Weekly news picks: nanocups and quantum doughnuts

My pick of the stories from the news wires this past week include the early detection of retinal damage in the eye, metamaterials made from nano-sized cups, and putting the brakes on light... with doughnuts.

Retinal scarring from diabetic retinopathy
Photo courtesy of Wellcome Images

Researchers at the Keck School of Medicine, University of Southern California, have come up with a new approach to detecting the early stages of diabetic retinopathy^{1, 2}. Using a modified form of optical coherence tomography (OCT), they were able to measure blood flow to the retina from the shift in frequency of the reflected light, thereby distinguishing between two diabetic patients, one with the disease and the other without.

The blood vessels which supply the retina suffer increasing damage as the condition progresses, which results in restricted blood flow to the retina. If it can be diagnosed early, there are treatments available, including laser surgery. This technique could become a cheaper alternative to current diagnostic methods, which would allow ophthalmologists to perform check ups for the disease on a routine basis.

Quantum doughnuts aren't going to fill you up, but they might slow you down if you're a photon. These doughnuts are failed quantum dots because they didn't form properly during production, but researchers from the UK and Brazil believe they have found a use for them³. Their theoretical model shows how they might be used to slow down and even freeze light. An incoming photon produces an exciton - an electron and its corresponding positively charged state known as a hole - which re-emits a photon when the pair recombine. By applying magnetic and electric fields, they demonstrate that it is theoretically possible to delay recombination. Such a technology could revolutionise communications and optical computing, by carrying out many of the operations which are conventionally done by transporting and manipulating electrons, but doing it faster.

Researchers from Rice University in the US have also discovered a use for some nano-scale by-products after studying the properties of the particles that were left over from the production of perforated gold films ⁴. Their "nanocups" were produced by evaporating gold onto nano-particles from multiple directions which, when lifted from their substrate, preserved their uniform orientation. The result was a transparent metamaterial which was capable of directing incident light arriving from a range of angles in one specific direction. There are many possible applications for materials which exhibit such properties, such as more efficient solar collectors; superlenses with the ability to resolve beyond the limits imposed on conventional lenses; and cloaking devices that can render objects invisible.

And finally, Scientists at the Lawrence Berkeley National Laboratory in California have discovered a viable photo-catalyst which is one step in the process of creating artificial photosynthesis⁵. By shrinking cobalt oxide crystals from the micron scale to the nanometre scale, they saw a massive increase in the efficiency with which this abundant material could oxidise water with light. Artificial photosynthesis could produce liquid fuels from sunlight by extracting electrons and oxygen from water and reacting them with carbon dioxide. This could one day lead to renewable, carbon-neutral fuels.

You can find optics news from across the web, throughout the week, by visiting the news page at OpticalFutures.com.

1. Shining light on diabetes-related blindness
2. Y. Wang, A. Fawzi, O. Tan, J. Gil-Flamer, and D. Huang, "Retinal blood flow detection in diabetic patients by Doppler Fourier domain optical coherence tomography," Opt. Express 17, 4061-4073 (2009). doi:10.1364/OE.17.004061
3. Quantum doughnuts slow and freeze light at will: 'Fast computing and slow glass'
4. Nanocups brim with potential
5. Turning Sunlight into Liquid Fuels: Berkeley Lab Researchers Create a Nano-sized Photocatalyst for Artificial Photosynthesis