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AN OPTICAL motor could power the micromachines of the future, according to
scientists at the University of St Andrews. The motor has already been used to
spin chromosomes and other small particles without any physical contact. It
works in much the same way as optical tweezers, but instead of using a single
laser beam it has two. Particles are trapped in the beams, rather like a
fountain trapping a tennis ball in its jet. Spinning is achieved by overlapping
two beams to create a spiral interference pattern that can be twisted very
precisely, turning the trapped particle with it (Science, vol 292, p
912).