Crosstalk Correction

For background on the crosstalk, see Michael Feser's thesis. The crosstalk is determined by raster scanning the detector through a collimated beam (10 $\mu$m diameter pinhole downstream of exit window). An image of the detector segments is obtained. In the following, we will denote the detector segments by the number of the software channel which reads it out (see Fig. 18). Refer to table 6 to see which software channel corresponds to which detector segment, as given by the chip design.

Table 6: Software channels and corresponding detector segments, as given by the chip design

Software Channel	Detector Segment
0	1d
1	2d
2	3d
3	4d
4	5d
5	6d
6	7d
7	8d

Figure 18: Image of the detector segments, obtained by a detector scan with a pinhole installed. The numbers correspond to the ADC channels. The image shows the detector chip turned by 90 degrees because for detector scans, the Y axis is the fast axis (the chip is actually installed with the three inner segments horizontally).

For each segment $n=0 \dots 7$, you will have to correct the crosstalk with all other segments $m = 0 \dots 7$ (except $n$). Refer to these indices in the following description.

Start the detector calibration routine with the keyword crosstalk set:

    IDL> det_cal, /crosstalk

• Select the microscope you are using (sxtmi, stxmo or cryo).

• Select the detector map file that you just recorded in the popup.

• Another popup window will display the data channel (ADC channel) $n=0$. This will be the first segment for which you correct the crosstalk with the other segments $m$. It will be clearly visible, and any other segments $m$ "crosstalking" to it will be faintly visible.

• By typing m, you can change the display maximum to any value between 0 and 100%, where lower values will show the crosstalking channels more clearly.

• For all segments $m = 1 \dots 7$ crosstalking to segment 0, do the following:
  • Type the number of the channel (segment) you want to correct, let's say $m=1$.

  • Then give a guess for the crosstalk in per cent. If the crosstalking segment is brighter than the surrounding, you will have to give a negative number, and vice versa.

  • Repeat the above until the crosstalking segment disappears. You have to type in the channel number each time.

  • By typing m, you can change the display maximum setting at any time, to make slight brightness differences more clearly visible.

  • Do the correction for all other channels $m$ by just typing the corresponding channel number and playing around with the crosstalk percentage.

  • Then type x to exit. The program will jump to the next channel $n=1$.

• For all other segments $n=1 \dots 7$, do the same.