A tilted mirror unstable resonator laser cavity

A simple unstable resonator cavity using flat optics which provides a nonannular low-divergence output beam from a large mode volume is described. The resonator uses as output the "spillover" from a walkoff mode established between a pair of tilted flat mirrors; this also allows continuous adjustability of the output coupling. An extra pass of this spillover output through the gain medium helps to provide a saturated output. Results obtained using this resonator on a CO
2
oscillator are described.