Solenoidal optical forces from a plasmonic Archimedean spiral

Area of Science:

• Nanophotonics and Plasmonics
• Microparticle Manipulation
• Optical Forces

Background:

• Plasmonic Archimedean spirals (PAS) are engineered nanostructures that interact with light.
• Understanding optical forces is crucial for manipulating micro- and nanoparticles.
• Circularly polarized light can induce complex force fields.

Purpose of the Study:

• To map and analyze optical forces generated by a right-handed PAS.
• To investigate the influence of excitation polarization handedness on force profiles.
• To provide an intuitive explanation for microparticle motion in PAS-generated force fields.

Main Methods:

• Utilizing a right-handed plasmonic Archimedean spiral (PAS).
• Employing circularly polarized light with varying handedness.
• Applying the Helmholtz-Hodge decomposition method to separate force components.
• Using vector field topology for visualization.

Main Results:

• The PAS exhibits switchable force profiles (trapping vs. rotating) based on excitation handedness.
• Helmholtz-Hodge decomposition quantifies solenoidal and conservative force components.
• Right-hand circularly polarized excitation generates significant solenoidal forces.
• The analysis aligns with numerical and experimental findings.

Conclusions:

• The study provides an intuitive framework for understanding optical forces from PAS structures.
• Decomposition of forces aids in predicting micro- and nanoparticle behavior.
• This analysis offers a computationally efficient approach for designing lab-on-a-chip systems.