Electromagnetically induced transparency in a cascade-type quantum well subband system under intense picosecond excitation

The coherent light–matter interaction in a 4-level cascade-type subband system of an asymmetric GaAs/AlGaAs quantum well structure is studied in pump-probe transmission experiments with picosecond (ps) time resolution. Coupling two excited subbands by an intense mid-infrared laser pulse at low sample temperatures is found to result in a substantially increased transparency of the fundamental e1–e2 transition. We find a reduction of the absorption coefficient by ~80%, which is one of the most pronounced electromagnetically induced transparency in solid state systems observed so far.