YuefanGuo - 18:32, Thursday 17 August 2017 (547)
More details about local control reset and AOM installation
Since we already lost the beam on the CCD in the end room, as usual we took the second target as the reference to move the picomotor. We were quite lucky, as soon as we put back the beam on the second target, we also recovered the beam on the CCD. With fine adjustment, we are able to lock the cavity and take all the reference we want, we put another aperture between the bench and the PR chamber, remade the reference out of the PR chamber and BS chamber.
With all this reference today we started to install the AOM. The first lens has 100mm focal length which put as close as the original beam splitter. Then installed a new beam splitter after this lens and align both the transmission and reflection path of it.
The AOM was put after the mirror to get a good beam size, with the steering mirror, I aligned the first order straight first and then by adjusting the stage to increase the efficiency of the first order. It took long time for us to adjust the AOM, but still cannot get a perfect round beam, then we check the beam entering the AOM, from there the beam already has some strange shape halo around it. But before the beam splitter, we did not see this strange things, I think this is what we expected to see here, since when we installed the original third lens of the telescope, we already found out the shape affected a lot by the lens position. We will try to align better.
Just for testing the new telescope works or not, we put the other two lenses at their position, but it seems this combination does not works well as we tested it. One of the reason I think it may because when we did the test, the first lens position is not as close as now to the beam splitter, but I preferred to keep the first lens position like it is now, since this one has smaller divergence. This means we need to find other lenses, so we measured the beam size of the first order again after the AOM. Now the result I got is that we need to put the other two 250mm lens, one is at 40.5cm, the other at 88cm, which is doable.
Another problem we found it is that all the optics on the second Faraday path is not along the holes. So if we put the lens on the rail, the beam will be quite off-center and the range we can move with the screw is not enough to let the beam pass through the lens center.
With all this reference today we started to install the AOM. The first lens has 100mm focal length which put as close as the original beam splitter. Then installed a new beam splitter after this lens and align both the transmission and reflection path of it.
The AOM was put after the mirror to get a good beam size, with the steering mirror, I aligned the first order straight first and then by adjusting the stage to increase the efficiency of the first order. It took long time for us to adjust the AOM, but still cannot get a perfect round beam, then we check the beam entering the AOM, from there the beam already has some strange shape halo around it. But before the beam splitter, we did not see this strange things, I think this is what we expected to see here, since when we installed the original third lens of the telescope, we already found out the shape affected a lot by the lens position. We will try to align better.
Just for testing the new telescope works or not, we put the other two lenses at their position, but it seems this combination does not works well as we tested it. One of the reason I think it may because when we did the test, the first lens position is not as close as now to the beam splitter, but I preferred to keep the first lens position like it is now, since this one has smaller divergence. This means we need to find other lenses, so we measured the beam size of the first order again after the AOM. Now the result I got is that we need to put the other two 250mm lens, one is at 40.5cm, the other at 88cm, which is doable.
Another problem we found it is that all the optics on the second Faraday path is not along the holes. So if we put the lens on the rail, the beam will be quite off-center and the range we can move with the screw is not enough to let the beam pass through the lens center.
Images attached to this report
