This afternoon, after recovering CARM NULL 1F, we performed an absorption measurement using HWS-DET.

After approximately one hour of stable lock, the ITF was manually unlocked in gentle configuration, keeping all optics along the HWS-DET optical path aligned, including NE.

• 16:21 UTC: HWS acquisition started (dataset: 20261012T1821).

• 18:26 UTC: Gentle unlock performed (wavefront 9). 

Since this was our last opportunity to perform measurements with HWS-DET before the baffle installation scheduled for next week, I asked to continue the data acquisition for the remaining hour of the shift.

A preliminary comparison with the ANSYS simulation indicates an absorption of approximately 38 mW in the NI mirror (see Fig. 1).

At 12 W, the circulating power was estimated to be around 80 kW. Scaling this to the current input power of 17.5 W gives an estimated circulating power of approximately 116 kW.

Based on an estimated absorbed power of 35 mW, this gives a WI absorption of approximately 0.3 ppm.

After completing the measurement at 19:29 UTC, we switched the CHs back on, and Fabio left the ITF in the arms locked on IR configuration.