Laser-induced angular momentum of spheroidal metal nanoparticle in a medium

Abstract

A theory for the generation in a spheroidal metallic nanoparticle of an angular momentum under the action of ultrashort laser pulse is developed. We proposed the mechanism for generation of rotation force associated with nanoparticle polarization in the frequency region close to the surface plasmon resonances. Under illumination of the laser field the nanoparticle with an asymmetrical shape is polarized and becomes a dipole. The pair of electric field forces tends to turn the dipole along the field direction. As a result, the angular momentum arises. It is considered that the polarization becomes a tensor quantity for the nanoparticle sizes smaller than the electron mean free path in it. It is shown that the rotation direction can be controlled by varying the wavelength of the incident light. The expressions for the components of the polarization tensor and for the angular momentum of a spheroidal metal nanoparticle are obtained.