META 2021, META'12

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Dipolar and quadrupolar plasmon LASER modes for core-shell composites
Rémi Vincent, S. Derom, G. Colas des Francs

Last modified: 2011-12-05


Spasers are based on a combination of the localized plasmon field properties of the
metallic material with an amplification medium [1]. The optical properties of these compound
systems are based on a compensation of the metallic losses trough the optical gain of the
amplification medium. Recently it was demonstrated experimentally that coating a gold
nanoparticle with a silica shell containing Oregon Green 558 allows to overcome the loss-of-surface
plasmon resonance [2]. One of the consequences of the compensation of the losses is an extremely
large enhancement of the local field amplitudes (giant resonances). Rising the gain leads to a
singularity stricking the transition between amplified spontaneous emission (SE) to SPASING
regime [3,4,5]. Based on Mie Theory, the optical properties of the core-shell systems are
determined by the scattering coefficients. The poles of the Mie coefficients give the critical
resonances frequencies (!n ), and the critical value of gain ! ("n ) giving the SPASER threshold.
Based on the fact that dipolar and quadrupolar modes for spherical nanoparticle own high Purcell
factors [6], we analyze the critical gain values of these modes for two configurations: the metallic
core-gain medium shell nanoparticle and metallic shell-gain medium core nanoparticle. Finally, we
discuss the applications.