Collinear Photothermal Gas Sensing With a Custom-Made Dichroic and Fiber-Coupled Fabry-Pérot Etalon

Here, we present the implementation of a compact, collinear photothermal interferometry configuration for gas sensing based on a custom-made dichroic and fiber-coupled Fabry-P´erot etalon. By overcoming the design obstacles imposed by such a configuration, advantage of the strong signal enhancement due to the larger overlap of the pump and probe beam volumes was taken. A competitive NNEA of 4.2 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−7</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup>W/ √ Hz and a limit of detection of 38.8 ppmv were achieved. Additionally, the more compact architecture of the sensing unit allows for further miniaturization of photothermal gas sensors. The proposed solution has been fabricated and tested, showing great promise for highly sensitive, selective and miniaturized gas sensors.