When a laser changes metals in all colors

Methods of laser coloring of metals accessible to both artists and mass production: this is what Russian researchers are proposing today. A new means of expression that is efficient and accurate, without chemicals that are potentially toxic.

Images of color labeled laser on metals, it is not new. But researchers from the ITMO University (Russia) today explain how, thanks to a single laser emitting nanosecond pulses, they have been able to implement three different colorization techniques.

"After the laser treatment, various micro and nanostructures are formed. This creates optical effects that change the color of the treated surface, " says Nadezhda Shchedrina. A technique that can be implemented in a limited time, to create both small and large images.

A laser and three techniques for a color palette

The color of the metal can first be modified by oxidation. The laser produces a thin film of oxide on the metal surface. When light hits this film, a color appears due to interference. Another method is the formation of nanoparticles of sizes between 5 and 50 nanometers. In this case, it is the phenomenon of resonance of plasmon surface that gives rise to colors, depending on the size of the particles. Finally, the laser structuring technique consists in melting a part of the metal surface to create a periodic network of grooves or slots. The scattered light then produces colors that depend on the viewing angle.

These methods can find applications in the field of art, but also in that of mass production of jewelry, for example. They could also be used to create systems that help fight counterfeit.

Metals of all colors thanks to a femtoliter

By sculpting, literally, the surface of a metal using very short laser pulses, an American team claims to be able to give just about any color to any metal.

Article by Jean-Luc Goudet published on 05/02/2008

In 2006, Chunlei Guo and his team at the Institute of Optics at the University of Rochester, New York, had already exhibited an amazing black metal. It was not a particular alloy, but any metal made almost completely black, that is, capable of absorbing light in all wavelengths of the visible. The same team has perfected the principle and is able to change the color of metal to give it any shade.

How do they do? The laboratory of Chunlei Guo is specialized in the use of fem to lasers, emitting a pulse of extremely short duration, of the order of several femtoseconds (1 femtosecond is worth 10 -15 seconds). We can thus arrive at powers of the order of a hundred terawatts. In their laboratory, Chunlei Guo's team manages to concentrate this photonic flood on a very small surface.

How to cut cauliflowers

The energy is such that the metal is deformed. The secret of these scientists is to have managed to control these deformations to carve reliefs at the nanometer scale and the micrometer. In 2006, the metal thus obtained had a much larger surface, because of this roughness which formed furrows, crests and various forms, cauliflower for some. This surface increase made the method an interesting way to manufacture catalysts, for example for fuel cells, which act by adsorption, that is to say by temporarily fixing the active ingredients on their surface.

If the metal turned black, it was because these multiple forms, with various dimensions but of the order of the wavelengths of the visible light, absorbed them all. Since 2006, the team has made progress and can now obtain patterns of different sizes. Chunlei Guo and his assistant Anatoliy Vorobyev are now able to choose the color of metal. An apple - green steel, lemon - yellow aluminum or purple gold should be achievable ... The authors believe that the process could become industrialize, to tint objects without painting.
It will still solve some problems, such as reducing the cost of fem to lasers and, for the process itself, reduce the processing time, currently about thirty seconds for a surface of a few square centimeters. A little long to color a car ... Moreover, the team does not say how these delicate nanometric or micrometric structures resist wearing.