Three-dimensional orientation of single molecules in a tunable optical λ/2 microresonator

A tightly focused radially polarized laser beam forms an unusual bimodal field distribution in an optical λ/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. © 2010 American Chemical Society.