Coherent zone-folded longitudinal acoustic phonons in semiconductor superlattices: Excitation and detection

Coherent zone-folded acoustic phonons are excited in GaAs/AlAs superlattice s by femtosecond laser pulses via resonant impulsive stimulated Raman scatt ering in both forward and backward scattering directions. The relative ampl itudes of three distinct modes of first and second backfolded order match w ell with scattering intensities calculated within an elastic continuum mode l. The detection of the coherent acoustic modes is based on the modulation of the interband transitions via the acoustic deformation potential and exh ibits a strong enhancement at interband transitions.