Multiple Gases Detection Based on Periodical Mode-Locked Cavity-Enhanced Absorption Spectroscopy Using a Single-Mode Diode Laser

In this work, we report a general technique named periodical mode-locked cavity-enhanced absorption spectroscopy (PML-CEAS) for detecting multigas with a single-mode diode laser. To acquire the absorption spectrum of multigas, a periodical mode-locking technique was present which can realize rapid and stable frequency locking at different cavity modes, actively interrupting the locking status and automatic relocking of the laser frequency. Then, a multigas detection strategy was proposed to improve the response speed of the system for multigas detection. To verify the effectiveness of this technique, a fiber-coupled distributed feedback (DFB) laser emitting at $1.53~ \mu \text{m}$ was used as the light source to detect $\text{C}_{{2}}\text{H}_{{2}}$ and $\text{H}_{{2}}\text{O}$ . A 15-cm long Fabry–Perot cavity was designed as the gas absorption cell with an effective absorption length of $\sim $ 49.7 m. Finally, $\text{C}_{{2}}\text{H}_{{2}}$ and $\text{H}_{{2}}\text{O}$ measurements were conducted and the performance of the system was obtained. The proposed multigas detection technique addresses the issues of narrow tuning range and poor anti-interference ability of traditional CEAS, which has wide application prospects in environmental monitoring, exhaled breath analysis, and industrial applications.