Monday, February 04, 2008

It looks like gold, it smells like gold, but it's aluminum

All that glitters golden is not gold. It could be aluminum. Or tungsten. Or another metal of Chunlei Guo’s choosing.

Colorizing Metals With Femtosecond Laser Pulses (Applied Physics Letters)In a feat of optical alchemy, Dr. Guo, a professor of optics at the University of Rochester, and Anatoliy Y. Vorobyev, a postdoctoral researcher, use ultrashort laser bursts to pockmark the surface of a metal in a way that is not perceptible to the touch — it still feels smooth to the finger — but that alters how the metal absorbs and reflects light.

The result is that pure aluminum looks like gold, and the appearance is literally skin deep.

“I cannot tell it’s not gold,” Dr. Guo said. “It looks very pretty.”

Dr. Guo and Dr. Vorobyev reported their findings in the journal Applied Physics Letters published online Thursday.

The golden aluminum follows work a little more than year ago where Drs. Guo and Vorobyev reported that they could make gold and other metals look black — indeed a black that is blacker than the usual black, sucking up almost all light that impinged upon it.

The laser bursts — each lasting only about 60 millionths of a billionth of a second — melt and vaporize metal atoms near the surface, which then reassemble in minuscule structures including pits, spheres and rods that are a fraction of a millionth of a meter in size.

By changing the length, strength and number of pulses, the researchers found they could vary the resulting color.

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