Transverse mode control in high gain free electron lasers with grazing incidence, unstable ring resonators

Abstract

Grazing incidence, ring resonators have been proposed [1,2] to alleviate the problem of inordinately high irradiance on the intracavity optics in free electron lasers. Such resonators are also relatively compact, and consequently their alignment tolerances are more manageable. In this paper we present the transverse mode characteristics of an unstable, grazing incidence ring resonator under high gain conditions, and examine the issue of transverse mode control as a function of key resonator parameters.