Keywords:Laser trapping, gold nanoparticles, light scattering
We report that a single large assembly with dynamically swarming gold nanoparticles is formed by laser trapping at a glass/solution interface. The component nanoparticles dynamically interact with each other keeping their long interparticle distance, and their movement looks like swarms of the nanoparticles. Two swarms are directionally extended outside the focal spot, and the assembly is arranged perpendicularly to the linear polarization like a radiation pattern of dipole scattering. On the other hand a doughnut shaped swarm is prepared by circularly polarized trapping laser. The light field is expanded as scattered light through the trapped nanoparticles, this modified light field further traps the nanoparticles, and scattering and trapping cooperatively develop. Due to these nonlinear dynamic processes, the dynamically fluctuating swarms are evolved up to few tens micrometer. This finding will open a way to create various swarms of nanoscale objects which are interacted and bound through scattered light depending on properties of laser beam and nanomaterials.