Thin-disk laser with multipass unstable ring resonator

We propose a scheme of a ring unstable resonator with multipass geometry, which allows overcoming the problem of low gain of a disk active element. The original design of the laser resonator enables power scaling using a larger pump aperture of the active element, maintaining good beam quality. The developed resonator operates with a disk Yb:YAG active element and output beam quality M^2=2 at 2.5 magnification, which agrees well with the results of modeling.