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nardecchia, ballardin, kraja, gherardini, ruggi, spinicelli - 21:50 Monday 31 August 2026 (69675) Print this report
NI RH ON to check HWS-DET

This afternoon, we performed several checks before starting the HWS-DET acquisition with the NI RH ON.

As a first step, we checked the HWS-DET acquisition and encountered an issue with the MATLAB version called by the Python code of the acquisition software. Giulio solved the problem by updating the acquisition code to make it compatible with the  MATLAB version 2023.

Now the command to launch the acquisition is:  

./hwsAna2022_R2023a.py -d/r/l DET 

In parallel, Fabio went to the Central Building to switch on the power supply of the NI and PR RHs.

At this point, we prepared the ITF for the measurement. After being locked in CITF with the additional loop on the NI MIR engaged by Paolo, the ITF was set in NI single bounce.

The HWS-DET illumination is shown in fig. 1. The voltage of the SLED has been settled to 1.45 V.

14.41 UTC: HWS ACQUISITION START (20260831T1641)

14.58 UTC: NI RH ON at around 10 W (V=19 V)

16.49 UTC: NI RH OFF  (WAVEFRONT #42)

The RH signal was clearly visible in the HWS map (see Fig. 2).

The HWS beam appears to be displaced with respect to the center of the mirror by approximately 1 cm and 2 cm along the two directions..

To verify the alignment of the NI CO₂ actuators, I switched on the NI CH at 17.12 UTC.

An example of the wavefront map with CH ON is shown in fig. 3. The CO₂ actuators and the RH appear to be well aligned in the horizontal direction, while the CH appears to be slightly lower than the center of the mirror in the vertical direction. However, I would like to repeat the measurement with the CH, since this measurement was performed after several hours in SB.

At the end of the measurement, I closed the NI CH flip mirror (19.38 UTC).

Paolo will disengage the additional loop later this evening.

The North arm will most likely need some time before it can be relocked.
 

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Comments to this report:
mwas - 21:09 Tuesday 01 September 2026 (69682) Print this report

As mentioned by Romain Gouaty during the daily meeting the SDB1 bench angle has been changing during this measurement, due to the B5 drift control loop which was closed and trying to follow the beam

Figure 1-5 show a few different examples of the B1p and B5 beam shape during the measurement, both of them change shape and size. I expect that this is due to the thermal lens in the NI CP detuning the detection telescope, either by just moving the camera position with regard to the beam waist, and the beam being astigmatic. Or more likely, because the beam stops being collimated at the input of the parabolic telescope, and parabolic telescopes become more abberrated when used for converging or diverging beams.

Especially on figure 5 the beam stops being round. For the B5 beam the cross beam shape is normal, as the B5 pick-off is highly polarized by two mirrors actiing as polarizers before the B5 camera, so most of the beam on the camera is in P-polarization and shows the cross pattern of the injection Faraday depolarization. 

Following a beam which changes shape with the B5 quadrant is not a right choice, and the better solution is to turn of the drift control. Note that today when the drift control was turned off the beam moved by ~20urad, and turning off the floating set points, and adjusting the fixed set points to restore the bench orientation was needed.

 

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