Calibration-Free Gas Quantification through Wavelength Modulation Spectroscopy in the Millimeter-Wave/Terahertz Range

Millimeter-Wave/Terahertz (mmW/THz) spectroscopy affords high precision and specificity, useful for analyzing complex gas mixtures. In conjunction with wavelength modulation spectroscopy (WMS), it stands out as a sensitive technique for trace gas detection. The complex nature of the WMS absorption line shape, however, remains challenging to quantify and interpret. In this work, we propose a practical procedure for processing and analyzing the WMS signal to derive a calibration-free quantification of the target gas. To validate the method, we compared the results to reference measurements of methanol and water and found a good agreement.