Abstract

High-repetition rate femtosecond pulses in the 200-nm spectral region are very interesting for dynamic studies of adsorbates on metal surfaces and are advantageous over using longer wavelengths with multiphoton processes or lower repetition rate amplifiers since the latter can cause surface damage. Generation of the fourth harmonic (FH) of mode-locked Ti:sapphire lasers seems at present to be the most straightforward method to create a high-repetition rate short pulse laser source near 200 nm. Previous experiments on frequency quadrupling resulted in average powers on the 10 mW level in the picosecond regime [1], but in the femtosecond regime only attempts near 205 nm have been reported where the output power levels were not sufficient for any temporal characterization. [2] Here we report for the first time to our knowledge efficient FH pulse generation in the femtosecond regime below 205 nm. The shortest wavelength achieved is 193.7 nm.

© 1998 IEEE