Plasmon-assisted optical trapping and anti-trapping.

Area of Science:

• Optics and Photonics
• Nanotechnology
• Surface Science

Background:

• Focused laser beams enable manipulation of small objects for scientific investigation.
• Nanophotonic and plasmonic structures enhance optical trapping through confined near-fields.
• Interactions between excitation fields, scattered fields, and structural eigenmodes yield unique optical effects.

Purpose of the Study:

• To investigate particle trapping by laser light near metal surfaces.
• To explore the role of surface plasmon excitation in tailoring optical forces.
• To analyze a novel plasmon-assisted anti-trapping effect for particle sorting.

Main Methods:

• Utilizing focused laser beams for optical trapping near metal surfaces.
• Investigating the influence of surface plasmon excitation at metal substrates.
• Analyzing the effects of beam focus position relative to the metal-dielectric interface.
• Developing analytical theory to understand electromagnetic channels and optical forces.

Main Results:

• Achieved order-of-magnitude enhancement or reduction in optical trap stiffness compared to glass substrates.
• Demonstrated particle trapping near metal surfaces, with surface plasmons playing a key role.
• Predicted and studied a novel plasmon-assisted anti-trapping effect (particle repulsion).
• Analyzed a highly accurate particle sorting scheme based on the anti-trapping effect.

Conclusions:

• Surface plasmon excitation significantly tailors optical forces for particle manipulation near metal surfaces.
• The developed analytical theory provides guidelines for designing nanostructures for precise nanoscale motion control.
• The novel anti-trapping effect offers a new mechanism for advanced particle sorting applications.