Yuefan and Yuhang

Last Friday, for better understanding to beam situation, we decided to check again the simulation.

According to the beam size measured by Yuhang and Aritomi-san a while ago after the 500mm lens, we could get the original beam waist size and position of the reflection green beam. The beam waist is 2.5m before the 500mm lens, and the beam waist size is 440um which is different from what we expected (~1mm) and mearsured very long time ago by Yuhang and Marc(1008um).

Anyway then we checked the telescope I already designed with this beam, the result didn't seem good. The quadrant position for gouy phase 0 and 90 degree didn't change a lot, but the size became 100um on NF quadrant and 2.5mm on FF, both are bad for our requirement.

To increase the beam size on the NF quadrant, we could change the 500mm to longer one, but then this will limited mainly by the space we have. We decided to check again the beam profile next week when we get the cavity back to decide if we need to change the design or not.

Another thing we have to check is the astigmatism of the beam, because during the installation we found that the second lens which has a focal length of 50mm could induce a lot of astigmatism on the FF quadrant even we could not see by eyes the beam is off center. And if the beam already has a very strong astigmatism as measured in entry 1598, the final beam on the FF quadrant will have a really ugly shape. So after we check the beam again next, if it is still the same, we would like to check the injection path to see where the astigmatism come from.