Nanosecond Laser Switching of Phase‐Change Random Metasurfaces with Tunable ON‐State

Abstract Random metasurfaces based on disordered phase‐change nanostructures with broadband ultraviolet–visible plasmonic properties are fantastic platforms for the development of active photonic components due to their versatility. Here optical ON–OFF switching upon nanosecond laser irradiation of Bi‐based random metasurfaces is demonstrated profiting from the solid–liquid phase transition of the Bi nanostructures. The fast switching time is revealed by using single‐pulse real‐time reflectivity measurements with sub‐nanosecond temporal resolution. A sudden reflectivity decrease is observed upon laser excitation, triggered by heating and melting of the embedded Bi nanostructures of the metasurface. This transient state of low reflectivity remains constant until the Bi solidifies upon cooling, recovering the initial reflectivity level, and showing full reversibility of the process. The duration of this ON‐state, defined by characteristic low reflectivity values, can be tuned from 10 to >700 ns by adjusting the nanostructure components of the metasurface and laser fluence. Furthermore, it is demonstrated that this ON–OFF switch process is repeatable for more than 100 000 times without observable degradation of the metasurface. These results pave the way for the development of a new generation of fast, robust, and integrable nanophotonic switching devices.