Absolute fluorescence and absorption measurements over a dynamic range of 10⁶ with cavity-enhanced laser-induced fluorescence

We present a novel spectroscopic technique that exhibits high sensitivity and a large dynamic range for the measurement of absolute absorption coefficients.We perform a simultaneous and correlated laser- induced fluorescence and cavity ring-down measurement of the same sample in a single pulsed laser beam. The combined measurement offers a large dynamic range and a lower limit of detection than either technique on its own. The methodology, dubbed cavity-enhanced laser-induced fluorescence, is developed and rigorously tested against the electronic spectroscopy of 1,4-bis(phenylethynyl)benzene in a molecular beam and density measurements in a cell. We outline how the method can be used to determine absolute quantities, such as sample densities, absorption cross sections, and fluores- cence quantum yields, particularly in spatially confined samples.