Space-selective modification of Au-doped optical grade glass by the femtosecond laser beam

Femtosecond laser-induced modification of Au-doped phosphate glass at different pulse repetition rates using an Yb femtosecond amplifier emitting pulses of up to 120 μJ energy at 1030 nm with adjustable repetition rate up to 100 kHz is presented. At the repetition rate as low as 1 kHz, only refractive index modification and formation of red color centers are observed. Increasing the average output laser power resulted in increase of color intensity, but this color could be easily erased by the heat treatment at 300˚C for 20 min indicating athermal nature of these laser-induced effects. By contrast, at the repetition rate from 25 kHz to 100 kHz, cumulative heating effect was demonstrated and allowed to realize for the first time one-stage laser-induced growth of Au nanoparticles in the solid glass accompanied by the appearance of a thermally stable red color. Z-scan analysis of nonlinear properties of the studied glass samples is carried out. Details of Au nanoparticles growth and phosphate glass modification by the tightly focused femtosecond laser beam are discussed.