Efficient Probing Of Few Atom Fluorescence through the Guided Mode of an Optical Nanofiber

We show that fluorescence of a very small number of atoms around a subwavelength-diameter silica-fiber, an optical nanofiber, can be measured efficiently by detecting the photons coupled to the guided mode of the nanofiber. Also such a technique enables us to probe the van der Waals interaction between atoms and surface with high precision.