More than 50 years after the invention of the laser, scientists have built the world’s first anti-laser, paving the way for novel technologies with applications in everything from optical computing to radiology. Scientists at Yale University created the device, in which incoming beams of light interfere with one another in such a way that they cancel one another out. Called a coherent perfect absorber (CPA), the device was built using silicon. While conventional lasers use a gain medium, a semiconductor like gallium arsenide, to produce a focused beam of coherent light, the anti-laser uses a silicon wafer to act as its “loss medium.” To demonstrate the anti-laser, the researchers focused two laser beams with a specific frequency into the cavity containing the wafer. The light waves were aligned by the wafer in such a way that they became trapped, bouncing back and forth indefinitely until they were absorbed and transformed into heat. The results were published in Science, Feb. 18, 2011 (doi: 10.1126/ science.1200735). Because of experimental limitations, the team’s current CPA, which measures 1 cm across, absorbs only 99.4 percent of incoming light. Theoretically, the CPA could absorb as much as 99.999 percent of light and be as small as 6 µm. While they were able to demonstrate the effect for near-infrared radiation, they have determined that with some tweaking of the cavity and loss medium in future versions, the CPA will be able to absorb visible light in addition to the specific infrared frequencies used in fiber optic communications. The scientists believe that one day the anti-laser could be used as an optical switch, a detector or as other components in next-generation computing. Additionally, it could be used in radiology applications for therapeutic or imaging purposes.