Quartz-Enhanced Laser Spectroscopy Revolutionizes Gas 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. In a new paper published in Light: Science & Applications, a team of scientists, led by Professor Yufei Ma from National Key Laboratory of Laser Spatial Information, Department of Electronic Science and Technology, Harbin Institute of Technology, China, and co-workers have provided a comprehensive and detailed review and highlights pivotal innovations in QEPAS and LITES techniques. For QEPAS, there are several approaches to enhance the performance of QEPAS systems: 1) using high-power laser to actuate more gas molecules achieve absorption; 2) applying novel excitation source with strong absorption coefficient to strengthen the absorption; 3) utilizing a custom QTF to increase detected signal; 4) employing acoustic resonator to amplify acoustic wave or adopting multi-pass structure to generate multiple acoustic wave source. A detailed overview of these recent advancements of QEPAS technique is presented in the paper. Regarding LITES, the optimization of gas sensor sensitivity has primarily focused on improving optical absorption, enhancing QTF detection performance, and increasing system response speed. The currently effective strategies for optimizing the detection performance of LITES sensors were summarized in the paper and categorized as follows: 1) employing cavity enhancement techniques to boost absorbance; 2) improving detection capabilities through QTF modification or the use of custom QTFs; 3) utilizing the transient response characteristics of QTFs to build a heterodyne system to enhance the response speed of the LITES sensor; and 4) leveraging the advantages of QEPAS technology to maximize laser energy utilization. Additionally, prospects for future technological developments are also discussed in the paper. In the future, as cross-disciplinary convergence with various fields and technologies deepens, these two QTF-based spectroscopic technologies will evolve towards higher sensitivity, higher integration, even on-chip integration, and greater ease of practical application.