Improving the Performances of Optical Tweezers by Using Simple Binary Diffractive Optics

Abstract

Usually, optical tweezers for trapping atoms or nanoparticles are based on the focusing of a Gaussian laser beam (GB). The optical trap is characterised by its longitudinal stability (LS), expressed as the ratio of the backward axial gradient and the forward scattering forces. Replacing the GB with a LGp0 beam (one central peak surrounded by p rings) does not improve the LS because the on-axis intensity distribution is the same whatever the mode order p. However, it has been recently demonstrated that a restructured LGp0 beam can improve greatly the LS. In this paper, we consider the restructuring of a LGp0 beam when passing through a simple binary diffracting optical element called a circular π-plate (CPP). For a particular radius of the dephasing zone of the CPP, it is found that the LS is multiplied by a factor corresponding to a relative increase of about 220% to 320%.

Keywords

• optical tweezers
• improved longitudinal stability
• high-order Laguerre–Gauss modes
• laser beam shaping
• binary diffractive optical element