Cost-effective terahertz generator leverages electron spin

Cost-effective terahertz generator leverages electron spin

Technology News |
By Christoph Hammerschmidt

In the electromagnetic spectrum, the terahertz waves occupy the space between the microwaves and the infrared light, ranging from 1 to 30 THz. The radiation is very useful because it can penetrate many materials including clothing and plastics. Other materials absorb the radiation in specific ways. In contrast to x-rays, terahertz waves pose no risk to health. For this reasons, terahertz waves are used in body scanners in airports or other security-relevant locations. Other applications include quality control in the food industry.


An obstacle for usage on a broad basis lies in the fact that equipment capable of generating waves across the entire terahertz spectrum is clumsy, large and expensive. Therefore, scientists from the Forschungszentrum Jülich along with partners from France, Germany, Sweden and the USA have devised a scalable terahertz emitter that suits for desktop (or benchtop) equipment.


The new THz source utilizes a femto second laser that generates ultra-short flashes of light – up to 80 million times per second. Existing THz sources require laser sources that consume much more power and hence are more expensive, more complex and more spacious. The new emitter resembles a photo diode or solar cell. The illumination of the emitter material with an ultra-short laser flash generates a voltage pulse that in turn emits an electromagnetic pulse. In contrast to solar cells however, the emitter consists of a metal film with a thickness of just 5.8 nanometers, resulting in almost no attenuation of the terahertz radiation within the emitter material. After systematic improvements of the materials used and the layers, a relatively weak laser beam is sufficient to generate waves covering the entire spectrum from 1 to 30 terahertz.


One reason for the high energy and spectral efficiency is that the device is leveraging the spin of the electrons as well as their charge. “The spin is a magnetic property of the electronics; it is the reason why electric current behaves different in magnetic and non-magnetic metals”, explains Frank Freimut from the junior group of topological nanoelectronics at the Forschungszentrum Jülich. The new source makes use of this effect – it controls the electron transport in such a way that the terahertz wave can be radiated off particularly efficiently.

An algorithm also developed at the research center enables the physicists selecting materials suited for this task and understanding the results of their experiments.

More information: Prof. Dr. Yurij Mokrousov, and Dr. Frank Freimuth,


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