Sequential two-photon laser-induced fluorescence: A new technique for detecting hydroxyl radicals

A new approach to the detection of the chemically important transient species, the hydroxyl radical (OH), is reported. This new approach, labeled two-photon laser-induced fluorescence (TP-LIF), has now been tested in the laboratory under atmospheric conditions. The method involves combining IR laser pumping (e.g., 1.4 or 2.8 fim) with UV laser excitation (e.g., 345 or 351 nm). Theoretical predicted signal levels were found to agree very favorably with laboratory measured signal levels. Using laboratory data reported in this study, in conjunction with projected IR energy improvements, it appears that the TP-LIF OH method could be of great value both as a laboratory instrument for studying fundamental chemical processes and as an OH field detection system.