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Reports until 19:11, Wednesday 10 April 2013
robert.schofield@LIGO.ORG - posted 19:11, Wednesday 10 April 2013 (6023)
Beam splitter beam spot views for investigating scattering

Figure 1 shows beam spot views associated with the BS. I use these to look for potential scattering problems; the camera and flash is placed very close to the center of the optic where the beam spot will be. The flash mimics the scattering of interferometer light from the beam spot and lights up regions that will retroreflect interferometer light back to the beam spot, where it can recombine with the main beam to produce scattering noise. Of course the technique is limited by different angular distributions of scattered IFO light and light from the flash, as well as by color differences, but it gives a rough idea. I worry a bit about how bright the ITMY cage is, as viewed from the BS beam spot. 

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