Ultrafast lasers create metal surfaces with minimal reflectivity

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The blackened sample fabricated by the circularly polarized laser and its morphology. (Image: XIOPM)

Ultrafast lasers have been used to produce metal surfaces that exhibit exceptional light absorption properties.

The technique could have applications in fields such as aerospace, solar power, infrared imaging and the creation of artificial black bodies.

A research team from the Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) has proposed an effective and simple method for fabricating micro/nano hybrid structures on metal surfaces by adjusting femtosecond laser fluence, scanning interval, and polarisation.

In Chinese Optics Letters the scientists describe how a 25 × 25 × 10mm TC7 titanium alloy sample was mechanically polished and cleaned in an ultrasonic cleaner with anhydrous ethanol and deionized water, before being treated with an ultrafast laser. 

An industrial femtosecond laser with a 1MHz repetition rate and the 20W average power was used to modify the surface.

The morphology of the sample changed greatly under different laser processing parameters, resulting in an ultralow average reflectivity of 2 per cent in the 250–2,300nm spectral band, and a minimum of 1.5 per cent reflectivity in the UV band.

‘According to the absorption principle of periodic nanostructures, the smaller the fringe period is, the better the resonance absorption of the short wave is,’ said the researchers. ‘Since the hybrid nanostructure induced by circularly polarised light has a smaller fringe period, it has an excellent absorption of the short wave.’

By employing the proposed method, they say that large areas of the micro/nano hybrid structures with high consistency could be achieved for practical applications, for example in the creation of solar cells.

For more information, see the paper in Chinese Optics Letters.

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