Since the reflection of IR beam on septum window AR is so small, we shot a red laser pointer beam from HAM5 through septum so the beam clears the HAM6 iris closer to HAM5, and falls on the second iris closer to VOPO within a mm from the center. Sheila calculated the deflection difference between IR and red, and it's so small it doesn't make much difference over the lever arm (a meter or two) in this case.
There were two beams coming through the septum, we took the first one (brighter, and towards +X) as the main beam.
There were three beams reflected off of the septum into HAM5. We took the first two towards +X as the main beams to dump.
We also confirmed that the scribe mark showing the thickest side of the septum is -X for the ZM path and +X for the OMC path.
Pictures will be added later.
1. Looking at the zm path septum window from HAM6. Laser pointer is in HAM5, already aligned. The beam spot on the septum is all inch or so away from the +X edge.
2. How the two AR reflections are on the beam dump but the third beam which should be AR of AR is not caught. This should be ok.
3. ZM path in HAM5.
4. ZM path septum scribe mark, -X.
5. OMC path septum scribe mark, +X.
SYSTEMS alert:
Potentially, the location of the HAM5 septum baffle needs to be adjusted accordingly because the septum window for the main OMC path is rotated 180 degrees WRT the design.
The first reflection by the septum window is not affected but the second reflection (i.e. reflection by the surface on the HAM6 side) will move from -X side to +X side of the first reflection.
TJ is contacting systems to figure that one out.