Abstract

The use of a phase-conjugate mirror in a double-pass oscillator/amplifier laser system has received a lot of attention because the phase-conjugate mirror can correct some of the optical aberrations introduced by the laser amplifier. To reduce the feedback of the amplified pulse to the oscillator, an optical isolator must be used. A commonly used isolation system is the combination of a λ/4 plate and a linear polarizer. Because the amplifier rod(s) often has thermally induced birefringence, the amount of feedback will depend on the location of the λ/4 plate. We observed that the feedback is smaller when the λ/4 plate is located in front of the amplifier system (two Nd:YAG rods) than when it is behind the amplifier system. A matrix theory describing the birefringent effect is developed to explain the experimental result. The ratio of feedback intensities corresponding to the λ/4 plate's being behind versus being in front of the amplifiers depends on the ratio of the depolarization coefficient to the linear-polarized amplification coefficient.

© 1990 Optical Society of America