Hm. Vandriel et G. Mak, FEMTOSECOND PULSES FROM THE ULTRAVIOLET TO THE INFRARED - OPTICAL PARAMETRIC PROCESSES IN A NEW LIGHT, Canadian journal of physics, 71(1-2), 1993, pp. 47-58
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 nonline
ar optical crystals. Pump lasers with high peak intensities are usuall
y required, which, unfortunately, run the risk of damaging the crystal
s, especially if their pulse duration is nanoseconds or picoseconds. R
ecently, however, the emergence of new, more efficient, nonlinear crys
tals and the development of continuously mode-locked, solid-state lase
rs, 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 avera
ge power of over 1 W, with pulses less-than-or-equal-to 100 fs 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 mum with av
erage power as high as 200 mW. Harmonic generation of the OPO or the T
i:sapphire laser beams provides wavelength coverage from 200 nm to 4 m
um. 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 m
um. This broad-band, stable light source will open up new areas of inv
estigation in physics, chemistry, and engineering.