Broadly tunable high repetition rate femtosecond optical parametric oscillator

We report a new source of femtosecond light pulses which is broadly tunable in the infrared. A singly resonant optical parametric oscillator based on a thin crystal of KTiOPO4 is pumped by intracavity femtosecond pulses at 620 nm from a standard colliding-pulse passively mode-locked dye laser. Oscillation results in stable, continuous outputs of femtosecond pulses at 108 Hz repetition rate and milliwatt average power levels in both signal and idler beams. Here we demonstrate tuning from 820 to 920 nm and 1.90 to 2.54 μm with a single set of mirrors. With multiple sets of mirrors, continuously tunable outputs from ∼0.72 to ∼4.5 μm should be possible, making this a uniquely versatile femtosecond laser source.