Polariton Formation Enhances Lifetimes of Dense Exciton Gasses in Cuprous Oxide by Suppressing Two-Exciton Decay*

Collective excitonic states form at high densities, but in dense gases the long lifetime of excitons in cuprous oxide (Cu$_{2}$O) is compromised by two-exciton annihilation processes. Using the picosecond streak camera spectroscopy facility at the Center for Nanoscale Materials at Argonne National Laboratory we directly measured the decay of orthoexciton-polaritons generated by two photon absorption. The two-body decay lifetime is an order of magnitude longer than for excitons uncoupled to photons. The extended lifetime opens opportunities for experiments that manipulate polariton collective states. Unlike time-averaged measurements of two-body processes, streak camera detection shows decay suppression without effects from production efficiency or additional density dependent processes.