Highly efficient subpicosecond pulse generation at 211 nm

We report the efficient generation of high-contrast subpicosecond fifth-harmonic pulses with a Nd:glass laser. Highly reproducible 340-µJ, 850-fs pulses at 211 nm were generated in 0.5-mm-thick β barium borate (BBO) crystal with a 33% energy conversion efficiency in the fifth-harmonic generation stage. By use of fifth-harmonic pulses, a two-photon absorption coefficient of β=2.45±0.15 cm/GW at 211 nm for the BBO crystal was measured.