Behavior Analysis of a Gaussian Beam Optical Trap in the Rayleigh Regime.

Recently optical trapping has emerged as a very powerful tool for manipulating micro and nanometer sized particles. In this paper, we present a comprehensive study of the behavior of nanometer sized trapped particles in a Gaussian beam optical trap using Rayleigh model of trapping forces. Along with the working principle of an optical trap, the force equations in the Rayleigh regime have been derived considering focused Gaussian beam. Then numerical simulations are performed for a 30 nm particle with refractive index 1.57 considering water as the surrounding medium. We assume that the wavelength of the light source to be 850 nm easily obtainable from cheap GaAs-based vertical-cavity surface-emitting laser technology. When the light hits a particle, it influences the particle with two forces–the scattering force in the direction of propagation and the gradient force in the direction of gradient of light intensity. We explore the effects of particle size, refractive index of the particle, beam waist radius, position of the particle with respect to the trap center both on scattering and gradient forces. This analysis will be helpful for understanding optical manipulation of nanoparticles and designing suitable trap modules for nanoparticle manipulation.