Frequency conversion of Ti : sapphire-based femtosecond laser systems to the 200-nm spectral region using nonlinear optical crystals

Abstract

We review the linear and nonlinear optical properties of crystals transparent near and below 200 nm and suitable for up conversion of femtosecond Ti:sapphire laser sources. beta-BaB2O4, the crystal with the largest birefringence of all presently available materials, is investigated experimentally as a quadrupler by mixing the fundamental and the third harmonic both using a 1-kHz repetition rate Ti:sapphire regenerative amplifier and a 82-MHz mode-locked Ti:sapphire laser. Milliwatt average powers near 200 nm are achieved in both cases. The sub-200-fs pulses at the fourth harmonic are almost bandwidth limited. Sum-frequency generation as a method for upconversion of femtosecond pulses is experimentally studied by mixing the fourth harmonic generated down to 189 nm by the regenerative amplifier with a parametrically generated femtosecond pulse in the infrared. Pulse energies at the microjoule level are produced with LiB3O5 above 180 nm, Li2B4O7 shows superior performance in the 170-180-nm range, and the shortest wavelength achieved with KB5O8. H2O is 166 nm