Phase-locking of a 3.4-THz Quantum Cascade Laser using a harmonic super-lattice mixer

We report on a phase locking experiment of a 3.4 THz Quantum Cascade Laser (QCL) by using only room temperature electronics. A super-lattice harmonic mixer was used to produce a bit signal between the QCL signal and the 18
^th
harmonic of a 190 GHz reference generator. The beat signal more than 30 dB above the noise level for 1 MHz RBW was observed. Such a signal to noise ratio was sufficient to provide high quality phase-locking and synchronize to a microwave reference up to 99% of the emitted QCL power.