Orbital angular momentum of a high order Bessel light beam

Summary form only given. We demonstrate experimentally for the first time, that a high order Bessel beam possesses orbital angular momentum (OAM). We demonstrate transfer of OAM from such a beam to trapped transparent particles in optical tweezers. Additionally, we examine theoretically, within a rigorous vectorial treatment, the local angular momentum density for a high order Bessel beam (HOBB) and find local variations in this density when compared to Laguerre-Gaussian beams. For transparent particles the orbital angular momentum is transferred by scattering/reflection of the incident light beam as in the case of metallic particles. Importantly we obtained quantitative results for the rotation rate which has a linear dependence on the orbital angular momentum content of the light beam. The measured rotation rates correspond to a transfer of about 1% of the Bessel beam's orbital angular momentum which is consistent with calculations based on a transfer mechanism due to scattering.