Abstract

Most of the experiments on ultrafast hot carrier dynamics have been explained theoretically within the framework of the semiclassical Boltzmann equation. On this level, the various scattering mechanisms are modeled assuming that every single collision strictly conserves energy and momentum. Using femtosecond two-color spectroscopy, we demonstrate that for ultrashort time scales the semiclassical picture breaks down and wave mechanical memory effects start to play an important role [1]. In Fig. 1 we present energy resolved transmission changes ΔT/T in a GaAs sample (T_L=15K) reflecting the distribution of the electrons excited form the heavy hole band by an ultrashort laser pulse of a duration of 120fs. A shot-noise limited femtosecond pump-probe system allows us to study excitation densities as low as 8×10¹⁴ electron-hole pairs per cm³ in order to keep carrier-carrier scattering inefficient [2].

© 1998 IEEE