Sheila, Kiwamu, Robert, Daniel, Stefan

After a lot of discussion about possible ways for jitter noise to end up as intensity noise, still nothing really added up. Nevertheless, here are some related numbers:

Quoting the noise around 300Hz, we have

For beam jitter:

- DBB measurement of the laser amplifier: relative beam jitter (rad/divergence angle): 2-10 e-6/rtHz (alog 28729)
- IM4 relative beam jitter (PIT/SUM, YAW/SUM): 2-5e-8/rtHz (plot 1)

For Intensity noise:

- Excess noise in DCPD-sum 1.5e-7mA/rtHz --> 20mA --> 8e-9/rtHz RIN (plot 2)
- RIN coupling from entering main IFO to DCPD (measured) up to 0.05 RIN/RIN around 300Hz (alog 29644), but varying a lot.
    - thus we need the equivalent of 1e-7/rtHz RIN entering the IFO
- The REFL_A_LF_OUT_DQ, calibrated in RIN, reports a rin of 4e-9/rtHz (plot 3)
- The ISS out of loop PD reports a RIN of 7e-9/rtHz (alog 30026)

The number we were missing is an experimental measurment of the (power) transfer function beam jitter after the IMC (e.g. added through the IMs), directly to DCPD_SUM RIN.

Also, the spectum of plot 2 was taken at a time when almost none of the jitter peaks shoed up in DARM - however there is still a clear broadband hump visible. We seem to be fighting two different phenomena here. Robert also had a plot that shows that this broadband stuff is coherent with the ISS_SECONDLOOP control signal... as I promised, no conclusion.