Today we have tried to recover the IR alignment.

 

1) We have checked the references on the PR viewport. According to the attached scheme, they come from the transmission of the first and the second PBS of the Faraday.

 

We have observed that when the beam transmitted by the Faraday is well centerd on the cross on the plastic film out of the wieport, the other reference beam is slightly hitting the edge of the second PBS of the Faraday and this makes the beam to have a quite irregular shape on the cross. Since the irregurity is not so evident we wondered if it was like this also when the reference was done or if it a sign that the beam is not well aligned. 

 

2) We have put a camera to look inside the BS and we coud spot the beam on the 2 inch telescope mirror.  We did it by moving the steering mirrors on the bench in order to make it hit the edge of the mirror and we have verfied that it is reasonably circular.

 

3) Then twe continued to follow the beam path: we have looked at the PR mirror with a camera and we have done a scan in the horizontal direction. We could see a dim shape hitting the leg of the PR suspension and we could see it moving on the leg on the other side of the suspension while performing the scan.

 

4) We have out a camera to look at the input mirror but we coudn‘t see any light even when scanning the beam position in the two direction.

 

5) Finally we have used the camera to look at the first target. We coud observe a very irregular light shape, much larger than the expected beam. At the beginning we thought it was the light diffracted by the beam hitting the pipe but when we moved the PR we observed that the shape was mooving accordingly. (You can see a video here). It probably suggests that the beam is reaching the target but it is clipped along its path before the BS.

 

6) As reported in entry 630, we have also cheked the dimension of the beam on the bench, finding a difference of about a factor two with the value measured previously by Yuefan. Since the main laser has been mooved, it is likely that the the telescope has to be retuned. i don‘t know how much this discrepancy can contribute to the strange effect we observed.

 

We have also measured the power of the references, wich gives a lower limit on the losses of the Faraday. For an input power of 15.7 mW we found that the transmission of the fist BPS of the Farady is 270 uW and while that of the second one is 120 uW. We have verified that changing the IR polarization from s to p most of the light is transmitted by the the first PBS.

 

CONCLUSION: we suspect that the beam is clipped somewhere in its in vacuum path e have been working on the IR aligment.

 

1) We have checked the references on the PR viewport. According to picture 1, they come from the transmission of the first and the second PBS of the Faraday. We have checked that when the beam

transmitted by the Faraday is wel centerd on the cross on the plastic ï¬Âlm out of the wieport, the other reference beam is slightly hitting the edge of the second PBS of the Faraday and this makes the

beam to have a quite irregular shape on the cross. Since the irregurity is not so evident we wondered if it was like this also when the reference was done or if it means that the beam is not well aligned.

2) We have put a camera to look inside the BS and we coud spot the beam on the 2 inch telescope mirror. By mooving the steering mirrors on the bench we moved it in order to make it hit the edge of

the mirror and we have veriï¬Âed that it is reasonably circular.

 

3) Then twe continued to follow the beam path: we have looked at the PR mirror with a camera and we have moved the beam. We coud see a dim shape hitting the leg of the PR suspension and we

could see it moving on the leg onother side of the suspension.

 

4) We have out a camera to look at the input mirror but we coudn‘t see any light even when mcoving the beam.

 

5) Finally we have used the camera to look at the first target. We coud observe a strange, irregular light shape, much larger than the expected beam. At the beginning we thought it was the light

diffracted by the beam hitting the pipe but when we moved the PR we observed that the shape was mooving accordingly. (You can see a video here). It probably suggest that the beam is reaching the

target but it is getting clipped along its path.

 

6) As reported in entry. we have also chech the dimension of the beam on the bench finding a difference about a factor two with the value measured previously by Yuefan. Since the laser has been

mooved. it is likely that the the telescope has to be retuned. i don‘t know how much this discrepancy can contribute to the strange effect we observed.

 

We have also measured the power of the referencies. wich give a lower limits on the losses of the Faraday. For an input power of we find that the translission of the fist BPS of the Farady is and the

second one is. We have veryfled that chaging the IR polarization from s to p almost all the light is transmitted by the the first PBS

 

CONCLUSION: we suspect that the beam is clipped somewhere in its in vacuum pathhave been working on the IR aligment.

 

1) We have checked the references on the PR viewport. According to picture 1, they come from the transmission of the first and the second PBS of the Faraday. We have checked that when the beam

transmitted by the Faraday is wel centerd on the cross on the plastic ï¬Âlm out of the wieport, the other reference beam is slightly hitting the edge of the second PBS of the Faraday and this makes the

beam to have a quite irregular shape on the cross. Since the irregurity is not so evident we wondered if it was like this also when the reference was done or if it means that the beam is not well aligned.

2) We have put a camera to look inside the BS and we coud spot the beam on the 2 inch telescope mirror. By mooving the steering mirrors on the bench we moved it in order to make it hit the edge of

the mirror and we have veriï¬Âed that it is reasonably circular.

 

3) Then twe continued to follow the beam path: we have looked at the PR mirror with a camera and we have moved the beam. We coud see a dim shape hitting the leg of the PR suspension and we

could see it moving on the leg onother side of the suspension.

 

4) We have out a camera to look at the input mirror but we coudn‘t see any light even when mcoving the beam.

 

5) Finally we have used the camera to look at the first target. We coud observe a strange, irregular light shape, much larger than the expected beam. At the beginning we thought it was the light

diffracted by the beam hitting the pipe but when we moved the PR we observed that the shape was mooving accordingly. (You can see a video here). It probably suggest that the beam is reaching the

target but it is getting clipped along its path.

 

6) As reported in entry. we have also chech the dimension of the beam on the bench finding a difference about a factor two with the value measured previously by Yuefan. Since the laser has been

mooved. it is likely that the the telescope has to be retuned. i don‘t know how much this discrepancy can contribute to the strange effect we observed.

 

We have also measured the power of the referencies. wich give a lower limits on the losses of the Faraday. For an input power of we find that the translission of the fist BPS of the Farady is and the

second one is. We have veryfled that chaging the IR polarization from s to p almost all the light is transmitted by the the first PBS

 

CONCLUSION: we suspect that the beam is clipped somewhere in its in vacuum path