[Nakano, Enomoto]

Today we measured the profile of the beam after the lenses after the FI and installed an EOM for acquiring length error signal of PMC.

According to the profile we had got yesterday, we moved a lens (Lb) by several centimeters in -z direction, and after some trial and error we got the following profile (see attached figure).
The beam shape looks elliptic where the position is far from the waist, but the fitting results show that the current profile seems acceptable.

We installed an EOM for acquiring length error signal of PMC. To make the polarization of the beam be s-pol, we put a half-wave plate after the FI (between Lb and Mb, due to the space constraint).
This EOM was used for the same purpose in iKAGRA. The resonant frequency is 15 MHz.
Transmissivity of the EOM was 95%.
Current top view of the table can be seen in the attached picture.

= Next =
-- put a broadband EOM for a frequency actuator. Just before the 15 MHz EOM should be ideal.
-- roughly put mirrors on the main path; pedestals with proper height just arrived.

= Note =
Without a half-wave plate, which means both s-pol and p-pol go into the EOM, the beam after the EOM split into two.
This is probably because of birefrengence of EOM and wedge of EOM surface.