Calibration-free wavelength modulation spectroscopy based on even-order harmonics

TL;DR

This paper introduces a fast, calibration-free wavelength modulation spectroscopy method using even-order harmonics, which simplifies gas absorption analysis by avoiding complex simulations and fitting, especially useful at high pressures or temperatures.

Contribution

It presents a novel analytical algorithm based on Voigt line-shape that directly extracts gas parameters from harmonic peak values, eliminating the need for extensive calibration and line-shape fitting.

Findings

Achieves millisecond-level gas parameter calculation.

Relative error less than 4% in experiments.

Effective at high pressure and temperature conditions.

Abstract

This paper proposes a novel and rapid calibration-free wavelength modulation spectroscopy algorithm based on even-order harmonics. The proposed algorithm, analytically deduced from Voigt line-shape function, only involves simple algebraic operations to describe the actual gas absorption spectra, thus eliminating the time-consuming simulations and line-shape fitting procedures adopted in traditional algorithms. Instead of acquiring the entirely scanned absorption line-shape, the proposed technique only requires extraction of the peak values of the harmonics. This characteristic significantly benefits gas diagnosis at elevated pressure and/or temperature, in which the entirely scanned absorption is very difficult to be obtained due to the broadened line-shapes. The proposed algorithm is validated by both numerical simulation and condition-controlled experiment, indicating millisecond-level calculation of gas parameters with the relative error less than 4% in the experiments.