Generation of narrow-band THz radiation due to the collision of laser wake waves with a small-scale transverse structure in a plasma

A new method is considered for generating high-power narrow-band terahertz radiation in the process of nonlinear interaction of counterpropagating laser wake waves, in which the potential profiles are modulated in the transverse direction and locally do not coincide with each other. It is shown that in order to achieve a high radiation efficiency at the doubled plasma frequency, the period of such modulation must coincide with the length of the generated electromagnetic wave. Each of the plasma waves with such a small-scale transverse structure is proposed to be produced by a pair of interfering laser pulses propagating at a small angle to each other. Numerical simulation by the particle-in-cell method confirms the possibility of achieving a narrow (2%) spectral emission line and a high energy conversion efficiency at a level of 1% in such a scheme. With the design parameters of XCELS, the proposed method opens a way to achieving a record terawatt radiation power level in the THz frequency range.