Optical characterization and selective addressing of the resonant modes of a micropillar cavity with a white light beam

We have performed white light reflectivity measurements on GaAs/AlAs micropillar cavities with diameters ranging from 1 μm up to 20 μm. We are able to resolve the spatial field distribution of each cavity mode in real space by scanning a small-sized beam across the top facet of each micropillar. We spectrally resolve distinct transverse-optical cavity modes in reflectivity. Using this procedure we can selectively address a single mode in the multimode micropillar cavity. Calculations for the coupling efficiency of a small-diameter beam to each mode are in very good agreement with our reflectivity measurements.