Real-Time Molecular Spectroscopy through Self-Mixing in a Terahertz Quantum-Cascade Laser

We report on a new detection method for real-time molecular spectroscopy with a terahertz quantum-cascade laser. The self-mixing effect is exploited to tune the lasing frequency across molecular absorption lines of D
₂
O and CH
₃
OD and for the detection of the self-mixing signal. The method allows for realtime monitoring of gas mixtures in an absorption cell.