[Pablo and Kiwamu]

 We adjusted the rotation angle of HWP1 which is an in-vac half wave plate in HAM1 to convert the polarization of the REFL beam from S to P.

We took HWP1 out of the HAM1 chamber and brought it to the optics lab because it is much easier to do it in a lab rather than in a chamber. Then we setup a 1064 nm fiber laser and some optics in the optics lab to adjust it. The first picture below shows the setup where we used two PBSs. We minimized the amount of S-polarizing beam by looking at the power of the rejected beam from the second PBS. At the PBS we got a rejected (S-pol) beam of 0.5 uW out of 10 mW incident (S-pol) beam on HWP1. The last picture shows the rotational angle of HWP1 after the adjustment. We locked the rotational part so that it won't rotate any more.