Terahertz generation by beat-wave mechanism of two Gaussian laser beams with corrugated noble-metal nanospheres in external magnetic field

Abstract

An analytical model is presented that deals with THz generation by nonlinear mixing of two Gaussian laser beams with different frequencies ω1 and ω2 and wave vectors k1→ and k2→simultaneously propagating through an array of spatially corrugated noble-metal nanoparticles placed in the presence of a static magnetic field where ponderomotive nonlinearities are operative. The two co-propagating laser beams exert a nonlinear ponderomotive force on the plasma electrons, causing them to acquire nonlinear oscillatory velocity. This velocity leads to the generation of nonlinear macroscopic current density at the beat frequency ω (ω1-ω2) which further gives rise to strong terahertz radiation. The beat frequency lies in the THz region and density ripple provides the necessary phase-matching conditions. The externally applied magnetic field enhances the nonlinear coupling between the electric field of the lasers and causes resonant interaction of the laser beam with electrons of the NPs. THz radiations being non-invasive and biologically innocuous, play an important role in medical imaging, biomedical and pharmaceutical fields, and THz spectroscopy.