Since we found something wrong last week, we tried to carefully measure the beam parameters again after the first Faraday Isolator. As Yuefan did, we also set the origin as the BS on the bench.

For x direction, the beam waist is 118.2 um at the position z=-0.10 m. For y, the beam waist is 119.8 um at z=-0.093 m. See attached figure 1 for the fitting result.

Then we used this result to simulate the propagation of the beam using the software "Jammt". See attached figure 2 for this simulation.

We found that our beam parameter was very sensitive to the last lens position. We have fine tuned its position in order to have a reasonable beam dimension. By using a steering mirror on the beam path we could propagate it for several meters in the central area and check that the beam size should be reasonable at the input of the in vacuum faraday.

After that we have keep trying to recover the alignment of the infrared without success. We have collected as many cameras and screens as possible as use them to look insides the input vacuum chamber simultaneously. 

Despite many tries the situation is not different from that of the last time:

1) We can recover the references for the IR on the plastic film but for one of them the beam as a quite irregular shape.

2) We could see the beam on the mount of the 2 inch mirrors and we tried to center it.

3) We could see the beam hit the leg of the PR telescope mirror and tried to center it on the PR.

After that we cannot see the beam on the BS or on the input mirror but just some strange quite dim shape on the first target.

As already observed in entry 631, when moving the PR or BS mirror with the local controls we can move accordingly the shape on the target. This is different from what we expect if the beam was hitting the pipe, since normally in this condition we observe a change in the intensity and in the shape of the scattered light.

Conclusions: We are probably not understanding what is happening inside the chambers and we need some new ideas to go on.