We received the super-polished lens from CVI with 30mm focal length. With this super-polished lens we should have less parasitic interference.

So we compared the back scattering and squeezing level.

As shown in the attached figure, there are some difference at low frequency which is more back scattering(worse) and more squeezing(better). 

Actually the low frequency part, we have already ovserved some uncertainty during different measurment. So it seems the replacement of lens doesn't improve system obviously.