KAGRA MIR (Polarization)
MarcEisenmann - 11:29, Wednesday 05 March 2025 (3934)
Comment to restart of birefringence measurements (Click here to view original report: 3906)

[Marc, Michael M. , Shalika]

We removed the previous birefringence readout from the imaging unit which was using PBS and several optics installed on a small breadboard.

Instead, we now use Thorlabs polcam that was aligned to the input beam.

We tuned the input QWP/HWP to reach circular polarization, then installed and aligned a polarizer to inject pure linear polarization.

While testing the polarizer alignment vs rotation, the power control HWP was mistakenly rotated sending up to about 300mW to the polcam.

It disabled itself crashing the vi but could be somehow recovered after sometimes.

It seems that the camera is still able to properly read polarization (at least linear) as the read value corresponds to the expected polarizer rotation.

This issue arised because when 2 motorized rotator controller are connected to the pc, only one is detected... For safety, after recovering the appropriate input power, we disconnected the power controller HWP.