Magazine article Science News

Shocking Changes to Light's Properties. (Crystal Bash)

Magazine article Science News

Shocking Changes to Light's Properties. (Crystal Bash)

Article excerpt

Sometimes a good, hard whack makes things work better. That's what a new study suggests about light-manipulating microstructures known as photonic crystals.

Those orderly arrangements of tiny films, rods, balls, or even holes exclude specific wavelengths of light--a trait of growing importance for many optical components, including lasers and optical fibers.

Given the potential of photonic crystals, researchers are racing to find better ways to make the structures (SN: 5/25/02, p. 334). Now, a team at the Massachusetts Institute of Technology (MIT) suggests potential capabilities of photonic crystals that nobody had suspected.

Evan J. Reed and his colleagues have calculated the effects of smacking a photonic crystal to launch a wave of compression--a shock wave--through the structure. To simplify the calculations and computer simulations based on them, the team considered a so-called one-dimensional photonic crystal--a stack of thin alternating sheets of materials that differ in how quickly light traverses them.

Analyzing what would happen when a laser pulse enters a crystal and hits a shock wave, the scientists find that the light changes in unexpected and technologically interesting ways.

A Doppler shift of light underlies the new effects. Imagine a beam rebounding from a mirror that's rushing toward the light source. The reflected light's frequency is shifted slightly upward.

A related effect should, occur in head-on collisions between light pulses and shock waves in photonic crystals, report Reed, Marin Soljacic, and John D. Joannopoulos in an upcoming Physical Review Letters. However, the frequency shift can be tens of thousands of times as large as normal Doppler shifts, Reed says.

In the MIT scenario, light becomes trapped and bounces around within the thin, moving zone where the shock wave is compressing the crystal. …

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