[Aritomi, Yuhang and Yao-Chin]

According to the previous R&D result (entry 1616), we found some issues for old isolator (IO-3-1064-VHP) including its aperture size too small and position too far relative to OPO cavity. Today, we installed isolator (FI-1060-5SC-HP) and put closer to OPO cavity to reduce back reflection. I also checked that the input/output aperture (Ø-5mm) of isolator was larger than old isolator. Fig 1 shows new optical layout. We main installed optical elements in blue frame zone.

Because SQZ and p-pol light were different polarization after OPO cavity, we could use PBS to separate them. Thus, the p-pol light is reflected from input PBS of isolator to right angle prism mirror (MRA10-K13) and its height was 54mm as shown in Fig 2. However, the polarization of SQZ light was rotated 45 degree after isolator. We used half wave plate to rotate its polarization keeping S polarization. In addition, we also re-installed the TAMA PD's position in order to add more space putting isolator.

We also check SQZ and LO overlap by using alignment mode cleaner, moving the lens (f:100mm) before isolator to improve mode matching.