As part of the effort to characterize stray light due to dust particle contamination in the SQZ subsystem, four 3" silicon dust witness samples have been placed at LAPP on SQB1 (Figure 1: T1, T2, L1, L2 are the samples' positions), in order to monitor dust contamination during installation. Before shipping to EGO, two of them were removed, while the other two were left on the bench to monitor dust eventually deposited as consequence of packing and transport. 

These last wafers were removed yesterday and a new wafer was placed (Figure 2: at position T1). The chosen position should allow the wafer to be representative of the optics and not to interfere with operations on the bench. The goal is to monitor dust contamination on SQB1 under vacuum. 

Please do not move the sample and report any activity that may need to be performed in the close proximity of it and may compromise its representability of the average cleanliness condition of its location.