[Ushiba, Haba, Komori]

We measured the transfer function from three degrees of freedom of the MNs (Length, Yaw, and Pitch) at four test masses (ETMX, ETMY, ITMX, and ITMY) to DARM length yesterday.
The purpose of this measurement is to perform the noise projection of the contribution from the locally-controlled degrees of freedom onto DARM.

The attached figures show the 3x4 results of the gain and coherence, including another locally-controlled degree of freedom of ITMY Roll.
These measurements were done by injecting the white noise and comparing the ratio of the input and DARM signals.
The unit of the gain is calibrated to be [m / count], with considering three whitening filter at 1-100 Hz and a factor of 10^(-9) to compensate [nm] to [m].
Corresponding xml data are located at /users/Commissioning/data/NoiseBudget/TFs/2022/1013.

Discussion

• The pitch coupling is larger than others with all test masses. The worst one (ITMY Pitch) has the coupling of 10^(-11) m/count at 10 Hz. However, the frequency dependence is very clean, f^(-4) toward the resonance at 44 Hz.
• The yaw coupling is around 10^(-14) m/count at 10 Hz. There are many resonant peaks in this frequency range, and the frequency dependence is not large. Some gains are almost flat. We are not sure whether these peaks come from the real yaw motions.
• The length coupling is around 10^(-15) m/count at 10 Hz. The gains are very similar with those of the yaw. The length and yaw motions seem to be mixed much.
• The roll coupling of ITMY is around 10^(-13) m/count at 10 Hz. The same peaks as the yaw or length can be seen also in this roll modes.

We will perform the noise budget soon using these results and the noise during the FPMI lock.