Enhancement of terahertz generation by using a circularly-polarized two-color field

We experimentally demonstrated that the circularly polarized two-color femtosecond pulses with the same helicity can effectively enhance terahertz intensity by a factor of 5 in comparison with the linearly polarized counterparts. The quantum mechanical simulations confirm this enhancement based on the analysis of residual current calculated by time-dependent Schrödinger equation in three dimensions. The report not only provides a technique to increase the terahertz intensity but also arouses the interest to study the formation of the air plasma induced by circularly-polarized two-color laser-field.