Electron-detection breakthrough could unleash next-generation technologies

February 29, 2012

(PhysOrg.com) -- Physics researchers at the University of Kansas have discovered a new method of detecting electric currents based on a process called “second-harmonic generation,” similar to a radar gun for electrons that can remotely detect their speed.

Their new idea could improve many present-day renewable-energy technologies — like solar cells, batteries, artificial photosynthesis and water splitting — that rely on detection of . Further ahead, sensors that better read the motion of electrons could underpin next-generation cell phones and computers.

“So far, most techniques to detect electric currents are very much like measuring the speed of a car by tracking it with a camera, and later analyzing how the position changes with time,” said Hui Zhao, assistant professor of at KU. “But for moving cars, a radar gun is a much better tool, since radar allows us to instantaneously measure the speed. Yet, for electrons, there has been no tool available that allows us to directly ‘see’ the motion like this.”

Zhao collaborated on the research at KU’s Ultrafast Laser Lab with Judy Wu, University Distinguished Professor of Physics, and graduate students Brian Ruzicka, Lalani Werake, Guowei Xu. Their findings recently were published in Physical Review Letters.

The researchers discovered that by shining light from a high-power laser onto a material that contains moving electrons, light of a different color is generated. They looked at thin crystals of gallium arsenide — a material commonly used in high-speed electronics and photonics. By applying a voltage across the crystal, they set electrons to move through it with a specified speed. By illuminating the crystal with an infrared laser pulse, invisible to human eyes, they found that visible red light was produced — a signature of the second-harmonic generation process.

Additionally, they observed that the brightness of the red-light scales with the speed of electrons. When the electrons have no directional motion, no red light comes out.

“By detecting the red light, one can accurately determine the of electrons without making any contact with the sample and without disturbing the ,” Zhao said. “Before this study, it was generally known that an electric current has three effects: It can charge the system, change its temperature and produce a magnetic field. As a result, all experimental techniques of current detection were based on these effects. This newly discovered optical effect of currents opens up a new way of using lasers to study currents.”

The KU researchers’ experimental results are consistent with theoretical studies performed by professors Jacob Khurgin of John Hopkins University and Eugene Sherman from Spain.

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1 / 5 (2) Feb 29, 2012
"...without making any contact with the sample..."!

IF Einstein is correct and photons are JUST particles then the process DOES make contact but if photons are just waves then this statement is correct.
4.7 / 5 (3) Feb 29, 2012
IF Einstein is correct and photons are JUST particles then the process DOES make contact but if photons are just waves then this statement is correct

Photons exhibit patricle-LIKE behavior at times and wave-LIKE behavior at times. Photons are not particles, nor are they waves.
Taking macrosocopic analogies to the microscopic is bound to cause confusion.

The concept of 'contact' is also very iffy when talking about the microscale. When you lean on your desk no atom is touching another atom (no contact of particles happens - if that were the deciding factor then you would fall through your desk since atoms are overwhelmingly empty space). The electrostatic forces keep this from happening.
What they are saying this is that they're not using atomic distances that at such small scales but remote sensing via photons.
3 / 5 (2) Feb 29, 2012
Indeed, as antialias said, the meaning of "contact" here has to be inferred as being "from outside the system with negligible influence on the system itself at scales commonly used in present-day electronics".

Otherwise, the mere existence of the electrons means that they are in "contact" with everything else in the universe, as information about gravity and distance and applicable forces is being "exchanged" constantly in the exact same manner that information about repulsion is exchanged between atoms in a "physical contact" such as antialias' leaning-on-a-desk example. It has been shown within the current limits of provability that there is no "maximum range" at which interactions between particles occur.

The "exact manner" I refer to, of course, is as of yet unknown.
not rated yet Feb 29, 2012
But why is detecting electron flow important? What impact is this technology going to have? I can't understand it.

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