Improved orotron performance in the 50- to 75-GHz frequency region

New experimental results for the Harry Diamond Laboratories (HDL) orotron, a Smith-Purcell free-electron laser, have been obtained. Emphasis was placed on improving the 100-mW output power previously obtained with this device by using a new, more powerful ribbon-beam electron gun and a new open resonator. The orotron was tuned continuously from about 50 to 75 GHz on a TEM208Fabry-Perot mode; more than a watt of output power was measured on this mode. Considerably more power, approximately 5 W, was obtained at 65.65 GHz on a TEM209mode. Oscillation of the orotron was also observed on backward wave modes. In addition, it was found that improvements in beam quality lead to higher power orotron operation.