By Patricia Daukantas

Metals are going multicolored, thanks to the femtosecond-laser-ablation technique developed by Chunlei Guo at the University of Rochester. Without paint, aluminum and platinum can look just like gold—or like a blue sky.

Guo, an assistant professor of optics, and postdoctoral fellow Anatoliy Vorobyev have been studying the roughness of metallic surfaces at the nanoscale level. Their research on precision control of the surface structures at the nanometer scale led to the new colorizing technique.

The February 2007 issue of OPN described the previous work of Guo and Vorobyev in blackening gold surfaces. However, the multicolor technique is a significant advance over the research that preceded it.

The Rochester team’s original “black metal” surfaces absorbed all wavelengths of light. However, “the key to the coloring technique is that we now can control the spectral responsivity of metals,” Guo said.

In other words, the researchers change the size of the tiny, polarization-dependent structures etched onto the metallic surfaces in order to change the surface colors.

“The most significant step forward is that we now have a precise control in the range of nanostructure sizes formed, and these nanostructures can affect the light response of the metal surface and give us the appearance of a color or range of colors,” Guo said.

The researchers control the size of the region that gets colored by varying the width of the focused laser beam, which is typically 100 microns to 1 mm wide. A narrowly focused beam produces a tinier area of color change, opening the potential for using the technique to etch multicolored patterns on metallic surfaces.

Guo and Vorobyev have produced solid gold, blue and gray colors on the surfaces of aluminum, platinum, titanium, tungsten and silver. In addition, the researchers have produced iridescent surfaces, which make a metal appear variously colored at different viewing angles.

The research was recently published in Applied Physics Letters and also garnered attention with an article in the New York Times.

2008-02 February, Miscellaneous Optics metamaterials, transformational optics, nanotechnology