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Doped crystal catches a light pulse

17 Jun 2002

For the first time, physicists have managed to store laser light pulses in a solid.

Using a praesodynium-doped yttrium crystal, physicists in the US have slowed-down and stored light in a solid for the first time.

Phil Hemmer of the Air Force Research Laboratory, and his colleagues at the Massachusetts Institute of Technology, used a technique that had previously only been shown to work in gases. By demonstrating the same effects in a solid, the team is hoping that its technique might one day be of use in quantum information storage (Phys. Rev. Lett. 88 023602).

The light-storing technique works thanks to an effect known as electromagnetically-induced transparency (EIT). In EIT, the material through which light propagates can have a very high refractive index, which slows the light down, without becoming almost completely opaque - which is normally the case.

Lene Hau from Harvard University has pioneered this technique in gases, and a year ago both her group and a second team at the Harvard-Smithsonian Center for Astrophysics managed to "stop" a light pulse as it travelled through an atomic vapor before recovering it with a second laser.

Hemmer and his team excited a 606 nm transition in the crystal using a dye laser, with the exciting pulse stored in the crystal thanks to EIT. The pulse can be retrieved using another laser - and the direction of this second laser determines the direction in which the retrieved pulse propagates.

Compared to a gas, the solid medium is not only much more convenient for making devices, but also has potentially much longer storage times and larger storage capacity.

Hemmer, who is now at Texas A&M University, US, says that the next steps in the research will be to attempt storage of single photons, and to improve the storage efficiency to near 100%.

Michael Hatcher is technology editor of Opto & Laser Europe magazine.

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