Optical spin-to-orbital plasmonic angular momentum conversion in subwavelength apertures

Area of Science:

• Plasmonics
• Optics
• Nanophotonics

Background:

• Surface plasmons (SP) are collective electron oscillations at metal-dielectric interfaces.
• Controlling SP modes is crucial for nanophotonic devices.
• Angular momentum transfer in light-matter interactions is a key phenomenon.

Purpose of the Study:

• To investigate the coherent superposition of surface plasmon modes.
• To analyze the excitation of SPs by circularly polarized light through subwavelength holes.
• To understand the formation of phase singularities and angular momentum transfer.

Main Methods:

• Utilizing the Huygens-Fresnel approach for theoretical analysis.
• Simulating the propagation of circularly polarized light through an array of subwavelength holes.
• Evaluating the resulting plasmonic field distribution and phase structure.

Main Results:

• Observed a rich structure in the plasmonic distribution.
• Revealed the creation and annihilation of vortex arrays in the field phase.
• Demonstrated total transfer of spin angular momentum (AM) to orbital AM of SPs.

Conclusions:

• The study elucidates the complex interplay between light polarization and surface plasmon excitation.
• Phase singularities in SP fields arise from efficient angular momentum transfer.
• This work provides insights into controlling light at the nanoscale.