Production of 1s quadrupole-orthoexciton polaritons in Cu2O by two-photon pumping - art. no. 125323

We have studied the angular (at 1.8 K) and temperature dependence (from 1.8 to 70 K) of the time-integrated luminescence spectra of 1s orthoexcitons f rom the yellow series in Cu2O arising from resonant two-photon pumping to b oth the 1s and 2s levels. For resonant pumping to the 1s level, the direct (denoted as X-o) emission is strongly enhanced at low temperature. It is fo rward directed, however, with an angular width substantially larger than th e divergence of the excitation beam. excitation to the 2s level (which subs equently decays into a 1s level) results in a more isotropic angular distri bution of X-o emission. The lifetime of the X-o emission resulting from res onant excitation to the 1s level at 1.8 K is similar to2 ns, shorter than t he decay time of thermalized orthoexcitons. The results support the idea th at resonant two-photon excitation to the 1s level results primarily in a qu adrupole-orthoexciton-polariton formation, whereas 2s excitation does not. The behavior of the phonon-assisted luminescence is essentially independent of the mode of excitation.