Frequency noise and phase-locking of a quantum cascade laser-pumped, 1.073THz molecular laser using a 1560nm frequency comb

We report the measurement of the frequency noise power spectral density (PSD) of a THz molecular laser (ML) pumped by a mid-infrared (MIR) quantum cascade laser (QCL). This is obtained by beating the ML frequency with the harmonic of the repetition rate of a 1560nm frequency comb (FC). We find a frequency noise PSD <; 10Hz
²
/Hz (-95dBc/Hz) at 100kHz from the carrier, limited by the noise of the QCL current driver. We also show that it is possible to actively phase-lock the QCLpumped ML to the FC repetition rate harmonic by controlling the QCL drive current.