Two-step saturated fluorescence detection of atomic hydrogen in flames

We report a new variation on fluorescence detection, two-step saturated fluorescence spectroscopy, which can provide significant advantages over existing methods for detecting some atomic and molecular species. The method uses multiple-photon excitation of the selected atom or molecule, followed by saturated excitation of an optical transition from the initially excited state and subsequent detection of fluorescence emitted from the final state populated by the saturated excitation. The technique is demonstrated with the detection of atomic hydrogen in flames.