Wednesday, August 10, 2016

Theoretical and experimental studies on optical trapping using radially polarized beams

Zhehai Zhou, Yuling Zhang, Lianqing Zhu

Optical trapping using radially polarized beams is studied theoretically and experimentally. First the geometric ray model is introduced to calculate the trapping efficiencies, and simulation results using three kinds of pupil apodization functions are presented to disclose the influences of pupil apodization functions of incident beams on trapping efficiencies, which indicates the better trapping performances can be achieved by modulating the polarization and amplitude distributions of incident beams using designated pupil filters. Furthermore, the optical tweezers using radially polarized beams are built up based on an inverted microscope and a spatial light modulator (SLM), where better trapping efficiencies can be achieved. Yeast cells about 10μm in diameter are trapped and manipulated using the optical tweezers and the cells can be trapped stably and shifted along the tracks of the focusing spot, which can be programmed by a computer. In addition, the values of trap stiffness for different pupil apodization functions are measured at different laser powers based on the Boltzmann statistics method, which indicates the AL-types pupil apodization function is a better choice for general trapping and manipulation of cells.

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