EFFECTS OF THERMALLY INDUCED BIREFRINGENCE IN HIGH-OUTPUT-POWER ELECTROOPTICALLY Q-SWITCHED ND-YAG LASERS AND THEIR COMPENSATION

We show that thermally induced birefringence in an electro-optical crystal can play an important role in Q-switched Nd:YAG lasers with a high average power output. A compensation of the thermal effects in both active-element and electro-optical crystals is achieved by employing two identical Pockels cells instead of one, with a pi/2 polarization rotator between them in the so-called ring modulator. Experiments that are carried out show that undesirable thermopolarization effects are essentially eliminated by using this new optical configuration. A detailed description in terms of Jones matrices of the properties of the proposed resonator is also included.