Computational study of radiation torque on arbitrary shaped particles with MLFMA

Area of Science:

• Computational electromagnetics
• Optical forces and torques
• Nanophotonics and plasmonics

Background:

• Radiation torque is crucial for manipulating small particles using light.
• Accurate computation of radiation torque on non-spherical particles is challenging.
• Existing methods often rely on approximations that limit accuracy for complex geometries.

Purpose of the Study:

• To develop and validate a rigorous computational method for calculating radiation torque on arbitrarily shaped homogeneous particles.
• To enhance the efficiency and capability of the surface integral equation (SIE) method using the Multilevel Fast Multipole Algorithm (MLFMA).
• To demonstrate the method's applicability to complex particle shapes and large size parameters.

Main Methods:

• Utilizing the surface integral equation (SIE) method for electromagnetic scattering analysis.
• Implementing the Multilevel Fast Multipole Algorithm (MLFMA) to accelerate SIE computations.
• Solving iterative matrix equations to obtain equivalent electric and magnetic currents.
• Computing radiation torque using near-field analytical expressions for incident waves.

Main Results:

• The developed SIE-MLFMA method accurately predicts radiation torque for various non-spherical particles.
• The method is validated for particles with size parameters up to 650.
• Demonstrated capability in calculating radiation torque on complex shapes like ellipsoids, cell-like particles, and motors.

Conclusions:

• The SIE-MLFMA method provides a rigorous and efficient approach for computing radiation torque on complex particles.
• The method overcomes limitations of far-field approximations, ensuring accuracy for incident beams.
• This work enables precise prediction of optical forces for advanced particle manipulation and characterization.