Measuring the mode volume of plasmonic nanocavities using coupled optical emitters

Abstract

Metallic optical systems can confine light to deep subwavelength dimensions, but verifying the level of confinement at these length scales typically requires specialized techniques and equipment for probing the near field of the structure. We experimentally measured the confinement of a metal-based optical cavity by using the cavity modes themselves as a sensitive probe of the cavity characteristics. By perturbing the cavity modes with conformal dielectric layers of subnanometer thickness using atomic layer deposition, we find the exponential decay length of the modes to be less than 5$%$ of the free-space wavelength ($\ensuremath{\lambda}$) and the mode volume to be of order ${\ensuremath{\lambda}}^{3}$/1000. These results provide experimental confirmation of the deep subwavelength confinement capabilities of metal-based optical cavities.