The Inverse Smith-Purcell Effect at Submillimeter Wavelengths

本研究计划通过实验验证关于逆Smith-Purcell （ISP）效应的理论预测，该效应是加速梯度为数GeV/m的激光驱动直线机的候选效应。在ISP效应中，当电子束的速度与倏逝波的相速度相同时，电子束与光栅上的倏逝波同步作用。相互作用的强度和空间也随入射激光功率、波长、倏逝波的空间谐波阶数和电子的初始速度而变化。为了从实验上研究这些问题，我们测量了电子与一阶或二阶空间谐波相互作用所产生的能量扩散。这些波是由波长分别为496mum和185mum的两种不同的亚毫米波激光器驱动的。实验结果与实验前的计算机模拟结果进行了比较。综上所述，我们对该理论得到了以下验证。(1)上述速度匹配条件在实验上得到了消隐波的一阶和二阶空间谐波的验证。(2)倏逝波的振幅随距离光栅表面的距离呈指数衰减，其衰减常数在实验误差范围内与理论预测值一致。例如，在激光波长为185mum时，该值为1/(18<正负bbb80mum)，而理论值为1/(16.6mum)。(3)随入射激光功率的变化，电子的能量扩散与理论预测值一致，校正系数为2。

This research project has been planned to experimentally verify the theoretical predictions on the inverse Smith-Purcell (ISP) effect which is a candidate for laser- driven linacs with an accelerating gradient of several GeV/m.In the ISP effect, an electron beam interacts synchronously with an evanescent wave on the grating when the velocity of electron is the same as the phase velocity of the wave. The interaction-strength and -space also vary with an incident laser power, the wavelength, an order of space harmonics of the evanescent wave, and an initial velocity of electron. In order to investigate these experimentally, we have measured energy spread of electron resulted from the interaction with the 1st or the 2nd space harmonics. These waves have been induced by two different driving submillimeter wave lasers with the wavelengths of 496mum and 185mum. Experimental results have been compared with computer simulated one performed before the experiment. In summary, we have obtained the following verifications for the theory.(1) The velocity matching condition described above has been confirmed experimentally for the 1st and the 2nd space harmonics of the evanescent wave.(2) The amplitude of the evanescent wave falls off exponentially with the distance from the grating surface, and its decay constant agrees with the theoretically predicted one within our experimental errors. For example, in the laser-wavelength of 185mum, this value is 1/(18<plus-minus>8mum) as compared with the theoretical one of 1/(16.6mum) for the 1st space harmoni(3) The energy spreads of electron depended on the incident laser power agree with theoretically predicted one within correction factor of 2.