  The tremendous applications of terahertz (THz) spectroscopy and imaging
require THz sources in different parameters. We propose a novel scheme to
generate single-cycle powerful THz pulses by ultrashort intense laser pulses
incident obliquely on a tenuous plasma slab of few THz wavelengths in
thickness. This is made possible by driving a large amplitude electron plasma
wave in the plasma slab, thus producing a net transient current at the plasma
surfaces. Theory and simulations show that such a THz source is capable of
providing megawatt power and field strength of MV/cm, which may open up new
horizons for nonlinear THz science and applications.
