Effect of various outcoupling options on free-electron ring laser performance

The power extraction and lowest-order transverse-mode structure of a free-electron ring laser with hyperboloid-paraboloid grazing incidence telescopes are studied as a function of the method used to outcouple the beam. Four different resonator configurations, with various outcoupling and intracavity optics, are modeled using a free-electron laser, wave optics computer code. A stable ring with a diffraction grating outcoupler gives better power extraction and transverse-mode structure than unstable rings and scrapers which outcoupled either an annular ring or central spot. Efforts to reshape the intracavity beam after scraper outcoupling in order to improve interaction with the electron beam in the wiggler did not produce power extraction equivalent to that of the stable ring