Anomalous optical absorption in Cu2O in the presence of an excitonic Bose condensate

Experimental results are presented on the additional absorption of resonant light induced by the interceptive passage of a travelling packet of excitons in Cu2O, and on the possible implications this effect may have on the amplification of a Bose–Einstein condensate of such excitons. Condensates are created at T=1.8 K with high intensity YAG laser pulses (λ=532 nm), and then stimulated by a second lateral pulse tuned around the 1S orthoexciton resonance (λ=609.51 nm). The induced attenuation of the lateral pulse varies only with the number of excitons within the initial packet, which is controlled by the intensity of the initial YAG illumination, and varies neither with the resonant pulseʹs intensity nor with the resonant pulseʹs polarization-dependent absorption.