Retardation and nonstationarity effects on the generation of terahertz radiation by the e-h plasma in a semiconductor

Radiative processes in a nonequilibrium e-h plasma are theoretically studied using a self-consistent solution of the kinetic equation and Maxwell’s equations. The terahertz emission from a finite-thickness semiconductor sample is due to the retardation and nonstationarity of the electromagnetic interaction of the photocurrent in the e-h plasma and the radiation field. The duplex waveform of the terahertz electromagnetic pulse for an arbitrary ratio of the radiation formation length and the plate thickness originates due to coherent radiative processes accompanying the generation of the e-h plasma at the input boundary and its extinction at the output boundary of a semiconductor plate through which a weakly absorbed ultrashort laser pulse propagates. The theoretical conclusions show analogies with the radiative phenomena accompanying the start-stop motion of external currents (Tamm problem) and the nonlinear interaction of optical waves in a finite-thickness medium.