Yuhang and Chien-Ming

As we said before, we need a better PD for the coherent control1 lock. (PD set at OPO reflection) So we talked and tested several things.

1. Change the amplification factor of the op-amp. We tried two combinations of (500Om, 50kOm) and (500Om, 7.5kOm).  For the first combination, we tested the signal, but the amplitude and SNR are the same as before. While for the second combination, the amplitude is smaller while the SNR is a bit better.

We checked the spec of AD8057. The maximum gain we should give for this op-amp is 10. The further increase of the gain will degrade the bandwidth. And this is exactly what we see for increasing further the amplification factor.

It seems that we are also reaching the saturation current of the op-amp.

2. We also tried to use the RF amplifier, because maybe there is an optimal input level for the mixer to make it work better. But it seems RF amplifier increases both signal and noise.

3. We also tried to change the capacitor of the PD circuit. But we are still trying.