Antiresonant hollow core fiber-assisted photothermal spectroscopy of nitric oxide at 5.26 μm with parts-per-billion sensitivity

Laser-based gas sensors are undergoing constant and rapid development due to their usability in numerous applications focused on e.g. monitoring of greenhouse gases concentration, safety in harsh environments or medicine. Amongst many types of such sensors, gas detectors employing the photoacoustic or photothermal effect are characterized by an exceptional capability of delivering high selectivity combined with superb signal-to-noise ratio (SNR). In this work, we demonstrate a novel, compact and sensitive nitric oxide (NO) sensor targeting its strong transition near 5.26 mu m by combining the photothermal interferometry (PTI) technique and a gas absorption cell based on a self-fabricated antiresonant hollow-core fiber (ARHCF). Having only a 25 cm long interaction length, the sensor reached a minimum detection limit (MDL) of 11 ppbv (parts per billion by volume) for an integration time of 144 s. Proper design of the ARHCF utilized as the gas cell enabled combining a mid-infrared (mid-IR) pump laser to induce the refractive index modulation and a Fabry-Perot interferometer-based readout of the photothermal effect with a near-infrared probe laser. The presented results document the first experimental attempt to detect gas molecules having transitions beyond 4.5 mu m in an ARHCF-aided photothermal detection scheme.