Firstly, I checked that PDH signal coming from Q-phase gives basically 0 when crossing carrier frequency (DDS2 channel3 phase 150deg). Then to check the RF gain/demodulation gain, a check of PDH singal in time was performed by looking at I-phase channel.

To have values for each segment, the alignment was checked to be as good as possible. (green tra dc is around 5200~5300) (a moment of flash is shown in attached figure 1) For each measurement, the light beam is centered on separate segment of QPDs by adjusting its closest steering mirror. (as shown in attached figure 2)

After checking demodulation phase, alignment and beam centering, the PDH singal was measured (several measurement is attached) and summarized as the following table.

Note that: the value showed in above table comes from a single measurement. The PDH signal actually have small variation around 10mV.

Although this measurement is not very much precise, it gives information about the signal coming from each QPD's segment.