Photosensitivity in photo-thermo-refractive (PTR) glass can be triggered by UV and near-infrared fs laser irradiation. Here we focus on the nonlinear photochemical process triggered by ultrashort laser Gaussian-Bessel beams. The transmission and absorption spectra show that the primary difference between UV and fs laser exposure is the formation of color centers and kinetic process of silver nanoparticles growth. It is contributed to the nonlinear ionization of PTR glass matrix and thermal effects during interaction of glass matrix and ultrashort laser pulses. Transmission electron microscopy verifies the generation of nanoscale crystals in the irradiated region, and X-ray diffraction shows the existence of quartz crystal and NaF after laser irradiation and thermal treatment. Moreover, the dependence of photochemical reaction on laser parameters is investigated, as well as the tailoring of silver nanoparticles. On this basis, volume Bragg gratings with ultrashort laser Gaussian-Bessel beams are inscribed as an application which possess good diffraction characteristics.

(a)   Measured optical transmission spectra and (b) calculated absorption spectra of PTR glass. (c) Decomposition of absorption spectra with Gussian functions (A: initial untreated, B: after irradiation, C: after irradiation and thermal treatment).