YuefanGuo - 18:55, Tuesday 01 August 2017 (543)
AOM re-test
According to the last test of the AOM and the simulation, the last lens should changed to 200mm one in order to have a good size on the 2inch mirror. So today we tried to test on the bench to see if the simulation works or not.
As usual, we tested the AOM on the transmission of the beam splitter. From our last test the AOM should be put 17.5cm from the beam splitter, but after checking, there is not enough space to put the AOM before the mirror, as close as we could to the mirror we can put the AOM 25cm from the beam splitter. And then if we put the second and third lens more or less at the same position as our last test, when the beam arrives at the position of FI, the diffraction orders are not separated enough to filter by the aperture. Then we tried to move the two lenses, situation did not get better.
So our idea is to filter the beam after the AOM but before the second lens. So we tried to do this and wanted to check the beam size after so we can find another proper combination of lens. When we measure the beam with the beam profiler, we found out the first order is very elliptical. We tried to align the AOM better, in the picture you can see there are some black lines which cut the beam into many pieces. Actually we had this kind of lines from the very beginning, but before we can get rid of them and get more or less a round first order with good alignment. This time we tired again and again, but still cannot get a good beam shape. We already sent an email to the company to ask if the black lines are only caused by bad alignment or something else. Meanwhile we checked the beam and found out the beam transmitted by the beam splitter itself has some tilt, and also the first 100mm lens could bring some astigmatism.
The other thing is that with the AOM position we decided today, we have only about 30cm to put lenses and recover the beam, although without the beam size measurement we cannot say if this space is enough or not, but if it is not, the other solution we considered is that after the FI and the waveplate, we have about 7.5cm space where we can put the lens. If we have to do this, one problem is that we can only take the reference outside the PR chamber, the other problem is that we are not sure if this will effect the beam reflect back to the PD which is used to lock the filter cavity.
As usual, we tested the AOM on the transmission of the beam splitter. From our last test the AOM should be put 17.5cm from the beam splitter, but after checking, there is not enough space to put the AOM before the mirror, as close as we could to the mirror we can put the AOM 25cm from the beam splitter. And then if we put the second and third lens more or less at the same position as our last test, when the beam arrives at the position of FI, the diffraction orders are not separated enough to filter by the aperture. Then we tried to move the two lenses, situation did not get better.
So our idea is to filter the beam after the AOM but before the second lens. So we tried to do this and wanted to check the beam size after so we can find another proper combination of lens. When we measure the beam with the beam profiler, we found out the first order is very elliptical. We tried to align the AOM better, in the picture you can see there are some black lines which cut the beam into many pieces. Actually we had this kind of lines from the very beginning, but before we can get rid of them and get more or less a round first order with good alignment. This time we tired again and again, but still cannot get a good beam shape. We already sent an email to the company to ask if the black lines are only caused by bad alignment or something else. Meanwhile we checked the beam and found out the beam transmitted by the beam splitter itself has some tilt, and also the first 100mm lens could bring some astigmatism.
The other thing is that with the AOM position we decided today, we have only about 30cm to put lenses and recover the beam, although without the beam size measurement we cannot say if this space is enough or not, but if it is not, the other solution we considered is that after the FI and the waveplate, we have about 7.5cm space where we can put the lens. If we have to do this, one problem is that we can only take the reference outside the PR chamber, the other problem is that we are not sure if this will effect the beam reflect back to the PD which is used to lock the filter cavity.
Images attached to this report
