Abstract

Negative feedback-controlled, mode-locked Nd:YAG or Nd:YLF lasers are attractive pump sources for parametric oscillators (OPO)^1,2 because of their exceptional stability, and extended pulse train and the short duration of the pulses. In this work we demonstrate effective parametric compression down to 600 fs in a simple synchronously pumped linear cavity OPO using a KTP crystal. As pump source, the active-passive, mode-locked Nd:YAG laser with passive-negative feedback was used (Continuum model PY-61C-10). This laser generated stable (less than ± 0.2% pulse to pulse fluctuation) picosecond pulse trains of 600 ns (85 pulses) with energy of 4.7 mJ at a repetition rate of 10 Hz. A minimum pulse duration of 9.5–10 ps is achieved after an initial transient of 7–10 roundtrips in the laser cavity. The pulse duration increases after the first 200 ns to reach a maximum of 13–15 ps towards the end of the train. The OPO crystal is pumped through a 1-m focal distance lens by the second harmonic of this source, generated in a 6-mm-long KTP crystal. The OPO cavity, resonant for the idler only, was formed by two flat mirrors: Al-coated and dielectric output mirror (R ≈ 50% between 1.2 and 3 μm). We used a noncollinear scheme for parametric interaction, with an angle between pump beam and optical cavity axis of ≈ 3°). As nonlinear OPO element 14-mm and 6-mm-length KTP crystals cut at θ = 54° and ϕ = 0°, and θ = 90° and ϕ = 23.5°, respectively, were used.

© 1994 IEEE