Photothermal Gas Sensing with a Custom-Made, Fiber-Coupled Fabry-Pérot Etalon

Growing awareness of the adverse health effects of nitrogen oxides has increased the demand for reliable, sensitive and mass-producible sensor systems. Photothermal interferometry has shown great promise towards sensitive, selective and miniaturized sensor solutions. This work describes the development of a macroscopic photothermal sensor system with a sensor head consisting of a low-cost, custom-made and fiber-coupled Fabry-Pérot etalon. The sensor was tested with NO₂, achieving a 3σ limit of detection of 2.5 ppmv (1 s). Exhibiting little drift, a limit of detection of 100 ppbv is achievable for 200 s integration time. Compensating for the low excitation power, the normalized noise equivalent absorption was calculated to be 2.2 × 10^-8 cm^-1W/√Hz. The sensor system is not limited to NO₂, but can be used for any gas or aerosol species, by exchanging the excitation laser source.