Reverse orbiting of microparticles in optical vortices

Area of Science:

• Optics and Photonics
• Soft Matter Physics
• Surface Science

Background:

• Optical trapping commonly utilizes light's orbital angular momentum (OAM) to manipulate particles.
• Particle shape is often assumed to be spherical or its influence on momentum transfer is neglected in optical trapping models.

Purpose of the Study:

• To investigate the behavior of particles trapped at an air-water interface under optical illumination.
• To explain the observed anomalous orbital motion of trapped particles.
• To highlight the role of particle shape in optical momentum transfer.

Main Methods:

• Experimental optical trapping setup at an air-water interface.
• Observation and analysis of particle trajectories.
• Theoretical modeling considering particle asymmetry and surface confinement.

Main Results:

• Particles trapped at the air-water interface exhibited retrograde orbits, moving opposite to the light's OAM.
• The observed motion is attributed to the interplay between asymmetric particle shape and confinement on the 2D interface.
• Particle shape significantly impacts momentum transfer, deviating from standard optical trapping predictions.

Conclusions:

• Asymmetric particle shape is a critical factor in optical trapping at interfaces.
• The findings challenge conventional assumptions in optical trapping, emphasizing the need to consider particle morphology.
• This work opens new avenues for controlling microparticle dynamics using tailored light-matter interactions at surfaces.