Evanescent wave quartz-enhanced photoacoustic spectroscopy employing a side-polished fiber for methane sensing

Cian F Twomey; Gabriele Biagi; Albert A Ruth; Marilena Giglio; Vincenzo Spagnolo; Liam O'Faolain; Anton J Walsh

doi:10.1016/j.pacs.2024.100586

Evanescent wave quartz-enhanced photoacoustic spectroscopy employing a side-polished fiber for methane sensing

Photoacoustics. 2024 Jan 22:36:100586. doi: 10.1016/j.pacs.2024.100586. eCollection 2024 Apr.

Authors

Cian F Twomey¹, Gabriele Biagi^{1

2}, Albert A Ruth³, Marilena Giglio², Vincenzo Spagnolo², Liam O'Faolain^{1

4}, Anton J Walsh¹

Affiliations

¹ Centre for Advanced Photonics and Process Analysis, Munster Technological University, Cork, T12 P928, Ireland.
² PolySense Lab, Dipartimento Interateneo di Fisica, University and Politecnico of Bari, Bari, CNR-IFN, Via Amendola 173, Bari 70126, Italy.
³ School of Physics and Environmental Research Institute, University College Cork, Cork, Ireland.
⁴ Tyndall National Institute, Lee Maltings Complex Dyke Parade, Cork, T12 R5CP, Ireland.

Abstract

We present an all-fiber-based laser gas analyzer (LGA) employing quartz-enhanced photoacoustic spectroscopy (QEPAS) and a side-polished fiber (SPF). The LGA comprises a custom quartz tuning fork (QTF) with 0.8 mm prong spacing, two acoustic micro-resonators (mR) located on either side of the prong spacing, and a single-mode fiber containing a 17 mm polished section passing through both mRs and QTF. The SPF polished face is positioned to enable the evanescent wave (EW) to create a photoacoustic wave and excite the fundamental flexural mode of the QTF. Sensor performance was demonstrated using methane in nitrogen gas mixtures, with CH $_{4}$ mixing ratios ranging from 75 ppmv to 1% (by volume), measured with an accumulation time of 300 ms, and a minimum detection limit of 34 ppmv subsequently determined. The EW-QEPAS sensor is ideal for miniaturization, as it does not contain any free-space optics and is suitable for gas sensing in harsh environments and where mobility is required.

Keywords: Evanescent wave QEPAS; Evanescent wave spectroscopy; Gas detection; Methane leak detection; Parts-per-million sensitivity; Quartz-enhanced photoacoustic spectroscopy (QEPAS); Side-polished fiber.