Simultaneous laser-induced fluorescence and sub-Doppler polarization spectroscopy of the CH radical

The first application of polarization spectroscopy (PS) to the CH radical is demonstrated. In particular, we report on the simultaneous application of laser-induced fluorescence (LIF) and sub-Doppler PS to CH. The conventional experimental setup for PS was supplemented with a second detection system in order to collect the LIF emission. At the same time a Fabry–Perot etalon and molecular iodine were utilized to obtain a precise relative and absolute frequency scale, respectively. CH was investigated in a low pressure methane–oxygen flame. The R2(5) transition of the B–X (0, 0) band corresponding to a wavelength around 387.3 nm was scanned while fluorescence emission was collected in the spectral region around 431 nm from the B–X (0, 1), A–X (1, 1) and A–X (0, 0) bands. The saturation behavior of both techniques is investigated as well as line broadening effects due to the pump laser pulse energy or rather fluence. Saturation fluence for LIF was found to be more than one order of magnitude higher as compared to PS.