YuefanGuo - 18:56, Tuesday 22 August 2017 (549)
AOM installation and cavity realignment
Today the installation of the AOM and the accompany lenses have been finished. Like I mentioned in the entry 547, the shape of the AOM first order is not very good, so yesterday we tried to check the beam with the beam profiler and adjust the stage to have a better beam shape. At the end, we can improve a bit the beam shape but not very perfect.
Also last week we found out the lens combination did not work well because I made some mistake in the calculation, so we tried to measure the better shape first order again, and found a new solution. The second lens should be put 40.1cm from the MZ beam splitter and the third 62cm. In this new configuration, all the lenses are in front of Faraday, so we don't need to worry about the affect to the reflection beam.
The other problem we mentioned in entry 457 is that all the optics on the 2nd FI path are not along the hole, so we can not screw the rail on the bench, so we used clamps. The path finished shows in the pictures, the way of clamping the rail now does not look very fixed, we will improve it later.
Since the new beam splitter has been installed, the green power injected into the cavity now is around 8mW.
With everything settling down, we could inject the beam into the chamber and align the cavity again. But today we are not able to lock the cavity, one reason is that the input mirror local control cannot hold the mirror fixed for long time, so while we were trying to find better mode matching, we continued to lose the alignment of the input. The other side, the beam produced by the new configuration is different from before, according to the calculation, the beam size arrive at 2 inch mirror should be close to our previous one, but the beam from the bench is much smaller than before and reflection of the input is larger than before. It could be the reason why we always have some Laguerre modes. So tomorrow we can try to change the driving matrix of the input and PR mirror, get better control of them and try to see if we are able to lock or not.
Also last week we found out the lens combination did not work well because I made some mistake in the calculation, so we tried to measure the better shape first order again, and found a new solution. The second lens should be put 40.1cm from the MZ beam splitter and the third 62cm. In this new configuration, all the lenses are in front of Faraday, so we don't need to worry about the affect to the reflection beam.
The other problem we mentioned in entry 457 is that all the optics on the 2nd FI path are not along the hole, so we can not screw the rail on the bench, so we used clamps. The path finished shows in the pictures, the way of clamping the rail now does not look very fixed, we will improve it later.
Since the new beam splitter has been installed, the green power injected into the cavity now is around 8mW.
With everything settling down, we could inject the beam into the chamber and align the cavity again. But today we are not able to lock the cavity, one reason is that the input mirror local control cannot hold the mirror fixed for long time, so while we were trying to find better mode matching, we continued to lose the alignment of the input. The other side, the beam produced by the new configuration is different from before, according to the calculation, the beam size arrive at 2 inch mirror should be close to our previous one, but the beam from the bench is much smaller than before and reflection of the input is larger than before. It could be the reason why we always have some Laguerre modes. So tomorrow we can try to change the driving matrix of the input and PR mirror, get better control of them and try to see if we are able to lock or not.
Images attached to this report
Comments related to this report
Add the video of the modes we got from the cavity.
https://www.dropbox.com/s/nerrc4i4yx3bw8v/VID_1.MOV?dl=0
https://www.dropbox.com/s/nerrc4i4yx3bw8v/VID_1.MOV?dl=0