Phase-modulated injection seeding for testing laser-induced damage of thick optics with Q-switch lasers

Injection seeding with Nd:YAG Q-switch lasers ensures single-longitudinal mode (SLM) pulses that are temporally smooth and repeatable. However, SLM pulses carry a narrow spectrum that may trigger backward-stimulated Brillouin scattering during laser-induced damage testing of transmissive optics. We present a custom and patented injection seeding laser called Φimo. We implemented this system on two similar laser-induced damage testbeds equipped with Nd:YAG Q-switch lasers. Φimo generates a phase-modulated injection seeding laser to annihilate backward stimulated Brillouin scattering during tests while ensuring a very slightly modulated and repeatable temporal profile. This is achieved with a fine control of the modulation frequency of the phase modulator for each laser. With this system, we can correctly estimate the damage density of 34 mm thick fused silica optics at 355 nm.