Singly resonant continuous-wave mode-locked KTiOPO_4 optical parametric oscillator pumped by a Nd:YAG laser

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Abstract
We present detailed design considerations and performance of a singly resonant cw mode-locked optical parametric oscillator based on KTiOPO4. The oscillator is synchronously pumped by 2.2-ps, 1.064-µm pulses at a 75-MHz repetition rate with 4-W average power generated by temporal compression of pulses from a lamp-pumped mode-locked Nd:YAG laser. We obtained output pulses 2-3 ps long with hundreds of milliwatts of average power from 1.57 to 1.59 µm in the signal branch and from 3.21 to 3.30 µm in the idler branch. At three times above threshold we measured the pulse width of the 1.573-µm signal to be ~2.8 ps, and the corresponding spectral width was ~1.5 nm, indicating that the time-bandwidth product is 0.51. The total conversion efficiency as measured by the pump-pulse depletion is 15%. With active stabilization of the pump laser, the amplitude fluctuation of the oscillator is <15% peak to peak.