YuefanGuo - 02:33, Tuesday 11 April 2017 (445)
Check the green beam
I tried to put lens on the green path, for one side, to reduce the beam size for easier measurement, the other side to check if the distortion of the beam change or not.
I put the 500mm focal length lens after the lens we have now, shows in the first picture, under this circumstance, the beam is still circular after the bs mirror of the MZ, but after the mirror of the MZ, it becomes two separated circular beams because the second surface reflection of that mirror. These two beam goes along the path, at some point around the last mirror on the bench, they overlapped. So before the beam goes into the window, it is a really good beam, but after the window it’s separated into two again, so at first I thought maybe this is the reason of the distortion.
Then I blocked the reflection beam from the mirror on the bench, only left the main one, the second beam after the window is still there, so this second beam is produced by the reflection of the window.
Then inside the chamber, the beam after the window, only the main one arrives at the first dichoric mirror, the other one hit the frame of the suspension. So till here, we only have one circular beam, then I checked beam between the PR chamber and the BS chamber, it turns into ellipses. We talked with Matteo and we thought the problem is from the dichoric mirror which combine the green and the infrared. But since now we are not in a very good alignment, we will do the alignment again, and then check the shape of the beam. If it is still the same, we will change the dichoric mirror and to see if we can have some positive result.
For choosing the lens to reduce the beam, now I don't know what kind of focal length I should use. I think I will do one calculation with the measurement I did, got some result, and to see the roughly range of the focal length I can use, then put them there and do the measurement again to find better combination.
About re-align the beam, Matteo also gave us some steps to do that:
(All the things we need to move including, the turning mirror for green, the dichoric mirror for combining the green and infrared, the 2 inch mirror of the telescope, the PR suspension mirror, the BS suspension mirror. The mirrors are in the order of the beam pass through.)
1.Put the target in front of the 2 inch mirror, move the turning mirrors to center it.
2.Put the infrared card in front of the PR suspension mirror, center the green (and infrared?) with moving the 2 inch mirror.
3.Target in front of the BS suspension mirror, move the PR suspension mirror.
4.Check if the beam is centered at the 2 inch mirror(?)
5.Center the infrared beam on the BS suspension mirror with moving the dichoric mirror.
6.Check at the 2 inch mirror, the green and the infrared surpass or not.
Repeat these steps, until everywhere is centered.
I put the 500mm focal length lens after the lens we have now, shows in the first picture, under this circumstance, the beam is still circular after the bs mirror of the MZ, but after the mirror of the MZ, it becomes two separated circular beams because the second surface reflection of that mirror. These two beam goes along the path, at some point around the last mirror on the bench, they overlapped. So before the beam goes into the window, it is a really good beam, but after the window it’s separated into two again, so at first I thought maybe this is the reason of the distortion.
Then I blocked the reflection beam from the mirror on the bench, only left the main one, the second beam after the window is still there, so this second beam is produced by the reflection of the window.
Then inside the chamber, the beam after the window, only the main one arrives at the first dichoric mirror, the other one hit the frame of the suspension. So till here, we only have one circular beam, then I checked beam between the PR chamber and the BS chamber, it turns into ellipses. We talked with Matteo and we thought the problem is from the dichoric mirror which combine the green and the infrared. But since now we are not in a very good alignment, we will do the alignment again, and then check the shape of the beam. If it is still the same, we will change the dichoric mirror and to see if we can have some positive result.
For choosing the lens to reduce the beam, now I don't know what kind of focal length I should use. I think I will do one calculation with the measurement I did, got some result, and to see the roughly range of the focal length I can use, then put them there and do the measurement again to find better combination.
About re-align the beam, Matteo also gave us some steps to do that:
(All the things we need to move including, the turning mirror for green, the dichoric mirror for combining the green and infrared, the 2 inch mirror of the telescope, the PR suspension mirror, the BS suspension mirror. The mirrors are in the order of the beam pass through.)
1.Put the target in front of the 2 inch mirror, move the turning mirrors to center it.
2.Put the infrared card in front of the PR suspension mirror, center the green (and infrared?) with moving the 2 inch mirror.
3.Target in front of the BS suspension mirror, move the PR suspension mirror.
4.Check if the beam is centered at the 2 inch mirror(?)
5.Center the infrared beam on the BS suspension mirror with moving the dichoric mirror.
6.Check at the 2 inch mirror, the green and the infrared surpass or not.
Repeat these steps, until everywhere is centered.
Images attached to this report
