Holograms  

The interactive holograms featured in films like Iron Man and Big Hero 6 may be closer to reality thanks to work done by Japanese researchers with femtosecond lasers.

Researchers in Japan have created a mid-air 3D holographic plasma display that also features haptic feedback.

"This study is the first step to discuss and design laser-based aerial volumetric displays," write the researchers.

The system, demonstrated in the video below, works by way of using a femtosecond laser to turn small pockets of air (voxels) into plasma.

"This study is the first step to discuss and design laser-based aerial volumetric displays."

The holographic system, which will be presented at SIGGRAPH 2015 next month, can render up to 200,000 voxels per second, but the physical size of the display is limited to about a cubic centimeter.

The researchers commented on the details of the theoretical principles, system setup, and experimental evaluations, and also discusses the scalability of the system, along with limitations, and applications. "Although we focus on laser-induced plasma, the same considerations can be applied to
other emission techniques such as fluorescence and cavitation," they write.

A femtosecond laser is a laser that fires for a short burst—on the order of one quadrillionth of a second. The laser hits an atom or molecule, causing an electron to become ionized and then the electron loses its extra energy in the form of a photon that is emitted as visible light.

To transform the single plasma dot into a full 3D display, the researchers passed the laser through a spatial light modulator (SLM) connected to a PC to create the hologram, and then a galvano scanner and varifocal lens to "draw" each voxel with specific X, Y, and Z coordinates.

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One of the more intriguing aspects of the 3D display is that it also incorporates haptic feedback. According to the research paper, when you touch one of the voxels, "shock waves are generated by plasma ... the user feels an impulse on the finger as if the light has physical substance." The researchers don't go into any further detail on the topic, however.

The paper also notes that using a femtosecond laser (as opposed to a picosecond or nanosecond laser) is one of the novel aspects of the system. Because the laser bursts are so short, the plasma is not that energetic, and so it's safe to touch. The researchers also tested a nanosecond laser, but found that it burned a piece of leather within 100 milliseconds.

The femtosecond laser setup appears to be safe and doesn't cause any skin damage when a user touches the display, though you still shouldn't look into the laser source. When touched, the laser feels like sandpaper, says principal investigator Yoichi Ochiai, although some participants thought the plasma felt a little like a static shock.

For now, the holographic plasma display is too small to be of much use—and perhaps more importantly, the equipment used to produce the display is too large and expensive for anything outside of the lab. The principles are all quite sound, though, and there's a lot of interest in free-space display technologies that don't require some kind of screen or other medium to project the image onto.



SOURCE  Popular Science

By 33rd Square

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 Superconductivity  

Researchers have found that an infrared laser pulse briefly modifies the structure of a high-temperature superconductor and removes its electrical resistance even at room temperature.

I
n the 1980s, physicists first discovered a new class of materials based on ceramics. These materials conduct electricity at temperatures of around minus 200 degrees Celsius without losses, and were therefore called high-temperature superconductors. The compound yttrium barium copper oxide (YBCO) is one of these high-temperature superconductors and is one of the most promising materials for technical applications of the material, such as superconducting cables, motors and generators.

YBCOs crystal have a special structure: thin double layers of copper oxide alternate with thicker intermediate layers which contain barium as well as copper and oxygen. The superconductivity has its origins in the thin double layers of copper dioxide. This is where electrons can join up to form so-called Cooper pairs.

Cooper pairs can “tunnel” between the different layers, meaning they can pass through these layers like ghosts can pass through walls,in a type of quantum effect. The crystal only becomes superconducting however below a "critical temperature."

Above the critical temperature, this coupling between the double layers is missing, and the material becomes a poorly conducting metal.

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Andrea Cavalleri at the Max Planck Institute first discovered that when YBCO is irradiated with infrared laser pulses it briefly becomes superconducting at room temperature in 2013. The laser light had apparently modified the coupling between the double layers in the crystal.

The precise mechanism was unclear until the physicists were able to solve the mystery with an experiment at the Linac Coherent Light Source (LCLS) laser in the US, the world’s most powerful X-ray laser.

"It could assist materials scientists to develop new superconductors with higher critical temperatures and ultimately to reach the dream of a superconductor that operates at room temperature and needs no cooling at all."

“We started by again sending an infrared pulse into the crystal, and this excited certain atoms to oscillate,” explains Max Planck physicist Roman Mankowsky, lead author of the current study published in Nature. “A short time later, we followed it with a short X-ray pulse in order to measure the precise crystal structure of the excited crystal.”

According to the researchers, the infrared pulse had not only excited the atoms to oscillate, but had also shifted their position in the crystal as well. This briefly made the copper dioxide double layers thicker - by two picometres, or one hundredth of an atomic diameter - and the layer between them became thinner by the same amount. This in turn increased the quantum coupling between the double layers to such an extent that the crystal became superconducting at room temperature for a few picoseconds.

On the one hand, the new result helps to refine the still incomplete theory of high-temperature superconductors. “On the other, it could assist materials scientists to develop new superconductors with higher critical temperatures,” says Mankowsky. “And ultimately to reach the dream of a superconductor that operates at room temperature and needs no cooling at all.”

Until now, superconducting magnets, motors and cables required cooling to temperatures far below zero with liquid nitrogen or helium. If this complex cooling were no longer necessary, it would mean a breakthrough for this technology. This research may point to promising directions for understanding and development of higher temperature superconductors.


SOURCE  Max Planck Institute

By 33rd Square

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