Vicky, Camilla, Sheila, Georgia
Today we took Robert's IR camera into HAM7 and took photos of the beam which travels back from the IFO to the VOPO (emmulated using a retroreflector after ZM4). I've done a quick pass of the photos we took and will sort them out by what the photo is of and put them in the comments.
The conclusions we have are:
- The retroreflected beam which emulates the beam coming from the IFO towards the squeezer is high and right on its PD
- The SFI2 rejected beams are hitting their aperture stops, and we can't trace down the beams reflected off the aperture stops
We looked at the beam on the OFI rejected PD (AKA B:PD1), and saw the beam was high and right of the photodiode surface. This is similar to what we were seeing with the first round of photos through the viewport with the IFO locked, but different to Robert's more recent conclusions. We couldn't find a ghost beam, only the main beam. The reflection off the PD is currently dumped in the black glass dump. I think we should align the PD for this beam.
We looked at the aperture stop on B:L1, which dumps the s-polarized light coming from the IFO (if I understand the diagram from this assembly procedure correctly). The beam hits the aperture stop which is good (first attachment). There was another beam on the other side of the cone but this is still there when the beam is blocked (second attachment).
We tried to hunt down the beam which is reflected off the cone, thinking it might be the origin of the strange IR ghost beam on green path (see bottom right arrow in robert's slides), but couldn't see anything suspicious (third and fourth attachments).
When we rotate the polarization of our beam propagating backwards through SFI2 we only see a weak beam on the aperture (fifth attachment). Makes sense.
Edit: adding 3 photos of the G:M1, G:L1, G:L2 area, trying to find the spot identified by Robert and hypothesized by Camilla to be off the B:L1 aperture stop.
We rotated the polarization of the emulated IFO beam so that most of it will be in the P-polarization and hence rejected by the first polarizated in SFI2. We see a spot on the SFI2 aperture (first, second, third attachments).
We tried to look for the reflected beam off the cone aperture but didn't see anything (fourth, fifth attachments).
The output to SFI2 (input if youre the retro beam) is quite bright (sixth, seventh attachments) compared to when the OPO is unlocked (eighth attachment) but that isn't so shocking because the retroreflector is not at a waist and the retroreflected beam is larger than the IFO beam would be.
We took some nice photos of the VOPO with the retro reflected beam blocked (first photo), and the VOPO (other photos)
And some photos of Vicky, Sheila, Camilla!
