Optical vortices generated by an S-waveplate enable tuning optical angular momentum without altering the intensity distribution. With the initial polarization state varying from linear to circular, the torque transferred to the trapped silica beads is gradually controlled. The continuous transition from the maximum rotation speed to zero without changing the trapping potential enables the study of complex tribological interactions. Vortices with tunable orbital angular momentum may allow precise control of particle rotation of any material types and bio-objects such as DNA molecules measuring not only linear but rotational response.

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