CO2 monitoring using a simple Fabry–Perot-based germanium bolometer

We report on the design, simulation and experimental characterization of a simple germanium bolometer utilizing a Fabry–Perot absorbing structure, which can be used for monitoring, e.g., CO2 where no additional filter is required. CO2 absorbs IR-radiation in a major band centered around a vacuum wavelength of 4.26 μm. The selectivity of the whole sensor-configuration is mainly accomplished by the wavelength-response associated with the Fabry–Perot structure. The analysis shows, that the designed bolometer has an adequate response-function for the measurement of CO2 concentration. Combining the analysis for the bolometer with ray tracing simulations for a connected sample chamber yields the response for an entire IR-absorption sensor system which is proven to be in good agreement with measurements.