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Ultrafast lasers used to create a ‘perfect’ solar energy absorber

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Researchers at the University of Rochester have used ultrafast laser processing to develop metal surfaces capable of absorbing solar energy at exceptional efficiency.

In Light: Science & Applications the researchers described how they have used powerful femtosecond laser pulses to etch metal surfaces with nanoscale structures that selectively absorb light at the solar wavelengths, while not absorbing other wavelengths.

While the researchers had previously succeeded in creating black hydrophobic surfaces using ultrafast lasers that were also highly absorptive of solar energy, some of this energy was being lost at wavelengths beyond the solar spectrum. Now, however, they have created a new selective absorber that is both highly efficient at absorbing sunlight while also being able to reduce the heat dissipated at other wavelengths. According to the researchers, this makes the surface the first ‘perfect metallic solar absorber’.

The researchers used a ti:sapphire laser from Coherent. A maximum pulse energy of 7mJ, a maximum average power of 7W and a 1kHz repetition rate was used.

After experimenting with aluminium, copper, steel, and tungsten, the researchers found that tungsten – already commonly used as a thermal solar absorber – had the highest solar absorption efficiency when treated with the new nanoscale structures. Using a thermal electric generator, they demonstrated that solar energy harnessing efficiency was 130 per cent higher with the treated tungsten, compared to untreated tungsten.

‘This will be useful for any thermal solar energy absorber or harvesting device, particularly in places with abundant sunlight,’ commented Professor Chunlei Guo, who led the team at the university's Institute of Optics.

The research was funded by the Bill and Melinda Gates Foundation, the US Army Research Office, and the US National Science Foundation.

Paper in Light: Science & Applications.

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