This work covers absorption spectroscopy sensors that use two newly developed optical access methods: backscatter and conformed polymer film.
First, we demonstrate feasibility of a new class of absorption spectroscopy sensors, which can use return scattering from native surfaces such as the piston of an automotive engine. Our demonstration experiment collects backscatter through a 2-mm-diameter aperture, consistent with a small sensor footprint.
Second, we demonstrate use of a polymer film sealed to a duct to optically access the gas within the duct.
Finally, we extend both backscatter and polymer film access to spatially resolved measurements of gas mole fractions. In both cases, spatial resolution is offered by scanning the measurement laser beam. Tomographic imaging through a polymer film is applied to image H2O concentration in a practical diesel aftertreatment system. Both polyimide (PI) and polybenzimidazole (PBI) films are identified as candidates for extending the technique to enable NH 3 imaging in a diesel aftertreatment system.