Femtosecond pulses from the ultraviolet to the infrared: Optical parametric processes in a new light

Although the optical parametric oscillator (OPO) is more than 25 years old, it has not seen widespread use unlike other tunable sources such as the dye laser. Part of the reason for this is the low-gain – high-threshold associated with the weak conversion mechanism in the nonlinear optical crystals. Pump lasers with high peak intensities are usually required, which, unfortunately, run the risk of damaging the crystals, especially if their pulse duration is nanoseconds or picoseconds. Recently, however, the emergence of new, more efficient, nonlinear crystals and the development of continuously mode-locked, solid-state lasers, such as the Kerr-lens mode-locked Ti:sapphire laser, has led to a renaissance for OPOs. For example, the Ti:sapphire laser with an average power of over 1 W, with pulses [Formula: see text] long at a 100 MHz repetition rate, has allowed us to construct a stable, low-noise, synchronously pumped OPO. The output pulses are as short as 60 fs and can be produced in the wavelength range from 1 to 4 μm with average power as high as 200 mW. Harmonic generation of the OPO or the Ti:sapphire laser beams provides wavelength coverage from 200 nm to 4 μm. Through difference-frequency-mixing of the two output beams of the OPO in chalcopyrite or proustite crystals we anticipate being able to generate femtosecond pulses at wavelengths from 200 nm to beyond 20 μm. This broad-band, stable light source will open up new areas of investigation in physics, chemistry, and engineering.