Hydroxyl Molecular Line Shapes in Laser-Ignition of Air

Abstract

Abstract This work communicates measurement and analysis of diatomic molecular hydroxyl (OH) spectra after generation of laser-induced plasma. A relative laboratory-air humidity of the order of 25% causes the occurrence of OH recombination radiation that is recorded with optical emission spectroscopy. A Q-switched, 150 mJ, 6 ns pulsed Nd:YAG laser beam at the fundamental wavelength of 1064 nm is focused in air with f/5 optics. Formation of OH is clearly discernible at time delays of several dozen microseconds after plasma initiation. Optical emissions are dispersed by a 0.64-m Czerny-Turner spectrometer and an intensified charge-coupled device records the data along the wavelength and slit dimensions.