Generation and control of multiple Bessel beams for optical micromanipulation

In the area of optical micro-manipulations Bessel beams are well known for their unique properties such as non-diffracting propagation over a large area or their ability to reconstruct themselves after passing a disturbing obstacle. In this paper we demonstrate how the spatial spectrum phase modulation of such Bessel beam can be used for its precise three-dimensional position control or even splitting it in several parallel Bessel beams. Applying these features to a simple computer-driven interactive setup enabled us to guide selected particles between remote planes demonstrating the possibility of active sorting of micro-objects. In the case of two axially shifted co-axial Bessel beams a system of counter-propagating Bessel beams can be obtained using a mirror. The interference of such counter-propagating beams provide a standing-wave axial modulation of the field intensity. The position of this standing wave peaks can be controlled altering phase of one of the beams leading to the concept of an 'Optical conveyor belt' for transport of micro-objects. However, using a time-sharing between the two beams causes that the interference is suppressed, but their correct axial overlap assures a stable position for object confinement. This geometry can be used then for real-time interactive three-dimensional position control of several objects. Such light fields have broader applications, for example in two-photon processes in biophysics such as photoporation of living cells providing transport of modified DNA from surrounding medium inside the cell volume and consequent synthesis of fluorescent protein.