Wavevector distribution of metal photoluminescence from a gold film coupled microsphere antenna

Abstract

Herein we report wavevector distribution of metal photoluminescence (PL) from a hybrid metallo-dielectric optical antenna. We utilize microsphere coupled to a metal film as a prototypical system to understand the directionality of the coupled metal PL. Individual microspheres of size 5 μm coupled to 100 nm thick gold film were excited by 532 nm laser and the PL was collected and analyzed in the Fourier space. The metal PL was enhanced due to the large electric field at the metal-microsphere interface, thanks to the photonic nanojet effect of the microsphere. The metal PL outcouples to a narrow range of wavevectors through the whispering gallery modes of the microsphere and was confined to an angular spread of 21.1°. We also investigate the effect of different sizes of microsphere on the directionality of the emission. Our results provide an interesting connection between the directionality of the metal PL and the generated whispering gallery modes of the microsphere. The results were supported by finite element method based numerical simulations. We anticipate that these results will impact the design of efficient microresonators and metallo-dielectric antennas.