Phase-locking of a 2.7-THz quantum cascade laser

Abstract

We successfully realized phase‐locking of a 2.7‐THz metal‐metal waveguide quantum cascade laser (QCL) to a reference, which is generated from an external microwave signal by applying two stages of frequency multiplication. The reference is the 15th harmonic of a signal at 182 GHz, which is produced by a semiconductor superlattice nonlinear device. The signal at 182 GHz is generated by a multiplier‐chain (×12) from a microwave synthesizer at ∼15 GHz. Both QCL laser and reference radiations are coupled into a superconducting NbN hot electron bolometer mixer, resulting in a beat signal, which is fed into a phase‐lock loop. Spectral analysis of the beat signal confirms that the QCL is phase locked. This result is a crucial demonstration for a QCL used for local oscillator and opens the possibility to extend heterodyne interferometers into the far‐infrared range.