Fast Step Heterodyne Light-Induced Thermoelastic Spectroscopy Gas Sensing Based on a Quartz Tuning Fork with High-Frequency of 100 kHz

• • The high-frequency QTF (100 kHz) achieves a tenfold faster response time compared to the commercial 32.768 kHz QTF, reducing the measurement cycle to 33 ms—a 90% reduction—enabling real-time monitoring of combustion processes that occur within tens of milliseconds. • • The SH-LITES technique further shortens the scanning time to 15 ms, the shortest LITES measurement time reported to date, which is critical for capturing transient gas concentration spikes in exhaled breath during asthma attacks or rapid breathing patterns. • • In respiration monitoring, SH-LITES with the 100 kHz QTF accurately resolves H2O concentration fluctuations during fast breathing, whereas the commercial QTF-based H-LITES fails to capture these rapid changes, demonstrating superior temporal resolution for clinical diagnostics. • • The integration of a high-frequency QTF with heterodyne detection provides a pathway for compact, high-speed gas sensors with potential cost parity to existing commercial systems, as the QTF is a low-cost component and the heterodyne scheme simplifies signal processing.