Narrowband Thz generation by colliding plasma waves with different transverse sizes

It has been recently found that nonlinear interaction of counterpropagating plasma wakes with different potential profiles can generate high-power narrowband THz radiation. Such radiation is concentrated near the second harmonic of the plasma frequency with the line width of several percent and can easily escape from the plasma. In this work, we discuss effects of ion dynamics on THz emission duration in the case of short laser drivers and study whether the radiation efficiency in such a scheme can be significantly increased by using long-pulse electron beams driving plasma waves via the two-stream instability. This mechanism can be a basis for efficient and easily tunable sources of narrow-band terahertz radiation capable of reaching the gigawatt power level and millijoule energy content.