Calculation of the optical force on dielectric nanoparticles by FDTD method

Abstract

The optical forces can be used to manipulate the particles whose dimensions ranging from some tens of nanometers to larger than a hundred nanometers. An electromagnetic wave exerting force on a metal particle at the wavelength far from the particle's plasmon resonance wavelength resembles trapping high refractive index dielectric particle. When designing the optical trapping experiments, we must consider the power of the incident light, the optical force produced by the incident light and the size of the particle being manipulated. The trapping of dielectric nanoparticles was studied with numeric simulation of Finite-Difference Time-Domain (FDTD) method. We use the total-field/scattered-field consistency boundary approach in FDTD method to simulate the focused incident beam interacting with the dielectric particles. The ten-cell-thick uniaxial perfectly matched layer (UPML) absorbing boundary condition is introduced to simulate the extension of the computation domain to infinity. The result field distributions in FDTD then are substituted into the Maxwell stress tensor to calculate the optical forces. The numeric simulation demonstrates the possibility of trapping dielectric particles transversely whose radii are comparable to wavelength.