Hydrogen-enhanced light-induced thermoelastic spectroscopy sensing

A hydrogen (H₂)-enhanced light-induced thermoelastic spectroscopy (LITES) sensor is proposed for the first time, to our knowledge, in this paper. The enhancement with H₂ significantly reduces the resonance damping of a quartz tuning fork (QTF), leading to a 2.5-fold improvement in the quality factor (Q-factor) to 30,000 without introducing additional noise into the LITES sensor system. Based on the H2-enhancement effect, a self-designed round-head QTF with a low resonance frequency (f₀) of 9527 Hz and a fiber coupled multipass cell (MPC) with an optical length of 40 m were utilized to increase the energy accumulation time of QTF and the optical absorption of the target gas, respectively, to demonstrate an ultra-highly sensitive C₂H₂-LITES sensor. The long-term stability of the H²-enhanced C₂H₂-LITES sensor was investigated based on Allan deviation analysis. With an optimal integration time of 140 s, the minimum detection limit (MDL) was improved to 290 parts per trillion (ppt). Compared to other reported state-of-the-art C2H2-LITES techniques with similar parameters, this sensor shows a 241-fold improvement in the MDL. This H₂-enhancement technique proves to be a highly effective method for achieving a high Q-factor QTF, characterized by its simplicity and efficiency. It offers substantial potential for applications in QTF-based gas sensing.