POLARITON FUSION AND 2ND-HARMONIC GENERATION IN SEMICONDUCTORS

The second harmonic generation response is derived through a fully qua ntum mechanical calculation by considering the fusion of two exciton-p olaritons. We calculate the expectation value of the electric field in the final polariton state evolved by the effect of the fusion Hamilto nian. Our result can be expressed in a form directly comparable to the classical derivation and takes into account nonresonant excitation of polariton waves which cannot be fully described by previous derivatio ns and gives rise to a coherent background and interference effects in the second harmonic intensity as a function of frequency.