[RyanS, Jenne, Jason]
Today we changed the mount that the IO / ISC EOM sits on from a 5 axis New Focus mount to the more sturdy replacement that was designed several years ago. We think the alignment and everything is basically complete, and our next major step is to find a time when we can have the LVEA in laser hazard so we can try locking the IMC. Jason also got a set of as-built final photos of the table layout.
We turned down the power going to the EOM, and then checked that the irises over by the periscope we centered in early Feb of this year were still good references; they were. At this point in the day, we were using just the wave plate after the PMC to lower the power, although later in the day we also used the high power attenuator right after the second shutter (before the PMC) to lower the total power coming out of the PMC.
We turned off the 9 MHz and 45 MHz EOM drivers on their front panels, and removed the DC power cables on the RF combiner that sums the 24 MHz with the 45 MHz. We unplugged the cables from the EOM, and immediately put a terminator on the 118 MHz line (since there isn't an easy way to turn it off).
We pulled the EOM + mount out, and then test fit the new mount and noted that since it is orientented 90 degrees from the old mount, and is larger, and some of our secondary paths (toward a beam dump) aren't in the same locations as the drawing, we needed to first make some space by changing the lens mount that increases the spot size in the water cooled beam dump that is right after the PMC. We also needed to change where the fork sat for the thin film polarizer that reflects beam to that beam dump. When I loosened that fork, the polarizer moved a bit, so we used a low power beam to confirm that the beam was still centered on the dump.
We mounted the EOM in the new mount, and placed the mount on the table. It was pretty easy to adjust the mount so that the beam went through the EOM apertures, although the beam was quite low in the apertures. Also, we noticed that the beam at the second 2 inch lens after the EOM was off in yaw, and the beam was off in yaw at the two irises. Yaw-ing the EOM mount didn't change the beam spot in any noticeable way.
We ended up using the steering mirror right after the PMC to get the beam nicely centered in the EOM (mostly by raising the beam), and then used the beam splitter that reflects the main path to the EOM to tweak up the alignment at the irises.
At this point, we're pretty nicely aligned on our two irises, and we think the next step is to check the alignment into the IMC. Since we're in the process of venting and will soon be opening doors, we'll need to coordiate a time when we can have the LVEA in laser hazard. We plugged in the RF cables, and re-maximized the laser power going through both attenuation stages that we had touched today.
When I plugged the 18 V power cable in to the RF combiner chassis, Ryan noticed that lots of green lights on the ISC racks blinked off, then back on. So, we may need to check to see that those are all working properly :/ We also re-enabled the 9 MHz and 45 MHz drivers.
Tomorrow: We will double check our alignment through the EOM now that the cables are plugged in (we think that the new mount is sturdy enough that it didn't move, but we'll check anyway), as well as to the ALS path (since we very slightly adjusted mirrors upstream of that path). We will also start thinking about our other small cleanup tasks, such as tweaking up the ref cav alignment, swapping cameras for GigE cameras, etc.
This morning Ryan and I double-checked the that the alignment on our irises was still good after yesterday's mount swap and found that it is still good. We did find that the ALS path needed re-aligning. The beam was clipping on the ALS Faraday isolator, so we used mirror ALS-M1 to aleviate the clipping. Once this was done we checked our ALS irises; with the beam now centered on the FI, the only slight adjustment needed was a small yaw adjustment to center on the irises. The ALS beam alignment on ISCT1 will need to be checked once we are able. We also had adjust the alignment into the ALS/SQZ fiber pick-off; the PD that reads the fiber output in the distribution chassis came back to its original level with small tweaks to the mirror in front of the fiber. I've attached several pictures of the EOM on its new mount. The RF cables are secured both to the table behind the EOM and to the post on the mount, so they are not going anywhere; the new mount did have strain relief for these cables, but it was too small to fit them in so we removed it.
That done, we took a power budget on the FSS beam path to see if we needed to tweak that alignment; we did this with the ISS ON. We had last done this in February 2022, so it's been a good 7 months. Results:
While we've had the double-pass diffraction efficiency a little bit higher in the past, while in the enclosure we didn't think this was too much of an issue so we decided to not tweak the beam alignment. We did double check the beam alignment through the EOM (provides the 21.5 MHz sidebands for PDH locking the RefCav), and found that the alignment was off. We took power measurements on either side of the EOM and they matched, so it wasn't clipping, but it's possible the off-alignment here could be impacting the RefCav TPD. So we adjusted the EOM alignment so the beam was centered on the input and output apertures (we did not adjust the beam alignment, only the EOM). We then immediately saw a small shift in the position of the RefCav reflected spot on the REFL camera (ah-hah!). We tried to lock the RefCav with the autolocker, and it locked without issue, but the TPD was down around 0.2V. We manually tweaked the alignment of mirror M23 and that brought the TPD back up to around 0.65V. Still not great, but we didn't want to use the picomotors with the pending vent. We'll have to tweak that remotely with the picomotors once the vertex is vented at air. Lastly, we tweaked the alignment onto the RefCav RFPD, as this does wander slightly with repeated remote alignments.
Finally, we re-centered the PMC REFL camera, so the image will be easier to see (it's not hanging off of the right edge of the screen anymore). This completed our in-enclosure PSL work for today.