Page History

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• Giacomo is doing spatial, Ryan is spectral (roughly speaking)
  • both are interferometric, so the background we had in LCLS1 is mostly gone, but still have some background from stray light, for example
• Formula that should work for both:  (S-B)/(S(delayed)-B(delayed)). (note: division is similar to normalized subtraction:  (S-GB)/G B = (S/GB)-1
• B is different for S and S(delayed) (background at time "delayed" is taken)
• Giacomo thinks we won't need the "delayed" subtraction/division for 80% of the experiments
• Giacomo will ensure that we run in a regime where (S(delayed)-B(delayed)) is not close to zero
• sxrx34917 (being analyzed by Giacomo and Stefan Droste).  this data is "zoomed out" in the time dimension, but will be more zoomed-in for LCLS-II.
• S(delayed) comes from moving the laser out of the time window, and is done "offline" according to Giacomo every few hours
• Giacomo wants a fit to the minimum of dI/dt (derivative of I-B) to a parabola
• Giacomo thinks that the feedback will be slower (millisecond level).  Contradicts what we learned before where Joe Frisch was going to do fpga stuff with the laser-locking system
• algorithm should be same for spatial/spectral
• Giacomo wants a way to look at S-Delay when the timing edge is out of the window.  Tells them if it's on the "right" or the "left".
• Questions for Giacomo:
  • the edge looks big in sxrx34917, do we definitely need to divide? Answer: no, as long as we can set an ROI.  i.e. don't need
  • does the "delayed" contain background from stray light, for example?  Answer: "delayed" is the pump laser delayed off the end of the camera image
  • is B just pedestal, or does B include laser-pump?  If it's laser-pump, do we need to use IIR to compute B?  Answer:  B is remaining background (same as LCLS-I) not eliminated by interferometric approach.
  • do we use the same B in the numerator/denominator?  Answer: no

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