Abstract

When compared with other laser configurations, stronger terahertz (THz) waves can be generated from gaseous plasmas driven using two-color $\omega + 2\omega$ circularly polarized laser fields with the same helicity (CP-S), but consideration of the THz polarization state shows that these waves are linearly polarized. Here, we show that polarization-controlled THz radiation, including circularly polarized radiation, can be generated using CP-S pump fields. Unlike the conventional multi-cycle ${{800}}\;{\rm{nm}}\;{ + }\;{{400}}\;{\rm{nm}}$ combination, we use longer-wavelength or few-cycle laser pulses to generate nonzero net currents along two orthogonal directions with a ${\sim}\pm \!\pi /2$ phase difference between them because of laser field symmetry breaking. When the current distribution’s axis of symmetry is ascertained, the THz polarization direction can be confirmed.

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