Fluorescence correlation spectroscopy on a mirror

Abstract

Fluorescence correlation spectroscopy when fluorescent nanoemitters are diffusing in the vicinity of a dielectric mirror is studied both theoretically and experimentally. We demonstrate that two important effects occur when the confocal detection volume is located on the mirror’s surface. First, the count rate per emitter is significantly enhanced owing to control of spontaneous emission and enhancement of the excitation field. Second, interference fringes in the excitation beam give rise to a new characteristic time in the photocurrent’s autocorrelation function. This new time is found to be independent of the transverse excitation field’s beam waist and permits accurate measurement of diffusion coefficients without any a priori knowledge of the confocal volume geometry.