Sensitivity enhancement of a cantilever-enhanced photo-acoustic spectroscopic sensor by an optical build-up cavity

Laser photo-acoustic spectroscopy (LPAS) is a highly sensitive and selective method for trace gas analysis. One of the most advanced LPAS techniques is cantilever-enhanced photo-acoustic spectroscopy (CEPAS), which can reach down to low-ppt and sub-ppt level trace gas detection sensitivities with high power lasers [1,2]. The selection of wavelengths and tunability of high power narrow linewidth lasers is, however, limited. They are also rarely suitable for field deployable analysers, which would require a small and robust form factor. An alternative approach, potentially overcoming these weaknesses, is to build up the optical power of a standard distributed feedback diode laser (DFB) or a quantum cascade laser in an external optical cavity [3,4]. © 2019 IEEE.