Sep 14, 2021 |
Spintronics: Physicists develop miniature terahertz sources
(Nanowerk News) Researchers at Martin Luther University Halle-Wittenberg (MLU) and Freie Universität Berlin have developed a new, simple approach for generating terahertz radiation. Strong optical laser pulses enable terahertz electromagnetic fields to be generated directly at a specific point.
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The team has published its findings in the journal ACS Applied Nano Materials ("On-Chip Generation of Ultrafast Current Pulses by Nanolayered Spintronic Terahertz Emitters"). Potential applications for terahertz radiation are wide ranging - from materials testing to communications and security technology.
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Illustration of the new miniature terahertz sources. (© ACS)
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Terahertz radiation lies between microwaves and invisible infrared radiation in the electromagnetic spectrum. It is used, for instance, in materials science to study opaque materials.
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"Terahertz radiation has no ionizing effect; it does not remove electrons from atoms and therefore, unlike X-rays, poses no risk to health. That’s why it’s used in full-body scanners at airports," explains Professor Georg Woltersdorf, a physicist at MLU.
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Until now, the radiation could only be generated using relatively complex equipment, which is why it is currently not being very widely used in research. Woltersdorf’s team worked on a new approach together with researchers from Freie Universität Berlin.
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"The general idea was to miniaturise the process and generate the radiation exactly where it is needed - for example, directly on an electronic chip," says Woltersdorf.
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For their experiments, the physicists used a high-power laser which generates light pulses that last around 250 femtoseconds. One femtosecond equals one quadrillionth of a second. These extremely short optical pulses were then directed onto a magnetic nanostructure to excite the electrons inside.
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"This generates an intense spin current pulse," Woltersdorf explains.
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Simply put, spin is the intrinsic angular momentum of electrons and forms the basis of magnetism. When the electrons are excited, a so-called spin current flows through the interface layers of the nanostructure. The inverse spin Hall effect converts it into a terahertz current pulse. This produces the desired terahertz radiation on the chip, which can be directly coupled into wire structures and utilised.
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"In addition, an external magnetic field can adjust the polarity of the current. This has not been possible until now," says Woltersdorf in conclusion.
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The potential applications of this miniature terahertz source range from research to high-frequency electronics, medicine, materials testing and communications technology.
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