STIMULATED SCATTERING IN AN OPTICAL LATTICE

We present a study of pump-probe spectroscopy experiments in an optica l lattice. The probe transmission spectrum contains three types of res onances similar to those found in usual nonlinear media: Raman, Brillo uin and Rayleigh resonances. We show evidence of the existence of a pr opagating elementary excitation in the lattice which involves no inter action between the particles and lead to a Brillouin-like scattering. We discuss the central Rayleigh resonance and show that its shape is s ensitive to the radiation pressure.