We describe a confocal two-photon laser-induced fluorescence scheme for the detection of gaseous NO. Excitation from a simple YAG-pumped Coumarin 450 dye system near 452.6 nm was used to promote the two-photon NO(<i>A</i><sup>2</sup>Σ<sup>+</sup>, ν′ = 0 ← <i>X</i><sup>2</sup>Π, ν″ = 0) transition in the γ(0, 0) band. Subsequent fluorescence detection in the range 200–300 nm permitted almost total rejection of elastic and geometric scatter of laser radiation for excellent signal/noise ratio characteristics. The goal of the research was to apply NO fluorescence to a relatively realistic limited optical access combustion environment. A confocal optical arrangement was demonstrated for single-point measurements of NO concentration in gas samples and in atmospheric-pressure flames. The technique is suitable for applications that offer only a single direction for optical access and when significant elastic scatter is present.
© 1998 Optical Society of America
Mark Reeves, Mark Musculus, and Patrick Farrell, "Confocal, Two-Photon Laser-Induced Fluorescence Technique for the Detection of Nitric Oxide," Appl. Opt. 37, 6627-6635 (1998)