We have remeasured the intensity noise coupling to DARM when PRFPMI is locked and ISS is turned off at 2020-02-19 18:10:50 UTC.
New coupling factor is incorporated in our sensitivity DTT (DARMsens.xml).
CMRR for the intensity noise during this measurement was about 1/55 at 100 Hz.

Method:
 1. Turned ISS off and measured the transfer function from K1:CAL-CS_PROC_DARM_DISPLACEMENT_DQ to K1:PSL-ISS_FIRST_SERVO_PDA_RIN_OUT_DQ (see this figure). The transfer function is calibrated to RIN to DARM coupling by inverting it and applying 5 zeros @ 10 Hz and 5 poles @ 1 Hz, gain of 1e-9 to account for the whitening filter and nm to m conversion (see this figure; error bar estimated from the coherence is shown with the shaded region). The measured coupling is eyeball fitted with gain of 1.1e-12 and zeros at 100 Hz, 2500 Hz. This zpk is used in the sensitivity DTT.

 2. Also measured the transfer function from K1:PSL-ISS_FIRST_SERVO_PDA_INF_OUT_DQ to K1:OMC-TRANS_DC_SUM_OUT_DQ to calculate CMRR to intensity noise with the same method described in klog #13008. The result is shown in this figure (error estimated from the coherence is shown with the shaded rigion).

Discussion:
 Compared with Yokozawa-san's measurement in klog #12983, the coupling is a factor of 2 smaller. A factor of 1.5 comes from a new DARM calibration factor (klog #12992). The rest is probably from better interferometer alignment. CMRR for intensity noise is also better than that measured in klog #13008.
 It seems like the intensity noise is not limiting the sensitivity below 1 kHz when the interferometer alignment is good.