Detection of CH4 in the mid-IR using difference frequency generation with tunable diode laser spectroscopy

This paper demonstrates detection of methane using tunable diode laser spectroscopy (TDLS) through difference frequency generation (DFG) in order to address fundamental rotational-vibrational absorption lines, located around 3404 nm. Direct detection confirms that wavelength referencing of recovered lineshapes, developed for Near infra-red (Near-IR) systems, has been successfully transferred to the presented Middle infra-red (Mid-IR) system. Traditional 1f and 2f TDLS with WMS detection regimes are also functionally confirmed analogous to their Near-IR equivalents.