Midinfrared properties of cuprous oxide:: High-order lattice vibrations and intraexcitonic transitions of the 1s paraexciton -: art. no. 235210

This contribution addresses both the general mid-infrared (MIR) properties of Cu2O and induced absorption due to intraexcitonic 1s -> 2p transitions under simultaneous cw laser excitation. After an overview of the current state of knowledge and remaining open questions concerning excitons in Cu2O we will first discuss several absorption bands in the spectral range between approximately 100 and 150 meV in terms of multiphonon and biphonon features. The second, more extensive part will concern a pump-probe experiment in the limit of low densities of 1s excitons where we investigated intraexcitonic transitions appearing in the MIR spectral range as well. We find a signal which can be clearly assigned to a 1s para -> 2p para transition and present various data depending on excitation conditions and sample temperature. Applying the results of detailed theoretical considerations we can estimate the density and lifetime of the 1s para-exciton and at least speculate about its dispersion.