ULTRAFAST DYNAMICS OF OPTIC PHONONS IN A 2D ELECTRON-GAS

Absorption of ultrafast laser pulses in a III-V semiconductor heterost ructure is used to excite a coherent optical phonon population. The de phasing and decay of the phonon wavepacket is directly monitored on a femtosecond timescale. Localised injection of phonons within a 2D elec tron gas is shown to reveal strong interactions whose strength can be tuned using the laser wavelength. Experiments utilizing this source of high-wavevector acoustic phonons are discussed.