daniel.sigg@LIGO.ORG - posted 12:49, Monday 30 December 2024 - last comment - 08:48, Thursday 02 January 2025(82057)
OPO green power
We seem to be running into repeated problems where the green power is not sufficient to get to the nominal OPO green transmitted power.
Today the SHG output was particular low, so I adjusted the input pointing as well as lowered the temperature to 35.0C (from 35.5C). This gave us about 10% more green power, but still not enough! I then further increased the green power by adjusting the waveplate in front of the cube.
The rejected power (H1:SQZ-SHG_REJECTED_DC_POWERMON) is currently showing 1.8mW, down from around 4.7mW when I started. There is a little bit further to go, but we may have to realigning the green fiber coupler on the table. And if this doesn't work, we probably need to coonsider moving the OPO crystal.
Adding some plots related to Daniel's assesment above. The first time cursor (in the first attachment) is Oct 3 2024, the time of our most recent OPO crystal move 80451, you can see that the SHG launch power and OPO refl power have climbed back up as crystal losses have increased.
The second attachment shows that since Daniel's intervention described above (the time when SHG rejected power drops), the SHG power has been more stable, and the ISS control signal has been around 3V. I think that this means we can wait until Monday to move the crystal, so that we can do the temperature adjustments as we settle into our new crystal position during the workweek rather than over the weekend.