Abstract
An interaction between a light field with complex field spatial distribution and a micro-particle leads to forces that drag the particle in space and may confine it in a stable position or a trajectory. The particle behavior is determined by its size with respect to the characteristic length of the spatially periodic or symmetric light field distribution. We study theoretically and experimentally the behavior of a microparticle near the center of an optical vortex beam in a plane perpendicular to the beam propagation. We show that such particle may be stably trapped either in a dark spot on the vortex beam axis, or in one of two points placed off the optical axis. It may also circulate along a trajectory having its radius smaller or equal to the radius of the first bright vortex ring.
Highlights
An optical force arises from the interaction between light and a microparticle as the result of light scattering by the microparticle
We identified three different regimes of particle behavior: the particle can orbit along the high intensity ring of the vortex beam, it can be stably localized at the dark spot placed on the vortex beam axis or at one of two points placed off the optical axis
For other parameters the coincidence is slightly worse for lower ρ0 where the radius of the innermost vortex beam ring is in the range of 1 to 3 wavelengths because small disturbances in the beam propagation cause intensity or phase inhomogeneities that are not considered in the theoretical description of the beam and cause differences between the predicted and the observed particle behavior
Summary
An optical force arises from the interaction between light and a microparticle as the result of light scattering by the microparticle. The experimental verification of the transfer of angular momentum upon a particle has been demonstrated by rotation of an absorbing particle in the dark center of the vortex beam [36, 37] or orbiting of microparticles around the beam axis in the high-intensity ring of the vortex beam [19, 38,39,40,41,42,43,44,45,46,47,48,49,50,51,52] Even though in these cases the sizes of such particles were comparable to the laser beam wavelength, no quantitative comparison between the theory and the experiment has been performed. We identified three different regimes of particle behavior: the particle can orbit along the high intensity ring of the vortex beam, it can be stably localized at the dark spot placed on the vortex beam axis or at one of two points placed off the optical axis
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