Several tens of femtoseconds after optical excitation, scattering proc
esses in semiconductors are not completed, thus, relaxation has not ye
t become irreversible. This opens the fascinating possibility of actua
lly reversing or enhancing incompleted scattering events. Here, we use
attosecond time scale coherent control to suppress or amplify the non
-Markovian phonon oscillations in the model semiconductor GaAs. [S0031
-9007(98)05370-8].