Construction of an optical tweezers - Calculation and experiments

We report the construction of an optical tweezers system and the results of the trapping and the moving of living algal cells. Experimental study on t rapping polystyrene spheres demonstrates the effects of the system paramete rs on the trap. The trapping forces on dielectric spheres are calculated us ing Ashkin's ray-optics model. The result shows that an objective with high er numerical aperture can build a more stable trap along axial direction th an an objective with lower numerical aperture, though their transverse trap ping forces are on the same order.