Abstract

We report the observation of fast electromagentic transients with terahertz band widths, radiated perpendicular to a GaAs/air interface. With a femtosecond laser pulse at normal incidence, free carriers are generated at the GaAs surface. These carriers radiate a fast EM transient when accelerated by the electric field present at the GaAs/air interface. In a simple dipole model no radiation is emitted perpendicular to the interface, along the direction of the driving field. We, however, observe a fast transient radiated perpendicular to the surface, and we ascribe this effect to the strong change in the angular distribution of the radiating dipoles due to the presence of the interface and the presence of a small dielectric lens near the interface.

© 1992 Optical Society of America