Design and implementation of optical tweezers arrays using diffractive optical elements

Although optical tweezers have been a valuable research tool since their invention in the 1980s, they have remained limited for many years to trapping only one particle per laser beam. One of the most exciting developments in optical tweezers in recent years has been the creation of two- and three-dimensional arrays of optical traps by using diffractive optical elements (DOEs). We have developed our own algorithms and codes to design phase DOEs that can transform a single laser beam into an array of independent traps, each with individually specified characteristics, arranged in various geometrical configurations. The DOEs were fabricated by means of e-beam lithography in PMMA and recently were implemented in computer addressed liquid crystal spatial modulators. This allows us to control the configuration of the optical tweezers almost in real time. Experimental results presented in this paper show trapping and manipulation of multiple silica micro-spheres immersed in water. The trapped particles are moved independently along the x-y-z directions and rotated along circular trajectories with different angular velocities.