Peter, Lisa

(same entry as  LLO log entry 37917)

Following up the discussion we had at the ISC meeting today about the scattered light peaks in DARM at LLO when the SQZ beam diverter is closed, Peter pointed out that the black glass used on the back of all of the beam diverters is not coated, so there is probably no good reason to believe that the reflectivity is much lower than that of uncoated glass, R=8%.

So we went back and look at HAM6 drawings and pictures, and the most likely explanation is that we are simply sending some light from the beam diverter toward the region of HAM6 where OM2 and the HR in the OMC transmission path is, and light can easily find a path to the OMC. So, it seems that the simplest thing to do at LHO is to put a beam dump to catch the reflection off the beam diverter black glass.