Abstract

Due to the poor reflectivity of mirrors in the extreme ultraviolet when used at normal incidence, it has been suggested that resonators for free-electron lasers operating in this wavelength region employ grazing incidence mirrors in ring type configurations.¹ An algorithm using Gaussian beam propagation rules has been used to determine the cavity parameters for two types of such a resonator. Both types of resonator incorporate four off-axis conic mirrors into their designs to provide the desired degree of beam expansion and focusing as well as a number of flat mirrors to assure that appropriate grazing angles of incidence are maintained. As the beam travels around these cavities, it is passed though a focus in one design type while in the other it remains collimated. Both design types support Gaussian TEMoo mode propagation. The two cavity designs have been analyzed in vacuum conditions; that is, without the wiggler gain interaction, using a diffraction-based computer simulation code and with a paraxial ray trace treatment of their thin lens analogs. Cavity stability as it relates to the degree of beam expansion, laser wavelength, and choice of resonator design type is discussed.

© 1989 Optical Society of America