Abstract
We report on lasing at visible wavelengths in arrays of ferromagnetic Ni nanodisks overlaid with an organic gain medium. We demonstrate that by placing an organic gain material within the mode volume of the plasmonic nanoparticles both the radiative and, in particular, the high ohmic losses of Ni nanodisk resonances can be compensated. Under increasing pump fluence, the systems exhibit a transition from lattice-modified spontaneous emission to lasing, the latter being characterized by highly directional and sub-nanometer line width emission. By breaking the symmetry of the array, we observe tunable multimode lasing at two wavelengths corresponding to the particle periodicity along the two principal directions of the lattice. Our results are relevant for loss-compensated magnetoplasmonic devices and topological photonics.
Highlights
Plasmonic resonators and cavities provide small mode volumes and ultrafast light−matter interactions at the nanoscale
Periodic arrays of metallic nanoparticles support collective surface lattice resonances (SLRs) that originate from radiative coupling of lossy single particle plasmon resonances with lowloss diffracted orders (DOs) of the lattice.[32−37] In optical transmission spectra, the DOs of an array appear as maxima at λ ≈ np, where n is the refractive index of the surrounding medium and p is the particle periodicity
The gain medium consisting of 35 mM Rhodamine 6G (R6G) in 1:2 dimethyl sulfoxide (DMSO)/benzyl alcohol (BA) was inserted between the substrate with Ni nanodisk arrays and a cover glass
Summary
Plasmonic resonators and cavities provide small mode volumes and ultrafast light−matter interactions at the nanoscale. Hybridized Fano-like SLR modes reduce the signal, causing minimum transmission at a wavelength that deviates from the DO.[33−37] Despite the plasmonic component, SLRs in arrays of noble metal nanodisks have narrow line widths that can be utilized in lasing[13−17,19,20,22] and Bose−Einstein condensation.[38] Recently, it was demonstrated that collective SLR modes can be excited in arrays of higher-loss ferromagnetic nanoparticles.[39,40]. Reduced line widths provided by the SLRs together with a carefully optimized lattice geometry and gain medium produce lasing at visible wavelengths, despite the broad plasmonic resonances of the individual nanodisks. We observe lasing at two wavelengths corresponding to λ ≈ n × pi for different particle periodicities (px and py) along the two principle axes of the lattice
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