Sub-Doppler optothermal overtone spectroscopy of ethylene and dichloroethylene

Sub-Doppler optothermal spectroscopy of ethylene has been performed in a collimated molecular beam with a single-mode color center laser tunable around 1.6 μm and a silicon bolometer cooled to 1.6 K. The spectra of the ν5+ν9 overtone transitions and their perturbations are analyzed. With an enhancement cavity, overtone transitions of di- and trichloroethylene have also been measured.