Abstract
The concept of spaser as the coherent near-field generator and nanolaser based on nanoscale plasmonic resonators has been successfully demonstrated in number of experiments. Here we have developed the theoretical framework for the basic linewidth description of these active plasmonic structures and, in particular, linewidth enhancement - additional line broadening due to the resonator noise. In order to achieve this, we have introduced explicitly the time dependence in the quasistatic description of localized surface plasmon resonances via inclusion of the dispersion of a spectral parameter defining the resonant frequency. Linewidth enhancement factor was estimated for semiconductor gain medium and was found to be of order of 3 to 6, strongly depending on carrier density in the active layer, and resulting in more than order of magnitude broader linewidth compared to that, predicted by the Schawlow-Townes theory.
Highlights
One of the most basic properties of a laser is its linewidth, which represents the measure of temporal coherence of the output beam
The physical dimensions of a laser are defined by its cavity, which generates optical feedback, based on constructive interference of propagating waves
Quasistatic description of localized surface plasmon resonances defining the “cavity” of a spaser does not include the radiation losses, causing underestimation of real thresholds, material losses are predominant for particles, less than 20 nm in dimensions
Summary
One of the most basic properties of a laser is its linewidth, which represents the measure of temporal coherence of the output beam. In order to investigate the spaser linewidth, we have introduced the time dependence via the dispersion of spectral parameter, defining the localized plasmon wavelength.
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