Hopfield coefficients measured by inverse polariton series

Abstract

We report observation of the inverse polariton series and a detailed experimental study of the exciton components in polaritons (Hopfield coefficients). Spontaneous emission of excitonic molecules into outgoing polaritons associated with the $i(=1,2,3,4,5)\mathrm{th}$ exciton states in bulk CuCl is detected and analyzed by the bipolariton model. Because the intensities of the emission lines, which form the inverse polariton series, are determined by the exciton components in the final-state polaritons, we are able to measure the Hopfield coefficients for the highly composite outgoing polaritons. Quantum interference in the optical decay of excitonic molecules, due to the multiple exciton components in the polariton and biexciton states, is also demonstrated.