Optical pulling force on a uniaxial anisotropic sphere by a high-order Bessel (vortex) beam

Area of Science:

• Optics and Photonics
• Soft Matter Physics
• Nanotechnology

Background:

• Optical manipulation relies on forces exerted by light on particles.
• Bessel beams offer unique properties for optical trapping, including extended depth of focus.
• Anisotropic particles present unique scattering and force interactions compared to isotropic ones.

Purpose of the Study:

• To theoretically investigate the axial radiation force (AOF) on a uniaxial anisotropic sphere illuminated by high-order Bessel vortex beams (HOBVBs).
• To explore conditions for realizing optical tractor beams capable of inverse motion for anisotropic spheres.
• To extend the understanding of optical pulling force (OPF) from isotropic to anisotropic spherical particles.

Main Methods:

• Utilizing generalized Lorenz-Mie theory (GLMT) and scattering theory for uniaxial spheres.
• Applying Maxwell's stress tensor to derive analytical expressions for AOF.
• Validating theoretical results by comparing with known cases (isotropic sphere, plane wave, Gaussian beam).

Main Results:

• An analytical expression for AOF on uniaxial anisotropic spheres by HOBVBs was derived.
• The study identified conditions for HOBVBs (l=2, 3) to act as effective tractor beams for anisotropic spheres.
• Optical pulling force on anisotropic spheres is significantly influenced by anisotropic parameters and topological charges, differing from isotropic spheres.

Conclusions:

• High-order Bessel vortex beams can induce inverse motion in anisotropic spheres, expanding their use in optical micromanipulation.
• The findings provide a theoretical basis for manipulating biological and complex anisotropic particles using optical tractor beams.
• Anisotropic parameters and beam characteristics critically affect optical pulling forces, offering new possibilities for particle control.