Experimental evidence of the inverse Smith–Purcell effect

Abstract

Interest in the development of laser-driven linacs has been stimu-lated recently by the advent of the high-power lasers. The use of a laser to accelerate charged particles was first proposed by K. Shimoda in 1962¹. He noticed that high values of acceleration per metre (acceleration gradient) could be obtained with an intense electric field in the output of a high-power laser. The inverse Smith–Purcell (ISP) effect proposed by us² is a candidate for laser-driven linacs with a metallic grating as an interaction circuit. In 1953 Smith and Purcell demonstrated that light is emitted when a high-voltage electron beam moves parallel and close to a metallic optical diffraction grating in a direction perpendicular to the grating rulings³. The dispersion relationship is a synchronous condition between the electrons and the wave on the grating. Therefore, the inverse Smith-Purcell effect (ISP), or the extended interaction between electrons and an incident light wave should occur when the same relation is satisfied between the electrons and the incident wave (Fig. 1)². Lawson pointed out⁴ that this effect would fail to accelerate relativistic particles. This difficulty was solved by Palmer⁵, who showed that acceleration is possible either if the particles travel skew to the grating lines, or if the radiation is falling at a skew angle onto the grating. Several authors have described possibilities for producing a grating linac (ISP effect) with accelerating field of a few GeV m⁻¹ in the infrared or optical wave region⁶. Here we report the first observational evidence for this effect using a submillimetre-wave laser as a driving source. The experimental results give good agreement with theoretical predictions.