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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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