Simultaneous detection of Raman- and collision-induced molecular rotations of O2 and N2 via femtosecond multi-pulses in combination with quartz-enhanced photoacoustic spectroscopy

Molecular rotational states of nitrogen and oxygen molecules at room temperature and atmospheric pressure are excited by femtosecond double- and multi-pulses with variable temporal pulse distances, and quartz-enhanced photoacoustic spectroscopy is used for their detection. A simple extrapolation of measured double-pulse data is presented, which predicts form and position of Raman-excited spectral features and thus enables us to distinguish between spectral lines caused by Raman-scattering- and collision-induced absorption both appearing when excitation by pulse trains is used.