Multiple optical tweezers generated from phase Fresnel lens array

We report a new method to generate multiple optical traps by using phase Fresnel lens (PFL) array. We also demonstrate its applications on manipulating micro particles in experiment. In our experiment, the PFL array is formed by a spatial light modulation. The multiple beams generated by PFL array are directed into the inverted microscope and are highly focused in the focus plane of the objective. The 1.4µm polystyrene spheres are trapped in the experiment. Each of the trapped particles can be controlled by changing the position of the corresponding Fresnel zone plate in the array. Comparing with the hologram methods, which is the most popular method in generating optical trap arrays, the PFL array method has increased the trapping efficiency. Because the power of the useless zero-order light in the hologram method can be used in PFL array method. Besides, each of the trapped particles can be controlled separately in PFL array method, which makes micromanipulation more conveniently.