Simplifying miniature terahertz sources
Researchers in Germany have developed a new, simple approach for generating terahertz radiation.
The researchers at Martin Luther University Halle-Wittenberg (MLU) and Freie Universität Berlin generate ultrafast current pulses by optical means with the aid of the inverse spin Hall effect.
In ferromagnet/normal metal bilayer structures, intense spin current pulses are generated by optical pumping with intense 250fs laser pulses. These spin current pulses are converted into a charge current pulse via the inverse spin Hall effect and launched into waveguide structures.
These nanolayered emitters act as on-chip THz sources and robust ultrafast photodetectors, which can be combined with metallic waveguide structures.
“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,” said Professor Georg Woltersdorf, a physicist at MLU. 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. “The general idea was to miniaturise the process and generate the radiation exactly where it is needed – for example, directly on an electronic chip,” he said.
“This generates an intense spin current pulse,” said Woltersdorf. 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. “In addition, an external magnetic field can adjust the polarity of the current. This has not been possible until now,” he said.
The miniature terahertz source could be used for high-frequency electronics, medicine, materials testing and communications technology.
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