[Anchal, Paco]

We investigated the low power issue with POX11 photodiode.

• We used a power meter to confirm that above 12 uW of power is reaching the ITMX oplev table.
• But the power reaching the photodiode was only 3 uW, because the 2 steering mirrors used were discarding half of the light. These mirrors were taken from former POP setup and are probably BS or meant for different incidence angle/polarization.
• We used flashlight to test that the photodiode gives a response, so it is not dead.
• We also put in a db15 breakout board in line to the PD and confirmed that power input is correct, temperature is nominal, enable is ON, and DC out is responsive to flashlight.
• So we decided to redo the path with Y1-45P 1inch mirrors. I found two such mirrors in the lab.
• When setting up the path again, I realized that the beam shape is not even. I took a photo of the beam on the card (see attachment 1) and indeed the POX beam that is coming to the table is half clipped.
• So tomorrow, we'll open the chamber and find out where this is happening. For now, I've setup a nominal path to the POX11 photodiode, but we'll tune it after we get a clear POX beam on the table.