Ultrafast interband pumping of quantum-cascade structures: A feasibility study of a THz pulse amplifier.

Gain spectra of a three-well GaAs/AlGaAs quantum-cascade structure under interband pumping by ultrashort optical pulses are studied within the framework of the density matrix theory. A mathematical model for intersubband kinetics is derived taking into account many-body interactions and ultrafast interband optical pumping. It is found that pulsed interband pumping leads to an increase in intersubband gain by an order of magnitude, which is characterised by 1 ps rise time and 8 ps recovery time under pumping by 100 fs pulses with a peak intensity of 100 MW/cm2. Possible implementations of the concept are highlighted. The results uncover a new possibility for ultrafast switching of the material gain in quantum-cascade structures. [ABSTRACT FROM AUTHOR]