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Physicists create 'anti-laser' Feb 17, 2011
by James Dacey, reporter for
In a fascinating case of physics being turned on its head, a group of researchers at Yale University in the US has created an "anti-laser" that almost perfectly absorbs incoming beams of coherent light. The invention is based on a theoretical study reported last summer in which Douglas Stone and his Yale colleagues claimed that such a system could be possible in a device that they call a coherent perfect absorber (CPA). Instead of generating coherent light beams with a laser, the devices absorb incoming coherent light and convert it into either heat or electricity.

Now, having teamed up with experimental physicists at Yale, Stone has built a version of the device by creating an "interference trap" inside a silicon wafer. Two laser beams – originally split from a single beam – are directed onto opposite sides of the wafer and their wavelengths are fixed so that an interference pattern is established. In this way, the light waves get stalled indefinitely, bouncing back and forth within the wafer, with 99.4% of both beams being transformed into heat.

The group argues that there is no theoretical reason why 100% of the light could not be absorbed using the technique. The researchers are also confident that the current size of the device, 1 cm in diameter, can be reduced to just 6 µm. "It is surprising that the possibility of the 'time-reversed' process of laser emission has not been seriously discussed or studied previously," says Stone.