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Optical microresonators as single-particle absorption spectrometers

Nature Photonics volume 10, pages 788795 (2016) | Download Citation

Abstract

Optical measurements of nanoscale objects offer major insights into fundamental biological, material and photonic properties. In absorption spectroscopy, sensitivity limits applications at the nanoscale. Here, we present a new single-particle double-modulation photothermal absorption spectroscopy method that employs on-chip optical whispering-gallery-mode (WGM) microresonators as ultrasensitive thermometers. Optical excitation of a nanoscale object on the microresonator produces increased local temperatures that are proportional to the absorption cross-section of the object. We resolve photothermal shifts in the resonance frequency of the microresonator that are smaller than 100 Hz, orders of magnitude smaller than previous WGM sensing schemes. The application of our new technique to single gold nanorods reveals a dense array of sharp Fano resonances arising from the coupling between the localized surface plasmon of the gold nanorod and the WGMs of the resonator, allowing for the exploration of plasmonic–photonic hybridization. In terms of the wider applicability, our approach adds label-free spectroscopic identification to microresonator-based detection schemes.

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Acknowledgements

We thank M. Stolt and S. Jin for technical assistance with electron microscopy, A. Sheth for useful references regarding the statistical analysis and N. Eason (nipaeason.com) for graphic design contributions to this work. This work was partially supported by the NSF under award numbers DBI-1556241 and UW-MRSEC DMR-1121288 (R.H.G.), CHE-1253775 (D.J.M.), DGE-1256082 (N.T.), and DGE-1256259 (K.A.K.).

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Affiliations

  1. Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, USA

    • Kevin D. Heylman
    • , Erik H. Horak
    • , Kassandra A. Knapper
    •  & Randall H. Goldsmith
  2. Department of Applied Mathematics, University of Washington, Seattle, Washington 98195-3925, USA

    • Niket Thakkar
    •  & David J. Masiello
  3. Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA

    • Steven C. Quillin
    • , Charles Cherqui
    •  & David J. Masiello

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Contributions

K.D.H. and E.H.H. built the spectrometer and carried out the measurements and analysis with help from R.H.G. N.T., S.C.Q. and C.C. formulated the theoretical model and performed simulations with help from D.J.M. K.A.K. fabricated the resonators. K.D.H., N.T., R.H.G. and D.J.M. wrote the paper with contributions from all co-authors.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to David J. Masiello or Randall H. Goldsmith.

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https://doi.org/10.1038/nphoton.2016.217

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