Madi, Camilla

Yesterday Camilla and I went down to EX to measure the return-from-vacuum ALS beam
We placed a pellicle beamsplitter between the PBS and the LPM to pick off the ALS return beam and observe its shape and size
We put the pellicle in two different locations

• Location 1 : 175mm from PBS
• Location 2: 31inches from PBS -> 787.4mm from PBS
  • (Equivalent to 13inches from LPM -> 330.2mm from LPM)

Multiple measurements taken at each location, photos attached. The beam was quite large, and has two bumps on the peak. It was also too bright to take an image on a CCD. Looks better than former 'mickey mouse' shape observed, but still very far from a nicely shaped beam.