Growth rate enhancement of free-electron laser by two consecutive wigglers with axial magnetic field

The operative mechanism for a free-electron laser (FEL) with two consecutive helical wigglers having opposite circular polarization in the presence of an axial magnetic field is proposed and analysed. With the help of fluid theory, a tenth-degree polynomial dispersion equation for electromagnetic and space–charge waves is derived. The results are used to illustrate and discuss the dependence of growth rate on different system parameters. Finally, it is shown that for the same system parameters the growth rate of the proposed structure is more than the growth rate of instability in a conventional FEL.     

一种新型短波长自由电子激光

本文提出一种可以工作在软X射线区的用孤子激光抽运的新型自由电子激光器,利用孤立子激光的波型以及单粒子小信号分析方法,发现这种自由电子激光具有以下两个不同于以往电磁波振荡器自由电子激光的特点:(1)很小的“质量漂移效应”(mass-shift effect),这是由孤立子激光抽运的特征所决定;(2)具有一个附加的“频率调谐性”,即可展宽自由电子激光的频率调谐能力。对获得的小信号增益也进行了一些分析和讨论。 关键词：     

Free electron laser pumped by a powerful traveling electromagneticwave

A three-wave free-electron laser (FEL) was operated with a powerful 8.4-GHz electromagnetic pump wave replacing the usual magnetostatic wiggler. The presence of a uniform axial magnetic field B₀ produced cyclotron-harmonic idler waves. Peaks in the emission spectrum corresponding to cyclotron harmonics were observed covering a frequency range from 16.5 to 130 GHz. The frequency spectrum of this novel FEL mechanism was tuned continuously by the variation of B₀     

A slow wave free-electron laser

A simple calculation of a free-electron laser in the Compton regime that uses a dielectric-lined waveguide is presented. The introduction of a dielectric lining in a free-electron laser considerably reduces the requirements on beam voltage for generating a given frequency ω₁=k₀c/(1 - v_b η/c), where k₀ is the wiggler wave period η is the effective index of refraction (1<η<√ϵ) and ϵ is the permittivity. The system supports electromagnetic waves whose Poynting flux is largely concentrated in the dielectric; hence the electron beam is required to propagate close to the dielectric lining. The mode structure and dispersion behavior of the guiding system without the beam are discussed. a thin annular beam is introduced, and a perturbation theory is used to obtain the frequency and growth rate of radiation     

Study of crystals in medium-and long-wavelength IR ranges by surface-electromagnetic-wave spectroscopy

First observation of excitation of surface electromagnetic waves (SEW) is reported in the reststrahlen region in for biaxial crystal KTiOPO₄ (KTP) using a tunable CO₂ laser around 10 μm, and for CaF₂, BaF₂, MgO (cubic crystals), and LiNbO₃ (uniaxial crystal) in the far IR using ith a free-electron laser. The parameters of SEW propagation in these crystals have been obtained by the interference method of SEW phase spectroscopy, and the possibility of determining the complex dielectric permittivity of crystals from the SEW propagation parameters demonstrated in the range of SEW existence. Fiz. Tverd. Tela (St. Petersburg) 40, 237–241 (February 1998)     

高斯束激光摇摆场中的电子运动轨道分析

对高斯束激光摇摆场中的电子运动轨道进行了分析．推导出轴向导引磁场与反向传播的激光摇摆场作用下的单粒子电子运动轨道，并对轨道的稳定性进行了分析．发现当瑞利长度较大时，得到的结果与平面电磁波摇摆场的结果相一致．与静磁摇摆场的自由电子激光相似，在激光摇摆场中的电子轨道也存在两类分立轨道，但是，与静磁摇摆场不同的是，这两类轨道都是稳定的 关键词：     

导引场下电磁泵浦自由电子激光的非线性理论

本文以Vlasov-Maxwell方程组为基础,用非线性动力学理论研究了存在导引场情况下电磁波泵浦的自由电子激光器的作用机制,导出了线性及非线性色散关系式,求出了非线性不稳定性增长率和自由电子激光的能量转换效率.结果表明,只要合理地选择参量条件,附加导引场可以大大提高自由电子激光的增长率和能量转换效率.     

An exact solution of the relativistic equation of motion of acharged particle driven by a circularly polarized electromagnetic waveand a constant magnetic field

An exact solution is found for the relativistic equation of motion of a charged particle driven by a circularly polarized electromagnetic wave and a constant magnetic field. The explicit expressions of particle position and velocity are obtained for certain initial conditions. The results are of interest to the interaction of the high-power laser with the magnetized plasma, electromagnetically pumped free-electron laser with a guide magnetic field, propagation of electromagnetic wave signals through a re-entry plasma sheath in the presence of a strong magnetic field, and magnetic confinement plasmas     

Frequency Spectrum of Plasma-Filled Free-Electron Laser Pumped by Electromagnetic Wave

The frequency spectrum of free-electron laser pumped by electromagnetic wave with magnetized and unmagnetized background plasma is analyzed by the theory of three-wave interaction and PIC simulation, respectively. The frequencies of PIC simulation are in agreement with the results of the three-wave interaction theory. The results show that the frequency spectrum is very plentiful.     

Amplifying autophase free-electron laser

The amplification of an electromagnetic wave in an autophase free-electron laser with the righthand polarized wiggler field and the oppositely directed focusing field is considered.     

Scattering by an array of parallel metallic carbon nanotubes

The scattering of electromagnetic wave by an array of parallel metallic single-walled carbon nanotubes is investigated based on the boundary-value method. Electronic excitations over each nanotube surface are modeled as an infinitesimally thin cylindrical layer of the free-electron gas. The scattering cross section of both transverse magnetic （TM） and transverse electric （TE） uniform plane waves by the system at normal incidences is obtained.     

Effect of dispersion on the operation of free-electron lasers driven by short electron bunches

The effect of dispersion on the lasing of waveguide free-electron lasers driven by short periodic electron bunches is considered. In the high-Q cavity approximation, the generation of electromagnetic pulses is described in terms of a parabolic equation. For the linear stage of interaction, starting lasing conditions are found analytically and the spatio-temporal structure of supermodes, which represent a set of phase-locked eigenmodes of the cold cavity, is determined. Dispersion is shown to allow the free-electron laser to operate at both positive and negative mismatches between the period of electron bunch injection and the time taken for the electromagnetic pulse to circulate over the cavity. The simulation of the nonlinear lasing conditions with allowance for dispersion spread makes it possible to find the stationary profile of radiated pulses and the optimum values of the group and time detunings that provide a maximum efficiency of the waveguide free-electron laser. It is also shown that, when the length of interaction is much longer than the starting value, the laser operates under the conditions of periodic or chaotic pulse profile self-modulation.     

Two-color operation in high-gain free-electron lasers

Two-color operation in free-electron laser (FEL) amplifiers is studied using a 3D nonlinear polychromatic simulation. We assume the FEL is seeded at two closely spaced wavelengths within the gain band, and study the growth of the seeds and a discrete spectrum of beat waves that are outside the gain band. The beat waves grow parasitically due to electron bunching in the seeded waves with growth rates higher than the seeded waves. Injection of narrow-band seeds ensures a discrete spectrum. An example is discussed corresponding to an x-ray FEL; however, the physics is applicable to all spectral ranges.     

Electronic subband structure in two-dimensional electron gases under intense laser radiations

We present a theoretical study on the influence of intense terahertz (THz) electromagnetic (EM) radiations on the electronic structures in a modulation-doped two-dimensional (2D) semiconductor system. We find that in the presence of a THz EM radiation field polarised linearly along the 2D-plane of a 2D electron gas (2DEG), the electron density of states will be modified strongly by the intensity and the frequency of the radiation field. As a consequence, the Fermi-energy and the electron density in the system will be affected markedly by the EM radiations. The results have indicated that the photon-modified electronic subband structure in a 2DEG device can be observed by using the recently developed free-electron laser sources.     

A SURVEY OF SOME IDEAS FOR ACCELERATORS USING LASER LIGHT

Many Suggestions have been made for accelerating particles in the intense fields associated with laser light. Those which rely on direct interaction with the laser field in vacuo (as opposed to acceleration in a plasma medium) are examined and their fundamental limitations discussed. Three schemes are considered, the first of these utilizes slow electromagnetic waves near a surface, the second relies on a fast electromagnetic wave with "phase jumps" and the third used parametric interaction with particles moving on a modulated orbit.     

A free-electron laser pumped by the soliton laser

We propose a scheme for building a free-electron laser in the soft X-ray region pumped by the soliton laser. Making use of soliton laser wave evolution shape and single-pass small signal analysis, we find that this laser has two special advantages over the previous electromagnetic wave undulator free-electron lasers. One is a very small mass-shift effect because of the special characteristics of soliton laser; the other is that it has an additional frequency tuning effect based on the conventional free-electron laser's tunability. We also obtain the small signal gain and present some discussion.     

Analysis of the uniform magnetic field free-electron laser with scalarized photons in the microwave-spectral region

The recently developed concept of scalarized photons (formally photons of any polarization) is used to analyze the spontaneous and stimulated emission in the uniform magnetic field free-electron laser in the microwave spectral region. In fact, this free-electron laser is the simplest of many other, wiggler and wiggler-free free-electron lasers whose analyses could be done with scalarized photons in the small signal regime and whose physical parameters can be conveniently chosen for radiation to be generated in the microwave spectral region. As to the uniform magnetic field free-electron laser, which is treated here in some detail, with the electron beam energy of up to 10 MeV and the uniform magnetic field of up to 4 Tesla, the radiation (occurring with the fundamental and higher harmonic frequencies) can cover easily a 10 to 10,000 GHz spectral region.     

The effects of self-fields on the electron trajectory and gain in a two-stream electromagnetically pumped free-electronlaser with axial guiding field

A theory of a two-stream free-electron laser in a combined electromagnetic wiggler (EMW) is developed, in which we use an axial-guide magnetic field and take into account the effects of the self-fields. The electron trajectories and the small signal gain are derived. The stability of the trajectories, the characteristics of the linear-gain, and the normalised maximum gain are studied numerically. The results show that there are nine stable groups of orbits in the presence of self-fields instead of seven groups reported in the absence of the self-field. It is also shown that the normalised gains of four groups of the orbits are decreasing and those for the rest of them are increasing with growing \barΩ₀. Furthermore, it is found that the two-stream laser with self-field enhances the maximum gain in comparison with the single stream case.     

独立调谐热阴极微波电子枪实验研究

为了研制紧凑型自由电子激光装置,开展自由电子激光太赫兹技术研究,需要研制微波电子枪作为高品质电子束源,为此,中国工程物理研究院研制了独立调谐热阴极微波电子枪。在前期进行了初步热测实验的基础上,通过改进实验环境、优化实验参数,进一步开展大量实验,深入研究了热阴极微波电子枪的热测实验结果。实验结果表明:微波电子枪出口处束流强度可超过500 mA,电子反轰效应随着首腔电场的相位和幅度调节发生显著变化。该热阴极微波电子枪已经应用于紧凑型自由电子激光装置。