Using the EOM driver excitation cable that was installed yesterday we measured a driven transfer function from the 45MHz oscillator amplitude RIN to the OMC_DCPD_SUM.

Bottom line: We have a coupling of about 9e-2mA/RIN (9e-5A/RIN) coupling at 1kHz (flatish), measured at max power = 22W. (plot 1) Around 50Hz it is about 2x higher.
This coupling is the same as the (not driven) estimate from alog 20182. We also (accidentally) measured the coupling at 17W input power, and found 6e-2mA/RIN. (plot 2)

Remarks:
- This is the coupling into both DCPD's.
At 22 W, we have:
- Without injection the DCPD_NULL currently has 7.8e-8mA/rtHz, while DCPD_SUM is at 8.63e-8mA/rtHz. This suggests the extra noise is at 3.7e-8mA/rtHz.
- The coherence between DCPD_SUM and the (pre-EOM dirver) RIN read-back is 0.17, suggesting a noise floor of about 3.2e-8mA/rtHz in DCPD_SUM - close enough.
- Using the measured 9e-2mA/RIN we would need a RIN of about 4.1e-7/rtHz.

The same numbers at 17 W are:
- Without injection the DCPD_NULL currently has 7.8e-8mA/rtHz, while DCPD_SUM is at 8.25e-8mA/rtHz. This suggests the extra noise is at 2.7e-8mA/rtHz.
- The coherence between DCPD_SUM and the (pre-EOM dirver) RIN read-back is 0.1, suggesting a noise floor of about 2.5e-8mA/rtHz in DCPD_SUM - close enough.
- Using the measured 6e-2mA/RIN we would need a RIN of about 4.5e-7/rtHz.

The full template is available on the DCC: T1500441
https://dcc.ligo.org/T1500441


Related alogs: 20539, 20182, 19856