Recent work on the development of high-repetition-rate, synchronously
pumped picosecond and femtosecond Optical Parametric Oscillators (OPOs
) is reviewed. With KTP, BBO or LBO crystals and solid-state pumps suc
h as cw mode-locked Ti:Sapphire, Nd:YAG or Nd:YLF lasers, the singly r
esonant OPOs or their nonlinear optical accessories yield pulses as sh
ort as 40 fs, average powers up to hundreds of milliwatts, and tunabil
ity from 200 nm to > 10 mu m.