Unidirectional spaser in symmetry-broken plasmonic core-shell nanocavity

Area of Science:

• Quantum optics
• Plasmonics
• Nanophotonics

Background:

• Spasers are coherent light sources utilizing surface plasmons for subwavelength optical field confinement.
• Controlling the directionality of spasing, particularly in single-particle nanocavities, remains an underexplored area.
• Plasmon resonance is the sole source of optical feedback in single-particle spasing nanocavities.

Purpose of the Study:

• To numerically investigate the directionality of emission from an asymmetric spaser.
• To explore the potential of symmetry breaking in spaser design for enhanced performance.
• To examine the spasing efficiency of a novel core-shell nanocavity configuration.

Main Methods:

• Numerical examination of an asymmetric spaser model.
• Utilizing a resonant system with a dielectric core and a metal semishell cap.
• Analyzing optical feedback solely through plasmon resonance.

Main Results:

• The asymmetric spaser exhibits unidirectional emission along the semishell axis.
• Emission directionality is independent of incident pump polarization and angle.
• Spasing efficiency is enhanced by an order of magnitude compared to closed core-shell structures.

Conclusions:

• Symmetry breaking is a viable strategy for designing unidirectional spasers.
• The proposed asymmetric spaser acts as a highly intense, single-particle coherent light source at the subwavelength scale.
• This work offers a new route for controlling light at the nanoscale.