Marc, Michael, Yuhang

Today we finished the cleaning of #5 and the 1.5 inch sapphire.

Then, we tried to fine tune the rotation angle of the mirror.

This time, we placed a flexible ruler on the mirror and could precisely (+/-0.2 mm) estimate the arc length of the rotation.

The results are attached in figure 1.

Actually I made a mistake and rotated the HWP by +0.7 deg before this measurement so we need to add this value to the effective rotation of the mirror.

Note that for some points the mirror was a bit tilted which creates stronger coupling between s and p polarizations.

That's why we repeated measurements at some rotation angle.

We started measurement at -2.9 deg rotation with HWP = 0 deg.

In the end, before starting polarization measurement, we checked the HWP position that minimized the Ip power to be +0.8 deg.