Baseline-free Quantitative Absorption Spectroscopy Based on Cepstral Analysis

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.

References in corpus (5)

• Frequency comb spectroscopy
• Coherent Dual Comb Spectroscopy at High Signal to Noise
• Mid-Infrared Frequency Comb Fourier Transform Spectrometer
• Broadband Dual Frequency Comb Spectroscopy in a Rapid Compression Machine
• Optical frequency comb Faraday rotation spectroscopy

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• Spatially resolved mass flux measurements with dual comb spectroscopy
• Resolving nonuniform temperature distributions with single-beam absorption spectroscopy. Part II: Implementation from broadband spectra
• Measurement and assignment of J = 5 to 9 rotational energy levels in the 9070-9370 cm${}^{-1}$ range of methane using optical frequency comb double-resonance spectroscopy
• Combined frequency comb and continuous wave cavity-enhanced optical-optical double-resonance spectrometer in the 1.7 $\mu$m range