NAOJ GW Elog Logbook 3.2
participaint: Yuhang and Matteo
After the pre-alignment of crystal, I did final algnment yesterday. The method is to move Newport 9071, vertically and herizontally.
The experience is to move two of those four adjustment screws the OPO hole where the beam comes in. The requirement of this adjustment is to make the reflection beam overlap with incident beam. However, at the same time, pay attention that the whole OPO housing should be bascially looking like not tilt. Because we know the beam is bascially aligned pretty well.
During the alignment, I found the reflection looks like the attached figure 1(for the good alignment).
Then we can move the two another side sctews. At the same time, look at the transmission, at a certain point, we can see the trasmission is bright and looks round.
We still need to do aligment of the combination of two horizental screws to make it look better. While doing this, I found the beam is cutted by the crystal after move the incident tilt screw. This means the beam we are looking at is what we want to find. While moving the outgoing tilt screw, we can see the beam is cutted and then many small blocks of lights. This looks like many reflectivity of beam inside the crystal.
In the end, I got the transmission as in attached figure 2 and 3.
Participants: Yuhang, Eleonora, Matteo
The transmission found before seems to come from a beam passing through a gap beside the crystal (it was too bright and the reflection was very small and with a strange shape)
Therefore we have restarted the alignment from the beginning. We moved the the 9071 newport Four-Axis Tilt Aligner under the OPO following the usual procedure:
1. Make the reflection superpose the incoming beam
2. Look for a good transmission, always taking care to keep the reflection superposed to the incoming beam.
After may tries we could find a resonably good shaped transmitted beam with a power of 0.047mW. The input power was 210mW. This means the reflectivity is 99.977%, which is in agreement with what we expect.
We put a dichroic mirror after the OPO. The reflection is focused on a photodiode while the trasmission is sent to a camera. Before installing the OPO we have marked the position of the transmitted beam on the screen in order to use it as a reference for the alignment.
Unfortunaltely the tramission after the dichroic mirror is too low and we cannot see any light on the camera, therefore we were not able to use the reference we took for the transmitted beam.