A research group at TU Wien has developed a terahertz radiation source that is both efficient and creates a broad spectrum, generating different wavelengths from the entire terahertz range. Both aspects are said to have broken previously held records. The research group believes the new radiation source will allow short radiation pulses to be generated with high radiation intensity. Claudia Gollner and the laser system at TU Wien. Courtesy of TU Wien. “Terahertz radiation has very useful properties,” said Claudia Gollner from the Institute of Photonics at TU Wien. “It can easily penetrate many materials, but unlike x-rays, it is harmless because it is not ionizing radiation.” Terahertz radiation is located in a frequency region that is difficult for researchers to access. Radiation with higher frequencies can be generated by ordinary solid-state lasers, while low-frequency radiation is emitted by antennas. Researchers’ greatest challenges lie in between, in the terahertz range. “Our starting point is the radiation of an infrared laser system. It was developed at our Institute and it is unique in the world,” Gollner said. First, the laser light is sent through a nonlinear medium. In this material, the infrared radiation is modified; part of it is converted into radiation with twice the frequency. “So now we have two different types of infrared radiation,” Gollner said. “These two kinds of radiation are then superimposed. This creates a wave with an electric field with a very specific asymmetric shape.” 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. “Our method is extremely efficient,” said Gollner, “with 2.3% of the supplied energy 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.” Gollner says another important advantage of the new method is that a broad spectrum of terahertz radiation can be generated. Diverse wavelengths throughout the terahertz range are emitted simultaneously, producing intense radiation pulses. The larger the spectrum of different terahertz wavelengths, the shorter and more intense pulses can be generated. “This means that for the first time a terahertz source for extremely high-intensity radiation is now available,” said Andrius Baltuska, the head of the research group at the Vienna University of Technology. “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.” The new terahertz technology has now been published in the journal Nature Communications.