Optics and Photonics Society of Iran

Abstract- Optical Tweezers (OT) are powerful tools for understanding the physics of biological processes. This device can be used for force spectroscopy in the force range of femto-Newton to nano-Newton. In the most of the biological applications of OT for which, large forces are on demand cranking up the laser power would damage the sample. In such applications optimal trapping is very crucial. In this Paper we show that for a given bead size there would be an optimal numerical aperture for the focusing objective, which maximizes the trapping efficiency in the transvers direction. We also show that a polystyrene bead with a diameter of about 4 micrometer provides the largest transverse trapping efficiency. There is a very good compatibility between our theoretical and experimental results.