沟道辐射

最近,人们发现,带电轻粒子在晶体沟道中运动发射与相干韧致辐射既有联系又有本质区别的新的辐射—沟道辐射。这种强度大、单色性好、高度定向且极化的辐射具有重要的理论和实验研究价值。本文讨论了沟道辐射的主要特征、实验进展状况、结果和装置及其可能的应用。并与其他有关辐射现象作了比较。     

Radiation source for medical X-ray examination,based on the use of electron radiation during channeling in crystals

One of the possible applications of relativistic electron radiation during channeling in crystals, i.e., the use of radiation for medical visualization, is considered.A setup scheme is proposed, the results of numerical simulation of electron dynamics in crystals and radiation generation and the results of calculations of dose loads are presented.     

Electromagnetic radiation of relativistic channeling particles (the Kumakhov effect)

A new type of electromagnetic radiation characteristic for channeling in single crystals relativistic particles which has been recently predicted by Kumakhov and proved experimentally is reviewed. It is observed as one or several strong peaks in the soft part of the Bremsstrahlung, surpassing it by a factor of nearly one hundred. At moderate electron energies sharp peaks corresponding to spontaneous transitions between quantum eigenstates of the channeling particles were detected. But for high energy channeling electrons these peaks merge into one broad classical peak with the frequency determined by the collective potential of an atomic row or plane. This radiation also strongly depends on the charge sign, velocity and mass of the particle.     

Second harmonic generation in graphene

Second harmonic generation in graphene has been theoretically studied. Phenomenological analysis based on symmetry arguments is carried out. It is demonstrated that second harmonic generation in ideal graphene samples is possible only if the radiation wave vector or its magnetic field is taken into account. Microscopic theory is developed for the classical regime of radiation interaction with electrons, where the photon energy is much lower than the characteristic energy of charge carriers. It is demonstrated that the emitted radiation can be strongly circularly polarized for the linearly polarized incident wave.     

Coherent effect in the radiation of relativistic electrons in the field of bent atomic crystallographic planes

The effect of the intense monochromatic radiation arising when relativistic electrons intersect periodically bent atomic crystallographic planes in a crystal is predicted. This effect is independent of the channeling of the particles in the crystal and is possible for relativistic positrons and electrons.     

Multicrystal microundulator

The mode of propagation of relativistic, positively charged particles through a system of mutually oriented and periodically arranged ultrathin crystals whose thicknesses are equal to the half-period of the particle trajectory during planar channeling in a thick crystal is considered. In the case of an incidence angle that is less than the critical channeling angle, a certain fraction of particles is specularly reflected from the atomic planes of the crystal. Therefore, passing through a stack of crystals, a particle moves along quasiundulator trajectories. The characteristics of the radiation of a particle passing through such a “multicrystal microundulator” are found. The radiation spectrum is discrete, and the first-harmonic frequency and the number of harmonics in the spectrum are dependent on the distance between the crystals, the particle energy, and the potential of atomic planes of the crystal. Radiation is concentrated in a narrow cone in the direction of the average velocity of particles and is mainly polarized in a plane that is orthogonal to the atomic planes of the crystal. The microundulator can be composed of separate crystals with micron thicknesses and can be fabricated using modern methods of microlithography and micromechanics with deep, for example, plasmochemical etching of the crystal surface.     

Electromagnetic radiation of MeV electrons in thick aligned single crystals

Abstract

Earlier published theoretical models for MeV electrons are generalized in this paper. Different theoretical predictions for planar channeling and accompanying electromagnetic radiation in thick crystals are presented. A comparative analysis of theoretical and experimental spectra of photon radiation is given. Thickness dependences of channeling quantum state populations, radiation line broadening and photon flux intensities are obtained. The existence of planar electron channeling at 54 MeV in a silicon single crystal with a thickness of several millimetres is shown.     

影响单电子非线性汤姆孙散射因素的研究

应用电子汤姆孙散射的经典理论，通过理论分析和计算机模拟，研究了超短超强激光脉冲作用下电子产生的辐射脉冲的性质.计算表明，在这种情况下，电子的辐射通常以阿秒脉冲列的形式出现.讨论了不同激光场参数（包括激光强度、脉宽、初相位和偏振态）、不同电子初始状态（初始速度和位置）对辐射脉冲的时间和空间特性的影响.通常在相对论光强条件下，激光强度越大，电子辐射越强，脉宽越窄，中心频率越大，并且方向性越好；电子在线偏振激光中产生的辐射效率，比在同样强度下圆偏振激光中产生的效率更高；无论入射光是线偏振光，还是圆偏振光,辐射场呈现较复杂的偏振态, 并且它与辐射方向有关.当电子具有一定的初始能量时，通常辐射场的振幅随电子初始能量的增大而增大.不管电子的初始能量以及运动方向如何，做相对论运动的电子产生的辐射趋向于出现在靠近电子运动方向的角度区域.     

高能电子和正电子在晶体沟道中的辐射

介绍了高能电子和正电子在晶体中的沟道辐射,对超相对论电子和正电子在周期弯曲晶体中的相干辐射进行了分析,并提出了初步的实验设想. The channeling radiation of high energy electrons and positrons in crystals was introduced. According to the new idea proposed by A.V.Korol, the coherent radiation of ultra relativistic electrons and positrons channeled in periodically bent crystals was analyzed. The characteristics of the radiation were obtained by using classic electromagnetic theory and a tentative experimental plan for testing was suggested.     

Quantum beats from channeling relativistic electrons

Possibility has been explored of periodic time variation of intensity (quanturn beats) of radiation emitted from relativistic electrons channeling along the 〈110〉 axis of a crystal of f.c.c. (diamond) lattice structure.     

Polarization of photons emitted in the process of resonant coherent excitation of relativistic ions under planar channeling conditions

Owing to the recent observation of the strong anisotropy of characteristic X-ray radiation accompanying the resonant coherent excitation of relativistic Fe²⁴⁺ ions under planar channeling conditions in a silicon crystal, the resonant coherent excitation method can be considered as a candidate for a source of polarized X-ray radiation. The Stokes parameters of the radiation have been calculated using the density matrix approach. The behavior of the polarization characteristics of the radiation in various directions has been explained by considering the properties of the resonance part of the crystal field, which excites an ion and has the form of an elliptically polarized electric field.     

On the electromagnetic radiation of channeled particles in a curved crystal

A simple model calculation of the channeling of charged particles in a curved crystal is presented. The characteristics of the powerful radiation from relativistic particles associated with the motion in a curved channel are discussed.     

The polarization of radiation in single crystals in the semiclassical approach

The radiation emission spectra of polarized photons emitted from charged particles in single oriented crystals are obtained in Bayer-Katkov-Strakhovenko semiclassical approach. The results of numerical calculations are presented in the region of small angles of incidence for which the coherent theory fails but the magnetic bremsstrahlung region is not yet achieved. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 171–175 (10 February 1999)     

Investigation of inverse Raman scattering using the method of intra-cavity spectroscopy

The detectability of Raman absorption lines is enhanced by inserting the Raman sample into the cavity of a broad-band dye laser where the sample is simultaneously pumped by monochromatic radiation. With this technique we were able to detect Raman samples with good scattering efficiencies in a concention of 10^?3 mole/? or to obtain nearly complete Raman spectra within a time interval of 30 nsec.Exposures in which the dye laser radiation and the strong monochromatic radiation are polarized parallel or perpendicularly to each other are compared with spontaneous Raman spectra which are polarized parallel or perpendicularly.     

Statistical simulation of multiple Compton backscattering process

A number of laboratories are currently developing monochromatic sources of X-rays and gamma quanta based on the Compton backscattering (CBS) of laser photons by relativistic electrons. Modern technologies are capable of providing a concentration of electrons and photons in the interaction point such that each primary electron can emit several hard photons. In contrast to the well-known nonlinear CBS process, in which an initial electron “absorbs” a few laser photons and emits a single hard one, the above-mentioned process can be called a multiple CBS process and is characterized by a mean number of emitted photons. The present paper is devoted to simulating the parameters of a beam of back scattered quanta based on the Monte Carlo technique. It is shown that, even in the case of strong collimation of a resulting photon beam, the radiation monochromaticity may deteriorate because of the contribution coming from the multiple photon emission, which is something that must be considered while designing new CBS sources.     

Generation of X-ray radiation during planar channeling of relativistic electrons in crystals

A classical model of the emission of radiation by relativistic electrons in a crystal has been developed using the form of the potential maximally close to its actual form. The dynamics of electrons with energies 20–25 MeV performing channeling in crystals is simulated numerically. The generation of electromagnetic radiation that accompanies this motion has been considered. It has been shown that, in the given electron energy range, this radiation corresponds to the X-ray spectral band with characteristic photon energies of up to 40 keV. The radiation yield is estimated. The requirements to the electron beam parameters are formulated based on the results of the simulation. It has been shown that numerical simulation gives results that correlate with the analytic results obtained earlier and with the experimental data.     

Relativistic electron radiation spectra at axial channeling in crystals

Typical trajectories of relativistic electrons and the corresponding radiation spectra at axial channeling in silicon and diamond crystals are revealed and constructed using the ©Mathematica 6.01 computer code. The radiation spectrum of 300 MeV electrons averaged over the trajectories in the 〈100〉 direction in a diamond crystal well coincides with the experimental spectra measured in work [6].     

On Coherent radiation in collisions of short bunches of relativistic particles

Suppression of coherent radiation arising in collisions of relativistic electrons with a short bunch of relativistic particles is predicted. It is shown that this effect must occur in the low-frequency range of emitted photons if radiation has a not purely dipole character. The mechanism of this effect differs from the mechanism of electron synchrotron radiation in the field of the incident particle bunch.     

Observation of phase-matched relativistic harmonic generation

Phase-matched relativistic harmonic generation in plasmas is observed for the first time. Third-harmonic light is detected and discriminated spectrally and angularly from the harmonics generated from competing processes. Its angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma. The signal level is found to be on the same order of magnitude for a circularly polarized pump pulse as for a linearly polarized pump pulse.     

能量连续可调LCS光源SINAP-III

X/γ探测器在航天等国家战略需求领域具有非常广泛和重要的应用。 然而, X/γ探测器要在其有效能区进行精确的标定后才能发挥作用。 目前我国缺乏sub MeV～MeV能量连续可调、 单色性好的γ源, 而用于航天的X/γ探测器无法完成精确定标, 从而使航天探测的发展出现瓶颈问题。 提出了升级原有的激光康普顿散射(LCS)原理性实验装置的方案, 建立了一个通过改变激光入射角来连续调节散射光子能量、 准单色、 极化、 sub MeV～MeV LCS光源(SINAP-III), 从而开拓LCS光源在我国航天领域（如用于航天的X/γ探测器能量定标和抗辐射加固评估研究）的崭新应用前景, 并为将来建设一个基础和应用研究相结合的多功能的γ源实验平台打下基础。 The X/γ detectors in the field of national stratagem, such as astronautical technology, have very broad and important application. These detectors, however, will play their role properly only after accurate calibrations in effective energy region. For the shortage of continuously adjustable and quasi monochromatic γ source in China, it is impossible for the detector employed in aerospace to achieve an accurate calibration so that development of such detector has encountered a big obstacle (or a bottleneck). Therefore, we propose to upgrade the original LCS device to an adjustable photon energy by changing incident angle of laser beam, monochromatic, and polarized sub MeV~MeV LCS γ source(SIMAP III) , in order to explore the new applications of LCS γ source in aerospace as well as to establish a platform for a multifunctional of γ source.