During this shift we perform a re-alignment of the squeezer and after that we measure the squeezing and anti squeezing level at different pump phase powers.

For eacg point we perform:

• a phase scan 240s of shot noise, 180 deg of phase scan with steps of 1deg and 3 seconds for each steps
• 10 minutes of squeezing injection
• 10 minutes of anti-squeezing injection

Point 1 (figure 1)

• OPA pump power = 1.9mW
• Sqz = -2.42 dB
• Asqz = 4.23 dB
• GPS shot noise: 1242206578
• GPS start scan: 1242206818
• GPS stop scan: 1242207372
• Sqz - Mag distance = -0.135 rad
• Dither demod phase = 5.2 rad
• Min mag phase = 0.92 rad
• SQZ phase = 0.8 rad
• Asqz_phase = 2.478 rad 
• SQZ GPS = 1242208221  18 May 2019 09:50:03 UTC
• ASQZ GPS = not performed (problem into OPO lock)

Point 2 (figure 2)

• OPA pump power = 2.8mW
• SQZ = -2.79 dB
• Asqz = 5.18 dB
• GPS shot noise: 1242209895
• GPS start scan: 1242210136
• GPS stop scan: 1242210690
• Sqz - Mag distance = -0.135 rad  
• Min mag phase = 0.89
• SQZ phase = 0.733 rad
• ASQZ Phase = 2.496 rad
• SQZ GPS = 1242211334  18 May 2019 10:41:56 UTC
• ASQZ GPS = 1242211990  18 May 2019 10:52:52 UTC
• End measurement = 1242212583  18 May 2019 11:02:45 UTC

From here we reduce the shot noise of each steps from 240s to 60, because before the scan the ITF was in low noise 3 thus the shot noise reference was automatically taken during the operation of the squeezer

Point 3 (figure 3)

• OPA pump power = 4.4mW
• Sqz = -2.96 dB
• Asqz = 6.68 dB
• GPS shot noise: 1242213670
• GPS start scan: 1242213730
• SQZ phase = 0.7854 rad
• ASQZ phase = 2.513 rad
• SQZ GPS = 1242214691  18 May 2019 11:37:53 UTC
• ASQZ GPS = 1242215435  18 May 2019 11:50:17 UTC
• End measurement = 1242216035  18 May 2019 12:00:17 UTC

Point 4 (figure 4)

• OPA pump power = 6.3mW
• Sqz = -3.25 dB
• Asqz = 8.46 dB
• GPS shot noise: 1242216765
• GPS start scan: 1242216825
• GPS stop scan: 1242217378.51
• Sqz - Mag distance = -0.228160360316577
• Min mag phase = 1.012 rad
• SQZ phase = 0.7854 rad
• ASQZ phase = 2.583 rad 
• SQZ GPS = 1242217846  18 May 2019 12:30:28 UTC
• ASQZ GPS = 1242218571  18 May 2019 12:42:33 UTC
• End measurement = 1242219172  18 May 2019 12:52:34 UTC

Analysis (figure 5): 

From the plot in figure 5 we can derive an optical loss for the squeezing of 30% and a phase noise which seems to be non-stationary but in the range between 120-150mrad. For the first three points a phase noise of 150mrad agreed well, for the 6.3mW pump power measurement a phase noise level of 120mrad fits better…This seems to be the main limitation for detecting higher squeezing levels at the moment.

After that we try to increase the squeezing level acting on the coherent control loop gain. We reduce it from 55 to 20, the RMS of the in loop and out of loop error signal was decreased (figure 6):

• In loop (B1 PD1): from 1.6e-4 V to 8.2e-5 V, i.e a factor 2
• Out of loop (B1 PD2): from 4.9 e-15 V 2.6e-15 V, i.e a factor 1.9

After that we reperform a phase scan (figure 7) but near the maximum of the anti-squeezing the CC loop oscillated:

• Shot noise:  1242220187.98 (4 mins)
• Phase scan:  1242220428.1

We found a squeezing level comparable to the previous, i.e. -3.25 dB, thus acting on the CC gain seem not useful to decrease the phase noise. 

After this work we performed other OPA alignment into the DET lab and finally we re-perform a phase scan

Final position (figure 8)

• Squeezing Level 3.0 dB
• Anti-squeezing Level 6.0 dB
• Squeezing phase = 0.3 rad
• CC loop slow set = 0.5e-3 V
• GPS phase scan: 1242227728 (4 min shot noise before)