Micromanipulation with Bessel beams: Studies of angular momentum and reconstruction

Bessel beams have a number of properties that make them useful for optical manipulation. These include a central core which does not diffract over a characteristic distance, the reconstruction of the cross sectional intensity around obstacles and the ability of the beams to possess orbital angular momentum. Here we examine the utility of the Bessel beam to quantitatively examine the transfer of spin and orbital angular momentum to particle trapped away from the beam axis. We show the simultaneous transfer of orbital and spin angular momentum to an off-axis particle. We experimentally study how both the spin and orbital angular momentum of light behaves upon passage through microscopic optically trapped particles. Particles trapped with Gaussian and, separately, Bessel light beams in two spatially distinct sample chambers are studied with trapped objects in the first chamber acting as distorting obstacles. We examine the differences between Bessel beams and Gaussian beams in such experiments. We also show how the Bessel beam can be used to simultaneously trap particles that can be as much as 1cm away from each other. We discuss applications of these results and suggest other topics where the Bessel beam may be of use.