(Alexa, Stefan, Dick)

ISCT1 REFL BEAM Polarization Measurement: We used a cube to measure the polarization of the ISCT1 REFL beam out of the periscope. We found the polarization to be s-pol. 

Optics Added: With the PSL at 1Watt, the power of the ISCT1 REFL beam at the periscope is 0.68W. However, the PD on the table used as a trigger for the shutter saturates at 6mW. Thus, we placed a W1 45S beam splitter with the AR coating in front of the shutter to reflect 2mW of light onto the PD. We also placed an iris in front of the PD to single out the beam. And finally, we placed a lens in front of the PD to reduce the beam size.

Note: One of the shutter controller boxes has been modified (see LIGO-E1300580-v1); however, the top one remains to be changed.