Tunable Diode Laser Absorption Spectroscopy (TDLAS) technology, as a highly selective, interference-resistant, and rapid-response (<1 s) optical gas detection method, demonstrates significant advantages in real-time monitoring of multi-component toxic and hazardous gases (such as CH₄, CO, H₂S, etc.) in coal mines. It is progressively replacing traditional electrochemical sensors and gas chromatography techniques. This paper systematically reviews the key technical pathways, current engineering applications, and future challenges of TDLAS in complex coal mine environments. It highlights the performance differences between Direct Absorption Spectroscopy (DAS) and Modulation Spectroscopy (MS), emphasizing the mainstream role of the WMS-2f/1f normalization method in enhancing trace gas detection sensitivity and anti-interference capabilities. For multi-component detection, the paper thoroughly examines the advantages and disadvantages of time-division multiplexing (TDM) Technology, frequency-division multi-plexing (FDM) Technology, and their hybrid strategy (F-TDM). It also explores the potential of overlapping spectral line separation strategies based on single lasers and machine learning algorithms for achieving low-cost, compact multi-component sensing. Although TDLAS has achieved preliminary applications in duct monitoring and in-situ detection, challenges persist, including nonlinear responses to high-concentration gases, laser costs, system complexity, and adaptability to extreme environments (high humidity, high dust, strong vibration). Future research should focus on developing high-concentration correction algorithms, low-cost laser sources, enhanced environmental robustness, and multi-technology integration to advance the comprehensive application of TDLAS in intelligent gas safety monitoring systems for mining environments.

Accurate and stable measurement of carbon dioxide (CO₂) concentrations in industrial flue gases is critical for emissions monitoring and carbon management. The present study developed a wavelength-modulated tunable diode laser absorption spectroscopy (WMS-TDLAS) system for measuring high-concentration carbon dioxide (CO₂) in flue gases, covering a range of 3–20% (by volume). To mitigate optical intensity fluctuations caused by particle scattering and detector gain drift in harsh flue gas environments, a normalized second harmonic (2f/1f) detection scheme based on a single-harmonic peak was employed. A digital phase-locked amplification algorithm replaces the conventional hardware lock-in amplifier, enabling simultaneous demodulation of multiple harmonic components and enhancing system integration. A comparison of the digital locking method with a commercial lock-in amplifier reveals that the former demonstrates comparable or superior stability, with relative standard deviations of 0.04% for the 2f signal and 0.02% for the first-harmonic signal. In order to address the sensitivity degradation of WMS-TDLAS at elevated CO₂ concentrations, a pressure control strategy was introduced. Maintaining the measurement cell pressure at 70 ± 0.005 kPa resulted in a 2.74-fold enhancement in system sensitivity at 13.01% CO₂ and a more than one-order-of-magnitude increase at 20.01% CO₂ compared to operation at atmospheric pressure. Concentration measurement error under reduced pressure also decreased from 1.101% to 0.075%. The system exhibited 0.6% repeatability in high-concentration CO₂ measurements, signifying its aptitude for industrial flue gas monitoring applications.