Efficient generation of <3-cm-1 bandwidth mid-IR pulses by difference-frequency mixing of chirped pulses

We report on a laser system that produces near-transform-limited picosecond pulses in the 3-5-mum wavelength range with bandwidths adjustable from values close to the pump bandwidth (similar to16 cm(-1)) to more than fivefold narrower bandwidths (<3 cm(-1)) and with the pulse energies that exceed 48 μJ at 3 μm and 5 μJ at 5 μm. The system employs difference-frequency mixing in a potassium titanyl arsenate crystal pumped by an amplified Ti:sapphire laser and seeded by a traveling-wave optical parametric generator. The difference-frequency bandwidth narrowing is achieved by equal chirping of the seed and the pump pulses with two pulse stretchers before mixing. (C) 2002 Optical Society of America.