Tunable ultrafast near-infrared nonlinear optical properties of Eu3+ and silver nanoparticles doped alkali borate glasses

Abstract

Achieving strong optical nonlinearities in vitreous nanocomposites is imperative for the advancement of futuristic telecommunication and photonic technologies. In this regard the borate materials (vitreous) are deemed to be important and currently available commercial hosts. In the current work, we demonstrate the tuning of the third-order nonlinear optical (NLO) attributes of borate-based glass samples doped with metal nanoparticles (NPs) and rare earth ions through annealing process. The NLO attributes, such as nonlinear optical absorption and refraction have been analysed by the sensitive Z-scan approach in the open and closed aperture configurations, respectively. The NLO features were examined in the near-infrared spectral region using ultrafast laser pulses fired at a high repetition rate from a Ti: sapphire laser oscillator. The open aperture data unveiled the existence of two-photon absorption whilst closed aperture indicated the occurrence of self-focusing nonlinear refraction. The NLO coefficients improved with heat treatment duration but the nonlinear absorption coefficient reduced at longer heat treatment schedules. The enhancement in the NLO coefficients is ascribed to the local field enriched by metallic silver NPs in the proximity of the rare earth ions when high-energy laser pulses irradiate the hosts. The results suggest the glasses routed with rare earth ions and metallic silver NPs annealed for 40 hrs at 450 °C are beneficial for optical communication and nonlinear photonic device applications, including optical limiting functionalities.