Nonlinear microscope objective using thin layer of organic dye for optical tweezers

The microscope objective for optical tweezers requires a high resolving power and a large numerical aperture. For these purposes, the oil immersion objective can be improved. However, the index of the oil immersion objective and glass cover-slip must be matched resulting in a limit to enhance numerical aperture, and then optical trap efficiency. The optical trap efficiency can be enhanced by using a thin layer of organic dyelike an added nonlinear lens. To improve the resolving power and the optical trap efficiency of nonlinear tweezers, a thin layer of organic dye glued by microscope objective like the nonlinear microscope objective is proposed in this paper. The explicit expressions of the focal length, numerical aperture, axial optical trap efficiency of nonlinear microscope objective are theoretically derived. Some interesting properties of particular nonlinear microscope objective used like nonlinear optical tweezersare numerically observed. The obtained results show that the numerical aperture and optical trap efficiency are significantly improved. Our proposed nonlinear microscope objective has advantages such as more compact and smooth focal shift in the range of micrometers suitable to stretch DNA molecules in comparison with the previous ones. Graphical abstract