R&D (FilterCavity)
NaokiAritomi - 22:46, Wednesday 17 July 2019 (1479)
Polarization problem

[Aritomi, Yuhang]

First we tried DC balance of homodyne with s pol, but power unbalance of BS was large for s pol. Reflection of BS is 630 uW and transmission is 600 uW for s pol while it's almost balanced for p pol. So we decided to use p pol for the moment. We made LO p pol with HWP and confirmed its polarization with cubic PBS (Newport,10BC16PC.9). However, when we put plate PBS (thorlabs, PBSW-1064) instead of cubic PBS, most of the LO was reflected by plate PBS. Actually I didn't check the direction of plate PBS and maybe it's wrong, but even in that case we cannot explain this behavior. We'll check the direction of plate PBS and check the polarization with AMC tomorrow.

Anyway, today we managed to make LO DC balanced with "p pol".

Comments related to this report
YuhangZhao - 14:48, Thursday 18 July 2019 (1481)

Aritomi and Yuhang

Today, we checked together about the polarization again with PBS plate.

  • The mirror was mounted as flipped(the uncoated side was facing laser). We flipped it back to the correct side.
  • The angle of the PBS plate was quite far from 45 deg. We checked today this angle. When we have all the light reflected, the angle was quite far from 45 deg(at that time, around 35 deg). When we turn the mirror to the direction of 45 deg, this reflection disappeared.

So we concluded that the beam we were using is p polarization. And we also need to pay attention next time about the surface of mirror and the angle of PBS plate.