Pulses on photodiodes in entry 20 

1. seem wide, so we also looked at qswitch signal; also seemes wide.
2. Have a tail

1.:

We investigated this and came to the conclusion, that the CFD is the issue:
- On an oscilloscope, when looking at both HF signal (CFD input) and CFD output, there is a 2ns jitter.
- The same jitter is visible when looking at the CFD output when triggering on a freq. generator signal with same frequency and amplitude as HF signal (1.54263 MHz; 1V peak to peak).
- There is not significant jitter when comparing the CFD output and the qswitch signal

We tried differents CFD (also a leading edge CFD / different thresholds), but this did not significantly improve what we saw on the oscilloscope.
Applying a 10MHz filter to the HF signal only made the jitter worse.
There might be an option to get a logic (NIM) signal from ESR instead of the sin-signal
Alternatively, one could think about using a PLL.
Note: the 2ns might also be limited by the trigger of the oscilloscope. We saw that if the trigger of the oscilloscope is not on the steepest part of the HF signal, the jitter "gets worse".

2.:

We saw on the qswtich signal, that there are instances, when  the q-switch signal is too early; 
Ww will try to find out which NIM module between the CFD and the final qswitch signal causes this
Preliminary: It's coincidance crate