Phase-matched generation of a terahertz surface wave by a subluminous optical strip

We show that a weakly focused ultrashort laser pulse with tilted intensity front can efficiently excite a terahertz surface wave via phase-matched optical rectification at the surface of a semiconductor. The surface wave is excited by a strip of nonlinear polarization moving along the semiconductor surface with subluminous velocity. The amplitude and power of the radiated surface wave are calculated. For a 90-fs optical pulse with a peak intensity of 2GW∕cm2, we estimate the energy conversion coefficient to be 10−7 at the surface of GaAs. The direct excitation of surface waves at terahertz frequencies can be particularly attractive for terahertz spectroscopy of semiconductor surfaces.