The goal of the shift was:
1) Measure the mode matching with SR aligned and Misaligned and hot ITF. In both the cases 15% of mismatch
2) Measure the losses in LN2 with SR aligned: about 50% of losses
3) Receck of the system in LN3 and SR misaligned
All the details will follow
We left the ITF in LN3 and the SQB1 shutter closed
Check of the mismatch in CARM_NULL_1f
When the shift started the ITF was unlocked thus we started checking the matching in CARM_NULL_1F.
Once the ITF arrived in CARM_NULL_1f we open the DET Shutter, then I moved the OMC temperature at 22.617 C and I started to SCAN the SC frequency to see TEM00, TEM10 and TEM20. The Scan that I used is between 28200 and 27500 in 60 sec or in 5 sec.
We measured the Matching with SR aligned and we found
@20: UTC TEM00 1.72e-3mW, TEM10: 0.281e-3 mW, TEM02: 0.336e-3 mW => 14.5% of mismatch
@20:41 UTC we misaligned the SR by +1.7urad in TY
@20:55 UTC we measured again the matching and we obtained TEM00 0.912e-3mW, TEM10 = 0.756 e-3 mW TEM20 = 0.337 e-3 mW about 17% of mismatch but a very high 17%.
LN2 SR alined and phase scan
We arrived in LN2 then we acquired the shot noise reference at 22:06 UTC. We saw that the 4MHz magnitude on B1 was only 0.5mV (in LOW_NOISE_3 usually is 2mV).
We performed a phase scan of the CC loop: Shot: 1294143858, SCAN: 1394143983. With this scan the amount of losses is very high and we did not see the usual level of SQZ in the sensitivity of the past phase scans
Then we tried to find if some clippng is present and we started to move the alignment and SQB1 bench:
After that we reached about 1.92mV of 4 MHz mag and we measured a parametric gain of 2.7 i.e. 8.6 dB of SQZ generated
Then we asked low noise 3 and we misaligned the SR. Now the magnitude was again 0.2mV so we had to reput SQB1 in its original positon except SQB1_TX that we left at 320 urad instead 290 urad.
The 4MHz mag was 1.9mV but during the process we saw it around at 2.05mV.
We saw that the sensitivity was spoiled by some peaks and we have the impression that some clipping caused some excess of stray light in the sensitivity and some instability of the 4 MHz mag on B1.
We closed the SQB1 shutter and in a couple of hours the sensitivity improves by ~2-3 Mpc. To be ckecked.
