Multi-polariton scattering via excitonic molecules

We develop the theory of multi-polariton scattering via excitonic molecules under strong excitation. New emission lines, denoted by X- and L-bands, were observed at slightly lower energy side of two-photon Raman line in CuCl under strong excitation. In terms of the present theory, these lines can be for the first time assigned to the multi-polariton scatterings associated with the coherently (virtually) and incoherently (realy) created excitonic molecules, respectively.