We describe a new Stark interaction in the 10μm region which is resonant at zero Stark field and produces large absorption changes at low voltages. The resonance is due to the interaction between the R(18) line at 10.78μm from a13CO2laser and the asQ
This Letter presents for the first time the observation of the resonant optical Stark effect in a semiconductor. The excitonic system of Cu2O is well suited to the investigation of this effect because of its rather large binding energy and well-resolved resonances at low temperatures. The mixing between the 1S and 2P excitons by the electric field of a tunable high-power CO2 laser leads to drastic changes in the one-photon spectrum around the 2P absorption line. Even details of the line shape are consistently described in terms of the frequency-dependent nonlinear susceptibility.