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  • the relevant data is the Arrivaltime FLASH.SDIAG/BAM/4DBC3/LOW_CHARGE_ARRIVAL_TIME
  • besides the arivaltime from FLASH1 there is also the FLASH2/3 electron arrival time saved. The BAM data is saved for the complete RF pulse. First bunches are from FLASH1 then there is a gap for switching and then there is a second part for FLASH2 (starting at the FLASH2 start time (recorded in DAQ as /FL2/Timing/start time flash2))

  • There are now (since March 2017) LOW and HIGH charge channels. for now the LOW_CHARGE Channel is the relavant one.
  • bigger numbers indicate later arrivaltime of the electrons
  • the arrivaltime sould be within -20 ps and +20 ps . otherwise there might be a problem ...
  • There is a BAM status parameter: FLASH.SDIAG/BAM/4DBC3/BAM_STATUS.1 (the 1 indicates FLASH1)
    • bit 0 (value: 1) = data is valid,
    • bit 1 (value: 2) = at least 1 bunch is present,
    • bit 2 (value: 4) = calibration is on,
    • bit 3 (value: 8) = internal feedback is on,
    • bit 4 (value: 16) = tuning mode is on

  • if DBC3 is not working then also 3DBC2 can be used. there is a linear correlation between BC2 and BC3

more Info to the BAM:

General information for the data analysis of pump-probe experiments

please have a close look to the publication:

Evgeny Savelyev, et al,  Jitter-Correction for IR/UV-XUV Pump-Probe Experiments at the FLASH Free-Electron Laser,
New J. Phys. 19, 043009 (2017),

describing in detail the usage of BAM, streak camera and delay line data in order to get the actual time axis as reliable as possible.

Here is a summary of the ideas:

Streak camera info

  • the streak camera measures the delay between optical (amplified) laser and FEL (dipole radiation). - not in respect to the master clock !
  • streak camera ONLY delivers data which is averaged over several 10 seconds. There is NO shot to shot info.
  • a larger value of the streak camera delay (typically) indicates that the optical laser comes later than the FEL (or FEL earlier than the laser ...)

Correction of pump-probe delay

  • BAM measurement: difference between electrons and timing system
    • usually the BAM signal has to be added to the delay ...
    • it is the best to test addition/subtraction and check the results on a step function (more/less sharp) - if there is no change of the data with + and - there is anyway something wrong. please contact your local contact for more information / help
  • Streak camera: difference between electrons and optical laser
    • it is a slow signal and should only be used as a rolling average over multiple minutes
    • if you see a drift in the streak camera which you do not see in the BAM it is resulting from the optical laser
    • if this (BAM - streak camera signal) is significant e.g. 200 fs over 1 h, it means the drift compensation was probably off and it should be compensated
    • addition/subtraction is dependent on the setup and have to be checked
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