Frequency conversion and amplification by stimulated electromagnetic shock radiation (SESR)

The coherent response of a polarizable medium to the radiation stimulated by the interaction of an incident coherent electromagnetic wave with a charged-particle beam, moving with greater than critical speed, results in intense electromagnetic radiation in the form of one or more shock fronts. The shock frequencies are shifted significantly from that of the incident wave and are tunable by parametric variation of the incident beams. The mechanism for this new effect (SESR) differs fundamentally from the laser mechanism. Production of intense quasi-coherent x-ray radiation by SESR obviates the need for x-ray mirrors and is not inhibited by the large spontaneous emission rates at these frequencies. Substantial fraction of the particle-beam energy can be converted into frequency-shifted radiation, with intensity larger than that of the incident wave, because of quadratic dependence on the interaction distance in the medium of the energy radiated into SESR, as compared to the linear dependence of Cerenkov radiative energy. Specific shock frequencies cross from below to above a given resonance frequency of the medium as the relevant two level populations become inverted. This dynamical dependence of the shock frequencies on the level populations provides the basis for new pumping and amplification mechanisms. An example of a possible SESR-based transducing-amplification system is described.     

Observation of the second harmonic in Thomson scattering from relativistic electrons

A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and gamma-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO2 laser beam.     

Interaction of a surface magnetostatic wave with an inhomogeneous granular HTSC medium

In the present paper the dispersion properties of surface magnetostatic waves (SMSWs) propagating in a stratified structure, ferrite film—high-temperature superconducting layer, have been investigated. The problem of SMSW propagation in an inhomogeneous stratified medium has been solved and the dispersion equation has been obtained. In the solution of this problem, the granular nature of the high-temperature superconducting (HTSC) medium and the exposure to a constant magnetization field have been taken into account. Upon exposure to the constant magnetic field the HTSC film becomes an inhomogeneous anisotropic medium with respect to a variable magnetic field. The nonhomogeneous wave equation describing the SMSW field in a granular HTSC medium has been solved by the method of sequential iterations. Corrections for the SMSW velocity and attenuation, calculated with the use of the exact dispersion equation, are significant in comparison with previously obtained approximate values and exceed 20 and 40%, respectively. The method of analyzing electromagnetic fields in inhomogeneous granular high-temperature media can be used to solve some other problems, where spatially inhomogeneous HTSC media are used. Tomsk State University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 45–48, April, 1999.     

Dissipative soliton-like plasmon-polariton pulses in extended medium

The propagation of the coupled state of the electron density perturbation in an extended metallic medium and the excitation of a two-level resonant medium are analyzed. The one- and two-photon transitions in the resonant medium are considered. The electron density perturbation is described using the hydrodynamic approximation. The formation of plasmon-polariton pulses is analyzed in the case when losses in the extended medium are compensated for by the pumping of the two-level dielectric medium. Numerical analysis carried out for the two models revealed that the losses in a soliton-like pulse in a thin metallic medium can be compensated for due to the energy transfer from the amplifying medium to electron density waves. It is shown that the dispersion of a medium containing a two-level component may considerably affect the characteristics of the pulses. The possibility of effectively controlling the evolution of soliton-like pulses by varying an external electromagnetic field and the characteristics of the matrix is demonstrated.     

Three-dimensional Wigner-function description of the quantum free-electron laser

A free-electron laser (FEL) operating in the quantum regime can provide a compact and monochromatic x-ray source. Here we present the complete quantum model for a FEL with a laser wiggler in three spatial dimensions, based on a discrete Wigner-function formalism taking into account the longitudinal momentum quantization. The model describes the complete spatial and temporal evolution of the electron and radiation beams, including diffraction, propagation, laser wiggler profile and emittance effects. The transverse motion is described in a suitable classical limit, since the typical beam emittance values are much larger than the Compton wavelength quantum limit. In this approximation we derive an equation for the Wigner function which reduces to the three-dimensional Vlasov equation in the complete classical limit. Preliminary numerical results are presented together with parameters for a possible experiment.     

Two-stream instability in free electron lasers

The analysis of the interaction between electromagnetic waves and electron beams in semi-infinite wigglers is presented. The beam is assumed to include two cold streams of electrons; hence, its space-charge waves may be unstable (two-stream instability). In the wiggler, this instability is shown to yield much larger growth rates (up to seven times greater) than in the conventional one-stream free electron laser (FEL). Accordingly, the gain per pass is enhanced by orders of magnitude. The enhancement of the two-stream instability is shown to be most effective for short-period wigglers     

Dynamics of electromagnetic field in two-level doped systems

The dynamics of solitons of self-inducted transparency is theoretically and numerically investigated in the case when atoms described in the two-level approximation fit into a medium with ferroelectric properties. The interaction between electromagnetic pulses in the medium and two-level dopant atoms is considered.     

Specific features of amplification of almost ultimately short pulses in media with a permanent dipole moment

Amplification of electromagnetic field pulses approximately one cycle in duration in multilevel media with an effective permanent dipole moment is studied theoretically without application of the approximation of slowly varying envelopes for the case of unidirectional propagation of the radiation. For three-level and quasi-two-level media, it is shown that the set of Maxwell-Schrödinger equations can be reduced to an integrable set of equations for an effective two-level medium. The presence of an (effective) permanent dipole moment of the medium was found to lead to new specific features of the amplification and control of the dynamics of field pulses.     

自由电子激光器中电子与波的相互作用及其增益分析

分析了自由电子激光器中电子与波的相互作用过程，导出了相应的增益表达式。结果表明，它不仅能很好地反映自由电子激光器中相干辐射，而且表明了具有激光输出饱和特性。分析结果更加符合实验情况。 关键词：     

Chaotic electron trajectories in electromagnetic wiggler free-electron laser with a guide magnetic field

Summary The Hamiltonian for an electron travelling through a large-amplitude backward electromagnetic wave, an axial guide magnetic field and radiation field is formulated. Poincaré surface-of-section plots show that this Hamiltonian is non-integrable, and leads to chaotic trajectories. Equilibrium conditions are derived in the limit where the radiation field approaches zero. Compared to conventional FEL, the total energy of the system at pondermotive resonanceE _c is large, while the electron's critical energy γ_c is low for electromagnetic wiggler FEL. Moreover, the threshold wave amplitude (A _r=A _c) of beam chaoticity is found at lower values of the radiation field amplitude compared to magnetostatic wiggler FEL. Previous features confirmed that electromagnetic wiggler FEL can operate more coherently and more efficiently at moderated particle's energy compared to magnetostatic wiggler FEL.     

A new mechanism of electromagnetic electron radiation in a medium (spin light)

Based on the method of exact solutions to the quantum equations for the wave functions of particles in external fields and media within the framework of the standard interaction model, the modified Dirac equation for the electron is derived that allows its interaction with the medium to be considered. An exact solution to the equation and energy spectrum of the electron states are determined. In the context of this approach, a new type of electromagnetic radiation-spin light of electron in a neutron medium-is predicted and studied. General expressions for the probability of the process in unit time and for the radiation intensity are derived, and a dependence of the radiation intensity on the electron energy and density of the medium is analyzed. The limiting cases of the process and polarization properties of radiation are investigated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 66–73, June, 2007.     

自由电子激光的计算机模拟

本文使用1(2/2)维电磁相对论粒子程序对自由电子激光进行计算机模拟。在线性段,计算机模拟与用解析理论计算的增长率符合很好。与没有轴向引导磁场的自由电子激光相比,加一弱轴向引导磁场时,Wiggler场的强度可降得较低。加一强轴向引导磁场时,波能量达到饱和水平所需时间较短。     

Fully coherent x-ray pulses from a regenerative-amplifier free-electron laser

We propose and analyze a regenerative-amplifier free-electron laser (FEL) to produce fully coherent, hard x-ray pulses. The method makes use of narrow-bandwidth Bragg crystals to form an x-ray feedback loop around a relatively short undulator. Self-amplified spontaneous emission (SASE) from the leading electron bunch in a bunch train is spectrally filtered by the Bragg reflectors and is brought back to the beginning of the undulator to interact repeatedly with subsequent bunches in the bunch train. The FEL interaction with these short bunches regeneratively amplifies the radiation intensity and broadens its spectrum, allowing for effective transmission of the x rays outside the crystal bandwidth. The spectral brightness of these x-ray pulses is about 2 to 3 orders of magnitude higher than that from a single-pass SASE FEL.     

Diffracted X Rays and Resonance (Coherent) Transition Radiation Generated by High-Energy Charged Particles

The present review is devoted to the current status of research in electromagnetic radiation generated by relativistic charged particles that pass with constant velocities through periodic media. Two particular examples are considered: the first conserves Bragg's scattering of the pseudo-photon field of the charged particle in crystals, and the second concerns the Fresnel scattering of pseudo-photons in a periodic medium. Both effects are very promising for the development of new compact adjustable x-ray sources.     

Modification of gravitational redshift of x-ray burst produced by pulsar surface magnetoplasma

In this paper, the propagation of x-ray bursts in the magnetoplasma of pulsar magnetosphere is discussed. The electromagnetic interaction between x-ray bursts and magnetoplasma is described as some geometry. The electromagnetic effects of surface superstrong magnetic field and dynamic effects of outflowing magnetoplasma of pulsars are treated as an optical metric. The Gordon metric is introduced to represent the gravitational metric and optical metric. So the propagation of x-ray bursts in magnetoplasma of pulsars can be described as x-ray bursts transmitting in an effective space characterized by Gordon metric. The modification of gravitational redshift, attributed to the flowing magnetoplasma of pulsars, is obtained and it is shown that the modification is of redshift and can reach the same magnitude as the gravitational redshift for ordinary pulsars.     

Modification of gravitational redshift of x-ray burst produced by pulsar surface magnetoplasma

In this paper, the propagation of x-ray bursts in the magnetoplasma of pulsar magnetosphere is discussed. The electromagnetic interaction between x-ray bursts and magnetoplasma is described as some geometry. The electromagnetic effects of surface superstrong magnetic field and dynamic effects of outflowing magnetoplasma of pulsars are treated as an optical metric. The Gordon metric is introduced to represent the gravitational metric and optical metric. So the propagation of x-ray bursts in magnetoplasma of pulsars can be described as x-ray bursts transmitting in an effective space characterized by Gordon metric. The modification of gravitational redshift, attributed to the flowing magnetoplasma of pulsars, is obtained and it is shown that the modification is of redshift and can reach the same magnitude as the gravitational redshift for ordinary pulsars.     

无碰撞等离子体中电子束流不稳定性的时空演化研究

应用二、三维相对论电磁粒子模拟程序研究双电子束流在无碰撞等离子体中传播引起的横向 电磁(Weibel类型)不稳定性和纵向静电不稳定性的发展演化过程.讨论了纯粹Weibel不稳定 性的发生和非线性饱和过程，观察到电流束合并、磁场重联等引起的电子横向加热现象.研 究了电流束传播方向激发的静电场对快电子束传播的影响，观察到其导致的束的横向调制、 磁场通道破坏现象.对这些过程的细致研究对更好的理解快点火物理中自生磁场的产生、快 电子输运等过程有重要意义.     

光阴极注入器型能量回收射频加速器

 光阴极注入器型能量回收射频加速器（PERL）是新一代加速器，在高平均功率自由电子激光和下一代高亮度光源等研究中有很好的应用前景。分析了PERL的强流与高平均功率特性，对注入器输出束流品质的要求及光阴极注入器、超导加速腔等关键技术进行了研究，设计分析了一种特殊结构的高压DC Gun光阴极注入器，能有效地提高DC加速腔中的加速场强，当高压为1MV和加速场达到10MV/m时，产生的电子束流能够基本满足PERL应用要求。同一超导加速段中的束流加速和能量回收的数值模拟计算结果表明，能获得高效率电子束流能量回收效果。     

Efficiency enhancement of a two-beam free-electron laser using a nonlinearly tapered wiggler

A nonlinear and non-averaged model of a two-beam free-electron laser (FEL) wiggler that is tapered nonlinearly in the absence of slippage is presented. The two beams are assumed to have different energies, and the fundamental resonance of the higher energy beam is at the third harmonic of the lower energy beam. By using Maxwell's equations and the full Lorentz force equation of motion for the electron beams, coupled differential equations are derived and solved numerically by the fourth-order Runge-Kutta method. The amplitude of the wiggler field is assumed to decrease nonlinearly when the saturation of the third harmonic occurs. By simulation, the optimum starting point of the tapering and the slopes for reducing the wiggler amplitude are found. This technique can be applied to substantially improve the efficiency of the two-beam FEL in the XUV and X-ray regions. The effect of tapering on the dynamical stability of the fast electron beam is also studied.     

Superheterodyne electron-wave free-electron lasers

A new class of free electron lasers (electron wave superheterodyne FEL) has been described. They differed from traditional ones by construction based on utilization of one of electron wave (plasma-beam, two-stream and others) instability mechanisms. In this case a parametrical interaction mechanism was used only for transformation of the longitudinal beam waves into the transverse electromagnetic ones. Nonlinear superposition the electron wave and parametric instabilities was interpreted as an effect of superheterodyne amplification.