In this study, we investigated the morphological and optical properties of the femtosecond laser-induced structures in fluorotellurite glass. The refractive index change of laser-induced structures exhibited positive and negative under different focusing condition. The threshold was then estimated to be 1.5 × 10 12 W/cm 2 using axicon shaped Bessel beam scanning. The followed thermal annealing shows that the thermal stability of laser-induced structures with negative refractive index change is much higher. Then the pump-probe shadowgraph revealed that the intensity of laser-induced plasma (LIP) that formed laser-induced structures with negative refractive index change is an order of magnitude greater than that of LIP that formed structures with positive refractive index change, which indicates the structural change of the main framework of fluorotellurite glass.
Li et al. (Sat,) studied this question.