Theoretical study on optical force on coupled chiral particles

Abstract

The main purpose of this report is to develop a theoretical understanding of the scattering of light by a pair of chiral particles under the incidence of a time-harmonic electromagnetic plane wave in the Rayleigh regime, where a particle can be approximated as an oscillating electric dipole.1 We present the method to determine the optical force on the particle using multipole expansion that gives the dipole moments induced in the particle.2 This method is useful in understanding the intricate physics behind the optical force as it breaks down the force contribution by the irreducible dipoles. The optical force can also be evaluated numerically using the Maxwell stress tensor method which can be used to verify the results of the analytical method.3 Lastly, we show that the structural chirality of the particles gives rise to interesting behaviour in the optical binding forces of the particles, where the particles of the same handedness exhibit electric and magnetic dipole of the same sign, but different signs when it comes to particles of the opposite handedness.