Magazine article Science News

Opening a Window of Transparency

Magazine article Science News

Opening a Window of Transparency

Article excerpt

There's no invisible man lurking in the laboratory, but researchers have now discovered a way to make atoms of a gas transparent to light at wavelengths the gas would normally absorb. They achieve this surprising effect by using an intense laser beam to interfere with the usual, quantum-mechanical process by which an atom absorbs light.

"We face the really exciting prospect of making opaque materials transparent at particular wavelengths," says physicist Stephen E. Harris of Stanford University.

Harris, Klaus-Jochen Boller and Atac Imamoglu report the first observation of electromagnetically induced transparency, involving strontium vapor, in the May 20 PHYSICAL REVIEW LETTERS.

Atoms typically absorb light of wavelengths that correspond to the energies required for electrons to jump from one atomic energy level to another. To prevent absorption and induce transparency at one of these wavelengths (corresponding to the transition from energy level 1 to energy level 3 in the accompanying diagram), the idea is to apply an intense laser beam of a wavelength that would cause a transition between level 3 and another state, 2. Because of quantum-mechanical interference, a second laser beam normally capable of exciting the atom from level 1 to level 3 and applied at the same time as the first beam would pass right through without being absorbed.

Although the concept, in the guise of "population trapping," has been around for more than a decade, theorists failed to appreciate its significance when applied to a gas or a vapor instead of just to individual atoms. Harris changed that perception. "What we said is that you can use it to make an opaque material transparent," he says.

"All this had always been available to people, but we somehow never thought of it," adds laser expert Boris P. Stoicheff of the University of Toronto in Ontario. …

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