Abstract:

I designed new PRCL filters that can also be used during lock acquisition.
By updating the guardian and performing the same actions in the PRCL1 module instead of PRCL2, the lock acquisition should proceed smoothly, and the new final filters can be applied.

Details:

To develop appropriate PRCL filters compatible with the lock acquisition process, I investigated which filters are enabled or disabled at each stage.

• FM5 is enabled from the beginning.

• During PRMI 3F locking, FM9 is enabled and the gain is ramped up to -1.0.

• After the IR handover, during the transition to 1F, FM3 and FM7 are turned on.

• In the observation state, FM7 is turned off and FM2 is enabled.

These operations are currently handled within the PRCL2 module.
I have now implemented new filters in the same filter modules (FMs), corresponding to each IFO state, but within the PRCL1 module.

I compared the open-loop transfer functions under two conditions:

• During PRMI 3F locking (FM9 on, gain applied), shown in Fig.1.

• During the transition to 1F (FM3 and FM7 on), shown in Fig.2.

In both figures, the red line represents the new filter configuration, and the blue line represents the current one.
As discussed in the original post, the filters in the observation state (FM7 off, FM2 on) will reduce the PRCL coupling.

Since the new filters produce relatively similar transfer functions at all stages, the lock acquisition and observation should work well if the guardian is modified to use the PRCL1 module instead of PRCL2.