Previously, orders of magnitude enhancement of THz radiation has been observed when femtosecond optical pulses illuminate an electrically biased semiconductor-metal interface as compared with THz radiation emitted from free surfaces or photoconductive gaps. Indeed, the fastest THz emission was reported from a Metal-GaAs interfac.1 We have experimentally characterized this behavior in detail and have found that the results can be explained in terms of a previously unreported strong field enhancement near the anode. On an 80μm electrode separation, 90% of the applied potential exists within 5μm of the anode. This field enhancement results from two mechanisms; i) geometric effects, and ii) space charge formation near the anode. Numerical analysis of the current transport supports the interpretation of the experimental results and the existence of extremely large (105 V/cm) fields near the anode.

© 1991 Optical Society of America

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