Plasmon Gun: high-power mid-IR emission at a temporal interface

We propose a mechanism for the generation of intense ultrafast mid-infrared radiation from heavily doped semiconductors. An ultrafast optical pulse transfers a finite impulse to the free carriers, displacing the screening clouds surrounding ionized dopants and inducing coherent plasma-frequency oscillations of the resulting polarization. We derive an exact analytical solution for the corresponding nonequilibrium dynamics and the resulting far-field radiation emitted by a thin semiconductor film. For realistic parameters of heavily doped GaAs, the emitted mid-infrared pulses can reach electric-field amplitudes on the order of $10^7\,{\rm V/m}$ directly in the far field, without relying on optical focusing.