Polarized Stimulated Emission of 2D Ensembles of Plasmonic Nanolasers

Abstract

Plasmonic nanolasers produce coherent light with wavelengths on a scale similar to their own or larger. In the past decade they have attracted intense interest, particularly from the emerging areas of integrated photonic circuits and biomedicine. Despite these capabilities, plasmonic nanolasers are still not completely understood, and this lack of understanding leads to confusing them with spasers and random lasers. Herein, the operation of pure spaser-based plasmonic nanolaser arrays is presented. For this, a monolayer of silver nanoparticles (NPs) affixed to a dielectric surface and covered with a fluorescent polymethyl methacrylate (PMMA)?coumarin solid composite is investigated. The input?output characteristic measured for the composites on a bare substrate (without Ag NPs) reveals that the emission at pump pulse energies above 2.4?mJ (at 355?nm excitation wavelength) stops growing, and instead is inhibited by saturation. In contrast, in such structures with Ag NPs an additional emission band pops up over a fluorescence background. It has a spectral width order of units of nanometers and its intensity grows faster than at lower pump pulse energies, revealing a nonlinear dependence of the input?output characteristic. The spaser-based lasing observed is completely linearly polarized and clearly directed as 45° from the substrate.