Orbital rotation of nanoparticles in a single Gaussian beam driven by converted orbital angular momentum

Particles trapped in optical beams can undergo orbital rotations at the micro/nano-scale and thus find applications in constructing micro-motors/machines, advancing the investigation of micro-rheology, etc. Rather than using the doughnut beams, here we report the orbital rotation of particles in a single Gaussian beam at the wavelength scale. By involving the transverse scattering forces of the light beam in the off-focal plane, the off-axis trapping of nanoparticles is possible and a rotation orbit has been built with small radius even less than the wavelength. Through focusing the incident Gaussian beam with circular polarization, there is the orbital angular momentum converted from the spin angular momentum, and the orbital angular momentum can then drive the particles to undergo orbital rotation. By changing the position of the offfocus plane, the rotation radius and speed can be tuned. The orbital rotation scheme with simple and flexible setup here can find applications in micro-motors and micro-machines.