Fig. 5

Gain reference of our US1000FT-XP 2 detector in the middle, acquired by adding up 30 images under homogeneous illumination conditions in TEM mode and then subtracting 30 dark frame images with the same exposure of \(t \approx 0.85\, \text {s}\). The mean intensity of each image was targeted at \(\hat{S}_{ref} \approx\) 7050 counts. Due to differences in the glue and the fluorescence layer in the manufacturing, the gain reference shows stripes superimposed to artifacts from the fiber optics. The gain reference is surrounded by the individual frequency distributions of the gain values in the four detector quadrants Q1-Q4, where each dot represents an interval of 0.01 around its center. Since the gain reference normalizes with respect to all quadrants, the respective mean values of the quadrants differ from 1. The standard deviations \(\sigma \approx 0.067\) are similar for all quadrants indicating a rather homogeneous gain distribution across the detector, however the aforementioned stripes and artifacts lead to small differences. Overall, the gain distributions are slightly skewed to the right for all quadrants, as a result of the inversion. Therefore, the overall mean of the inverse gain reference differs slightly from 1 (see Eq. 7).