Three-dimensional optical manipulation of trapped light-absorbing particles based on a hollow beam

We report a method for optical trapping and three-dimensional manipulation of light-absorbing particles in air based on a hollow beam. The particles can be stably trapped for hours in the focused hollow beam with either horizontal or vertical trapping configuration. Particle revolution in the lateral plane (x-y plane) is achieved by employing a wedge prism to deviate and rotate the optical traps. And the particle movement along the laser propagating direction (z-direction) is realized by changing the size of the hollow trapping beam. The mechanism of particle trapping and manipulation in air is analyzed based on the characteristics of photophoretic force. As high trapping power is avoided, this method is meaningful for the particles of low damage threshold and provides a useful tool for in situ analysis of the single aerosol particle in a non-destructive and non-contact manner.