Instability of cavity-dumped YAG laser due to time-varying reflections

A spatially periodic variation in machined hole size was observed when thin bismuth films were irradiated with pulses cavity dumped from a Nd³⁺:YAG laser. When one of the two colinear extracted beams was blocked in the cavity, the variation disappeared. The effect is caused by a reflection-induced cavity instability that arises from fluctuations in the film-effective reflection, occurring asynchronously with the dumping rate as the beam is swept across the film. The reflection isolation needed to achieve stable operation is established and results for two isolation methods are given.