= Laser power entering the RF PD =
In average, the output of REFLAIR_B is 500 (+/- 100) counts when REFL port is kept dark (see the attachment), while 1800 (+/- 100) counts when the reflection from only one end is coming coming back to REFL table.
Therefore, the laser power entering the RF PD (REFLAIR_A) in the dark fringe condition is 0.20 mW * (500/1800) = 0.056(10) mW.