Engineering multi-state transparency on demand

Materials are, in general, either transparent or not. In principle, it is impossible to switch a material from a reflective optical state to a fully transparent one. Transparency has received relatively less research attention compared to other optical properties such as absorption, research on which have successfully produced perfect blacks, that is, highly absorbing materials. The ability to change optical transparency, especially locally and on demand, can enable several applications. Here, we present an absorbing three-layer system whose transparency can be altered by pulsed laser processing to realize different states, ranging from full transparency to mirror, black, and combinations thereof. An initially black surface can be made highly reflective or transparent by changing the laser pulse energy. The corresponding process window, including the influence of the substrate material, was investigated in detail.