Frequency noise power spectral density of a molecular THz-laser using a fs- fibre laser comb with 1 GHz repetition rate

We report the measurement of the frequency noise power spectral density (FNPSD) of a CO
₂
pumped molecular-laser emitting at 2.5THz. The measurement relies on the generation of a beatnote between the THz frequency and the harmonic of the IGHz repetition rate of a fs-fiber comb. We obtain a frequency noise of ~0.1 Hz
²
/Hz at 50kHz, limited by the phase noise of the frequency comb. This shows the potential of (i) molecular lasers as ultra-low phase noise sources of THz radiation, and of (ii) fs-fiber combs, in combination with electro-optic detection, as frequency-agile and low phase-noise THz local oscillators.