Terahertz pulse generation by laser-created, strongly magnetized plasmas: a one-dimensional study

We investigate, both numerically and theoretically, laser-driven generation of intense terahertz (THz) waves embedded in external magnetic (B) fields in excess of 100 T. Depending on the interaction geometry and the B-field orientation, one-dimensional particle-in-cell simulations reveal that two distinct mechanisms can operate as efficient laser-to-THz converters. At nonrelativistic laser intensities, photocurrents induced by two-color laser pulses are shown to supply THz field strengths < 10 GVm(-1) for B fields parallel to the laser propagation axis. The THz field can be intensified when using circularly polarized pump pulses. By contrast, when the B field is perpendicular to the laser propagation axis, ponderomotive effects are found to prevail at relativistic intensities, leading to the emission of much stronger THz fields (> 30 GVm(-1)) via Cerenkov wake radiation. Laser-to-THz conversion efficiencies above 10(-3) are predicted, together with full transmission of the THz waves across the rear plasma boundary, provided that the ratio of the electron cyclotron and plasma frequencies exceeds unity. The main trends revealed by the simulations are interpreted in light of simple analytical models.