Abstract
We study the effect of nanoparticle (NP) array spacing on plasmon-enhanced lasing using a computational model that combines classical electrodynamics for arrays of gold NPs interacting with a four-level model of the laser dye photophysics. Parameters of the model are related to a laser system that was recently demonstrated experimentally, but in this work we consider arrays that tune away from the lattice plasmon resonance condition. We show that approximate matching of the lattice plasmon with the red branch of the dye emission spectrum leads to lower laser thresholds and higher intensities than can be achieved with plasmon excitation that does not satisfy the Bragg condition, even for anisotropic NPs. Surprisingly, there is a range of lattice spacings where both purely photonic enhancement of the bulk dye simulated emission and mixed photonic/plasmonic enhancement of emission by dye molecules within 50 nm of the NPs have comparable laser thresholds and intensities above threshold. We also show there is a tradeoff between sharpness of the lattice plasmon and overlap of the lattice mode with the dye emission maximum such that the highest intensity modes are not necessarily those with the highest plasmon enhancement.
© 2015 Optical Society of America
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