Cavity-Modified Fluorescence in the Weak and Strong Coupling Regimes

In this study, we demonstrate that the fluorescence of fluorescein dye molecules can be significantly modified in both the weak and strong coupling regimes by placing the molecules inside a perturbative or non-perturbative Fabry-Perot cavity. By controlling the cavity thickness and dye concentration, we selectively altered the frequency and number of cavity transmission peaks, thereby establishing conditions for weak or strong coupling for fluorescein molecules. Using steady-state fluorescence spectroscopy, we confirmed that both the excitation and emission spectra were substantially tuned in these coupling regimes, enabling tunable and multicolor fluorescence from a single type of dye molecule, fluorescein.