Yesterday evening we resumed tuning the ITF working point, since the fringe level in CARM NULL 1f was too high to proceed in LN3 (0.04 mW).
In particular, the DAS actuation setpoints were re-optimized. I initially adjusted the WI DAS, since the WI CO2 laser experienced some issues, but this only worsened the fringe.
I then moved on to the NI, and the actuator that had the largest effect in reducing the fringe was the NI inner ring, lowering it to about 0.03 mW (see attached figure).
The nominal powers previously used, together with the updated values applied yesterday evening, are summarized in the table below (the latter are highlighted in bold).
|
| Reference | CH [W] | INNER DAS [W] | OUTER DAS [W] |
|---|---|---|---|---|
| W | on the ITF | 0.043 →0.043 | 0.150→0.150 | 1.79→1.66 |
| on the pickoff | 0.27→ 0.27 | 0.025→0.025 | 0.29→0.27 | |
| N | on the ITF | 0.117→0.117 | 0.350→0.743 | 3.1 →3.1 |
| on the pickoff | 0.721→0.721 | 0.057→0.121 | 0.502→0.502 |
The 'bold' powers have been left for the night.
