To take high-quality images of the stars, astronomers usually need thick, curved lenses to bend the light precisely. But researchers have designed a flat lens that can take sharp images of the night sky thanks to billions of nanostructures in the material. It is lightweight and resilient to damage, so it could eventually be incorporated into satellites.
These so-called 鈥渕etalenses鈥� use metamaterials and tend to be hundreds of times thinner than conventional lenses. One metalens can often replace several more bulky components to make devices like cameras more compact. Usually these are quite small and only work with a few frequencies of light. Now, at Harvard University and his colleagues have made one that is 10 centimetres in diameter and works with visible light.
鈥淭here are applications where people want to have larger metalenses, like for DSLR cameras. And some people want even larger metalenses for astronomical imaging,鈥� says Park.
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The researchers made a metamaterial 鈥� a type of engineered material with properties not found in nature 鈥� out of glass with 18.7 billion nanometre-sized structures etched into it. Conventional lenses must be thick and curved to bend and bounce light in a way that produces a high-quality image. On the thin metalens, the nanostructures bend the light to create the same effect.
Making metalenses becomes difficult when many nanostructures must be created on one surface, but the researchers worked out how to stitch together smaller sections of glass that are easier to fabricate. They made some of the largest metalenses to date, each 10 centimetres wide and 0.5 millimetres thick and well suited to be mass produced.
Currently, it works with visible light, but only produces clear images when combined with a filter that blocks out everything but red wavelengths. The researchers say they want to improve the metalens so that it can be used with all visible light.
at the University of Massachusetts Amherst says that as metalenses get larger their performance suffers if they are used with more than one colour of light, so it may be better to use arrays of smaller metalenses instead of making ever larger ones.
Park says that they could eventually be used for imaging the cosmos aboard satellites, where their compactness and small mass would be a real advantage over bulkier equipment, but they would have to withstand the launch first. His team exposed the metalens to strong vibrations and radical temperature changes from cold to hot and vice versa, and he says the results were promising, but testing at more specialised facilities is still needed before a metalens is sent to space.
For now, Park has taken some stunning images of the night sky by building a simple device that, unlike conventional telescopes with multiple lenses, only has this special one.
鈥淚 like to put it on the rooftop and watch the stars. That鈥檚 the most fun part,鈥� he says.
arXiv
