Ultra-stable, widely tunable and absolutely linked mid-IR coherent source

We report on a new coherent source that, using a phase-lock scheme to an optical frequency-comb synthesizer, achieves a 10-Hz intrinsic linewidth, is tunable from 4 to 4.5 um with a presettable absolute frequency and, when coupled to a high-finesse cavity, can provide a short-term absorption sensitivity of 1.3 · 10-11 cm -1Hz-1/2. These unique spectral features make this source a precise tool for molecular physics.