Theory of intersubband Raman laser in modulation-doped asymmetric coupled double quantum wells

A microscopic theory is developed for the laser gain due to stimulated intersubband electronic Raman scattering pumped by CO2 laser in modulation-doped GaAs/AlGaAs asymmetric coupled double quantum wells (ACDQWs). Based on the charge-density-excitation (CDE) mechanism, the formula for electronic Raman scattering cross-section is given, taking into account the coupling between intersubband plasmon and optical phonons including GaAs confined LO phonons and interface phonons. Stimulated Raman gain factor is then derived from the cross-section. The optimization of Raman gain, the gain saturation and threshold condition are also discussed. Numerical analysis for temporal variation of stimulated Stokes photon density, subband populations and output Raman laser power is carried out by using the self-consistent conventional rate equations. The theory can predict the presence or lack of coupled modes in lasing in agreement with the recent experimental results.