NAOJ GW Elog Logbook 3.2
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YuefanGuo - 10:41, Tuesday 16 May 2017 (467)
Recheck green beam
We checked again the green beam waist size and position, because it was a little hard to believe in the result we got last week.
At the beginning, we found out that the beam shape in the beam profiler moved a lot, it was a ellipse with a very large e. But if we sent the beam far away from the bench, it was round,(pic 1), but only with some fringe on one side, it seems from the dichroic mirror.
Then we tried to turn the dichroic mirror a little to see if the beam change. Since the dichroic is also working for sending the infrared beam into the cavity, we moved it, so we need to align the infrared beam to get the green back. Then we also find out the green power is low, so we adjusted the thermal control to find a good temperature, finally we got 50mW over 240mW of infrared, efficiency around 20%.
When everything was ready, we found out the beam size is much smaller compared to the data we got last week, so maybe the temperature also effect the beam size of the green, we took several points, did the calculation, this time the beam waist has more or less the same position of the infrared(-7.3cm),but half of the size(26 micrometer). In picture two it is the points we got in two axis of the beam profiler, and picture three it is the data points and the fitting result in one of the axis.
Also we check again the polarization just after the cavity, we got 49mW reflected by the PBS and 1mW transmitted, so we can say that the green beam come out from the cavity is in S polarization which we want it be.
We did these measurement with the air conditioner off, since the wind from all the air conditioner meet at the bench, produced a lot of fluctuation in the green beam. Then when we left, we turned the air conditioner on,which means we need to adjust the thermal control again.
The other thing is after we realigned the cavity, we found every time we locked the cavity, there is the high frequency oscillation, so we reduced the gain of the Stanford from 500 to 50, then we are fine now.
At the beginning, we found out that the beam shape in the beam profiler moved a lot, it was a ellipse with a very large e. But if we sent the beam far away from the bench, it was round,(pic 1), but only with some fringe on one side, it seems from the dichroic mirror.
Then we tried to turn the dichroic mirror a little to see if the beam change. Since the dichroic is also working for sending the infrared beam into the cavity, we moved it, so we need to align the infrared beam to get the green back. Then we also find out the green power is low, so we adjusted the thermal control to find a good temperature, finally we got 50mW over 240mW of infrared, efficiency around 20%.
When everything was ready, we found out the beam size is much smaller compared to the data we got last week, so maybe the temperature also effect the beam size of the green, we took several points, did the calculation, this time the beam waist has more or less the same position of the infrared(-7.3cm),but half of the size(26 micrometer). In picture two it is the points we got in two axis of the beam profiler, and picture three it is the data points and the fitting result in one of the axis.
Also we check again the polarization just after the cavity, we got 49mW reflected by the PBS and 1mW transmitted, so we can say that the green beam come out from the cavity is in S polarization which we want it be.
We did these measurement with the air conditioner off, since the wind from all the air conditioner meet at the bench, produced a lot of fluctuation in the green beam. Then when we left, we turned the air conditioner on,which means we need to adjust the thermal control again.
The other thing is after we realigned the cavity, we found every time we locked the cavity, there is the high frequency oscillation, so we reduced the gain of the Stanford from 500 to 50, then we are fine now.
Images attached to this report
