Baseline-free direct absorption spectroscopy and its application in line intensity measurement of ammonia

Abstract

A method based on direct absorption spectroscopy (DAS) without baseline fitting procedure, which we called baseline-free DAS (BFDAS), is proposed. The BFDAS utilizes three transmission spectra at different pressures and a simulated absorbance at the smallest pressure to derive the difference of integral absorbances at the other two pressures, where gas concentration or line intensity can be obtained. The proposed method is experimentally validated by comparing the line intensities of ammonia measured by conventional DAS and BFDAS, which demonstrates good performance of the BFDAS in broadened or narrowly scanned spectra where baseline fitting is difficult to be implemented.