Baseline-free Quantitative Absorption Spectroscopy Based on Cepstral Analysis

TL;DR

This paper introduces a baseline-free method for quantitative absorption spectroscopy using cepstral analysis to convert transmission spectra into a form that isolates molecular signals from source intensity variations, enabling more accurate measurements.

Contribution

The paper presents a novel cepstral analysis technique that eliminates the need for baseline correction in absorption spectroscopy, applicable to complex and broad absorption spectra.

Findings

Effective in complex absorption scenarios

Independent of source intensity variations

Compatible with any absorption spectrometer

Abstract

The accuracy of quantitative absorption spectroscopy depends on correctly distinguishing molecular absorption signatures in a measured transmission spectrum from the varying intensity or "baseline" of the light source. Baseline correction becomes particularly difficult when the measurement involves complex, broadly absorbing molecules or non-ideal transmission effects such as etalons. We demonstrate a technique that eliminates the need to account for the laser intensity in absorption spectroscopy by converting the measured transmission spectrum of a gas sample to a modified form of the time-domain molecular free induction decay (m-FID) using a cepstral analysis technique developed for audio signal processing. Much of the m-FID signal is temporally separated from and independent of the source intensity, and this portion can be fit directly with a model to determine sample gas properties without correcting for the light source intensity. We validate the new approach in several complex absorption spectroscopy scenarios and discuss its limitations. The technique is applicable to spectra obtained with any absorption spectrometer and provides a fast and accurate approach for analyzing complex spectra.