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Scientists at TU Wien, Austria, have developed an extremely efficient terahertz radiation source that has a very broad spectrum – generating different wavelengths from the entire terahertz range. This opens up the possibility of creating short radiation pulses with extremely high radiation intensity. The new terahertz technology has now been presented in the journal Nature Communications.

The "Terahertz Gap" Between Lasers and Antennas

Terahertz radiation today is used for security checks at airports, for medical examinations and also for quality checks in industry. According to Claudia Gollner from the Institute of Photonics at TU Wien, terahertz radiation has very useful properties. It can easily penetrate many materials, but unlike X-rays, it is harmless as it doesn’t ionize the radiation. From a technical point of view, however, terahertz radiation is located in a frequency region which is very hard to access – in sort of a no man’s land between two well-known areas: Radiation with higher frequencies can be generated by ordinary solid-state lasers. Low-frequency radiation, on the other hand, as it is used in mobile communications, is emitted by antennas. The greatest challenges lie exactly in between, in the terahertz range.

In the laser laboratories of TU Wien, a great deal of effort must, therefore, be put into generating the desired high-intensity terahertz radiation pulses. The starting point of the development is the radiation of an infrared laser system. It was developed at TU Wien’s Institute and it is unique in the world. First, the laser light is sent through a so-called non-linear medium. In this material, the infrared radiation is modified and a part of it is converted into radiation with twice the frequency. There are then two different types of infrared radiation. These two kinds of radiation are then superimposed. This creates a wave with an electric field with a very specific asymmetric shape.

Turning Air into Plasma

This electromagnetic wave is intense enough to rip electrons out of the molecules in the air. The air turns into a glowing plasma. Then, the special shape of the wave’s electric field accelerates the electrons in such a way that they produce the desired terahertz radiation. According to Claudia Gollner, their method is extremely efficient: 2.3% of the supplied energy is converted into terahertz radiation - that is orders of magnitude more than can be achieved with other methods. This results in exceptionally high THz energies of almost 200 µJ.’ Another important advantage of the new method is that a very broad spectrum of terahertz radiation is generated. Very different wavelengths throughout the terahertz range are emitted simultaneously. This produces extremely intense short radiation pulses. The larger the spectrum of different terahertz wavelengths, the shorter and more intense pulses can be generated.

Numerous Possible Applications

According to Andrius Baltuska, the Head of the research group at the Vienna University of Technology, this  means that for the first time a terahertz source for extremely high-intensity radiation is now available. Initial experiments with zinc-telluride crystals already show that terahertz radiation is excellently suited to answer important questions from material science in a completely new way. We are convinced that this method has a great future.

Click here to read the published paper.