Characterization of trapping force on metallic mie particles.

Transverse trapping force on three types of metallic Mie particles (gold, nickel, and silver) is measured for different values of the numerical aperture of an objective used for trapping. The experimental results are compared with those calculated with a modified ray-optics model. It is found that, unlike the situation for a trapped dielectric particle, the maximum transverse trapping efficiency for a trapped metallic particle is increased with the numerical aperture of the trapping objective. After consideration of radiometric force, which is caused by the heating effect, and spherical aberration, which is induced by the refractive-index mismatch, the measured results agree well with the theoretical prediction. The magnitude of the radiometric force is approximately ten times stronger than the maximum transverse trapping force.