Femtosecond laser-induced darkening in optical glasses

The thresholds of laser-induced darkening in different optical glasses irradiated by a 800 nm, 120 fs, 1 kHz Ti:sapphire laser are reported for the first time. Absorption spectra of the glasses before and after irradiation were measured. The absorption in visible region of the irradiated glasses increased greatly after irradiation and then decreased slightly along with time. The mechanism of the laser-induced darkening was demonstrated based on the ESR measurement and excimer laser irradiation results.