Hollow-Core Fiber Fabry–Pérot Photothermal Gas Sensor: Temperature-Dependent Behavior

Photothermal spectroscopy is a promising gas detection technique, providing high selectivity, high sensitivity, and wide dynamic range. Here, we systematically investigate the temperature-dependent behavior of the photothermal signal in a compact hollow-core fiber gas sensor in a Fabry–Pérot cavity configuration. Temperature affects the absorption properties of the target gas, the thermal characteristics of the gas medium, as well as the stability of in-cavity pump power via multi-path interference, thereby impacting the photothermal signal. Rigorous theoretical formulation and experimental investigation are carried out. With an 11-cm-long hollow-core fiber, we achieved a detection limit of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>1 ppb acetylene at room temperature. By optimizing the wavelength modulation amplitude to minimize the in-cavity pump power fluctuation and using a temperature compensation scheme, we reduce the signal variation from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>48% to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula>2% over a wide temperature range of 256-354 K, demonstrating good adaptability of the technique under different temperature conditions.