Mon 19th September - Preliminary activities:

After a week end of SQZ Measurements with the Delay line on, we started by recovering the IR alignment. The idea was to fix the IR path before rising the SQB1 retroreflector.

• The SC alignment into the OPA was checked at 10:12:52 UTC with the SC AA loop. We before aligned the SC AA PD with Thorlabs actuators then we closed the loop. After that the DC value of the channel EQB1_HD_RF_DEMOD was equal to 3.77V We don't gain anything closing the loop. The SC was well aligned into OPA
• We commented the line 1147 of SQZ FLT with the aim to not discharge the IR AA in DOWN.
• At 10:24 UTC we finished to align the filter cavity with IR and the Homodyne detector acting on HD_m6 and SQB1_M13
  • ASQZ measurement 11:00:00 UTC angle 0.725 rad, level 7.7±0.1 dB, magnitude 8.04mV
  • SQZ measurement 11:00:45 UTC angle 1.85 rad, level 5.35 ± 0.1 dB, magnitude 3.05mV
  • CC open and scan 11:13:51 UTC 8.05/2.785=2.89 of parametric gain i.e. 9.2 dB of produced SQZ
• At 11:18:00 UTC we reput the Delay Line and we aligned again it using EQB1 DL M4 and M5
  • ASQZ measurement 11:46:16 UTC angle 0.91 rad, level 8.1±0.1 dB, magnitude 8.05mV
  • SQZ measurement 11:51:00 UTC angle 2.15 rad, level 6.2± 0.1 dB, magnitude 3.11mV
  • CC open and scan  8.26/2/87=2.87 of parametric gain i.e. 9.2 dB of produced SQZ
• Comparing the maximum of the magnitude between DL and FCIM we estimate that the propagation losses after DL are 3%. N.B. this method is not correct for the propagation losses because the visibility in the two configurations is different. We also noticed that the level of SQZ and ASQZ measured is less than expected thus we asked to Moritz to check the OPA status and he found that the temperature of the crystal was not well tuned. Opa Tuned at 12:24:30 UTC
• With DL we measured the parametric gain 9.08/3.192=2.84=9.1dB
  • The level of ASQZ at 12:57:40 UTC angle 0.8 rad, level 8.7±0.1 dB, magnitude 9.02mV
  • The level of SQZ at 13:08:00 UTC angle 2.3 rad, level 6.43±0.08 dB, magnitude 3.24mV
  • Tuning of SQB1 HWP +20 steps, 6.44±0.09 dB of SQZ at 13:19:00 UTC
• Delay Line removed again 13:24:00 UTC and checked IR alignment 13:28:00 UTC 
  • The level of ASQZ at 13:52:40 UTC angle 0.55 rad, level 8.34±0.08 dB, magnitude 9.65mV
  • The level of SQZ at 13:57:00 UTC angle 1.95 rad, level 5.5±0.1 dB, magnitude 3.14mV
  • CC open and scan 14:04:30 UTC parametric gain 8.7/3.095=2.91 i.e. 9dB of generated SQZ

Once the system was well aligned we started to raise the retroreflector. Its initial position was -1 million of steps. From this position, after +350000 steps the beam disapperead again. With the retroreflector raised we started to move tthe H and V DOFs with SC on looking the HD_CamNF camera. We noticed that H and V are switched. After a couple of hours of work we found the SC beam from the RR. We switched off the SC and we removed EQB1_HD_MIR and we maximized the HD 4MHz mag acting on the RR (coarse) and HD_M4 (fine) .

Once the RR was raised and aligned we did the following things:

• ASQZ measurement at 16:40:45 UTC phase 0.8 rad, level 8.4±0.1 dB
• SQZ measurement at 16:50:30 UTC phase 2.25 rad, level 5.8±0.1 dB
• We moved SQB1 HWP1,2  to maximize the FI isolation factor:
  • SQZ after tuning at 17:00:00 level 5.8±0.1 dB
  • ASQZ after HWP1 and HWP2 tuning at 17:19:30 UTC, level 8.5±0.1 dB
  • SQZ after HWP1 and HWP2 tuning at 17:23:30 UTC, level 5.8±0.1 dB

No particular gains tuning the two HWPs. We left the SQZ at the and of the shift until the following Morning.

Tue 20th September - Pump Power scan with the retroreflector on:

Once arrived we slightly realigned the system (about 0.2 dB of SQZ recovered) and we started with the Pump power scan

Shot noise reference at 11:77:20 UTC, level 0.0±0.1 dB

Fig 1. shows the spectra of the measurements, they are flat above 30 Hz. Fig 2 shows the result of the fit of the SQZ and ASQZ level. We measure 14.9 ± 0.4 % of losses and 20 ± 11 mrad of phase noise. The level of phase noise is compatible with the one measured with the DL line, whereas for the losses we measure 4% more (11 % with the DL line).

After the pump power scan we checked also the level propagation losses using EQB1 IR PD Moni and the HD DIFF RF 4MHz mag

N.B. the magnitude is not a good way to measure the propagation losses it depends also from visibility and from polarization. In any case the 4% of propagation losses netween RR and DL is compatible with the performed measurements.

We left the system for the night with FDS, phi 1.95 rad (SQZ) rotation at 420 Hz and MZ offset -0.02V.