Methane sensing via unbalanced nonlinear interferometry using a CMOS camera and undetected mid-infrared light

Here, we present a high-sensitivity, rapid, and low-cost method for methane sensing based on a nonlinear interferometer. This method utilizes signal photons generated by stimulated parametric downconversion (ST-PDC), enabling the use of a silicon detector to capture high-precision methane absorption spectra in the mid-infrared region. By controlling the system loss, we achieve more significant changes in visibility, thereby increasing sensitivity. A low-cost CMOS camera is employed to capture spatial interference fringes, ensuring fast and efficient detection. Thereby, we demonstrate an accurate measurement of methane concentration within a gas cell. In addition, we show that ST-PDC enables long-distance sensing and the capability to measure open-path low ambient methane concentrations in the real world.