Coherent perfect absorber
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A coherent perfect absorber (CPA), or anti-laser, is a device which absorbs coherent waves, such as coherent light waves, and converts them into some form of internal energy, e.g. heat or electrical energy.[1][2] It is the time-reversed counterpart of a laser.[3] Coherent perfect absorption allows control of waves with waves (light with light) without a nonlinear medium. The concept was first published in the July 26, 2010, issue of Physical Review Letters, by a team at Yale University led by theorist A. Douglas Stone and experimental physicist Hui W. Cao.[4][5] In the September 9, 2010, issue of Physical Review A, Stefano Longhi of Polytechnic University of Milan showed how to combine a laser and an anti-laser in a single device.[6] In February 2011 the team at Yale built the first working anti-laser.[7][8] It is a two-channel CPA device which absorbs two beams from the same laser, but only when the beams have the correct phases and amplitudes.[9] The initial device absorbed 99.4 percent of all incoming light, but the team behind the invention believe it will be possible to achieve 99.999 percent.[7] Originally implemented as a Fabry-Pérot cavity that is many wavelengths thick, the optical CPA operates at specific optical frequencies. In January 2012, thin-film CPA has been proposed by utilizing the achromatic dispersion of metal-like materials, exhibiting the unparalleled bandwidth and thin profile advantages.[10] Shortly after, CPA was observed in various thin film materials, including photonic metamaterial,[11] multi-layer graphene,[12] single[13] and multiple[14] layers of chromium, as well as microwave metamaterial.[15]