Minimal spaser threshold within electrodynamic framework: Shape, size and modes.

Area of Science:

• Plasmonics
• Quantum Mechanics
• Electromagnetism

Background:

• Spaser (Surface Plasmon Amplification by Stimulated Emission of Radiation) threshold gain is typically analyzed using quantum mechanical or energetic principles.
• These analyses often overlook the fundamental dependence of threshold gain solely on dielectric functions of metal and gain materials.

Purpose of the Study:

• To derive the threshold gain dependence on dielectric functions from a classical electromagnetic scattering framework.
• To demonstrate the simplicity and applicability of classical electrodynamics for spaser modeling.
• To separate the influences of material dispersion and spaser geometry on threshold gain.

Main Methods:

• Classical electromagnetic scattering theory.
• Derivation of threshold gain from scattering parameters.
• Inclusion of retardation effects.
• Analysis of plasmonic resonance and spectral gain.

Main Results:

• The threshold gain of quasi-static spasers is shown to depend only on the dielectric functions of the metal and gain material.
• Spaser geometry influences threshold gain indirectly by defining the resonant wavelength.
• A minimum threshold gain exists as a function of wavelength, independent of geometry.
• This minimum persists beyond the quasi-static limit when retardation is included.

Conclusions:

• Classical electrodynamic modeling offers a simpler alternative to quantum mechanical approaches for spaser analysis.
• Material properties fundamentally limit the achievable threshold gain.
• Nanoparticle geometry can optimize resonance but cannot surpass material-imposed gain limits.