Tunable 50-fs pulse generation in the 250-310-nm ultraviolet range

A newly designed high-repetition rate regenerative amplifier system producing sub-50 fs, /spl sim/7 /spl mu/J pulses at 100 kHz (/spl sim/4 /spl mu/J at 250 kHz) is used to pump a fully tunable optical parametric amplifier (OPA). The resulting transform limited visible pulses in the 510-610-nm range have pulsewidths of /spl sim/40 fs and energies in the range of 350-550 nJ. Doubling these pulses in thin (0.110-0.150 mm) BBO crystals results in near transform-limited ultraviolet (UV) pulses (255-305 nm) with high efficiency (20%-30%) across this tunable wavelength range. The upconverted pulsewidths in the 0.110-mm crystal vary from 55 to 40 fs in the range from 255 to 305 nm correspondingly. These pulsewidths are limited, particularly at the shortest wavelength, by group velocity mismatch of the fundamental and second harmonic pulses in the BBO. This system can be further optimized for the production of even shorter pulses at these UV wavelengths.