Light-controlled tuning of the optical properties of nanoporous glass

Materials having tunable optical properties are of great interest for photonic applications. Promising candidates in that context are transparent nanoporous media whose optical properties change after infiltration of a liquid into the pores. Herein we present an all-optical method to tune the light scattering properties of a nanoporous glass based on the light-induced phase change of the fluid filling the pores. The thermodynamic state of the gas inside the nanopores determines the light scattering, thereby the light transmission. The extent of capillary condensation inside the nanoscale pores is controlled by heat generated from light absorption inside the medium. The material can be configured in such a way that a laser beam of sufficient intensity either opens up or shuts down its own light path on a time scale of a few seconds. The scattering events inside the medium change the beam profile from Gaussian to super-Gaussian with a more homogeneous intensity distribution close to the beam axis. Our results demonstrate a new way of tuning the light transmission properties of nanoporous materials that could find various applications in integrated optical systems and optofluidic devices.