Generation of pulse bursts at 212.8 nm by intracavity modulation of an Nd:YAG laser

Bursts of 1064 nm pulses at a repetition rate of 120 kHz were generated by placing a resonant, acoustooptic birefringence modulator inside the cavity of a flash-pumped Nd:YAG laser. The resulting pulse trains were converted to 532, 266, and 213 nm by a three-step nonlinear generation process in crystals that permit 90° phase matching for these wavelengths. An average power of 2.6 mW at 213 nm was achieved. This method of pulse generation develops much lower peak powers than are obtained with ordinary -switching at the same average power, and is therefore useful in applications which require that the power be focused on a small sample without damage. Construction of the 120 kHz modulator and details of the nonlinear experiments are presented. The phase matching temperature for sum frequency generation of 212.8 nm in KDP was found to be -35°C, which is 50°C warmer than the value predicted from refractive index data in the literature.