High-Resolution terahertz gas-phase spectroscopy based on external optical feedback in a quantum cascade laser

We demonstrate the feasibility of high-resolution terahertz gas spectroscopy via the self-mixing effect in a quantum-cascade laser. Tuning the frequency of the quantum-cascade laser across a molecular absorption line of CH
₃
OH leads to a reduction of the optical feedback, which can be detected by monitoring the voltage across the quantum-cascade laser.