Self-calibrated wavelength modulation spectroscopy based on 2f/1f amplitude and integral area for trace gas sensing

A self-calibrated wavelength modulation spectroscopy (WMS) based on the simulated calibration curves of the 1 f -normalized 2 f spectra is proposed for high precision and high resolution trace gas sensing. The new method not only eliminates the complicated manual standard gas calibration process of traditional WMS, but also reduces the time consumption of calibration-free WMS based on the iterative fitting. Here, we use two approaches to observe the simulated calibration curves, described as the WMS-2 f /1 f amplitude and WMS-2 f /1 f integral area. A mid-infrared (MIR) continue-wave quantum cascade laser (CW-QCL @ 4.56 μm)-based CO and N 2 O spectrometer is developed to verify the effectiveness of the proposed method. Compared with the 2 f /1 f amplitude implementation, the 2 f /1 f integral area improves the detection precision, with 37.5% and 48.8% improvement for CO and N 2 O at the optimal integration time, respectively, and the long-term stability of the system effectively, as well as reduces the measurement error caused by wavelength drift.