梯度磁场作用下的自由电子激光器增益特性研究

本文数值计算了在空间周期磁场摆动器上迭加轴向梯度磁场后自由电子激光器的增益特性,结果表明:采用梯度磁场比均匀磁场可获得更佳的激光增益特性。     

康普顿型自由电子激光器的实验研究

这里介绍我国第一台康普顿型自由电子激光器的实验研究情况。这是一台以30 MeV直线加速器为基础,配置上电子束输运系统、常周期磁摆动器(Undulator)和光学系统构成的器件。辐射输出波长在9～11μm。1986年11月,在这台器件上获得了平均功率1.4W的10μm辐射输出。下面我们介绍一下康普顿型自由电子激光器的实验装置,如     

喇曼自由电子激光器的实验研究

我们研制了一台基于受激喇曼散射的自由电子激光器。精心设计的无箔二极管发射出柱状或空心柱状电子束。电子束打靶实验表明它是高度准直的;利用Lamor运动实验测试出电子束的归一化发射度为23π·mrad-cm,完全满足受激喇曼散射模式判据。该电子束在抽空为5×10~(-5)Torr、内径φ20mm的漂移管中传输,受到右旋圆偏极双绕电磁波荡器或轴对称铁环波荡器(周期分别为2.2cm及2.25cm)的泵浦,均获得超辐射模式的自由电子激光辐射。测     

螺旋磁场泵浦的自由电子激光器的能谱

在Bambini—Renieri坐标系中讨论了螺旋磁场泵浦的自由电子激光器的能谱。     

磁场误差对自由电子激光器增益的影响

用随机数构造了摇摆器磁场的误差分布．基于CAEPFEL的理论设计，研究了磁场误差对自由电子激光器增益的影响．     

关于轴向磁场的自由电子激光器增益特性

本文从流体力学麦克斯韦方程组出发,用拉氏变换方法求得了考虑轴向磁场的自由电子激光器的增益公式。数值计算和色散关系的分析表明,当迴旋频率接近于入射波频率i与电子等离子体频率p之差#em/em#p时,增益会大大下降,并且增益与泵浦-信号失配关系曲线的峰值的位置也会由原来的p向低的方向移动,我们可以利用i-p时出现增益零点的现象来推算p。     

喇曼自由电子激光器二极管的实验研究

文章给出了用于一台喇曼自由电子激光器磁场浸没型无箔二极管工作特性的实验研究。比较了不同结构、不同电极参量、不同电极材料和不同磁场下的典型结果。分析了不同的束输出条件下所遵循的规律。     

自由电子激光器

一 自由电子激光器的特点 自由电子激光器是一种新型的激光器,问世以来,爱到很大的重视,它的基本特点是:它不需要气体、液体、或固体作为工作物质,而是由高能电子注的能量转变为激光的能量。也可以说,自由电子激光器的工作物质就是自由电子,它和已有的激光器比较起来,具有一系列优点如下:     

The effects of field errors on low-gain free-electron lasers

The effects of random wiggler magnetic field errors on low-gain free-electron lasers (FELs) are examined analytically and numerically through the use of ensemble averaging techniques. Wiggler field errors perturb the electron beam as it propagates and lead to a random walk of the beam centroid, variations in the axial beam energy, and deviations in the relative phase of the electrons in the ponderomotive wave. The random walk of the beam centroid and the consequent variations in the axial beam energy are discussed. The deviations in the relative phase resulting from the field errors are examined. The effect of the field errors on the FEL gain in the low-gain regime is determined. The benefits of beam steering are analyzed, and addition methods for reducing the detrimental effects of field errors are discussed     

Simulation of free-electron lasers in the presence of correlatedmagnetic field errors

The authors address the numerical simulation of field errors that possess statistical correlations. The inevitable errors of actual magnetic wigglers yield a degraded performance of the free-electron laser (FEL) with respect to the performance obtained from ideally modeled magnetic wigglers. The impact of these errors has been theoretically and computationally investigated for simple error modes, in which the field errors have uniform or sinusoidal spatial extent and amplitudes that are statistically independent for each magnet pole piece. These simple models have been recently extended to include more complicated spatial structures and statistically correlated field errors in the analysis of FEL performance. Numerical simulations of the FEL are presented that verify the analytic predictions of the recently extended model     

Finite-temperature effects in free-electron lasers

The effect of energy spread on the gain of a dense-beam free-electron laser amplifier is analyzed. The formalism includes collective effects and allows for the use of an arbitrary distribution function. The dispersion relation is solved numerically. Besides broadening of the spectrum and decrease in gain, lowering of the central emission frequency with energy spread is observed. An initial-value problem is formulated and numerically solved, with power computed as a function of distance. The relative contributions of the different modes when temperature changes are analyzed. In particular, the competing effects of a decrease in coupling loss with temperature together with Landau damping are investigated.     

New instabilities of free-electron laser with an axial guide magnetic field

In this paper, the unperturbed orbits, their stable conditions and the single-pass gain of a free-electron laser have been treated with a single-particle theory to show the existence of a couple of new instabilities and moreover, to discuss their effects. Numerical analyses reveal that the new instabilities will probably affect the operation of free-electron laser when the guide field increases and get into the vicinity of its stability boundary.     

The effect of wiggler imperfections on nonlinear harmonicgeneration in free-electron lasers

The generation of harmonics through a nonlinear mechanism driven by bunching at the fundamental has sparked interest in using this process as a path toward an X-ray free-electron laser (FEL). An important issue in this regard is the sensitivity of the nonlinear harmonic generation to wiggler imperfections. Typically, linear instabilities in FELs are characterized by increasing sensitivity to both electron beam and wiggler quality with increasing harmonic number. However, since the nonlinear harmonic generation mechanism is driven by the growth of the fundamental, the sensitivity of the nonlinear harmonic mechanism is not severely greater than that of the fundamental. In this paper, we study the effects of wiggler imperfections on the nonlinear harmonics in a 1.5-Å FEL, and show that the decline in the third harmonic emission with increasing levels of wiggler imperfections roughly tracks that of the fundamental     

Nonlinear harmonic generation in free-electron lasers

A three-dimensional nonlinear simulation code to treat multiple frequencies simultaneously is described and used to study nonlinear harmonic generation in free-electron lasers (FELs). Strong nonlinear harmonic gain is found where the gain length varies inversely with the harmonic number. Substantial power levels are found in the harmonics. The odd harmonics are favored with generally higher power levels since a planar wiggler geometry is employed; however, the second harmonic exhibits substantial power as well. The analysis is relevant to the emission expected from self-amplified spontaneous emission (SASE) free-electron laser schemes     

Intensity saturation mechanism in free-electron lasers

It is shown that the free-electron laser (FEL) exhibits a scaling of the gain saturation versus the intensity analogous to that of conventional lasers. The concept of FEL intensity saturation is introduced and its link to the maximum output intensity is discussed     

Suppression of feedback oscillations in free-electron lasers

The suppression of feedback oscillations in a free-electron laser (FEL) oscillator has been investigated. It is found, through numerical simulation that a narrow attenuating strip inserted in a waveguide will not reduce FEL performance at the desired frequency and will attenuate feedback oscillations. Simulations are presented for a 5-mm-wavelength FEL with a 40-dB attenuator inserted in the interaction region     

Wavelength and emittance requirements in free-electron lasers

Improvements in electron beam quality are required for operation of free-electron lasers (FELs) at short wavelengths and low voltages. The authors investigated this scaling for a FEL amplifier in the exponential regime of operation wherein the optical beam is tied to the electron beam as a result of gain focusing, subject to the requirements of (1) good geometrical overlap between the radiation beam and the matched electron beam and (2) cold-electron-beam interaction. The scaling is given by simple analytical formulas     

Equations of motion for a free-electron laser with an electromagnetic pump field and an axial electrostatic field

The equations of motion for a free-electron laser (FEL) with an electromagnetic pump field and a static axial electric field are derived using a Hamiltonian formalism. Equations governing the energy transfer between the electron beam and each of the electromagnetic fields are given, and the phase shift for each of the electromagnetic fields is derived from a linearized Maxwell wave equation. The relation between the static axial electric field and the resonant phase is given. Laser gain and the fraction of the electron energy converted to photon energy are determined using a simplified resonant particle model. These results are compared to those of a more exact particle simulation code.