Abstract

Ultrashort optical pulses tunable in the vacuum ultraviolet (VUV) spectral region are of great interest for spectroscopic investigations of various ultrafast processes, e.g. photodissociation of molecules and clusters. We report on the generation of femtosecond pulses in the wavelength range from 175 to 182 nm by phase matched sum frequency mixing of femtosecond ultraviolet and near infrared optical pulses in lithium triborate (LBO). Due to its superior transparency range down to 160 nm and its high nonlinear coefficients only this crystal can be used for nonlinear conversion processes in the wavelength range below 189 nm. Unfortunately phase matching is possible only for two widely separated wavelength, e.g. λ_UV < 205 nm and λ_IR >1.7µm to obtain a wavelength at 185 nm or below (Ref.1). To ensure the synchronism both the ultraviolet (UV) and infrared (IR) pulses have to be derived from a single ultrashort pulse source. Up to now the shortest wavelength generated by sum frequency mixing in nonlinear crystals was 187.7 nm using nanosecond pulses (Ref.2).

© 1994 Optical Society of America