Terahertz radiation, defined in the frequency range of O. 1-10 THz, has been exploited to demonstrate unique properties that do not apply to the adjacent domains of the electromagnetic waves, such as infrared and microwave. Recent advances in terahertz science and technology hold promise for a wide variety of essential applications, particularly in spectroscopy, sensing, imaging,
A survey on the mechanisms of powerful terahertz （THz） radiation from laser plasmas is presented.Firstly,an analytical model is described,showing that a transverse net current formed in a plasma can be converted into THz radiations at the plasma oscillation frequency.This theory is applied to explain THz generation in a gas driven by two-color laser pulses.It is also applied to THz generation in a tenuous plasma driven by a chirped laser pulse,a few-cycle laser pulse,a DC/AC bias electric field.These are well verified by particle-in-cell simulations,demonstrating that THz radiations produced in these approaches are nearly single-cycles and linear polarized.In the chirped laser scheme and the few-cycle laser scheme,THz radiations with the peak field strength of tens of MV/cm and the peak power of gigawatt can be achieved with the incident laser intensity less than 10 17 W/cm 2.
