Indirect detection of hydrogen based on light-induced thermoelastic spectroscopy

Hydrogen (H₂), as a low-density and high-efficiency clean energy source, is widely used in the H₂ energy sector. However, its colorless, odorless nature and wide explosive concentration range (4-75%) demand rapid and accurate detection techniques. Conventional H₂ detection methods based on quartz tuning forks (QTFs) suffer from time-consuming full-frequency scanning, complex data processing, and frequency errors caused by parasitic capacitance. In this study, an indirect H₂ detection method based on light-induced thermoelastic spectroscopy (LITES) is proposed for the first time. A universal pump gas is innovatively employed, allowing H₂ concentration information to be obtained solely through the excitation of a LITES signal. Two demodulation schemes are developed: a frequency-tracking demodulation that establishes a linear relationship between QTF resonant frequency and H₂ concentration, and a fixed-frequency demodulation that divides the demodulation frequency into three characteristic blocks, enabling H₂ concentration retrieval without full-frequency scanning. Experimental results demonstrate that the LITES system exhibits excellent linearity with respect to the pump gas concentration. The QTF resonant frequency shows a linear response to H₂ concentration with a sensitivity of 6.8845 mHz/% and a minimum detection limit of 0.36%. The proposed method effectively eliminates frequency errors caused by parasitic capacitance and features high sensitivity, fast response, and simplified data processing, offering a reliable approach for H₂ safety monitoring.