Negative optical spin torque wrench of a nondiffracting non-paraxial fractional Bessel vortex beam

摘要

An absorptive Rayleigh dielectric sphere in a non-diffracting non-paraxialfractional Bessel vortex beam experiences a spin torque. The axial andtransverse radiation spin torque components are evaluated in the dipoleapproximation using the radiative correction of the electric field. Particularemphasis is given on the polarization as well as changing the topologicalcharge and the beam's half-cone angle. When the beam order is zero, the axialspin torque component vanishes. However, when the beam order becomes a realpositive number, the vortex beam induces left-handed (negative) axial spintorque as the sphere shifts off-axially from the center of the beam. Theresults show that a non-diffracting non-paraxial fractional Bessel vortex beamis capable to induce a spin reversal of an absorptive Rayleigh sphere placedarbitrarily in its path. Potential applications are yet to be explored inparticle manipulation, rotation in optical tweezers, optical tractor beams, thedesign of optically-engineered metamaterials to name a few areas.