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.
KEYWORDS: Waveguides, Chemical species, Resonators, Finite-difference time-domain method, Refractive index, Scattering, Waveguide modes, Light scattering, Silica, Signal to noise ratio
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.
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