THz-Wave Difference Frequency Generation by Phase-Matching in GaAs/Al_xGa_1−xAs Asymmetric Quantum Well

An asymmetric quantum well (AQW) is designed to emit a terahertz (THz) wave by using difference frequency generation (DFG) with the structure of GaAs/Al_0.2Ga_0.8As/Al_0.5Ga_0.5As under a doubly resonant condition. It is found that the second−order nonlinear susceptibility χ⁽²⁾ varies with the two pump wavelengths, and it can reach the peak value of 1.61 µm/V when the wavelengths are given as λ_p1=9.756 µm and λ_p2=10.96 µm, respectively. The numerical results show that the refractive index of one pump wave in the AQW is concerned with not only its own wavelength but also the other wavelength. Phase-matching inside the AQW can be obtained through the tuning of the two pump wavelengths.