Three-Dimensional Orientation of Single Molecules in a Tunable Optical λ/2 Microresonator

A tightly focused radially polarized laser beam forms an unusual bimodal held distribution in an optical lambda/2-microresonator. We use a single-molecule dipole to probe the vector properties of this field distribution by tuning the resonator length with nanometer precision. Comparing calculated and experimental excitation patterns provides the three-dimensional orientation of the single-molecule dipole in the microresonator.