Abstract

Bloch oscillations of coherent wave packets in semiconductor superlattices observed in femtosecond time-resolved experiments have become a subject of great current interest.¹ Since the first prediction of Bloch oscillations (BOs) in semiconductor superlattices,² the first experimental observation of BOs succeeded in femtosecond time-resolved experiments in GaAs/AlGaAs superlattices by means of four-wave mixing.³ These observations have been followed by the detection of tunable THz emission from this system⁴ and the electro-optic detection of the internal dipole moment associated with the real-space motion of the coherent wave packet.⁵ BOs are now well established as being a quantum mechanical interference of several Wanniner - Stark (WS) states of a biased superlattice. For this reason, the observation of a WS ladder in cw photocurrent or absorption spectra⁶ is a prerequirement for the observation of BOs. The time-resolved observation of BOs gives substantially more information on the system as compared with the cw optical techniques, since information on the intraband coherence time of electronic wave packets becomes now accessible.^4,5

© 1996 Optical Society of America