A thermal birefringence compensator for a double pass laser system, which
includes a polarization or conventionally outcoupled laser resonator, a
gain medium and a compensator optically coupled to the gain medium. In one
implementation, the compensator, which acts as an end reflector, includes
a Benson prism, a first quarter waveplate with its principle axes aligned
to the fold axis of the Benson prism, and a second quarter waveplate with
its principle axes at 45.degree. to the fold axis of the Benson prism.
Alternatively, the compensation's prism can be a Porro prism.