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AdV-TCS (CO2 laser projector)
lumaca, amagazzu - 23:57 Sunday 24 August 2025 (67548) Print this report
WI CO2 CH and NI CO2 main laser issues

At 20:10 UTC Andrea informed me about an unlock; the first attempt to relock failed, and he contacted me in case it was necessary to check the WI CH ( 67546 ).
Since I was awake, I connected to follow the situation live. While adjusting the WI CH power by rotating the waveplate (action completed at 20:28 UTC), we noticed that the flag TCS_NI_CO2_PWROUT was red.

Looking more carefully at the signals, I found a sudden drop (about a factor 2) in the NI CO2 laser power at 19:40 UTC, clearly visible in PWROUT, ISSIN, POWER_CH_PICKOFF. Interestingly, the effect was not as evident in PWRLAS and CO2laser_TE. See figure attached.

Since the change seemed real, I checked the NI CO2 laser powers individually (by closing flip mirrors) and restored the correct values injected into the ITF (action completed at 20:50 UTC).
I also asked Andrea to go to the TCS room to verify whether anything unusual could be seen or heard macroscopically, but no clear culprit was identified. The cause of the power drop remains to be further investigated.

Currently, the DMS flag TCS_NI_CO2_PWROUT will remain red, as I had to rotate the waveplate to send more power toward the ITF. The reference value should be re-centered, but we prefer to wait a few days before applying the change.

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lumaca, nardecchia - 1:16 Monday 25 August 2025 (67549) Print this report

At 00.30 LT, Diana acquired a thermal image of the NI CO2 bench and we compared it with the previous one taken during the 19 August maintenance (see Fig. 1).

The  image of this evening shows a localized hot spot not present in the earlier image, suggesting a possible partial obstruction of the beam path leading to power loss. This is consistent with the fact that the beam sampler at the laser output (TCS_NI_CO2_PWRLAS) shows no variation, while other bench signals do (see Fig. 2).

The sudden power drop is not correlated with temperature changes. The nominal power injected into the ITF was recovered by rotating the waveplate, but the beam shape (and consequently the DAS) may be affected by the possible obstruction.

This issue could prevent the ITF lock.
An urgent inspection of the NI bench is recommended to check for any foreign object or obstruction.

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