Simultaneous measurement of gas absorption and path length based on the dual-sideband heterodyne phase-sensitive detection of dispersion spectroscopy

We present a novel approach based on dual-sideband heterodyne phase-sensitive detection of dispersion spectroscopy to realize simultaneous measurement of the gas absorption signal and corresponding path length. The details of heterodyne phase-sensitive detection of dispersion spectroscopy are derived. A standard Mach-Zehnder intensity modulator (MZM) is adopted to generate a spectrum of a carrier and two sidebands. Phase shift of the beatnote signal generated by the two sidebands is detected to retrieve the path length as well as the gas absorption signal. The measurement range of the path length can be adapted by changing the modulation frequency. Proof-of-principle experiments are conducted with methane (CH4) as the absorber which is filled into a gas cell with a variable path length. We also utilize this approach to evaluate the path length of a White cell and meanwhile calibrate the experimental system with different concentrations of methane. The proposed method has a great potential for detecting the path length and gas absorption in multipass cells and the open path environment. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

A novel approach based on dual-sideband heterodyne phase-sensitive detection of dispersion spectroscopy is presented for simultaneous measurement of gas absorption signal and path length. The method involves using a standard Mach-Zehnder intensity modulator to generate a spectrum and detecting phase shift to retrieve path length and gas absorption signal, with the ability to adapt the measurement range of path length by changing modulation frequency. Proof-of-principle experiments conducted with methane as the absorber demonstrate the potential of the proposed method for detecting path length and gas absorption in multipass cells and open path environments.