Generation of elliptical terahertz radiation in two-color laser field: From single atom to extended gas response

One of the promising methods of the terahertz (THz) radiation generation is the use of the two-color laser field (ω-2ω) focused in the gas medium [1]. Typically, the polarization of the low frequency THz field generated in gas is linear [2], but, in some conditions, it can be elliptical due to modulation of the laser pulse phase and its polarization in the gas plasma [3]. For some practical applications, it is useful to have the elliptically polarized THz radiation. Usually, methods based on the mixing of the elliptically polarized ω with a linear (or elliptically polarized) 2ω, producing low-frequency elliptically polarized THz emission (<;5THz) [4] are used.