Hossein Gorjizadeh Alinezhad, Sajad Meydanloo, and S. Nader S. Reihani
Optical tweezers are indispensable force spectroscopes. The trap stiffness and the linear force range of the instrument determine the working force range of the instrument. Here we show both theoretically and experimentally that utilizing a circular obstruction at the back focal plane of the objective can significantly increase the maximum linear force. For instance, utilizing a disk with an obstruction ratio of 0.773 could increase the maximum linear force by a factor of ∼39 when a 3.4 μm polystyrene bead is trapped. We also show that this simple beam shaping method can significantly improve the maximum applicable force per unit power of the laser entering the objective lens.
DOI
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