[Michimura, Komori]
We tweaked various offset related to ASC and LSC degrees of freedom.
At this moment, we got slighly smaller peak at 116 Hz with tuning of the input pitch ASC, but basically we have not succeeded in improving the sensitivity drastically.
The details will be reported tomorrow.
Abstract:
At this point, it appears very difficult to further reduce the input jitter noise by adjusting ASC and LSC offsets.
Detail:
Combined with the previous trial (klog:33027), the degrees of freedom I have already attempted to tune are as follows:
ASC-INP2_P_OFFSET and ASC-PRC2_P_OFFSET (individually and in combination)
ASC-INP2_Y_OFFSET
ASC-PRC2_Y_OFFSET
IMC-DOF{1,2,3,4,5}_P_OFFSET
ASC-{D,C}HARD_P_OFFSET
ASC-MICH_P_OFFSET
BPC-PIT_{I,E}TMX_INF_OFFSET
BPC-PIT_ETMY_INF_OFFSET
BPC-YAW_ITMX_INF_OFFSET
Among these, tuning the combination of ASC-INP2_P_OFFSET and ASC-PRC2_P_OFFSET, which correspond to the input beam axis and PRC alignment, has shown some ability to reduce the jitter noise.
However, the reduction is within the range of the usual breathing and not significant.
Previously, setting ASC-INP2_P_OFFSET to 0.8 minimized the noise, but that no longer seems effective, so I have currently set the offset to zero.
Tweaking the other degrees of freedom sometimes enhances the noise but does not reduce it.
I also attempted to optimize the length degrees of freedom—PRCL, MICH, CARM, and DARM offsets—but none of these led to improved sensitivity.
Based on these results, it currently seems very challenging to reduce input jitter noise further through adjustments to ASC and LSC offsets.
These findings may suggest that the input jitter noise originates from birefringence in the ITMs.
If that is the case, identifying and mitigating the actual noise sources might be more effective than continuing to optimize IFO alignment.
Another potential approach is to drastically change the beam spot position on ITMX, as I may currently be observing only a local minimum.