Fabry-Perot resonators for high-resolution infrared gas sensors

A new Fabry-Perot filter based on a silicon wafer spacer is proposed in this work. IR gas sensors based on these filters would combine excellent selectivity and signal-to-noise ratio with an overall scheme similar to that of the simplest non-dispersive IR sensors. The filter can be fitted to the fine structure of different gases, in particular those diatomic with unlike atoms as carbon monoxide among others. The spacer of the filter is a silicon wafer of defined thickness. Fine tuning to gas absorption peaks can be reached by coupling it to other multilayers. In this work the properties of silicon wafers as spacers of the proposed filters are studied. From the study it derives that the most determining factor of the filter properties is the loss of coherence caused by surface roughness. However, as we demonstrate in this work, surface roughness limitations are not very severe and easily obtained by standard polishing procedures.