Abstract
Recent experiments by Roskos et al.,1 in ultrashort optical pulse excitation of biased coupled quantum wells have shown remarkable generation of terahertz electromagnetic radiation. Two different effects were identified: (i) an oscillatory field of frequency corresponding to the separation between the coupled levels in the quantum-well pair (~1.5 THz); and (ii) an instantaneous electromagnetic field pulse that appears to follow the time evolution of the exciting laser pulse. The oscillatory field is understood to be caused by the coherent oscillation of optically created electrons from one well to the other.1 The instantaneous part we believe is caused by a new mechanism proposed in Ref. 2. The essence of this instantaneous mechanism is that electron-hole pairs are created in a biased semiconductor with a net polarization. The density of these pairs follows the light field, as does the induced polarization, generating an electromagnetic source that follows the light pulse.
© 1992 Optical Society of America
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