Triply resonant second-order Raman scattering in GaAs

We have achieved conditions for triply resonant second-order Raman scattering induced by the iterated electron-one-phonon interaction by applying uniaxial stress on bulk GaAs and thus producing an energy splitting between the light- and heavy-hole valence bands equal to the energy of two scattering phonons. We show that all three energies involved in this process, the incident and the outcoming photon energy, and also the intermediate energy, are simultaneouly in resonance with an electronic transition. Under such conditions we observe, even for crossed polarizations, scattering intensities much larger than the ones seen in resonant 2LO-phonon Fröhlich intraband Raman scattering for unstressed samples.