Optical steering of high and low index microparticles by manipulating an off-axis optical vortex

We demonstrate the use of a rotating off-axis optical phase singularity, generated through an intentional misalignment of a high optical efficiency spiral phase plate (SPP), to optically steer both high and low index microparticles trapped within the optical beam in a controlled manner. This intentional misalignment of the SPP creates an asymmetrical intensity beam pattern due to the optical vortex being displaced from the centre of the beam propagation axis. By using this optical beam pattern, we propose that a cell can be trapped by an optical beam of matching beam diameter while its internal structure can be manipulated by the off-axis optical vortex.