Power Balance and Temperature in Optically Pumped Spasers and Nanolasers

Spasers and nanolasers produce a significant amount of heat, which impedes their realizability. We numerically investigate the farfield emission and thermal load in optically pumped spasers with a coupled electro-magnetic/thermal model, including additional temperature discontinuities due to interfacial Kapitza resistance. This approach allows to explore multiple combinations of constitutive materials suitable for robust manufacturable spasers. Three main channels of heat generation are quantified: metal absorption at pumping and spasing wavelengths and nonradiative relaxations in the gain material. Out radiated power becomes comparable with absorption for spasers of realistic dimensions. Two optimized spaser configurations emitting light near 520 nm are compared in detail: prolate metal-core/gain-shell and an oblate gain-core/metal-shell. The metal-shell design, which with the increasing size transforms into a metal-clad nanolaser, achieves an internal light-extraction efficiency of 22.4%, and stably operates up to several hundred picoseconds, an order of magnitude longer than the metal-core spaser.