Cavity and quartz enhanced photo-acoustic mid-IR sensor

We report on a novel intracavity quartz enhanced photoacoustic (I-QEPAS) gas sensing technique taking advantage from both the high Q-factor of standard tuning forks and the power build-up of a high-finesse optical resonator. This first prototype employs a distributed feedback quantum cascade laser operating at 4.3 mu m. CO2 has been selected as gas target. Preliminary results demonstrate an improved sensitivity, close to the cavity enhancement factor (similar to 500) times the optical coupling efficiency (about 0.5), with respect to standard QEPAS technique. The detection limit was pulled from 7 ppm (obtained with standard QEPAS) down to 32 ppb, corresponding to normalized noise-equivalent absorption in the 10(-9) W.cm(-)1.Hz(- 1/2) range.