Probing Bose-Einstein condensation of excitons with electromagnetic radiation

We examine the absorption spectrum of electromagnetic radiation from excito ns, where an exciton in the Is state absorbs a photon and makes a transitio n to the 2p state. We demonstrate that the absorption spectrum depends stro ngly on the quantum degeneracy of the exciton gas, and that it will general ly manifest many-body effects. Based on our results we propose that absorpt ion of infrared radiation could resolve recent contradictory experimental r esults on excitons in Cu2O.