Asymmetric ${\rm TEM}_{00}$ -Mode Cavity for Birefringence-Compensated Two-Rod Solid-State Lasers

An asymmetrical two-rod Nd:YAG laser system was investigated theoretically and experimentally in a cw-operated TEM₀₀-mode cavity. A revised birefringence compensation condition is presented considering the thickness of the 90 ^deg polarization rotator. By means of equivalent thermal lens of the two rods, the roles of the two arms of the cavity are discussed. The asymmetrical cavity results in twice larger output power and lower misalignment sensitivity of the mirrors than the symmetrical cavity. 61 W linearly polarized output with M² = 1.6 was obtained experimentally, which is the state of the art for a lamp pumped laser. Cavity mirrors misalignments and thermal induced spherical aberration have great influence on the performance of the resonator such as diffraction loss and beam quality. Beam filling factor turns out to play an important role in reducing their influence. The design of an asymmetrical resonator for birefringence compensation is useful also for high power diode pumped solid state lasers.