On the problem of normal electromagnetic waves in crystals

Abstract

After elimination of the effects of nonconservation of quasiparticles the energy spectrum corresponding to normal electromagnetic waves in a crystal is analysed. The derived expressions for the dispersion law and for the coefficients connecting polariton, exciton and photon creation and anihilation operators are more nearly correct and in any case simpler in structure than the corresponding earlier results which follow from the application of the standard approximate second-quantization (ASQ) method and the u-v transformation. As a further improvement due to the elimination of the nonconservation of quasiparticles it is found that the fourth-order part of the hamiltonian does not contain terms corresponding to the simultaneous annihilation or creation of four polaritons, terms which were present in papers based on earlier standard approaches. The new improved approach is used also for the analysis of nonlinear optical effects such as polariton-polariton scattering and the three-polariton absorption. The obtained theoretical estimations are in agreement with the experimental results. © 1975.