Nonlinear theory of free-electron lasers and efficiency enhancement
Nonlinear theory of free-electron lasers and efficiency enhancement
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DOI：
10.1103/physreva.21.302
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发表时间：
1980
影响因子：
2.9
通讯作者：
P. Sprangle;Cha-Mei Tang;W. Manheimer
中科院分区：
文献类型：
--
作者：
P. Sprangle;Cha-Mei Tang;W. Manheimer
以相对论性自由电子流为活跃介质的激光器的发展最近引起了人们极大的兴趣。这种自由电子激光器的潜在优势包括，除其他外，频率可连续调谐，非常高的工作功率和高效率。自由电子激光（FEL）的特征是一个泵浦场，例如一个从相对论电子束散射出来的空间周期性磁场。散射辐射的波长远小于泵浦波长，这取决于电子束的能量。作者提出了FEL过程的一般自洽非线性理论。时间稳态FEL问题的非线性公式得到了一组耦合微分方程，该方程控制着辐射场和空间电荷场的振幅和波长的空间演化。由于振幅和波长在与输出辐射的增长长度相当的空间尺度上变化，因此这些方程很容易在数值上求解。提出了从光学到亚毫米波长范围的许多数值和分析插图。将我们的非线性公式与线性理论进行了比较，发现两者的一致性非常好。饱和效率和辐射振幅的解析表达式也与我们的非线性数值解非常吻合。得到了固定磁泵参数下光学和亚毫米级自由电子激光器的效率曲线。结果表明，适当地控制磁泵周期可以大大提高这些固有效率。在光学自由电子激光器中，适当减小泵浦周期和增大泵浦磁场可以使理论单通效率大于20%。«少
The development of lasers in which the active medium is a relativistic stream of free electrons has recently evoked much interest. The potential advantages of such free-electron lasers include, among other things, continuous frequency tunability, very high operating power, and high efficiency. The free-electron laser (FEL) is characterized by a pump field, for example, a spatially periodic magnetic field which scatters from a relativistic-electron beam. The scattered radiation has a wavelength much smaller than the pump wavelength, depending on the electron-beam energy. The authors present a general self-consistent nonlinear theory of the FEL process. The nonlinear formulation of the temporal steady-state FEL problem results in a set of coupled differential equations governing the spatial evolution of the amplitudes and wavelength of the radiation and space-charge fields. These equations are readily solved numerically since the amplitude and wavelength vary on a spatial scale which is comparable to a growth length of the output radiation. A number of numerical and analytical illustrations are presented, ranging from the optical to the submillimeter-wavelength regime. Our nonlinear formulation in the linear regime is compared with linear theory, and agreement is found to be excellent. Analytical expressions for the saturated efficiency and radiation amplitude are alsomore » shown to be in very good agreement with our nonlinear numerical solutions. Efficiency curves are obtained for both the optical and submillimeter FEL examples with fixed magnetic-pump parameters. It is shown that these intrinsic efficiencies can be greatly enhanced by appropriately contouring the magnetic-pump period. In the case of the optical FEL, the theoretical single-pass efficiency can be made greater than 20% by appropriately decreasing the pump period and increasing the pump magnetic field.« less