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KAGRA MIR (Polarization)
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ShalikaSingh - 13:35, Thursday 15 May 2025 (4022)Get code to link to this report
Optics change on PCI table for birefringence

The optics (marked in pic 1) as 1 and 2 were changed. Previously we had some mirrors(perhaps 5104), and they were causing the polarization to change too much. So, they were replaced with Silver mirror PF10-03_P01-10. Then the polarizer was installed in rotation mount at place (a) shown in pic. 

I have taken the Thorlabs cube polarizer from LC table. The previously used one in PCI was newport one, and it was not properly installed in the thorlabs cage rotator. 

The polarizer alignment has to be tuned slightly more, but for now the polarization at the camera goes from azimuth (-90,90), and ellitpcity (0-2) degrees.

Images attached to this report
4022_20250515063403_screenshot20250515133256gallery.jpg
Comments related to this report
ShalikaSingh - 19:07, Friday 16 May 2025 (4024)

After moving the mirrors, I had to realign the beam. The alignment was tuned to obtain horizontal  and vertical  to be within 0.027deg and -0.016deg. See the plot 1 and 2 showing the horizontal  and vertical alignment.

Images attached to this comment
4024_20250516120734_horizontal20250516.png 4024_20250516120741_vertical20250516.png
MarcEisenmann - 16:45, Monday 19 May 2025 (4033)

Actually the reason to install the metallic mirrors was to remove the polarizer to avoid possible power discrepancy at different rotation angle.

The HWP is mounted inside the motorized rotator and provides good azimuth coverage with only minimal ellipticity (~<1 deg)