Generation of terahertz radiation by beating of two color lasers in hot clustered plasma with step density profile

Abstract

A theoretical model of terahertz generation is presented using nonlinear mixing of two lasers in clustered plasma with step density profile. The cluster is used as a target to enhance the optical to THz conversion efficiency. The lasers are incident obliquely to the clustered plasma surface and exert a ponderomotive force on cluster and plasma electrons. The ponderomotive force has a transverse component that drives nonlinear current and produces THz radiation in the reflected component. The enhancement in the efficiency of THz radiation generation occurs due to cluster plasmon resonance and by coupling between plasma and THz wave. The amplitude of generated THz wave is maximum when the plasma frequency approaches to THz frequency and laser frequency is equal to , where ωpe is cluster plasma frequency. Also, the amplitude is enhanced at an optimum angle of incidence. The dependence of efficiency of THz radiation generation on laser intensity, cluster radius and electron thermal velocity is also studied. We report the normalized THz wave amplitude ∼0.044 from Ar cluster at 0.89 μm and 0.44 μm wavelengths of incident lasers with intensity = 7 × 1014 W cm−2.