Study of coherent LO phonon-plasmon-coupled modes by double-pulse excitation

The coherent LO phonon-plasmon-coupled mode in n-GaAs has been studied by using a double-pulse excitation. When the irradiation power of the second pump pulse in the double-pulse excitation is increased, the lower branch (L_ mode) of the LO phonon-plasmon-coupled mode generated by the second pump pulse are shifted to the higher-frequency side than that generated by the first pump pulse. When the separation time between the two pulse components of the double-pulse excitation is varied, the amplitude of the L_ mode after the second pump pulse changes dramatically. These results indicate that the first coherent L_ mode generated by the first pump pulse changes to a new state by the second pump pulse and influences the amplitude of the new coherent L_ mode generated by the second pump pulse. (C) 2000 Elsevier Science B.V. All rights reserved.