Intensity-dependent frequency shift in surface plasmon amplification by stimulated emission of radiation

The operation of a surface plasmon amplification by stimulated emission of radiation-(spaser)-based nanolaser is theoretically investigated. We find that the lasing frequency undergoes a shift as the lasing intensity increases, a result that agrees with recent experiments. We show that the mechanism of the intensity-dependent shift involves a spatial deformation of the lasing mode, which is induced by the spatial hole burning in the surrounding gain media. We develop a general analytical scheme to account for the mode deformation. Our numerical calculations demonstrate good correspondence of the lasing frequency shift with the experimental data for the simplest (spherical) geometry of the spaser.