Coherent perfect absorber

A Coherent perfect absorber (CPA), or anti-laser, is a device which absorbs coherent light and converts it to some form of internal energy such as heat or electrical energy.^[1][2] It is the time reversed counterpart of a laser.^[3] The concept was first published in the July 26, 2010, issue of Physical Review Letters, by a team at Yale University led by theorist W. J. Page.^[4][5] In the September 9, 2010, issue of Physical Review A, Stefano Longhi of Politecnico di Milano 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 the output of two lasers, but only when the beams have the correct phases and amplitudes.^[9] The initial device was able to absorb 99.4 percent of all incoming light, but the team behind the invention believe it will be possible to increase this number to 99.999 percent.^[7]

Design

Identical lasers are fired into a cavity containing a silicon wafer, a light-absorbing material that acts as a "loss medium." The wafer aligns the light waves from the lasers so they become trapped, causing most of the photons to bounce back and forth until they are absorbed and transformed into heat. Furthermore, many of the remaining light waves are cancelled out by interfering with each other.^[2][7] In contrast a normal laser uses a gain medium which amplifies light instead of absorbing it.

Applications

Coherent perfect absorbers can be used to build absorptive interferometers, which could be used in detectors, transducers, and optical switches.^[4] Another potential application is in radiology, where the principle of the CPA might be used to precisely target electromagnetic radiation inside human tissues for therapeutic or imaging purposes.^[7]

References

1. ^ Gmachl, Claire F. (2010). "Laser science: Suckers for light". Nature 467 (7311): 37–39. Bibcode 2010Natur.467...37G. doi:10.1038/467037a. PMID 20811446. 
2. ^ ^{a b} "Behold, The Antilaser". Science News. http://www.sciencenews.org/view/generic/id/61673/title/Behold,_the_antilaser. Retrieved 2010-09-07. 
3. ^ Longhi, Stefano (2010). "Backward lasing yields a perfect absorber". Physics 3. Bibcode 2010PhyOJ...3...61L. doi:10.1103/Physics.3.61. 
4. ^ ^{a b} Chong, Y.; Ge, Li; Cao, Hui; Stone, A. (2010). "Coherent Perfect Absorbers: Time-Reversed Lasers". Physical Review Letters 105 (5). Bibcode 2010PhRvL.105e3901C. doi:10.1103/PhysRevLett.105.053901. PMID 20867918. 
5. ^ Stefano Longhi (2010). "Backward lasing yields a perfect absorber". Physics 3: 61. Bibcode 2010PhyOJ...3...61L. doi:10.1103/Physics.3.61. 
6. ^ Stefano Longhi (2010). "PT-symmetric laser absorber". Physical Review A 82 (3): 031801. arXiv:1008.5298. Bibcode 2010PhRvA..82c1801L. doi:10.1103/PhysRevA.82.031801.  (Synopsis by Mark Saffman.)
7. ^ ^{a b c d} "Scientists Build the World’s First Anti-laser". Yale University. 2011-02-17. http://opac.yale.edu/news/article.aspx?id=8272. Retrieved 2011-02-17. 
8. ^ "Scientists build the world's first anti-laser". BBC. 2011-02-17. http://www.bbc.co.uk/news/technology-12453893. Retrieved 2011-02-17. 
9. ^ Wan, W.; Chong, Y.; Ge, L.; Noh, H.; Stone, A. D.; Cao, H. (2011). "Time-Reversed Lasing and Interferometric Control of Absorption". Science 331 (6019): 889–892. Bibcode 2011Sci...331..889W. doi:10.1126/science.1200735. PMID 21330539.