Abstract

Resent advances and developments regarding laser based mid-IR gas sensors based on cavity enhanced - quartz enhanced photoacoustic spectroscopy (QEPAS) as well as interferometric cavity assisted photothermal spectroscopy (ICAPS) are reported. A resonant linear Brewster window cavity was added to a commercial prototype of a QEPAS sensor system to increase the power of the employed quantum cascade laser (QCL) at the place of measurement by a factor of more than hundred. In ICAPS, a Fabry-Perot cavity facilitates the sensitive detection of the refractive index change induced by mid-IR absorption. Using a balanced ICAPS detection scheme efficiently eliminates excess noise and resulted in shot noise limited performance. Results obtained when studying small molecules like CO, N₂O and SO₂ using these techniques are presented and compared. The dependence of the generated signal as a function of the applied modulation frequency will be discussed.

© 2019 The Author(s)