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Revealing plasmonic-photonic interaction via single-particle microresonator spectroscopy and tailoring weak-to-strong coupling
- 1. 1 Feng Pan Department of Chemistry University of Wisconsin Madison Group: https://goldsmith.chem.wisc.edu/ Revealing Plasmonic-Photonic Interaction via Single-Particle Microresonator Spectroscopy and Tailoring Weak-To-Strong Coupling Email: fpan22@wisc.edu APS March Meeting 2020 March 2-6 Denver, CO
- 2. 2 Localized surface plasmon (LSP) = electron cloud Au nanorod (AuNR) Longitudinal dipolar mode wikipedia Plasmonic-Photonic Cavity Low Q factor (~10) Ultrasmall mode volume (10^-6 λ3) Electron cloud oscillation Photonic cavity Lončar, M. Appl. Phys. Lett. 2009, 94, 121106. Heylman, K.D. et al. Adv. Mater. 2017, 29, 1700037 High Q factor (up to 108) Tunable mode volume (down to λ3)
- 3. 3Baaske et al Nat. Photon., 2016, 10, 733 Why Plasmonic-Photonic Cavity? Label-free sensing Low Q factor (~10) Ultrasmall mode volume (10-6 λ3) High Q factor (up to 108) Tunable mode volume (down to λ3) Plasmonic cavity Photonic cavity Can plasmonic-photonic cavity inherit some characteristics? Hybrids win!!! Strong light-matter interaction Applications Cavity quantum electrodynamics Single photon sources Enhanced Raman spectroscopy … Higher Purcell factor? Koenderink, A.F. et al. Nanophotonics 2019, 8, 1513
- 4. 4 Our Plasmonic-Photonic Cavity Whispering-gallery-mode (WGM) microresonator Au nanorod (AuNR) Q factor 106-107 (@~1550 nm) ~14 (@~1320 nm) Mode volume ~300 μm3 ~10-6 λ3 Heylman, K.D. et al. Nat. Photonics 2016, 10, 788 Plasmonic-photonic interaction
- 5. 𝟐𝝅𝑹 ∗ 𝒏(𝑻) = 𝒎 ∗ 𝝀 Silicon 10 µm Silica Silicon 10 µm How do we study it? Toroidal Optical Microresonator Absorption Spectrometer APL, 2013 JPCL, 2014 Adv. Mater. 2016 Nat. Photonics, 2016 Nano Lett. 2017 Δλ Nano Lett. 2018 Opt. Expr. 2018 APL 2018 Nano Lett. 2019 Δλ 𝒒 𝝈 Comsol simulation resonance shift Dissipated heat from target Excitation intensity Cross section Oxide-on-silicon 5
- 6. AuNR Absorption Spectrum • High resolution scan yields strange results 𝜔1 𝛾1 𝜔0 𝛾0 Heylman, K.D. et al. Nat. Photonics 2016, 10, 788 Fano resonances 6
- 7. 7 What does the absorption spectrum inform us? RLC circuit analog ω0 ω1 γ0 g 𝜔0 = 1/ 𝐿0 𝐶0 𝜔1 = 1/ 𝐿1 𝐶1 g What else?
- 8. 8 Pan F.*, Smith K.C.*, et al. Nano Lett. 2020, 20, 50 (Cover article) Tracing energy pathways in a plasmonic-photonic cavity
- 9. Coupled oscillator model Observables 𝜎abs 𝜎abs 0 = 𝛾0,NR 𝛾0,NR 𝐹 𝜔 𝜎scat 𝜎scat 0 = 𝛾0,Rad 𝛾0,Rad 𝐹 𝜔 𝜎ext 𝜎ext 0 = 𝛾0,Tot 𝛾0,Tot 𝐹 𝜔 WGM-dressed LSP damping rate 𝐹 𝜔 = 𝑞F + 𝜖 𝜖 + 𝑖 2 𝜎T = 𝛾1,Fib 𝛾1,Tot 1 − 𝛾0,Tot 𝛾0,Tot 𝜎ext 𝑚 𝑥 + 𝑚𝛾0,NR 𝑥 + 𝑚𝜔0 2 𝑥 + 𝑔 𝑚 𝑉 𝑞 = 2𝑒2 3𝑐3 𝑥 + 𝑒𝐸ext 𝑒−𝑖𝜔𝑡 1 𝑉 𝑞 + 1 𝑉 𝛾1,NR + 𝛾1,Rad + 𝛾1,Fib 𝑞 + 1 𝑉 𝜔1 2 𝑞 − 𝑔 𝑚 𝑉 𝑥 = 0 LSP WGM Fano line shape function 9 LSP damping LSP radiation force WGM damping rates These two are experimental observables Equations of Motion Pan F.*, Smith K.C.*, et al. Nano Lett. 2020, 20, 50 (Cover article)
- 10. Simultaneous fits 10 Pan F.*, Smith K.C.*, et al. Nano Lett. 2020, 20, 50 (Cover article)
- 11. ℏ𝜔0 (eV) ℏ𝜔1 (eV) ℏ𝛾0,NR (𝑚eV) ℏ𝛾0,Rad (𝑚eV) ℏ𝑔 (𝑚eV) ℏ𝛾1,NR (𝜇eV) ℏ𝛾1,Rad (𝜇eV) ℏ𝛾1,Fib (𝑛eV) Mean 0.9326 0.9426 62.20249 5.293 0.332 1.74 0.18 26 S.D. 0.0001 0.0002 0.00009 0.002 0.004 0.04 0.02 1 Determining all system parameters Spanning 9 orders of magnitude! 11 Pan F.*, Smith K.C.*, et al. Nano Lett. 2020, 20, 50 (Cover article)
- 12. Contribution from individual system parameters • LSP nonradiative dissipation is dominant regardless of observables • WGM-character dissipations gain more weight in transmission 12 Pan F.*, Smith K.C.*, et al. Nano Lett. 2020, 20, 50 (Cover article)
- 13. 13 Tailoring weak-to-strong coupling (ℏg∼10−4 eV, ℏγ0,Tot∼10−2 eV, ℏγ1,Tot∼10−6 eV) Ω ∝ 𝑔 ∗ 𝑁 • Multiple LSPs interact with a common WGM • LSP-WGM coupling: mode overlapping Dicke effect Armani A. et al. Opt. Lett. 2010, 35, 459 Polymer matrix
- 14. 14 0 µm 0.2 µm 0.4 µm 0.8 µm 1.0 µm 1.5 µm 2.0 µm 3.0 µm Li, B. et al. APL, 2010, 96, 251109 Simulation • Coating thickness is controllable, i.e. g is tunable • g can be scaled by up to 50 times according to numerical simulation PDMS (index-matching material) Drawing out WGM electromagnetic (EM) field Coating microresonators with PDMS Advantages IncreasingPDMSthickness EM field maximizes at the interface
- 15. PDMS droplet coating (Demo) 15 More results to come!
- 16. 16 Acknowledgements Collaborators: Kevin Smith, Niket Thakkar, David Masiello (UWashington) Prof. Randall Goldsmith Goldsmith Group Members: Dr. Hoang Nguyen Dr. Kassandra Knapper Dr. Kevin Heylmen Dr. Erik Horak Morgan Rea NSF-CHE NSF-DMR NSF-IDBR
Editor's Notes
- Cannot be achieved by microcavities alone.
- In our technique, we’re doing absorption on a toroidal microresonator, which is made of a silica disc and silicon pillar. This type of resonator has a very quality factor which allows light to propagate within it millions of times. Along with small mode volume, this device is very powerful for label-free detection and SM measurements. How do we measure absorption? Specifically, when a tapered optical fiber is brought very close to the resonator, light of wavelength meeting the resonant condition will be coupled into the resonator. If we measure the transmission of light through the fiber, a transmission dip will show up. When there is an object sitting on the toroid and being excited by a free-space pump beam, the excited species will dissipate the heat to local environment, i.e. the resonator, changing the refractive index and shifting the resonance. Using the res shift as a probe, we can calculate how much heat is being dissipated and then divide it by the power density, which is the abs cross section.
- Shape of the fano seems to depend on the part of the spectrum we examine. So we see peaks go up and down. We also only see these weird lineshapes, called fano resonance, when the object is on the outer rim of our toroid, where the WGM and the object can interact most strongly.