Abstract
Alter all, we gave up switching the current KAGRA's high-power laser to a new one this time.
Detail:
We did two things this morning.
- Changing the crystal temperature of the new laser to the last value from 22.62 to 21.64.
- Set the halfwave plate to the point which is thought that the polarization axis is the same axis of the EOM crystal.
Then we looked at the laser power drift at the output of PSL table. It looked quite flat for the first 1 hour. But after 2 hours steep dropping started (Fig. 1).
The slope became a bit better than yesterday, but the shape of the behavior of drift looked surprisingly similar to the shape of drift exactly 1day before (Fig. 2). Difference is laser frequency that is thought as avoiding modehop. The position of half wave plate is the almost same as yesterday, Still we are not sure why the shape is so simillar.
At this point, we realized that we have something we do not understand, and we gave up switching the current high-power laser to the new one this time.
We switched the new laser to the old one soon, and Ushiba-kun tried the IFO lock. He said he reached to the observation mode.
We need a little more independent investigation, especially for the polarization of the new HPL
