Whispering gallery modes of a microdisk resonator are useful for the optical detection of single rubidium and cesium atoms near the surface of a substrate. Light is coupled into two high-Q whispering-gallery modes of the disk which can provide attractive and/or repulsive potentials, respectively, via their evanescent fields. The sum potential, including van der Waals/Casimir-Polder surface forces, may be tuned to exhibit a minimum at distances on the order of 100 nm from the disk surface. Simultaneously optically trapping and detecting is possible, with the back-action of an atom held in this trap on the light fields being suffciently strong to provide a measurable effect. Atom trapping and detection depend on a variety of system parameters and experimental realizations differ for different atoms.
We investigate simultaneous optical trapping and optical detection of a single Rb atom near the
surface of a toroidal microdisk. Light is coupled into two high-Q whispering-gallery modes of the
disk which provide attractive and repulsive potentials, respectively, via their evanescent fields. The
sum potential including van-der-Waals and Casimir-Polder surface forces exhibits a minimum at
distances of the order of 100 nm from the disk surface. The back-action of an atom held in this trap on the light fields is sufficiently strong to provide a measurable effect. We discuss atom trapping
and detection properties in dependence on a variety of system parameters.
We investigate the bound and evanescent fields of the optical whispering gallery modes which are supported by a toroid microcavity and which may be used for a wide range of applications. Results of simulations using finite-difference time domain solutions of Maxwell's equations are compared with semi-analytical solutions based on coupled mode theory. Key parameters such as resonance frequencies, transmittance characteristics, coupling efficiencies, and bending/scattering losses are analyzed as a function of experimental variables such as size, distance, and fabrication roughness. Finally, the feasibility of single-atom detection is discussed.