Broadband optical cavities for infrared free electron lasers: analysis and preliminary experimental results

One advantage of the free electron laser (FEL) is related to its capability for broadband tuning through variation of either the wiggler magnetic field strength or the electronic energy. As in any laser system, broadband optical feedback is needed for the practical attainment of broadband tunability. Cutolo and Madey (1984) have concluded that, in the IR, broadband optical feedback could best be accomplished through the use of metallic mirrors in a stable optical cavity configuration. As a solution to the output coupling problem, it has been proposed to employ an intracavity acoustooptic output coupler. A description has been given of several different possible configurations for the output coupler, and an analysis of thermal effects and effects of finite bandwidth has been conducted. The present investigation has the aim to provide a description of the complete design of the 2-10-micron optical cavity for the Mark III FEL, taking into account the experimental performance of the acoustooptic couplers.