We noticed that the 2 photodiodes on B4, PD1 and PD2, show a different behavior when the TCS is turned on (see figure 1).

At the DAS thermal lensing steady state the 112MHz measured by PD1 is higher with respect to the value with DAS off, while PD2 measures the same value when no DAS applied. PD1 is the photodiode that we usually consider to evaluate the gain.