Johannes Vermeer’s “Girl With a Pearl Earring” is not a very large painting, but the replica recently created by researchers in China and the USA is even smaller. Scientists at Nanjing University, University of Maryland and the National Institute of Standards and Technology have fine-tuned an existing technology so that it not only filters through light of different colors using an array of nanoscale structures, but also projects light with different intensities. To show their new method in action, they used it to generate a projection of Vermeer’s painting, including all the detail of the shaded areas.
The mechanism they used involved a set of tiny titanium dioxide pillars mounted on a small glass plate. The pillars are only about 600 nanometers tall, and arranged on the glass slide in groups of pillars with different thickness. When light shines through, the pillars capture and let through only particular wavelengths, based on their width. That makes it possible to treat these groups of pillars as a type of pixels, and generate images with them.
Up until now, these tiny pillars could be generated in such a way that they selectively let through a certain color of light, but it wasn’t yet possible to adjust the intensity of the light. A particular color or wavelength of light would either pass through the pillar entirely, or not at all. But this current research paper from China and the USA showed that these researchers were able to adjust the light intensity within the image, by changing the shape of the tip of the pillars. Instead of a flat surface, their pillars ended at an angle, like the end of the straw that you punch through a juice box. This adjustment made it possible to not only project images with different colors, but with detailed shading as well.
This type of technology could be used, for example, in optical fiber communication, or as a security system – like a multicolor watermark. But to demonstrate exactly how well the newly designed nanopillars were able to deal with light intensity and shadows, the researchers used the system to replicate “Girl With A Pearl Earring” by 17th century painter Johannes Vermeer.
Vermeer’s piece is characterized by very detailed shading, or chiaroscuro, giving depth to the subjects in his images. The physicists obtained that same effect by shining light through the nanopillar array.
The technique makes use of light polarization. By cutting the top of each pillar, incoming light would be distributed at different angles. Then, a polarizing filter at the other end only lets through light at a certain angle. It’s essentially the same principle as polarizing sunglasses.
By combining different colors and intensities of light, the researchers were able to use their nanopillars to project a small image of “Girl With a Pearl Earring”. This demonstration showed that they were able to achieve a level of shading that hadn’t previously been possible with this system, and that opens up new possibilities for the technology. For example, it could be used as a security feature on documents or currency that are prone to fraud. This kind of high-tech watermark would be difficult to recreate in such a way that the correct details are visible with all the right subtleties in light intensity.
With it’s striking shadows, Vermeer’s “Girl With a Pearl Earring” was the perfect subject to test this new technology, but it opens the door for many other miniscule projections and future applications. As the authors say at the end of their research paper in Optica, “We envision such a color and brightness tuning metasurface to provide a promising platform for applications in both the sciences and the arts.”