Enhancement of terahertz radiation by using circularly polarized two-color laser fields

Terahertz radiation from tunneling ionization of gaseous atoms and molecules in the two-color laser fields with various polarizations has been investigated. We experimentally demonstrate that the efficiency of terahertz emission in the circularly polarized laser fields with the same helicity is 5 times higher than that with linearly polarized two-color femtosecond pulses in high laser intensity. By solving time-dependent Schrodinger equation, this enhancement is well explained based on the analysis of electron tunneling ionization and subsequent dynamics.