Comparative study of whispering gallery modes in fluorescence and dark-field scattering spectra of single microspheres

Herein, we report the comparative analysis of whispering gallery modes (WGMs) in fluorescence and dark-field scattering spectra of single dye-doped dielectric microspheres. In detail, single dye-doped microspheres are selected, and the fluorescence and dark-field scattering spectra for each microsphere are recorded one after another using a transmission-mode dark-field optical microscope with fluorescence attachment. Later, the quality factors, intensities, and wavelengths of the WGMs in both types of spectra obtained for each microsphere are compared. The experimentally observed WGMs are characterized using the Lorenz–Mie scattering theory. Moreover, the role of the numerical aperture of the microscopic objective lens on the WGMs observed in these spectra is studied in detail. Finally, the merits and demerits of the WGMs observed in both types of spectra are discussed in detail. To the best of our knowledge, this is the first report presenting a direct comparison of WGMs in fluorescence and dark-field scattering spectra obtained from the same single optical microspheres.