Investigation of photolytic interferences in nanosecond and picosecond excitation schemes for two-photon laser-induced fluorescence imaging of atomic hydrogen in flames

Detection of atomic hydrogen in flames and plasmas requires multi-photon excitation schemes because single-photon excitation in the vacuum ultraviolet (VUV) is impractical in these optically thick environments. Quantitative measurement of atomic hydrogen in flames using two-photon-excited laser-induced fluorescence (TP-LIF) is complicated by photolytic interference and rapid loss of excited-state population via stimulated emission. We investigate the sources of photolytic interference and the effects of stimulated emission using nanosecond and picosecond lasers for TP-LIF line imaging of atomic hydrogen in premixed methane/air, hydrogen/oxygen and hydrogen/air flames. A laser beam at 205 nm is used for two-photon excitation of the (n=1 n=3) transitions of atomic hydrogen. Line images of the LIF signal from the (n=3 n=2) transitions at 656 nm are recorded using a state-of-the-art intensified CCD camera. Stimulated emission is monitored using a fast PIN photodiode. Signals produced by picosecond and nanosecond excitation are directly compared for a range of flame conditions, and recommendations for optimal detection are presented.

Investigation of photolytic interferences in nanosecond and picosecond excitation schemes for two-photon laser-induced fluorescence imaging of atomic hydrogen in flames Conference Paper