The absorbance is of great importance in the tunable diode laser absorption spectroscopy (TDLAS) as it contains information of both gas properties and spectroscopic parameters. A novel, calibration-free wavelength modulation-direct absorption spectroscopy (WM-DAS) is proposed and experimentally verified in this two-part paper. This method combines the capability of absorbance measurement from DAS and the advantages of enhanced noise rejection and high sensitivity from WMS. In this Part I, we focus on the full theoretical basis and procedures of this method from the following three aspects: the high-accuracy characterizations of laser frequency and intensity, noise rejection ability by extracting the characteristic spectra through the fast Fourier transform (FFT) of the light intensity, and the simultaneous fitting strategy for both baseline and absorbance. The preliminary validation experiment of CO transition at 4300.6999 cm-1 in a static gas cell shows the high accuracy of the proposed method.

中文翻译：

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用于恢复吸光度的高灵敏度、免校准 WM-DAS 方法 - 第 I 部分：理论分析。


吸收率在可调谐二极管激光吸收光谱（TDLAS）中非常重要，因为它包含气体性质和光谱参数的信息。这篇由两部分组成的论文提出了一种新颖的免校准波长调制直接吸收光谱（WM-DAS）并进行了实验验证。该方法结合了 DAS 的吸光度测量能力和 WMS 的增强噪声抑制和高灵敏度的优点。在第一部分中，我们从以下三个方面重点介绍该方法的完整理论基础和流程：激光频率和强度的高精度表征，通过快速傅里叶变换（FFT）提取特征光谱的噪声抑制能力。光强度，以及基线和吸光度的同时拟合策略。静态气室中CO在4300.6999 cm-1处跃迁的初步验证实验表明了该方法的高精度。