Substrate and Superstrate
Substrate
Material on which the ALU structure is laid. It is assumed to be infinitely thick. For DALHAI, it is defined by its refractive index (n1 in pyGDM), which is a number. Generally the substrate is made of glass, so n1=1.5.
Superstrate
Semi-infinite medium in which the substrate + plasmonic structure are immersed. For DALHAI, it is simply defined by its refractive index (n2 in pyGDM), which is a number. Generally, the superstrate is air, so n2=1.
