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

摘要

We review the linear and nonlinear optical properties of crystalsntransparent near and below 200 nm and suitable for up conversion ofnfemtosecond Ti:sapphire laser sources, Β-BaB2O4n, the crystal with the largest birefringence of all presentlynavailable materials, is investigated experimentally as a quadrupler bynmixing the fundamental and the third harmonic both using a 1-kHznrepetition rate Ti:sapphire regenerative amplifier and a 82-MHznmode-locked Ti:sapphire laser. Milliwatt average powers near 200 nm arenachieved in both cases. The sub-200-fs pulses at the fourth harmonic arenalmost bandwidth limited. Sum-frequency generation as a method fornupconversion of femtosecond pulses is experimentally studied by mixingnthe fourth harmonic generated down to 189 nm by the regenerativenamplifier with a parametrically generated femtosecond pulse in theninfrared. Pulse energies at the microjoule level are produced with LiBn3O5 above 180 nm.nLi2B4O7 shows superior performance innthe 170-180-nm range, and the shortest wavelength achieved with KB5nO8·4H2O is 166 nm