The various decay mechanisms of excitons in cuprous oxide (Cu2O) are highly sensitive to defects which can relax selection rules. Here we report cryogenic hyperspectral imaging of exciton luminescence from cuprous oxide crystals grown via the floatin
g zone method showing the samples have few defects. Some locations, however, show strain splitting of the 1s orthoexciton triplet polariton luminescence. Strain is reduced by annealing. In addition, annealing causes annihilation of oxygen and copper vacancies, which leads to a negative correlation between luminescence of unlike vacancies.
We report measurements of the attenuation of a beam of orthoexciton-polaritons by a photoionizing optical probe. Excitons were prepared in a narrow resonance by two photon absorption of a 1.016 eV, 54 ps pulsed light source in cuprous oxide (Cu2O) at
1.4 K. A collinear, 1.165 eV, 54 ps probe delayed by 119 ps was used to measure the photoionization cross section of the excitons. Two photon absorption is quadratic with respect to the intensity of the pump and leads to polariton formation. Ionization is linear with respect to the intensity of the probe. Subsequent carrier recombination is quadratic with respect to the intenisty of the probe, and is distinguished because it shifts the exciton momentum away from the polariton anticrossing; the photoionizing probe leads to a rise in phonon-linked luminescence in addition to the attenuation of polaritons. The evolution of the exciton density was determined by variably delaying the probe pulse. Using the probe irradiance and the reduction in the transmitted polariton light, a cross section of 3.9*10^(-22) m^2 was deduced for the probe frequency.
For an ultra-dense exciton gas in cuprous oxide (Cu$_2$O), exciton-exciton interactions are the dominant cause of exciton decay. This study demonstrates that the accepted Auger recombination model overestimates the exciton decay rate following intens
e two photon excitation. Two exciton decay is relevant to the search for collective quantum behavior of excitons in bulk systems. These results suggest the existence of a new high density regime of exciton behavior.
