Search Menu
Photonics Media Photonics Buyers' Guide Photonics Spectra BioPhotonics EuroPhotonics Vision Spectra Photonics Showcase Photonics ProdSpec Photonics Handbook
More News

Physicists Bring Light to a Crawl

Facebook Twitter LinkedIn Email Comments
Aaron J. Hand

Light travels in a vacuum at 186,282 miles a second. Experiments at the Rowland Institute for Science have slowed that speed 20 million times, essentially allowing light to travel along a typical suburban throughway without getting a speeding fine. If the researchers have their way, light could race a tortoise -- and lose.
The physics team -- led by Lene Vestergaard Hau, a researcher at Rowland and at Harvard University -- used a Bose-Einstein condensate to slow laser light down to 38 mph. Detailed in the Feb. 18 issue of Nature, the experiment sends a coupling beam through an ultracold cloud of sodium atoms, turning it into an electromagnetically induced transparent medium through which a pulsed probe beam can pass (without the coupling beam, the atoms would absorb the probe pulse). It's the second light pulse that is slowed down as it travels through what Hau describes as "a bizarre refractive index medium."
The experiment uses a green argon-ion laser to pump a ring dye laser, which -- at 589 nm, where it interacts best with sodium -- feeds every laser beam within the experiment, including a third imaging beam.
Unlike the slowing of light that occurs because of refractive index changes, this extreme slowing is induced by a quantum mechanical effect. A steep variation in the refractive index -- created and controlled by the coupling laser when it combines with the dense, slow-moving atoms in the Bose-Einstein condensate -- is used to achieve the remarkably slow light propagation. (The condensate begins to form at 450 nK, but the researchers have cooled the cloud to lower than 50 nK, Hau said.)
The researchers are getting new lasers in the laboratory that should enable them to slow the speed of light to 1 cm/s, Hau said, matching the speed of sound in the condensate. They will still use an argon-ion laser to pump a dye laser, but the new lasers will enable them to use sodium's D1 line, which should help do away with system loss.
If the system can be made practical, Hau sees tremendous opportunities to use this new optical medium to produce a range of optical devices, such as programmable optical delay lines, or optical switches that can be controlled by a very weak beam of light. "It's opening up doors to totally new regimes of optics," she said.

Photonics Spectra
Apr 1999
Research & TechnologyTech Pulse

back to top
Facebook Twitter Instagram LinkedIn YouTube RSS
©2019 Photonics Media, 100 West St., Pittsfield, MA, 01201 USA,

Photonics Media, Laurin Publishing
x Subscribe to Photonics Spectra magazine - FREE!
We use cookies to improve user experience and analyze our website traffic as stated in our Privacy Policy. By using this website, you agree to the use of cookies unless you have disabled them.