Highly focused and efficient terahertz radiation generation by photo-mixing of lasers in plasma in the presence of magnetic field

A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies omega(1), omega(2) and wave numbers k(1), k(2) in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency omega' = omega(1) - omega(2) and wave number k' = k(1) - k(2) which couples with density ripples in the plasma and leads to a strong nonlinear oscillatory current that resonantly excites highly focused and intense THz radiation at frequency omega(UH) = root(omega(2)(p) + omega(2)(c)) (where omega(c) is electron cyclotron frequency). The efficiency of emitted THz radiation of the order of 15% is obtained under optimum conditions. It is observed that focus and intensity of emitted radiation can be controlled by selecting a proper profile index of the lasers, ripple parameters, and tuning of external magnetic field. (C) 2014 AIP Publishing LLC.