Terahertz radiation generation from short-pulse laser interaction with electron-hole plasmas

Abstract

In semiconductors, electrons and their corresponding holes exist as free carriers that are created in pairs in inter-band transitions. At very high carrier densities, the carrier-carrier collisions dominate over carrier-lattice collisions and these carriers begin to behave collectively to form a plasma. In this study, we present phase-matched terahertz (THz) radiation generation from laser interaction with electron-hole plasmas. Two collinear laser pulses of finite spot size propagate in an electron-hole plasma to generate THz radiation. The lasers beat and exert a ponderomotive force on electrons and holes. The carriers oscillate with oscillatory velocity at the laser beat frequency. The laser beat wave interacts with the plasma density perturbation and produces a nonlinear transverse current with nonzero curl. This nonlinear current drives coherent THz radiation. Spacial density modulation of hole density is considered to satisfy the phase-matching condition for resonant interaction. The systematic analysis of this mechanism shows an efficient and tunable source of THz radiation, which varies with various parameters such as the density modulation, laser intensity and other laser parameters.