[Gregg, Jason, Aidan, TVo, TJ, Jon]

We located the correct Siskiyou 2" mirror mounts (IXM200) for the HAM4 work this morning. Thanks to Corey, who pointed us to two spares that were in the optics lab and were Class A cleaned.

HAM4

Recall that yesterday, we discovered that the 2" mirror mounts that we had been given for mounting the DCBS were DLC mounts, not Siskiyou mounts. The DLC mounts put the optic height 0.5" higher than the Siskiyouu mounts do.

We removed the existing DLC mounts that were added yesterday and removed the dichroic beam splitters (DCBS - T = 300ppm for 1064nm at normal incidence [MI1000]) from these mounts. In doing so, we noted that both DCBS had visible particulates on them. Additionally, the DCBS on the X-arm had a small smudge on the optic and a chip in the barrel. We decided to proceed with the install of the new Siskiyou mounts and assess the action to be taken with the optics after install.

The ITMY laser was turned on again and we were able to use the leakage of this laser through SR2 to align the Y-arm DCBS. We pitched it down a considerable way and confirmed that the reflection from it was dumped on the scraper baffle well below the optical axis.

We adjusted the SR3 alignment to get a ghost beam coming off HWS STEER M1 aligned through the HWSX optics. We installed the new Siskiyou mount on the existing pedestal and noted the height was approximately 6mm higher than neighbouring optics. The pedestal and mount were shifted towards the in-vacuum lens by approximatley 3" (new position is shown in the attached image). Original assembly shown in D1101083-v2.

We centered the DCBS on the laser beam and then adjusted the pitch so that the return beam was dumped on the scraper baffle. For reference, we measured the return beam as it hit HWSX STEER M3 and it was 10mm below the incident beam on that optic. Since the DCBS is approximately 12" away, this puts the reflected beam angle at -1.9 degrees. This put the return beam about 45mm down from center on the HWS SCRAPER BAFFLE.

Conclusion:

The optical mounts are installed and aligned, however, the optics themselves almost certainly need to be cleaned if not replaced. For reference, the HWSX DCBS sees about 300mW of 1064nm light (at about 25W input power into the IFO). The HWSY DCBS sees about 100nW.