The all-optical trapping of microscopic particles has a range of practical applications in biology, physical chemistry and condensed matter physics. The optical tweezing of transparent particles relies on counterbalancing the scattering and gradient force. However, absorbing particles in gaseous and liquid media are mainly affected by the photophoretic force that can exceed the scattering and gradient force by orders of magnitude. In most cases, the photophoretic force pushes the particles away from the regions of maximum light intensity, thus precluding optical trapping and manipulation with conventional Gaussian beams. Only recently, by employing hollowcore vortex beams, has the very possibility of photophoretic trapping and guiding of lightabsorbing particles along the beam axis in air been demonstrated.
© 2012 Optical Society of AmericaPDF Article