Photoionization cross section of1sorthoexcitons in cuprous oxide

Abstract

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 (${\mathrm{Cu}}_{2}\mathrm{O}$) 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 intensity 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 $(3.9\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}$ ${\mathrm{m}}^{2}$ was deduced for the probe frequency.