Coherent suppression of plasmon-phonon oscillations in a semiconductor using two ultrashort optical pulses

An ultrafast optical pulse can create an electron-hole plasma in the depletion layer of a polar semiconductor, such as GaAs, and excite plasmon-phonon modes. We show that another optical pulse, which arrives later, always suppresses the excited plasmon-phonon modes and the suppression rate varies dramatically with the delay. The energy of the oscillations transfers to free-streaming currents which are not sustained by any electric field. The free-streaming currents consist of counter-directed streams of the carriers created by the first and second pulses. Our predictions are based on an analytical solution of the coupled equations for plasmon-phonon modes with nonperturbative treatment of plasma density.