Sudarshan, Keita, Evan, et al.

The source of excess power on ISS PD is  Aux laser at IOT2R.

We were seeing a lot of power on the ISS PD than usual. This power level in the PD changed (went up significantly- about a factor of 4) sometime around 12/11/2014. I was trying to figure out if this was the real signal or something in the electronics went bad but with no luck. However I noticed that the power level on ISS PD was reasonable since 3:30 on Wednesday. These power level on PD corresponded with the power on IM4_TRANS_QPD as well (See trend plots below).

Yesterday after looking through a lot of possible explanation about the power level changes in IM4_TRANS_QPD with Keita and coimmissioning crew, we realized this excess power was coming from the Aux Laser setup on IOT2R for Schnupp asymmetry. The power level change coincides with the timeline of Schnupp measurment setup (alog 15566), and on Wednesday at 3:30 PM  Evan blocked this aux laser beam with the beam dump. Evan and I went down to IOT2R this morning to do a sanity check if this was indeed the source and no surprise.