- 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 ...)
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