By Patricia Daukantas
For hundreds of years, stained-glass windows have decorated medieval cathedrals and awed onlookers with their intricate, translucent designs. Now a researcher in Australia has discovered that some windows that date back to the Middle Ages contain 21st-century-style light-activated nanotechnology.
Medieval windows painted with pigments containing gold particles actually purify the air when lit by sunlight, according to Huai Yong Zhu, associate professor of chemistry at Queensland University of Technology in Brisbane.
Zhu and colleagues found that the gold nanoparticles found in many pigmented glass windows in Europe become activated when struck by sunlight and remove volatile organic compounds (VOCs) from the air. VOCs are light hydrocarbons that vaporize easily, and many of them are considered pollutants in the gas phase.
In Zhu’s words, sunlight causes the small gold particles to act like a “photocatalytic air purifier.” The solar energy boosts the magnetic field on the surface of the nanoparticles and this in turn breaks apart airborne VOCs. Zhu is interested in the process because it is solar-powered and thus energy-efficient.
By Patricia Daukantas
Most OSA members, I’m sure, are aware that negative-refractive-index metamaterials have been a hot topic of research for the past few years. Although scientists have found success making materials “invisible” to microwaves, several teams have been racing to extend these materials into the optical range – a development that would have much more interesting applications.
This week, two new papers from a California-based team hit the news wires. The researchers, based at the University of California at Berkeley and Lawrence Berkeley National Laboratory, made a prism out of optically negative-index metamaterial that closely resembles layers of tiny fishnets, according to the letter that appeared in Nature.
Xiang Zhang’s group made their metamaterial out of a stack of alternating layers of silver and magnesium fluoride; the size of the “fishnet” cells was on the order of a few hundred nanometers. The scientists tested the prism’s refractive index at near-infrared wavelengths from 1,200 to 1,800 nm and found that the index went to zero at around 1,475 nm.
In the brief Science paper, Zhang and colleagues reported on a different experiment that refracted red light via an aluminum-oxide array of nanometer-sized holes filled with silver. Negative refraction, however, happened only for transverse magnetic polarized light, not for transverse electric polarized light.
Journalistic interest, of course, is driven by the age-old human dream of invisibility, never mind the cloak and cloaking devices in the Harry Potter and “Star Trek” tales. Fortunately, some of the news coverage took pains to explain that practical devices made from negative-index metamaterials are still many years in the future.
Posted by Christina Folz, OPN Managing Editor
With 92 years of history under our belt, the Optical Society has accumulated scores of photos. Although we’ve captured many moments, we haven’t always captured the who, what and where information that must have seemed so obvious at the time the photo was snapped. Help us breathe new life into our images by providing your own imaginative captions to one of the images below. It could be a cartoon-style quote or a creative description of what you see. We’ll share your best captions in a future issue of OPN.
Send your captions to opn@osa.org or post them on our blog at www.osa-opn.org. (Remember to specify which image you are captioning…or don’t; it might be more fun that way.)
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