Tuning the Stiffness Asymmetry of Optical Tweezers via Polarization Control

We report an experimental demonstration of tailoring the landscape of the optical potential by using the polarization state of a trap laser beam as a tuning knob. Two groups of polystyrene spheres, i.e., 300 nm and 1 μm, are optically trapped individually to investigate the effect of the intrinsic and a strongly-modified optical field distribution on the resulting trap stiffness, respectively. The angular variations of the orthogonal pair of stiffnesses, kx and ky, with the polarization state of the trap laser beam were systematically analyzed, and the results show that polarization control could provide a wide tuning range of trap-stiffness asymmetry (sT = 1 − kx/ky). The implication of asymmetry control of the optical potential is briefly discussed.