[Ushiba, Komori]

We conducted measurements of the dark noise for the OMC DC PD using two different trans-impedance gains: 100 Ohm and 400 Ohm.
The results are presented in the attached figure.
The 100 Ohm gain was utilized during the O4a experiment.
The measurement was taken at the K1:OMC-TRANS_DC_SUM_OUTPUT port after closing the shutter in the PSL room.

Both measurements exhibit peaks at 4 Hz and its harmonics in the spectra.
In addition, the 400 Ohm result shows significantly higher power supply line noise.
This issue should be addressed at some point to mitigate its impact.

The contribution of the dark noise to DARM sensitivity, along with the shot noise contribution, will be provided in an upcoming post.