Advanced micromanipulation using Bessel beams

Bessel beams can be used as optical tweezers, to trap and manipulate small particles, including biological specimens. Here we demonstrate the use of such beams to trap and manipulate particles simultaneously that may reside in completely separate sample chambers, separated by distances that preclude trapping with a Gaussian beam. This also demonstrates another property of the Bessel beam, in that since it is a set of rings it can trap both low and high refractive index particles. The distance behind the particle that the Bessel beam reconstructs is dependent on the properties of the particle, and this may be useful in cell characterisation. We also demonstrate the generation of more complex patterns of nondiffracting light beams, by using interfering Bessel beams. We generate these by using a Mach-Zender interferometer in which each of the arms has a Laguerre-Gaussian beam of differing handedness.