Filter-Units
- Filter control
- Filter transmission - measurements and oxide layers
- More details about damage of filters or oxide layers
- Documentation of the filter protection in jddd
- More (special) info
Filter control
General infos
The filter control panel can be used to move in filters AND to calculate the transmission of the fundamental wavelength of the FEL and its 3rd harmonic.
The moving procedure is supervised by a protection system. First of all the fast shutter is closed before moving the filter wheel (to protect the filters during moving) and blocked till the movement is over. Then the fast shutter has to be opened again with the Fast shutter control button. It does not open automatically!
In addition the pulse energy and the number of bunches in the FEL is monitored. IF the radiation dose exceeds a certain limit the filters can not be moved into the beam. Then the beam has to be attenuated using the gas attenuator to a range where the filters can be used again. More info: JdddFilterProtection
Current limits are: 
(until Nov 2021 we had 300 µJ for single pulse and 2000µJ for the bunch train integral as limit. This turned out to be to much since several filters (mainly Nd and Zr) got damaged in 2020 and 2021)
Calculation of the transmission
The shown transmission values for the filters are based on the CXRO webpage AND on measurements performed at the PTB (data see below).
The transmission is given for the fundamental Wavelength and in addition for the third harmonic of the FEL ( which is typically 1% of the fundamental). The bars below the shown transmission are just a guide to the eye to distinguish between large and weak transmission easier. The values are calculated for the current wavelength set in the FEL.
Since for certain combinations of filters the transmission of the third harmonic can be significantly higher than for the fundamental it may happen that more third harmonic as fundamental passes ... thus there is a warning indicating that this may be a problem ...
By pressing on the transmission values of a certain filter one can open the window showing the transmission as function of the photon energy / Wavelength:
To help finding the right filter setting one can also have an overview of all filters available and look on the transmission for a certain wavelength / photon energy independent of the actual FEL wavelength. Using the tab "transmission" one can type in a photon energy or wavelength → press "calculate transmission" and then see transmission of the fundamental and the 3rd harmonic for this wavelength ... (this is a separate transmission calculator and playing with it does not alter anything on the filter wheels or in the FEL / undulator settings!)
Filter transmission - measurements and oxide layers
- The transmission data for the transmission calculation in jddd uses combined data from CXRO and the measures transmission from BESSY / PTB.
- Thin oxide layers may alter the transmission significantly. As was found for the thin Al foils a transmission of 6 nm (2x3nm) Al2O3 fits well with the measured data - at least much better as compared to only using Al without oxide layer.
- similar results are obtained for Si and Zr ... see filter details below
More details about damage of filters or oxide layers
Documentation of the filter protection in jddd
More (special) info
Mounted filters, replacement in N2 box
- Filter History and mounted filters of FLASH1 and FLASH2: what filter was mounted at which motor position
- Replacement filters in N2 flow box