Abstract

With time-resolved tetrahertz emission spectroscopy, Bloch oscillations of optically excited wave packets in semiconductor superlattices have been observed. All time-resolved experiments conducted up to now with other measurement techniques have concentrated on wave packets generated by resonant excitation of Wannier-Stark-lad- der (WSL) states evolving from the first electron miniband. In this paper we present evidence for Bloch oscillations in the WSL at nonresonant excitation as high as 80 meV above the fundamental band gap. This is, to our knowledge, the first observation of coherent charge oscillations after excitation of high-lying states, in which ultrafast dephasing has been assumed to suppress such oscillations.

© 1995 Optical Society of America