Dispersion, spatial growth rate, and start current of a Cherenkov free-electron laser with negative-index material
Dispersion, spatial growth rate, and start current of a Cherenkov free-electron laser with negative-index material
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DOI：
10.1063/1.4928089
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发表时间：
2015-08
影响因子：
2.2
通讯作者：
Yuanyuan Wang;Yanyu Wei;Dazhi Li;K. Takano;M. Nakajima;Xuebing Jiang;Xianfeng Tang;Xianbao Shi;Y. Gong;Jinjun Feng;S. Miyamoto
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文献类型：
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作者：
Yuanyuan Wang;Yanyu Wei;Dazhi Li;K. Takano;M. Nakajima;Xuebing Jiang;Xianfeng Tang;Xianbao Shi;Y. Gong;Jinjun Feng;S. Miyamoto
我们提出了一个切伦科夫自由电子激光器的基础上，由负折射率材料制成的单一板条的分析。在该系统中，一束有限厚度的扁平电子束在接近平板表面时与同向传播的电磁表面模相互作用。为了研究负折射率介质表面模的色散关系，推导了100 μ m厚平板的色散方程，并进行了数值求解，计算结果与时域有限差分程序的模拟结果吻合较好。我们发现，在适当的条件下，由于负折射率材料的特性，这种方案中存在固有的反馈，这意味着当束流超过阈值时，系统可以在没有外部反射器的情况下振荡，即，启动电流。利用流体动力学方法，我们建立了该系统的耦合方程，并在小信号范围内解析求解这些方程，得到了空间增长率和启动电流的公式。
We present an analysis of a Cherenkov free-electron laser based on a single slab made from negative-index materials. In this system, a flat electron beam with finite thickness travelling close to the surface of the slab interacts with the copropagating electromagnetic surface mode. The dispersion equation for a finitely thick slab is worked out and solved numerically to study the dispersion relation of surface modes supported by negative-index materials, and the calculations are in good agreement with the simulation results from a finite difference time domain code. We find that under suitable conditions there is inherent feedback in such a scheme due to the characteristics of negative-index materials, which means that the system can oscillate without external reflectors when the beam current exceeds a threshold value, i.e., start current. Using the hydrodynamic approach, we setup coupled equations for this system, and solve these equations analytically in the small signal regime to obtain formulas for the spatial growth rate and start current.