In order to clean the photon beam emitted by the source from unwanted radiation such as seed laser, higher harmonics or first stage (for FEL2), a system of filtering stations is installed along PADReS. In particular, each FEL has a dedicated filtering station in the undulator hall, with two discs hosting up to 11 filters each. Moreover, another 2-disc filtering station is installed in the experimental hall serving the following endstations: EIS-TIMEX, DiProI and LDM.
The filters can be mounted and replaced before each experimental run, and several materials and filter-thicknesses are available for users.
For each filtering station it is possible to select up two different filters, one on the "IN" disc and the other on the "OUT" disc.

In the following figure the location of the three filtering stations is reported.

The mechanical layout of a filtering station is reported in the following left figure.
The right figure reports typical examples of FEL radiation filtering for FEL1 and FEL2. In oboth cases only the fundamental FEL radiation is selected, while all the rest (including seed laser, higher harmonics, different stage photons) is cut.
NOTE: for each experiment a proper selection of filter can/should be done. Depending on the wavelength, it could be not possible to find a single filter that cut everything except the wavelength of interest. In that case, multiple filters can be use (affecting also the final intensity).
For some cases also the Gas Absorber, normally used just to reduce the FEL intensity, could have a filtering effect depending on the used gas.


Last Updated on Friday, 15 November 2019 12:07