Washington: Using the technique of intense laser light, optical scientists at the University of Rochester in US have been able to change the colour of some metals to create variations like gold aluminum, black platinum and blue silver.
What this technique originally does is that it alters the properties of a variety of metals to render them pitch black.
This was observed in late 2006, when researchers created nanostructures on metal surfaces that absorbed virtually all light, making something as simple as regular aluminum into one of the darkest materials ever created.
Now, the process has been further pushed to make it possible for metals to be turned into any colour—even multi-coloured iridescence like a butterfly's wings.
"Since the discovery of the black metal we've been determined to get full control on getting metals to reflect only a certain colour and absorb the rest, and now we finally can make a metal reflect almost any colour we wish," said Chunlei Guo, associate professor of optics at the Institute of Optics at the University of Rochester.
As part of the procedure, Guo and his assistant, Anatoliy Vorobeyv, used an incredibly brief but incredibly intense laser burst that changes the surface of a metal, forming nanoscale and microscale structures that selectively reflect a certain colour to give the appearance of a specific color or combinations of colours.
Guo and Vorobyev also achieved the iridescent colouring by creating microscale lines covered with nanostructures. The lines, arranged in regular rows, cause reflected light of different wavelengths to interfere differently in different directions.
The result is a piece of metal that can appear solid purple from one direction, and gray from another, or multiple colours all at once.
"When we first found the process that produced a gold colour, we couldn't believe it. We worked in the lab until midnight trying to figure out what other colours we could make," said Guo.
"Since the process changes the intrinsic surface properties of the metal itself and is not just a coating, the colour won't fade or peel," he added.
According to Guo, the new process has worked on every metal that the research team has tried, and the results are so consistent that he believes it will work for every metal known.
His team is currently working to find the right tuning to create the rest of the rainbow for the solid-coloured metal, including red and green.
This technique might further lead to applications ranging from making better solar energy collectors, to more advanced stealth technology.
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