Quantum-cascade lasers for terahertz high-resolution spectroscopy

We have developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures for the application-defined emission frequencies of 3.36, 3.92, and 4.75 THz, which correspond to fine-structure transitions of Al atoms, N
⁺
ions, and O atoms, respectively. These THz QCLs can be operated in a mechanical cryocooler in continuous-wave mode, while a sufficient intrinsic tuning range of more than 5 GHz is maintained. This allows them to be implemented as local oscillators in airborne astronomical instruments and as radiation sources for high-resolution absorption spectroscopy to determine absolute densities of atoms and ions in plasmas.