Nano-crystal and microstructure formation in fluoride photo-thermo-refractive glass using chirp-controlled ultrafast laser bessel beams

Nano-crystals were formed in the exposed regions of photo-thermo-refractive glass un-dergoing irradiation with zeroth order chirp-controlled ultrafast laser Bessel beams and subse-quent heat treatment. Effects of various writing powers, pulse durations and heat treatment time on the distribution and the size of the nano-crystals were investigated. The results show that nano-crystals’ distribution depended on the laser power density spatial shape, while the size of the nano-crystals is quasi-independent. However, the average diameter of the nano-crystals was af-fected by the heat treatment time, decreasing from 175 to 105 nm with the time halved. In addition, using crystallographic characterization by X-ray diffraction, the nano-crystal composition in the laser-exposed regions was detected to be sodium fluoride.