Small signal gain of free electron lasers with nonuniform wigglers

The small-signal gain of free electron lasers is calculated by solving the single-electron equations of motion to second order in the laser field. Analytic results for free electron lasers with linearly varying wiggler resonant frequency show that the small signal gain of such lasers behaves differently from that of lasers with uniform wiggler resonant frequency and is significantly smaller.     

气动CO_2激光器小信号增益的实验研究

用放大法测量了分别在甲苯和乙醇两种液体燃烧驱动下气动CO2 激光器的小信号增益系数。实验发现 ,用甲苯作为燃料时激光器的平均小信号增益系数可达 0 .62m- 1,远远高于乙醇作燃料时的小信号增益系数。结合甲苯和乙醇分别与空气燃烧后产物组分的配比 ,对实验结果进行了分析 ,得出甲苯是燃烧驱动气动CO2 激光器的一种比较理想的燃料     

Hole coupling in free electron lasers

Numerical simulations of the performance of a far-infrared free electron laser with an aperture in the upstream cavity mirror are presented. Two different applications of mirror apertures are studied: broadband extraction of radiation and injection of the electron beam. The emphasis is on the effect of the aperture on the amplitude of the higher-order transverse modes. It is shown that the mode distribution at saturation can be greatly influenced by variation of the mirror radius of curvature. A simple formula which is quite useful for predicting the dominant higher-order modes is derived. This permits optimization of the cavity with respect to the application in question     

Orbit stability in free electron lasers

Helical magnetic wigglers for free electron lasers can produce non-helical electron trajectories if a uniform axial guide magnetic field is imposed. Friedland's necessary criterion for the existence of helical orbits is reviewed and shown to apply for non-relativistic electron energies. An experiment designed to test this criterion is described and results are compared with theory.     

一种测量CO_2激光器小信号增益的方法

测量CO_2激光器的小信号增益,通常是将被测放电管作为一支放大器,测量其放电时的输入输出光强;或者在腔内插入衰减片,测量其停振时的腔损耗。这里我们提出另一种可以方便地测量小信号增益的方法。该方法是在腔内置入一个电光晶体,由于晶体的损耗可随加在它上面的电压而连续地改变,于是便得到一种可连续调整腔内损耗的元件。改变施加在晶体上的电压,很容易测出恰好使激光振荡停止的阈值电压。然后根据内腔耦合调制的理论,也就很容易算出不同电压下由晶体引入的损耗,从而也就得到放电管的小信号增益。     

Beam wave interactions in free electron lasers

This paper presents a direct and simple ballistic approach to the analysis of interactions taking place in free electron lasers. By keeping the analysis quite simple and general, including self fields and space charge, it is found that five different interactions can occur in these devices, and that they can be classified in three groups with pertinent characteristics. The ‘synchronous’ interaction, in which the beam electrons remain (approximately) in a fixed phase of the rf-wave, is characterized by a bunching effect which occurs along the DC trajectories with no radial displacements, and results in a gain usually proportional to the cube root of the beam current. Under certain conditions, however, this gain can be proportional to the fifth root of the current. The two other classes of interactions are ‘resonant’ and non-relativistic, and are characterized by large radial displacements. No bunching can occur and the gain is usually found to be proportional to the square root of the current. However, under well defined conditions, the gain is found to be proportional to the cube root of the current. The analysis results in dispersion relations involving coupling and beam impedances which are determined for TE modes in cylindrical waveguides, neglecting space charge     

平面形自由电子激光器中的边带不稳定性

本文对平面形自由电子激光器中的边带不稳定性进行了动力学研究。提供了一种处理平面形和螺旋形自由电子激光边带不稳定性的方法,同时解释了平面形自由电子激光边带不稳定性的特点。     

自由电子激光器的位相条件

基于相对论电子在光场和静态磁场作用下的能量方程和洛仑兹方程,分析了自由电子激光器运转的位相条件。结果表明,入射光波相对于相对论电子束的初位相ψ在第1和第4象限,相对论电子的能量将主要表现为能量减低,初位相ψ在第2和第3象限主要表现为使相对论电子进一步被加速。     

自由电子激光器引导场的研制与实验

一、前言 自由电子激光器目前面临一个重要问题乃是如何提高能量转换效率。虽然理论上预示它的能量转换效率可以高达50％,然而,实际获得几乎低一个量级。为此,科学工作者目前主要围绕这一目标进行工作,除了选择合适的Wiggler结构参数之外,在空间周期磁场下再迭加一个适当均匀磁场也可以提高激光器的增益,这是由于均匀磁场能引起回旋共振的结果。 二、磁体结构     

Free electron laser small signal gain measurement at 10.6 µm

Small signal gain has been observed for 10.6 μm radiation using a constant (untapered) wiggler. The permanent magnet wiggler was 2.65 m long, had a period of 3.56 cm (75 periods) and a magnetic field on axis of 2.67 kG. The gain measured was 1.5 ± 0.4 percent agreeing well with the predicted gain corresponding to the experimental electron beam conditions (E = 25MeV,DeltaE/E = 0.75percent,epsilon = 8pimm . mrad, andI = 10A).     

气动CO2激光器小信号增益的实验研究

用放大法测量了分别在甲苯和乙醇两种液体燃烧驱动下气动CO2激光器的小信号增益系数。实验发现,用甲苯作为燃料时激光器的平均小信号增益系数可达0.62m-1,远远高于乙醇作燃料时的小信号增益系数。结合甲苯和乙醇分别与空气燃烧后产物组分的配比,对实验结果进行了分析,得出甲苯是燃烧驱动气动CO2激光器的一种比较理想的燃料。     

连续波HF化学激光器小信号增益的测量

描述了测量连续波HF化学激光器小信号增益空间分布的装置。给出了CL—9喷管的几个跃迁增益分布的测量结果并对实验结果及误差作了简单讨论。     

THE LONG PULSE EFFECT IN FREE ELECTRON LASERS

The spontaneous radiation from a single pulse electron beam in Free Electron Lasers is dealt withby solving one-dimensional wave equations.The obtained results show that there is the long pulse effect aswell as the well-known short pulse effect.     

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     

自由电子激光器输出性能的研究

研究了自由电子激光器的输出功率,指出红外波段的自由电子激光器将较紫外波段器件容易获得高功率输出;讨论了相对论电子束的脉冲宽度和共振腔透过率的选择,获得了超辐射输出的工作条件;讨论了相对论电子束能量发散度Δγ_0/γ_0对激光能量转换效率的影响。     

变参数自由电子激光器的研究

在单粒子模型基础上用一种简便的能量模型计算了变参数Wiggler自由电子激光器的增益。结果表明,周期磁场振幅沿z方向增加,或空间周期长度沿z变化都可以提高增益。但前者比后者的效果更明显。     

High-gain free electron lasers using induction linear accelerators

High-power free electron lasers (FEL's) can be realized using induction linear accelerators as the source of the electron beam. These accelerators are currently capable of producing intense currents (10²-10⁴A) at moderately high energy (1-50 MeV). Experiments using a 500 A, 3.3 MeV beam have produced 80 MW of radiation at 34.6 GHz and are in good agreement with theoretical analysis. Future experiments include a high-gain, high-efficiency FEL operating at 10.6 μm using a 50 MeV beam.     

Sideband suppression in free electron lasers using a grating rhomb

The phase shift produced by a grating rhomb is included in free-electron laser (FEL) pulse calculations to investigate whether or not grating rhombs can be used to suppress the sideband instability. The idea is that because the group travel time through a rhomb is an increasing function of the laser wavelength, an FEL oscillator can be designed such that the optical pulse at a chosen central wavelength and the pulse of electrons overlap spatially when they enter the wiggler. Over many passes, light in a small bandwidth about the chosen wavelength receives the greatest amplification because it overlaps the electrons, and light at sideband instability wavelengths that does not overlap the electrons is suppressed by losses in the oscillator cavity. For a 5-m tapered wiggler, the range in rhomb dispersion and cavity loss that yields acceptable FEL performance is defined. At low values of cavity loss, for example 15%, a wide range of rhomb dispersion exists for which both the sideband instability is largely suppressed and the energy extracted from the electrons is high. At larger values of cavity loss, for example 30%, a critical value for rhomb dispersion exists below which the laser pulse is compressed by the rhomb, leading to reduced energy extraction     

A 70-period high-precision microwiggler for free electron lasers

We have designed, constructed, and operated a 70-period microwiggler for free electrons lasers (FEL's). The device is a pulsed ferromagnetic-core electromagnet with a period of 8.8 mm, which generates an on-axis peak magnetic field of 4.2 kG. The pulses, of 0.5 ms duration, are generated at a rate of 0.5 Hz. Each field peak is independently tunable. We employed a novel tuning regimen to reduce the RMS spread in the peak amplitudes to 0.12%, the lowest value thus far attained in a sub-cm-period periodic magnetic field