Study on the laser-induced darkening in Nd-doped laser glasses

Abstract Laser induced darkening in the soda-lime silicate (15Na 2 O · 15CaO · 70SiO 2 ) based glass and type N 31 barium metaphosphate Ba(PO 3 ) 2 based glass were studied by exposing the glass samples in frequency-quadrupled Nd:YAG (266 nm, 5 ns) laser and Ti:Sapphire (800 nm, 120 fs) laser. Both types of the glasses were doped with Nd 2 O 3 at doping levels less than 3 wt%. Hole center HC 1 formed after UV laser exposure in soda-lime silicate based laser glass, and both HC 1 hole center and SiE ′ center formed in it after IR fs laser irradiation. In phosphate glass, UV ns laser and IR fs laser generated the same types of color centers, intermediate structure of oxygen ions type II and type III. The experimental results also showed that the soda-lime silicate laser glass is easier to be darkened than the phosphate glass, irradiated by either 266 nm UV laser or fs laser. While free electrons from single photon ionization is considered to be the main cause of defect formation in glasses irradiated by nanosecond UV laser, rapid cooling of the melted glasses heated by energetic electrons generated from multi-photon and avalanche ionization should be the causes of defect formation in glasses irradiated by fs laser.