Quartz-enhanced laser spectroscopy sensing

Gas sensing technology is widely applied in various fields, including environmental monitoring, industrial process control, medical diagnostics, safety warnings, and more. As a detection element, the quartz tuning fork (QTF) offers advantages such as high-quality factor (Q-factor), strong noise immunity, compact size, and low cost. Notably, its resonant characteristics significantly enhance system signal strength. Two spectroscopic techniques based on QTF detection, Quartz-enhanced photoacoustic spectroscopy (QEPAS) and light-induced thermoelastic spectroscopy (LITES), are currently research hotspots in the field of spectral sensing. This paper provides a comprehensive and detailed review and highlights pivotal innovations in these two QTF-based spectroscopic techniques. For QEPAS, these encompass high-power excitation methods, novel excitation sources, advanced QTF detection elements, and acoustic wave amplification strategies. Regarding LITES, the researches on optical cavity-enhanced approaches, modified QTF improvement mechanisms, integration with heterodyne demodulation technique, and combination with QEPAS were analyzed. These advances have enabled quartz-enhanced laser spectroscopy to achieve detection limits ranging from parts-per-billion (ppb) to parts-per-trillion (ppt) levels for trace gases such as methane (CH₄), acetylene (C₂H₂), carbon monoxide (CO), and so on. Additionally, prospects for future technological developments are also discussed in the concluding section.