Introduction

Since their introduction a decade ago [1,2], optical tweezers have become indispensable tools for physical studies of macromolecular [3] and biological [4] systems. Formed by bringing a single laser beam to a tight focus, an optical tweezer exploits optical gradient forces to manipulate micrometer-sized particles. Optical tweezers have allowed scientists to probe the fantastically small forces which characterize the interactions of colloids [5,6,7,8,9], polymers [10,11,12,13,14,15,16] and membranes [17,18,19,20], and to assemble small numbers of colloidal particles into mesoscopic structures [21,22]. These pioneering studies each required only one or two optical tweezers. Extending their techniques to larger and more complex systems will require larger and more complex arrays of optical tweezers.

We describe a simple and effective means to create multiple optical tweezers in arbitrary patterns from a single laser beam using diffractive optical elements. These tweezer arrays and their variants should have immediate applications for probing phenomena in biological systems and complex fluids and in organizing soft matter into mesoscopically textured composite materials.