The inverse Smith-Purcell effect in the subillimeter region

逆Smith-Purcell效应是利用金属栅作相互作用电路来产生几GeV/m的加速度梯度的激光驱动直线加速器的候选方案之一。本项目的目的是利用亚毫米波(SMM)激光器对逆Smith-Purcell效应进行实验验证，并验证理论预测的正确性。我们对SMM区域的逆Smith-Purcell效应进行了理论分析，以便设计必要的实验装置来演示它。通过对正前方电场分布的分析，确定了不同SMM激光谱线下矩形轮廓光栅的最佳刻槽尺寸。同时，通过计算机模拟发现，当激光功率为1W时，电子能谱可增加[30 eV]。该系统由光泵浦SMM激光器和电子束系统组成，电子束系统包括按照理论设计在铣床上加工的金属光栅。用本项目研制的EQ开关CO_2激光器泵浦了波长为496µm的SMM CH_3F分子激光器。CH3F激光器的最大峰值功率为46W，重复频率高达9.2 kHz，输出脉冲形状规则，1987年初我们首次成功地观测到了isp效应。实验结果表明，LW激光功率可使电子能谱全宽增加约18 eV。更重要的是。我们测量了电子能量随激光功率和初始电子能量的变化。这些实验结果与理论预测吻合较好。

The inverse Smith-Purcell (ISP) effect is one of the candidates for laser-driven linacs with a metallic grating as an interaction circuit to produce acceleration gradient of a few GeV/m. The purposes of the project are to demonstrate experimentally the ISP effect by using a submillimeter wave (SMM) laser and confirm validity of theoretical predictions on the effect.We performed the theoretical analyses of the ISP effect in the SMM region in order to design the experimental equipents necessary to demonstrate it. The optimum groove dimensions of the grating with rectangular profile were determined for various SMM laser lines by analyzing the electric field distribution just in front of the grating surface. Also with computer simulations, it has been found that a laser power of lW can produce [[30eV increase in the electron energy spectrum.We have constructed the experimental system based upon the theoretically analyzed results. The system consists of an optically pumped SMM laser and the electron beam system which includes the metallic grating fabricated on a milling machine according to the theoretical design. The SMM CH_3F molecular laser with the wavelength of 496<mu>m was pumped by an EQ- switched CO_2 laser newly developed for this project. The CH_3F laser had the maximum peak power of 46W, the repetition rate of up to 9.2kHz, and regular output pulse shape under the fundamental transverse mode of operation.In early 1987, we have successfully observed the ISP effect for the first time. The experimental results showed that lW laser power produces an increase of approximately 18eV in the full width for the energy spectrum of electrons. Furthermore. we measured electron energy change as a function of the laser power and of the initial electron energy. These experimental results gave good agreement with the theoretical perdictions.