Terahertz radiation mechanism in a laser plasma filament

Since 1993, the first experiment already shows there are strong terahertz (THz) radiations when an intense laser pulse is focused into gas. More recently, delicate experiments display conical forward THz emission from a femtosecond laser filament, which is explained by a transition-Cherenkov radiation (TKR) model. In fact, there is a long dispute about THz emission mechanism in a laser plasma filament. This paper investigates the THz radiation mechanism from a plasma filament by using of two-dimensional (2D) particle-in-cell (PIC) simulations and analytic model. The PIC code includes tunnelling ionisation and fully relativistic particle motion. The simulations contain all substantial physics for possible THz emission mechanism. Simulations find that ionisation process plays a minor role. The problem can be reduced to the interaction between laser and a plasma column.