Plasmonic Archimedes spiral for selective optical trapping and rotation of optically isotropic particles

摘要

Optical manipulation of small particles has long been challenging mainly due to reduced gradient force. Rotation of particles by light is even more difficult since that requires the particle to be absorbing or to exhibit large polarizability and optical anisotropy. Otherwise, the optical field has to carry orbital angular momentum. Recently surface-plasmon-enhanced optical near field has been used to effectively trap small particles. However, rotation and spinning of isotropic dielectric particles by light has not been demonstrated, not to mention a single device capable of multiple functions. Here, we report the first demonstration of selective trapping or rotation of isotropic dielectric micro-particles using one single plasmonic device, a plasmonic Archimedes spiral. Such functionality is of great interest and may find applications in various fields, such as protein folding analysis and local mixing in microfluidic channels.