Friday, February 1, 2008

Researchers Turn Aluminum Gold!

Researchers from University of Rochester have turned aluminum gold just with the help of a laser, meaning they changed its color into gold. Not only that, but they have been able to recreate a series of other colors in several other metals such as platinum, tungsten and gold. Almost one year before, Chunlei Guo had demonstrated that he could turn just about any metal by shinning it with intense laser beams.

Since then, he has been trying and succeeded in altering the physical properties of metal, in order to reflect
any color he desired, or even to create a series of iridescent multicolored structures. Because the laser light is actually modifying the structure of the top layer of the metal, the imprinted color would not fade away over time. Such coloring techniques could be used in the near future for obtaining multicolored painting designs, or even to imprint pictures on metal sheets.

The original experiment was able to create a material that had the capability of absorbing most of the shinned light, however the improved technique used currently can be used to determine the surface of a metal to reflect any desired color and absorb the rest.

By using brief intense lasers, Guo is able to create nanoscale and microscale structures on the surface of the metal, which have the capability of selectively reflecting a specific light wavelength. The laser produces bursts of light lasting only a femtosecond, but with a power comparable to that of the whole electric grid in the North American continent, focused on a area smaller than that of a needlepoint.

The intense release of energy is enough to create nanostructures in different shapes and sizes, such as pits, globules or strands, each reflecting light in an unique way. What kind of shapes are created on the surface of the metal is in direct relation to the pulsing laser beam. Controlling the final configuration of the nanostructure is made by varying in the light intensity, light pulse length or the number of individual light pulses. The sizes and the shapes of the structures on the metal surface greatly affect the spectrum of light reflected, as the created structures are usually smaller in size than the wavelength of light that hits them.

Iridescent coloring is obtained by creating microscale lines, after which a process of embedding nanostructures is followed. For example, such a configuration using regular rows of microscale lines determined the light to be reflected in different directions, in order to interfere in different ways, resulting in a piece of metal that usually appears in different colors, depending on the angle from which it is observed.

Guo claims that the process of altering the surface of a small coin could take as much as 30 minutes, while the powerful laser device used in the process can be powered by a single house outlet, despite the fact that it delivers a massive amount of energy. Experiments have shown that the process works on every type of metal and the scientists are now trying to develop a technique that would create a solid-colored metal surface.