If you want to catch light, you need a mighty small cage. One option is carefully constructed material with segments almost as small as a wavelength of light. Even though most light scatters when it hits layers of so-called photonic material, certain wavelengths get trapped inside. Now a team has come up with a new way to sculpt photonic materials in three dimensions--a key step on the way to ultrasmall lasers and computer chips that calculate with photons.
It's not easy to create materials that contain repeating structures the size of a light wave, about half a micrometer wide. Until now, materials scientists made photonic materials by stacking layers of delicately etched silicon. The new technique builds on a different method: creating flat structures with light-wave-scale subdivisions by hardening special resins, called photoresists, with light. But these structures were too thin to catch light. Now scientists have discovered a way to bulk up photoresists to make them thick enough to serve as photonic materials.
The team--led by physicist Andrew Turberfield and chemist Bob Denning, both of the University of Oxford, United Kingdom--started by building photoresist films thick enough to carve a 3D matrix out of. They mixed the material with light-sensitive molecules that help link resin molecules. The team pointed four laser beams at the photoresist film. The beams interfered, creating alternating dark and light patterns. The bright spots contained enough photons to force the light-sensitive molecules to link up and harden. The researchers then dissolved away the underexposed regions and filled those voids with a bath of titanium dioxide. They burned away the remaining resin, producing a honeycomb of cells about half a micrometer wide.
"This is pioneering work," says materials scientist Ray Baughman of Honeywell International in Morristown, New Jersey. But the challenge remains to make the photonic structures large and thick enough to serve in computer chips and microlasers, he says.