Gas In Scattering Media Absorption Spectroscopy Based On Tunable Laser

Absorption spectroscopy is a widely used tool for gas sensing. This thesis focuses on gas ab-sorption spectroscopy with tunable diode laser absorption spectroscopy, TDLAS. In particular, the absorption of gases inside porous scattering media has been studied. Such analysis needs a new method, which is called gas in scattering media absorption spectroscopy (GASMAS). The light from diode laser is scanned over the absorption line of the studied gas, and the transmitted intensity is detected. In contrast to the bulk material, the free gas exhibits narrow absorption lines. Thus even if the surrounding solid-state material would absorb, there would be a negligible variation over the gas absorption.Studies in this thesis include developing a compact and flexible system for study on gas ab-sorption in scattering media, and studying porous alumina ceramics and aerogels with the sys-tem. The gas absorption enhancement properties of porous alumina ceramics with different po-rosities and different types of aerogels have been investigated using GASMAS technique. The gas exchange for the ceramics with70%porosity has also been studied. Gas detection in porous samples also allows fundamental studies of material.With their high absorption path length enhancement effect, small size and rapid gas exchange, porous ceramics have the potential to be used as a tiny multi-pass cell for gas sensing. A probe based on porous media has been developed and initial gas concentration detection has been per-formed. In the end, we investigated the possibility to measure gas inside the food package with porous scattering media.