Plasmonic lasing in highly lossy nanocylinder arrays under optical pumping

This paper presents both theoretical and numerical evidence of surface plasmon amplification by stimulated emission of radiation (SPASER) in a highly lossy periodic array of gold nanoparticles. The system consists of a series of metallic nanocylinders that support a localized surface plasmon mode with poor quality (large spectral bandwidth and high losses), covered by a gain slab. Our study aims to determine the feasibility and fundamental properties of lasing in this system. We found that laser based on such very high lossy nanostructures requires higher concentration of gain (three times) and higher pumping energy (one order of magnitude) compared to lasing in a high-quality lattice plasmon mode, which is experimentally achievable. After optimizing the laser design, we focus on the system’s fundamental properties and show that the achieved laser mode is purely plasmonic and has no photonic features. We demonstrate that the far-field photons are mainly generated through a near-field coupling between the gain molecules and the nanostructure. We also investigate the dynamics of pumping, gain, and stimulated emission, and show that the surface plasmon is amplified and photons are emitted coherently in the far field when the maximum amplification is reached. The relaxation dynamics changes from nanoseconds below the threshold to picoseconds above it, reflecting an ultrafast energy exchange between the gain molecule and the plasmon. Finally, we highlight the key role of spontaneous emission in triggering this energy exchange. Our results support the concept of SPASER and provide new insights for the scientific community. Graphical abstract