Annealing and intensity dependent femtosecond nonlinear optical studies of sodium zinc borate oxide glasses incorporated with gold nanoparticles

Herein, we explored the annealing and intensity–dependent femtosecond (fs) nonlinear optical (NLO) studies on sodium zinc borate (NZB) glasses embedded with gold nanoparticles (NPs). The glasses were prepared by the melt–quench process and subjected for thermal treatment at 450 °C at different schedules in a normal atmosphere. It was identified that the glass annealed for 12 hr (i.e., the NZBAu12 glass) had the maximum saturation intensity and negative nonlinear refraction values. Therefore, the intensity–sensitive NLO investigations then conducted on that glass to understand the influence of intensity of laser radiation on NLO proeprties on gold NPs embedded glasses. The saturable absorption observed at lower intensity was switched to reverse saturable absorption (two–photon absorption) during the exposure with high fluence laser pulses. However, the nonlinear refraction sign was unchanged with increase of intensity of laser radiation. The strategy explored in this work might pave the way for achieving the strong nonlinear traits in borate–based glasses routed with gold NPs. The study outcomes endorse the benefits of NZBAu12 glass for optical switching functionalities under low–intensity pulse excitation, as well as for optical limiting applications under high–intensity pulse excitation.