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Gizmorama - May 9, 2018

Good Morning,


When you're thinking of a way to search for contaminants in water, you think levitation, right? Well, I guess you're not the only one.

Learn about this and more interesting stories from the scientific community in today's issue.

Until Next Time,
Erin


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*-- Scientists levitate water droplets to look for contaminants --*

It turns out it's easier to find heavy metal contaminants in water when droplets are levitated using sound waves.

Trace amounts of heavy metals are difficult to measure, but even tiny amounts can be dangerous. Thus, detecting metal toxins is essential to protecting human health.

"Despite the large variety of water sensors that offer continual monitoring, detection of multiple heavy metals dissolved in water can only be performed by sending samples off for specialized laboratory analysis," Victor Contreras, a physicist at the National Autonomous University of Mexico, said in a news release. "Our new technique is one step toward the development of a simpler analysis approach that could be applied on-site and in real time. This type of water analysis could be used by agricultural, pharmaceutical, water purification and other industries to monitor water for contaminants."

To identify contaminants, scientists used laser induced breakdown spectroscopy. By levitating water droplets with sound waves, scientists can isolate the evaporation process and increase the concentration of contaminants in the tiny sample.

Using the technique, researchers were able to identify small amounts of barium, cadmium and mercury. The analysis process takes just a few minutes.

Laser induced breakdown spectroscopy uses a high-energy laser pulse to vaporize the droplet and produce a plasma. The plasma absorbs the light and reemits unique wavelengths. Encoded in these wavelengths are the spectral signatures of different molecules, thus, revealing the sample's chemical composition.

Usually, scientists place a water sample on a substrate, like a slide disk, and allow it to evaporate. This lets them uses a slightly smaller and more energy-efficient laser, but it takes a while. As well, water evaporation can allow impurities to contaminate the sample and interfere with the analysis.

Scientists solved the problem by levitating tiny drops of water with sound waves.

"Acoustic levitation is a simple and inexpensive method to preconcentrate the elements of interest while avoiding contamination from the substrate surface," said Contreras. "Moreover, it does not require the sample to have any type of electric or magnetic response like some other methods used to achieve levitation."

Researchers detailed their new methodology in a paper published Thursday in the journal Optics Letters.



*-- Microscopic roundabout directs light without a magnet --*

Circulators direct light on optical chips, a process essential to communication technology. The component relies on a tiny magnet, but miniaturizing magnets is difficult.

Enter the magnet-free optical circulator. The roundabout can route light without the assistance of a tiny magnet. Researchers say it's the first of its kind.

Using a unique combination of entrance and exit ports, circulators ensure that light is directed to the proper place and that no light -- or information -- is lost on the path from one port to another.

"Light propagation is symmetric in nature, which means if light can propagate from A to B, the reverse path is equally possible. We need a trick to break the symmetry," lead researcher Ewold Verhagen, scientist at the Dutch research institute AMOLF, said in a news release. "Usually this 'trick' is using centimeter-sized magnets to impart directionality and break the symmetric nature of light propagation. Such systems are difficult to miniaturize for use on photonic chips."

Verhagen and his research partners, including scientists from the University of Texas, replaced the magnetized circulator with a microscale glass ring resonator. Structural vibrations control when light can exit and where.

"By shining light of a 'control' laser in the ring, light of a different color can excite vibrations through a force known as radiation pressure, but only if it propagates in the same direction as the control light wave," Verhagen said. "Since light propagates differently through a vibrating structure than through a structure that is standing still, the optical force breaks symmetry in the same way as a magnetic field would."

Scientists still had to find a way to ensure the propagated light exited at the proper port, the next available exit. They realized the control laser can use a phenomenon called optical interference to propagate the light out of a specific exit.

"We demonstrated this circulation in experiments, and showed that it can be actively tuned," said postdoc John Mathew. "The frequency and power of the control laser allow the circulation to be turned on and off and change handedness."

The breakthrough -- detailed in the journal Nature Communications -- could do more than improve communication technologies, it could also power quantum computers.

"The fact that the circulator can be actively controlled provides additional functionality as the optical circuits can be reconfigured at will," Verhagen said.

***

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