Temporal rainbow scattering at boundary-induced time interfaces

Since the dawn of modern optics and electromagnetics, optical prism is one most fascinating elements for refracting light. Exploiting its frequency dispersive behavior, a able to refract different frequencies in directions, realizing polychromatic light rainbows. Recently, thanks their engineerable electromagnetic response, metamaterials have been exploited achieving novel refractive scattering processes, going beyond classical effects. In this Letter, we report on rainbow-like process taking place at interface boundary-induced temporal metamaterial realized by instantaneously opening boundary conditions parallel plate waveguide. Changing abruptly conductivity two metallic plates, demonstrate that an equivalent between media realized, monochromatic wave propagating into waveguide gets scattered rainbow free space. We derive relationships mode raising terms amplitude as function elevation angle with respect axis. apply underlying physics control imposing principal direction design. Full-wave numerical simulations are performed computing verifying design guidelines controlled scattering.