ABSTRACT
Quantum cascade laser (QCL) was rst demonstrated in 1994 [1]. Since the invention, QCLs have become important coherent mid-infrared (mid-IR) [1] and terahertz (THz) [2] radiation sources. Room-temperature continuous-wave operation of midIR QCLs has been achieved in the ~3-14 μm wavelength range. However, due to the challenges on building up enough optical gain in long-wavelength emission devices above cryogenic temperatures [3], THz QCLs with wavelengths covering from 60 to 300 μm are still operated below room temperatures. The best temperature performance has been obtained at ~200 K using a resonant-phonon (RP) design [4]. Further improvement on the existing designs requires a better understanding of effects of the electron transport on optical properties, for example, optical gain of THz QCLs.
