Beam-steering-effect immune laser absorption spectrum extraction for precise and robust temperature measurement

Tunable diode laser absorption spectroscopy is widely used for temperature measurement in combustion monitoring due to its merits of rapidity, non-contact capability, and high precision. In actual applications, the beam-steering effect will cause time-varying distortion in the laser intensity signal, resulting in a low signal-to-noise ratio and inaccurate extraction of the absorption spectrum. This work proposes a cost-effective distortion detection scheme and adaptive distortion filter and compensation algorithm for the extraction of the beam-steering effect immune laser absorption spectrum. Turbulent flame monitoring experiment results prove the proposed method can improve the signal-to-noise ratio of the raw transmitted absorptive laser signal by 35 dB after the beam-steering distortion has been compensated. When compared with the temperature results calculated from the distorted absorptive laser signal, the results from the distortion-compensated absorptive laser signal show a significant improvement in both robustness and precision. The experimental results demonstrate that the successful temperature fitting rate has increased from 93.7 % to 100 % (over 1000 repetitions), and the average standard deviations of temperature have decreased from 296.6 K to 61.8 K. The proposed method is cost-effective and compact, which will potentially play an important role in dynamic combustion monitoring and diagnosis.