An optical tweezer uses the forces exerted by a strongly focused beam of light to trap, manipulate, and transform a small volume of matter. Originally introduced by Bell Labs researchers in 1986, optical tweezers have become indispensible tools for research in physics, chemistry and biology.
Holographic optical trapping, developed in Prof. David Grier's lab, extends this technique by using computer-generated holograms to dynamically structure the light field before
it is brought to focus. In this way, a single laser beam can power hundreds of optical traps that move independently in three dimensions. Holographic control thus lends itself to lends itself to analyzing and sorting microscopic fluid-borne objects and for assembling them into complex three-dimensional structures such as the icosahedral quasicrystal shown in the figure.
Each holographically projected trap, furthermore, can have an independently specified optical mode structure. Wavefront engineering is useful for extending point-like optical tweezers into holographic line traps, ring traps and optical solenoid beams. The force profiles along these extended traps can be precisely specified through control of their intensity and phase profiles. Extended holographic traps therefore constitute model low-dimensional systems for studying colloidal interactions and nonequilibrium statistical physics. They also have immediate practical applications in medical diagnostics.
