A compact, automated and long working distance optical tweezer system

Abstract

We demonstrate a compact, automated, long working distance optical tweezer system using a novel mechanism for controlling the position of the optical trap. Our system uses a single focusing lens with a working distance of 4.5 mm and the trapping beam is steered by moving the lens with a miniature coil-magnet assembly. The sample is imaged through a 100× microscope objective and a CCD camera captures the magnified image. A custom image processing software detects the position of the laser beam and identifies the sample objects. This information is used to generate appropriate electrical signals to drive the coils which move the focusing lens along the desired path. The system is fairly simple and power efficient due to minimal usage of optical elements in the laser path; hence our setup is simple, low-cost and requires low optical power. Computer-generated arbitrary trapping paths and time-shared trapping patterns are successfully demonstrated. Efficient trapping of micron size spheres with laser powers as low as 1.5 mW is observed.