Intense multi-terahertz fields of order MV/cm are used to coherently promote optically dark and dense para excitons in Cu2O from the 1s into the 2p state. The nonlinear field response of the intra-excitonic degrees of freedom is directly monitored in the time domain via ultrabroadband electro-optic sampling. The experimental results are analyzed with a microscopic many-body theory, identifying up to two internal Rabi cycles. The effects of population inversion and ponderomotive contributions are disentangled.
The original publication is available at link DOI: 10.1103/PhysRevLett.101.246401