microstructure profiler. Here we present values of Cn2 taken from aboard the R/V Walton Smith during the Bahamas optical turbulence exercise (BOTEX) in the Tongue of the Ocean between June 30 and July 12, 2011, spanning a range from 10-14 to 10-10 m-2/3. To the best of our knowledge, this is the first time such measurements are reported for the ocean.
Relativistic nonlinearity and wave-guide propagation of rippled laser beam in plasma
Indian Academy of Sciences (India)
R K Khanna; K Baheti
2001-06-01
In the present paper we have investigated the self-focusing behaviour of radially symmetrical rippled Gaussian laser beam propagating in a plasma. Considering the nonlinearity to arise from relativistic phenomena and following the approach of Akhmanov et al, which is based on the WKB and paraxial-ray approximation, the self-focusing behaviour has been investigated in some detail. The effect of the position and width of the ripple on the self-focusing of laser beam has been studied for arbitrary large magnitude of nonlinearity. Results indicate that the medium behaves as an oscillatory wave-guide. The self-focusing is found to depend on the position parameter of ripple as well as on the beam width. Values of critical power has been calculated for different values of the position parameter of ripple. Effects of axially and radially inhomogeneous plasma on self-focusing behaviour have been investigated and presented here.
Propagation of Gaussian Schell-model Array beams in free space and atmospheric turbulence
Mao, Yonghua; Mei, Zhangrong; Gu, Juguan
2016-12-01
Based on the extended Huygens-Fresnel principle, the evolution behavior of the spectral density and the spectral degree of coherence of the beam produced by a recently introduced novel class of Gaussian Schell-model Arrays (GSMA) source in free space and turbulence atmospheric are explored and comparatively analyzed. And the influence of the fractal constant of the atmospheric power spectrum and refractive-index structure constant on the spectral density and the spectral degree of coherence of beams are analyzed. It is shown that the optical lattice profile is stable when beams propagate in free space, but the spectral density eventually is suppressed and transformed into a Gaussian profiles when it passes at sufficiently large distances through the turbulent atmosphere. The distributions of the spectral degree of coherence in far field eventually transformed into a shrink Gaussian profile relative to free space which means that the degree of spatial coherence turns worse.
Propagation of a Pearcey-Gaussian-vortex beam in free space and Kerr media
Peng, Yulian; Chen, Chidao; Chen, Bo; Peng, Xi; Zhou, Meiling; Zhang, Liping; Li, Dongdong; Deng, Dongmei
2016-12-01
The propagation of a Pearcey-Gaussian-vortex beam (PGVB) has been investigated numerically in free space and Kerr media. In addition, we have done a numerical experiment for the beam in free space. A PGVB maintains the characteristics of auto-focusing, self-healing and form-invariance which are possessed by a Pearcey beam and a Pearcey-Gaussian beam. Due to the influence of the optical vortex, a bright speck occurs in front of the main lobe. Compared with a Pearcey beam and a Pearcey-Gaussian beam, a PGVB has the most remarkable intensity singularity and the phase singularity. It is worth noting that the impact of the vortex at the coordinate origins means that a PGVB in the vicinity carries no angular momentum or transverse energy flow. We have investigated and numerically simulated the transverse intensity of a PGVB in Kerr media. We find that the auto-focusing of a PGVB in a Kerr medium becomes stronger with increasing power.
Mitri, F. G.
2016-08-01
In this work, counterintuitive effects such as the generation of an axial (i.e., long the direction of wave motion) zero-energy flux density (i.e., axial Poynting singularity) and reverse (i.e., negative) propagation of nonparaxial quasi-Gaussian electromagnetic (EM) beams are examined. Generalized analytical expressions for the EM field's components of a coherent superposition of two high-order quasi-Gaussian vortex beams of opposite handedness and different amplitudes are derived based on the complex-source-point method, stemming from Maxwell's vector equations and the Lorenz gauge condition. The general solutions exhibiting unusual effects satisfy the Helmholtz and Maxwell's equations. The EM beam components are characterized by nonzero integer degree and order (n ,m ) , respectively, an arbitrary waist w0, a diffraction convergence length known as the Rayleigh range zR, and a weighting (real) factor 0 ≤α ≤1 that describes the transition of the beam from a purely vortex (α =0 ) to a nonvortex (α =1 ) type. An attractive feature for this superposition is the description of strongly focused (or strongly divergent) wave fields. Computations of the EM power density as well as the linear and angular momentum density fluxes illustrate the analysis with particular emphasis on the polarization states of the vector potentials forming the beams and the weight of the coherent beam superposition causing the transition from the vortex to the nonvortex type. Should some conditions determined by the polarization state of the vector potentials and the beam parameters be met, an axial zero-energy flux density is predicted in addition to a negative retrograde propagation effect. Moreover, rotation reversal of the angular momentum flux density with respect to the beam handedness is anticipated, suggesting the possible generation of negative (left-handed) torques. The results are particularly useful in applications involving the design of strongly focused optical laser
Generation and propagation of high-brightness electron beams from a magnetically crowbarred injector
Humphries, S., Jr.; Len, L. K.; Allen, C. B.
1987-05-01
Tests of a 300-keV electrostatic electron beam injector with a magnetic crowbar switch are described. The saturable ferrite core switch allows generation of a constant voltage, 80-ns pulse directly from a Marx generator. Inductive isolation in the switch permits direct access to the high-voltage electrode for thermionic or active plasma cathode experiments. The pulse modulator can drive a 1.5-kA load. A high brightness 290-A beam from a felt plasma-emission cathode was extracted and propagated in vacuum. Because of the reliability of the magnetic crowbar switch, more than 500 shots were accumulated on the cathode at over 1 kA/sq cm with no degradation of the output. The output beam had a normalized brightness of 2.6 x 10 to the 8th A/(m rad) sq. A solenoidal lens was used to match the space-charge-dominated beam into a 1-m-long periodic focusing system with 25 reversing solenoidal coils. A beam current of 150 A was successfully transported through the 1.7-cm radius tube.
Dios, Federico; Recolons, Jaume; Rodríguez, Alejandro; Batet, Oscar
2008-02-04
Temporal analysis of the irradiance at the detector plane is intended as the first step in the study of the mean fade time in a free optical communication system. In the present work this analysis has been performed for a Gaussian laser beam propagating in the atmospheric turbulence by means of computer simulation. To this end, we have adapted a previously known numerical method to the generation of long phase screens. The screens are displaced in a transverse direction as the wave is propagated, in order to simulate the wind effect. The amplitude of the temporal covariance and its power spectrum have been obtained at the optical axis, at the beam centroid and at a certain distance from these two points. Results have been worked out for weak, moderate and strong turbulence regimes and when possible they have been compared with theoretical models. These results show a significant contribution of beam wander to the temporal behaviour of the irradiance, even in the case of weak turbulence. We have also found that the spectral bandwidth of the covariance is hardly dependent on the Rytov variance.
Ebrahimi, Farzad; Reza Barati, Mohammad; Haghi, Parisa
2016-11-01
In this paper, the thermo-elastic wave propagation analysis of a temperature-dependent functionally graded (FG) nanobeam supported by Winkler-Pasternak elastic foundation is studied using nonlocal elasticity theory. The nanobeam is modeled via a higher-order shear deformable refined beam theory which has a trigonometric shear stress function. The temperature field has a nonlinear distribution called heat conduction across the nanobeam thickness. Temperature-dependent material properties change gradually in the spatial coordinate according to the Mori-Tanaka model. The governing equations of the wave propagation of the refined FG nanobeam are derived by using Hamilton's principle. The analytic dispersion relation of the embedded nonlocal functionally graded nanobeam is obtained by solving an eigenvalue problem. Numerical examples show that the wave characteristics of the functionally graded nanobeam are related to the temperature distribution, elastic foundation parameters, nonlocality and material composition.
Three-dimensional beam propagation method based on the variable transformed Galerkin's method
Institute of Scientific and Technical Information of China (English)
XIAO Jinbiao; SUN Xiaohan; ZHANG Mingde
2004-01-01
A novel three-dimensional beam propagation method (BPM) based on the variable transformed Galerkin's method is introduced for simulating optical field propagation in three-dimensional dielectric structures. The infinite Cartesian x-y plane is mapped into a unit square by a tangent-type function transformation. Consequently, the infinite region problem is converted into the finite region problem. Thus, the boundary truncation is eliminated and the calculation accuracy is promoted. The three-dimensional BPM basic equation is reduced to a set of first-order ordinary differential equations through sinusoidal basis function, which fits arbitrary cladding optical waveguide, then direct solution of the resulting equations by means of the Runge-Kutta method. In addition,the calculation is efficient due to the small matrix derived from the present technique.Both z-invariant and z-variant examples are considered to test both the accuracy and utility of this approach.
Institute of Scientific and Technical Information of China (English)
Tang Qian-Jin; Chen Da-Ming; Yu Yong-Ai; Hu Qi-Quan
2006-01-01
Based on the Collins integral formula, the analytic expressions of propagation of the coherent and the incoherent off-axis Hermite-cosh-Gaussian (HChG) beam combinations with rectangular symmetry passing through a paraxial first-order optical system are derived, and corresponding numerical examples are given and analysed. The resulting beam quality is discussed in terms of power in the bucket (PIB). The study suggests that the resulting beam cannot keep the initial intensity shape during the propagation and the beam quality for coherent mode is not always better than that for incoherent mode. Reviewing the numerical simulations of Gaussian, Hermite-Gaussian (HG) and cosh-Gaussian (ChG) beam combinations indicates that the Hermite polynomial exerts a chief influence on the irradiance profile of composite beam and far field power concentration.
Effects of propagation conditions on radar beam-ground interaction: impact on data quality
Directory of Open Access Journals (Sweden)
A. Fornasiero
2005-01-01
Full Text Available A large part of the research in the radar meteorology is devoted to the evaluation of the radar data quality and to the radar data processing. Even when, a set of absolute quality indexes can be produced (like as ground clutter presence, beam blockage rate, distance from radar, etc., the final product quality has to be determined as a function of the task and of all the processing steps. In this paper the emphasis lies on the estimate of the rainfall at the ground level taking extra care for the correction for ground clutter and beam blockage, that are two main problems affecting radar reflectivity data in complex orography. In this work a combined algorithm is presented that avoids and/or corrects for these two effects. To achieve this existing methods are modified and integrated with the analysis of radar signal propagation in different atmospheric conditions. The atmospheric refractivity profile is retrieved from the nearest in space and time radiosounding. This measured profile is then used to define the `dynamic map' used as a declutter base-field. Then beam blockage correction is applied to the data at the scan elevations computed from this map. Two case studies are used to illustrate the proposed algorithm. One is a summer event with anomalous propagation conditions and the other one is a winter event. The new algorithm is compared to a previous method of clutter removal based only on static maps of clear air and vertical reflectivity continuity test. The improvement in rain estimate is evaluated applying statistical analysis and using rain gauges data. The better scores are related mostly to the ``optimum" choice of the elevation maps, introduced by the more accurate description of the signal propagation. Finally, a data quality indicator is introduced as an output of this scheme. This indicator has been obtained from the general scheme, which takes into account all radar data processing steps.
Differential Geometry applied to Acoustics : Non Linear Propagation in Reissner Beams
Bensoam, Joël
2013-01-01
Although acoustics is one of the disciplines of mechanics, its "geometrization" is still limited to a few areas. As shown in the work on nonlinear propagation in Reissner beams, it seems that an interpretation of the theories of acoustics through the concepts of differential geometry can help to address the non-linear phenomena in their intrinsic qualities. This results in a field of research aimed at establishing and solving dynamic models purged of any artificial nonlinearity by taking advantage of symmetry properties underlying the use of Lie groups. The geometric constructions needed for reduction are presented in the context of the "covariant" approach.
Wave propagation in fractal-inspired self-similar beam lattices
Energy Technology Data Exchange (ETDEWEB)
Lim, Qi Jian [Engineering Science Programme, National University of Singapore, Singapore 117576 (Singapore); Wang, Pai [Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States); Koh, Soo Jin Adrian [Engineering Science Programme, National University of Singapore, Singapore 117576 (Singapore); Department of Mechanical Engineering, National University of Singapore, Singapore 117576 (Singapore); Khoo, Eng Huat [Engineering Science Programme, National University of Singapore, Singapore 117576 (Singapore); A*STAR Institute of High Performance Computing, Singapore 138632 (Singapore); Bertoldi, Katia [Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States); Kavli Institute, Harvard University, Cambridge, Massachusetts 02138 (United States)
2015-11-30
We combine numerical analysis and experiments to investigate the effect of hierarchy on the propagation of elastic waves in triangular beam lattices. While the response of the triangular lattice is characterized by a locally resonant band gap, both Bragg-type and locally resonant gaps are found for the hierarchical lattice. Therefore, our results demonstrate that structural hierarchy can be exploited to introduce an additional type of band gaps, providing a robust strategy for the design of lattice-based metamaterials with hybrid band gap properties (i.e., possessing band gaps that arises from both Bragg scattering and localized resonance)
Institute of Scientific and Technical Information of China (English)
LIU Shi-Bing; CHEN Tao; CHEN Shi-Gang
2004-01-01
An essential dispersion relation,which can describe the dynamic properties of stimulated Raman scattering instability as a laser beam propagates through plasmas,is derived analytically.The development of growth mode,angle distribution,and temperature dependence of the instabilities are presented by solving this dispersion relation numerically.A significant dynamic characteristic has been revealed that the temperature increasing of the electron would result in redshift of scattered spectrum at high laser intensities.Furthermore,a novel modulational instability with double-peak temporal structure appears in a limited density region because of the coupling of scattered upshift and downshift waves.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The fundamental algorithm of light beam propagation in high powerlaser system is investigated and the corresponding computational codes are given. It is shown that the number of modulation ring due to the diffraction is related to the size of the pinhole in spatial filter (in terms of the times of diffraction limitation, i.e. TDL) and the Fresnel number of the laser system; for the complex laser system with multi-spatial filters and free space, the system can be investigated by the reciprocal rule of operators.
Beam filter and splitter based on surface plasmon propagation in ring metal heterowaveguide
Indian Academy of Sciences (India)
Gaige Zheng; Linhua Xu; Yunyun Chen; Wei Su; Yuzhu Liu
2014-12-01
Surface plasmon polaritons (SPPs) beam filter (BF) and beam splitter (BS) constructed using metal heterostructures are proposed and demonstrated numerically. Both structures have a ring metal heterowaveguide, which is constructed by a metal cylinder and a ring dielectric cladding. The two-dimensional finite-difference time-domain (2D-FDTD) method is employed to study the properties of the proposed BF and BS, and the results show that SPPs can effectively propagate on bended plasmonic waveguides with dielectric claddings. By introducing dielectric and plasmonic waveguides on both sides of the resonant ring, SPPs can be efficiently excited at the output of the waveguide ring resonator (WRR) through mode coupling. The planar metal heterostructures provide a way for constructing various nanoscale counterparts of conventional planar integrated devices such as filters, splitters, resonators, sensors, optical switches, and so on.
The propagation and growth of whistler mode waves generated by electron beams in earth's bow shock
Tokar, R. L.; Gurnett, D. A.
1985-01-01
In this study, the propagation and growth of whistler mode waves generated by electron beams within earth's bow shock is investigated using a planar model for the bow shock and a model electron distribution function. Within the shock, the model electron distribution function possesses a field-aligned T greater than T beam that is directed toward the magnetosheath. Waves with frequencies between about 1 and 100 Hz with a wide range of wave normal angles are generated by the beam via Landau and anomalous cyclotron resonances. However, because the growth rate is small and because the wave packets traverse the shock quickly, these waves do not attain large amplitudes. Waves with frequencies between about 30 and 150 Hz with a wide range of wave normal angles are generated by the beam via the normal cyclotron resonance. The ray paths for most of these waves are directed toward the solar wind although some wave packets, due to plasma convection travel transverse to the shock normal. These wave packets grow to large amplitudes because they spend a long time in the growth region. The results suggest that whistler mode noise within the shock should increase in amplitude with increasing upstream theta sub Bn. The study provides an explanation for the origin of much of the whistler mode turbulence observed at the bow shock.
Energy Technology Data Exchange (ETDEWEB)
Wang, Li; Hong, Xue-Ren, E-mail: hxr_nwnu@163.com; Sun, Jian-An, E-mail: sunja@nwnu.edu.cn; Tang, Rong-An; Yang, Yang; Zhou, Wei-Jun; Tian, Jian-Min; Duan, Wen-Shan
2017-07-12
The propagation of q-Gaussian laser beam in a preformed plasma channel is investigated by means of the variational method. A differential equation for the spot size has been obtained by including the effects of relativistic self-focusing, ponderomotive self-channeling and preformed channel focusing. The propagation behaviors and their corresponding physical conditions are identified. The comparison of the propagation between q-Gaussian and Gaussian laser beams is done by theoretical and numerical analysis. It is shown that, in the same channel, the focusing power of q-Gaussian laser beam is lower than that of Gaussian laser beam, i.e., the q-Gaussian laser beam is easier to focus than Gaussian laser beam. - Highlights: • Some behaviors for Gaussian laser are also found for q-Gaussian one. • The parameter regions corresponding to different laser behaviors are given. • Influence of q on the laser propagation behavior is obvious. • The q-Gaussian laser beam is easier to focus than the Gaussian one.
Propagation of a laser-driven relativistic electron beam inside a solid dielectric.
Sarkisov, G S; Ivanov, V V; Leblanc, P; Sentoku, Y; Yates, K; Wiewior, P; Chalyy, O; Astanovitskiy, A; Bychenkov, V Yu; Jobe, D; Spielman, R B
2012-09-01
Laser probe diagnostics: shadowgraphy, interferometry, and polarimetry were used for a comprehensive characterization of ionization wave dynamics inside a glass target induced by a laser-driven, relativistic electron beam. Experiments were done using the 50-TW Leopard laser at the University of Nevada, Reno. We show that for a laser flux of ∼2 × 10(18) W/cm2 a hemispherical ionization wave propagates at c/3 for 10 ps and has a smooth electron-density distribution. The maximum free-electron density inside the glass target is ∼2 × 10(19) cm-3, which corresponds to an ionization level of ∼0.1%. Magnetic fields and electric fields do not exceed ∼15 kG and ∼1 MV/cm, respectively. The electron temperature has a hot, ringlike structure with a maximum of ∼0.7 eV. The topology of the interference phase shift shows the signature of the "fountain effect", a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields driven by laser. The very low ionization observed after the laser heating pulse suggests a fast recombination on the sub-ps time scale.
Directory of Open Access Journals (Sweden)
K. Sauer
2010-06-01
Full Text Available Isotropic electron beams are considered to explain the excitation of whistler waves which have been observed by the STEREO satellite in the Earth's radiation belt. Aside from their large amplitudes (~240 mV/m, another main signature is the strongly inclined propagation direction relative to the ambient magnetic field. Electron temperature anisotropy with T_{e⊥}>T_{e||}, which preferentially generates parallel propagating whistler waves, can be excluded as a free energy source. The instability arises due to the interaction of the Doppler-shifted cyclotron mode ω=−Ω_{e}+kV_{b}cosθ with the whistler mode in the wave number range of kc/ω_{e}≤1 (θ is the propagation angle with respect to the background magnetic field direction, ω_{e} is the electron plasma frequency and Ω_{e} the electron cyclotron frequency. Fluid and kinetic dispersion analysis have been used to calculate the growth rate of the beam-excited whistlers including the most important parameter dependencies. One is the beam velocity (V_{b} which, for instability, has to be larger than about 2V_{Ae}, where V_{Ae} is the electron Alfvén speed. With increasing V_{Ae} the propagation angle (θ of the fastest growing whistler waves shifts from θ~20° for V_{b}=2V_{Ae} to θ~80° for V_{b}=5V_{Ae}. The growth rate is reduced by finite electron temperatures and disappears if the electron plasma beta (β_{e} exceeds β_{e}~0.2. In addition, Gendrin modes (kc/ω_{e}≈1 are analyzed to determine the conditions under which stationary nonlinear waves (whistler oscillitons can exist. The corresponding spatial wave profiles are calculated using the full nonlinear fluid approach. The results are compared with the STEREO satellite observations.
Sjöqvist, Lars; Henriksson, Markus; Steinvall, Ove
2005-11-01
Understanding and predicting laser beam propagation effects in the atmosphere is of importance for laser countermeasures and related applications. Turbulence effects cause beam wander, beam broadening and intensity scintillations reducing e.g. the power in bucket and the tracking accuracy. Modelling laser beam propagation in turbulence using successive phase screens provides an efficient tool for performance predictions. In this work phase screens are used to model laser beam propagation over land and sea. Different phase screens generators utilising the Kolmogorov or von Karman spectra were considered. Critical parameters using phase screens include the number of screen applied along the propagation path, inner- and outer scale size, variations in the structure parameter and spatial frequencies. Effects such as beam wander, angle-of-arrival fluctuations and intensity scintillations are discussed. The simulated results are compared with experimental data recorded at different ranges, various turbulence strengths and for single- and double paths. A generic example describing laser countermeasure against an infrared homing missile in a naval scenario is presented.
Beam propagation and stray radiation in the ITER EC H&CD Upper Launcher
Directory of Open Access Journals (Sweden)
Platania Paola
2015-01-01
Hydrodynamic instabilities with the deposition of Electron Cyclotron power. According to the present design, each launcher comprises two rows of four input waveguides, whose output beam is focused and driven towards the plasma by four sets of mirrors. In order to study the beam-launcher interaction throughout quasi-optical propagation, with particular attention to straylight behaviour, and to verify analytical calculations, a 3D model of the UL optical system has been implemented with the electromagnetic code GRASP® and the Physical Optics method. Detailed description of the components are introduced: pure hybrid mode HE11 from cylindrical waveguide as input beams, real shapes of the mirror contours, semi-analytical description of the ellipsoidal surfaces of focussing mirrors. A conceptual calculation scheme has been developed in order to take into account not only the direct contribution of the single source on its next scatterer but also the first order indirect effects: crosstalk from different lines of the same row and crosstalk from different rows have been evaluated after reflection on the first and third set of mirrors. The evaluations presented have been performed on the preliminary UL design, the last major milestone before finalization; however, the numerical model is suitable to be applied to future evolutions of the setup and/or other configurations.
Heavy ion beam propagation through a gas-filled chamber for inertial confinement fusion
Energy Technology Data Exchange (ETDEWEB)
Barboza, Nigel Oswald [Univ. of California, Berkeley, CA (United States)
1996-10-01
The work presented here evaluates the dynamics of a beam of heavy ions propagating through a chamber filled with gas. The motivation for this research stems from the possibility of using heavy ion beams as a driver in inertial confinement fusion reactors for the purpose of generating electricity. Such a study is important in determining the constraints on the beam which limit its focus to the small radius necessary for the ignition of thermonuclear microexplosions which are the source of fusion energy. Nuclear fusion is the process of combining light nuclei to form heavier ones. One possible fusion reaction combines two isotopes of hydrogen, deuterium and tritium, to form an alpha particle and a neutron, with an accompanying release of ~17.6 MeV of energy. Generating electricity from fusion requires that we create such reactions in an efficient and controlled fashion, and harness the resulting energy. In the inertial confinement fusion (ICF) approach to energy production, a small spherical target, a few millimeters in radius, of deuterium and tritium fuel is compressed so that the density and temperature of the fuel are high enough, ~200 g/cm^{3} and ~20 keV, that a substantial number of fusion reactions occur; the pellet microexplosion typically releases ~350 MJ of energy in optimized power plant scenarios.
Heavy ion beam propagation through a gas-filled chamber for inertial confinement fusion
Energy Technology Data Exchange (ETDEWEB)
Barboza, N.O.
1996-10-01
The work presented here evaluates the dynamics of a beam of heavy ions propagating through a chamber filled with gas. The motivation for this research stems from the possibility of using heavy ion beams as a driver in inertial confinement fusion reactors for the purpose of generating electricity. Such a study is important in determining the constraints on the beam which limit its focus to the small radius necessary for the ignition of thermonuclear microexplosions which are the source of fusion energy. Nuclear fusion is the process of combining light nuclei to form heavier ones. One possible fusion reaction combines two isotopes of hydrogen, deuterium and tritium, to form an alpha particle and a neutron, with an accompanying release of {approximately}17.6 MeV of energy. Generating electricity from fusion requires that we create such reactions in an efficient and controlled fashion, and harness the resulting energy. In the inertial confinement fusion (ICF) approach to energy production, a small spherical target, a few millimeters in radius, of deuterium and tritium fuel is compressed so that the density and temperature of the fuel are high enough, {approximately}200 g/cm{sup 3} and {approximately}20 keV, that a substantial number of fusion reactions occur; the pellet microexplosion typically releases {approximately}350 MJ of energy in optimized power plant scenarios.
Li, Fengming; Zhang, Chuanzeng; Liu, Chunchuan
2017-04-01
A novel strategy is proposed to actively tune the vibration and wave propagation properties in elastic beams. By periodically placing the piezoelectric actuator/sensor pairs along the beam axis, an active periodic beam structure which exhibits special vibration and wave propagation properties such as the frequency pass-bands and stop-bands (or band-gaps) is developed. Hamilton's principle is applied to establish the equations of motion of the sub-beam elements i.e. the unit-cells, bonded by the piezoelectric patches. A negative proportional feedback control strategy is employed to design the controllers which can provide a positive active stiffness to the beam for a positive feedback control gain, which can increase the stability of the structural system. By means of the added positive active stiffness, the periodicity or the band-gap property of the beam with periodically placed piezoelectric patches can be actively tuned. From the investigation, it is shown that better band-gap characteristics can be achieved by using the negative proportional feedback control. The band-gaps can be obviously broadened by properly increasing the control gain, and they can also be greatly enlarged by appropriately designing the structural sizes of the controllers. The control voltages applied on the piezoelectric actuators are in reasonable and controllable ranges, especially, they are very low in the band-gaps. Thus, the vibration and wave propagation behaviors of the elastic beam can be actively controlled by the periodically placed piezoelectric patches.
Yang, Yang; Zhang, Lixiang; Lim, C. W.
2011-04-01
This paper is concerned with the characteristics of wave propagation in double-walled carbon nanotubes (DWCNTs). The DWCNTs is simulated with a Timoshenko beam model based on the nonlocal continuum elasticity theory, referred to as an analytically nonlocal Timoshenko-beam (ANT) model. The governing equations of the DWCNTs beam consist of a set of four equations that are derived from the variational principle of the beam with high-order boundary conditions at the both ends, in which the effects of the nano-scale nonlocality and the van der Waals interaction between inner and outer tubes are inclusive. The characteristics of the wave propagation in the DWCNTs beam were analyzed with the new ANT model proposed and the comparisons with the partially nonlocal Timoshenko-beam (PNT) models in publication were made in details. The results show that the nonlocal effects of the ANT model proposed in the present study on the wave propagations are more significant because it is in stronger stiffness enhancement to the DWCNTs beam.
Zhao, Chenglong; LeBrun, Thomas W.
2015-08-01
Gold nanoparticles (GNP) have wide applications ranging from nanoscale heating to cancer therapy and biological sensing. Optical trapping of GNPs as small as 18 nm has been successfully achieved with laser power as high as 855 mW, but such high powers can damage trapped particles (particularly biological systems) as well heat the fluid, thereby destabilizing the trap. In this article, we show that counter propagating beams (CPB) can successfully trap GNP with laser powers reduced by a factor of 50 compared to that with a single beam. The trapping position of a GNP inside a counter-propagating trap can be easily modulated by either changing the relative power or position of the two beams. Furthermore, we find that under our conditions while a single-beam most stably traps a single particle, the counter-propagating beam can more easily trap multiple particles. This (CPB) trap is compatible with the feedback control system we recently demonstrated to increase the trapping lifetimes of nanoparticles by more than an order of magnitude. Thus, we believe that the future development of advanced trapping techniques combining counter-propagating traps together with control systems should significantly extend the capabilities of optical manipulation of nanoparticles for prototyping and testing 3D nanodevices and bio-sensing.
Cai, Yangjian; Zhu, Shijun
2014-04-01
We derive the general expression for the orbital angular momentum (OAM) flux of an astigmatic partially coherent beam carrying twist phase [i.e., twisted anisotropic Gaussian-Schell model (TAGSM) beam] propagating through an astigmatic ABCD optical system with loss or gain. The evolution properties of the OAM flux of a TAGSM beam in a Gaussian cavity or propagating through a cylindrical thin lens are illustrated numerically with the help of the derived formula. It is found that we can modulate the OAM of a partially coherent beam by varying the parameters of the cavity or the orientation angle of the cylindrical thin lens, which will be useful in some applications, such as free-space optical communications and particle trapping.
Li, Peng; Zhang, Yi; Liu, Sheng; Cheng, Huachao; Han, Lei; Wu, Dongjing; Zhao, Jianlin
2017-03-06
We propose a generalized model for the creation of vector Bessel-Gauss (BG) beams having state of polarization (SoP) varying along the propagation direction. By engineering longitudinally varying Pancharatnam-Berry (PB) phases of two constituent components with orthogonal polarizations, we create zeroth- and higher-order vector BG beams having (i) uniform polarizations in the transverse plane that change along z following either the equator or meridian of the Poincaré sphere and (ii) inhomogeneous polarizations in the transverse plane that rotate during propagation along z. Moreover, we evaluate the self-healing capability of these vector BG beams after two disparate obstacles. The self-healing capability of spatial SoP information may enrich the application of BG beams in light-matter interaction, polarization metrology and microscopy.
Multi-beam laser beacon propagation over lunar distance: comparison of predictions and measurements
Biswas, A.; Piazzolla, S.
2017-02-01
A multi-beam beacon was transmitted from the Optical Communication Telescope Laboratory (OCTL) located at Table Mountain, CA to the Lunar Laser Space Terminal (LLST), on-board the Lunar Atmospheric Dust and Environment Explorer (LADEE) spacecraft, during NASA's recent Lunar Laser Communication Demonstration (LLCD). The laser beacon (1568+/-0.1 nm) was square wave modulated and sensed by a quadrant sensor on LLST. While link acquisition and tracking proceeded with the sensed signal, on-board processing extracted power incident on the quadrant sensor and telemetered it down over the optical downlink. Subsequently, post-processing of the codewords received at OCTL retrieved the power time series recorded at LLST. Analysis comparing measured and predicted mean irradiance delivered to LLST consistently agreed to within < 1 decibel (dB). Irradiance fluctuations detected at LLST were reconciled with an uplink wave-propagation simulation model using Kolmogorov phase screens.
Effects of laser beam propagation and saturation on the spatial shape of sodium laser guide stars.
Marc, Fabien; Guillet de Chatellus, Hugues; Pique, Jean-Paul
2009-03-30
The possibility to produce diffraction-limited images by large telescopes through Adaptive Optics is closely linked to the precision of measurement of the position of the guide star on the wavefront sensor. In the case of laser guide stars, many parameters can lead to a strong distortion on the shape of the LGS spot. Here we study the influence of both the saturation of the sodium layer excited by different types of lasers, the spatial quality of the laser mode at the ground and the influence of the atmospheric turbulence on the upward propagation of the laser beam. Both shape and intensity of the LGS spot are found to depend strongly on these three effects with important consequences on the precision on the wavefront analysis.
Institute of Scientific and Technical Information of China (English)
Xueqiong; Chen; Xiaoyan; Li; Ziyang; Chen; Jixiong; Pu; Guowen; Zhang; Jianqiang; Zhu
2013-01-01
The intensity distributions of a high-power broadband laser beam passing through a nonlinear optical medium with defects and then propagating in free space are investigated based on the general nonlinear Schr¨odinger equation and the split-step Fourier numerical method. The influences of the bandwidth of the laser beam, the thickness of the medium,and the defects on the light intensity distribution are revealed. We find that the nonlinear optical effect can be suppressed and that the uniformity of the beam can be improved for a high-power broadband laser beam with appropriate wide bandwidth. It is also found that, under the same incident light intensity, a thicker medium will lead to a stronger self-focusing intensity, and that the influence of defects in the optical elements on the intensity is stronger for a narrowband beam than for a broadband beam.
Institute of Scientific and Technical Information of China (English)
Chen Bao-Xin
2006-01-01
An elliptical Gaussian wave formalism model of a charged-particle beam is proposed by analogy with an elliptical Gaussian light beam.In the paraxial approximation.the charged-particle beam can be described as a whole by a complex radius of curvature in the real space domains.Therefore,the propagation and transform of charged-particle beam passing through a first-order optical system is represented by the ABCD-like law.As an example of the application of this model,the relation between the beam waist and the minimum beam spot at a fixed target is discussed.The result.well matches that from conventional phase space model,and proves that the Gaussian wave formalism model is highly effective and reasonable.
Excitation of monochromatic and stable electron acoustic wave by two counter-propagating laser beams
Xiao, C. Z.; Liu, Z. J.; Zheng, C. Y.; He, X. T.
2017-07-01
The undamped electron acoustic wave is a newly-observed nonlinear electrostatic plasma wave and has potential applications in ion acceleration, laser amplification and diagnostics due to its unique frequency range. We propose to make the first attempt to excite a monochromatic and stable electron acoustic wave (EAW) by two counter-propagating laser beams. The matching conditions relevant to laser frequencies, plasma density, and electron thermal velocity are derived and the harmonic effects of the EAW are excluded. Single-beam instabilities, including stimulated Raman scattering and stimulated Brillouin scattering, on the excitation process are quantified by an interaction quantity, η =γ {τ }B, where γ is the growth rate of each instability and {τ }B is the characteristic time of the undamped EAW. The smaller the interaction quantity, the more successfully the monochromatic and stable EAW can be excited. Using one-dimensional Vlasov-Maxwell simulations, we excite EAW wave trains which are amplitude tunable, have a duration of thousands of laser periods, and are monochromatic and stable, by carefully controlling the parameters under the above conditions.
Mitri, F G
2016-09-01
Energy and angular momentum flux density characteristics of an optical nondiffracting nonparaxial vector Bessel vortex beam of fractional order are examined based on the dual-field method for the generation of symmetric electric and magnetic fields. Should some conditions determined by the polarization state, the half-cone angle as well as the beam-order (or topological charge) be met, the axial energy and angular momentum flux densities vanish (representing Poynting singularities), before they become negative. These negative counterintuitive properties suggest retrograde (negative) propagation as well as a rotation reversal of the angular momentum with respect to the beam handedness. These characteristics of nondiffracting nonparaxial Bessel fractional vortex beams of progressive waves open new capabilities in optical tractor beam tweezers, optical spanners, invisibility cloaks, optically engineered metamaterials, and other applications.
Sokolenko, Bogdan; Kudryavtseva, Maria; Zinovyev, Alexey; Konovalenko, Victor; Rubass, Alex
2012-01-01
We have experimentally analyzed the topological reactions occurred in the elliptic vortex-beam transmitting orthogonally to the optical axis of the SiO2 crystal. We have revealed that the oscillations of the polarization state when propagating the beam are accompanied by reconstruction of the polarization singularities at the beam cross-section that, in turn, entails the reconstruction of the wavefront in each circularly polarized beam component. Both synchronic oscillations of the spin angular momentum and the sign of the vortex topological charge are expressing in a field structure as birth and annihilation of topological dipoles. Also periodical conversion of the vortex ellipticity along the crystal length z and huge splash of spin angular momentum were analysed. The run of the dislocation reactions in the beam component results in converting the sign of the topological charge in the centered optical vortex, the distance of the vortex conversion being about 0.05 of the wavelength.
Energy Technology Data Exchange (ETDEWEB)
Purohit, Gunjan, E-mail: gunjan75@gmail.com; Rawat, Priyanka [Department of Physics, Laser-Plasma Computational Laboratory, DAV PG College, Dehradun, Uttarakhand (India); Chauhan, Prashant [Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Uttar Pradesh (India); Mahmoud, Saleh T. [Department of Physics, College of Science, UAE University, PO Box 17551 Al-Ain (United Arab Emirates)
2015-05-15
This article presents higher-order paraxial theory (non-paraxial theory) for the ring ripple formation on an intense Gaussian laser beam and its propagation in plasma, taking into account the relativistic-ponderomotive nonlinearity. The intensity dependent dielectric constant of the plasma has been determined for the main laser beam and ring ripple superimposed on the main laser beam. The dielectric constant of the plasma is modified due to the contribution of the electric field vector of ring ripple. Nonlinear differential equations have been formulated to examine the growth of ring ripple in plasma, self focusing of main laser beam, and ring rippled laser beam in plasma using higher-order paraxial theory. These equations have been solved numerically for different laser intensities and plasma frequencies. The well established experimental laser and plasma parameters are used in numerical calculation. It is observed that the focusing of the laser beams (main and ring rippled) becomes fast in the nonparaxial region by expanding the eikonal and other relevant quantities up to the fourth power of r. The splitted profile of laser beam in the plasma is observed due to uneven focusing/defocusing of the axial and off-axial rays. The growths of ring ripple increase when the laser beam intensity increases. Furthermore, the intensity profile of ring rippled laser beam gets modified due to the contribution of growth rate.
Institute of Scientific and Technical Information of China (English)
BAI Long; ZHANG Rong; WENG Jia-Qiang; FANG Jin-Qing
2008-01-01
We study an intense beam propagating through the double periodic focusing channel by the particle-core model, and obtain the beam envelope equation. According to the Poincare-Lyapunov theorem, we analyze the stability of beam envelope equation and find the beam halo. The soliton control method for controlling the beam halo-chaos is put forward based on mechanism of halo formation and strategy of controlling beam halo-chaos, and we also prove the validity of the control method, and furthermore, the feasible experimental project is given. We perform multiparticle simulation to control the halo by using the soliton controller. It is shown that our control method is effective. We also find the radial ion density changes when the ion beam is in the channel, not only the halo-chaos and its regeneration can be eliminated by using the nonlinear control method, but also the density uniformity can be found at beam's centre as long as an appropriate control method is chosen.
Institute of Scientific and Technical Information of China (English)
Hadi Haeri
2016-01-01
A simultaneous experimental and numerical study on crack propagation in the pre-cracked beams specimens (concrete-like materials) is carried out using three-point bending flexural test. The crack propagation and coalescence paths of internal cracks in side beam specimens are experimentally studied by inserting double internal cracks. The effects of crack positions on the fracturing path in the bridge areas of the double cracked beam specimens are also studied. It has been observed that the breaking of concrete-like cracked beams specimens occurs mainly by the propagation of wing cracks emanating from the tips of the pre-existing cracks in the numerical and experimental analyses, respectively. The same specimens are numerically simulated by an indirect boundary element method (IBEM) known as displacement discontinuity method (DDM) using higher displacement discontinuity. These numerical results are compared with the existing experimental results. This comparison illustrates the higher accuracy of the results obtained by the indirect boundary element method by using only a small number of elements compared with the discrete element method (PFC2D code).
Golmohammady, Sh; Ghafary, B.
2016-06-01
In this study, generalized Stokes parameters of a phase-locked partially coherent flat-topped array beam based on the extended Huygens-Fresnel principle and the unified theory of coherence and polarization have been reported. Analytical formulas for 2 × 2 cross-spectral density matrix elements, and consequently Stokes parameters of a phase-locked partially coherent flat-topped array beam propagating through the turbulent atmosphere have been formulated. Effects of many physical attributes such as wavelength, turbulence strength, flatness order and other source parameters on the Stokes parameters, and therefore spectral degree of polarization upon propagation have been studied thoroughly. The behaviour of the spectral degree of coherence of a delineated beam for different source conditions has been investigated. It can be shown that four generalized Stokes parameters increase by raising the flatness order at the same propagation distance. Increasing the number of beams leads to a decrease in the Stokes parameters to zero slowly. The results are of utmost importance for optical communications.
CSIR Research Space (South Africa)
Litvin, IA
2007-01-01
Full Text Available were calculated using β = 61 for: (a) a = 2w, (b) a = 2.25w, (c) a = 2.75w, and (d) a = 4w. 3. PROPAGATION RESULTS Having noted the differences in the phase of element C discussed above, we now turn our attention to the impact... of the beam in Figure 4 (b) after 0.1 m (first row), 0.25 m (second row) and 0.5 m (third row) propagation when: (a) Ideal phase correcting element is present, as calculated using the Fresnel diffraction equation, (b) the phase element calculated using Eq...
Wang, Aichen; Lu, Renfu; Xie, Lijuan
2016-01-01
Spatially resolved spectroscopy provides a means for measuring the optical properties of biological tissues, based on analytical solutions to diffusion approximation for semi-infinite media under the normal illumination of an infinitely small light beam. The method is, however, prone to error in measurement because the actual boundary condition and light beam often deviate from that used in deriving the analytical solutions. It is therefore important to quantify the effect of different boundary conditions and light beams on spatially resolved diffuse reflectance in order to improve the measurement accuracy of the technique. This research was aimed at using finite element method (FEM) to model light propagation in turbid media, subjected to normal illumination by a continuous-wave beam of infinitely small or finite size. Three types of boundary conditions [i.e., partial current (PCBC), extrapolated (EBC), and zero (ZBC)] were evaluated and compared against Monte Carlo (MC) simulations, since MC could provide accurate fluence rate and diffuse reflectance. The effect of beam size was also investigated. Overall results showed that FEM provided results as accurate as those of the analytical method when an appropriate boundary condition was applied. ZBC did not give satisfactory results in most cases. FEM-PCBC yielded a better fluence rate at the boundary than did FEM-EBC, while they were almost identical in predicting diffuse reflectance. Results further showed that FEM coupled with EBC effectively simulated spatially resolved diffuse reflectance under the illumination of a finite size beam. A large beam introduced more error, especially within the region of illumination. Research also confirmed an earlier finding that a light beam of less than 1 mm diameter should be used for estimation of optical parameters. FEM is effective for modeling light propagation in biological tissues and can be used for improving the optical property measurement by the spatially resolved
Doster, Timothy; Watnik, Abbie T
2016-12-20
As a means of increasing the channel capacity in free-space optical communication systems, two types of orbital angular momentum carrying beams, Bessel-Gauss and Laguerre-Gauss, are studied. In a series of numerical simulations, we show that Bessel-Gauss beams, pseudo-nondiffracting beams, outperform Laguerre-Gauss beams of various orders in channel efficiency and bit error rates.
Directory of Open Access Journals (Sweden)
Han S. Uhm
2003-03-01
Full Text Available The dispersion relation for the resistive hose instability in a charged particle beam with a flattop density profile is derived from the linearized Vlasov-Maxwell equations. Stability properties of the resistive hose instability where the perturbations are initiated at the beam entrance are investigated. In particular, the complex eigenfrequency Ω in the dispersion relation is expressed as a function of the real oscillation frequency ω of the excitation at the beam entrance. As expected, the growth rate ImΩ=Ω_{i} decreases rapidly as the conducting wall approaches the beam (r_{w}/r_{b}→1. The growth rate also decreases substantially as the frequency ratio ω/ν_{c} increases, where ν_{c} is the electron collision frequency. Stability properties for perturbations propagating through the beam pulse from its head to tail are also investigated. In this case, the growth rate Imω is calculated in terms of the real oscillation frequency Ω of each beam segment. It is shown that the resonance frequency Ω=Ω_{r} corresponding to the infinite growth rate detunes considerably from the betatron frequency ω_{β} of the beam particles. It is also found that the bandwidth corresponding to instability is narrow when the plasma electron collision time (1/ν_{c} is long compared with the magnetic decay time (τ_{d}.
Sjöqvist, Lars; Henriksson, Markus; Fedina, Ekaterina; Fureby, Christer
2010-10-01
The exhaust from jet engines introduces extreme turbulence levels in local environments around aircrafts. This may degrade the performance of electro-optical missile warning and laser-based DIRCM systems used to protect aircrafts against heat-seeking missiles. Full scale trials using real engines are expensive and difficult to perform motivating numerical simulations of the turbulence properties within the jet engine exhaust. Large Eddy Simulations (LES) is a computational fluid dynamics method that can be used to calculate spatial and temporal refractive index dynamics of the turbulent flow in the engine exhaust. From LES simulations the instantaneous refractive index in each grid point can be derived and interpolated to phase screens for numerical laser beam propagation or used to estimate aberration effects from optical path differences. The high computation load of LES limits the available data in terms of the computational volume and number of time steps. In addition the phase screen method used in laser beam propagation may also be too slow. For this reason extraction of statistical parameters from the turbulence field and statistical beam propagation methods are studied. The temporal variation of the refractive index is used to define a spatially varying structure constant. Ray-tracing through the mean refractive index field provides integrated static aberrations and the path integrated structure constant. These parameters can be used in classical statistical parameterised models describing propagation through turbulence. One disadvantage of using the structure constant description is that the temporal information is lost. Methods for studying the variation of optical aberrations based on models of Zernike coefficients are discussed. The results of the propagation calculations using the different methods are compared to each other and to available experimental data. Advantages and disadvantages of the different methods are briefly discussed.
Institute of Scientific and Technical Information of China (English)
Chaojun Yan; Wenbiao Peng; Haijun Li
2007-01-01
@@ The alternate-direction implicit finite difference beam propagation method (FD-BPM) is used to analyze the two-dimensional (2D) symmetrical multimode interference (MMI) couplers. The positions of the images at the output plane and the length of multimode waveguide are accurately determined numerically. In order to reduce calculation time, the parallel processing of the arithmetic is implemented by the message passing interface and the simulation is accomplished by eight personal computers.
Higher-Order Wide-Angle Split-Step Spectral Method for Non-Paraxial Beam Propagation
2013-06-25
GPU ) using compute unified device architecture ( CUDA ) technology from NVIDIA™. 2. Formulation Beam propagation in a medium with a non-uniform...448 CUDA cores at 574 MHz core clock speed (750 MHz memory clock speed) and 6 GB of dedicated GPU DDR5 RAM. The simulation was run using the...NVIDIA compute unified device architecture ( CUDA ) to make use of the processing power of the graph- ics processing unit ( GPU ). Modern GPUs possess
Directory of Open Access Journals (Sweden)
Bahman O. Taha
2015-06-01
Full Text Available The reinforced concrete with fiber reinforced polymer (FRP bars (carbon, aramid, basalt and glass is used in places where a high ratio of strength to weight is required and corrosion is not acceptable. Behavior of structural members using (FRP bars is hard to be modeled using traditional methods because of the high non-linearity relationship among factors influencing the strength of structural members. Back-propagation neural network is a very effective method for modeling such complicated relationships. In this paper, back-propagation neural network is used for modeling the flexural behavior of beams reinforced with (FRP bars. 101 samples of beams reinforced with fiber bars were collected from literatures. Five important factors are taken in consideration for predicting the strength of beams. Two models of Multilayer Perceptron (MLP are created, first with single-hidden layer and the second with two-hidden layers. The two-hidden layer model showed better accuracy ratio than the single-hidden layer model. Parametric study has been done for two-hidden layer model only. Equations are derived to be used instead of the model and the importance of input factors is determined. Results showed that the neural network is successful in modeling the behavior of concrete beams reinforced with different types of (FRP bars.
Peng, Sun; Jin, Guo; Tingfeng, Wang
2013-07-01
Based on the generalized Huygens-Fresnel diffraction integral (Collins' formula), the propagation equation of Hermite-Gauss beams through a complex optical system with a limiting aperture is derived. The elements of the optical system may be all those characterized by an ABCD ray-transfer matrix, as well as any kind of apertures represented by complex transmittance functions. To obtain the analytical expression, we expand the aperture transmittance function into a finite sum of complex Gaussian functions. Thus the limiting aperture is expressed as a superposition of a series of Gaussian-shaped limiting apertures. The advantage of this treatment is that we can treat almost all kinds of apertures in theory. As application, we define the width of the beam and the focal plane using an encircled-energy criterion and calculate the intensity distribution of Hermite-Gauss beams at the actual focus of an aperture lens.
Institute of Scientific and Technical Information of China (English)
Qian Xian-Mei; Zhu Wen-Yue; Rao Rui-Zhong
2012-01-01
Propagation properties of spatially pseudo-partially coherent Gaussian Schell-model beams through the atmospheric turbulence over a long-distance uplink path are studied by numerical simulation.A linear coordination transformation is introduced to overcome the window effect and the loss-of-resolution problem.The beam spreading,beam wandering,and intensity scintillation as functions of turbulence strength,source correlation length,and change frequency of random phase that models the partial coherence of the source are analyzed. It is found that the beam spreading and the intensity scintillation of the partially coherent beam are less affected by the turbulence than those of the coherent one,but it suffers from a more severe diffractive effect,and the change frequency of random phase has no evident influence on it.The beam wandering is insensitive to the variation of source correlation length,and decreases firstly then goes to a fixed value as the change frequency increases.
Zhu, Ziren; Liu, Lin; Wang, Fei; Cai, Yangjian
2015-03-01
Analytical expressions for the cross-spectral density function and the second-order moments of a Laguerre-Gaussian correlated Schell-model (LGCSM) beam propagating in uniaxial crystals orthogonal to the optical axis are derived. Based on the formulas derived, we study the propagation properties, such as beam irradiance, beam diameters, and the spectral degree of coherence, of a LGCSM beam inside uniaxial crystals in detail. The effect of the initial beam parameters (mode order and spatial coherence length) and the parameters of the uniaxial crystals on the evolution properties of a LGCSM beam is revealed through numerical examples. The uniaxial crystals provide one way to modulate the properties of a LGCSM beam.
Propagation instabilities of high-intensity laser-produced electron beams.
Tatarakis, M; Beg, F N; Clark, E L; Dangor, A E; Edwards, R D; Evans, R G; Goldsack, T J; Ledingham, K W D; Norreys, P A; Sinclair, M A; Wei, M-S; Zepf, M; Krushelnick, K
2003-05-01
Measurements of energetic electron beams generated from ultrahigh intensity laser interactions (I>10(19) W/cm(2)) with dense plasmas are discussed. These interactions have been shown to produce very directional beams, although with a broad energy spectrum. In the regime where the beam density approaches the density of the background plasma, we show that these beams are unstable to filamentation and "hosing" instabilities. Particle-in-cell simulations also indicate the development of such instabilities. This is a regime of particular interest for inertial confinement fusion applications of these beams (i.e., "fast ignition").
Directory of Open Access Journals (Sweden)
Ronald C. Davidson
2002-08-01
Full Text Available The Vlasov-Maxwell equations are used to investigate the nonlinear evolution of an intense sheet beam with distribution function f_{b}\\(x,x^{′},s\\ propagating through a periodic focusing lattice κ_{x}\\(s+S\\=κ_{x}\\(s\\, where S=const is the lattice period. The analysis considers the special class of distribution functions with uniform phase-space density f_{b}\\(x,x^{′},s\\=A=const inside of the simply connected boundary curves, x_{+}^{′}\\(x,s\\ and x_{-}^{′}\\(x,s\\, in the two-dimensional phase space \\(x,x^{′}\\. Coupled nonlinear equations are derived describing the self-consistent evolution of the boundary curves, x_{+}^{′}\\(x,s\\ and x_{-}^{′}\\(x,s\\, and the self-field potential ψ\\(x,s\\=e_{b}φ\\(x,s\\/γ_{b}m_{b}β_{b}^{2}c^{2}. The resulting model is shown to be exactly equivalent to a (truncated warm-fluid description with zero heat flow and triple-adiabatic equation of state with scalar pressure P_{b}\\(x,s\\=const[n_{b}\\(x,s\\]^{3}. Such a fluid model is amenable to direct analysis by transforming to Lagrangian variables following the motion of a fluid element. Specific examples of periodically focused beam equilibria are presented, ranging from a finite-emittance beam in which the boundary curves in phase space \\(x,x^{′}\\ correspond to a pulsating parallelogram, to a cold beam in which the number density of beam particles, n_{b}\\(x,s\\, exhibits large-amplitude periodic oscillations. For the case of a sheet beam with uniform phase-space density, the present analysis clearly demonstrates the existence of periodically focused beam equilibria without the undesirable feature of an inverted population in phase space that is characteristic of the Kapchinskij-Vladimirskij beam distribution.
Energy Technology Data Exchange (ETDEWEB)
Lee, Jai Hyung; Chang, Joon Sung; Lee, Won Kyu; Jeon, Jin Ho [Seoul National University, Seoul (Korea)
2000-04-01
We studied the conical emission(CE) in samarium(Sm) vapor under the near-resonant condition. The incident dye laser was tuned to the transition line, 4f{sup 6}6s{sup 2} {sup 7}F{sub 0} {yields} 4f{sup 6}({sup 7})6s6p({sup 1}P{sup 0}), of Sm atom. Using a high temperature oven, we could obtain the atomic density of 8 x 10{sup 14} atoms/cm{sup 3} large enough to observe the CE. We observed 1 {approx} 3 rings around the original laser beam and the number of the rings depended on the laser intensity, the laser wavelength and the atomic density. These results are attributed to the self-phase-modulation of the laser beam interacting with the near-resonant atomic medium. We obtain a simple expression that describes the dependence of the locations of the rings on the laser intensity. We compare the experimental results with this expression quantitatively and then estimate the nonlinear susceptibility of Sm vapor. The laser beam propagating through the resonant medium undergo severe deformation because of nonlinear interaction such as self-focusing, self-defocusing, etc. When strong pump beam coexists with the probe beam, propagation characteristics can be changed. We use samarium(Sm) vapor as the nonlinear medium. Probe laser is tuned around 4f{sup 6}s{sup 2} {sup 7}F{sub 0} {yields} 4f{sup 6}({sup 7}F)6s6p({sup 1}P{sup 0}) transition line of Sm (562.601 nm). Pump laser is tuned around 4f{sup 6}s{sup 2} {sup 7}F{sub 1} {yields} 4f{sup 6}({sup 7}F)6s6p({sup 1}P{sup 0}) transition line of Sm (572.019 nm). The probe and the pump beams are {lambda} -type configuration. The transmission and beam width of the probe beam is changed as the intensity and the detuning of the probe beam are varied. 17 refs., 16 figs., 1 tab. (Author)
Wang, X; Hopkins, C
2016-10-01
Advanced Statistical Energy Analysis (ASEA) is used to predict vibration transmission across coupled beams which support multiple wave types up to high frequencies where Timoshenko theory is valid. Bending-longitudinal and bending-torsional models are considered for an L-junction and rectangular beam frame. Comparisons are made with measurements, Finite Element Methods (FEM) and Statistical Energy Analysis (SEA). When beams support at least two local modes for each wave type in a frequency band and the modal overlap factor is at least 0.1, measurements and FEM have relatively smooth curves. Agreement between measurements, FEM, and ASEA demonstrates that ASEA is able to predict high propagation losses which are not accounted for with SEA. These propagation losses tend to become more important at high frequencies with relatively high internal loss factors and can occur when there is more than one wave type. At such high frequencies, Timoshenko theory, rather than Euler-Bernoulli theory, is often required. Timoshenko theory is incorporated in ASEA and SEA using wave theory transmission coefficients derived assuming Euler-Bernoulli theory, but using Timoshenko group velocity when calculating coupling loss factors. The changeover between theories is appropriate above the frequency where there is a 26% difference between Euler-Bernoulli and Timoshenko group velocities.
Directory of Open Access Journals (Sweden)
Navia C. E.
2007-01-01
Full Text Available A laser diffraction experiment was conducted to study light propagation in air. The experiment is easy to reproduce and it is based on simple optical principles. Two optical sensors (segmented photo-diodes are used for measuring the position of diffracted light spots with a precision better than 0.1 μ m. The goal is to look for signals of anisotropic light propagation as function of the laser beam alignment to the Earth’s motion (solar barycenter motion obtained by COBE. Two raster search techniques have been used. First, a laser beam fixed in the laboratory frame scans in space due to Earth’s rotation. Second, a laser beam mounted on a turntable system scans actively in space by turning the table. The results obtained with both methods show that the course of light rays are affected by the motion of the Earth, and a predominant first order quantity with a Δ c/c = − β (1 + 2 a cos θ signature with ˉ a = − 0.393 ± 0.032 describes well the experimental results. This result differs in amount of 21% from the Special Relativity Theory prediction and that supplies the value of a = − 1 2 (isotropy.
Bespamyatnov, Igor O; Rowan, William L; Granetz, Robert S
2008-10-01
Charge exchange recombination spectroscopy on Alcator C-Mod relies on the use of the diagnostic neutral beam injector as a source of neutral particles which penetrate deep into the plasma. It employs the emission resulting from the interaction of the beam atoms with fully ionized impurity ions. To interpret the emission from a given point in the plasma as the density of emitting impurity ions, the density of beam atoms must be known. Here, an analysis of beam propagation is described which yields the beam density profile throughout the beam trajectory from the neutral beam injector to the core of the plasma. The analysis includes the effects of beam formation, attenuation in the neutral gas surrounding the plasma, and attenuation in the plasma. In the course of this work, a numerical simulation and an analytical approximation for beam divergence are developed. The description is made sufficiently compact to yield accurate results in a time consistent with between-shot analysis.
Kaganovich, Igor D.
2015-11-01
In this paper we study the effects of the two-stream instability on the propagation of intense nonrelativistic ion and electron beams in background plasma. Development of the two-stream instability between the beam ions and plasma electrons leads to beam breakup, a slowing down of the beam particles, acceleration of the plasma particles, and transfer of the beam energy to the plasma particles and wave excitations. Making use of the particle-in-cell codes EDIPIC and LSP, and analytic theory we have simulated the effects of the two-stream instability on beam propagation over a wide range of beam and plasma parameters. Because of the two-stream instability the plasma electrons can be accelerated to velocities as high as twice the beam velocity. The resulting return current of the accelerated electrons may completely change the structure of the beam self - magnetic field, thereby changing its effect on the beam from focusing to defocusing. Therefore, previous theories of beam self-electromagnetic fields that did not take into account the effects of the two-stream instability must be significantly modified. This effect can be observed on the National Drift Compression Experiment-II (NDCX-II) facility by measuring the spot size of the extracted beamlet propagating through several meters of plasma. Particle-in-cell, fluid simulations, and analytical theory also reveal the rich complexity of beam- plasma interaction phenomena: intermittency and multiple regimes of the two-stream instability in dc discharges; band structure of the growth rate of the two-stream instability of an electron beam propagating in a bounded plasma and repeated acceleration of electrons in a finite system. In collaboration with E. Tokluoglu, D. Sydorenko, E. A. Startsev, J. Carlsson, and R. C. Davidson. Research supported by the U.S. Department of Energy.
Lack of low frequency variants masks patterns of non-neutral evolution following domestication.
Directory of Open Access Journals (Sweden)
Céline H Frère
Full Text Available Detecting artificial selection in the genome of domesticated species can not only shed light on human history but can also be beneficial to future breeding strategies. Evidence for selection has been documented in domesticated species including maize and rice, but few studies have to date detected signals of artificial selection in the Sorghum bicolor genome. Based on evidence that domesticated S. bicolor and its wild relatives show significant differences in endosperm structure and quality, we sequenced three candidate seed storage protein (kafirin loci and three candidate starch biosynthesis loci to test whether these genes show non-neutral evolution resulting from the domestication process. We found strong evidence of non-neutral selection at the starch synthase IIa gene, while both starch branching enzyme I and the beta kafirin gene showed weaker evidence of non-neutral selection. We argue that the power to detect consistent signals of non-neutral selection in our dataset is confounded by the absence of low frequency variants at four of the six candidate genes. A future challenge in the detection of positive selection associated with domestication in sorghum is to develop models that can accommodate for skewed frequency spectrums.
Lack of low frequency variants masks patterns of non-neutral evolution following domestication.
Frère, Céline H; Prentis, Peter J; Gilding, Edward K; Mudge, Agnieszka M; Cruickshank, Alan; Godwin, Ian D
2011-01-01
Detecting artificial selection in the genome of domesticated species can not only shed light on human history but can also be beneficial to future breeding strategies. Evidence for selection has been documented in domesticated species including maize and rice, but few studies have to date detected signals of artificial selection in the Sorghum bicolor genome. Based on evidence that domesticated S. bicolor and its wild relatives show significant differences in endosperm structure and quality, we sequenced three candidate seed storage protein (kafirin) loci and three candidate starch biosynthesis loci to test whether these genes show non-neutral evolution resulting from the domestication process. We found strong evidence of non-neutral selection at the starch synthase IIa gene, while both starch branching enzyme I and the beta kafirin gene showed weaker evidence of non-neutral selection. We argue that the power to detect consistent signals of non-neutral selection in our dataset is confounded by the absence of low frequency variants at four of the six candidate genes. A future challenge in the detection of positive selection associated with domestication in sorghum is to develop models that can accommodate for skewed frequency spectrums.
Sound propagation in two-axis underwater channel based on beam-displacement ray-mode theory
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Sound propagation in a deep ocean two-axis underwater channel is often complex and difficult to simulate between surface channel and sound fixing and ranging (SOFAR) channel. The beam-displacement ray-mode (BDRM) theory is a normal mode method for propagation modeling in horizontally stratified shallow water. An improved method for computing the upper boundary reflection coefficient in the BDRM is proposed and applied to calculate the acoustic fields of a two-axis underwater channel. Transmission losses in the two-axis underwater channel are calculated in the new BDRM. The corresponding results are in good agreement with those from the Kraken code, and furthermore the computed speed of the new BDRM excels the other methods.
Laserna, J J; Reyes, R Fernández; González, R; Tobaria, L; Lucena, P
2009-06-08
We report on an experimental study of the effect of atmospheric turbulence on laser induced breakdown spectroscopy (LIBS) measurements. The characteristics of the atmosphere dictate specific performance constraints to this technology. Unlike classical laboratory LIBS systems where the distance to the sample is well known and characterized, LIBS systems working at several tens of meters to the target have specific atmospheric propagation conditions that cause the quality of the LIBS signals to be affected to a significant extent. Using a new LIBS based sensor system fitted with a nanosecond laser emitting at 1064 nm, propagation effects at distances of up to 120 m were investigated. The effects observed include wander and scintillation in the outgoing laser beam and in the return atomic emission signal. Plasmas were formed on aluminium targets. Average signal levels and signal fluctuations are measured so the effect of atmospheric turbulence on LIBS measurements is quantified.
Modulation instability, solitons and beam propagation in spatially nonlocal nonlinear media
DEFF Research Database (Denmark)
Krolikowski, Wieslaw; Bang, Ole; Nikolov, Nikola Ivanov
2004-01-01
We present an overview of recent advances in the understanding of optical beams in nonlinear media with a spatially nonlocal nonlinear response. We discuss the impact of nonlocality on the modulational instability of plane waves, the collapse of finite-size beams, and the formation and interaction...
Ding, Lan; Zhu, Hong-Ping; Wu, Li
2016-07-01
The propagation and attenuation properties of waves in ordered and disordered periodic composite Timoshenko beams, which consider the effects of axial static load and structural damping, resting on elastic foundations are studied when the system is subjected to moving loads of constant amplitude with a constant velocity. The transfer matrix methodology is adopted to formulate the model in a reference coordinate system moving with the load. The localization factor is calculated to determine the wave velocity pass bands and stop bands. The interactions between the static axial load and moving load, structural damping and disorder on the bands are analyzed.
Institute of Scientific and Technical Information of China (English)
DUAN Sai-Liang; LI Jian-Feng; ZHAO Wei; WANG Yi-Shan
2008-01-01
@@ Based on the expansion expression of the fundamental mode of a single-mode fibre in terms of Laguerre-Gauss modes, the propagation of a beam of a weakly guiding fibre laser through an optical ABCD system with a circular aperture at the fibre end is studied. The results show that there is much difference between the propagation of the laser beam described by the expansion expression and by the Gaussian mode approximation. The depth of focus of the laser beam is longer than that of the Gaussian modes.
Guo, Q L; Liang, B L; Wang, Y; Deng, G Y; Jiang, Y H; Zhang, S H; Fu, G S; Simmonds, P J
2014-10-01
The propagation characteristics of a focused laser beam in a SBN:75 photorefractive crystal strongly depend on the signal-to-background intensity ratio (R=Is/Ib) under reverse external electric field. In the range 20>R>0.05, the laser beam shows enhanced self-defocusing behavior with increasing external electric field, while it shows self-focusing in the range 0.03>R>0.01. Spatial solitons are observed under a suitable reverse external electric field for R=0.025. A theoretical model is proposed to explain the experimental observations, which suggest a new type of soliton formation due to "enhancement" not "screening" of the external electrical field.
ARTICLES: Propagation of an intensity-modulated laser beam through a pulsed CO2 amplifier
Fedorov, S. V.; Yur'ev, M. S.
1987-01-01
A theoretical study was made (by a self-consistent solution of the equations of vibrational kinetics, hydrodynamics, and quasioptics) of the influence of self-interaction of laser radiation on the transmission of a beam through a CO2 amplifier. It was found that for times exceeding the time for collisional decay of the upper active level the radiation wavefront becomes unstable in the presence of small-scale perturbations of the transverse structure of the beam. It was shown that the harmful influence of the self-interaction on the divergence can be weakened by raising the intensity of the incident beam and the gain of the amplifier.
Giant narrowband twin-beam generation along the pump-energy propagation direction
Pérez, Angela M.; Spasibko, Kirill Yu; Sharapova, Polina R.; Tikhonova, Olga V.; Leuchs, Gerd; Chekhova, Maria V.
2015-07-01
Walk-off effects, originating from the difference between the group and phase velocities, limit the efficiency of nonlinear optical interactions. While transverse walk-off can be eliminated by proper medium engineering, longitudinal walk-off is harder to avoid. In particular, ultrafast twin-beam generation via pulsed parametric down-conversion and four-wave mixing is only possible in short crystals or fibres. Here we show that in high-gain parametric down-conversion, one can overcome the destructive role of both effects and even turn them into useful tools for shaping the emission. In our experiment, one of the twin beams is emitted along the pump Poynting vector or its group velocity matches that of the pump. The result is markedly enhanced generation of both twin beams, with the simultaneous narrowing of angular and frequency spectrum. The effect will enable efficient generation of ultrafast twin photons and beams in cavities, waveguides and whispering-gallery mode resonators.
DEFF Research Database (Denmark)
Mamaev, A.V.; Saffman, M.; Zozulya, A.A.
1996-01-01
We analyze the evolution of (1+1) dimensional dark stripe beams in bulk media with a photorefractive nonlinear response. These beams, including solitary wave solutions, are shown to be unstable with respect to symmetry breaking and formation of structure along the initially homogeneous coordinate....... Experimental results show the complete sequence of events starting from self-focusing of the stripe, its bending due to the snake instability, and subsequent decay into a set of optical vortices....
Wave propagation analysis of edge cracked circular beams under impact force.
Directory of Open Access Journals (Sweden)
Şeref Doğuşcan Akbaş
Full Text Available This paper presents responses of an edge circular cantilever beam under the effect of an impact force. The beam is excited by a transverse triangular force impulse modulated by a harmonic motion. The Kelvin-Voigt model for the material of the beam is used. The cracked beam is modelled as an assembly of two sub-beams connected through a massless elastic rotational spring. The considered problem is investigated within the Bernoulli-Euler beam theory by using energy based finite element method. The system of equations of motion is derived by using Lagrange's equations. The obtained system of linear differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. In the study, the effects of the location of crack, the depth of the crack, on the characteristics of the reflected waves are investigated in detail. Also, the positions of the cracks are calculated by using reflected waves.
A Monte Carlo approach for simulating the propagation of partially coherent x-ray beams
DEFF Research Database (Denmark)
Prodi, A.; Bergbäck Knudsen, Erik; Willendrup, Peter Kjær
2011-01-01
by sampling Huygens-Fresnel waves with Monte Carlo methods and is used to propagate each source realization to the detector plane. The sampling is implemented with a modified Monte Carlo ray tracing scheme where the optical path of each generated ray is stored. Such information is then used in the summation...
Manning, Robert M.
2012-01-01
The method of moments is used to define and derive expressions for laser beam deflection and beam radius broadening for high-energy propagation through the Earth s atmosphere. These expressions are augmented with the integral invariants of the corresponding nonlinear parabolic equation that describes the electric field of high-energy laser beam to propagation to yield universal equations for the aforementioned quantities; the beam deflection is a linear function of the propagation distance whereas the beam broadening is a quadratic function of distance. The coefficients of these expressions are then derived from a thin screen approximation solution of the nonlinear parabolic equation to give corresponding analytical expressions for a target located outside the Earth s atmospheric layer. These equations, which are graphically presented for a host of propagation scenarios, as well as the thin screen model, are easily amenable to the phase expansions of the wave front for the specification and design of adaptive optics algorithms to correct for the inherent phase aberrations. This work finds application in, for example, the analysis of beamed energy propulsion for space-based vehicles.
Calculation of Beam Propagation through a Defected or a Misaligned Two-Lens System
Khwaja, Tariq Shamim
2016-01-01
An inadvertent or unwanted angular deviation to a passing beam can be introduced by any single optical component within an optical system. The problem arises due to an imperfect tilt alignment of the optical component or manufacturing defects which results in a slightly different response than expected from an ideally aligned/manufactured component. The resulting beam deviation can plague any well-designed optical system that assumes the use of ideal components. The problem is especially introduced by non-ideal lenses, transparent plates and optical windows. Here we present a simple method of manually introducing a deviation error angle which we assume to be constant for all beam incidence angles over the paraxial range.
Wave propagation in beams with periodic arrays of airfoil-shaped resonating units
Casadei, Filippo; Bertoldi, Katia
2014-12-01
This paper presents an analytical and numerical study on the dispersion properties of an Euler-Bernoulli beam immersed in a steady fluid flow with periodic arrays of airfoil-shaped vibration absorbers attached to it. The resonance characteristics of the airfoils generate strong attenuation of flexural waves in the beam occurring at frequencies defined by the properties of the airfoils and the speed of the incident fluid. Analytical and numerical tools are developed to investigate the effects of the incident flow on the dispersion properties and the bandgaps of the system. Both steady and unsteady aerodynamic models are used to model the lift force and the pitching moment acting on the resonators and their effect on the dispersion relations of the system is evaluated. Finally, an effective medium description of the beam is developed to capture its behavior at long-wavelengths. In this regime, the system can be effectively considered as an acoustic metamaterial with adaptive dispersion properties.
Creation of polarization gradients from superposition of counter propagating vector LG beams.
Vyas, Sunil; Kozawa, Yuichi; Miyamoto, Yoko
2015-12-28
We present a detailed theoretical analysis of the formation of standing waves using cylindrically polarized vector Laguerre-Gaussian (LG) beams. It is shown that complex interplay between the radial and azimuthal polarization state can be used to realize different kinds of polarization gradients with cylindrically symmetric polarization distribution. Expressions for four different cases are presented and local dynamics of spatial polarization distribution is studied. We show cylindrically symmetric Sisyphus and corkscrew type polarization gradients can be obtained from vector LG beams. The optical landscape presented here with spatially periodic polarization patterns may find important applications in the field of atom optics, atom interferometry, atom lithography, and optical trapping.
Wave propagation in magneto-electro-elastic nanobeams via two nonlocal beam models
Ma, Li-Hong; Ke, Liao-Liang; Wang, Yi-Ze; Wang, Yue-Sheng
2017-02-01
This paper makes the first attempt to investigate the dispersion behavior of waves in magneto-electro-elastic (MEE) nanobeams. The Euler nanobeam model and Timoshenko nanobeam model are developed in the formulation based on the nonlocal theory. By using the Hamilton's principle, we derive the governing equations which are then solved analytically to obtain the dispersion relations of MEE nanobeams. Results are presented to highlight the influences of the thermo-electro-magnetic loadings and nonlocal parameter on the wave propagation characteristics of MEE nanobeams. It is found that the thermo-electro-magnetic loadings can lead to the occurrence of the cut-off wave number below which the wave can't propagate in MEE nanobeams.
CSIR Research Space (South Africa)
Belyi, VN
2011-05-01
Full Text Available or Gaussian-type beams, the simultaneous fulfillment of these conditions, strictly speaking, is unrealizable. The reason for this is that BBs are made up of plane waves trav- eling on a cone, and it is quite possible for the cone angle to be larger than...
Giant Narrowband Twin-Beam Generation along the Pump Energy Propagation
Perez, Angela M; Sharapova, Polina R; Tikhonova, Olga V; Leuchs, Gerd; Chekhova, Maria V
2014-01-01
Walk-off effects, originating from the difference between the group and phase velocities, limit the efficiency of nonlinear optical interactions. While transverse walk-off can be eliminated by proper medium engineering, longitudinal walk-off is harder to avoid. In particular, ultrafast twin- beam generation via pulsed parametric down-conversion (PDC) and four-wave mixing (FWM) is only possible in short crystals or fibres or in double-path schemes. Here we show that in high-gain PDC, one can overcome the destructive role of both effects and even turn them into useful tools for shaping the emission. In our experiment, one of the twin beams is emitted along the pump Poynting vector or its group velocity matches that of the pump. The result is dramatically enhanced generation of both twin beams, with the simultaneous narrowing of angular and frequency spectrum. The effect will enable efficient generation of ultrafast twin photons and beams in cavities, waveguides, and whispering-gallery mode resonators.
High power infrared super-Gaussian beams: generation, propagation and application
CSIR Research Space (South Africa)
Du Preez, NC
2009-09-01
Full Text Available In this paper researchers present the design of a CO2 laser resonator that produces as the stable transverse mode a super–Gaussian laser beam. The resonator makes use of an intra–cavity diffractive mirror and a flat output coupler, generating...
Wave propagation and absorption of sandwich beams containing interior dissipative multi-resonators.
Chen, H; Li, X P; Chen, Y Y; Huang, G L
2017-04-01
In this study, a sandwich beam with periodic multiple dissipative resonators in the sandwich core material is investigated for broadband wave mitigation and/or absorption. An analytical approach based on the transfer matrix method and Bloch theorem is developed for both infinite and finite sandwich structures. Wave attenuation constants are theoretically obtained to examine the effects of various system parameters on the position, width and wave attenuation performance of the band gaps. The wave absorption coefficient of the sandwich beam is quantitatively studied to distinguish wave attenuation mechanisms caused by reflection and absorption. It is numerically demonstrated that a transient blast-induced elastic wave with broadband frequencies can be almost completely mitigated or absorbed at a subwavelength scale. The results of this study could be used for developing new multifunctional composite materials to suppress impact-induced and/or blast-induced elastic waves which may cause severe local damage to engineering structures.
Energy Technology Data Exchange (ETDEWEB)
Fuchs, J [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau (France); Nakatsutsumi, M [Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan); Marques, J-R [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau (France); Antici, P [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau (France); Bourgeois, N [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau (France); Grech, M [CELIA, UMR 5107 Universite Bordeaux 1-CNRS-CEA, 33405 Talence Cedex (France); Lin, T [Fox Chase Cancer Center, Philadephia, PA 19111-2497 (United States); Romagnani, L [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau (France); Tikhonchuk, V [CELIA, UMR 5107 Universite Bordeaux 1-CNRS-CEA, 33405 Talence Cedex (France); Weber, S [CELIA, UMR 5107 Universite Bordeaux 1-CNRS-CEA, 33405 Talence Cedex (France); Kodama, R [Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871 (Japan); Audebert, P [LULI, Ecole Polytechnique, CNRS, CEA, UPMC, Route de Saclay, 91128 Palaiseau (France)
2007-12-15
We have performed a systematic study of beam propagation (400 ps, I = 10{sup 10}-10{sup 14} W cm{sup -2}) in underdense plasmas (n{sub e} = 10{sup 19}-10{sup 20} cm{sup -3}) at a level of reduced complexity compared with the smoothed beams currently used in inertial confinement fusion studies, using one or two well-controlled filaments. These experiments have been performed on the LULI 100 TW laser facility. The use of well-controlled, diffraction-limited single filaments is possibly due to the use of adaptative optics. We have used either a single filament or two filaments having variable distance, delay, intensity ratio and polarization. The single filament configuration allows to study basic beam propagation and reveals occurrence of filamentation at low intensity levels. The use of two filaments demonstrates the occurrence of beam coupling and merging, and the importance of cross-talk effects supported by the plasma.
1994-01-03
D. S. Prono , J. T. Weir, and F. W. Chambers, "Status of Beam Transport with the ETA and ATA Accelerators," NTIS Document No. DE84013205, 1984...Copies may be ordered from the National Technical Information Service, Springfield, VA 22161. 34 17. D. S. Prono , et al., in Proceedings of the 1989 IEEE...Particle Accelerator Conference (Institute of Electrical and Electronics Engineers, Piscataway, NJ, 1989), p. 1441. 18. D. S. Prono , IEEE Trans. Nucl
Optical Connecting of Fibers by Laser Beams Propagating from the Fibers Edges
Directory of Open Access Journals (Sweden)
Sergey Nikolayevich Mensov
2008-01-01
Full Text Available A possibility to connect nonprecise positioned fibers in photopolymerizable compositions is under discussion in this paper. The processes of optical synthesis of connective waveguiding structures forming in such mediums directly by the radiation leaving the edges of connecting fibers are investigated numerically and experimentally as well. It was shown that nonlinear interaction of the light beams allows to connect misaligned and transversally shifted fibers with high efficiency.
J. Rodnizki, D. Berkovits, K. Lavie, I. Mardor, A. Shor and Y. Yanay (Soreq NRC, Yavne), K. Dunkel, C. Piel (ACCEL, Bergisch Gladbach), A. Facco (INFN/LNL, Legnaro, Padova), V. Zviagintsev (TRIUMF, Vancouver)
AbstractBeam dynamics simulations of SARAF (Soreq Applied Research Accelerator Facility) superconducting RF linear accelerator have been performed in order to establish the accelerator design. The multi-particle simulation includes 3D realistic electromagnetic field distributions, space charge forces and fabrication, misalignment and operation errors. A 4 mA proton or deuteron beam is accelerated up to 40 MeV with a moderated rms emittance growth and a high real-estate gradient of 2 MeV/m. An envelope of 40,000 macro-particles is kept under a radius of 1.1 cm, well below the beam pipe bore radius. The accelerator design of SARAF is proposed as an injector for the EURISOL driver accelerator. The Accel 176 MHZ β0=0.09 and β0=0.15 HWR lattice was extended to 90 MeV based on the LNL 352 MHZ β0=0.31 HWR. The matching between both lattices ensures smooth transition and the possibility to extend the accelerator to the required EURISOL ion energy.
Zhao, Y.; Ge, Z. Y.; Ma, Y. Y.; Yang, X. H.; Xu, B. B.; Ramis, R.
2017-03-01
X-ray emission from laser irradiating solid target is an important X-ray source for various potential applications. Counter-propagating (C-P) laser beams configuration is proposed to enhance the laser to X-ray conversion efficiency (CE) from laser irradiating solid targets. One-dimensional radiation hydrodynamics simulations show that the total X-ray CE for the C-P lasers case is as high as 65%, which has a 13% improvement compared with the single laser case. The improvement is mainly caused by the enlarged radiation region, and the enhancement of X-ray emission is from soft X-ray. Detailed energy term distributions and influences of the foil thickness on the X-ray CEs for both cases are presented. It is found that the enhancement of radiation is attributed to lower thermal and kinetic energy of the C-P lasers scheme.
Institute of Scientific and Technical Information of China (English)
Xiao Jin-Biao; Sun Xiao-Han
2006-01-01
A modified alternating direction implicit algorithm is proposed to solve the full-vectorial finite-difference beam propagation method formulation based on H fields. The cross-coupling terms are neglected in the first sub-step, but evaluated and doubly used in the second sub-step. The order of two sub-steps is reversed for each transverse magnetic field component so that the cross-coupling terms are always expressed in implicit form, thus the calculation is very efficient and stable. Moreover, an improved six-point finite-difference scheme with high accuracy independent of specific structures of waveguide is also constructed to approximate the cross-coupling terms along the transverse directions. The imaginary-distance procedure is used to assess the validity and utility of the present method. The field patterns and the normalized propagation constants of the fundamental mode for a buried rectangular waveguide and a rib waveguide are presented. Solutions are in excellent agreement with the benchmark results from the modal transverse resonance method.
Cai, H.; Wang, X.
2006-01-01
Based on Timoshenko laminated beam models, this paper investigates the influence of initial stress on the vibration and transverse wave propagation in individual multi-wall carbon nanotubes (MWNTs) under ultrahigh frequency (above 1 THz), in which the initial stress in the MWNTs can occur due to thermal or lattice mismatch between different materials. Considering van der Waals force interaction between two adjacent tubes and effects of rotary inertia and shear deformation, results show that the initial stress in individual multi-wall carbon nanotubes not only affects the number of transverse wave speeds and the magnitude of transverse wave speeds, but also terahertz critical frequencies at which the number of wave speeds changes. When the initial stress in individual multi-wall carbon nanotubes is the compressive stress, transverse wave speeds decrease and the vibration amplitude ratio of two adjacent tubes increases. When the initial stress in individual multi-wall carbon nanotubes is the tensile stress, transverse wave speeds increase and the vibration amplitude ratio of two adjacent tubes decreases. The investigation of the effects of initial stress on transverse wave propagation in carbon nanotubes may be used as a useful reference for the application and the design of nanoelectronic and nanodrive devices, nano-oscillators, and nanosensors, in which carbon nanotubes act as basic elements.
On the control of filamentation of intense laser beams propagating in underdense plasma
Energy Technology Data Exchange (ETDEWEB)
Williams, E A
2005-10-21
In indirect drive ICF ignition designs, the laser energy is delivered into the hohlraum through the laser entrance holes (LEH), which are sized as small as practicable to minimize X-ray radiation losses. On the other hand, deleterious laser plasma processes, such as filamentation and stimulated back-scatter, typically increase with laser intensity. Ideally, therefore, the laser spot shape should be a close fit to the LEH, with uniform (envelope) intensity in the spot and minimal energy at larger radii spilling onto the LEH material. This keeps the laser intensity as low as possible consistent with the area of the LEH aperture and the power requirements of the design. This can be achieved (at least for apertures significantly larger than the laser's aberrated focal spot) by the use of custom-designed phase plates. However, outfitting the 192 beam (National Ignition facility) NIF laser with multiple sets of phase plates optimized for a variety of different LEH aperture sizes is an expensive proposition. It is thus important to assess the impact on laser-plasma interaction processes of using phase plates with a smaller than optimum focal spot (or even no phase plates at all!) and then de-focusing the beam to expand it to fill the LEH and lower its intensity. We find significant effects from the lack of uniformity of the laser envelope out of the focal plane, from changes in the characteristic sizes of the laser speckle, and on the efficacy of additional polarization and/or SSD beam smoothing. We quantify these effects with analytic estimates and simulations using our laser plasma interaction code pF3D.
Time-Dependent Propagation of High-Energy Laser Beams through the Atmosphere: II
2007-11-02
Equation (Al) can be written <xi> 2 <x. > i = p I dx± dx2 ^1^(^,^2,3)1 , = p I &c1 da?2 x±\\S{x1,x2,z)\\ , ( A4a ) i = 1, 2 (A4b...where "P is the beam power given by P = / dx± dx2 \\${x±,x2)| 2 46- (A5) By differentiating Eqs. ( A4a ) and (A4b) with respect to z and making
Stabilizing Effect of Gas Conductivity Evolution on the Resistive Sausage Mode of a Propagating Beam
1983-06-08
and S. Yu, "Model of Emittance Growth in a Self-Pinched Beam," Lawrence Livermore Laboratory Report UCID-18330 (1979). 18. J. C. Clark, T. J. Fessenden ...and K. W. Struve, Bull. Am. Phys. Soc. 27, 1133 (1982). 19. R. J. Briggs, D. L. Birx, G. J. Caporaso, T. J. Fessenden , R. E. Hester, V fR. Melendez...V. K. Neil, A. C. Paul, and K. W. Struve, IEEE Trans. Nucl. Sci. NS-28, 3360 (1981). 23 20. E. J. Lauer, R. J. Briggs, T. J. Fessenden , R. E. Rester
Energy Technology Data Exchange (ETDEWEB)
Henesian, M.A.; Renard, P.; Auerbach, J. [and others
1997-03-17
An exhaustive set of Beamlet and Nova laser system simulations were performed over a wide range of power levels in order to gain understanding about the statistical trends in Nova and Beamlet`s experimental data sets, and to provide critical validation of propagation tools and design ``rules`` applied to the 192-arm National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL). The experiments considered for modeling were at 220-ps FWHM duration with unpumped booster slabs on Beamlet, and 100-ps FWHM with pumped 31.5-cm and 46-cm disk amplifiers on Nova. Simulations indicated that on Beamlet, the AB (the intensity pendent phase shift parameter characterizing the tendency towards beam filamentation) for the booster amplifier stage without pumping, would be nearly identical to the AB expected on NIF at the peak of a typical 20-ns long shaped pulse intended for ICF target irradiation. Therefore, with energies less than I kJ in short-pulses, we examined on Beamlet the comparable AB-driven filamentation conditions predicted for long ICF pulseshapes in the 18 kJ regime on the NIF, while avoiding fluence dependent surface damage. Various spatial filter pinhole configurations were examined on Nova and Beamlet. Open transport spatial filter pinholes were used in some experiments to allow the direct measurement of the onset of beam filamentation. Schlieren images on Beamlet of the far field irradiance measuring the scattered light fraction outside of 33-{micro}radians were also obtained and compared to modeled results.
Experimental and Numerical Study of Interface Crack Propagation in Foam Cored Sandwich Beams
DEFF Research Database (Denmark)
Berggreen, Carl Christian; Simonsen, Bo Cerup; Borum, Kaj Kvisgård
2007-01-01
This article deals with the prediction of debonding between core and face sheet in foam-cored sandwich structures. It describes the development, validation, and application of a FEM-based numerical model for the prediction of the propagation of debond damage. The structural mechanics is considered...... to be geometrically nonlinear while the local fracture mechanics problem is assumed to be linear. The presented numerical procedure for the local fracture mechanics is a further development of the crack surface displacement method, here denoted as the crack surface displacement extrapolation method. The considered...... application example is to tear off one of the face laminates from the sandwich. This configuration can be found in many applications but is considered here to be occurring in a ship structure, particularly at the hard spot where the superstructure meets the deck. Face tearing experiments are carried out...
Yi, Xiang; Li, Zan; Liu, Zengji
2015-02-20
In clean ocean water, the performance of a underwater optical communication system is limited mainly by oceanic turbulence, which is defined as the fluctuations in the index of refraction resulting from temperature and salinity fluctuations. In this paper, using the refractive index spectrum of oceanic turbulence under weak turbulence conditions, we carry out, for a horizontally propagating plane wave and spherical wave, analysis of the aperture-averaged scintillation index, the associated probability of fade, mean signal-to-noise ratio, and mean bit error rate. Our theoretical results show that for various values of the rate of dissipation of mean squared temperature and the temperature-salinity balance parameter, the large-aperture receiver leads to a remarkable decrease of scintillation and consequently a significant improvement on the system performance. Such an effect is more noticeable in the plane wave case than in the spherical wave case.
Optical wave beam propagation in two-lens scheme with arbitrary parameters
Kazakov, Vasily I.
2016-04-01
Two-lens optical scheme as a system of the optical information processing and transmission is considered. On the basis of applying radio-optics methods, the theory of linear systems and system approach a mathematical model describing the transformation of the optical wave beam in this system is proposed. Input-output ratio of the system in the form of a general spatial impulse response of all linear units included in the system is established. The problem of energy losses of the optical radiation in such a system is considered. As the input and output of system of the single-mode optical fiber is used. The equations defining the minimum possible level of energy losses caused by the diffraction of beam is obtained. The analysis showed that the losses depend explicitly on several parameters: the radiation wavelength, the distance between the end of fiber and the aperture, and the ratio of the diameter of fiber and lens aperture. With the help of computer simulation in Matlab system the losses depending on the parameters mentioned above is presented.
Jump Conditions of a Non-Neutral Plasma Shock with Current and Potential Difference
Institute of Scientific and Technical Information of China (English)
胡希伟
2002-01-01
Jump conditions about the total momentum flux and energy flux in a non-neutral plasma shock with electric current and field are given, which are derived from the double fluid equations and the Poisson equation for electron and ion fluids. Furthermore, we derive the relations between the upstream and downstream velocities and temperatures, and the minimum upstream Mach number for the plasma shock existence M1min, which depend on the current through the shock front J0, the electric potential difference between the upstream and downstream of shock △φ, and the ion charge Z.
Jump Conditions of a Shock with Current in Cylindrical Non-Neutral Plasma
Institute of Scientific and Technical Information of China (English)
HE Yong; HU Xi-Wei; HU Ye-Min
2006-01-01
Jump conditions of the parameters (mass flow, momentum flow and energy Bow) of a shock with current (thereby, electric and magnetic field) in cylindrical non-neutral plasma are presented and derived from Maxwell's equations and two fluid equations for electron and ion fluid. The critical Mach number for the shock existence is calculated, which depends on the shock carried current, the ion charge, and the composition of the magnetic and thermal pressure. The numerical results show that both the strength and profiles of the downstream shock parameters will be affected obviously by the shock carried current, electric and magnetic field in the two-dimensional shock.
Long distance propagation of a polarized neutron beam in zero magnetic field
Energy Technology Data Exchange (ETDEWEB)
Schmidt, U.; Bitter, T.; El-Muzeini, P. (Heidelberg Univ. (Germany). Physikalisches Inst.); Dubbers, D. (Technische Univ. Muenchen, Garching (Germany). Fakultaet fuer Physik E21); Schaerpf, O. (Inst. Laue Langevin, 38 - Grenoble (France))
1992-09-01
A beam of fully polarized cold neutrons was transported through a zero magnetic field region of 70 m length without loss of polarization. The purpose of this exercise was twofold: Firstly, to demonstrate that the new zero-field neutron spin-echo method will work also for very long neutron flight paths; secondly, to prove in the most direct way that the neutron free-flight region of the ILL neutron-antineutron oscillation experiment was indeed sufficiently field-free ('quasifree condition') by using the neutrons themselves as a magnetometer. To this purpose the residual magnetic field integrals in the long 'zero-field' region were measured with a conventional neutron spin-echo method. The overall spin precession angle of the neutrons during their flight through the long zero-field region was found to be less than 2[sup 0]. (orig.).
Analytical approach of laser beam propagation in the hollow polygonal light pipe.
Zhu, Guangzhi; Zhu, Xiao; Zhu, Changhong
2013-08-10
An analytical method of researching the light distribution properties on the output end of a hollow n-sided polygonal light pipe and a light source with a Gaussian distribution is developed. The mirror transformation matrices and a special algorithm of removing void virtual images are created to acquire the location and direction vector of each effective virtual image on the entrance plane. The analytical method is demonstrated by Monte Carlo ray tracing. At the same time, four typical cases are discussed. The analytical results indicate that the uniformity of light distribution varies with the structural and optical parameters of the hollow n-sided polygonal light pipe and light source with a Gaussian distribution. The analytical approach will be useful to design and choose the hollow n-sided polygonal light pipe, especially for high-power laser beam homogenization techniques.
Lamy, L.; Cecconi, B.; Zarka, P.; Canu, P.; Schippers, P.; Kurth, W. S.; Mutel, R. L.; Gurnett, D. A.; Menietti, D.; Louarn, P.
2011-04-01
The Cassini mission crossed the source region of the Saturn kilometric radiation (SKR) on 17 October 2008. On this occasion, the Radio and Plasma Wave Science (RPWS) experiment detected both local and distant radio sources, while plasma parameters were measured in situ by the magnetometer and the Cassini Plasma Spectrometer. A goniopolarimetric inversion was applied to RPWS three-antenna electric measurements to determine the wave vector k and the complete state of polarization of detected waves. We identify broadband extraordinary (X) mode as well as narrowband ordinary (O) mode SKR at low frequencies. Within the source region, SKR is emitted just above the X mode cutoff frequency in a hot plasma, with a typical electron-to-wave energy conversion efficiency of ˜1% (2% peak). The knowledge of the k vector is then used to derive the locus of SKR sources in the kronian magnetosphere, which shows X and O components emanating from the same regions. We also compute the associated beaming angle at the source θ‧ = (k, -B) either from (1) in situ measurements or a model of the magnetic field vector (for local to distant sources) or (2) polarization measurements (for local sources). Obtained results, similar for both modes, suggest quasi-perpendicular emission for local sources, whereas the beaming pattern of distant sources appears as a hollow cone with a frequency-dependent constant aperture angle: θ‧ = 75° ± 15° below 300 kHz, decreasing at higher frequencies to reach θ‧ (1000 kHz) = 50° ± 25°. Finally, we investigate quantitatively the SKR polarization state, observed to be strongly elliptical at the source, and quasi-purely circular for sources located beyond approximately two kronian radii. We show that conditions of weak mode coupling are achieved along the raypath, under which the magnetoionic theory satisfactorily describes the evolution of the observed polarization. These results are analyzed comparatively with the auroral kilometric radiation at
Joint effect of polarization and the propagation path of a light beam on its intrinsic structure.
Abdulkareem, Sarkew; Kundikova, Nataliya
2016-08-22
The well-known effects of the spin-orbit interactions of light are manifestations of the pair's mutual influence of the three types of angular momentum (AM) of light, namely, the spin AM, the extrinsic orbital AM and the intrinsic orbital AM. Here we propose a convenient classification of the effects of the spin-orbit interactions of light and we observe one of the new effects in the frame of this classification, which is determined by the joint influence of two types of the AM on the third type of the AM, namely, the influence of the spin AM and the extrinsic orbital AM on the intrinsic orbital AM. We experimentally studied the propagation of circularly polarized light through an optical fiber coiled into a helix. We have found that the spin AM and the helix parameters affect the spatial structure of the radiation transmitted through the optical fiber. We found out that the structure of the light field rotates when changing the sign of circular polarization. The angle of rotation depends on the parameters of the helix. The results can be used to develop the general theory of spinning particles and can find application in metrology methods and nanooptics devices.
Joint effect of polarization and the propagation path of a light beam on its intrinsic structure
Abdulkareem, Sarkew
2016-01-01
The well-known effects of the spin-orbit interaction of light are manifestations of pair mutual influence of the three types of the angular momentum of light, namely, the spin angular momentum, the extrinsic orbital angular momentum and the intrinsic orbital angular momentum. Here we propose the convenient classification of the effects of the spin-orbit interaction of light and we observe one of the new effects in the frame of this classification, which is determined by the joint influence of two types of the angular momentum on the third type of the angular momentum, namely, the influence of the spin angular momentum and the extrinsic orbital angular momentum on the intrinsic orbital angular momentum. We experimentally studied the propagation of circularly polarized light through an optical fiber coiled into a helix. We have found that the spin angular momentum and the helix parameters affect the spatial structure of the radiation transmitted through the optical fiber. We found out that the structure of the ...
Ulrich, Peter B. (Editor); Wilson, Leroy E. (Editor)
1991-01-01
Consideration is given to turbulence at the inner scale, modeling turbulent transport in laser beam propagation, variable wind direction effects on thermal blooming correction, realistic wind effects on turbulence and thermal blooming compensation, wide bandwidth spectral measurements of atmospheric tilt turbulence, remote alignment of adaptive optical systems with far-field optimization, focusing infrared laser beams on targets in space without using adaptive optics, and a simplex optimization method for adaptive optics system alignment. Consideration is also given to ground-to-space multiline propagation at 1.3 micron, a path integral approach to thermal blooming, functional reconstruction predictions of uplink whole beam Strehl ratios in the presence of thermal blooming, and stability analysis of semidiscrete schemes for thermal blooming computation.
Lamy, L; Zarka, P; Canu, P; Schippers, P; Kurth, W S; Mutel, R L; Gurnett, D A; Menietti, J D; Louarn, P
2011-01-01
The Cassini mission crossed the source region of the Saturn kilometric radiation (SKR) on 17 October 2008. On this occasion, the Radio and Plasma Wave Science (RPWS) experiment detected both local and distant radio sources, while plasma parameters were measured in situ by the magnetometer (MAG) and the Cassini Plasma Spectrometer (CAPS). A goniopolarimetric inversion was applied to RPWS 3-antenna electric measurements to determine the wave vector k and the complete state of polarization of detected waves. We identify broadband extraordinary (X) as well as narrowband ordinary (O) mode SKR at low frequencies. Within the source region, SKR is emitted just above the X mode cutoff frequency in a hot plasma, with a typical electron-to-wave energy conversion efficiency of 1% (2% peak). The knowledge of the k-vector is then used to derive the locus of SKR sources in the kronian magnetosphere, that shows X and O components emanating from the same regions. We also compute the associated beaming angle at the source thet...
Institute of Scientific and Technical Information of China (English)
XIAO Jinbiao; LIU Xu; CAI Chun; FAN Hehong; SUN Xiaohan
2006-01-01
A modified alternating direction implicit approach is proposed to discretize the three-dimensional full-vectorial beam propagation method (3D-FV-BPM) formulation along the longitudinal direction. The cross-coupling terms (CCTs) are neglected at the first substep, and then double used at the second substep. The order of two substeps is reversed for each transverse electric field component so that the CCTs are always expressed in an implicit form, thus the calculation is efficient and stable. Based on the multinomial interpolation, a universal finite difference scheme with a high accuracy is developed to approximate the 3D-FV-BPM formulation along the transverse directions, in which the discontinuities of the normal components of the electric field across the abrupt dielectric interfaces are taken into account and can be applied to both uniform and non-uniform grids. The corresponding imaginary-distance procedure is first applied to a buried rectangular and a GaAs-based deeply-etched rib waveguide. The field patterns and the normalized propagation constants of the fundamental and the first order modes are presented and the hybrid nature of the full-vectorial guided-modes is demonstrated, which shows the validity and utility of the present approach. Then the modal characteristics of the deeply- and shallow-etched rib waveguides based on the InGaAsp/InGaAsP strained multiple quantum wells in InP substrate are investigated in detail. The results are necessary for modeling and the design of the planar lightwave circuits or photonic integrated circuits based on these waveguides.
PRICE RIGIDITY AND MONETARY NON-NEUTRALITY IN DEVELOPING COUNTRIES: EVIDENCE FROM NIGERIA
Directory of Open Access Journals (Sweden)
Nathaniel E. Urama
2013-04-01
Full Text Available In an attempt to find out the degree of monetary non-neutrality in Nigeria we started from finding out the size of price rigidity in the country. Computation with Ball and Romer method showed that price rigidity is optimal decision for firms in Nigeria only when the menu cost is well above 2.28% of the firm’s revenue which is on the high side, showing the likelihood of weak price rigidity in the country. Confirming this, the IRFs of the SVAR shows that the response of inflation to nominal shock has only one period lag. These combined results led to a small though persistent response of output to the nominal shock. The result of the study therefore points towards large nominal and small real effect of monetary policy in Nigeria and conclude that monetary policy will be a better option for contractionary plan but not for an expansionary plan.
Dispersive MHD waves and alfvenons in charge non-neutral plasmas
Directory of Open Access Journals (Sweden)
K. Stasiewicz
2008-08-01
Full Text Available Dispersive properties of linear and nonlinear MHD waves, including shear, kinetic, electron inertial Alfvén, and slow and fast magnetosonic waves are analyzed using both analytical expansions and a novel technique of dispersion diagrams. The analysis is extended to explicitly include space charge effects in non-neutral plasmas. Nonlinear soliton solutions, here called alfvenons, are found to represent either convergent or divergent electric field structures with electric potentials and spatial dimensions similar to those observed by satellites in auroral regions. Similar solitary structures are postulated to be created in the solar corona, where fast alfvenons can provide acceleration of electrons to hundreds of keV during flares. Slow alfvenons driven by chromospheric convection produce positive potentials that can account for the acceleration of solar wind ions to 300–800 km/s. New results are discussed in the context of observations and other theoretical models for nonlinear Alfvén waves in space plasmas.
Simulations of Damping of Trapped Particle Asymmetry Modes in Non-Neutral Plasma Columns
Mason, Grant W.; Spencer, Ross L.
2002-11-01
Kabantsev et al.(A. A. Kabantsev, C. F. Driscoll, T. J. Hilsabeck, T. M. O'Neil and J. H.Yu, in Non-Neutral Plasma Physics IV), AIP Conference Proceedings 606, 2001, pp. 277-286 have reported experimental observations and theory for trapped particle asymmetry modes on cylindrical electron columns. In particular, the m=1; k_z=odd mode exhibits strong damping from an unknown mechanism that is conjectured by Kabantsev et al. to be either diffusive mixing of trapped and untrapped populations of particles or spatial Landau damping. We have observed similar damping within a 3-dimensional particle-in-cell simulation. The simulation model does not include diffusive mixing. Spatial Landau damping is also ruled out because the mode frequencies in the simulation intersect the rotation frequency curve outside the plasma. We describe efforts to isolate the mechanism of the damping.
Neutral and Non-Neutral Evolution of Duplicated Genes with Gene Conversion
Directory of Open Access Journals (Sweden)
Jeffrey A. Fawcett
2011-02-01
Full Text Available Gene conversion is one of the major mutational mechanisms involved in the DNA sequence evolution of duplicated genes. It contributes to create unique patters of DNA polymorphism within species and divergence between species. A typical pattern is so-called concerted evolution, in which the divergence between duplicates is maintained low for a long time because of frequent exchanges of DNA fragments. In addition, gene conversion affects the DNA evolution of duplicates in various ways especially when selection operates. Here, we review theoretical models to understand the evolution of duplicates in both neutral and non-neutral cases. We also explain how these theories contribute to interpreting real polymorphism and divergence data by using some intriguing examples.
A Study of Non-Neutral Networks with Usage-based Prices
Altman, E; Caron, S; Kesidis, G; Rojas-Mora, J; Wong, S
2010-01-01
Hahn and Wallsten wrote that network neutrality "usually means that broadband service providers charge consumers only once for Internet access, do not favor one content provider over another, and do not charge content providers for sending information over broadband lines to end users." In this paper we study the implications of non-neutral behaviors under a simple model of linear demand-response to usage-based prices. We take into account advertising revenues and consider both cooperative and non-cooperative scenarios. In particular, we model the impact of side-payments between service and content providers. We also consider the effect of service discrimination by access providers, as well as an extension of our model to non-monopolistic content providers.
DEFF Research Database (Denmark)
Kristensen, M. V.; Lindballe, T.; Kylling, A.
2010-01-01
An experimental characterization of the 3D forces, acting on a trapped polystyrene bead in a counter-propagating beam geometry, is reported. Using a single optical trap with a large working distance (in the BioPhotonics Workstation), we simultaneously measure the transverse and longitudinal trapp...... power of 2x35 mW) for displacements in opposite directions. The Equipartition method is limited by mechanical noise and is shown to be applicable only when the total laser power in a single 10 µm counter-propagating trap is below 2x20 mW....... trapping force constants. Two different methods were used: The Drag force method and the Equipartition method. We show that the counterpropagating beams traps are simple harmonic for small displacements. The force constants reveal a transverse asymmetry as - = 9.7 pN/µm and + = 11.3 pN/µm (at a total laser...
Indian Academy of Sciences (India)
R K Khanna; R C Chouhan
2003-10-01
A somewhat more general analysis for solving spatial propagation characteristics of intense Gaussian beam is presented and applied to the laser beam propagation in step-index proﬁle as well as parabolic proﬁle dielectric ﬁbers with Kerr non-linearity. Considering self-action due to saturating and non-saturating non-linearity in the refractive index, a general theory has been developed without any kind of power series expansion for the dielectric constant as is usually done in other theories that make use of paraxial approximation. Result of the steady state self-focusing analysis indicates that the Kerr non-linearity acts as a perturbation on the radial inhomogeneity due to ﬁber geometry. Analysis indicates that the paraxial rays and peripheral rays focus at different points, indicating aberration effect. Calculated critical power matches with the experimentally reported result.
Energy Technology Data Exchange (ETDEWEB)
Georgoulis, Manolis K. [Research Center for Astronomy and Applied Mathematics of the Academy of Athens, 4 Soranou Efesiou Street, Athens GR-11527 (Greece); Titov, Viacheslav S.; Mikic, Zoran [Predictive Science, Inc., 9990 Mesa Rim Road, San Diego, CA 92121 (United States)
2012-12-10
Using solar vector magnetograms of the highest available spatial resolution and signal-to-noise ratio, we perform a detailed study of electric current patterns in two solar active regions (ARs): a flaring/eruptive and a flare-quiet one. We aim to determine whether ARs inject non-neutralized (net) electric currents in the solar atmosphere, responding to a debate initiated nearly two decades ago that remains inconclusive. We find that well-formed, intense magnetic polarity inversion lines (PILs) within ARs are the only photospheric magnetic structures that support significant net current. More intense PILs seem to imply stronger non-neutralized current patterns per polarity. This finding revises previous works that claim frequent injections of intense non-neutralized currents by most ARs appearing in the solar disk but also works that altogether rule out injection of non-neutralized currents. In agreement with previous studies, we also find that magnetically isolated ARs remain globally current-balanced. In addition, we confirm and quantify the preference of a given magnetic polarity to follow a given sense of electric currents, indicating a dominant sense of twist in ARs. This coherence effect is more pronounced in more compact ARs with stronger PILs and must be of sub-photospheric origin. Our results yield a natural explanation of the Lorentz force, invariably generating velocity and magnetic shear along strong PILs, thus setting a physical context for the observed pre-eruption evolution in solar ARs.
Matala, Andrew P; Ackerman, Michael W; Campbell, Matthew R; Narum, Shawn R
2014-01-01
Mounting evidence of climatic effects on riverine environments and adaptive responses of fishes have elicited growing conservation concerns. Measures to rectify population declines include assessment of local extinction risk, population ecology, viability, and genetic differentiation. While conservation planning has been largely informed by neutral genetic structure, there has been a dearth of critical information regarding the role of non-neutral or functional genetic variation. We evaluated genetic variation among steelhead trout of the Columbia River Basin, which supports diverse populations distributed among dynamic landscapes. We categorized 188 SNP loci as either putatively neutral or candidates for divergent selection (non-neutral) using a multitest association approach. Neutral variation distinguished lineages and defined broad-scale population structure consistent with previous studies, but fine-scale resolution was also detected at levels not previously observed. Within distinct coastal and inland lineages, we identified nine and 22 candidate loci commonly associated with precipitation or temperature variables and putatively under divergent selection. Observed patterns of non-neutral variation suggest overall climate is likely to shape local adaptation (e.g., potential rapid evolution) of steelhead trout in the Columbia River region. Broad geographic patterns of neutral and non-neutral variation demonstrated here can be used to accommodate priorities for regional management and inform long-term conservation of this species. PMID:25067950
Divergence at neutral and non-neutral loci in Drosophila buzzatii populations and their hybrids
DEFF Research Database (Denmark)
Andersen, Ditte Holm; Pertoldi, C.; Loeschcke, Volker;
2008-01-01
The impact of intraspecific hybridisation on fitness and morphological traits depends on the history of natural selection and genetic drift, which may have led to differently coadapted gene-complexes in the parental populations. The divergence at neutral and non-neutral loci between populations c...
智能悬臂梁横向振动的行波解%WAVE PROPAGATION SOLUTION OF SMART CANTILEVER BEAMS TRANSVERSE VIBRATION
Institute of Scientific and Technical Information of China (English)
郭兰满; 黄迪山; 唐亮; 朱晓锦
2011-01-01
介绍智能梁的行波建模方法及其横向振动固有频率的计算方法.行波建模方法主要步骤包括,①求出Timoshenko梁横向振动方程的谐波解.②根据弯曲波的传播特性,给出弯曲波的传递关系；在智能梁上截面尺寸改变处和边界处,根据其连续条件和平衡条件,给出波的反射关系和透射关系.③通过联立智能梁内所有的传递、反射、透射关系,求得整体智能梁的特征方程.文中以智能悬臂梁为算例,通过解析法(包括Timoshenko梁模型和Euler-Bernoulli梁模型)与有限元法得到横向振动频率的比较,验证行波建模方法的有效性.此外,为考虑压电片材料对智能梁整体模型的影响,引入等效弹性模量.%A smart beam is modeled by a wave propagation method, and is used for computing the natural frequency and mode of transverse vibration. The wave propagating modeling contains three steps. Firstly, a general solution in the form of harmonic is given from the governing equation of Timoshenko beam vibration. Secondly, in accordance with traveling manner of elastic bending wave, transfer matrices are determined. Also, the reflection and transmission incited by harmonic disturbance on those cross-section discontinuities and boundaries are derived respectively. Finally, all of these matrices are combined into the equation reflecting the global characteristic of the smart beam. Examples of cantilever beam are presented to illustrate the valid of wave propagation modeling by comparing analytical solutions of Timosheko beam with a FEA( finite element analysis) solution. To consider different materials in the smart beam where the foundational material is mixed with some piezoelectric components, an equivalent elastic modulus was applied in the model of smart beam as a whole.
2008-08-01
Foucault at SAIC. – 14 – The split-step wave optics propagation simulations were all run with a frame rate of 3,000 frames per second. These simulations...formulate the analysis so that such eigen values do not show up. 7). Lastly, I would like to thank Barry Foucault for making his wave optics propagation
Energy Technology Data Exchange (ETDEWEB)
Fiorina, D
1998-01-29
Some systems for the control and the surveillance of fast reactors are based on the characteristics of the ultrasonic wave propagation. We present here the results of a numerical and experimental study of ultrasonic propagation in a thermal turbulent medium. A numerical model, based on the technique of superposition of discrete Fourier modes for representing isotropic and homogeneous turbulence and on the Gaussian beam summation method for calculating the acoustic field, has been implemented in order to study the propagation of a point source wave in a bidimensional turbulent medium. Our model is based on the following principle: the medium is represented by a great number of independent realizations of a turbulent field and for each of them we calculate the acoustic field in a deterministic way. Statistics over a great number of realizations enable us to access to the different quantities of the distorted acoustic field: variance of the time of flight fluctuations, scintillation index and intensity probability density function. In the case of small fluctuations, the results for these three quantities are in a good agreement with analytical solutions. When the level of the fluctuations grows, the model predicts correct evolutions. However, a great sensitivity to the location of a receiver in the vicinity of a caustic has been proved. Calculations in the temporal domain have also been performed. They give an illustration of the possible effects of the turbulence on an impulsion signal. An experimental device, fitted with thermocouples and acoustic transducers, has been used to study the ultrasonic propagation in turbulent water. The different measures permitted to characterize the turbulent field and to get aware of the effect of the turbulence on the acoustic propagation. The acoustical measures agree well with the analytical solution of Chernov and Rytov. They are show the importance of the knowledge of the real spectrum of the fluctuations and the limitations of
Energy Technology Data Exchange (ETDEWEB)
Saberian, E. [Department of Physics, Faculty of Sciences, Azarbaijan Shahid Madani University, 53714-161 Tabriz (Iran, Islamic Republic of); Department of Physics, Faculty of Basic Sciences, University of Neyshabur, Neyshabur (Iran, Islamic Republic of); Esfandyari-Kalejahi, A.; Rastkar-Ebrahimzadeh, A.; Afsari-Ghazi, M. [Department of Physics, Faculty of Sciences, Azarbaijan Shahid Madani University, 53714-161 Tabriz (Iran, Islamic Republic of)
2013-03-15
The propagation of ion-acoustic (IA) solitons is studied in a plasma system, comprised of warm ions and superthermal (Kappa distributed) electrons in the presence of an electron-beam by using a hydrodynamic model. In the linear analysis, it is seen that increasing the superthermality lowers the phase speed of the IA waves. On the other hand, in a fully nonlinear investigation, the Mach number range and characteristics of IA solitons are analyzed, parametrically and numerically. It is found that the accessible region for the existence of IA solitons reduces with increasing the superthermality. However, IA solitons with both negative and positive polarities can coexist in the system. Additionally, solitary waves with both subsonic and supersonic speeds are predicted in the plasma, depending on the value of ion-temperature and the superthermality of electrons in the system. It is examined that there are upper critical values for beam parameters (i.e., density and velocity) after which, IA solitary waves could not propagate in the plasma. Furthermore, a typical interaction between IA waves and the electron-beam in the plasma is confirmed.
Almehmadi, Fares S.; Chatterjee, Monish R.
2014-12-01
Using intensity feedback, the closed-loop behavior of an acousto-optic hybrid device under profiled beam propagation has been recently shown to exhibit wider chaotic bands potentially leading to an increase in both the dynamic range and sensitivity to key parameters that characterize the encryption. In this work, a detailed examination is carried out vis-à-vis the robustness of the encryption/decryption process relative to parameter mismatch for both analog and pulse code modulation signals, and bit error rate (BER) curves are used to examine the impact of additive white noise. The simulations with profiled input beams are shown to produce a stronger encryption key (i.e., much lower parametric tolerance thresholds) relative to simulations with uniform plane wave input beams. In each case, it is shown that the tolerance for key parameters drops by factors ranging from 10 to 20 times below those for uniform plane wave propagation. Results are shown to be at consistently lower tolerances for secure transmission of analog and digital signals using parameter tolerance measures, as well as BER performance measures for digital signals. These results hold out the promise for considerably greater information transmission security for such a system.
Institute of Scientific and Technical Information of China (English)
蔡阳健; 林强
2002-01-01
The generalized Collins formula for partially coherent beams through axially non-symmetrical optical systems in the spatial-frequency domain is derived by means of the tensor method. Based on this formula, the tensor ABCD law in the spatial-frequency domain for partially coherent twisted anisotropic Gaussian-Schell model (GSM) beams is derived, which governs the transformation of the twisted anisotropic GSM beams in the spatialfrequency domain. An example of an application is provided.
Pramanik, Sourav; Kuznetsov, V. I.; Gerasimenko, A. B.; Chakrabarti, Nikhil
2016-10-01
An analytical study is presented on the steady states of a plasma diode that is uniformly occupied by infinitely massive ions of constant density and driven by a cold electron beam in the presence of an external transverse magnetic field. In contrast to our previous work [Pramanik et al., Phys. Plasmas 23, 062118 (2016)], here, we investigate the case when electrons are reflected back to the emitter by the magnetic field for arbitrary values of the neutralization parameter. Using the emitter electric field as a characteristic parameter, the steady-state solutions have been evaluated for the specific values of the diode gap, applied voltage, neutralization parameter, and magnetic field strength. It was found that unlike vacuum diodes (e.g., the Bursian diode), steady state solutions also exist for negative values of the emitter field strength. In case of the Bursian diode, only a single type of solutions (Bursian branches) was observed. However, for the Pierce diode, the new family of solutions appeared along with the Bursian ones. In the absence of the external magnetic field as well as when it is weak, the potential distribution shows a wavy nature. However, when the Larmor radius was ten times the beam Debye length, the wavy potential profile and non-Bursian branches disappeared. Based on this phenomenon, a non-neutral diode can be used to operate fast electronic switches.
Huang, Jiayao; Liang, Zijie; Deng, Fu; Yu, Weihao; Zhao, Ruihuang; Chen, Bo; Yang, Xiangbo; Deng, Dongmei
2015-11-01
The propagation of right-hand circularly polarized Airy-Gaussian beams (RHCPAiGBs) through slabs of right-handed materials (RHMs) and left-handed materials (LHMs) is investigated analytically and numerically with the transfer matrix method. An approximate analytical expression for the RHCPAiGBs passing through a paraxial ABCD optical system is derived on the basis of the Huygens diffraction integral formula. The intensity and the phase distributions of the RHCPAiGBs through RHMs and LHMs are demonstrated. The influence of the parameter χ0 on the propagation of RHCPAiGBs through RHM and LHM slabs is investigated. The RHCPAiGBs possess transverse-momentum currents, which shows that the physics underlying this intriguing accelerating effect is that of the combined contributions of the transverse spin and transverse orbital currents. Additionally, we go a step further to explore the radiation force including the gradient force and scattering force of the RHCPAiGBs.
Institute of Scientific and Technical Information of China (English)
LI Yan-Ping; YU Jin-Zhong; XIA Jin-Song; Chen Shao-Wu
2004-01-01
@@ Imaginary-distance beam propagation method under the perfectly matched layer boundary condition is applied to judge single-mode behaviour of optical waveguides, for the first time to our knowledge. A new kind of siliconon-insulator-based rib structures with half-circle cross-section is presented. The single-mode behaviour of this kind of waveguide with radius 2μm is investigated by this method. It is single-mode when the slab height is not smaller than the radius.
Korotkova, Olga; Farwell, Nathan; Mahalov, Alex
Calculations of the second-order statistical characteristics of a polarized, lowest-order Gaussian beam which propagates through a jet-stream layer, in the upper troposphere and lower stratosphere (UTLS) environment, are carried out. Comparison of the results based on the refractive-index structure parameter img style="vertical-align: text-bottom;" class="inlinematheqn" src="/ampp/image?path=/716100762/916167779/twrm_a_412938_o_ilm0001.gif" alt="TWRM_A_412938_O_XML_IMAGESTWRM_A_412938_O_ILM0001.gif" border="0" /> as predicted by a Hufnagel-Valley model and based on data taken at a recent campaign of measurements and high-resolution numerical simulations shows that the jet-stream can significantly affect the intensity distribution and spreading of the beam, especially at high zenith angles.
Shimozuma, Takashi; Kobayashi, Sakuji; Ito, Satoshi; Ito, Yasuhiko; Kubo, Shin; Yoshimura, Yasuo; Nishiura, Masaki; Igami, Hiroe; Takahashi, Hiromi; Mizuno, Yoshinori; Okada, Kohta; Mutoh, Takashi
2016-01-01
In a high-power electron cyclotron resonance heating (ECRH) system for plasma heating, a long-distance and low-loss transmission system of the millimeter wave is required. A real-time monitor of the millimeter-wave beam position and its intensity profile, which can be used in a high-power, evacuated, and cooled transmission line, is proposed, designed, manufactured, and tested. The beam-position and profile monitor (BPM) consists of a reflector, Peltier-device array, and a heat-sink, which is installed in the reflector-plate of a miterbend. The BPM was tested using both simulated electric heater power and high-power gyrotron output power. The profile obtained from the monitor using the gyrotron output was well agreed with the burn patter on a thermal sensitive paper. Methods of data analysis and mode-content analysis of a propagating millimeter-wave in the corrugated waveguide are proposed.
Yu, Hao; Rossi, Giammarco; Braglia, Andrea; Perrone, Guido
2016-08-10
The paper presents the development of a tool based on a back-propagation artificial neural network to assist in the accurate positioning of the lenses used to collimate the beam from semiconductor laser diodes along the so-called fast axis. After training using a Gaussian beam ray-equivalent model, the network is capable of indicating the tilt, decenter, and defocus of such lenses from the measured field distribution, so the operator can determine the errors with respect to the actual lens position and optimize the diode assembly procedure. An experimental validation using a typical configuration exploited in multi-emitter diode module assembly and fast axis collimating lenses with different focal lengths and numerical apertures is reported.
Yousefi, Masoud; Golmohammady, Shole; Mashal, Ahmad; Kashani, Fatemeh Dabbagh
2015-11-01
In this paper, on the basis of the extended Huygens-Fresnel principle, a semianalytical expression for describing on-axis scintillation index of a partially coherent flat-topped (PCFT) laser beam of weak to moderate oceanic turbulence is derived; consequently, by using the log-normal intensity probability density function, the bit error rate (BER) is evaluated. The effects of source factors (such as wavelength, order of flatness, and beam width) and turbulent ocean parameters (such as Kolmogorov microscale, relative strengths of temperature and salinity fluctuations, rate of dissipation of the mean squared temperature, and rate of dissipation of the turbulent kinetic energy per unit mass of fluid) on propagation behavior of scintillation index, and, hence, on BER, are studied in detail. Results indicate that, in comparison with a Gaussian beam, a PCFT laser beam with a higher order of flatness is found to have lower scintillations. In addition, the scintillation index and BER are most affected when salinity fluctuations in the ocean dominate temperature fluctuations.
Kaganovich, I. D.; Sydorenko, D.
2016-11-01
This paper presents a study of the two-stream instability of an electron beam propagating in a finite-size plasma placed between two electrodes. It is shown that the growth rate in such a system is much smaller than that of an infinite plasma or a finite size plasma with periodic boundary conditions. Even if the width of the plasma matches the resonance condition for a standing wave, a spatially growing wave is excited instead with the growth rate small compared to that of the standing wave in a periodic system. The approximate expression for this growth rate is γ≈(1 /13 )ωpe(nb/np)(L ωpe/vb)ln (L ωpe/vb)[1 -0.18 cos (L ωpe/vb+π/2 ) ] , where ωpe is the electron plasma frequency, nb and np are the beam and the plasma densities, respectively, vb is the beam velocity, and L is the plasma width. The frequency, wave number, and the spatial and temporal growth rates, as functions of the plasma size, exhibit band structure. The amplitude of saturation of the instability depends on the system length, not on the beam current. For short systems, the amplitude may exceed values predicted for infinite plasmas by more than an order of magnitude.
Dugast, Anne-Sophie; Chan, Ying; Hoffner, Michelle; Licht, Anna; Nkolola, Joseph; Li, Hualin; Streeck, Hendrik; Suscovich, Todd J; Ghebremichael, Musie; Ackerman, Margaret E; Barouch, Dan H; Alter, Galit
2014-01-01
Recent immune correlates analysis from the RV144 vaccine trial has renewed interest in the role of non-neutralizing antibodies in mediating protection from infection. While neutralizing antibodies have proven difficult to induce through vaccination, extra-neutralizing antibodies, such as those that mediate antibody-dependent cellular cytotoxicity (ADCC), are associated with long-term control of infection. However, while several non-neutralizing monoclonal antibodies have been tested for their protective efficacy in vivo, no studies to date have tested the protective activity of naturally produced polyclonal antibodies from individuals harboring potent ADCC activity. Because ADCC-inducing antibodies are highly enriched in elite controllers (EC), we passively transferred highly functional non-neutralizing polyclonal antibodies, purified from an EC, to assess the potential impact of polyclonal non-neutralizing antibodies on a stringent SHIV-SF162P3 challenge in rhesus monkeys. Passive transfer of a low-dose of ADCC inducing antibodies did not protect from infection following SHIV-SF162P3 challenge. Passively administered antibody titers and gp120-specific, but not gp41-specific, ADCC and antibody induced phagocytosis (ADCP) were detected in the majority of the monkeys, but did not correlate with post infection viral control. Thus these data raise the possibility that gp120-specific ADCC activity alone may not be sufficient to control viremia post infection but that other specificities or Fc-effector profiles, alone or in combination, may have an impact on viral control and should be tested in future passive transfer experiments.
DEFF Research Database (Denmark)
Hvid, Christian A.; Elstrøm, Ulrik V.; Jensen, Kenneth
2016-01-01
treatment fraction. An indirect approach, propagating contours to the first CBCT and from there to the last CBCT was also tested. Propagated contours were compared to manually corrected contours by Dice similarity coefficient (DSC) and Hausdorff distance (HD). Dose was recalculated on CBCTs and dosimetric...... consequences of uncertainties in DIR were reviewed. Results: Mean DSC values of ≥0.8 were considered adequate and were achieved in tongue base (0.91), esophagus (0.85), glottic (0.81) and supraglottic larynx (0.83), inferior pharyngeal constrictor muscle (0.84), spinal cord (0.89) and all salivary glands...... automated and corrected contours was within ±2.5% of planed dose except for esophagus inlet (-4.5%) and esophagus (5.0%) for the last CBCT using indirect propagation. Conclusion: Compared to manually corrected contours, the DIR algorithm was accurate for use in CBCT images of HNC patients and the minor...
Dutta, Moumita; Natarajan, Kamaraju; Betal, Soutik; Prasankumar, Rohit P; Bhalla, Amar S; Guo, Ruyan
2017-09-14
Magnetoelastoelectric coupling in an engineered biphasic multiferroic nanocomposite enables a novel magnetic field direction-defined propagation control of terahertz (THz) waves. These core-shell nanoparticles are comprised of a ferromagnetic cobalt ferrite core and a ferroelectric barium titanate shell. An assembly of these nanoparticles, when operated in external magnetic fields, exhibits a controllable amplitude modulation when the magnetic field is applied antiparallel to the THz wave propagation direction; yet the same assembly displays an additional phase modulation when the magnetic field is applied along the propagation direction. While field-induced magnetostriction of the core leads to amplitude modulation, phase modulation is a result of stress-mediated piezoelectricity of the outer ferroelectric shell.
Box, M. A.; Deepak, A.
1981-01-01
The propagation of photons in a medium with strongly anisotropic scattering is a problem with a considerable history. Like the propagation of electrons in metal foils, it may be solved in the small-angle scattering approximation by the use of Fourier-transform techniques. In certain limiting cases, one may even obtain analytic expressions. This paper presents some of these results in a model-independent form and also illustrates them by the use of four different phase-function models. Sample calculations are provided for comparison purposes
Kashani, Fatemeh Dabbagh; Yousefi, Masoud
2016-08-10
In this research, based on an analytical expression for cross-spectral density (CSD) matrix elements, coherence and polarization properties of phase-locked partially coherent flat-topped (PCFT) radial array laser beams propagating through weak oceanic turbulence are analyzed. Spectral degrees of coherence and polarization are analytically calculated using CSD matrix elements. Also, the effective width of spatial degree of coherence (EWSDC) is calculated numerically. The simulation is done by considering the effects of source parameters (such as radius of the array setup's circle, effective width of the spectral degree of coherence, and wavelength) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature and salinity fluctuations, Kolmogorov micro-scale, and rate of dissipation of the mean squared temperature) in detail. Results indicate that any change in the amount of turbulence factors that increase the turbulence power reduces the EWSDC significantly and causes the reduction in the degree of polarization, and occurs at shorter propagation distances but with smaller magnitudes. In addition, being valid for all conditions, the degradation rate of the EWSDC of Gaussian array beams are more in comparison with the PCFT ones. The simulation and calculation results are shown by graphs.
Manning, Robert M.
1988-01-01
Rain attenuation propagation data for 68 cities within the coverage area of the multiple beam and steerable antennas of the Advanced Communications Technology Satellite (ACTS) are presented. These data provide the necessary data base for purposes of communication link power budgeting and rain attenuation mitigation controller design. These propagation parameters are derived by applying the ACTS Rain Attenuation Prediction Model to these 68 locations. The propagation parameters enumerated in tabular form for each location are as follows: (1) physical description of the link and location (e.g., latitude, longitude, antenna elevation angle, etc.), link availability versus attenuation margin (also in graphical form), fading time across fade depths of 3, 5, 8, and 15 dB versus fade duration, and required fade control response time for controller availabilities of 99.999, 99.99, 99.9, and 99 percent versus sub-threshold attenuation levels. The data for these specific locations can be taken to be representative of regions near these locations.
Zhang, Hua; Mu, Jianwei; Huang, Wei-Ping
2007-09-01
For realization of highly integrated optical circuits, various metallic nanostructures supporting the propagation of surface plasmon polaritons have been extensively studied experimentally and theoretically in recent years. This paper reports on the development of a numerically stable and accurate finite-difference-based bidirectional beam propagation method (FD-BiBPM) for analyzing piecewise z-invariant plasmonic structures. Our method is developed based on the scattering operators. The adoption of complex coefficient rational approximations to the square root operator allows to correctly model the propagation of evanescent modes excited at discontinuity interfaces. In view of the large index contrast at metal-dielectric interfaces, a fourth-order accurate finite difference formulation for discretization is incorporated to the present method and its fine treatment of these interfaces guarantees accuracy. By using the present method, the reflection and transmission spectra of the Bragg gratings consisting of a thin metal film embedded in dielectric medium and an array of equidistant metal ridges on each side of the film are calculated. The good agreement of our results with the previously reported simulations illustrates the potential of the newly developed FD-BiBPM for the analysis of longrange surface plasmon polariton (LRSPP) waves guided along the described Bragg gratings.
Chen, Chunyi; Yang, Huamin; Kavehrad, Mohsen; Tong, Shoufeng; Li, Yanfang
2014-12-01
Two distinct methods based on which two different quadratic-form expressions for the two-source spherical wave structure function (WSF) can be derived are reviewed. The validity of closed-form expressions for the beam-wave cross-spectral density function (CSDF) due to generalized atmospheric turbulence featuring an arbitrary spectral index ranging from 3 to 4, developed based on the quadratic two-source spherical WSFs, is examined in detail. New formulations for the conditions under which the said closed-form expressions for the beam-wave CSDF are strictly valid are developed and several novel interesting findings are elucidated. In particular, the closed-form beam-wave CSDF derived based on the small-separation asymptotic two-source spherical WSF can be considered a rigorous asymptotic solution under the strong-turbulence condition only when the separation distance between the two observation points is much smaller than the inner scale of turbulence; moreover it is also a rigorous asymptotic solution when a certain relation among the initial beam radius, initial transverse coherence width and inner scale holds, regardless of the turbulence strength and spectral index. On the other hand, the accuracy of the closed-form beam-wave CSDF derived based on the large-separation-approximation two-source spherical WSF depends on the spectral index, and a spectral index closer to 4 results in better accuracy.
Kawai, K.; Sakamoto, M.; Noda, K.; Sasaki, T.; Kawatsuki, N.; Ono, H.
2017-02-01
Liquid crystal grating with three-dimensionally modulated anisotropic structure is fabricated by one-step exposure of an empty glass cell whose inner walls are coated with photocrosslinkable polymer liquid crystals to four-beam polarization interference UV beams. The diffraction properties were probed with a 633 nm wavelength laser and a 532 nm wavelength laser which were the coaxial incident. The novel properties, which diffraction directions are threedimensionally different depending on the wavelengths, are realized by the resultant liquid crystal grating. Furthermore, the resultant liquid crystal grating can be also applied to an advanced polarizing beam splitter which opposite circular polarization and linear polarizations are diffracted simultaneously. These diffraction properties were well-explained by Jones calculus. The resultant liquid crystal grating has the plural of the functions of optical elements such as wave plates, polarization beam splitter, dichroic beam splitter, Wollaston/Rochon prism, and tunable wavelength filter. Therefore, the resultant liquid crystal grating can contribute to miniaturization, sophistication, and cost reduction of optical systems using for, such as optical measurement, communication, and information processing.
Song, Sung-Jin; Kim, Chang-Hwan
2002-05-01
Phased array transducers are quite often mounted on solid wedges with specific angles in many practical ultrasonic inspections of thin plates phased array techniques with testing set-up, it is essential to have thorough understanding on the characteristics of radiation beam pattern produced in the interrogated medium. To address such a need, this paper proposes a systematic way to calculate full 3-D radiation beam patterns produced in the interrogated solid medium by phased array transducers mounted on a solid wedge. In order to investigate the characteristics of radiation beam patterns in steel, simulation is carried out for 7.5 MHz array transducers mounted on an acrylic wedge with the angle of 15.45 degrees with various of steering angles and/or focal planes.
Kaganovich, I D
2015-01-01
This paper presents a study of the two-stream instability of an electron beam propagating in a finite-size plasma placed between two electrodes. It is shown that the growth rate in such a system is much smaller than that of an infinite plasma or a finite size plasma with periodic boundary conditions. Even if the width of the plasma matches the resonance condition for a standing wave, a spatially growing wave is excited instead with the growth rate small compared to that of the standing wave in a periodic system. The approximate expression for this growth rate is $\\gamma \\approx (1/13)\\omega_{pe}(n_{b}/n_{p})(L\\omega_{pe}/v_{b})\\ln (L\\omega_{pe}/v_{b})[ 1-0.18\\cos ( L\\omega_{pe}/v_{b}+{\\pi }/{2}) ]$, where $\\omega_{pe}$ is the electron plasma frequency, $n_{b}$ and $n_{p}$ are the beam and the plasma densities, respectively, $v_{b}$ is the beam velocity, and $L$ is the plasma width. The frequency, wave number and the spatial and temporal growth rates as functions of the plasma size exhibit band structure.
Measurement of scintillation and link margin for laser beam propagation on 3.5-km urbanised path
Institute of Scientific and Technical Information of China (English)
Feng Pan; Qiqi Han; Jing Ma; Liying Tan
2007-01-01
An experiment of laser propagation was carried out at the urban terrain range of 3.5 km during the period of March to May of 2006. The received intensity scintillations and atmosphere turbulence strength in complex urban atmosphere circumstance were simultaneously measured concentratively. The results show the statistical characteristics of irradiance scintillation and atmosphere turbulence strength and link fade margin for urban free-space optical links.
Spatially-resolved spectroscopy provides a means for measuring the optical properties of biological tissues, based on analytical solutions to diffusion approximation for semi-infinite media under the normal illumination of infinitely small size light beam. The method is, however, prone to error in m...
The Effect of Multipole-Enhanced Diffusion on the Joule Heating of a Cold Non-Neutral Plasma
Chapman, Steven Francis
One proposed technique for trapping anti-atoms is to superimpose a Ioffe-Pritchard style magnetic-minimum neutral trap on a standard Penning trap used to trap the charged atomic constituents. Adding a magnetic multipole field in this way removes the azimuthal symmetry of the ideal Penning trap and introduces a new avenue for radial diffusion. Enhanced diffusion will lead to increased Joule heating of a non-neutral plasma, potentially adversely affecting the formation rate of anti-atoms and increasing the required trap depth. We present a model of this effect, along with an approach to minimizing it, with comparison to measurements from an intended anti-atom trap.
Vaisseau, X.; Morace, A.; Touati, M.; Nakatsutsumi, M.; Baton, S. D.; Hulin, S.; Nicolaï, Ph.; Nuter, R.; Batani, D.; Beg, F. N.; Breil, J.; Fedosejevs, R.; Feugeas, J.-L.; Forestier-Colleoni, P.; Fourment, C.; Fujioka, S.; Giuffrida, L.; Kerr, S.; McLean, H. S.; Sawada, H.; Tikhonchuk, V. T.; Santos, J. J.
2017-05-01
Collimated transport of ultrahigh intensity electron current was observed in cold and in laser-shocked vitreous carbon, in agreement with simulation predictions. The fast electron beams were created by coupling high-intensity and high-contrast laser pulses onto copper-coated cones drilled into the carbon samples. The guiding mechanism—observed only for times before the shock breakout at the inner cone tip—is due to self-generated resistive magnetic fields of ˜0.5 - 1 kT arising from the intense currents of fast electrons in vitreous carbon, by virtue of its specific high resistivity over the range of explored background temperatures. The spatial distribution of the electron beams, injected through the samples at different stages of compression, was characterized by side-on imaging of hard x-ray fluorescence.
Joglekar, D. M.; Mitra, M.
2016-08-01
An analytical-numerical method, based on the use of wavelet spectral finite elements (WSFE), is presented for studying the nonlinear interaction of flexural waves with a breathing crack present in a slender beam. The cracked beam is discretized using wavelet spectral finite elements which use compactly supported Daubechies scaling functions for approximating the temporal dependence of the transverse displacement. Rotational spring is used to model the open crack condition, and behavior of the beam in closed-crack condition is assumed to be similar to that of an intact beam. An intermittent switching between the open- and closed-crack conditions simulates crack-breathing, leading to a set of nonlinear equations which is solved using an iterative method. Results of the proposed method are compared with those obtained using the Fourier spectral finite element (FSFE) and 1D finite element (FE) methods, which show a close agreement. Existence of the higher-order harmonic components, indicative of the crack-induced bilinearity, is confirmed in the frequency domain response. Moreover, the time domain analysis reveals separation of harmonics resulting from the dispersive nature of the waveguide, which is further used for localizing the damage. A parametric study is presented to bring out the influence of crack-severity and -location on the extent of harmonic separation and on the relative strength of higher order harmonic. In addition to elaborating the use of WSFE in addressing the nonlinear wave-damage interaction, results of the present investigation can be potentially useful in devising strategies for an inverse analysis.
Goto, Yuta; Okamoto, Atsushi; Toda, Masataka; Kuno, Yasuyuki; Nozawa, Jin; Ogawa, Kazuhisa; Tomita, Akihisa
2016-08-01
We propose a digital confocal microscope using a virtual 4f-system based on numerical beam propagation for depth measurement without mechanical scanning. In our technique, the information in the sample target along the depth direction is obtained by defocusing the virtual 4f-system, which consists of two virtual lenses arranged in a computer simulation. The principle of our technique is completely different from that of the mechanical scanning method used in the conventional confocal microscope based on digital holography. By using the virtual 4f-system, the measurement and exposure time can be markedly reduced because multilayered tomographic images are generated using a single measurement. In this study, we tested the virtual depth imaging technique by measuring cover glasses arranged along the depth direction.
Directory of Open Access Journals (Sweden)
Nicola Acocella
2012-04-01
Full Text Available The main aim of this article is to investigate the sources of money non-neutrality in policy games involving one or more trade unions in simple analytical settings. We show that there are common roots in the non-neutrality results so far obtained in apparently different contexts. JEL Codes: E52, J51Keywords: Money, Policy, Trade Unions, Union
Directory of Open Access Journals (Sweden)
Brian J Laidlaw
2013-03-01
Full Text Available Seasonal epidemics of influenza virus result in ∼36,000 deaths annually in the United States. Current vaccines against influenza virus elicit an antibody response specific for the envelope glycoproteins. However, high mutation rates result in the emergence of new viral serotypes, which elude neutralization by preexisting antibodies. T lymphocytes have been reported to be capable of mediating heterosubtypic protection through recognition of internal, more conserved, influenza virus proteins. Here, we demonstrate using a recombinant influenza virus expressing the LCMV GP33-41 epitope that influenza virus-specific CD8+ T cells and virus-specific non-neutralizing antibodies each are relatively ineffective at conferring heterosubtypic protective immunity alone. However, when combined virus-specific CD8 T cells and non-neutralizing antibodies cooperatively elicit robust protective immunity. This synergistic improvement in protective immunity is dependent, at least in part, on alveolar macrophages and/or other lung phagocytes. Overall, our studies suggest that an influenza vaccine capable of eliciting both CD8+ T cells and antibodies specific for highly conserved influenza proteins may be able to provide heterosubtypic protection in humans, and act as the basis for a potential "universal" vaccine.
Research on laser beam propagation characteristic of Cassegrain optical antenna%卡塞格伦光学天线光传输特性研究
Institute of Scientific and Technical Information of China (English)
何文森; 杨华军; 江萍
2014-01-01
The laser beam propagation characteristic of Cassegrain optical antenna is analyzed theoretically.Several important factors (includes antenna gain factor,angle factor,distance factor,obscuration ratio,etc.)affecting the quality of laser beam in space optical communication have been researched in detail.This provides a theoretical basis for practical research on light-transfer characteristic of optical antenna in atmospheric laser communication system and has important practical value.%对卡塞格伦光学天线光传输特性进行了理论分析，重点研究了影响光学天线光传输质量的几个重要因素，并进行了测试结果与仿真验证。为实际研究大气激光通信系统中光学天线的光传输特性提供了理论依据，具有重要的实用价值。
Review of nondiffracting Bessel beams
Lapointe, Michael R.
1991-01-01
The theory of nondiffracting beam propagation and experimental evidence for nearly-nondiffractive Bessel beam propagation are reviewed. The experimental results are reinterpreted using simple optics formulas, which show that the observed propagation distances are characteristic of the optical systems used to generate the beams and do not depend upon the initial beam profiles. A set of simple experiments are described which support this interpretation. It is concluded that nondiffracting Bessel beam propagation has not yet been experimentally demonstrated.
Energy Technology Data Exchange (ETDEWEB)
Paroli, B., E-mail: bruno.paroli@unimi.it [Dipartimento di Fisica, Universitá degli Studi di Milano and INFN Sezione di Milano, via G. Celoria, 16, 20133 Milano (Italy); Chiadroni, E.; Ferrario, M. [INFN-LNF, via E. Fermi, 00044 Frascati (Italy); Mostacci, A. [“La Sapienza” University, SBAI Department, via A. Scarpa 14, 00161 Rome (Italy); INFN-LNF, via E. Fermi, 00044 Frascati (Italy); Petrillo, V.; Potenza, M.A.C.; Rossi, A.R.; Serafini, L. [Dipartimento di Fisica, Universitá degli Studi di Milano and INFN Sezione di Milano, via G. Celoria, 16, 20133 Milano (Italy)
2015-07-15
A 3-dimensional time-domain simulation of X-ray produced by a laser wakefield accelerated electron beam was performed in order to know its properties like intensity, spectrum, divergence and coherence. Particular attention was paid to the coherence around the acceleration axis. The broad spectrum of betatron radiation (1–10 keV) leads to a short coherence length. Nevertheless we observe that under particular detection condition the spatial coherence has a characteristic enlargement. We give a simplified interpretation of this effect in terms of phase shift of the electric field on a virtual detector. Moreover we describe a near field scattering technique to characterize the betatron radiation. This diagnostics will be used to map the transverse spatio-temporal coherence of X-ray radiation in the laser wakefield accelerator under development at Frascati National Laboratories (LNF)
Paroli, B.; Chiadroni, E.; Ferrario, M.; Mostacci, A.; Petrillo, V.; Potenza, M. A. C.; Rossi, A. R.; Serafini, L.
2015-07-01
A 3-dimensional time-domain simulation of X-ray produced by a laser wakefield accelerated electron beam was performed in order to know its properties like intensity, spectrum, divergence and coherence. Particular attention was paid to the coherence around the acceleration axis. The broad spectrum of betatron radiation (1-10 keV) leads to a short coherence length. Nevertheless we observe that under particular detection condition the spatial coherence has a characteristic enlargement. We give a simplified interpretation of this effect in terms of phase shift of the electric field on a virtual detector. Moreover we describe a near field scattering technique to characterize the betatron radiation. This diagnostics will be used to map the transverse spatio-temporal coherence of X-ray radiation in the laser wakefield accelerator under development at Frascati National Laboratories (LNF).
Ordenes-Huanca, C.; Velazquez, L.
2016-09-01
Experimental studies of non-neutral plasmas in magnetic traps undergo, in some degree of affectation, the incidence of evaporation. For example, the existence of a finite threshold energy {{\\varepsilon}c} for the escaping of plasma constituents can be favored by the external electrostatic forces near the grounded conducting walls of a cylindrical Penning trap. In contrast, the conventional statistical mechanics description of these situations is performed assuming the existence of a rigorous thermodynamic equilibrium (Dubin and O’Neil 1999 Rev. Mod. Phys. 71 87), dismissing thus the existence of evaporation effects. We propose in this work a two-dimensional toy model that describes the incidence of evaporation on thermo-statistics of a pure non-neutral plasma (a system composed of a single charge species like an infinitely long electron column). Considering the existing connections between the macroscopic descriptions of pure non-neutral plasmas and astrophysical systems, the treatment of evaporation along a quasi-stationary regime is developed here in analogy to some astrophysical models proposed in the literature. We start from a regularized microcanonical description that only considers those microscopic configurations where particles are trapped inside a confinement region of radius R c , which is implemented introducing a truncation of their velocity spectrum. These arguments lead us to a statistical procedure to predict the quasi-stationary particles distribution n≤ft(\\mathbf{r}\\right) similar to the maximum entropy approach. According to our analysis, the influence of evaporation for a non-zero temperature T crucially depends on the saturation parameter δ ={{r}\\text{B}}/{{R}c} , whose admissible values are located in the interval 0<δ <1 , with r B being the radius of Billouin steady state that appears in the limit T\\to 0 . The theoretical profiles predicted from this model are then compared to the metastable radial density distribution reported by
Ryazanov, A I; Vasilyev, Ya S; Ferrari, A
2014-01-01
The interaction of 450GeV protons with copper, which is the material of the collimators of the Large Hadron Collider, has been theoretically studied. A theoretical model for the formation and propagation of shock waves has been proposed on the basis of the anal ysis of the energy released by a proton beam in the electronic subsystem of the material owing to the deceleration of secondary particles appearing in nuclear reactions induced by this beam on the electronic subsy stem of the material. The subsequent transfer of the energy from the excited electronic subsystem to the crystal lattice through the electron–phonon interaction has been described within the thermal spike model [I.M. Lifshitz, M.I. Kaganov, and L.V. Tanatarov, Sov. Phys. JETP 4 , 173 (1957); I.M. Lifshitz, M.I. Kaganov, and L.V. Tanatarov, At. Energ. 6 , 391 (1959); K. Yasui, Nucl. Instrum. Methods Phys. Res., Sect. B 90 , 409 (1994)]. The model of the formation of shock waves involves energy exchange processes between excited electronic an...
Energy Technology Data Exchange (ETDEWEB)
Deng Peng; Yuan Xiuhua; Zeng Yanan; Zhao Ming; Luo Hanjun, E-mail: yuanxh@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei (China)
2011-02-01
In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received signal, affecting link performance. Most theoretical treatments have been described by Kolmogorov's power spectral density model through weak turbulence with constant wind speed. However, several experiments showed that Kolmogorov theory is sometimes incomplete to describe atmospheric turbulence properly, especially through the strong turbulence with variable wind speed, which is known to contribute significantly to the turbulence in the atmosphere. We present an optical turbulence model that incorporates into variable wind speed instead of constant value, a non-Kolmogorov power spectrum that uses a generalized exponent instead of constant standard exponent value 11/3, and a generalized amplitude factor instead of constant value 0.033. The free space optical communication performance for a Gaussian beam wave of scintillation index, mean signal-to-noise ratio
部分相干径向偏振光在自由空间中的传输%The Propagation of Partially Coherent Radially Polarized Beam in Free Space
Institute of Scientific and Technical Information of China (English)
林惠川
2011-01-01
Based on the propagation law of the cross-spectral density function and the unified theory of coherence and polarization of partially coherent beams,the transmission characteristics of partially coherent radially polarized doughnut beam in free space is investigated.It is found that,after propagated through free space,the intensity distribution and degree of polarization changed,which induced by coherence of the partially coherent beams.The doughnut beam spot of the partially coherent radially polarized beam becomes a circular Gaussian beam.In addition,different initial coherence of the partially coherent beam induced different change situation in propagation.%基于交叉谱密度函数的传输定律及相干与偏振的统一理论,研究了部分相干径向偏振光在自由空间中的传输。结果表明：由于相干诱导作用,部分相干径向偏振光在自由空间中传输时其光强与偏振度都发生了变化,传输过程中径向偏振光的光强由原来的空心逐渐变为平顶接着变为高斯型,而不同的相干度下光束的偏振度在传输过程中的变化情况不同。
贝塞尔高斯光束通过硬边光阑的衍射损耗%Losses of Bessel-Gaussian Beams Propagating through a Hard-Edge Aperture
Institute of Scientific and Technical Information of China (English)
王莉
2001-01-01
The losses Bessel-Gaussian beams, a kind of non-diffracting beam,propagating through a hard aperture are studied, and a general formula is derived. As an example of applications, numerical calculation is performed to calculate the losses of Bessel-Gaussian beams propagating through a circular aperture. The obtained results are analyzed and discussed. The proposed method can also be applied to calculation of the losses of other types of laser beams propagating through a hard-edge aperture.%对无衍射光束——贝塞尔高斯光束通过硬边光阑时的功率损耗作了研究，给出了普适的损耗公式。作为应用举例，对零阶贝塞尔高斯光束通过圆孔硬边光阑时的衍射损耗作了详细的计算。对计算结果进行了分析和讨论。该方法还可用于其它光束通过硬边光阑的衍射损耗计算。
Propagation Properties of Dark Hollow Beams in Linear Gain and Loss Media%空心光束在损耗和增益介质中的传输特性
Institute of Scientific and Technical Information of China (English)
朱焯炜; 赵琳琳; 苏宙平
2011-01-01
Based on the definition of complex wave number and the generalized Huygens-Fresnel diffraction integral,the closed-form propagation equation of Dark hollow beams passing through a paraxial optical ABCD system is derived. The beam-width propagation formula of Dark hollow beams through absorption media are obtained on the basis of the second-order moment method. By numerical analysis,the intensity distributions and beams waist width have been studied. The results show that, the dark hollow beams propagation in linear gain or loss media,when the media property is gain (loss) ,it will heighten (lower) the intensity;but it has little effect on the beams waist width.%从复数波数定义和广义惠更斯-菲涅尔积分出发,推导出空心光束在介质中通过旁轴ABCD光学系统后的一般传输公式.在此基础上,结合光强二阶矩方法,给出了相应的一般束宽变换公式.通过数值分析研究了介质传输场中强度分布和均方根束宽的变化特点.研究结果表明,空心光束在增益或者损耗介质中传输时,当其为增益(损耗)介质时,会增强(衰减)光束的强度;但对均方根束宽却没有太大的影响.
ATA gas propagation - 1 foot tank experiment
Energy Technology Data Exchange (ETDEWEB)
Chong, Y.P.; Caporaso, G.J.; Chambers, F.W.; Fawley, W.M.; Lauer, E.J.; Paul, A.C.; Prono, D.S.; Weir, J.T.
1984-06-27
The first gas propagation experiment on ATA is planned to be conducted in a 1-foot diameter tank of up to 10 m length. The primary objectives are to measure beam parameters at injection to determine whether the desired beam conditioning is achieved, and to observe how such conditioned beams propagate in air and neon.
Axial heating and temperature of RF-excited non-neutral plasmas in Penning-Malmberg traps
Maero, G.; Pozzoli, R.; Romé, M.; Chen, S.; Ikram, M.
2016-09-01
Electro-magnetostatic traps have been used for decades to provide long-term storage of charged particle samples or non-neutral plasmas. The dynamics and equilibrium states of these ideally simple systems can be strongly diverted from the usual working conditions (i.e. single-species, quiescent samples) in the presence of oppositely charged particles or external electric field perturbations. Both these conditions occur when the plasma is generated by means of a radio-frequency (RF) excitation continuously applied on a trap electrode. The application of RF drives of some volts over periods larger than typical collisional time scales leads to residual-gas ionization and to the accumulation of an electron plasma, a process that has previously been exploited as an alternative to thermionic or photoemission electron sources. The analysis of the axial energy distribution shows a deviation of the continuously excited final state from maxwellianity dependent on the radial position and the subsequent relaxation to equilibrium after the interruption of the drive. Systematic measurements also indicate the high sensitivity to the residual gas pressure of both the total confined charge and of the attainable densities and plasma profiles. The results are compared to the information obtained from a very simple one-dimensional electron heating model and show the validity of its most basic features together with its shortcomings.
Directory of Open Access Journals (Sweden)
Anastasiya Yermakova
Full Text Available The B subunit (RTB of ricin toxin is a galactose (Gal-/N-acetylgalactosamine (GalNac-specific lectin that mediates attachment, entry, and intracellular trafficking of ricin in host cells. Structurally, RTB consists of two globular domains with identical folding topologies. Domains 1 and 2 are each comprised of three homologous sub-domains (α, β, γ that likely arose by gene duplication from a primordial carbohydrate recognition domain (CRD, although only sub-domains 1α and 2γ retain functional lectin activity. As part of our ongoing effort to generate a comprehensive B cell epitope map of ricin, we report the characterization of three new RTB-specific monoclonal antibodies (mAbs. All three mAbs, JB4, B/J F9 and C/M A2, were initially identified based on their abilities to neutralize ricin in a Vero cell cytotoxicity assay and to partially (or completely block ricin attachment to cell surfaces. However, only JB4 proved capable of neutralizing ricin in a macrophage apoptosis assay and in imparting passive immunity to mice in a model of systemic intoxication. Using a combination of techniques, including competitive ELISAs, pepscan analysis, differential reactivity by Western blot, as well as affinity enrichment of phage displayed peptides, we tentatively localized the epitopes recognized by the non-neutralizing mAbs B/J F9 and C/M A2 to sub-domains 2α and 2β, respectively. Furthermore, we propose that the epitope recognized by JB4 is within sub-domain 2γ, adjacent to RTB's high affinity Gal/GalNAc CRD. These data suggest that recognition of RTB's sub-domains 1α and 2γ are critical determinants of antibody neutralizing activity and protective immunity to ricin.
Plasma-beam traps and radiofrequency quadrupole beam coolers.
Maggiore, M; Cavenago, M; Comunian, M; Chirulotto, F; Galatà, A; De Lazzari, M; Porcellato, A M; Roncolato, C; Stark, S; Caruso, A; Longhitano, A; Cavaliere, F; Maero, G; Paroli, B; Pozzoli, R; Romé, M
2014-02-01
Two linear trap devices for particle beam manipulation (including emittance reduction, cooling, control of instabilities, dust dynamics, and non-neutral plasmas) are here presented, namely, a radiofrequency quadrupole (RFQ) beam cooler and a compact Penning trap with a dust injector. Both beam dynamics studies by means of dedicated codes including the interaction of the ions with a buffer gas (up to 3 Pa pressure), and the electromagnetic design of the RFQ beam cooler are reported. The compact multipurpose Penning trap is aimed to the study of multispecies charged particle samples, primarily electron beams interacting with a background gas and/or a micrometric dust contaminant. Using a 0.9 T solenoid and an electrode stack where both static and RF electric fields can be applied, both beam transport and confinement operations will be available. The design of the apparatus is presented.
Coherent resonance stop bands in alternating gradient beam transport
Ito, K.; Okamoto, H.; Tokashiki, Y.; Fukushima, K.
2017-06-01
An extensive experimental study is performed to confirm fundamental resonance bands of an intense hadron beam propagating through an alternating gradient linear transport channel. The present work focuses on the most common lattice geometry called "FODO" or "doublet" that consists of two quadrupoles of opposite polarities. The tabletop ion-trap system "S-POD" (Simulator of Particle Orbit Dynamics) developed at Hiroshima University is employed to clarify the parameter-dependence of coherent beam instability. S-POD can provide a non-neutral plasma physically equivalent to a charged-particle beam in a periodic focusing potential. In contrast with conventional experimental approaches relying on large-scale machines, it is straightforward in S-POD to control the doublet geometry characterized by the quadrupole filling factor and drift-space ratio. We verify that the resonance feature does not essentially change depending on these geometric factors. A few clear stop bands of low-order resonances always appear in the same pattern as previously found with the sinusoidal focusing model. All stop bands become widened and shift to the higher-tune side as the beam density is increased. In the space-charge-dominated regime, the most dangerous stop band is located at the bare betatron phase advance slightly above 90 degrees. Experimental data from S-POD suggest that this severe resonance is driven mainly by the linear self-field potential rather than by nonlinear external imperfections and, therefore, unavoidable at high beam density. The instability of the third-order coherent mode generates relatively weak but noticeable stop bands near the phase advances of 60 and 120 degrees. The latter sextupole stop band is considerably enhanced by lattice imperfections. In a strongly asymmetric focusing channel, extra attention may have to be paid to some coupling resonance lines induced by the Coulomb potential. Our interpretations of experimental data are supported by theoretical
Institute of Scientific and Technical Information of China (English)
许森东; 徐弼军
2014-01-01
In order to study the propagation characteristics of Gaussian-Schell model(GSM) beams in negative index medium, the analytical expression was obtained for the cross-spectral density function of GSM beam passing through negative index medium based on the matrix optics theory , diffraction integral theory and unification theory of coherence and polarization .The spectral density and the spectral coherence degree of the beam passing through the negative index medium were obtained with the formula .Numerical examples show that both the spectral density and the coherence spectral degree of GSM beam can be modulated by the frequency of the negative index medium .The results provide a new modulation method for the beam propagation .%为了研究高斯-谢尔模型光束在负折射率介质中的传输特性，利用矩阵光学理论、衍射积分理论、相干偏振统一理论推导了高斯-谢尔模型光束通过负折射率介质中传输交叉谱密度方程的解析表达式，并利用该解析表达式得到了高斯-谢尔模型光束通过负折射率介质的谱密度和谱相干度。结果表明，高斯-谢尔模型光束的谱密度和谱相干度都可以通过负折射率介质的工作频率调控。此研究结果提供了一种新的调控光传输的方法和技术。
Directory of Open Access Journals (Sweden)
Taku Nakane
Full Text Available BACKGROUND: Antiviral antibodies, especially those with neutralizing activity against the incoming strain, are potentially important immunological effectors to control human immunodeficiency virus (HIV infection. While neutralizing activity appears to be central in sterile protection against HIV infection, the entity of inhibitory mechanisms via HIV and simian immunodeficiency virus (SIV-specific antibodies remains elusive. The recent HIV vaccine trial RV144 and studies in nonhuman primate models have indicated controversial protective efficacy of HIV/SIV-specific non-neutralizing binding antibodies (non-NAbs. While reports on HIV-specific non-NAbs have demonstrated virus inhibitory activity in vitro, whether non-NAbs could also alter the pathogenic course of established SIV replication in vivo, likewise via neutralizing antibody (NAb administration, has been unclear. Here, we performed post-infection passive immunization of SIV-infected rhesus macaques with polyclonal SIV-specific, antibody-dependent cell-mediated viral inhibition (ADCVI-competent non-NAbs. METHODS AND FINDINGS: Ten lots of polyclonal immunoglobulin G (IgG were prepared from plasma of ten chronically SIVmac239-infected, NAb-negative rhesus macaques, respectively. Their binding capacity to whole SIVmac239 virions showed a propensity similar to ADCVI activity. A cocktail of three non-NAb lots showing high virion-binding capacity and ADCVI activity was administered to rhesus macaques at day 7 post-SIVmac239 challenge. This resulted in an infection course comparable with control animals, with no significant difference in set point plasma viral loads or immune parameters. CONCLUSIONS: Despite virus-specific suppressive activity of the non-NAbs having been observed in vitro, their passive immunization post-infection did not result in SIV control in vivo. Virion binding and ADCVI activity with lack of virus neutralizing activity were indicated to be insufficient for antibody
Coulson, B S; Fowler, K J; White, J R; Cotton, R G
1987-01-01
Monoclonal antibodies were derived to a human rotavirus purified from stools. Three of the antibodies immunoprecipitated the rotavirus outer capsid glycoprotein gp 34 and were non-neutralizing. These antibodies reacted by enzyme immunoassay with cultivable rotaviruses showing the "long" RNA electropherotype but were inefficient as detectors of "long" RNA pattern rotaviruses in stools. Treatment of SA 11 rotavirus with 7.5 micrograms/ml porcine trypsin for 30 minutes at 37 degrees C irreversibly reduced binding of the antibodies to SA 11 rotavirus in enzyme immunoassays by 50 per cent. Binding was abolished in the presence of rotavirus-negative faecal extracts. These results indicate that non-neutralizing sites on gp 34 of rotaviruses can vary with RNA electropherotype and serotype, and that levels of trypsin currently in use to assist growth of rotaviruses in cell culture may alter the serological profile of the viruses.
Institute of Scientific and Technical Information of China (English)
李高清; 付文羽
2009-01-01
根据光束在介质中传输强度二阶矩计算公式,推导出部分相干平顶光束在增益或损耗介质中传输的M~2因子解析表达式,并将高斯-谢尔模型光束在增益或损耗介质中的传输作为特例统一于一般表达式中.研究结果表明:部分相干平顶光束在增益或损耗介质中传输时的M~2因子与光束传输距离、光束相干长度、光束阶数及介质的特性有关.光束在增益或损耗介质中传输的这种特性为应用和控制光束传输提供了理论依据.%According to the second-order moments intensity formula of the beam propagating in the gain or loss media, an analytical expression for M~2-factor of partially coherent flat-top beams propagating in the media is derived, and Gaussian-Schell model beams propagation in gain or loss media, which is taken as a particular case, is integrated into a common expression. The research result shows that the M~2-factor of partially coherent flat-top beams propagating in the gain or loss media is relative to the propagation distance, the coherent length, the order of the beams and the character of media. The propagation characteristic of the beams propagating in the gain or loss media provides a theoretical basis for the application and control of the beam propagation.
Institute of Scientific and Technical Information of China (English)
高明; 王菲
2012-01-01
基于广义Huygens-Fresnel原理,利用Collins公式,讨论了偏振部分相干激光波束在湍流大气中传输的交叉谱密度函数,推导出经过偏振后的高斯-谢尔模型光束(GSM)在外场不同距离水平传输时波束偏振度的解析表达式.对偏振激光在大气湍流中传输时光束的退偏变化进行数值仿真,得到相同传输距离下,不同的偏振角和初始束腰宽度对光束偏振度的影响；同时分析了不同波长激光的退偏现象以及相同的偏振角度下,不同的初始束腰宽度对波束偏振度的影响.研究结果表明,不同的偏振角对波束的退偏不产生影响；波长越大,波束在大气湍流中传输出现退偏的现象越迟缓；初始束腰越大,大气湍流对波束的退偏影响越快.由此得出:偏振部分相干激光波束比部分相干激光波束在大气湍流中传输的退偏变化更具有规律性和稳定性,退偏现象表现得更加持久,并且初始束腰宽度的变化对偏振部分相干激光偏振度产生影响,但对部分相干波束偏振度的变化几乎不产生任何影响.%Cross-spectral density function of polarized and partially coherent laser beam propagated in turbulent atmosphere was discussed based on the generalized Huygens-Fresnel Principle and Collins Formula. Analytical expressions for polarization degree of polarized Gaussian-shell model (GSM) beam under horizontal transmission at different distances of external fields were obtained. Changes in polarization degree of polarized laser propagated in turbulent atmosphere were simulated under the same propagation distance with different polarization angles and different initial waist widths. Similar simulation was also done by using the different wavelengths and the same polarization angles but with different propagation distances. The results indicate that depolarization of the beam is not affected by the different polarization angles; depolarization caused by turbulent
Emittance Measurements of Space Charge Dominated Electron Beam.
2014-09-26
measurement 2,3 have been introduced in the past, especially in particle accelerator physics. In free space, the envelope of a non -neutral charged...density no and thickness 2d is located on the y-axis. Let us assume that the velocity space distribution is a Maxwellian with a temperature T and the beam
Gao, Nan; Xie, Changqing
2014-06-15
We generalize the concept of diffraction free beams to parabolic scaling beams (PSBs), whose normalized intensity scales parabolically during propagation. These beams are nondiffracting in the circular parabolic coordinate systems, and all the diffraction free beams of Durnin's type have counterparts as PSBs. Parabolic scaling Bessel beams with Gaussian apodization are investigated in detail, their nonparaxial extrapolations are derived, and experimental results agree well with theoretical predictions.
Izdebski, Marek; Kucharczyk, Włodzimierz; Raab, Roger E
2004-01-01
The Jones matrix calculus is applied to an electro-optic crystal with uniaxial symmetry when the light beam is incident nearly normally on the crystal face. The approach allows one to treat refracted waves and rays that diverge in the crystal and are modulated by an external low-frequency field. The effect of partial interference of overlapping refracted beams is allowed for and calculated for the case of uniform intensity of the beam over its cross section. The method is employed to analyze optical systems containing an imprecisely cut and aligned electro-optic crystal plate.
On Characteristics of the Propagation of Airy Beams in Meta-materials%艾里光束在超常介质中的传输特性
Institute of Scientific and Technical Information of China (English)
王友文; 李舒; 游开明; 陈列尊; 陆世专; 戴志平; 凌晓辉
2014-01-01
艾里光束（Airy beam ）是近年来备受关注的新型无衍射激光束之一，艾里激光束具有自由加速、无衍射及自愈等奇异特性，并具有重要应用前景。超常介质为人工微结构材料，它使人们具备按需要设计介质参数的能力。基于一维光束传输方程，获得了超常介质中艾里光束复振幅传输解析表达式。数值计算结果表明，超常介质中艾里光束振幅的大小与在正常介质中完全相同，而振幅的虚部和相位正好相反。所得结果为人们操控艾里光束提供支持。%The Airy beam is a new kind of non-diffracting beam discovered in recent years .Airy beams have exotic characteris-tics such as free acceleration ,non-diffracting laser beam and self-healing ,and so have important application potentials .Meta-materials are artificial microstructures material ,which permit people to design electromagnetic parameters of media at will . Based on the paraxial wave equation ,the analytical expression of complex amplitude of Airy beams in meta-materials is ob-tained ;in addition ,the numerical results show that ,the module of complex amplitude of Airy beams in meta-materials is simi-lar to that of conventional medium ,while the imaginary part and the phase complex amplitude are opposite .The results may provide support for people to better manipulation of the Airy beam .
Institute of Scientific and Technical Information of China (English)
许森东; 徐弼军; 陆璇辉
2013-01-01
为了研究高斯-谢尔模型(GSM)光束在电磁感应透明(EIT)材料中的传输特性，利用矩阵光学理论、衍射积分理论、相干偏振统一理论推导了GSM光束通过EIT材料的传输交叉谱密度方程的解析表达式。该表达式可以用于计算和研究GSM光束通过EIT原子气体的谱密度和相干度的变化。分析显示GSM光束的谱密度和相干度都可以通过控制光的拉比频率调控。此研究结果提供了一种新的调控光传输的方法和技术，同时该发现也为控制部分相干光的谱密度和相干度提供了一种新方法。%In order to study the propagation characteristics of Gaussian Schell-model (GSM) beams in electromagnetically induced transparency atomic vapor, the analytical expression was obtained for the cross-spectral density function of a Gaussian Schell-model beam passing through the electromagnetically induced transparency atomic vapor based on the matrix optics theory, diffraction integral theory and unified theory of coherence and polarization. The formula can be used in the study of the changes in the spectral density and spectral degree of coherence of the beam through the EIT atomic vapor. Numerical examples show that both the spectral density and the spectral degree of coherence of the GSM beam can be modulated by the Rabi frequency of the control light. The results have been provided a new method and technique for modulation the beam propagation. The findings indicate a new technique for controlling the spectral density and the spectral degree of coherence of the partially coherent light beam.
Institute of Scientific and Technical Information of China (English)
包建勤; 张廷蓉; 霍雅洁
2013-01-01
Under paraxial approximation,using generalized Huygens-Fresnel diffraction integral,the propagation expressions of cosine-Gaussian beam through the left-handed material slab are got,and the influence of propagation properties of cosine-Gaussian beam due to the negative refractive index of left-handed material slab and the modulation parameter of cosine-Gaussian beam is studied.The results of the study show that:whether in the left-handed materials slab or image space,the location of the axial maximum light intensity is the position where cosine-Gaussian beam is focused,and the negative refractive index of the left-handed material slab will change the position of the cosine-Gaussian beam focusing.The negative refractive index will change the shape of the axial light intensity distribution in the internal of the lefthanded material slab,but it won't change the shape of the axial light intensity distribution in image space.Whether in the internal of slab or image space,the modulation parameters of cosine-Gaussian beam can influence the axial and transverse light intensities.%在傍轴近似下,利用广义惠更斯-菲涅尔衍射积分公式得到了余弦高斯光束通过左手平板材料的传输公式,研究了左手平板材料的负折射率与余弦高斯光束的调制参数对光束传输特性的影响.结果表明:余弦高斯光束无论在左手平板材料内部传输还是在像空间传输,轴上的最大光强位置是光束聚焦的位置,左手平板材料的负折射率会改变光束聚焦的位置；在介质内部,平板材料的负折射率会改变轴上光强分布的形状,但不会改变像空间轴上的光强分布形状；无论是在平板材料内部还是像空间,余弦高斯光束的调制参数对轴上与横向光强都会产生影响.
Institute of Scientific and Technical Information of China (English)
黎昌金; 邵毅全
2012-01-01
研究了阵列几何排布对多重径向阵列相干和非相干合成光束桶中功率（PIB）的影响。在较小的桶内阵列相干合成光束的PIB值随P增大而增大；非相干合成光束的PIB值与几何排布无关。%The effects of geometric distribution of multiple radial array beams on the power in the bucket（PIB） in both coherent and incoherent resulting beams are studied. It is shown that for a small bucket width the PIB in coherent resulting beam increases with increasing P, while the PIB in incoherent resulting beam is independent of geometric distribution of array beams.
Institute of Scientific and Technical Information of China (English)
张建柱; 李有宽; 张飞舟; 安建祝
2011-01-01
Through theoretic analysis and numerical simulation, the focal shift of a focused flat beam propagating in turbulent atmosphere is studied. When a focused flat beam propagates in turbulent atmosphere, the effect of turbulence will induce the focal spot to move toward the transmitter. The turbulence is stronger and the diameter of transmitter is smaller, the measure of focal shift is larger. When adjusting the focus of transmitter and letting the focal spot of beam locate on detector, the laser intensity received by detector is not the strongest. The laser intensity will be the strongest if the focus of transmitter equals to the distance from transmitter to detector.%通过理论分析和数值模拟,对聚焦平台光束大气传输的焦移问题进行了研究.聚焦平台光束在湍流大气中传输时,湍流将导致光束的束腰向发射点移动,且湍流越强移动的幅度越大;大气湍流强度相同时,聚焦平台光束发射口径越小,其束腰移动的幅度越大.另外,通过调节发射系统的焦距,使聚焦平台光束的束腰正好位于接收探测器处时,接收探测器上的激光功率密度并非最大,只有当发射系统的焦距等于激光的传输距离时,接收探测器上的激光功率密度才会最大.
Institute of Scientific and Technical Information of China (English)
仓吉; 张逸新
2009-01-01
The propagation properties of focused partially coherent Gauss-Schell model vortex beams in the turbulent atmosphere were investigated based on the extended Huygens-Fresnel principle and the quadratic approximation of phase structure function. Optical intensity expression on the focal plane was obtained. By use of the expression, the intensity distribution of such kind of beam on the focal plane in the turbulent atmosphere was studied. The results show that in the turbulent atmosphere, the singularity of the vortex beam lows down with the propagation distance increasing. The maintenance of singularity is better for the vortex beams with larger topological charge and longer spatially coherent length. When the focal length and turbulent strength are fixed, the topological charge and coherent length of the source can be adjusted to control the behavior of intensity distribution on the focal plane and size of the focal spot. Vortex beams with larger topological charge can be resistant to the turbulent effects on the intensity distribution on the focal plane to some extent.%基于广义惠更斯-菲涅耳原理和相位结构函数的平方近似,研究了部分相干高斯-谢尔模型涡旋光束被聚焦后在大气湍流中的传输特性,得到了焦平面上光强解析表达式.利用该表达式,详细研究了该类光束在大气湍流中传输焦平面上的光强分布特性.结果表明:在大气湍流中,随着传输距离的增加,涡旋光束的奇异性逐渐降低.对于拓扑荷大的以及空间相干长度较长的涡旋光束,光束奇异性的保持相对要好.在一定的焦距长度和湍流大气条件下,我们可以通过调整光源的拓扑荷和相干长度控制焦面光强分布和焦斑大小.另外,有一定拓扑荷的涡旋光束可以在一定程度上降低大气湍流对传输光束焦面光强分布的影响.
Müller, Angelina; Wallrabe, Ulrike
2016-01-01
We present a ring aperture with independently switchable segments for the three-dimensional control of quasi propagation invariant beams. We demonstrate that our liquid crystal design concept preserves coherence and generates the Bessel beam structure.
Richou, B; Schertz, I; Gobin, I; Richou, J
1997-03-01
A large-core multimode optical fiber of a few meters length is studied as a 10-MW beam delivery system for a 15-ns pulsed Nd:YAG laser. A laser-to-fiber vacuum coupler is used to inhibit air breakdown and reduce the probability of dielectric breakdown on the fiber front surface. Laser-induced damage inside the fiber core is observed behind the fiber front surface. An explanation based on a high power density is illustrated by a ray trace. Damaged spots and measurements of fiber output energies are reported for two laser beam distributions: a flat-hat type and a near-Gaussian type. Experiments have been performed to deliver a 100-pulse mean energy between 100 and 230 mJ without catastrophic damage.
Energy Technology Data Exchange (ETDEWEB)
Richou, B.; Richou, J. [Laboratoire d` Optoelectronique, Faculte des Sciences, Universite de Toulon et du Var, BP 132, La Garde 83957 (France); Schertz, I.; Gobin, I. [Commissariat a l`Energie Atomique/Vaujours, Moronvilliers, BP 7, Courtry 77181 (France)
1997-03-01
A large-core multimode optical fiber of a few meters length is studied as a 10-MW beam delivery system for a 15-ns pulsed Nd:YAG laser. A laser-to-fiber vacuum coupler is used to inhibit air breakdown and reduce the probability of dielectric breakdown on the fiber front surface. Laser-induced damage inside the fiber core is observed behind the fiber front surface. An explanation based on a high power density is illustrated by a ray trace. Damaged spots and measurements of fiber output energies are reported for two laser beam distributions: a flat-hat type and a near-Gaussian type. Experiments have been performed to deliver a 100-pulse mean energy between 100 and 230 mJ without catastrophic damage. {copyright} 1997 Optical Society of America
Polarization shaping for control of nonlinear propagation
Bouchard, Frédéric; Yao, Alison M; Travis, Christopher; De Leon, Israel; Rubano, Andrea; Karimi, Ebrahim; Oppo, Gian-Luca; Boyd, Robert W
2016-01-01
We study the nonlinear optical propagation of two different classes of space-varying polarized light beams -- radially symmetric vector beams and Poincar\\'e beams with lemon and star topologies -- in a rubidium vapour cell. Unlike Laguerre-Gauss and other types of beams that experience modulational instabilities, we observe that their propagation is not marked by beam breakup while still exhibiting traits such as nonlinear confinement and self-focusing. Our results suggest that by tailoring the spatial structure of the polarization, the effects of nonlinear propagation can be effectively controlled. These findings provide a novel approach to transport high-power light beams in nonlinear media with controllable distortions to their spatial structure and polarization properties.
Polarization Shaping for Control of Nonlinear Propagation.
Bouchard, Frédéric; Larocque, Hugo; Yao, Alison M; Travis, Christopher; De Leon, Israel; Rubano, Andrea; Karimi, Ebrahim; Oppo, Gian-Luca; Boyd, Robert W
2016-12-02
We study the nonlinear optical propagation of two different classes of light beams with space-varying polarization-radially symmetric vector beams and Poincaré beams with lemon and star topologies-in a rubidium vapor cell. Unlike Laguerre-Gauss and other types of beams that quickly experience instabilities, we observe that their propagation is not marked by beam breakup while still exhibiting traits such as nonlinear confinement and self-focusing. Our results suggest that, by tailoring the spatial structure of the polarization, the effects of nonlinear propagation can be effectively controlled. These findings provide a novel approach to transport high-power light beams in nonlinear media with controllable distortions to their spatial structure and polarization properties.
Directory of Open Access Journals (Sweden)
Rogier W Sanders
2013-09-01
Full Text Available A desirable but as yet unachieved property of a human immunodeficiency virus type 1 (HIV-1 vaccine candidate is the ability to induce broadly neutralizing antibodies (bNAbs. One approach to the problem is to create trimeric mimics of the native envelope glycoprotein (Env spike that expose as many bNAb epitopes as possible, while occluding those for non-neutralizing antibodies (non-NAbs. Here, we describe the design and properties of soluble, cleaved SOSIP.664 gp140 trimers based on the subtype A transmitted/founder strain, BG505. These trimers are highly stable, more so even than the corresponding gp120 monomer, as judged by differential scanning calorimetry. They are also homogenous and closely resemble native virus spikes when visualized by negative stain electron microscopy (EM. We used several techniques, including ELISA and surface plasmon resonance (SPR, to determine the relationship between the ability of monoclonal antibodies (MAbs to bind the soluble trimers and neutralize the corresponding virus. In general, the concordance was excellent, in that virtually all bNAbs against multiple neutralizing epitopes on HIV-1 Env were highly reactive with the BG505 SOSIP.664 gp140 trimers, including quaternary epitopes (CH01, PG9, PG16 and PGT145. Conversely, non-NAbs to the CD4-binding site, CD4-induced epitopes or gp41ECTO did not react with the trimers, even when their epitopes were present on simpler forms of Env (e.g. gp120 monomers or dissociated gp41 subunits. Three non-neutralizing MAbs to V3 epitopes did, however, react strongly with the trimers but only by ELISA, and not at all by SPR and to only a limited extent by EM. These new soluble trimers are useful for structural studies and are being assessed for their performance as immunogens.
Tan, Gene S; Leon, Paul E; Albrecht, Randy A; Margine, Irina; Hirsh, Ariana; Bahl, Justin; Krammer, Florian
2016-04-01
In the early spring of 2013, Chinese health authorities reported several cases of H7N9 influenza virus infections in humans. Since then the virus has established itself at the human-animal interface in Eastern China and continues to cause several hundred infections annually. In order to characterize the antibody response to the H7N9 virus we generated several mouse monoclonal antibodies against the hemagglutinin of the A/Shanghai/1/13 (H7N9) virus. Of particular note are two monoclonal antibodies, 1B2 and 1H5, that show broad reactivity to divergent H7 hemagglutinins. Monoclonal antibody 1B2 binds to viruses of the Eurasian and North American H7 lineages and monoclonal antibody 1H5 reacts broadly to virus isolates of the Eurasian lineage. Interestingly, 1B2 shows broad hemagglutination inhibiting and neutralizing activity, while 1H5 fails to inhibit hemagglutination and demonstrates no neutralizing activity in vitro. However, both monoclonal antibodies were highly protective in an in vivo passive transfer challenge model in mice, even at low doses. Experiments using mutant antibodies that lack the ability for Fc/Fc-receptor and Fc/complement interactions suggest that the protection provided by mAb 1H5 is, at least in part, mediated by the Fc-fragment of the mAb. These findings highlight that a protective response to a pathogen may not only be due to neutralizing antibodies, but can also be the result of highly efficacious non-neutralizing antibodies not readily detected by classical in vitro neutralization or hemagglutination inhibition assays. This is of interest because H7 influenza virus vaccines induce only low hemagglutination inhibiting antibody titers while eliciting robust antibody titers as measured by ELISA. Our data suggest that these binding but non-neutralizing antibodies contribute to protection in vivo.
Directory of Open Access Journals (Sweden)
Gene S Tan
2016-04-01
Full Text Available In the early spring of 2013, Chinese health authorities reported several cases of H7N9 influenza virus infections in humans. Since then the virus has established itself at the human-animal interface in Eastern China and continues to cause several hundred infections annually. In order to characterize the antibody response to the H7N9 virus we generated several mouse monoclonal antibodies against the hemagglutinin of the A/Shanghai/1/13 (H7N9 virus. Of particular note are two monoclonal antibodies, 1B2 and 1H5, that show broad reactivity to divergent H7 hemagglutinins. Monoclonal antibody 1B2 binds to viruses of the Eurasian and North American H7 lineages and monoclonal antibody 1H5 reacts broadly to virus isolates of the Eurasian lineage. Interestingly, 1B2 shows broad hemagglutination inhibiting and neutralizing activity, while 1H5 fails to inhibit hemagglutination and demonstrates no neutralizing activity in vitro. However, both monoclonal antibodies were highly protective in an in vivo passive transfer challenge model in mice, even at low doses. Experiments using mutant antibodies that lack the ability for Fc/Fc-receptor and Fc/complement interactions suggest that the protection provided by mAb 1H5 is, at least in part, mediated by the Fc-fragment of the mAb. These findings highlight that a protective response to a pathogen may not only be due to neutralizing antibodies, but can also be the result of highly efficacious non-neutralizing antibodies not readily detected by classical in vitro neutralization or hemagglutination inhibition assays. This is of interest because H7 influenza virus vaccines induce only low hemagglutination inhibiting antibody titers while eliciting robust antibody titers as measured by ELISA. Our data suggest that these binding but non-neutralizing antibodies contribute to protection in vivo.
Trofimov, M. Yu.; Zakharenko, A. D.; Kozitskiy, S. B.
2016-10-01
A mode parabolic equation in the ray centered coordinates for 3D underwater sound propagation is developed. The Gaussian beam tracing in this case is constructed. The test calculations are carried out for the ASA wedge benchmark and proved an excellent agreement with the source images method in the case of cross-slope propagation. But in the cases of wave propagation at some angles to the cross-slope direction an account of mode interaction becomes necessary.
Energy Technology Data Exchange (ETDEWEB)
Olivares, J. [Instituto de Optica ' Daza de Valdes' , CSIC, Madrid (Spain); Parque Cientifico de Madrid, Cantoblanco, Centro de Microanalisis de Materiales CMAM-UAM, Madrid (Spain); Garcia, G. [Parque Cientifico de Madrid, Cantoblanco, Centro de Microanalisis de Materiales CMAM-UAM, Madrid (Spain); Agullo-Lopez, F. [Universidad Autonoma de Madrid, Departamento de Fisica de Materiales, C-IV, Madrid (Spain); Parque Cientifico de Madrid, Cantoblanco, Centro de Microanalisis de Materiales CMAM-UAM, Madrid (Spain); Agullo-Rueda, F. [Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid (Spain); Kling, A. [Instituto Tecnologico e Nuclear (ITN), Sacavem (Portugal); Soares, J.C. [Centro de Fisica da Universidade de Lisboa (CFNUL), Lisboa (Portugal)
2005-11-01
The refractive-index profiles induced by high-energy (5 MeV, 7.5 MeV) silicon irradiation in LiNbO{sub 3} have been systematically determined as a function of ion fluence in the range 10{sup 13}-10{sup 15} cm{sup -2}. At variance with irradiations at lower energies, an optically isotropic ('amorphous') homogeneous surface layer is generated whose thickness increases with fluence. These results have been associated with an electronic excitation mechanism. They are discussed in relation to the well-documented phenomenon of latent (amorphous) track generation under ion irradiation, requiring a threshold value S{sub e,th} for the electronic stopping power S{sub e}. Our optical data have yielded a value of {approx}5 keV/nm for such a threshold, within the range reported by independent single-track measurements. The propagation of the amorphous boundary into the crystal during irradiation indicates that the threshold value decreases on increasing the fluence. Complementary Rutherford backscattering-channeling and micro-Raman (on samples irradiated at 30 MeV) experiments have been performed to monitor the induced structural changes. (orig.)
Non-paraxial Elliptical Gaussian Beam
Institute of Scientific and Technical Information of China (English)
WANG Zhaoying; LIN Qiang; NI Jie
2001-01-01
By using the methods of Hertz vector and angular spectrum transormation, the exact solution of non-paraxial elliptical Gaussion beam with general astigmatism based on Maxwell′s equations is obtained. We discussed its propagation characteristics. The results show that the orientation of the elliptical beam spot changes continuously as the beam propagates through isotropic media. Splitting or coupling of beam spots may occur for different initial spot size. This is very different from that of paraxial elliptical Gaussian beam.
Quality of Spatial Entanglement Propagation
Reichert, Matthew; Fleischer, Jason W
2016-01-01
We explore, both experimentally and theoretically, the propagation dynamics of spatially entangled photon pairs (biphotons). Characterization of entanglement is done via the Schmidt number, which is a universal measurement of the degree of entanglement directly related to the non-separability of the state into its subsystems. We develop expressions for the terms of the Schmidt number that depend on the amplitude and phase of the commonly used double-Gaussian approximation for the biphoton wave function, and demonstrate migration of entanglement between amplitude and phase upon propagation. We then extend this analysis to incorporate both phase curvature in the pump beam and higher spatial frequency content of more realistic non-Gaussian wave functions. Specifically, we generalize the classical beam quality parameter $M^2$ to the biphotons, allowing the description of more information-rich beams and more complex dynamics. Agreement is found with experimental measurements using direct imaging and Fourier optics...
艾里光束的远场特性及其演化规律%Propagation characteristics in the far-field and evolution regular of Airy beam
Institute of Scientific and Technical Information of China (English)
程振; 楚兴春; 赵尚弘; 邓博于; 张曦文
2015-01-01
The propagation characteristics of Airy beam in the far-field were detailly studied, which start with the theoretical foundation, including the evolution process of intensity distribution, spot diameter and Power in the Bucket (PIB). The change regular of intensity distribution was investigated with the truncation factor a and the arbitrary scale in the transverse x0 and how do a and x0 influence the propagation Distance with Keeping Non-diffraction (DKNd), the Distance in which the Evolution became similar Guassian(DEG) and Self-bending Degree(SbD). The research shows that in the evolution process of intensity distribution which transforms into similar Guassian, the DKNd, DEG and SbD increase with the increase of x0, the DKNd and DEG decrease with the increase of a and a has no effect on SbD. The evolution regular of spot diameter and PIB was also researched. The research shows that the spot diameter fistly remain unchanged and then increases, PIB firstly decreases, then increases and is 0.76 finally in the propagation progress under different values of a.%从艾里光束的理论基础出发,详细研究了艾里光束的远场传输特性,包括场强分布、光斑直径和桶中功率(Power in the Bucket,PIB)的演化过程.探讨了场强分布随截断因子a和任意横向刻度x0的变化规律,以及a和x0对艾里光束保持无衍射性质传输的距离 (Distance with Keeping Non-diffraction,DKNd)、演化成类高斯分布的距离(Distance in which the Evolution became similar Guassian, DEG)和自弯曲程度(Self-bending Degree,SbD)的影响.研究发现:场强分布在演化成类高斯分布过程中,DKNd、DEG和SbD都随着x0的增大而增大,DKNd和DEG随a的增大而减小,a对SbD无影响.研究了艾里光束的光斑直径和PIB的演化规律, 发现在a值不同的情况下,在传输过程中光斑直径先保持不变后增加,PIB先减小后增大,最终等于0.76.
Directory of Open Access Journals (Sweden)
Elena Gustchina
Full Text Available A series of mini-antibodies (monovalent and bivalent Fabs targeting the conserved internal trimeric coiled-coil of the N-heptad repeat (N-HR of HIV-1 gp41 has been previously constructed and reported. Crystal structures of two closely related monovalent Fabs, one (Fab 8066 broadly neutralizing across a wide panel of HIV-1 subtype B and C viruses, and the other (Fab 8062 non-neutralizing, representing the extremes of this series, were previously solved as complexes with 5-Helix, a gp41 pre-hairpin intermediate mimetic. Binding of these Fabs to covalently stabilized chimeric trimers of N-peptides of HIV-1 gp41 (named (CCIZN363 or 3-H has now been investigated using X-ray crystallography, cryo-electron microscopy, and a variety of biophysical methods. Crystal structures of the complexes between 3-H and Fab 8066 and Fab 8062 were determined at 2.8 and 3.0 Å resolution, respectively. Although the structures of the complexes with the neutralizing Fab 8066 and its non-neutralizing counterpart Fab 8062 were generally similar, small differences between them could be correlated with the biological properties of these antibodies. The conformations of the corresponding CDRs of each antibody in the complexes with 3-H and 5-Helix are very similar. The adaptation to a different target upon complex formation is predominantly achieved by changes in the structure of the trimer of N-HR helices, as well as by adjustment of the orientation of the Fab molecule relative to the N-HR in the complex, via rigid-body movement. The structural data presented here indicate that binding of three Fabs 8062 with high affinity requires more significant changes in the structure of the N-HR trimer compared to binding of Fab 8066. A comparative analysis of the structures of Fabs complexed to different gp41 intermediate mimetics allows further evaluation of biological relevance for generation of neutralizing antibodies, as well as provides novel structural insights into immunogen
Ferrarese, Giorgio
2011-01-01
Lectures: A. Jeffrey: Lectures on nonlinear wave propagation.- Y. Choquet-Bruhat: Ondes asymptotiques.- G. Boillat: Urti.- Seminars: D. Graffi: Sulla teoria dell'ottica non-lineare.- G. Grioli: Sulla propagazione del calore nei mezzi continui.- T. Manacorda: Onde nei solidi con vincoli interni.- T. Ruggeri: "Entropy principle" and main field for a non linear covariant system.- B. Straughan: Singular surfaces in dipolar materials and possible consequences for continuum mechanics
Institute of Scientific and Technical Information of China (English)
王朴; 张丽娟; 李建龙
2011-01-01
利用角谱表示和"逆规则"傅里叶模式理论,研究了非匀幅光束的典型代表TE线偏振高斯光束在亚波长三角形面型浮雕光栅体内的传输.数值分析表明浮雕层内不同透射深度处的光强分布随着透射深度的变化而变化.最后讨论了入射角、周期等光学参数对出射光强分布的影响.这些结论对高衍射效率亚波长光栅的制作和高功率激光光学元件设计等都具有现实意义.%Based on the angular spectrum representation and the "inverse rule" Fourier mode theory, the propagation of the super Gaussian beam through the sub-wavelength triangle relief grating is studied. Numerical calculation shows that the distribution of intensity in different penetration depths changes with the penetration depth in the relief layer. The article also discusses the effects of incident angle, period and other optical parameters on the distribution of the outgoing light intensity.
Directory of Open Access Journals (Sweden)
George K. Lewis
2015-09-01
Full Text Available The mechanism of antibody-mediated protection is a major focus of HIV-1 vaccine development and a significant issue in the control of viremia. Virus neutralization, Fc-mediated effector function, or both, are major mechanisms of antibody-mediated protection against HIV-1, although other mechanisms, such as virus aggregation, are known. The interplay between virus neutralization and Fc-mediated effector function in protection against HIV-1 is complex and only partially understood. Passive immunization studies using potent broadly neutralizing antibodies (bnAbs show that both neutralization and Fc-mediated effector function provides the widest dynamic range of protection; however, a vaccine to elicit these responses remains elusive. By contrast, active immunization studies in both humans and non-human primates using HIV-1 vaccine candidates suggest that weakly neutralizing or non-neutralizing antibodies can protect by Fc-mediated effector function, albeit with a much lower dynamic range seen for passive immunization with bnAbs. HIV-1 has evolved mechanisms to evade each type of antibody-mediated protection that must be countered by a successful AIDS vaccine. Overcoming the hurdles required to elicit bnAbs has become a major focus of HIV-1 vaccine development. Here, we discuss a less studied problem, the structural basis of protection (and its evasion by antibodies that protect only by potent Fc-mediated effector function.
Allanson, O; Neukirch, T
2016-01-01
We calculate exact one-dimensional collisionless plasma equilibria for a continuum of flux tube models, for which the total magnetic field is made up of the `force-free' Gold-Hoyle magnetic flux tube embedded in a uniform and anti-parallel background magnetic field. For a sufficiently weak background magnetic field, the axial component of the total magnetic field reverses at some finite radius. The presence of the background magnetic field means that the total system is not exactly force-free, but by reducing its magnitude the departure from force-free can be made as small as desired. The distribution function for each species is a function of the three constants of motion; namely the Hamiltonian and the canonical momenta in the axial and azimuthal directions. Poisson's Equation and Amp\\`{e}re's Law are solved exactly, and the solution allows either electrically neutral or non-neutral configurations, depending on the values of the bulk ion and electron flows. These equilibria have possible applications in var...
Injection of electron beam into a toroidal trap using chaotic orbits near magnetic null.
Nakashima, C; Yoshida, Z; Himura, H; Fukao, M; Morikawa, J; Saitoh, H
2002-03-01
Injection of charged particle beam into a toroidal magnetic trap enables a variety of interesting experiments on non-neutral plasmas. Stationary radial electric field has been produced in a toroidal geometry by injecting electrons continuously. When an electron gun is placed near an X point of magnetic separatrix, the electron beam spreads efficiently through chaotic orbits, and electrons distribute densely in the torus. The current returning back to the gun can be minimized less than 1% of the total emission.
Tunable Beam Diffraction in Infiltrated Microstructured Fibers
DEFF Research Database (Denmark)
Rosberg, Christian Romer; Bennet, Francis H.; Neshev, Dragomir N.;
We experimentally study beam propagation in two dimensional photonic lattices in microstructured optical fibers infiltrated with high index liquids. We demonstrate strongly tunable beam diffraction by dynamically varying the coupling between individual lattice sites....
Noncoaxial Bessel-Gauss beams.
Huang, Chaohong; Zheng, Yishu; Li, Hanqing
2016-04-01
We proposed a new family of noncoaxial Gauss-truncated Bessel beams through multiplying conventional symmetrical Bessel beams by a noncoaxial Gauss function. These beams can also be regarded as the exponential-truncated version of Bessel-Gauss beams since they can be transformed into the product of Bessel-Gauss beams and an exponential window function along a certain Cartesian axis. The closed-form solutions of the angular spectra and paraxial propagation of these beams were derived. These beams have asymmetrical intensity distributions and carry the same orbit angular momentum per photon as the corresponding Bessel-Gauss beams. While propagating along the z axis, the mth (m≠0) noncoaxial Bessel-Gauss beams rotate their intensity distributions and the mth-order vortex at the beam center has a transverse shift along the direction perpendicular to the offset axis. Depending on the product of the transverse scalar factor of the Bessel beams and the offset between the Gaussian window function and the center of the Bessel beams, the noncoaxial Bessel-Gauss beams can produce unit vortices with opposite signs in pairs during propagation.
Atmospheric Propagation and Combining of High-Power Lasers
2015-09-08
Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6703--15-9646 Atmospheric Propagation and Combining of High-Power Lasers W. NelsoN...ABSTRACT c. THIS PAGE 18. NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Atmospheric Propagation and Combining of High-Power Lasers W. Nelson,* P. Sprangle...Turbulence Beam combining In this paper we analyze the beam combining and atmospheric propagation of high-power lasers for directed-energy (DE
Optical Beams in Nonlocal Nonlinear Media
DEFF Research Database (Denmark)
Królikowski, W.; Bang, Ole; Wyller, J.
2003-01-01
We discuss propagation of optical beams in nonlocal Kerr-like media with the nonlocality of general form. We study the effect of nonlocality on modulational instability of the plane wave fronts, collapse of finite beams and formation of spatial solitons.......We discuss propagation of optical beams in nonlocal Kerr-like media with the nonlocality of general form. We study the effect of nonlocality on modulational instability of the plane wave fronts, collapse of finite beams and formation of spatial solitons....
Institute of Scientific and Technical Information of China (English)
李守军; 吴自银
2011-01-01
Total propagated error computation (TPE) algorithm is established to improve the efficiency of Multi-Beam Echo-Sounder data (MBES) processing and to avoid losing of terrain detail in trend surface model and median filter model. According to the IHO standard, TPE algorithm eliminates noises automatically based on the total propagated error computation. TPE establishes Digital Terrain Model (DTM) based on the combined estimation of the depth and related uncertainty of the MBES data. To evaluate the efficiency and quality of the TPE algorithm, TPE algorithm and man-machine editor are used respectively to process the same MBES data of Lau Basin. The data processing speed of TPE algorithm is 5 times of the man-machine editor. The TPE terrain model has much more detail than the man-machine model. It can be seen from the result that TPE algorithm is superior both in efficiency and uncertainty control and favorable for the research of complicated topography.%为了提高多波束数据处理效率,克服趋势面法、中值滤波法等对海底地形细节的损坏,采用总传播误差法进行多波束数据处理、构建海底地形模型(DTM).研究结果表明:总传播误差法以实测数据误差计算为基础,依据IHO标准设置滤波器进行粗差自动剔除,避免了人机交互式编辑主观性判断的干扰,数据处理速度是人机交互式编辑的5倍.总传播误差法依据水深变化设置可变网格,保证了地形模型具有较高的分辨率,很好地保留了地形细节.总传播误差模型具有更强的抗差性,适合于海底热液区等复杂地形环境研究.
Controlling Second Harmonic Efficiency of Laser Beam Interactions
Barnes, Norman P. (Inventor); Walsh, Brian M. (Inventor); Reichle, Donald J. (Inventor)
2011-01-01
A method is provided for controlling second harmonic efficiency of laser beam interactions. A laser system generates two laser beams (e.g., a laser beam with two polarizations) for incidence on a nonlinear crystal having a preferred direction of propagation. Prior to incidence on the crystal, the beams are optically processed based on the crystal's beam separation characteristics to thereby control a position in the crystal along the preferred direction of propagation at which the beams interact.
Institute of Scientific and Technical Information of China (English)
李晋红; 吕百达
2011-01-01
基于广义惠更斯一菲涅耳原理，以高斯-谢尔模型（GSM）涡旋光束作为典型的部分相干涡旋光束，推导出GSM涡旋光束通过大气湍流斜程传输的平均光强、均方根束宽和交叉谱密度函数的解析表达式，并用以研究了大气湍流中上行和下行对GSM涡旋光束传输和对相干涡旋的影响．结果表明，在相同条件下，GSM涡旋光束下行传输受大气湍流的影响要小于上行传输，下行传输时相干涡旋拓扑电荷守恒距离要长于上行传输．对所得结果做了物理解释．%Based on the extended Huygens-Fresnel principle, the propagations of a partially coherent vortex beam through atmospheric turbulence along an uplink path and a downlink path are studied, where the Gaussian Schell-model （GSM） vortex beam is taken as a typical example of partially coherent vortex beam. The analytical expressions for the average intensity, rms width and cross-spectral density function of GSM vortex beam propagating through atmospheric turbulence along a slant path are derived and used to study the influence of atmospheric turbulence along an uplink path and a downlink path on GSM vortex beam propagation and on coherence vortex. It is shown that under the same conditions the influence of atmospheric turbulence along a downlink path on GSM vortex beam propagation is smaller than that along a uplink path, and the conservation distance of the topological charge of GSM vortex beam along a downlink path is longer than that along a uplink path. The results are explained in physics.
Propagation of Vortex Electron Wave Functions in a Magnetic Field
Gallatin, Gregg M
2012-01-01
The physics of coherent beams of photons carrying axial orbital angular momentum (OAM) is well understood and such beams, sometimes known as vortex beams, have found applications in optics and microscopy. Recently electron beams carrying very large values of axial OAM have been generated. In the absence of coupling to an external electromagnetic field the propagation of such vortex electron beams is virtually identical mathematically to that of vortex photon beams propagating in a medium with a homogeneous index of refraction. But when coupled to an external electromagnetic field the propagation of vortex electron beams is distinctly different from photons. Here we use the exact path integral solution to Schrodingers equation to examine the time evolution of an electron wave function carrying axial OAM. Interestingly we find that the nonzero OAM wave function can be obtained from the zero OAM wave function, in the case considered here, simply by multipling it by an appropriate time and position dependent pref...
Optimal beam focusing through turbulence.
Charnotskii, Mikhail
2015-11-01
Beam spread and beam wandering are the most perceptible effects of atmospheric turbulence on propagating laser beams. The width of the mean irradiance profile is typically used to characterize the beam spread. This so-called long-term (LT) statistic allows for a relatively simple theoretical description. However, the LT beam size is not a very practical measure of the beam spread because its measurements are sensitive to the movements of the source and detector, and to the large-scale variations of the refractive index that are not associated with turbulence. The short-term (ST) beam spread is measured relative to the instantaneous position of the beam center and is free of these drawbacks, but has not been studied as thoroughly as the LT spread. We present a theoretical model for the ST beam irradiance that is based on the parabolic equation for the beam wave propagation in random media, and the Markov approximation for calculation of the statistics of the optical field, and discuss an approximation that allows introduction of the isoplanatic ST point spread function (PSF). Unlike the LT PSF, the ST PSF depends on the overall beam geometry. This allows optimization of the initial beam field in terms of minimizing the ST beam size at the observation plane. Calculations supporting this conjecture are presented for the simple case of the coherent Gaussian beam, and Kolmogorov turbulence.
CLIC Drive Beam Phase Stabilisation
Gerbershagen, Alexander; Schulte, Daniel
The thesis presents phase stability studies for the Compact Linear Collider (CLIC) and focuses in particular on CLIC Drive Beam longitudinal phase stabilisation. This topic constitutes one of the main feasibility challenges for CLIC construction and is an essential component of the current CLIC stabilisation campaign. The studies are divided into two large interrelated sections: the simulation studies for the CLIC Drive Beam stability, and measurements, data analysis and simulations of the CLIC Test Facility (CTF3) Drive Beam phase errors. A dedicated software tool has been developed for a step-by-step analysis of the error propagation through the CLIC Drive Beam. It uses realistic RF potential and beam loading amplitude functions for the Drive and Main Beam accelerating structures, complete models of the recombination scheme and compressor chicane as well as of further CLIC Drive Beam modules. The tool has been tested extensively and its functionality has been verified. The phase error propagation at CLIC h...
Directory of Open Access Journals (Sweden)
Oláh, János
2014-06-01
Full Text Available Based upon our previous reviews on the phylogenetic species concept, initial split criteria and fine structure analysis here we summarize population and model thinking as support to our diverged structure matrix procedure to test simply visually or, if required, by geometric morphometrics the stability of sexual selection-driven adaptive, non-neutral traits of the phallic organ. Complexity review helped us to establish plesiomorphic and apomorphic states of parameres of the phallic organ. Fine structure diversity of the adaptive traits of paramere and the apical portion of aedeagus has been applied to revise the Allogamus genus. All the known 22 taxa, 19 species and 3 subspecies, have been revised. Apomorphic fusion of parameres and complexity evolution of aedeagus directed us to erect 2 rediagnosed species groups, 1 new species group, 4 new species subgroups, 1 new species complex, 10 new species and 4 new or revised species status as follows: Allogamus auricollis species group, rediagnosed. Allogamus antennatus new subgroup: A. antennatus (McLachlan, 1876, A. ausoniae Moretti, 1991, stat. rev., A. morettii DePietro & Cianficconi, 2001, stat. rev., A. silanus Moretti 1991, stat. nov. Allogamus auricollis new subgroup: A. alpensis Oláh, Lodovici & Valle sp. nov., A. auricollis (Pictet, 1834, A. despaxi Decamps, 1967, A. zomok Oláh & Coppa sp. nov. Allogamus hilaris new subgroup: A. hilaris (McLachlan, 1876. Allogamus ligonifer new subgroup: A. gibraltaricus Gonzalez & Ruiz, 2001, A. kefes Coppa & Oláh sp. nov., A. laureatus (Navas, 1918, A. ligonifer (McLachlan, 1876, A. pertuli Malicky, 1974, A. pupos Coppa & Oláh sp. nov. Allogamus mortoni new species complex: A. kampos Oláh & Ruiz sp. nov., A. kettos Oláh & Ruiz sp. nov., A. kurtas Oláh & Zamora-Muñoz sp. nov., A. mortoni (Navas, 1907, A. pohos Oláh & Zamora-Muñoz sp. nov., A. tuskes Oláh & Sáinz-Bariáin sp. nov. Allogamus corsicus new species group: A. corsicus (Ris, 1897. A
Diffraction-free beams in fractional Schr\\"odinger equation
Zhang, Yiqi; Belić, Milivoj R; Ahmed, Noor; Zhang, Yanpeng; Xiao, Min
2015-01-01
We consider the propagation of one-dimensional and two-dimensional (1D, 2D) Gaussian beams in FSE without a potential, analytically and numerically. Without chirp, a 1D Gaussian beam splits into two nondiffracting Gaussian beams during propagation, while a 2D Gaussian beam undergoes conical diffraction. When a Gaussian beam carries linear chirp, the 1D beam deflects along the trajectories $z=\\pm2(x-x_0)$, which are independent of the chirp. In the case of 2D Gaussian beam, the propagation is also deflected, but the trajectories align along the diffraction cone $z=2r$ and the direction is determined by the chirp. Both 1D and 2D Gaussian beams are diffractionless and display uniform propagation. The nondiffracting property discovered in this model applies to other beams as well. Based on this nondiffracting and splitting property, we introduce the Talbot effect of diffractionless beams in FSE.
Generation of electron Airy beams.
Voloch-Bloch, Noa; Lereah, Yossi; Lilach, Yigal; Gover, Avraham; Arie, Ady
2013-02-21
Within the framework of quantum mechanics, a unique particle wave packet exists in the form of the Airy function. Its counterintuitive properties are revealed as it propagates in time or space: the quantum probability wave packet preserves its shape despite dispersion or diffraction and propagates along a parabolic caustic trajectory, even though no force is applied. This does not contradict Newton's laws of motion, because the wave packet centroid propagates along a straight line. Nearly 30 years later, this wave packet, known as an accelerating Airy beam, was realized in the optical domain; later it was generalized to an orthogonal and complete family of beams that propagate along parabolic trajectories, as well as to beams that propagate along arbitrary convex trajectories. Here we report the experimental generation and observation of the Airy beams of free electrons. These electron Airy beams were generated by diffraction of electrons through a nanoscale hologram, which imprinted on the electrons' wavefunction a cubic phase modulation in the transverse plane. The highest-intensity lobes of the generated beams indeed followed parabolic trajectories. We directly observed a non-spreading electron wavefunction that self-heals, restoring its original shape after passing an obstacle. This holographic generation of electron Airy beams opens up new avenues for steering electronic wave packets like their photonic counterparts, because the wave packets can be imprinted with arbitrary shapes or trajectories.
Laser absorption and electron propagation in rippled plasma targets
Shukla, Chandrasekhar; Das, Amita; Patel, Kartik
2016-10-01
Efficient absorption of laser energy and the collimated propagation of relativistic electron beams (generated by the laser target interaction) in plasma are two issues which are of significant importance for applications such as fast ignition scheme of inertial confinement fusion (ICF). It is shown with the help of 2-D Particle- In- Cell simulations that introducing density ripples transverse to the laser propagation direction enhances the efficiency of laser power absorption. Furthermore, the density ripples are also instrumental in suppressing the Weibel instability of the propagating electron beam (which is responsible for the divergence of the beam). A physical understanding of the two effects is also provided.
Photon propagation in slowly varying electromagnetic fields
Karbstein, Felix
2016-01-01
We study the effective theory of soft photons in slowly varying electromagnetic background fields at one-loop order in QED. This is of relevance for the study of all-optical signatures of quantum vacuum nonlinearity in realistic electromagnetic background fields as provided by high-intensity lasers. The central result derived in this article is a new analytical expression for the photon polarization tensor in two linearly polarized counter-propagating pulsed Gaussian laser beams. As we treat the peak field strengths of both laser beams as free parameters this field configuration can be considered as interpolating between the limiting cases of a purely right- or left-moving laser beam (if one of the peak field strengths is set to zero) and the standing-wave type scenario with two counter-propagating beams of equal strength.
Trofimov, M Yu; Kozitskiy, S B
2015-01-01
An adiabatic mode Helmholtz equation for 3D underwater sound propagation is developed. The Gaussian beam tracing in this case is constructed. The test calculations are carried out for the crosswedge benchmark and proved an excellent agreement with the source images method.
Viering, Kirsten; Medellin, David; Mo, Jianyong; Raizen, Mark G
2012-11-05
We report on an experimental method to align a laser beam to a cloud of atoms trapped in a magneto-optical trap (MOT). We show how balanced lock-in detection leads to a very sensitive method to align the laser beam to the atoms in the plane perpendicular to the propagation direction. This provides a very reliable and fast way of aligning laser beams to atoms trapped in a MOT.
Energy Technology Data Exchange (ETDEWEB)
Glinec, Y
2006-09-15
This experimental study concerns the generation of electron beams with original properties. These electrons beams originate from the interaction of an ultra-intense and short laser pulse with a gas jet. Previously, these electron beams had a large divergence and a broad spectrum. A major improvement in this field was achieved when an electron beam with low divergence (10 mrad) and a peaked spectrum (170 MeV) was observed during this thesis, using a new single shot electron spectrometer. A parametric study of the interaction allowed to observe the evolution of the electron beam. Experiments have been carried out to deepen the characterization of the electron beam. The observation of transition radiation generated by the electrons at an interface shows that the electron beam interacts with the laser pulse during the acceleration. Radial oscillations of the electron beam around the laser axis, named betatron oscillations, were also observed on the electron spectra. Such a quasi-monoenergetic spectrum is essential for many applications. In order to justify the interest of this electron beam, several applications are presented: a sub-milli-metric gamma-ray radiography of dense objects, a dose profile of the electron beam comparable to present capabilities of photon sources for radiotherapy, a very short temporal profile useful for water radiolysis and the generation of a bright X-ray source with low divergence. (author)
Symmetry-constrained electron vortex propagation
Clark, L; Béché, A; Lubk, A; Verbeeck, J
2016-01-01
Electron vortex beams hold great promise for development in transmission electron microscopy, but have yet to be widely adopted. This is partly due to the complex set of interactions that occur between a beam carrying orbital angular momentum (OAM) and a sample. Herein, the system is simplified to focus on the interaction between geometrical symmetries, OAM and topology. We present multiple simulations, alongside experimental data to study the behaviour of a variety of electron vortex beams after interacting with apertures of different symmetries, and investigate the effect on their OAM and vortex structure, both in the far-field and under free-space propagation.
Electromagnetic Wave Propagation in Random Media
DEFF Research Database (Denmark)
Pécseli, Hans
1984-01-01
The propagation of a narrow frequency band beam of electromagnetic waves in a medium with randomly varying index of refraction is considered. A novel formulation of the governing equation is proposed. An equation for the average Green function (or transition probability) can then be derived...
Directory of Open Access Journals (Sweden)
Vizcarra Herles Nina Eleonor
2011-08-01
Full Text Available Resumen:En el presente ensayo, los autores con base en la revisión de fuentes bibliográficas, abordan el tema de la no neutralidad de la evaluación de la calidad de la educación superior, se identifican factores de la no neutralidad en la evaluación y en la calidad relacionados con: el referente (modelo de referencia utilizado para la evaluación, las dimensiones explicativo-relacionales de la calidad y las demandas de calidad formuladas por actores sociales; estos factores expresan el propósito del evaluador, componente ideológico que determina la no neutralidad de la evaluación de la calidad. Se infiere que para los sistemas nacionales de evaluación la definición y la mejora de la calidad de la educación superior compromete la participación multisectorial.Abstract: In this essay, the authors based on a review of literature sources, address the issue of non-neutrality of the evaluation of the quality of higher education, identify factors of non-neutrality in the evaluation and quality related to: the reference model used for evaluation, the explanatory-relational dimensions of quality and quality demands made by social actors; these factors express the purpose of evaluator, ideological component that determines the non-neutrality of quality assessment. It is inferred that for the national assessment systems; the definition and the improving of the quality of higher education undertake multi-stakeholder participation.
Simulation and experiments of ultrasonic propagation in nickel-based alloy weldments
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
In order to obtain good understanding of complicated beam propagation behaviors in nickel-based alloy weldments, ray tracing simulation is established to predict the ultrasonic beam path in a special welded structure of dissimilar steels. Also experimental examinations are carried out to measure the ultrasonic beam paths in the weldment. Then comparisons of the modeling predictions with experimental results are presented to reveal the complicated beam propagation behaviors.
Beam splitter and combiner based on Bloch oscillations in spatially modulated waveguide arrays
Zhang, Yiqi; Zhong, Weiping; Wen, Feng; Guo, Yang; Guo, Yao; Lu, Keqing; Zhang, Yanpeng
2014-01-01
We numerically investigate the light beam propagation in periodic waveguide arrays which are elaborately modulated with certain structures. We find that the light beam may split, coalesce, deflect, and be localized during propagation in these spatially modulated waveguide arrays. All the phenomena originate from Bloch oscillations, and supply possible method for fabricating on-chip beam splitters and beam combiners.
Time-domain Wave Propagation in Dispersive Media①
Institute of Scientific and Technical Information of China (English)
无
1997-01-01
The equation of time-domain wave propagation in dispersive media and the explicit beam propagation method are presented in this paper.This method is demonstrated by the short optical pulses in a directional coupler with second order dispersive effect and shows to be in full agreement with former references.This method is simple,easy and practical.
Modeling paraxial wave propagation in free-electron laser oscillators
Karssenberg, J.G.; van der Slot, Petrus J.M.; Volokhine, I.; Verschuur, Jeroen W.J.; Boller, Klaus J.
2006-01-01
Modeling free-electron laser (FEL) oscillators requires calculation of both the light-beam interaction within the undulator and the light propagation outside the undulator. We have developed a paraxial optical propagation code that can be combined with various existing models of gain media, for
Modeling paraxial wave propagation in free-electron laser oscillators
Karssenberg, J.G.; Slot, van der P.J.M.; Volokhine, I.V.; Verschuur, J.W.J.; Boller, K.J.
2006-01-01
Modeling free-electron laser (FEL) oscillators requires calculation of both the light-beam interaction within the undulator and the light propagation outside the undulator. We have developed a paraxial optical propagation code that can be combined with various existing models of gain media, for exam
Repositioning and steering laser beam power via coherent combination of multiple Airy beams.
Zhang, Ze; Ye, Zhuoyi; Song, Daohong; Zhang, Peng; Chen, Zhigang
2013-12-10
We study numerically and experimentally laser coherent combination (LCC) with multiple one- or two-dimensional Airy beams. It is shown that the method of LCC using Airy beams leads to a higher combining efficiency and a better feature of propagation than that using conventional Gaussian beams. Based on such coherent Airy beams combination, we propose a laser steering approach that could achieve large-angle beam steering (over 0.6°) without the need of using any mechanical steering component.
Intra–cavity generation of Bessel–like beams with longitudinally dependent cone angles
CSIR Research Space (South Africa)
Litvin, IA
2010-02-01
Full Text Available The authors report on two resonator systems for producing Bessel–like beams with longitudinally dependent cone angles (LDBLBs). Such beams have extended propagation distances as compared to conventional Bessel– Gauss beams, with a far field pattern...
Non-diffractive beam in random media
Shiina, Tatsuo
2017-09-01
Beam propagation has been given important attention in a variety of applications in medicine, remote sensing and information science. Especially, the beam propagation in highly scattering media, which is called random media, is important. In general, the multiple scattering gets rid of beam characteristics, e.g., intensity distribution, phase front, and polarization. In this study, self-converging effect of annular beam was applied in random media. Diluted milk was used as random media, and the transmitted light was detected with a narrow view angle of 5.5mrad. The collimated annular beam of a few tens millimeters takes a few hundred meters to transform its beam shape into the non-diffractive beam in free space, while this transformation was shorten only to 20 cm in random media, that is, the collimated annular beam caused its transformation at only 20 cm in random media. The transformed beam kept its optical characteristics of ;non-diffractive beam;. Such transformation of the annular beam needs the appropriate condition of random media. Media concentration and propagation distance control the generation of the center peak intensity of the transformed beam. This study indicates the generation of the non-diffractive beam in random media and reveals its appropriate condition.
Measuring Propagation Speed of Coulomb Fields
Calcaterra, A; Finocchiaro, G; Patteri, P; Piccolo, M; Pizzella, G
2012-01-01
The problem of gravity propagation has been subject of discussion for quite a long time: Newton, Laplace and, in relatively more modern times, Eddington pointed out that, if gravity propagated with finite velocity, planets motion around the sun would become unstable due to a torque originating from time lag of the gravitational interactions. Such an odd behavior can be found also in electromagnetism, when one computes the propagation of the electric fields generated by a set of uniformly moving charges. As a matter of fact the Li\\'enard-Weichert retarded potential leads to a formula indistinguishable from the one obtained assuming that the electric field propagates with infinite velocity. Feyman explanation for this apparent paradox was based on the fact that uniform motions last indefinitely. To verify such an explanation, we performed an experiment to measure the time/space evolution of the electric field generated by an uniformely moving electron beam. The results we obtain on such a finite lifetime kinema...
Nijhof, Marten Jozef Johannes
2010-01-01
In this work, the accuracy, efficiency and range of applicability of various (approximate) models for viscothermal wave propagation are investigated. Models for viscothermal wave propagation describe thewave behavior of fluids including viscous and thermal effects. Cases where viscothermal effects a
Fractional Fourier transform of Lorentz beams
Institute of Scientific and Technical Information of China (English)
Zhou Guo-Quan
2009-01-01
This paper introduces Lorentz beams to describe certain laser sources that produce highly divergent fields. The fractional Fourier transform (FRFT) is applied to treat the propagation of Lorentz beams. Based on the definition of convolution and the convolution theorem of the Fourier transform, an analytical expression for a Lorentz beam passing through a FRFT system has been derived. By using the derived formula, the properties of a Lorentz beam in the FRFT plane are illustrated numerically.
Light propagation through anisotropic turbulence.
Toselli, Italo; Agrawal, Brij; Restaino, Sergio
2011-03-01
A wealth of experimental data has shown that atmospheric turbulence can be anisotropic; in this case, a Kolmogorov spectrum does not describe well the atmospheric turbulence statistics. In this paper, we show a quantitative analysis of anisotropic turbulence by using a non-Kolmogorov power spectrum with an anisotropic coefficient. The spectrum we use does not include the inner and outer scales, it is valid only inside the inertial subrange, and it has a power-law slope that can be different from a Kolmogorov one. Using this power spectrum, in the weak turbulence condition, we analyze the impact of the power-law variations α on the long-term beam spread and scintillation index for several anisotropic coefficient values ς. We consider only horizontal propagation across the turbulence cells, assuming circular symmetry is maintained on the orthogonal plane to the propagation direction. We conclude that the anisotropic coefficient influences both the long-term beam spread and the scintillation index by the factor ς(2-α).
Coherent beam combining of high powerfiber lasers: Progress and prospect
Institute of Scientific and Technical Information of China (English)
LIU; ZeJin; ZHOU; Pu; XU; XiaoJun; WANG; XiaoLin; MA; YanXing
2013-01-01
The recent research progress of coherent beam combining of high power fiber lasers is reviewed. Key technologies like coherently combinable fiber laser, phase control of multiple beams and beam tilling are specially analyzed. Prospects for single coherently combinable high power fiber amplifier, beam tilling and target-in-the-loop control for propagation in real atmosphere are presented.
Generation and propagation of optical vortices
Rozas, David
Optical vortices are singularities in phase fronts of laser beams. They are characterized by a dark core whose size (relative to the size of the background beam) may dramatically affect their behavior upon propagation. Previously, only large-core vortices have been extensively studied. The object of the research presented in this dissertation was to explore ways of generating small-core optical vortices (also called optical vortex filaments ), and to examine their propagation using analytical, numerical and experimental methods. Computer-generated holography enabled us to create arbitrary distributions of optical vortex filaments for experimental exploration. Hydrodynamic analogies were used to develop an heuristic model which described the dependence of vortex motion on other vortices and the background beam, both qualitatively and quantitatively. We predicted that pair of optical vortex filaments will rotate with angular rates inversely proportional to their separation distance (just like vortices in a fluid). We also reported the first experimental observation of this novel fluid-like effect. It was found, however, that upon propagation in linear media, the fluid-like rotation was not sustained owing to the overlap of diffracting vortex cores. Further numerical studies and experiments showed that rotation angle may be enhanced in nonlinear self-defocusing media. The results presented in this thesis offer us a better understanding of dynamics of propagating vortices which may result in applications in optical switching, optical data storage, manipulation of micro-particles and optical limiting for eye protection.
Divergence of optical vortex beams
Reddy, Salla Gangi; Prabhakar, Shashi; Anwar, Ali; Banerji, J; Singh, R P
2015-01-01
We show, both theoretically and experimentally, that the propagation of optical vortices in free space can be analysed by using the width ($w(z)$) of the host Gaussian beam and the inner and outer radii of the vortex beam at the source plane ($z=0$) as defined in \\textit{Optics Letters \\textbf{39,} 4364-4367 (2014)}. We also studied the divergence of vortex beams, considered as the rate of change of inner or outer radius with the propagation distance, and found that it varies with the order in the same way as that of the inner and outer radii at zero propagation distance. These results may be useful in designing optical fibers for orbital angular momentum modes that play a crucial role in quantum communication.
Institute of Scientific and Technical Information of China (English)
向宁静; 吴振森; 王明军
2013-01-01
Based on the extended Huygens-Fresnel integral, the cross-spectral density and Rytov's phase structure function, average intensity was derived by a formula for the Fourier transform of Gaussian function. Then mean squared root beam width, beam wander of a partially coherent Gaussian-Schell-model (GSM) beam in turbulent atmosphere were found out. It shows that beam spread and beam wander have relation with initial beam radius, initial coherence width, wavelength and transmitter hight in the atmospheric turbulence. At last, some measures were brought to decrease the effect of atmospheric turbulence.% 基广义惠更斯-菲涅耳理，交叉密度函数以及Rytov's相位结构函数二次近似，利用傅里高斯变换推导出部分相干高斯-谢尔(GSM)光束在大气湍流中的强度分布表达式，并在此基础上分析了大气湍流对光束展宽、以及光束漂移的影响。数值模拟表明：光束展宽和光束漂移与光束的初始半径、波长、光的相干宽度以及发射机的位置高度有关，并提出了减小湍流影响的措施。
Counter-propagating patterns in the BioPhotonics Workstation
DEFF Research Database (Denmark)
Palima, Darwin; Lindballe, T.; Kristensen, M.V.
2010-01-01
for stable three-dimensional manipulation of multiple particles. In this work, we analyze counter-propagating shaped-beam traps that depart from this conventional geometry. We show that projecting shaped beams with separation distances previously considered axially unstable can, in fact, enhance the trap...... by improving axial and transverse trapping stiffness. We also show interesting results of trapping and micromanipulation experiments that combine optical forces with fluidic forces. These results hint about the rich potential of using patterned counter-propagating beams for optical trapping and manipulation...
Schulte, Christian
2008-01-01
When implementing a propagator for a constraint, one must decide about variants: When implementing min, should one also implement max? Should one implement linear equations both with and without coefficients? Constraint variants are ubiquitous: implementing them requires considerable (if not prohibitive) effort and decreases maintainability, but will deliver better performance. This paper shows how to use variable views, previously introduced for an implementation architecture, to derive perfect propagator variants. A model for views and derived propagators is introduced. Derived propagators are proved to be indeed perfect in that they inherit essential properties such as correctness and domain and bounds consistency. Techniques for systematically deriving propagators such as transformation, generalization, specialization, and channeling are developed for several variable domains. We evaluate the massive impact of derived propagators. Without derived propagators, Gecode would require 140000 rather than 40000 ...
Vectorial rotating vortex Hankel laser beams
Kotlyar, Victor V.; Kovalev, Alexey A.; Soifer, Victor A.
2016-09-01
We propose a generalization of spherical waves in the form of linearly polarized beams with embedded optical vortices. The source of these beams is an infinitely narrow light ring with an infinitely small radius. These vectorial beams are obtained based on scalar Hankel beams discovered by the authors recently. We have derived explicit relations for complex amplitudes of all six components of vectorial vortex Hankel beams. A closed analytical expression for the axial projection of the orbital angular momentum density in far field has been obtained. We also showed that the intensity distribution of the electric vector rotates by 90 degrees upon the beam propagation in near field.
Photon Propagation in Slowly Varying Electromagnetic Fields
Karbstein, F.
2017-03-01
Effective theory of soft photons in slowly varying electromagnetic background fields is studied at one-loop order in QED. This is of relevance for the study of all-optical signatures of quantum vacuum nonlinearity in realistic electromagnetic background fields as provided by high-intensity lasers. The central result derived in this article is a new analytical expression for the photon polarization tensor in two linearly polarized counterpropagating pulsed Gaussian laser beams. Treating the peak field strengths of both laser beams as free parameters, this field configuration can be considered as interpolating between the limiting cases of a purely right- or left-moving laser beam (if one of the peak field strengths is set equal to zero) and the standing-wave type scenario with two counter-propagating beams of equal strength.
Influence of plasma turbulence on microwave propagation
Köhn, Alf; Leddy, Jarrod; Thomas, Matthew B; Vann, Roddy G L
2016-01-01
It is not fully understood how electromagnetic waves propagate through plasma fluctuations when the size of the fluctuations is comparable with the wavelength of the incident radiation. In this paper, the perturbing effect of a turbulent plasma density layer on a traversing microwave beam is simulated with full-wave simulations. The deterioration of the microwave beam is calculated as a function of the characteristic turbulence structure size, the turbulence amplitude, the depth of the interaction zone and the size of the waist of the incident beam. The maximum scattering is observed for a structure size on the order of half the vacuum wavelength. The scattering and beam broadening was found to increase linearly with the depth of the turbulence layer and quadratically with the fluctuation strength. Consequences for experiments and 3D effects are considered.
Piotrzkowski, Krzysztof
2007-01-01
If the recently observed anomaly in the PVLAS experiment is due to the axion, then the powerful beams of synchrotron photons, propagating through high magnetic field of the HERA beamline, become strong axion sources. This gives a unique opportunity of detection of the axion-photon interactions by installing a small detector in the HERA tunnel, and to corroborate the axion hypothesis within a few days of running. Comment: 5 pages, 1 figure
Bollini, C. G.; Rocca, M. C.
1998-01-01
We study the half advanced and half retarded Wheeler Green function and its relation to Feynman propagators. First for massless equation. Then, for Klein-Gordon equations with arbitrary mass parameters; real, imaginary or complex. In all cases the Wheeler propagator lacks an on-shell free propagation. The Wheeler function has support inside the light-cone (whatever the mass). The associated vacuum is symmetric with respect to annihilation and creation operators. We show with some examples tha...
Filament propagation length of femtosecond pulses with different transverse modes
Kaya, N; Kaya, G; Strohaber, J; Kolomenskii, A A; Schuessler, H A
2014-01-01
We experimentally studied intense femtosecond pulse filamentation and propagation in water for Gaussian, Laguerre-Gaussian, and Bessel-Gaussian incident beams. These different transverse modes for incident laser pulses were created from an initial Gaussian beam by using a computer generated hologram technique. We found that the length of the filament induced by the Bessel-Gaussian incident beam was longer than that for the other transverse modes under the conditions of the same peak intensity, pulse duration, and the size of the central part of the beam. To better understand the Bessel-Gaussian beam propagation, we performed a more detailed study of the filament length as a function of the number of radial modal lobes. The length increased with the number of lobes, implying that the radial modal lobes serve as an energy reservoir for the filament formed by the central intensity peak.
Beam halo studies in LEHIPA DTL
Roy, S.; Pande, R.; Rao, S. V. L. S.; Krishnagopal, S.; Singh, P.
2015-11-01
The Low Energy High Intensity Proton Accelerator (LEHIPA) project at Bhabha Atomic Research Centre (BARC) consists of a 20 MeV, 30 mA proton linac. The accelerator comprises of a 3 MeV Radio Frequency Quadrupole (RFQ) and a 20 MeV Drift Tube Linac (DTL). In such high intensity accelerators, beam halos are of concern as they not only cause an increase in emittance, but also lead to beam loss and radio activation. We have studied the effect of beam mismatch at the DTL input on halo formation and propagation. The particle core model is used to excite the three envelope eigen modes; the quadrupole mode, the fast mode and the slow mode by giving input beam mismatch. These modes get damped as the beam progresses through the DTL. The damping mechanism is clearly Landau damping and leads to increase in rms emittance of the beam. The evolution of these modes and the corresponding increase in beam emittance and maximum beam extent, as the beam propagates through the DTL, has been studied for different space charge tunes. The halo parameter based on the definition of Allen and Wangler has been calculated. It is seen that beam halos are very important for LEHIPA DTL, even at 20 MeV and leads to emittance and beam size increase and also to beam loss in some cases. The longitudinal halo is present even without mismatch and transverse halos arise in the presence of beam mismatch.
Andreasen, J; Kolesik, M
2012-09-01
Unidirectional pulse propagation equations [UPPE, Phys. Rev. E 70, 036604 (2004)] have provided a theoretical underpinning for computer-aided investigations into dynamics of high-power ultrashort laser pulses and have been successfully utilized for almost a decade. Unfortunately, they are restricted to applications in bulk media or, with additional approximations, to simple waveguide geometries in which only a few guided modes can approximate the propagating waveform. The purpose of this work is to generalize the directional pulse propagation equations to structures characterized by strong refractive index differences and material interfaces. We also outline a numerical solution framework that draws on the combination of the bulk-media UPPE method with single-frequency beam-propagation techniques.
DEFF Research Database (Denmark)
2007-01-01
The invention relates to a method and a system for synthesizing a set of controllable light beams by provision of a system for synthesizing a set of light beams, comprising a spatially modulated light source for generation of electromagnetic radiation with a set of replicas of a predetermined......(x-xs, y-ys), a Fourier transforming lens for Fourier transforming the electromagnetic radiation, a first spatial light modulator for phase shifting the Fourier transformed electromagnetic radiation with the phase -F(u, v) of S*, S* is the complex conjugate of the Fourier transformed symbol s, a Fourier...... transforming lens for Inverse Fourier transforming the spatially modulated radiation, whereby a set of light beams are formed propagating through the inverse Fourier plane (x', y') at desired positions (x's, y's), and a controller for controlling the position of a replica of the symbol, s, for movement...
Aharon, Oren
2014-02-01
In various modern scientific and industrial laser applications, beam-shaping optics manipulates the laser spot size and its intensity distribution. However the designed laser spot frequently deviates from the design goal due to real life imperfections and effects, such as: input laser distortions, optical distortion, heating, overall instabilities, and non-linear effects. Lasers provide the ability to accurately deliver large amounts of energy to a target area with very high accuracy. Thus monitoring beam size power and beam location is of high importance for high quality results and repeatability. Depending on the combination of wavelength, beam size and pulse duration , laser energy is absorbed by the material surface, yielding into processes such as cutting, welding, surface treatment, brazing and many other applications. This article will cover the aspect of laser beam measurements, especially at the focal point where it matters the most. A brief introduction to the material processing interactions will be covered, followed by fundamentals of laser beam propagation, novel measurement techniques, actual measurement and brief conclusions.
Propagating Characteristics of Pulsed Laser in Rain
Directory of Open Access Journals (Sweden)
Jing Guo
2015-01-01
Full Text Available To understand the performance of laser ranging system under the rain weather condition, we need to know the propagating characteristics of laser pulse in rain. In this paper, the absorption and attenuation coefficients were calculated based on the scattering theories in discrete stochastic media, and the propagating characteristics of laser pulse in rain were simulated and analyzed using Monte-Carlo method. Some simulation results were verified by experiments, and the simulation results are well matched with the experimental data, with the maximal deviation not less than 7.5%. The results indicated that the propagating laser beam would be attenuated and distorted due to the scattering and absorption of raindrops, and the energy attenuation and pulse shape distortion strongly depended on the laser pulse widths.
Measuring propagation speed of Coulomb fields
Energy Technology Data Exchange (ETDEWEB)
Sangro, R. de; Finocchiaro, G.; Patteri, P.; Piccolo, M.; Pizzella, G. [Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, Frascati (Italy)
2015-03-01
The problem of gravity propagation has been subject of discussion for quite a long time: Newton, Laplace and, in relatively more modern times, Eddington pointed out that, if gravity propagated with finite velocity, planet motion around the sun would become unstable due to a torque originating from time lag of the gravitational interactions. Such an odd behavior can be found also in electromagnetism, when one computes the propagation of the electric fields generated by a set of uniformly moving charges. As a matter of fact the Lienard-Weichert retarded potential leads to the same formula as the one obtained assuming that the electric field propagate with infinite velocity. The Feynman explanation for this apparent paradox was based on the fact that uniform motions last indefinitely. To verify such an explanation, we performed an experiment to measure the time/space evolution of the electric field generated by an uniformly moving electron beam. The results we obtain, on a finite lifetime kinematical state, are compatible with an electric field rigidly carried by the beam itself. (orig.)
2016-06-07
Shallow- Water Propagation William L. Siegmann Rensselaer Polytechnic Institute 110 Eighth Street Troy, New York 12180-3590 phone: (518) 276...ocean_acoustics LONG-TERM GOALS Develop methods for propagation and coherence calculations in complex shallow- water environments, determine...intensity and coherence. APPROACH (A) Develop high accuracy PE techniques for applications to shallow- water sediments, accounting for
Properties of the accelerator-produced beam
Energy Technology Data Exchange (ETDEWEB)
Caporaso, G.J.; Chambers, F.W.; Cole, A.G.; Fawley, W.M.; Struve, K.W.
1985-10-11
Obtaining detailed knowledge of the condition of the electron beam delivered to the experimental tank is of prime importance in the attempt to correlate the propagation data with theory. There are many interesting and unique features of the beam delivered by Advanced Test Accelerator (ATA) to the experimental tank.
Yuan, Yangsheng; Lei, Ting; Li, Zhaohui; Li, Yangjin; Gao, Shecheng; Xie, Zhenwei; Yuan, Xiaocong
2017-02-01
Optical beam wander is one of the most important issues for free-space optical (FSO) communication. We theoretically derive a beam wander model for Bessel beams propagating in turbulent atmosphere. The calculated beam wander of high order Bessel beams with different turbulence strengths are consistent with experimental measurements. Both theoretical and experimental results reveal that high order Bessel beams are less influenced by the turbulent atmosphere. We also demonstrate the Bessel beams based orbital angular momentum (OAM) multiplexing/demultiplexing in FSO communication with atmospheric turbulence. Under the same atmospheric turbulence condition, the bit error rates of transmitted signals carried by high order Bessel beams show smaller values and fluctuations, which indicates that the high order Bessel beams have an advantage of mitigating the beam wander in OAM multiplexing FSO communication.
Yuan, Yangsheng; Lei, Ting; Li, Zhaohui; Li, Yangjin; Gao, Shecheng; Xie, Zhenwei; Yuan, Xiaocong
2017-02-10
Optical beam wander is one of the most important issues for free-space optical (FSO) communication. We theoretically derive a beam wander model for Bessel beams propagating in turbulent atmosphere. The calculated beam wander of high order Bessel beams with different turbulence strengths are consistent with experimental measurements. Both theoretical and experimental results reveal that high order Bessel beams are less influenced by the turbulent atmosphere. We also demonstrate the Bessel beams based orbital angular momentum (OAM) multiplexing/demultiplexing in FSO communication with atmospheric turbulence. Under the same atmospheric turbulence condition, the bit error rates of transmitted signals carried by high order Bessel beams show smaller values and fluctuations, which indicates that the high order Bessel beams have an advantage of mitigating the beam wander in OAM multiplexing FSO communication.
Spatiotemporal structure of femtosecond Bessel beams from spatial light modulators.
Froehly, L; Jacquot, M; Lacourt, P A; Dudley, J M; Courvoisier, F
2014-04-01
We numerically investigate the spatiotemporal structure of Bessel beams generated with spatial light modulators (SLMs). Grating-like phase masks enable the spatial filtering of undesired diffraction orders produced by SLMs. Pulse front tilt and temporal broadening effects are investigated. In addition, we explore the influence of phase wrapping and show that the spatiotemporal structure of SLM-generated femtosecond Bessel beams is similar to Bessel X-pulses at short propagation distance and to subluminal pulsed Bessel beams at long propagation distance.
Space-variant polarized Airy beam
Chen, Hao
2015-01-01
We experimentally generate an Airy beam with polarization structure while keeping its original amplitude and phase profile intact. This class of Airy beam preserves the acceleration properties. By monitoring their initial polarization structure we have provided insight concerning the self-healing mechanism of Airy beams. We investigate both theoretically and experimentally the self-healing polarization properties of the space-variant polarized Airy beams. Amplitude as well as the polarization structure tends to reform during propagation in spite of the severe truncation of the beam by finite apertures.
Beam combining of quantum cascade laser arrays.
Lee, Benjamin G; Kansky, Jan; Goyal, Anish K; Pflügl, Christian; Diehl, Laurent; Belkin, Mikhail A; Sanchez, Antonio; Capasso, Federico A
2009-08-31
Wavelength beam combining was used to co-propagate beams from 28 elements in an array of distributed-feedback quantum cascade lasers (DFB-QCLs). The beam-quality product of the array, defined as the product of near-field spot size and far-field divergence for the entire array, was improved by a factor of 21 by using wavelength beam combining. To demonstrate the applicability of wavelength beam combined DFB-QCL arrays for remote sensing, we obtained the absorption spectrum of isopropanol at a distance of 6 m from the laser array.
Asymmetric Laguerre-Gaussian beams
Kovalev, A. A.; Kotlyar, V. V.; Porfirev, A. P.
2016-06-01
We introduce a family of asymmetric Laguerre-Gaussian (aLG) laser beams. The beams have been derived via a complex-valued shift of conventional LG beams in the Cartesian plane. While propagating in a uniform medium, the first bright ring of the aLG beam becomes less asymmetric and the energy is redistributed toward peripheral diffraction rings. The projection of the orbital angular momentum (OAM) onto the optical axis is calculated. The OAM is shown to grow quadratically with increasing asymmetry parameter of the aLG beam, which equals the ratio of the shift to the waist radius. Conditions for the OAM becoming equal to the topological charge have been derived. For aLG beams with zero radial index, we have deduced an expression to define the intensity maximum coordinates and shown the crescent-shaped intensity pattern to rotate during propagation. Results of the experimental generation and rotation of aLG beams agree well with theoretical predictions.
Laguerre-Gauss beams versus Bessel beams showdown: peer comparison.
Mendoza-Hernández, Job; Arroyo-Carrasco, Maximino Luis; Iturbe-Castillo, Marcelo David; Chávez-Cerda, Sabino
2015-08-15
We present for the first time a comparison under similar circumstances between Laguerre-Gauss beams (LGBs) and Bessel beams (BB), and show that the former can be a better option for many applications in which BBs are currently used. By solving the Laguerre-Gauss differential equation in the asymptotic limit of a large radial index, we find the parameters to perform a peer comparison, showing that LGBs can propagate quasi-nondiffracting beams within the same region of space where the corresponding BBs do. We also demonstrate that LGBs, which have the property of self-healing, are more robust in the sense that they can propagate further than BBs under similar initial conditions.
Partially coherent beam and its applications
Institute of Scientific and Technical Information of China (English)
LIN Qiang; CAI Yang-jian; WANG Li-gang
2007-01-01
The recent progresses on the propagation,generation and application of partially coherent beam(PCB)are reviewed in this paper.A new tensor ABCD law for treating the propagation of partially coherent Gaussian-Schell model(GSM)beams through a paraxial optical system is derived.The focusing,spectral shift and fractional Fourier transform of the GSM beam are investigated by using the tensor method.The generation of PCB with special optical resonator is studied both theoretically and experimentally.Furthermore,the ghost imaging and superluminal propagation of the PCB is discussed.The results show clearly that the coherence of light have strong influences on the ghost imaging and superluminal propagation.
Detection of Bessel beams with digital axicons.
Trichili, Abderrahmen; Mhlanga, Thandeka; Ismail, Yaseera; Roux, Filippus S; McLaren, Melanie; Zghal, Mourad; Forbes, Andrew
2014-07-14
We propose a simple method for the detection of Bessel beams with arbitrary radial and azimuthal indices, and then demonstrate it in an all-digital setup with a spatial light modulator. We confirm that the fidelity of the detection method is very high, with modal cross-talk below 5%, even for high orbital angular momentum carrying fields with long propagation ranges. To illustrate the versatility of the approach we use it to observe the modal spectrum changes during the self-reconstruction process of Bessel beams after encountering an obstruction, as well as to characterize modal distortions of Bessel beams propagating through atmospheric turbulence.
Neutrino oscillations and superluminal propagation
Magueijo, Joao
2011-01-01
We digress on the implications of recent claims of superluminal neutrino propagation. No matter how we turn it around such behaviour is very odd and sits uncomfortably even within "far-fetched" theories. In the context of non-linear realizations of the Lorentz group (where superluminal misbehaviour is run of the mill) one has to accept rather contrived constructions to predict superluminal properties for the neutrino. The simplest explanation is to require that at least one of the mass states be tachyonic. We show that due to neutrino mixing, the flavor energy does not suffer from the usual runaway pathologies of tachyons. For non-tachyonic mass states the theories become more speculative. A neutrino specific dispersion relation is exhibited, rendering the amplitude of the effect reasonable for a standard Planck energy. This uses the fact that the beam energy is close to the geometrical average of the neutrino and Planck mass; or, seen in another way, the beam energy is unexceptional but its gamma factor is v...
Propagation optical quarks after an uniaxial crystal: the experiment
Egorov, Yu. A.; Konovalenko, V. L.; Zinovev, A. O.; Anischenko, P. M.; Glumova, M. V.
2013-12-01
There is a lots of different papers reporting about the propagation of the different types of an optical beams in a uniaxial crystals are known by that time. This beams are: Lager-Gaussian and Bessel- Gaussian beams. It is common for all this types of beams, that if propagation axis and crystal axis coincides, and accident beam had a circular polarization, are can get type spiral type degenerated umbilici, which corresponds to the charge 2 optical vortex in the orthogonal polarized beam component, generated by crystal [1] (Fig 1). This generation accurse due to total angular momentum conservation law symmetry axis of the crystal. One to the changing of the spin momentum which is associated with the beam polarization, this leads to the orbital momentum changes that associated with topological charge of formed orthogonal circular component. Double charged optical vortex could be easily perturbed by tilting beam axis with respect to the crystal axis. If the tilt angles are small (<0.1°) central umbilici splits on two lemons and the surrounding ring umbilici splits on two pairs of monster-star. The further increasing of the tilt angle leads to the topological charge of circular components becomes, equal, and additional orbital moment correspond to the beam mass center displacement.
Localization of angular momentum in optical waves propagating through turbulence.
Sanchez, Darryl J; Oesch, Denis W
2011-12-01
This is the first in a series of papers demonstrating that photons with orbital angular momentum can be created in optical waves propagating through distributed turbulence. The scope of this first paper is much narrower. Here, we demonstrate that atmospheric turbulence can impart non-trivial angular momentum to beams and that this non-trivial angular momentum is highly localized. Furthermore, creation of this angular momentum is a normal part of propagation through atmospheric turbulence.
Detecting electromagnetic cloaks using backward-propagating waves
Salem, Mohamed
2011-08-01
A novel approach for detecting transformation-optics invisibility cloaks is proposed. The detection method takes advantage of the unusual backward-propagation characteristics of recently reported beams and pulses to induce electromagnetic scattering from the cloak. Even though waves with backward-propagating energy flux cannot penetrate the cloaking shell and interact with the cloaked objects (i.e., they do not make the cloaked object visible), they provide a mechanism for detecting the presence of cloaks. © 2011 IEEE.
Gear Crack Propagation Investigation
1995-01-01
Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios
Bollini, C G
1998-01-01
We study the half advanced and half retarded Wheeler Green function and its relation to Feynman propagators. First for massless equation. Then, for Klein-Gordon equations with arbitrary mass parameters; real, imaginary or complex. In all cases the Wheeler propagator lacks an on-shell free propagation. The Wheeler function has support inside the light-cone (whatever the mass). The associated vacuum is symmetric with respect to annihilation and creation operators. We show with some examples that perturbative unitarity holds, whatever the mass (real or complex). Some possible applications are discussed.
Beam delivery for stable isotope separation
Forbes, Andrew; Strydom, Hendrick J.; Botha, Lourens R.; Ronander, Einar
2002-10-01
In the multi-photon dissociation process of Carbon isotope enrichment, IR photons are used to selectively excite a molecule with the given isotopic base element. This enrichment process is very sensitive to the beam's intensity and wavelength. Because the intensity is determined by the propagation of the field, the enrichment factors are also very dependent on the field propagation. In this paper, the influence of the wavelength and intensity of the beam, on the isotope selective dissociation of a CFC compound is investigated both experimentally and theoretically. Consideration is also given to some of the factors that influence the delivery of various beams to the reactor chamber, and their subsequent propagation through the reactor. The results show that suitable beam forming can lead to an improved isotope separation process.
A laser beam quality definition based on induced temperature rise.
Miller, Harold C
2012-12-17
Laser beam quality metrics like M(2) can be used to describe the spot sizes and propagation behavior of a wide variety of non-ideal laser beams. However, for beams that have been diffracted by limiting apertures in the near-field, or those with unusual near-field profiles, the conventional metrics can lead to an inconsistent or incomplete description of far-field performance. This paper motivates an alternative laser beam quality definition that can be used with any beam. The approach uses a consideration of the intrinsic ability of a laser beam profile to heat a material. Comparisons are made with conventional beam quality metrics. An analysis on an asymmetric Gaussian beam is used to establish a connection with the invariant beam propagation ratio.
The CERN Beam Interlock System: Principle and Operational Experience
Puccio, B; Kwiatkowski, M; Romera Ramirez, I; Todd, B
2010-01-01
A complex Machine Protection System has been designed to protect the LHC machine from an accidental release of the beam energy, with about 20 subsystems providing status information to the Beam Interlock System that is the backbone of machine protection. Only if the subsystems are in the correct state for beam operation, the Beam Interlock System receives a status flag and beam can be injected into LHC (Large Hadron Collider). The Beam Interlock System also relays commands from the connected subsystems in case of failure for triggering the LHC Beam Dumping System. To maintain the required level of safety of the Beam Interlock System, the performance of the key components is verified before every fill of the machine and validated after every emergency beam dump before beam operation is allowed to continue. This includes all critical paths, starting from the inputs from connected systems triggering a beam dump request, followed by the correct interruption and propagation sequence of the two redundant beam permi...
Quantitative comparison of self-healing ability between Bessel–Gaussian beam and Airy beam
Energy Technology Data Exchange (ETDEWEB)
Wen, Wei [Department of Physics and Information Engineering, Huaihua University, Huaihua 418008 (China); Chu, Xiuxiang, E-mail: xiuxiangchu@yahoo.com [School of Sciences, Zhejiang Agriculture and Forestry University, Lin’an 311300 (China)
2015-09-15
The self-healing ability during propagation process is one of the most important properties of non-diffracting beams. This ability has crucial advantages to light sheet-based microscopy to reduce scattering artefacts, increase the quality of the image and enhance the resolution of microscopy. Based on similarity between two infinite-dimensional complex vectors in Hilbert space, the ability to a Bessel–Gaussian beam and an Airy beam have been studied and compared. Comparing the evolution of the similarity of Bessel–Gaussian beam with Airy beam under the same conditions, we find that Bessel–Gaussian beam has stronger self-healing ability and is more stable than that of Airy beam. To confirm this result, the intensity profiles of Bessel–Gaussian beam and Airy beam with different similarities are numerically calculated and compared.
Wavefront dislocations of Gaussian beams nesting optical vortices in a turbulent atmosphere
Institute of Scientific and Technical Information of China (English)
Yixin Zhang(张逸新); Chunkan Tao(陶纯堪)
2004-01-01
A phase singularity of the light field created by interference of two Gaussian singular beams which propagate in a weak and near ground turbulent atmosphere is analyzed by the Rytov approximation and the short-term averaging method of the dislocation-position. We demonstrate that an edge or circular dislocation may be formed by both parallel and coaxial or noncoaxial collimated beams with different or equal beam-width interfere. The edge or circular short-term wavefront dislocations of super position field depend on the atmospheric turbulence strength, beam propagation distance, amplitude ratio, dislocation of nesting vortices, and beam-width or beam-width ratio of the individual beams.
Institute of Scientific and Technical Information of China (English)
KANG Xiao-Ping; L(U) Bai-Da
2006-01-01
@@ The analytical expression characterizing the propagation of nonparaxial truncated cosine-Gaussian (CoG) beams in free space is derived, and some special cases are discussed. The extended power in the bucket (PIB) is proposed to characterize the beam quality of nonparaxial truncated beams in the far field. It is shown that the extended PIB is applicable to nonparaxial truncated beams, and the PIB of nonparaxial truncated CoG beams depends on the decentred parameter, waist-width-to-wavelength ratio, truncation parameter, and bucket size chosen.
Self-similar asymptotic optical beams in semiconductor waveguides doped with quantum dots
He, Jun-Rong; Yi, Lin; Li, Hua-Mei
2017-01-01
The self-similar propagation of asymptotic optical beams in semiconductor waveguides doped with quantum dots is reported. The possibility of controlling the shape of output asymptotic optical beams is demonstrated. The analytical results are confirmed by numerical simulations. We give a possible experimental protocol to generate the obtained asymptotic parabolic beams in realistic waveguides. As a generalization to the present work, the self-similar propagation of asymptotic optical beams is proposed in a power-law nonlinear medium.
Hierarchical Affinity Propagation
Givoni, Inmar; Frey, Brendan J
2012-01-01
Affinity propagation is an exemplar-based clustering algorithm that finds a set of data-points that best exemplify the data, and associates each datapoint with one exemplar. We extend affinity propagation in a principled way to solve the hierarchical clustering problem, which arises in a variety of domains including biology, sensor networks and decision making in operational research. We derive an inference algorithm that operates by propagating information up and down the hierarchy, and is efficient despite the high-order potentials required for the graphical model formulation. We demonstrate that our method outperforms greedy techniques that cluster one layer at a time. We show that on an artificial dataset designed to mimic the HIV-strain mutation dynamics, our method outperforms related methods. For real HIV sequences, where the ground truth is not available, we show our method achieves better results, in terms of the underlying objective function, and show the results correspond meaningfully to geographi...
David, P
2013-01-01
Propagation of Waves focuses on the wave propagation around the earth, which is influenced by its curvature, surface irregularities, and by passage through atmospheric layers that may be refracting, absorbing, or ionized. This book begins by outlining the behavior of waves in the various media and at their interfaces, which simplifies the basic phenomena, such as absorption, refraction, reflection, and interference. Applications to the case of the terrestrial sphere are also discussed as a natural generalization. Following the deliberation on the diffraction of the "ground? wave around the ear
Superdirected Beam of the Surface Spin Wave
Annenkov, Alexander Yu; Lock, Edwin H
2016-01-01
Visualized diffraction patterns of the surface spin wave excited by arbitrarily oriented linear transducer in tangentially magnetized ferrite film are investigated experimentally in the plane of ferrite film for the case where the transducer length D is much larger than the wavelength L. Superdirected (nonexpanding) beam of the surface spin wave with noncollinear wave vector k and group velocity vector V was observed experimentally: the angular width of this beam was about zero, the smearing of the beam energy along the film plane was minimal and the length of the beam trajectory was maximal (50 mm). Thus it was shown that such phenomenon as superdirected propagation of the wave exists in the nature.
Asymmetric acoustic transmission in graded beam
Energy Technology Data Exchange (ETDEWEB)
Jing, Li, E-mail: lj94172350@hotmail.com [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China); Wu, Jiu Hui, E-mail: ejhwu@mail.xjtu.edu.cn [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China); Guan, Dong; Lu, Kuan [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China); Gao, Nansha [School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an, Shaanxi 710072 (China); Songhua, Cao [School of Mechanical Engineering and State Key laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi’an, Shaanxi 710049 (China)
2016-12-01
We demonstrate the dynamic effective material parameters and vibration performance of a graded beam. The structure of the beam was composed of several unit cells with different fill factors. The dispersion relations and energy band structures of each unit cell were calculated using the finite element method (FEM). The dynamic effective material parameters in each unit cell of the graded beam were determined by the dispersion relations and energy band structures. Longitudinal wave propagation was investigated using a numerical method and FEM. The results show that the graded beam allows asymmetric acoustic transmission over a wide range of frequencies.
Energy Technology Data Exchange (ETDEWEB)
Stupakov, G.V. [Stanford Linear Accelerator Center, Menlo Park, CA (United States)
1996-08-01
The ionization of residual gas by an electron beam in an accelerator generates ions that can resonantly couple to the beam through a wave propagating in the beam-ion system. Results of the study of a beam-ion instability are presented for a multi-bunch train taking into account the decoherence of ion oscillations due to the ion frequency spread and spatial variation of the ion frequency. It is shown that the combination of both effects can substantially reduce the growth rate of the instability. (author)
Asymmetric acoustic transmission in graded beam
Jing, Li; Wu, Jiu Hui; Guan, Dong; Lu, Kuan; Gao, Nansha; Songhua, Cao
2016-12-01
We demonstrate the dynamic effective material parameters and vibration performance of a graded beam. The structure of the beam was composed of several unit cells with different fill factors. The dispersion relations and energy band structures of each unit cell were calculated using the finite element method (FEM). The dynamic effective material parameters in each unit cell of the graded beam were determined by the dispersion relations and energy band structures. Longitudinal wave propagation was investigated using a numerical method and FEM. The results show that the graded beam allows asymmetric acoustic transmission over a wide range of frequencies.
Free space propagation of concentric vortices through underwater turbid environments
Morgan, K. S.; Miller, J. K.; Cochenour, B. M.; Li, W.; Li, Y.; Watkins, R. J.; Johnson, E. G.
2016-10-01
Concentric optical vortex beams of 3-petal, 5-petal, and 6-petal spatial profiles are generated at 450 nm using a single diffractive optical element. The spatial and temporal propagation characteristics of these beams are then studied in a scattering underwater environment. Experimental results demonstrate a less than 5% reduction in the spatial pattern for turbidities in excess of 10 attenuation lengths. The temporal properties of concentric vortex beams are studied by temporally encoding an on-off keyed, non-return-to-zero (OOK-NRZ) data stream at 1.5 GHz.
Three-dimensional nonparaxial beams in parabolic rotational coordinates.
Deng, Dongmei; Gao, Yuanmei; Zhao, Juanying; Zhang, Peng; Chen, Zhigang
2013-10-01
We introduce a class of three-dimensional nonparaxial optical beams found in a parabolic rotational coordinate system. These beams, representing exact solutions of the nonparaxial Helmholtz equation, have inherent parabolic symmetries. Assisted with a computer-generated holography, we experimentally demonstrate the generation of different modes of these beams. The observed transverse beam patterns along the propagation direction agree well with those from our theoretical predication.
Propagation of polarized light through azobenzene polyester films
DEFF Research Database (Denmark)
Nedelchev, L; Matharu, A; Nikolova, Ludmila
2002-01-01
When elliptically polarized light of appropriate wavelength Corresponding to trans-cis-trans isomerisation process is incident on thin films of azobenzene polyesters, a helical structure is induced. We investigate the propagation of the exciting light beam (self-induced) as well as a probe light...
The Effect of Coherence in the Propagation through Periodic Structures
Bertolotti, M.; Hoenders, B.; Mandatori, A.; Sibilia, C.
2006-01-01
The effects of the coherence properties of light beams propagating through periodic structures are discussed. In particular, spatial coherence may influence the transmitted field. Some 2D structures which give transmittances strongly influenced by the coherence of the incoming field are discussed.
Asymmetric Bessel-Gauss beams.
Kotlyar, V V; Kovalev, A A; Skidanov, R V; Soifer, V A
2014-09-01
We propose a three-parameter family of asymmetric Bessel-Gauss (aBG) beams with integer and fractional orbital angular momentum (OAM). The aBG beams are described by the product of a Gaussian function by the nth-order Bessel function of the first kind of complex argument, having finite energy. The aBG beam's asymmetry degree depends on a real parameter c≥0: at c=0, the aBG beam is coincident with a conventional radially symmetric Bessel-Gauss (BG) beam; with increasing c, the aBG beam acquires a semicrescent shape, then becoming elongated along the y axis and shifting along the x axis for c≫1. In the initial plane, the intensity distribution of the aBG beams has a countable number of isolated optical nulls on the x axis, which result in optical vortices with unit topological charge and opposite signs on the different sides of the origin. As the aBG beam propagates, the vortex centers undergo a nonuniform rotation with the entire beam about the optical axis (c≫1), making a π/4 turn at the Rayleigh range and another π/4 turn after traveling the remaining distance. At different values of the c parameter, the optical nulls of the transverse intensity distribution change their position, thus changing the OAM that the beam carries. An isolated optical null on the optical axis generates an optical vortex with topological charge n. A vortex laser beam shaped as a rotating semicrescent has been generated using a spatial light modulator.
A numerical solution algorithm and its application to studies of pulsed light fields propagation
Banakh, V. A.; Gerasimova, L. O.; Smalikho, I. N.; Falits, A. V.
2016-08-01
A new method for studies of pulsed laser beams propagation in a turbulent atmosphere was proposed. The algorithm of numerical simulation is based on the solution of wave parabolic equation for complex spectral amplitude of wave field using method of splitting into physical factors. Examples of the use of the algorithm in the case the propagation pulsed Laguerre-Gaussian beams of femtosecond duration in the turbulence atmosphere has been shown.
Gamp, Alexander
2013-01-01
We begin by giving a description of the radio-frequency generator-cavity-beam coupled system in terms of basic quantities. Taking beam loading and cavity detuning into account, expressions for the cavity impedance as seen by the generator and as seen by the beam are derived. Subsequently methods of beam-loading compensation by cavity detuning, radio-frequency feedback and feedforward are described. Examples of digital radio-frequency phase and amplitude control for the special case of superconducting cavities are also given. Finally, a dedicated phase loop for damping synchrotron oscillations is discussed.
Urrutxua, Hodei; Sanjurjo-Rivo, Manuel; Peláez, Jesús
2016-01-01
In the year 2000 an in-house orbital propagator called DROMO (Peláez et al. in Celest Mech Dyn Astron 97:131-150, 2007. doi: 10.1007/s10569-006-9056-3) was developed by the Space Dynamics Group of the Technical University of Madrid, based in a set of redundant variables including Euler-Rodrigues parameters. An original deduction of the DROMO propagator is carried out, underlining its close relation with the ideal frame concept introduced by Hansen (Abh der Math-Phys Cl der Kon Sachs Ges der Wissensch 5:41-218, 1857). Based on the very same concept, Deprit (J Res Natl Bur Stand Sect B Math Sci 79B(1-2):1-15, 1975) proposed a formulation for orbit propagation. In this paper, similarities and differences with the theory carried out by Deprit are analyzed. Simultaneously, some improvements are introduced in the formulation, that lead to a more synthetic and better performing propagator. Also, the long-term effect of the oblateness of the primary is studied in terms of DROMO variables, and new numerical results are presented to evaluate the performance of the method.
2014-09-30
response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and...these modes decay much more slowly than leaky modes as they propagate. The initial focus is on modal phase and group velocity formulas, obtained from...acoustic quantities such as transmission loss and scintillation index. (C) Both physical understanding and reasonable estimates of
Microwave Propagation Through Cultural Vegetation Canopies
Tavakoli, Ahad
The need to understand the interaction of microwaves with vegetation canopies has markedly increased in recent years. This is due to advances made in remote sensing science, microwave technology, and signal processing circuits. One class of the earth's vegetation cover is man-made canopies, such as agricultural fields, orchards, and artificial forests. Contrary to natural vegetation terrain, location, spacing, and density of plants in a man-made vegetation canopy are deterministic quantities. As a result, the semi-deterministic nature of cultural vegetation canopies violate the random assumption of the radiative transfer theory and leads to experimented results that are in variance with model calculations. Hence, an alternative approach is needed to model the interaction of microwaves with such canopies. This thesis examines the propagation behavior through a canopy of corn plants. The corn canopy was selected as a representative of cultural vegetation canopies that are planted in parallel rows with an approximately fixed spacing between adjacent plants. Several experimental measurements were conducted to determine the transmission properties of a corn canopy in the 1-10 GHz range. The measurements which included horizontal propagation through the canopy as well as propagation at oblique incidence, were performed for defoliated canopies and for canopies with leaves. Through experimental observations and model development, the propagation behavior was found to be strongly dependent on the wavelength and the path length. At a wavelength in the neighborhood of 20 cm, for example, it was found that scattering by the stalks was coherent in nature for waves propagating horizontally through the canopy, which necessitated the development of a coherent-field model that uses Bragg scattering to account for the observed interference pattern in the transmitted beam. As the wavelength is made shorter, the semi-random spacing between plants becomes significant relative to the
Atmospheric propagation and combining of high-power lasers.
Nelson, W; Sprangle, P; Davis, C C
2016-03-01
In this paper, we analyze beam combining and atmospheric propagation of high-power lasers for directed-energy (DE) applications. The large linewidths inherent in high-power fiber and slab lasers cause random phase and intensity fluctuations that occur on subnanosecond time scales. Coherently combining these high-power lasers would involve instruments capable of precise phase control and operation at rates greater than ∼10 GHz. To the best of our knowledge, this technology does not currently exist. This presents a challenging problem when attempting to phase lock high-power lasers that is not encountered when phase locking low-power lasers, for example, at milliwatt power levels. Regardless, we demonstrate that even if instruments are developed that can precisely control the phase of high-power lasers, coherent combining is problematic for DE applications. The dephasing effects of atmospheric turbulence typically encountered in DE applications will degrade the coherent properties of the beam before it reaches the target. Through simulations, we find that coherent beam combining in moderate turbulence and over multikilometer propagation distances has little advantage over incoherent combining. Additionally, in cases of strong turbulence and multikilometer propagation ranges, we find nearly indistinguishable intensity profiles and virtually no difference in the energy on the target between coherently and incoherently combined laser beams. Consequently, we find that coherent beam combining at the transmitter plane is ineffective under typical atmospheric conditions.
In-situ observations on crack propagation along polymer/glass interfaces.
Vellinga, W.P; Timmerman, R.; van Tijum, R.; de Hosson, J.T.M.; Buchheit, TE; Minor, AM; Spolenak, R; Takashima, K
2005-01-01
The propagation of crack fronts along a PET-glass interface is illustrated. The experimental set-up consists of an Asymmetric Double Cantilever Beam in an optical microscope. Image processing techniques used to isolate the crack fronts are discussed in some detail. The fronts are found to propagate
Schippers, P.; Volker, A.W.F.; Golliard, J.; Jong, C. de
2006-01-01
Propagation and sonar performance are modelled by TNO’s ALMOST program, already being developed since the Eighties. It models propagation between sonar and target based on ray theory, including effects of sediment bottoms, reverberation and ambient noise. Moreover, antenna directivity (beam forming)
Laser propagation in simulations of low fill density hohlraums
Meezan, Nathan; Berzak Hopkins, L. F.; Izumi, N.; Divol, L.; Hinkel, D. E.; Ralph, J. E.; Moody, J. D.; Callahan, D. A.
2016-10-01
We present analysis of laser propagation in simulations of low fill density hohlraums on the National Ignition Facility (NIF). Simulations using the radiation hydrodynamic code hydra are compared in 2D and 3D. The absorption of laser rays in different materials and spatial locations is extracted from the simulations to identify where and when the inner cone laser beams undergo significant absorption. Inner cone laser beams can be absorbed in the outer cone ``gold bubble'' or in the region where the ablator and hohlraum material interact. The simulations provide guidance on which hohlraum mitigation methods will be most effective at improving inner beam propagation. Prepared by LLNL under Contract DE-AC52-07NA27344.
Robust Collimation Control of Laser-Generated Ion Beam
Kawata, S; Kamiyama, D; Nagashima, T; Barada, D; Gu, Y J; Li, X; Yu, Q; Kong, Q; Wang, P X
2015-01-01
The robustness of a structured collimation device is discussed for an intense-laser-produced ion beam. In this paper the ion beam collimation is realized by the solid structured collimation device, which produces the transverse electric field; the electric field contributes to reduce the ion beam transverse velocity and collimate the ion beam. Our 2.5 dimensional particle-in cell simulations demonstrate that the collimation device is rather robust against the changes in the laser parameters and the collimation target sizes. The intense short-pulse lasers are now available, and are used to generate an ion beam. The issues in the laser ion acceleration include an ion beam collimation, ion energy spectrum control, ion production efficiency, ion energy control, ion beam bunching, etc. The laser-produced ion beam tends to expand in the transverse and longitudinal directions during the ion beam propagation. The ion beam collimation is focused in this paper.
Beam steering effects in turbulent high pressure flames
Energy Technology Data Exchange (ETDEWEB)
Hemmerling, B.; Kaeppeli, B. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)
1997-06-01
The propagation of a laser beam through a flame is influenced by variations of the optical density. Especially in turbulent high pressure flames this may seriously limit the use of laser diagnostic methods. (author) 1 fig., 2 refs.
Propagating Instabilities in Solids
Kyriakides, Stelios
1998-03-01
Instability is one of the factors which limit the extent to which solids can be loaded or deformed and plays a pivotal role in the design of many structures. Such instabilities often result in localized deformation which precipitates catastrophic failure. Some materials have the capacity to recover their stiffness following a certain amount of localized deformation. This local recovery in stiffness arrests further local deformation and spreading of the instability to neighboring material becomes preferred. Under displacement controlled loading the propagation of the transition fronts can be achieved in a steady-state manner at a constant stress level known as the propagation stress. The stresses in the transition fronts joining the highly deformed zone to the intact material overcome the instability nucleation stresses and, as a result, the propagation stress is usually much lower than the stress required to nucleate the instability. The classical example of this class of material instabilities is L/"uders bands which tend to affect mild steels and other metals. Recent work has demonstrated that propagating instabilities occur in several other materials. Experimental and analytical results from four examples will be used to illustrate this point: First the evolution of L=FCders bands in mild steel strips will be revisited. The second example involves the evolution of stress induced phase transformations (austenite to martensite phases and the reverse) in a shape memory alloy under displacement controlled stretching. The third example is the crushing behavior of cellular materials such as honeycombs and foams made from metals and polymers. The fourth example involves the axial broadening/propagation of kink bands in aligned fiber/matrix composites under compression. The microstructure and, as a result, the micromechanisms governing the onset, localization, local arrest and propagation of instabilities in each of the four materials are vastly different. Despite this
Aperture Effects and Mismatch Oscillations in an Intense Electron Beam
Energy Technology Data Exchange (ETDEWEB)
Harris, J R; O' Shea, P G
2008-05-12
When an electron beam is apertured, the transmitted beam current is the product of the incident beam current density and the aperture area. Space charge forces generally cause an increase in incident beam current to result in an increase in incident beam spot size. Under certain circumstances, the spot size will increase faster than the current, resulting in a decrease in current extracted from the aperture. When using a gridded electron gun, this can give rise to negative transconductance. In this paper, we explore this effect in the case of an intense beam propagating in a uniform focusing channel. We show that proper placement of the aperture can decouple the current extracted from the aperture from fluctuations in the source current, and that apertures can serve to alter longitudinal space charge wave propagation by changing the relative contribution of velocity and current modulation present in the beam.