Theoretical study of detection of a dipole emitter through an objective with high numerical aperture

The problem of detecting electric dipole emitters (such as a fluorescing molecule) through a microscope objective with a high numerical aperture is considered. Exact vector-wave-optics results of the field distribution of the electromagnetic field in image space are derived. On the basis of these results, the collection-efficiency function (CEF) is calculated. This calculation is compared with a semigeometric approximation of the CEF, for which a new analytical formula is presented. The derived results are important for applications such as fluorescence correlation spectroscopy and single-molecule fluorescence detection with a confocal microscope.