Inverse Fitting Direct Absorption Spectroscopy Technology: Simplified Implementation and Enhanced Performance

The conventional direct absorption spectroscopy (DAS) technique has been plagued by the difficulty of obtaining accurate baseline, which is caused by photoelectric drift and the absence of non-absorbing regions in the transmitted light intensity signal. An inverse fitting direct absorption spectroscopy (IF-DAS) technique has been proposed to address this difficulty. The technique leverages the intrinsic nonlinear intensity response of tunable lasers to achieve baseline-free concentration measurements. It offers the advantages of being straightforward to implement, baseline-free, calibration-free, and resistant to photoelectric signal drift. Its efficacy was validated using an example under ambient temperature and atmospheric pressure conditions. The performance of the IF-DAS technique was compared with that of the conventional DAS technique through standard experimental tests. The results demonstrate that the IF-DAS technique is less susceptible to fluctuations in light intensity, exhibits superior linearity and accuracy, with an R2 value of 0.99986 and an overall error of less than 2%. This technique shows potential for application in harsh scenarios such as reactive flow fields and long-term engineering applications.