Intersubband absorption with difference-frequency generation in GaAs asymmetric quantum wells

An asymmetric quantum well (AQW) is designed to emit terahertz (THz) waves by using difference frequency generation (DFG) with the structure of GaAs/Al_0.2Ga_0.8As/Al_0.5Ga_0.5As. The characteristics of absorption coefficients are analysed under the parabolic and non-parabolic energy-band conditions in detail. We find that the absorption coefficients vary with the two pump optical intensities, and they reach the maxima when the pump wavelengths are given as λ _p1=9.70 μm and λ _p2=10.64 μm respectively. Compared with non-parabolic condition, the total absorption coefficient under parabolic condition shows a blue shift, which is due to the increase in the energy difference between the ground and excited states. By adjusting the two pump optical intensities, the wave vector phase-matching condition inside the AQW is satisfied.