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

We investigate the terahertz radiation from a filament in two-color laser fields with various polarizations. It has been experimentally demonstrated that the efficiency of terahertz emission in co-rotating two-color circularly polarized laser fields is eight times as strong as that in linearly polarized two-color laser fields with parallel polarization. This enhancement is explained based on the polarization-dependent clamping intensity inside a filament and the dynamics of electrons ionizing from a single atom or molecule. Our finding provides a simple method to improve the THz intensity from an air filament in two-color fields.