Mid-infrared Doppler-free saturation absorption spectroscopy of the Q branch of CH4 ν3=1 band using a rapid-scanning continuous-wave optical parametric oscillator

We have developed a mid-infrared Doppler-free saturation absorption spectroscopy apparatus that employs a commercial continuous-wave optical parametric oscillator (CW OPO), complemented by a home-built automation and wavelength scanning system. Here, we report a comprehensive spectral scan of the Q branch transitions of the ν