limit of the CRD measurement by several orders of magnitude.

Previously, several groups have used different combinations of CRD and LIF, not necessarily using a single laser beam, to measure, *e.g.*, fluorescence quantum yields and quenching rates.[@Spaanjaars1997; @Hagemeister1999; @Bahrini2006; @Tokaryk2007] Richman *et al.* detected fluorophor-doped aerosols within a cavity by their fluorescence signal.[@Richman2005] Furthermore, CRD spectroscopy, instead of Rayleigh scattering, has recently been used to calibrate density measurements in flames via LIF.[@Dreyer2001; @Luque2004; @Lamoureux2010] None of these previous studies used the cross-correlation of the CRD and LIF signals as presented here.

In this paper, we describe and fully characterize the novel CELIF technique in detail. We outline how absolute quantities, such as fluorescence quantum yields, can be directly extracted from the single beam CELIF measurement by cross-normalization of the LIF and CRD signals. Absorption coefficients are accessible with a single method and measurements can be carried out over a dynamic range spanning more than six orders of magnitude. The ring-down cavity rejects the majority of the laser light and stretches the laser pulse in time. The amount of light inside the cavity, generating the LIF signal, is measured by the integrated cavity ring-down signal. This measurement is used for a 