Pulsed EM Field Response of a Thin, High-contrast Layered ...

Pulsed EM Field Response of a Thin, High-contrast Layered ...

Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 Manipulating Electromagnetic Local Density of States by Graphene Plasmonics Presenter: Wei E.I. Sha Electromagnetics and Optics Lab Dept. of EEE, The University of Hong Kong, Hong Kong Personal Website: http://www.eee.hku.hk/~wsha/ Collaborators Dr. Yongpin Chen, University of Electronic Science and Technology Prof. Jun Hu, University of Electronic Science and Technology Prof. Li Jun Jiang, The University of Hong Kong Page 1 Dept. of Electrical and Electronic Engineering The University of Hong Kong

IMWS-AMP 2015 OUTLINE 1. Significance and History 2. Quantum Electrodynamics 3. Spontaneous Emission, Local Density of States, and Greens Tensor 4. Graphene Plasmonics to Control the Local Density of States 5. Conclusion Page 2 Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 WHY SPONTANEOUS EMISSION (DECAY) IS IMPORTANT? Control of spontaneously emitted light lies at the heart of quantum optics. It is essential for diverse applications ranging from lasers, light-emitting diodes, solar cells, and quantum

information. Purcell factor LED (photonic crystal cavity) M. Francardi et al. Appl. Phys. Lett. 93, 143102 (2008) Laser (metallic microcavity) C Walther et al. Science 327, 1495-1497 (2010) Page 3 Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 HISTORY OF SPONTANEOUS EMISSION RATE proportion to photon intensity Classical View:

Boltzmann statistics spontaneous emission: an exited atom/molecule decay to the ground state Page and4 emits a photon Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 THREE REGIMES IN OPTICS classical optics ray physics D>> nano-optics wave physics

D~ quantum optics quantum physics D<< At quantum regimes, the object size (<10 nm) is quite small compared to wavelength. In this situation, semi-classical Maxwell-Schrdinger system is required to describe the EM particle interaction. Moreover, if the number of photons is also quite small, Maxwells equations should be quantized. Page 5 Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 A MODERN INTERPRETATION: QUANTUM ELECTRODYNAMICS (1) Quantized form of Maxwell Equations

B E t D H J t B 0 D B A 2 0 Quantized Hamiltonian

eigenmodes wave-particle duality E A t 0 A non-interaction part interaction part Coulomb gauge wave function perturbation method could solve it! e: excited state of atom; g: ground state of atom; 0: no photon; 1: one photon Page 6

Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 A MODERN INTERPRETATION: QUANTUM ELECTRODYNAMICS (2) d | a (t ) |2 Spontaneous emission rate by Fermi golden rule dt Mode expansion of dyadic greens function Representation by Greens tensor Electromagnetic Local density of state (EMLDOS) Purcell factor Page 7

Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 GRAPHENE Atomic thickness; High optical transmittance and conductivity; Graphene Dynamically modify chemical potentials through tuning the gate voltage Graphite Carbon Nanotubes Fullerences (C60) Fabrication Physics World 19, 33 (2006) Page 8

Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 FORMULATIONS FOR GRAPHENE PERMITTIVITY Surface conductivity of Graphene given by Kubo formula Intraband Relaxation (plasmonic effect) Interband Transition (Be neglectable at THz frequencies) -Frequency, c-Chemical potential, -Carrier scattering rate and TTemperature; Where Fermi-Dirac distribution fd is Converts the surface conductivity to volume conductivity in modeling; Page 9 Dept. of Electrical and Electronic Engineering

The University of Hong Kong IMWS-AMP 2015 WHEN GRAPHENE IS APPLIED TO CONTROL SPONTANEOUS EMISSION Quantum Electrodynamics Spontaneous Emission Computational Electromagnetics Numerical Greens Function Low-Dimensional Materials Electrically Tunable Active Materials Page 10 Dept. of Electrical and Electronic Engineering The University of Hong Kong

IMWS-AMP 2015 GRAPHENE VS METAL FOR CONTROLLING SPONTANEOUS EMISSION sensitive to polarization sensitive to position tunable by chemical potential much larger enhancement than metals Page 11 Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 SPONTANEOUS EMISSION IN COMPLEX MULTILAYER NANOSTRUCTURE split ring + graphene

split ring only equivalent principle (PMCHWT) + multilayer Greens function Page 12 Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 PUBLICATIONS 1. Pengfei Qiao, Wei E.I. Sha, Wallace C.H. Choy, and Weng Cho Chew, Systematic Study of Spontaneous Emission in a Two-Dimensional Arbitrary Inhomogeneous Environment, APS, Physical Review A, vol. 83, no. 4, pp. 043824, Feb. 2011. 2. Yongpin P. Chen, Wei E.I. Sha, Wallace C.H. Choy, Li Jun Jiang, and Weng Cho Chew, Study on Spontaneous Emission in Complex Multilayered Plasmonic System via Surface Integral Equation Approach with Layered Medium Greens Function, OSA, Optics Express, vol. 20, no. 18, pp. 20210-20221, Aug. 2012. 3. Yongpin P. Chen, Wei E.I. Sha, Li Jun Jiang, and Jun Hu, Graphene Plasmonics for

Tuning Photon Decay Rate near Metallic Split-Ring Resonator in a Multilayered Substrate, OSA, Optics Express, vol. 23, no. 3, pp. 2798-2807, Feb. 2015. 4. Weng Cho Chew, Wei E. I. Sha, and Qi I. Dai, Greens Dyadic, Spectral Function, Local Density of States, and Fluctuation Dissipation Theorem, http://arxiv.org/pdf/1505.01586.pdf Page 13 Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 CONCLUSION 1. Graphene offers several flexible tuning routes for manipulating EMLDOS, including tunable chemical potential and the emitters position and polarization. It shows broadband enhancements of EMLOS compared to metal materials. 2. We study spontaneous emission rate of a quantum emitter near a metallic splitring resonator, which is embedded in a multilayered substrate incorporating a graphene layer. This design enables a mutual interaction between graphene plasmonics and metallic plasmonics. The boundary element method with a multilayered medium Greens function is adopted in the numerical simulation.

3. Strong plasmonic coupling with a switch on-off feature was observed, which is helpful to dynamically manipulate spontaneous emission rate in complex optical devices. Page 14 Dept. of Electrical and Electronic Engineering The University of Hong Kong IMWS-AMP 2015 THANKS FOR YOUR ATTENTION! Page 15

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