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Femtosecond Laser Pulse Turns Metals Pitch Black
A titanium-sapphire laser was used to repeatedly blast polished metal surfaces with pulses lasting just 65 femtoseconds. The result: a surface that absorbs almost 100% of incident light.
(Metal turned black with femtosecond laser pulse)
The secret is an ultra-brief, ultra-intense beam of light called a femtosecond laser pulse. The laser burst lasts only a few quadrillionths of a second.
"We've been surprised by the number of possible applications for this," says Chunlei Guo, assistant professor of optics at the University of Rochester. "We wanted to see what would happen to a metal's properties under different laser conditions and we stumbled on this way to completely alter the reflective properties of metals."
The laser releases as much power as the entire North American grid onto a spot the size of a needle point. Light that falls onto it is almost entirely absorbed. The pulse blasts the surface molecules into nanostructures that dramatically increase the area of the surface and capture radiation.
The reader who tipped me to this find remarked that it reminded him of what the bugs did to the asteroid Eros in the 1985 novel Ender's Game:
"...We learned efficient use of stellar energy because they blacked out this planet. In fact, that's how we discovered them. In a period of three days, Eros gradually disappeared from telescopes.
Update 10-Nov-2011: Here's an early reference to the idea of a "blacker than black" coating for materials; see the black coating from E.E. 'Doc Smith's 1939 novel Gray Lensman. Thanks to Winchell Chung of Project Rho for the tip on this item. End update.
Quick-witted readers have several other good connections that I had completely forgotten about (see comments). Read more about Dr. Guo's work at this press release. Thanks also to the reader who contacted me with the tip for this story.
Scroll down for more stories in the same category. (Story submitted 12/3/2006)
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