Gas Sensing Based on Heterodyne Mach–Zehnder Interferometric Phase-Dispersion Spectroscopy

Abstract A novel gas sensing method based on heterodyne Mach–Zehnder interferometric phase-dispersion spectroscopy (HMIPDS) was proposed for the first time in this work. The proposed method employed a heterodyne Mach–Zehnder interferometric configuration to realize gas sensing through cumulative optical phase shifts induced by refractive-index variations during laser-gas interaction. Specifically, the laser beam was divided into a signal arm interacting with the gas medium and a reference arm frequency-shifted by an acousto-optic modulator (AOM) to generate heterodyne interference. The gas-induced optical phase variation was then accurately extracted via quadrature demodulation of the interference signal, thereby enabling quantitative retrieval of gas concentration. Acetylene (C2H2) was used for experimental validation. Experimental results demonstrate the HMIPDS method achieved a detection limit of 708 ppb with an integration time of 500 s, corresponding to an approximately 11-fold improvement in detection sensitivity compared with the conventional WMS-2f detection system (8 ppm at 500 s). Furthermore, the linear dynamic detection range was extended from 0 to 2% for conventional WMS-2f to 0–5%, corresponding to an approximately 2.5-fold enhancement. The proposed HMIPDS method provides a high sensitivity, high stability, and wide dynamic range solution for gas sensing, showing strong potential for high-concentration and ultrasensitive trace gas detection applications.