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Circuit model of dipole-enhanced emission (Conference Presentation)
Author(s): Constantin R. Simovski
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Paper Abstract

Metal-enhanced fluorescence (MEF) is that enhanced by a localized surface plasmon. In the conventional scheme of MEF the RhB or other fluorescent molecules attached by Van-der-Waals forces to a plasmonic nanoparticle (PNP) form an array in which each element interacts separately with the PNP since the emission under the optical pumping is spontaneous (if we do not consider the case when the spaser generation threshold is achieved). This interaction is as a rule described in terms of the Purcell effect – the molecule at the fluorescence frequency is an electric dipole with very small dipole moment, which, however, induces a large resonant electric dipole in the PNP if the coupling is sufficient for the power transfer. The increase of the dipole moment, or, equivalently the increase of the radiative resistance of the quantum emitter is described by the radiative Purcell factor (the total Purcell factor corresponds to the increase of the effective resistance of the emitter, including the dissipative resistance). This concept of the Purcell effect introduced into nanophotonics by E. Yablonovich, however, did not comprise an equivalent scheme suitable for corresponding calculations. Purcell’s factor was calculated via the Green function until 2015 when our paper [1] was published. In the same year, this circuit model was extended to beyond the case of the weak near-field coupling (Purcell effect) and it turned out to be adequate for the description of the Lamb shift of the spectral maximum, of the Fano resonance, of the Rabi splitting of the fluorescence spectrum, and, finally, of the fluorescence quenching [2]. In fact, there is no physical difference does the resonance of the classical scatterer to which the quantum emitter is coupled result from the localized surface plasmon or from the Mie resonance of a dielectric particle. Therefore, the phenomenon of metal-enhanced or plasmon-enhanced fluorescence should unite with the electric or magnetic Mie resonance. The last case makes sense for chiral molecules and magnetic transitions. Thus, the effective circuit models the general phenomenon I call the dipole-enhanced emission. Besides the enhanced fluorescence, this term covers also conventional (without collective effects) schemes of surface-enhanced Raman scattering (SERS). The fundamental difference of the Raman scattering from the fluorescence is the robustness of the molecular vibration to the dipole-dipole coupling that is not capable to reshape the spectrum of the Raman signal. In this meaning, the interaction of the emitter with the resonant dipole keeps weak. Thus, in the equivalent circuit of SERS the emission of a molecule models by an effective current generator, whereas in the fluorescence the emission ability is an effective negative resistor. In the present report, I concentrate on the case of the weak coupling (Purcell effect) and consider only MEF. My goal is to show that the circuit model keeps ultimately simple for a core-shell PNP. Calculation of the circuit parameters does not require full-wave numerical simulations or numerical solution of any equations. The model is validated by a comparison with the literature data. References: 1. A.E. Krasnok, A.P. Slobozhanyuk, C.R. Simovski, S.A. Tretyakov, A.N. Poddubny, A.E. Miroshnichenko, Y.S. Kivshar, and P.A. Belov, Scientific Reports, vol. 5, 12956, 2015 2. C. Simovski, Photonics, vol. 2, 568-593, 2015

Paper Details

Date Published: 14 May 2019
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Proc. SPIE 11028, Optical Sensors 2019, 110280N (14 May 2019); doi: 10.1117/12.2522682
Show Author Affiliations
Constantin R. Simovski, Aalto Univ. (Finland)


Published in SPIE Proceedings Vol. 11028:
Optical Sensors 2019
Francesco Baldini; Jiri Homola; Robert A. Lieberman, Editor(s)

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