We worked on the OMC test over the weekend.
- At the beginning, the measured OMC transmission was ~85% even after subtracting the junk light and sidebands from the calculation.
- A pretty visible (by eye) dust were on CM1. Also a small residue of First Contact was found on the same mirror.
- We applied FC only on CM1 to remove these.
- The measued transmission went up to the level of 96%.
- We swept the incident power from 0.3mW to 30mW in order to see the dependence of the transmission against the incident power.
- The variation of the transmission ~10% was observed (attached figure 1, Red). This was compared with the similar dependence measured at Caltech (Magenta)
- So, the reduction of the transmission was observed as in eLIGO, although the measurements at Caltech and LLO are not consistent.
- Can this be attributed to the dependence of the PD efficiency? We measured the incident power on the PDs together with the preamp DC output. (Figure.2)
This gives us how the responsivity changes with the incident power.
- Nevertheless, the dependence remains. We'll make more accurate measurement today.