This entry is a log on Apr. 23.
I swapped the mirror to PBS for splitting beam into TEM00 path and HOMs path.
TEM00 path beam has ~2 mW power with slightly tilted PBS (HOMs has 16.6 mW).
The reason PBS has slightly tilted incident angle from 45 deg is that the PBS is 56 deg Brewster PBS, and very low transmitted power with 45 deg incident angle.

Then I confirmed polarization of both transmitted and reflected beam are not circular polarization.