Trapping of low and high refractive index nano-spherical particles by using a highly focused Laguerre-Gaussian beam.

We have investigated the trapping force on low and high refractive index nano-particles using a highly focused Laguerre-Gaussian beam. An analytical expression for the gradient force has been derived in closed form. It was clearly found that the increase of the beam mode p causes a substantial increase in the number of trapping zones, which frequently increases the number of particles to be captured simultaneously. Also, the decrease of p values would increase the trap area, which consequently leads to simultaneous trapping of multiple particles in the same area. The change of p , l , Δ n , and z 1 values has a direct influence on the gradient forces. The smaller values of scattering and thermal forces relative to the gradient force values represent essential conditions for the stability of the trapping performance.