Monday 24 October 2016
to 11:00 at
Peter van der Meulen (Chemical Physics Division)
The THz region of the electromagnetic spectrum, corresponding to a wavelength of roughly 30-3000 micrometer, has attracted an increasing number of researchers recently. The low-energy photons can be used to study a wide range of interesting physical and chemical phenomena such as low-frequency vibrations in molecules and crystals, ultrafast magnetic switching, superconductivity in strongly correlated materials and conformational dynamics in bio-molecules. However, for a long time researchers have struggled, and are still struggling, with a lack of suitable light sources in this particular spectral range.
A potentially attractive source of THz radiation is formed by the high-quality electron bunches used in modern X-Ray free electron lasers such as FLASH in Germany, LCLS in USA, SACLA in Japan and perhaps even in a future version of MAX IV in Lund. By sending these bunches through a thin metal foil, after they have been used for X-Ray generation, short and intense bursts of THz radiation can be generated via a mechanism known as Optical Transition Radiation (OTR). As a by-product of the generation of X-Rays the THz pulses are obtained (almost) for free. Furthermore, the THz pulses can be employed for diagnostic purposes and are automatically synchronized with the X-Ray pulses which opens up the possibility of exciting pump-probe style experiments.
Unfortunately, these OTR-based THz pulses are intrinsically radially polarized whereas most experiments require either linearly or circularly polarized radiation. In my presentation I will discuss several efficient and cost-effective strategies to convert the radially polarized THz pulses into linearly or circularly polarized ones. If successful in practice, they may greatly stimulate the application of OTR-based THz pulses in chemistry and physics research.