Techniques for stimulated Raman excitation and CARS detection of radicals created by photodissociation

CARS and SRE of radicals created by photodissociation were attempted using a laser system with a 1 cm−1 bandwidth. The difficulty of observing these spectra due to interference from non-resonant background and the resulting asymmetric CARS lineshape is discussed and demonstrated with N2O, HS and OH. Polarization filtering techniques are described and improvements resulting from their use are presented. The HS radical, which has a Raman frequency on the low energy side of the H2S precursor molecule, could not be detected, while OH, which has a Raman frequency on the high energy side of the HNO3 precursor molecule, was easily observed.