Image captures light as both wave and particle for very first time

In 1905, Albert Einstein provided an explanation of the photoelectric effect – that various metals emit electrons when light is shined on them – by suggesting that a beam of light is not simply a wave of electromagnetic radiation, but is also made up of discrete packets of energy called photons. Though a long accepted tenet in physics, no experiment has ever directly observed this wave/particle duality. Now, however, researchers at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland claim to have captured an image of this phenomenon for the first time ever.

To achieve this, a team of researchers led by Assistant Professor Fabrizio Carbone at EPFL has performed an experiment using electrons to image light.

In essence, the team used extremely short (femtosecond) pulses of laser light directed at a miniscule nanowire made of silver and suspended on graphene film that acted as an electrical isolator (or metal-graphene dielectric). The laser light pumped energy into the system that then directly affected the charged particles in the nanowire, causing them to vibrate and effectively making the nanowire behave as what is known as a quasi-1D plasmonic nanoantenna.

In other words, the nanowire acted as a tiny antenna that generated radiation patterns in sympathy with the received laser excitation. This laser light then oscillated back-and-forth between the two ends of the nanoantenna and, in so doing, set up a standing wave of surface plasmon polaritons (electromagnetic waves that travel along the surface of a metal-dielectric or metal-air interface) in the wire.

Put simply, the light traveled along the wire in two opposite directions and, when these waves bounced back to the middle, they intersected with each other to form a new wave that appeared to be standing in place. This standing wave, radiating around the nanowire, then became the source of light used in the experiment.

Next, the researchers aimed a stream of electrons into the field generated around the nanowire, and used them to image the standing wave of light. When the electrons intermingled with the restrained light contained on the nanowire – that is, where they crashed into individual photons – they either sped up (gained energy) or slowed down (lost energy).

The team then used an imaging filter to select out only those electrons that had gained energy, and focused a UTEM (ultrafast transmission electron microscopy) instrument on these to image where each of the changes in energy state occurred, thereby allowing them to visualize the standing wave and make visible the physical makeup of the wave-nature of the light.

Simultaneously, this also demonstrated the particle nature of the imaged light by demonstrating that the change in speed of the interacting electrons and photons shows as an exchange of energy “packets” (quanta) between the electrons and the photons. This demonstrated that the light on the nanowire was also behaving as particles.

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” said Professor Carbone.

Professor Carbone also believes that this experiment not only illustrates the physical observation of the wave/particle duality of light, but it is another step toward the realization of light-based quantum devices and future technologies.

“Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing,” he says.

The research was a collaboration between the Laboratory for Ultrafast Microscopy and Electron Scattering of EPFL, the Department of Physics of Trinity College (US) and the Physical and Life Sciences Directorate of the Lawrence Livermore National Laboratory.

The results of this research were recently published in the journal Nature Communications

The short video below shows an illustrated representation of the experiment.

Source: EPFL

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Bio-inks allow sensors to be drawn onto skin, leaves and other surfaces

You’ve probably heard about pens with conductive ink, that allow users to draw circuits onto materials such as paper. Now, researchers at the University of California, San Diego have gone a step or two farther – they’ve created “bio-inks” that could be used to draw sensors onto a variety of surfaces, using an ordinary ballpoint pen.

The inks are simply loaded into store-bought pens, and were initially designed as a means of measuring diabetics’ glucose levels by being applied to their skin.

Specific enzymes are used in each type of ink, depending on what chemical it’s designed to detect. Among the other ingredients are polyethylene glycol, which serves as a binder; graphite powder, for electrical conductivity; chitosan, which helps the ink adhere to surfaces; and xylitol, which stabilizes the enzymes. The mixture is reportedly safe for application to humans, and remains viable over long periods in storage prior to use.

So far, the bio-inks have been successfully used to measure both glucose beneath the skin, and pollutants on leaves. It was estimated that the ink in just one pen would be sufficient for about 500 individual glucose tests

Down the road, the researchers believe that the inks could also be used for applications such as detecting explosives on the battlefield, measuring toxic gases on building walls, or to add health-monitoring functionality to smartphones.

Currently, although the drawn-on ink serves as the sensor itself, a separate device known as a potentiostat must be brought into contact with it in order to actually read it. The UC Diego team hopes to change that, however, by developing bio-ink sensors that communicate wirelessly with monitoring devices.

The research was led by Joseph Wang, whose lab has previously developed temporary-tattoo-like sensors that measure lactate levels and detect metabolic problems. A paper on the bio-ink was recently published in the journal Advanced Healthcare Materials.

As a side note, scientists at MIT have previously used pencil lead containing carbon nanotubes to draw sensors onto paper.

Source: University of California, San Diego

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