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Laser Blasts Colorize Metals

Using a laser, scientists have turned aluminum into gold, or at least made it look like gold. They can also make it blue, gray or almost any color in the rainbow.

Chunlei Guo of the University of Rochester and his colleagues blasted extremely brief and intense laser bursts at small pieces of metal to change their surface properties. The laser blasts form nanoscale and microscale structures in the surface that reflect a certain color of light, making the metal appear a different color than it naturally would.

The laser is called a femtosecond laser because its pulses last for the tiniest fraction of a second. A femtosecond is to a second what a second is to 32 million years.

By varying the intensity of the laser, the length of the pulses and the number of pulses, Guo can control the configuration of the surface nanostructures and therefore what color the metal reflects.

A year ago, Guo used intense laser light to turn a variety of metals pitch black. The nanostructures in those experiments absorbed almost all of the light hitting them.

"Since the discovery of the black metal, we've been determined to get full control on getting metals to reflect only a certain color and absorb the rest," Guo said. "And now we finally can make a metal reflect almost any color we wish."

The process has worked on every metal Guo and his team have tried so far, including platinum, titanium, tungsten, silver and gold. Guo thinks it's likely that any metal can be colorized in this way, so that one day you could have a full-color family portrait etched into your refrigerator.

The process is detailed in the Feb. 1 issue of the journal Applied Physics Letters.

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