Tungsten Inverse Opal

Tungsten inverse opal, created for the first time in a lab at the University of Toronto, is a type of photonic crystal, which in turn is a material that excludes (or nearly excludes) all light at certain wavelengths. In general, opalescence is an optical effect in which light reflected from some object appears milky or pearly, or shimmering with various colors.

Inverse opalescence, then, is the opposite of this---it would be an effect of taking away or forbidding certain kinds of light---which is what a photonic crystals is supposed to do. (Inverse opals, if you were to look at them from the outside would be even shinier than their natural counterparts because they exclude more wavelengths of light.)

Early photonic crystals were built by stacking tiny rods criss cross fashion (or by etching out material from a solid) to create a material which would bottle up radiation of some wavelengths (see, for example, Update 348).

In the University of Toronto case, tiny silica beads are packed into a vessel. Later tungsten metal is introduced in the spaces between the beads and the beads themselves corroded away with acid. The remnant metallic lattice serves as an "inverse opal." It does a fair job of excluding some kinds of light, and possibly even converting what would be waste heat in the form of infrared radiation into more useful wavelengths.

Speaking at the Conference on Lasers and Electro-Optics (CLEO) next week in San Francisco, Georg von Freymann (freymann@physics.utoronto.ca) will report on the creation of his inverse opal material and on various absorption effects in the material. (Meeting website.)