Single-cycle strong terahertz pulse generation from a vacuum-plasma interface driven by intense laser pulses

Single-cycle strong terahertz pulses can be generated by irradiating ultrashort intense laser pulses onto a tenuous plasma slab. At the plasma surface, laser ponderomotive force accelerates electrons and induces net currents, which radiate terahertz pulses. Our theoretical model suggests that if τ_L>2π/ω_p, with τ_L as the laser-pulse duration and ω_p as the plasma frequency, the emission frequency is around τ_L⁻¹. On the other hand, the emission frequency is around ω_p/2π if τ_L<2π/ω_p. Our numerical simulations support the theoretical model, showing that such a terahertz source is capable of providing megawatt power, field strengths of MV/cm, and broad frequency tunability.