Beamline Description

Optical Layout

The THz light will then be propagated in the FERMI experimental room, which is located more than 20 meters far from the source, and separated by two shielding walls for radiation safety. Because of its large divergence properties, a collimated THz beam can not be propagated along distances of ten's of meters. For this reason, the TeraFERMI beamline employs 6 focusing and 4 mirrors which are thus allowing to keep the beam size within the optical pipes dimensions. With the present layout, the overall beamline length is of about 33 meters.


The propagation properties of the THz beam have been simulated with the help of the THzTransport code. THzTransport is a code based on scalar diffraction theory, developed at DESY in the group of B. Schmidt. The code calculates the complex electric field at any plane perpendicular to the optical axis, thus allowing to propagate the light emitted from a CTR source, throughout the whole set of 10 mirrors constituting the TeraFERMI beamline. An example of propagation at a frequency of 0.3 THz is provided in the figure below (simulation by C. Svetina).


The simulation shows that the efficiency of the beamline increases with frequency, up to 0.4-0.5 THz, and then saturates at very high transmission properties. This is a consequence of the decreased beam divergence and diffraction at the shorter wavelength. Above 0.5 THz (corresponding to 600 micrometer wavelength), diffraction effects become negligible with respect to the mirror size, and more than 90% of the radiation collected by the first mirror is transmitted throughout the beamline.

Ultima modifica il Venerdì, 01 Ottobre 2021 10:49