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Detector Characterisation (Broadband noise)
mwas - 15:53 Thursday 23 November 2017 (40134) Print this report
Shot noise changes with higher laser power
Figure 1, with the increase of laser power over the last week the high frequency noise has not improved much, about 15%.
Figure 2, the input power has increased from 14W to 26.5W so an increase of a factor 1.9, which should improve shot noise by sqrt(1.9)=1.37.
However the power in the arms has increased less than that, for B7 from 325mW to 510mW, so an increase of 1.57 that should correspond to only 1.25 improvement in shot noise

On top of that the PD are less shot noise + electronic noise dominated.
Figure 3 shows the situation before power increase, where the PD subtraction is 7% below the PD sum
Figure 4 shows the situation after the power increase, where the gap increases to 15%.

A large part of that is due to a decrease in CMRF.
Figure 5 shows that the coherence with LSC_PRCL is 15% (out of loop sensor of frequency noise)
Figure 6 shows that the noise projection of SSFS quantum noise is less than a factor 3 below shot noise.

So in total the 15% improvement in shot noise is roughly consistent with only 25% improvement in shot noise and a larger coupling of frequency sensing noise.
Images attached to this report
Comments to this report:
genin - 21:13 Thursday 23 November 2017 (40142) Print this report

It is likely that the discrepancy of the power "stored" in the arm cavities or transmitted through the end mirror and the increase of input power is related to a different mode matching originating from a different thermal lens in the SIB1 Faraday isolator and PR or cavity mirrors. When we will recommission the ITF we will have to readjust the mode matching.

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