Dynamic acquisition of the flat field

In case it is not possible to uniformely illuminate the detector due to its large dimensions, one of the solutions is to scan it in front of an illuminated are with a uniform speed such that the integrated number of counts during the exposure time is the same for all channels.

To do that, at the SLS we have optimized the dynamic acquisition of the flat fiel with the MYTHEN detector using a setup similar to the one sketched in figure 3.6. It is important that the scanning range of the detector is chose such that the detector is not illuminated both at the beginning and at the end of the acquisition. Moreover the movement of the detector should be as uniform as possible. To avoid this kind of systematic errors we normally sum two flat field images taken in the two opposite directions of translation.

Also take care that your sample does not emit fluorescent light at the chosen energy (e.g. a glass rod works at all energies, but heavier materials can be chosen to increase the efficiency at higher energies taking care that the fluorescence emission is negligible).

Figure 3.6: Sketch of the experimental setup for a dynamic acquisition of the flat field.