Defeating diffraction

Physics WorldJon Cartwright

Published in Physics World, 1 May 2012

Once thought to offer imaging at unlimited resolution beyond that permitted by diffraction, superlenses never quite worked in practice. Now, physicists have a host of other ideas to make perfect images, but can these concepts succeed where superlenses failed? Jon Cartwright reports

Ernst Abbe, one of the 19th-century pioneers of modern optics, has a concrete memorial sitting in the leafy grounds of the Friedrich Schiller University of Jena, Germany, engraved with a formula. Put simply, it describes a fundamental limit of all lenses: they cannot see everything. No matter how finely you grind and polish a lens, diffraction – the natural spreading of light waves – will always blur the smallest details.

Of course, theories should never be set in stone. At the turn of this century, physicists began to explore “superlenses” that could see past Abbe’s diffraction limit – that is, they could see features smaller than about half a wavelength of the light being used. Based on thin slabs of metal, these superlenses could bend light in unheard-of ways, counteracting diffraction so that an object’s features could be resolved into a perfect image. But there were problems: the lenses only worked if they were placed right next to an object and, even then, they were so lossy that their images were next to useless. Superlenses were not so super after all.

For many, that was a great shame. Biologists had been looking forward to imaging the tiniest parts of organisms in real time, which is almost impossible with current microscopy techniques. Perfect imaging could also have rebooted the computer-chip industry, allowing circuits and components to be etched smaller and more complex than before. Although other techniques exist that can see features smaller than half a wavelength – near-field scanning optical microscopy is one – they produce images by scanning a surface, which takes time. Only perfect imaging promised the ability to image objects at any resolution in a single snapshot.

Given the poor results of superlenses, some physicists have tried rehashing the blueprint in the hope that it can still offer practical applications. Others, however, have ditched the concept altogether, instead trying completely different approaches. These new approaches are in their nascent stages – most have not actually imaged anything, but only resolved point sources. Still, they are under high expectations, and could allow us to see more clearly than ever before. […]

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Video: Tiny Container Could Make Blood Tests Less Painful

ScienceJon Cartwright

Published in ScienceNOW, 24 Apr 2012

Good news for people who hate big needles: Researchers have invented a device that could allow diagnostics to be performed with just a single drop of blood. The apparatus is a container a few millimeters wide that consists of a conductive base covered with an elastic layer of polydimethylsiloxane or PDMS, a silicone compound. When liquid is dripped on the PDMS, the layer wraps around the ensuing droplet thanks to its surface tension—the same force that causes water to curl upward at the sides of a glass. […]

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Light Bends by Itself

ScienceJon Cartwright

Published in ScienceNOW, 19 Apr 2012

Any physics student knows that light travels in a straight line. But now researchers have shown that light can also travel in a curve, without any external influence. The effect is actually an optical illusion, although the researchers say it could have practical uses such as moving objects with light from afar.

It’s well known that light bends. When light rays pass from air into water, for instance, they take a sharp turn; that’s why a stick dipped in a pond appears to tilt toward the surface. Out in space, light rays passing near very massive objects such as stars are seen to travel in curves. In each instance, light-bending has an external cause: For water, it is a change in an optical property called the refractive index, and for stars, it is the warping nature of gravity. […]

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Introducing the ‘orbiton’

Physics WorldJon Cartwright

Published in Physics World, 18 Apr 2012

Condensed-matter physicists love quasiparticles, and now they have another entity to admire – the “orbiton”. First predicted a decade ago, the orbiton is a collective excitation of electrons in a 1D solid that behaves just like an electron – with orbital angular momentum but with no spin or electric charge. As well as completing the set of three electron-like quasiparticles predicted to exist in a 1D solid, the discovery, made by an international team of physicists, could offer new insights into the origin of high-temperature superconductivity.

Quasiparticles offer physicists a convenient quantum-mechanical description of the collective behaviour of electrons and atoms in solid materials. Perhaps the most famous example is the “hole”, which describes the absence of electrons in a semiconductor in terms of a positively charged electron-like particle. […]

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Turing’s Ideas Blossom

ScienceJon Cartwright

Published in Science, 6 Apr 2012

A sunflower is more than just a pretty face: It’s a floral expression of the so-called Fibonacci sequence—1, 1, 2, 3, 5, 8, and so on, where each number is the sum of its two preceding numbers. And now, a U.K.-based project is enlisting the help of gardeners around the world to help test a theory that originated with one of history’s greatest mathematicians, Alan Turing. […]

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Nanomachines could benefit from superlubricity

Physics WorldJon Cartwright

Published in Physics World, 5 Apr 2012

Researchers in China and Australia have observed superlubricity – the dropping of friction to near zero – on length scales much larger than before. They say that the phenomenon, which they measured in sheared pieces of graphite, could find applications in sensitive microscopic resonators or nanoscale gyroscopes.

Superlubricity is sometimes used to mean simply very low friction, but the original meaning is that the friction between two surfaces disappears almost completely. Proposed in the early 1990s by Motohisa Hirano, then at the Nippon Telegraph and Telephone Corporation in Tokyo, Japan, and others, it relies on a special arrangement of atoms on a material’s surface. In graphite, for instance, the surface atoms have a bumpy hexagonal arrangement like egg-boxes. In certain orientations, two surfaces of graphite can mesh in such a way that the “bumps” can slide past one other effortlessly – and friction drops towards zero. […]

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ScienceShot: Water Floats on Oil

ScienceJon Cartwright

Published in ScienceNOW, 5 Apr 2012

Two years ago, the explosion of the Deepwater Horizon oil rig covered hundreds of square miles of the Gulf of Mexico with oil (main image). The oil floated because it is less dense, and therefore lighter, than water. But now scientists say that water can sometimes float on oil—and their findings, which were published last month in Langmuir, could help to mop up oil slicks like the one created by the 2010 disaster. […]

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Plasma Flashlight Zaps Bacteria

ScienceJon Cartwright

Published in ScienceNOW, 4 Apr 2012

Killing harmful bacteria in hospitals is difficult; out in the field, it can be an even bigger problem. Now, researchers may have a means for remote disinfection in a portable “flashlight” that shines a ray of cold plasma to kill bacteria in minutes.

Medical scientists have high hopes for plasmas. Produced in electrical discharges, these gases of free electrons and ions have already been shown to destroy pathogens, help heal wounds, and selectively kill cancer cells. No one is exactly sure how all of this works, but it seems that plasmas generate so-called reactive oxygen species in the air. These highly reactive molecules, which are present in our own immune system, oxidize cell membranes and damage DNA. […]

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Hydrogen that mimics graphene

Chemistry WorldJon Cartwright

Published in Chemistry World, 2 Apr 2012

Researchers in the UK and the US claim to have discovered a new phase of hydrogen in which the diatomic molecules break apart to form six-atom rings, similar to graphene. The new phase, which occurs at very high pressures, could be a stepping stone towards a long-sought after phase: metallic hydrogen.

The quest for metallic hydrogen has been on since the late 19th century, when chemists pointed out that the element, which tops the periodic table’s column of alkali metals, ought to form a metal. In 1935, physicists Eugene Wigner and Hillard Bell Huntington predicted that hydrogen should become a metallic solid at high pressures – roughly 25GPa – but experiments later performed at these pressures showed no trace of a metal transition. More recent experiments have employed higher pressures still. Indeed, last year Mikhail Eremets and Ivan Troyan of the Max-Planck Institute for Chemistry in Mainz, Germany, claimed evidence for metallic hydrogen at pressures up to 260GPa. But other scientists believed that evidence was unreliable.  […]

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ScienceShot: Why Old Paper Turns Yellow

ScienceJon Cartwright

Published in ScienceNOW, 2 Apr 2012

Possibly the only formal self-portrait of Leonardo da Vinci resides in the Royal Library of Turin, Italy. Some of its details are obscured, however, thanks to 500 years of paper yellowing. Scientists have long known that such yellowing can stem from cellulose—the main component of old, handmade paper—which oxidizes over time to develop colored molecular structures known as chromophores. Until now, however, researchers haven’t identified which chromophores are responsible. […]

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