YuefanGuo - 22:50, Monday 12 June 2017 (500)
EOM, FI installation and the beam shape
We finished the EOM installation and finally compensated the effect of it with moving the third lens. We measured some data after the third lens, did the fitting and compared it to the result we got without EOM. So from the picture you can see, we even had a smaller beam waist than before. Also we sent the beam coming out from the BS chamber into the 300m corridor, check the beam from time to time, it seems the size of the beam did not change too much during the propagation.The second picture shows the comparison of size between the green and infrared before we well superpose them.
Since we are going to use the green beam reflect back from the end mirror to lock the cavity. We need to send the reflected beam into a PD, so we need to extract that beam out from the FI. But when we tried to do it, we found out the beam we need is reflected to the table direction, which is very hard to extract. Also the FI we are using, only the output polarizer can be turned to tune the frequency. Finally we found a way to do it, the final setup shows in the third and fourth pictures.
Today I tried to send the beam transmitted from the BS mirror out of the chamber. At first I used a one inch mirror, but the beam is almost the same size as the mirror, so it has been a little bit cut on the edge. So then I changed it into a two inch aluminium mirror. The beam is coming out from the spare window beside the tube which connected the PR chamber and the BS chamber.Then I put a aperture out side the window, center the beam on it and another beam damper after it.
There was another problem we found today. The beam looks good everywhere until it enter the tube, then when we check at the first target, it was cut.There is a bright spot in the middle and a large ring outside, the cut part is the outside part. When we tried to move the telescope mirror, the beam on the first target moved in a very strange pattern which we still cannot understand. Finally we decided to send the beam out after the BS mirror, sent into the corridor, then we checked it further but did not see either the outside part or the cut. Now we suspected that this large cut beam may come from the reflection between the target and the window. We will try to move each telescope mirror again tomorrow for better understanding the situation.
Since we are going to use the green beam reflect back from the end mirror to lock the cavity. We need to send the reflected beam into a PD, so we need to extract that beam out from the FI. But when we tried to do it, we found out the beam we need is reflected to the table direction, which is very hard to extract. Also the FI we are using, only the output polarizer can be turned to tune the frequency. Finally we found a way to do it, the final setup shows in the third and fourth pictures.
Today I tried to send the beam transmitted from the BS mirror out of the chamber. At first I used a one inch mirror, but the beam is almost the same size as the mirror, so it has been a little bit cut on the edge. So then I changed it into a two inch aluminium mirror. The beam is coming out from the spare window beside the tube which connected the PR chamber and the BS chamber.Then I put a aperture out side the window, center the beam on it and another beam damper after it.
There was another problem we found today. The beam looks good everywhere until it enter the tube, then when we check at the first target, it was cut.There is a bright spot in the middle and a large ring outside, the cut part is the outside part. When we tried to move the telescope mirror, the beam on the first target moved in a very strange pattern which we still cannot understand. Finally we decided to send the beam out after the BS mirror, sent into the corridor, then we checked it further but did not see either the outside part or the cut. Now we suspected that this large cut beam may come from the reflection between the target and the window. We will try to move each telescope mirror again tomorrow for better understanding the situation.
Images attached to this report
