Abstract

Impulsive generation of coherent phonons with ultrashort light pulses has been reported in a number of different materials. Possible generation mechanisms include impulsive stimulated Raman scattering ^[1] (ISRS), displacive excitation of coherent phonons (DECP)^[2] and generation of LO-phonons in surface space-charge regions.^[3] In the latter case, excitation of charged carriers with optical pulses of 50-fs duration at 2 eV in GaAs surface space charge fields gives rise to strong longitudional field changes due to charge seperation and screening effects.^[1] At sufficiently strong excitation impulsive generation of coherent LO-phonons is observed.^[3] Both the carrier transport dynamics as well as the amplitude and phase of the coherent LO-phonon displacement are detected on (100) oriented GaAs via the method of reflective-electro-optic-sampling (REOS). Here we will report on a detailed study of the initial coherent displacements as a function of the initial depolarization field, which in turn is closely related to the carrier transport dynamics.

© 1992 IQEC