Large spontaneous emission enhancement in plasmonic nanocavities

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Abstract

Cavity–emitter coupling can enable a host of potential applications in quantum optics, from low-threshold lasers to brighter single-photon sources for quantum cryptography1. Although some of the first demonstrations of spontaneous emission modification occurred in metallic structures2,3, it was only after the recent demonstration of cavity quantum electrodynamics effects in dielectric optical cavities4 that metal-based optical cavities were considered for quantum optics applications5,6,7,8,9,10,11,12,13. Advantages of metal–optical cavities include their compatibility with a large variety of emitters and their broadband cavity spectra, which enable enhancement of spectrally broad emitters. Here, we demonstrate radiative emission rate enhancements approaching 1,000 for emitters coupled to the nanoscale gap between a silver nanowire and a silver substrate. A quantitative comparison of our results with analytical theory shows that the enhanced emission rate of gap-mode plasmons in our structures can yield high internal quantum efficiency despite the close proximity of metal surfaces.

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Figure 1: Gap plasmon nanocavity containing coupled emitters.
Figure 2: Spectral and temporal characteristics of cavity-coupled Alq3 fluorescence.
Figure 3: Theoretical emission rate and efficiency versus spacer thickness for a silver gap structure.
Figure 4: Cavity enhancement characteristics.

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Acknowledgements

The authors acknowledge support from the NSF/NSEC (NSF/PHY-06-46094), the use of NSF/NNIN facilities at Harvard University's Center for Nanoscale Systems, and the use of the HPC computer cluster at Harvard.

Author information

K.J.R. designed and performed experiments, analysed data and wrote the paper. T.L.L. designed and performed experiments and analysed data. S.Y.C. performed experiments. E.L.H. designed experiments, analysed data and wrote the paper.

Correspondence to Kasey J. Russell.

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The authors declare no competing financial interests.

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Russell, K., Liu, T., Cui, S. et al. Large spontaneous emission enhancement in plasmonic nanocavities. Nature Photon 6, 459–462 (2012) doi:10.1038/nphoton.2012.112

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