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

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 lineshape 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.

A Time-of-Flight Estimation Method for Acoustic Ranging and Thermometry Based on Digital Lock-In Filtering

“…The digital lock-in filtering technique is a versatile signal processing method with a wide range of applications in spectroscopy [ 2 ], electricity [ 35 ], and magnetism [ 36 ] to extract signals at specific frequencies from harsh interference environments. Based on the DLF technique, this paper proposes a novel method that can be used to accurately estimate the TOF.…”

“…Traditional contact measurement methods such as scale and thermocouple cannot be applied to lengthy underground conduits. Ranging and thermometry methods based on laser [ 1 , 2 ] and imaging [ 3 , 4 ] technologies are constrained because light can only travel in straight line, so it is unsuitable for lengthy, curved underground pipeline applications. Ultrasonic and microwave ranging [ 5 , 6 ] and thermometry [ 7 , 8 ] methods require considerable power for long-distance measurements due to their shorter wavelengths and faster attenuation, while increased power means an increased size of the sensor, and hence they are inconvenient for such application, particularly for small diameter conduits.…”

Super-Accuracy Calculation for the Half Width of a Voigt Profile

“…The Voigt profile is widely used in optics, laser physics, plasma, astrophysics and spectroscopy [1][2][3][4][5][6]. By the convolution of both the Lorentzian and Gaussian profiles, the Voigt profile blends the physical characteristics of both profiles.…”

On the Highly Accurate Evaluation of the Voigt/Complex Error Function with Small Imaginary Argument

“…respectively. The real part of the complex error function K(x, y) also known as the Voigt function, occurs in great diversity in astrophysical spectroscopy, space science, neutron physics, plasma physics and statistical communication theory, as well as in some areas in mathematical physics and engineering associated with multi-dimensional analysis of spectral harmonics [4][5][6][7][8][9][10][11][12][13][14][15][16]. For example, the Voigt function is a fundamental component of the line-by-line (LBL) radiative transfer modeling for the analysis of planetary atmospheres [5][6][7].…”