Femtosecond continuum generation using a gas-filled hollow fiber

Summary form only given. Due to the large core diameter a hollow fiber combines the good spatial properties of a guided (single-mode) beam propagation with the capability to handle high energy pulses. 100 fs laser pulses at 800 nm with energies up to 1.2 mJ from a kHz-amplified Ti:sapphire laser were focused onto the entrance of a 70 cm long hollow fiber (bore diameter 170 m). The fiber was filled with argon at pressures up to 5 bar. The continuum extends from 300 nm to above 1 m, comparable to the spectral broadening achieved in solids. However, the continuum generated in the hollow fiber exhibits much better spatial properties than the white light generated in a solid. The intensity distributions of continua from a solid (BK 7 glass) and from the gas-filled hollow fiber are compared. While the continuum generated in glass shows a strongly distorted beam profile due to self-focusing, the intensity distribution of the white light generated in the hollow fiber remains smooth. The UV-transmittance of noble-gases will allow us to extend continuum generation to shorter wavelengths by using the frequency-doubled output of our Ti:sapphire laser. This broadband, short pulse source will then be used to study femtosecond laser induced phase transitions and ablation.