Optical modeling of the Jefferson laboratory IR demo FEL

The Thomas Jefferson National Accelerator Facility (Jefferson Lab) is in the process of a building a 1 kW free-electron laser operating 3 mu m The details of the accelerator driver are given in other papers in these proceedings. The optical cavity consists of a near-concentric resonator with transmissive outcoupling. Though several free-electron lasers have used similar designs, they have not had to confront the high average-power loading present in this laser. It is useful to know the limits of this type of optical cavity design. The optical system of the laser has been modeled using the commercial code GLAD(R) by using a Beer's-law region to mimic the FEL interaction. The effects of mirror heating have been calculated and compared with analytical treatments. The magnitude of the distortion for several materials and wave lengths has been estimated. The model developed here allows one to quickly determine whether the mirror substrates and coatings are adequate for operation at a given optical power level once the absorption of the coatings, substrate, and transmission are known. Results of calculations of the maximum power level expected using several different sets of mirrors will be presented, Measurements of the distortion in calcium fluoride from absorption of carbon dioxide laser light are planned to benchmark the simulations. Multimode simulations using the code ELIXER have been carried out to characterize the saturated optical mode quality. The results will be presented. (C) 1998 Elsevier Science B.V. All rights reserved.