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Quartz Enhanced Photothermal Spectroscopy (QEPTS) is a technique, which enables developing gas sensors characterized by a broadband operational range and superb sensitivity. QEPTS relies on the thermoelastic effect induced by the illumination of the Quartz Tunning Fork (QTF) with a modulated laser radiation, which generates a piezoelectric signal. QTF excitation can occur at any wavelength, which is impossible to observe in e.g. semiconductor detectors. The sub-dollar cost of a QTF delivers simultaneously broadband and sensitive detection capability and significantly reduced costs of the sensor. Furthermore, as in majority of laser-based sensors, the sensitivity of QEPTS-based systems can be easily enhanced by increasing laser-gas interaction path length. This is typically realized by using multipass cells (MPCs), which significantly increase the sensor’s complexity and decrease its robustness. Instead of using MPCs, an Antiresonant Hollow-Core Fiber (ARHCF), designed for light transmission in more than one spectral band can be used as a long gas absorption cell, leading to the increase in the sensor’s performance while keeping its design simple. Here, we present a sensor utilizing a combination of an ARHCF-based absorption cell and the QEPTS. In the developed system the gas-filled ARHCF substitutes an MPC. The spectroscopic signal analysis relies on the use of a simple QTF with a resonance frequency of 32.744 kHz connected with a self-made, low-noise amplifier and an addition of a wavelength modulation spectroscopy – based signal retrieval scheme for sensor’s performance enhancement. The sensor enables simultaneous detection of acetylene and methane at parts-per-million by volume level sensitivity, targeting their absorption lines in the near- and mid-infrared. The results confirm excellent suitability of the ARHCF-aided QEPTS sensors for being employed as a versatile gas detectors.
This research was funded by Narodowe Centrum Nauki (NCN), grant number UMO-2018/30/Q/ST3/00809.
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