Nanoparticle trapping and control in a hollow whispering gallery resonator

In this work, hollow whispering gallery resonators with thin walls are filled with a water solution containing 500 nm nanoparticles. The quasi-droplet modes of the hollow resonator create an optical scattering force which pushes the particles around with velocities far exceeding 1.2 mm/s. The optical modes are observed to shift up to tens of GHz in the presence of the nanoparticle. By using counter propagating modes, the position and direction of the particles are controlled, this is the first time trapping and control of nanoparticles has been demonstrated in a quasi-droplet micoresonator.