Stefan and Kiwamu

We continued working on the alignment of IMC today. We managed to get the alignment back i.e. the beam hits the center of the IM4_TRANS QPD with all WFSs in action. It is now happiy locking.

However, we found that the IM1 trans path, which is used for a camera and trigger PD, seemed clipped. By moving the mirrors on IOT2L, we concluded that the clipping happened in chamber, namely in HAM2. This is not a critical issue as this light is used only for triggering purpose and it still gives a reasonable amount of the light. We will keep studying what is happening in the chamber. Perhaps this could be due to the uncontrolled degrees of freedom in the IMC alignment control.

What we did:

• We tried to bring the alignment back to a good-in-air-alignment which was established 18 th of November (see alog)
  • We tweaked both HEPIs and MC SUSs.
  • This didn't give a signal on MC2_TRANS, indicating that the cavity axis is quite off from the MC2_TRAN didoe.
• We tried to bring the alignment back to a good-in-vac-alignment which exhibited a nice long streach around 15 th of September.
  • This didn't give a signal on MC2_TRANS either, indicating that the cavity axis is quite off from the MC2_TRAN diode.
• We brought the alignment back to that of yesterday by typing in the numbers from the previous alog (see alog)
  • Note that the HEPI offsets were kept the same as that of September 15 th.
  • This gave a power build up of about 2 counts on MC2_TRANS. This is still way too low.
• The setting of the whitening filters for the MC2_TRANS QPD signals were found to be wrong.
  • In particular, the gain was too low. It was found to be 0 dB while it used to be 36 dB.
  • We found the same issue on the IM4 TRANS QPD and set it back to how they were.
  • MC2_TRANS became approximately 200 counts when it was resonance.
• Because the beam hit the MC2_TRANS, we became confident that the alignment was getting better.
• We moved on the WFS loops.
  • We flipped the demodulation phases by 90 deg to compensate the mysterious RF phase rotation.
  • All of them worked OK.
  • The loops recovered the spot position on MC2_TRANS and now it is centered well.
  • We ran mcwfsreleive to offload the control signals to the suspensions sides
• We realigned the optics on the IOT2L table.
• Then we found that the IM1 trans beam was clipped.