Lasers blacken copper for better heat absorption

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Nanosecond lasers blackening copper's surface could lead to the metal being used in a wider variety of applications including solar energy absorption, irradiative heat transfer devices and thermophotovoltaics.

Copper and its alloys are important materials for many technical applications due to their unrivalled thermal and electrical conductivity. A nanosecond laser was used to modify the properties of the copper’s surface. Under a microscope the modified surface resembles an upturned egg carton whose individual dimples have been pushed in.

‘By making copper so much more heat-absorbent it means we can do so much more with it,’ said Professor Amin Abdolvand. He holds the University of Dundee’s chair in functional materials and photonics. ‘Because copper is normally shiny it reflects most of the light back. Blackening it allows it to absorb light throughout a broad spectrum, making it far more effective.’

Previously it was thought that only much more expensive ultrafast lasers could be used to make metals appear black. The researchers tested various firing patterns for the laser before finding the most effective pattern, which gave the greatest boost in absorption. The absorption boost is attributed to several mechanisms, including light-trapping in microcavities. This work was conducted under the aegis of the Engineering and Physical Sciences Research Council.