Bluer than blue: creating pure color with lasers

Autum C. Pylant

Dutch artist Rubins J. Spaans is known for experimenting with his painting surfaces, which include metal and linen. As a painter, he is accustomed to using pigments and dyes to create different colors, but the availability of hues and saturation with pigment and dyes can be limited. To move beyond these limitations, Spaans joined forces with Chunlei Guo, professor of optics at the University of Rochester in New York, whose research focuses on femtosecond laser-matter interactions at high intensities.

Rubins J. Spaans’ first artwork with angle-independent structural colors. Courtesy of Chunlei Guo.

Using a technique called femtosecond laser surface nanostructuring, which can be performed on metal surfaces, the artist and the researcher produce structural color. But the color is neither a paint nor a coating; it is part of the material itself. Professor Guo, the inventor of the technique, told Photonics Media that he uses a femtosecond laser to create a range of micro- and nanoscale multifunctional structures to give metal a colorful appearance.

“Through surface texturing, the change causes the structures to absorb a range of colors so that they cannot be seen,” Guo said. “But the colors that are not absorbed are reflected to give you the color rendition.” The structural color is noniridescent, which means it appears the same regardless of how the material is rotated or what the angle is between the light source and the eye.

Guo and Spaans are putting laser paintbrush to metal canvas in hopes of creating the purest colors — the blackest black and the bluest blue — while applying the technique to large surfaces. Thus far, Spaans has created two pieces of art with viewing angle-independent structural colors, with more to come.

Chunlei Guo and Rubins J. Spaans in the lab in Rochester, N.Y. Courtesy of Chunlei Guo.

“This technique makes it possible to produce pure, saturated colors with a specific, narrow wavelength range,” said Spaans. “In theory, all colors are possible — a new step in painting.” Structural colors do not fade and are durable. The femtosecond laser technique is safe, nontoxic, and fairly easy to apply.

Using blasts of laser light lasting a few million billionths of a second can turn the surface of a treated material any color. The color blue, for example, is made with Rayleigh scattering and plasmonic absorption. Rayleigh scattering occurs when light interacts with particles much smaller than its wavelength, causing certain frequencies of light to scatter and be more readily visible.

“[It’s similar to] how light going through the atmosphere is scattered off of air molecules that are much smaller than the wavelengths of light,” said Spaans. “In the blue titanium surface, due to the size of the formed nanoparticles, blue light is scattered, giving the surface a blue appearance.”

Part of the femtosecond laser setup in professor Chunlei Guo’s lab. Courtesy of Rubins J. Spaans.

Black is made primarily through light trapping and plasmonic absorption. By mixing two subtractive colorization effects, Guo and Spaans created the absence of color, or a “true black.” The duo said that their black is comparable with Vantablack used exclusively by artist Anish Kapoor. Developed by Surrey NanoSystems, Vantablack S-VIS is one of the darkest substances known, absorbing up to 99.6 percent of radiation in the visible spectrum.

While looking at techniques that go beyond the use of pigments and dyes, a scientist in Rochester, New York, and an artist in The Hague, Netherlands, have found a way to use lasers to stretch the boundaries of art, paint, and colors. “I see many possibilities using the technology of professor Guo,” said Spaans. “To be able to use these pure colors in art, architecture, and design in the near future is really amazing.”