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A radar gun for electrons

NSF Award:

Phase VI: Climate Change and Energy: Basic Science, Impacts, and Mitigation  (University of Kansas Center for Research Inc)

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Most techniques to detect electric currents operate in a manner similar to highway speed cameras: Images of electrons are recorded and later analyzed to measure the electrons' speed relative to position. However, for more accurate measurements researchers need a tool akin to a radar gun. 

As a result of efforts by physics researchers at the University of Kansas (KU), scientists now have such a tool. Using a nonlinear optical process known as second harmonic generation, a team, led by Hui Zhao, has created a way of remotely and immediately detecting electric current speed. 

For their experiment, the researchers applied a voltage across a gallium arsenide crystal, causing the crystal's electrons to move through it with a specified speed. By illuminating the crystal with an infrared laser pulse, one invisible to human eyes, the team produced visible red light--a signature of the second-harmonic generation process. The process records the speed of the electrons without contacting the sample or disturbing the electrons. The brightness of the red light scales with the speed of the electrons. When the electrons have no directional motion, no red light comes out.

This technique could improve many current renewable energy technologies. Solar cells, batteries, artificial photosynthesis and water-splitting all rely on detection of electric currents. Additionally, sensors that better read the motion of electrons could underpin next-generation cell phones and computers.

Zhao collaborated on the research at KU's Ultrafast Laser Lab with Judy Wu and graduate students Brian Ruzicka, Lalani Werake and Guowei Xu. All are supported by Kansas-EPSCoR (Experimental Program to Stimulate Competitive Research).

The findings were published in Physical Review Letters.   

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  • university of kansas students work with the tsunami laser
University of Kansas students work with the Tsunami laser.
Hui Zhao, University of Kansas

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