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AdV-SGD (FDS commissioning)
vardaro, delauren, zendri - 2:11 Friday 06 February 2026 (68636) Print this report
Realignment of the OPA and MZ, summary of all the phase scan with the Delay Line

4/02 Realignment of the squeezer

In the Morning we tried to align the PD photodiodes but we lost a bit the CMRR of the HD, and we also tuned a bit the EQB1 FI HWP1

Martina went in Det lab to exchange the discs for the dust monitoring so she also realigned the MZ and the OPA. We did not gain much in terms of MZ visibility Max ~1.6V. But we improved a bit the level of the coupling of the green beam into the OPA cavity.

5/02 Fine tuning of the alignment

As last work on the DL we aligned better its mirror, recovered the HD PD alignment and tuned again the HWP of EQB1 FI and the one in front of the HD Detector

We also restored the lock of all the PLLs

We investigated a bit a possible effect of phase noise

For all these operation we did a CC phase scan here a summary table

Time Param Gain Efficiency Phase Noise SQZ Level ASQZ Level Notes Fig
02/02 18:47:44 0.3826 = 8.34 dB 94.8(2)% 92(2) mrad 6.12 dB 8.11 dB Laser Multimode (Stand Alone) - After DL alignment Fig 1
03/02 14:35:42 0.3788 = 8.4307 dB 92.8(2)% 77(2) mrad 6.15 dB 8.13 dB Main PLL offset moved (no more multimode) Fig 2
04/02 09:56:12 0.3601 = 8.87 dB 91.9(2)% 65(2) mrad 6.40 dB 8.54 dB DL alignmen - t Stand alone - No multimode Fig 3
04/02 18:04:36 0.3474 = 9.18 dB 88.4(2)% 20(2) mrad 6.47 dB 8.71 dB Lost a bit HD alignment, OPA alignment No multimode Fig 4
05/02 10:27:27 0.3523 = 9.06 dB 92.1(2)% 66(2) mrad 6.48 dB 8.73 dB Improved HD alignment Fig 5
05/02 13:56:06 0.3587 = 8.9 dB 94.3(2) % 85(1) mrad 6.38 dB 8.65 dB No alignment, PSL laser freq Shift all PLL locked Fig 6
05/02 15:48:44 0.402 = 7.91 dB 94.1(2) % 110(1) mrad 5.53 dB 7.34 dB Less generated squeezing/ no alignment Fig 7

Phase scans in similar configurations gives a different level of losses and phase noise. In general the losses are under control between 6 and 10 % whereas it seems we have an excess of phase noise. To be investigated.

The amount of losses is quite well explained (4% from visibility) 1% OPA escape efficiency 1% HD PD Quantum efficiency 1% EQB1 FI 1%HD clearence. Known losses 8%

If we do an average of the results above the level of losses is 7.4±0.8% and the phase noise is 74±11 mrad. In September 2022 (with the Pump power scan) we obtained 11.0 ± 0.4% of losses, 14±12 mrad of phase noise.

Next step is to remove the delay line

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vardaro, zendri - 18:01 Tuesday 10 February 2026 (68654) Print this report

In order to check the phase noise issue we tried to measure the HD detector CMRR as was done in 2022.

We inserted HD Mir and we measured the DIFF/SUM gain that is still 2.1. Then we injected 0.0125 V of amplitude of white noise in the fast CC and we measuired about 58dB of CMRR (fig 1 and 2) 

In order to try to mitigate the phase noise we rotated the HWP of EQB1 in ASQZ as was donne in 2022 with the aim of removing all the peaks of mirror mounts resonances.

We performed other two CC phase scans (delay line)

  1. the first at 17:1:00 of 09/02
  2. the second at 18:54:30 of 09/02

In fig 3 and  it is visible that the pahase noise is sligthly decreased from 68 to 62 mrad by rotating the HWP. This variation is inside the measurement error so we are nto completely sure about this improvement.

Fig 5 we also checked the behaviour during night to see if the laser is running in single mode and it seems the case

Fig 6 ASQZ,SQZ and shot noise spectra with delay line Shot 20:03, ASQZ 20:12, SQZ 20:23 UTC
Fig 7 a phase scan with the retroreflector and comparison with delay line. In the same condition. The phase scan was run at  15:45:30 UTC of Tuesday 10 February. The amount of losses increased by 4% between DL and retroreflector and the phase noise remained similar

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