The attached plot is rather busy with traces, but it's a summary of the present performance of the ISS second loop.

In brief, the second loop is behaving well: the intensity noise is well within specifications above 30 Hz. If you're interested, more details follow.

The blue, red and green solid thin traces are measurements taken this morning. The blue one shows the intensity noise at the ISS box when the second loop is open. The green and red traces show the in-loop and out-of-loop intensity noise with the second loop closed. The light green dashed trace shows the expected level of out-of-loop noise assuming to be shot noise limited, for a total of 20 mW entering the array (which is what we're measuring right now). We see that the out-of-loop performances are very well explained by shot noise between 70 and 200 Hz. Above 300 Hz we are gain limited, so the suppression is not enough to go down to the shot noise level.

The other dashed traces show the intensity noise requirements. The black dashed curve is taken from the design document T1100265-v1. The other curves are the result of simulations with MIST: radiation pressure is included, SRC is in broad-band configuration, no asymmetry is introduced in the interferometer. The latter point is particularly important, since LLO experience and simulations showed that the coupling of intensity noise can increase a lot if we have IFO asymmetries, like lenses in the ITMs. However, at LLO a reduction of RIN coupling down to the ideal model has been demonstrated using TCS. The two curves corresponds to 125 W and 25 W in input. The IFO sensitivites are taken from here.

In summary, the present performance of the ISS is good enough to meet the requirements above 20 Hz for operations at 25 W. If we could fix the structures between 10 and 20 Hz, we would be ok at all frequencies. Clearly, this is the intensity noise measured at the ISS level, so far there is no guarantee that the same good level of intensity noise is maintained into the IFO. We'll have to take a look into that.