• 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:

• LINK to detailed infos from MSK (may only work inside DESY network)
• talk by Marie (2011)
• contact: Marie Kristin Czwalinna

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), https://doi.org/10.1088/1367-2630/aa652d

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 ...)

Calculate 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