ABSTRACT
Optical force has opened up the unique possibility of manipulating objects of micro-/nanoscale sizes by means of light. A typical application of optical forces is the so-called optical tweezer that was discovered by Ashkin in 1971. Plasmon-assisted optical forces can be discussed in two slightly different categories: with and without a focused laser beam that provides additional gradient force from the laser itself. In nanostructures that support surface plasmons, an enhanced electromagnetic (EM) near field is induced under resonant excitation, leading to a series of interesting applications in surface-enhanced spectroscopy and sensing. For propagating surface plasmons, the scattering force is also an interesting component to study—it pushes the trapped particle to move along the propagation direction. For near-field-coupled metal nanoparticles, the optical force is enhanced because of the enhanced EM field gradient. Due to the larger polarizability, metal nanoparticles experience much higher optical forces, including the gradient, scattering, and absorption forces.
