By default the shutter of these PDs remain closed, but they could be opened just after reaching dark fringe.
Figure 1, shows a case where B1p_PD1 and B1s1_PD1 have been manually enabled 10 minutes after lock (from yesterday).
B1p_PD1 sees ~10 times more power than B1p_PD2, and B1s1_PD1 (reflection of first OMC) sees ~100 times more power than B1p_PD2.
B1s1_PD1 has a better SNR but is a bit more tricky to use. This would work only if OMC1 remains unlocked, and currently fluctuations at 1.7Hz and 3.2Hz are causing the PD audio channel to saturate frequently. So it is an option only if these large power fluctuations are not present.
Looking at B1p_PD1 some of the violin modes (figure 2) and drum modes (figure 3) are visible. A list of modes indentified by the line tracker are attached in this logbook entry.
For the drum modes, B1s1_PD1 has a better SNR (figure 4), but it comes with the caveats mentioned before.
In conclusion it would be good to add B1p_PD1 shutter opening to the automation when reaching dark fringe. And if the SNR is sufficient attempt tracking the loudest lines.
