Simulating the Exerted Force on Nanoparticles in Optical Tweezers

Optical tweezers are the real realization of the dream of interaction between light and matter and they are an optical trap that enable the trapping and manipulation of nanometer-sized particles using a laser. In this study, we theoretically investigate the force exerted on the particles using optical forceps, which is decomposed into two components: the scattering force (Fs) in the direction of the beam propagation and the gradient force (Fg) in the direction of the beam intensity gradient. In the following, we will see the described forces by simulating the finite element of a single beam optical forces with the FDTD module of Lumerical software. According to the obtained results, with the increase of the refractive index of the medium, the force exerted on the particle also increases. In the examined sample, when the refractive index of the environment is more than 1.8, the applied force increases significantly. We also check the changes in force compared to the changes in particle size and observe that in the studied sample, particles with a radius of 40 to 70 nm can be easily moved or trapped with single beam optical tweezers. When the radius of the target particle is less than 30 nm, the applied force tends to zero.