Chen Zhaofu, Jin Mengmeng, Mao Leilei, Shi Xin, Bai Ningfeng, Sun Xiaohan
Opt Lett. 2022 Jun 1;47(11):2911-2914. doi: 10.1364/OL.455763.
Smith-Purcell radiation (SPR) is an important means of generating terahertz waves, and the enhancement of SPR is an attractive topic nowadays. Inspired by the phenomenon of special SPR, where the enhancement is achieved by using a high-duty-cycle grating, we describe a new, to the best of our knowledge, but more effective approach to this challenging problem. By deriving a simple analytical solution for the SPR from an annular electron beam passing through a cylindrical metallic grating, we show that the inverse structure, a low-duty-cycle grating can exhibit rather high SPR efficiencies in the presence of quasi-bound states in the continuum (quasi-BICs). The analytical prediction is supported by particle-in-cell simulations, which show that the quasi-BICs can enhance the superradiant SPR generated by a train of electron bunches by orders of magnitude. These results present an interesting mechanism for enhancing the SPR from metallic gratings, and may find applications in terahertz free-electron lasers.
史密斯-珀塞尔辐射（SPR）是产生太赫兹波的一种重要手段，增强SPR是当下一个引人关注的课题。受特殊SPR现象的启发，即通过使用高占空比光栅实现增强，我们描述了一种据我们所知全新但更有效的解决这一具有挑战性问题的方法。通过推导从环形电子束穿过圆柱形金属光栅产生的SPR的简单解析解，我们表明，在连续态准束缚态（quasi-BICs）存在的情况下，低占空比光栅这种逆结构可展现出相当高的SPR效率。粒子模拟支持了这一解析预测，模拟结果表明准BICs可将由一串电子束产生的超辐射SPR增强几个数量级。这些结果展示了一种增强金属光栅SPR的有趣机制，并可能在太赫兹自由电子激光器中得到应用。
