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.