We demonstrate the use of a magnetic field to switch and to control the direction and polarization of a THz beam radiated from a semiconductor emitter.

We report measurement of the influence of electric and magnetic fields on optically induced THz electromagnetic radiation from semiconductors at normal incidence. The measurements show that electric and magnetic fields strongly influence the amplitude and phase of transient carrier-generated THz radiation, but do not affect THz optical rectification generated by the bulk second order nonlinear susceptibility, for static electric fields up to 104 V/cm.

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A technique has been developed that allows single-shot measurement of the electric field over an extended area. A LiTaO J crystal, covering the entire active area of the GaAs photoconductive switch, coupled the surface field with the polarization of an optical probe pulse. When imaged onto a two-dimensional detector array, this system produced snapshots of the surface field profile with 200-ps time resolution and 3-,um spatial resolution. The technique was used to monitor the collapse of the electric field in the GaAs as it was switched with a A = 1.06,um optical pulse. The switching speed and generation of field enhancements were found to be dependent on the illumination configuration and the electric field. In particular, the switching efficiency was found to decrease with increasing field.