Compton scattering and electron-atom scattering in an elliptically polarized laser field of relativistic radiation power

Presently available laser sources can yield powers for which the ponderomotive energy of an electrons can be equal to or even larger than the rest energy mc ² of an electron. Therefore it has become of interest to consider fundamental radiation-induced or assisted processes in such powerful laser fields. In the present work we consider laser-induced Compton scattering and laser-assisted electron atom scattering in such fields, assuming that the laser beam has arbitrary elliptic polarization. We investigate in detail the angular and polarisation dependence of the differential cross-sections of the two laser-induced or laser-assisted nonlinear processes as a function of the order N of absorbed or emitted laser photons . The present work is a generalization of our previous analysis of Compton scattering and electron-atom scattering in a linearly polarized laser field [Phys. Rev. A 65, 022712 and 033408 (2002)].Received: 3 November 2002, Published online: 29 April 2003PACS: 34.50.Rk Laser-modified scattering and reactions - 34.80.Qb Laser-modified scattering - 32.80.Wr Other multiphoton processes     

Monte Carlo calculation of electron spectra produced in water phantoms by 20 keV-1 GeV photons

Abstract

A Monte Carlo calculation for the energy spectra of electrons and positrons produced in infinite and semiinfinite water phantoms by photons ranging in energies from 20 keV to 1 GeV are presented. The dominant processes considered are the photoelectric effect, Auger effect, Compton effect, pair, and triplet production. Bremsstrahlung produced by electrons and positrons with energies greater than 1 MeV is also included. The effect of multiple Compton scattering, not considered in the earlier calculation, for the infinite phantom for photon energies higher than 2 MeV has been incorporated. For a semi-infinite phantom, multiple Compton scattering and backscattering through the top are considered. The results are compared with the earlier calculations for the first-collision spectrum. It is found that the inclusion of multiple Compton scattering significantly increases the average number of electrons/cm³ per photon/cm² at all energies considered whereas bremsstrahlung reduces the number of high energy electrons and produces more low energy electrons in the spectrum.     

The polarization effect of a laser in multiphoton Compton scattering

The multiphoton Compton scattering in a high-intensity laser beam is studied by using the laser-dressed quantum electrodynamics(QED) method, which is a non-perturbative theory for the interaction between a plane electromagnetic field and a charged particle. In order to analyze in the real experimental condition, a Lorentz transformation for the cross section of this process is derived between the laboratory frame and the initial rest frame of electrons. The energy of the scattered photon is analyzed, as well as the cross sections for different laser intensities and polarizations and different electron velocities. The angular distribution of the emitted photon is investigated in a special velocity of the electron, in which for a fixed number of absorbed photons, the electron energy will not change after the scattering in the lab frame.We obtain the conclusion that higher laser intensities suppress few-laser-photon absorption and enhance more-laser-photon absorption. A comparison between different polarizations is also made, and we find that the linearly polarized laser is more suitable to generate nonlinear Compton scattering.     

多光子非线性Compton散射对等离子体中颗粒成长的影响

应用等离子体颗粒成长模型和多光子非线性Compton模型,研究了多光子非线性Compton散射对等离子体中颗粒成长的影响。提出了将入射光和多光子非线性Compton散射光作为颗粒成长的新机制,对颗粒凝合截面、凝合系数、颗粒收集的电子流和离子流的表达式进行了修正。结果表明,等离子体参数的变化与多光子非线性Compton散射成分、电子散射前的初始速度、入射角、与电子同时作用的光子数等因素有关。散射使生长过程中收集离子机制和凝合机制增强,颗粒的凝合截面增大,颗粒半径较快的非均匀增长。     

对非线性康普顿散射几种改进物理模型的比较

非线性康普顿散射被认为是未来超短超强激光与物质相互作用中的主导性物理过程之一。目前大多数相关研究都基于一种主流的非线性康普顿散射物理模型,该模型假设辐射形成距离足够短、对初态和末态自旋求平均与求和、并忽略了参与散射的激光光子的能动量。近年来,一些研究为了在更广阔的参数空间内,更准确地描述非线性康普顿散射,也对这个主流物理模型提出了几种修正和改进。回顾了对非线性康普顿散射主流物理模型进行的几种改进和修正,介绍了它们的适用范围,分析了它们的基本性质并对其物理效应进行了简单讨论。     

多光子非线性Compton散射的能量转换

研究了多光子非线性Compton散射中电子与光子的能量转换及其转换效率.结果表明:散射光子频率随电子吸收光子数n的增大而增大,随碰撞非弹性成分ξ的增大而迅速减小.在超强激光场中,当极端相对论性电子与光子发生多光子非线性Compton散射且被光场俘获时,能量转换效率趋于无限大,即电子可以从超强激光场中获得巨大的加速能量.用高速电子束入射并与光子发生多光子非线性Compton散射,是提高非线性Compton散射能量转换效率的重要途径.     

ALP production through non-linear Compton scattering in intense fields

We derive production yields for massive pseudo-scalar and scalar axion-like-particles (ALPs), through non-linear Compton scattering of an electron in the background of low- and high-intensity electromagnetic fields. In particular, we focus on electromagnetic fields from Gaussian plane wave laser pulses. A detailed study of the angular distributions and effects of the scalar and pseudo-scalar masses is presented. It is shown that ultra-relativistic seed electrons can be used to produce scalars and pseudo-scalars with masses up to the order of the electron mass. We briefly discuss future applications of this work towards lab-based searches for light beyond-the-Standard-Model particles.     

Compton scattering from isotropic electrons

The exact Compton cross section for scattering of photons from isotropic monoenergetic electrons is given in analytical form. It is shown that the moments of the Legendre expansion of the scattering kernel can be obtained analytically, apart from an integration over the unknown electron distribution function.     

Threshold phenomena in electron-atom scattering in a laser field

Effective-range theory is developed to describe the processes of multiphoton bremsstrahlung absorption and the emission of laser radiation that accompanies the scattering of electrons from atoms in a laser field. It is found that the cross sections for multiphoton absorption in the plateau region increases resonantly for electron energies corresponding to the thresholds of induced bremsstrahlung (i.e., multiples of the photon energy). It is shown that this effect is caused by the laser-field modified threshold phenomena in the cross sections for multichannel reactions (Baz’ threshold anomalies).     

X-ray amplification by laser controlled coherent bremsstrahlung

A coherent x-ray generation scheme is proposed which involves characteristics of free electron lasers and atomic high harmonic generation schemes. A thin solid layer or any other periodic atomic structure with limited dimensions is exposed to a short, superintense laser pulse. The electrons are extracted from the layer due to the extreme force and penetrate periodically through the ionic structure. Consequently, thousands of harmonics of the laser radiation field are shown to coherently amplify along the interaction length. The small signal gain of the generated x-ray radiation exceeds that arising from the multiphoton Compton process in plasmas and is competitive with that in the leading x-ray free electron lasers.     

Compton scattering of 59.54 keV γ‐rays from Fe and p‐Si samples in an external magnetic field

We report on the Compton scattering of photons from samples whose surface charge density distributions are changed by an external magnetic field. We performed a Compton scattering experiment known to be particularly sensitive to the behavior of the relatively slower moving outer electrons (valence electrons) involved in bonding in condensed matter. The external magnetic field was used to change the surface charge density distributions of Fe and p‐Si samples. Samples were located in the external magnetic field of intensity 215 G and in a direction which was perpendicular both to the current and surface of the samples bombarded by 59.5 keV γ‐photons emitted from an Am‐241 point source. Currents in the ranges 0–8.5 A and 0–300 µA were applied to the Fe and p‐Si samples, respectively. The Compton scattered photons at an angle of 100° were detected by an Si(Li) detector. It was observed that the counts acquired under the Compton peaks tended to decrease linearly with increasing current in a magnetic field. The results show that positive charge carriers behave like negative charge carriers and electrons are more effective than holes in the Compton scattering of γ‐rays. Copyright © 2003 John Wiley & Sons, Ltd.     

The use of mössbauer scattering spectroscopy for the determination of physical parameters

The procedures for the determination of the linewidth of the scatterer, the surface density of the scattering layer, the angular correlation function, the interference parameter, the Debye-Waller factor for Rayleigh scattering, Lamb-Mössbauer factors for the absorption and reemission of Mössbauer radiation, the mass resonance absorption coefficient of Mössbauer radiation, and attenuation coefficients for Rayleight and Compton scattering are considered. It is shown that for the conversion of experimentally determined reduced attenuation coefficients of different absorption or scattering processes to the cross sections or mass attenuation coefficients, one needs to know the photoelectric absorption cross section or mass photoelectric absorption coefficient of Mössbauer radiation in the K-shell of Fe, which can be determined experimentally.     

Relativistic double differential cross sections for Compton scattering by bound electrons: Test at low photon energies and predictions at intermediate photon energies

Cross section profiles d²σ/dΩdω′ for Compton scattering of photons by bound electrons are calculated for all subshells of the atom. Results obtained from the form factor approximation and from a relativistic version of the impulse approximation are compared with experimental data for Cu and Pb at a scattering angle ofθ=145° and a photon energy of 662 keV. The impulse approximation proves to be superior to the form factor approximation and is used to predict cross section profiles for a primary energy of 50 MeV and different scattering angles and charge numbers. It is shown that only for the heaviest atoms and scattering angles belowθ=5° there is a non-negligible contribution of Compton scattering to the elastic peak.     

BEPC Compton散射极化仪的理论研究

简要介绍了圆偏振激光在极化电子束上的Ｃｏｍｐｔｏｎ散射理论,研究了北京正负电子对撞机（ＢＥＰＣ）极化仪的测量原理,并根据ＢＥＰＣ极化仪的实验参数计算了散射的能谱、空间分布和强度．The theory of Compton scattering of polarized photons on polarized electrons, and the principle of Beijing Electron Positron Collider (BEPC) Compton polarimeter are shortly discussed. The energy spectrum, vertical distributions and the intensity of Compton scattering under particular conditions are also calculated.     

Momentum distribution in benzene: A comparison of compton scattering and positron annihilation

Probabilities in momentum space for the benzene molecule are calculated for two cases: An ordinary benzene molecule, and benzene with a bound positron which is coalesced with one of the electrons. The former probability is related to the Compton scattering profile; the latter, to angular correlation measurements made in positron annihilation experiments. In this work we make two comparisons on the basis of quantum mechanical calculations; a) between Compton scattering and positron annihilation results, and b) among the several possible positron annihilation results associated with different symmetries for the positronic molecular orbital (PMO). The Compton scattering results are found to be similar to the positron annihilation results for the more symmetrical PMOs; and all these are quite different from the positron annihilation results for the less symmetrical PMOs. A suggestion for a crucial experiment is made.     

The role of Compton scattering in the low‐Z elements X‐ray fluorescence formation

The paper reviews the ionization of elements with low atomic numbers (boron, carbon, nitrogen, oxygen, and fluorine) by incoherent scattering of primary radiation and under the influence of Compton electrons. It is shown that at high energy of primary photons, the total contribution of these processes to X‐ray fluorescence formation becomes significant; at the energy of 80 keV, it becomes dominant. Copyright © 2013 John Wiley & Sons, Ltd.     

Compton scattering of 0.279 MeV gamma rays fromK-shell electrons of lead

Differential cross-sections for Compton scatterig of 0.279 MeV gamma rays fromK-shell electrons of lead are measured at scattering angles ranging from 30 to 150° to study the effect of binding on the scattering process. Measurements are made employing two Nal(Tl) scintillation spectrometers and a slow-fast coincidence set-up of 30 nsec resolving time. The experimental results are compared with the available theoretical data. The totalK-shell Compton scattering cross-section is 34% of the free electron Compton cross-section.     

A perturbative description of coherent multiphoton resonant processes

We construct field equations and generalised Bloch equations for multiphoton processes involving the coherent interaction of a number of distinct electric fields with an arbitrary number of atomic eigenstates, and apply the equations to some physical examples. Transient stimulated hyper-Raman scattering, in the low-conversion regime and far from saturation, has been studied analytically. Assuming that the pump pulse interacts with the medium byn-photon absorption, we find expression for the intensity of the generated Stokes pulse.