Polarization-controlled terahertz generation by bicircular longer-wavelength laser fields

When compared with other laser configurations, stronger terahertz (THz) waves can be generated from gaseous plasmas driven using two-color ω + 2 ω 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 n m + 400 n m combination, we use longer-wavelength or few-cycle laser pulses to generate nonzero net currents along two orthogonal directions with a ∼ ± π / 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.