Thursday, July 27, 2017

Inspecting Matter with Terahertz Radiation

In the FLUTE linear accelerator, electron clouds are accelerated to generate terahertz radiation.

Nadine Klein

The FLUTE accelerator at Karlsruhe Institute of Technology (KIT) is designed to develop new accelerator technologies for compact and powerful terahertz radiation sources in order to harness the radiation for materials sciences.
In materials research, chemistry, biology and medicine, chemical bonds, and especially their dynamics, determine the properties of a system. These properties can be investigated very precisely with terahertz radiation in short pulses. The FLUTE (Ferninfrarot Linac- und Test-Experiment – Far-Infrared Linear Accelerator and Test Experiment) facility at KIT is a development platform for accelerator physics. The facility will be used initially to better understand the complex dynamics of ultra-short electron bunches, as well as to measure and control them. Only extremely small electron bunches enable intense and coherent terahertz radiation to be generated. For this purpose, the electron cloud has to be held so closely together during acceleration that its expansion is less than the wavelength of the generated electromagnetic radiation. Only then will the waves superpose with each other to create pulses of high intensity with durations of picoseconds or femtoseconds.
In the long term, control of the electron bunches has to be improved so that the terahertz radiation can be perfectly tailored to the needs of the users. Terahertz radiation could open up areas of application closed to neighbouring visible light and radio waves. As a research platform, FLUTE will also be used to develop measurement methods for terahertz radiation that can be used by materials and life sciences. Vibrations of proteins can be investigated equally as well as the behaviour of superconductors or novel semiconductors.
The electrons are accelerated to an energy of up to 50 MeV within the approximately twelve-metre-long accelerator. By compressing the electron cloud to a few microns, radiation with a frequency of 30 terahertz or more becomes possible. In addition to the Institute for Beam Physics and Technology at KIT, partners from all over Europe, especially the Paul Scherrer Institute PSI from Switzerland, have participated in the development of FLUTE.

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