Design and performance of high-gain free-electron lasers with grazing incidence, unstable ring resonators

Grazing incidence, ring resonators have been proposed for high-grain free-electron lasers to alleviate the problem of inordinately high irradiance on intracavity optics. Such resonators are also relatively compact, and consequently, their alignment tolerances are more manageable. A geometric design algorithm and detailed computer analysis of a high-gain free-electron ring laser with hyperboloid-paraboloid grazing incidence telescopes is presented. A 3-D wave optics computer code is used to determine the loaded-cavity transverse-mode characteristics of the high-gain unstable ring and to examine the issue of transverse-mode control as a function of the key resonator parameters. Perturbation sensitivity of the individual elements is also determined and compared to that of a corresponding long stable resonator.<>