Polarization and particle size dependence of radiative forces on small metallic particles in evanescent optical fields. Evidences for either repulsive or attractive gradient forces.

We have observed the motion of metallic particles above various optical waveguides injected by 1064nm radiation. Small gold particles (250nm diameter) are attracted towards the waveguide where the intensity of the optical field is maximum, and are propelled at high velocity (up to 350mum/s) along the waveguide due to radiation pressure. The behaviour of larger metallic particles (diameter >600nm) depends on the polarization of the evanescent field: for TM polarization they are attracted above the waveguide and propelled by the radiation pressure; for TE polarization they are expelled on the side of the waveguide and propelled at much smaller velocity.

Optical manipulation of microparticles and cells on silicon nitride waveguides.

We demonstrate the optical manipulation of cells and dielectric particles on the surface of silicon nitride waveguides. Glass particles with 2microm diameter are propelled at velocities of 15microm/s with a guided power of 20mW. This is approximately 20 times more efficient than previously reported, and permits to use this device on low refractive index objects such as cells.