keita.kawabe@LIGO.ORG - posted 18:27, Wednesday 18 February 2026 - last comment - 21:14, Wednesday 18 February 2026(89190)
All known ghost beams in HAM1 identified, dumped except for septum window reflection (Jason, Betsy, Keita)
We locked JAC with 1W input to find ghost beams. Details will come after we're done with the septum window reflection, but anyway here is the list:
- EOM AR reflection. Properly dumped today.
- L1 reflections (front and back surface) are reflected by JAC output coupler and go through L1. Properly dumped today.
- L2 reflections (front and back). Properly dumped today.
- L3 reflections (front and back). Properly dumped today.
- EOM wrong pol forward going beam. Changed the beam dump position today. This was brighter than I thought, we will measure the power again.
- JM2 transmission. Already dumped, confirmed it's still there.
- JM3 transmission. Already dumped, confirmed it's still there.
- Septum window reflection. This was coming back horizontally in -Y direction, was about half inch off from the main beam at the top periscope mirror, and hitting the metal part at the top edge of the bottom peri mirror. Not dumped yet.
- We'll have to improvise something so the beam is dumped at the top periscope position before entering into the periscope structure. Something like a variation of the beam dump behind the top mirror of the JAC input periscope.
None of the new beam dumps are interfering with the main beam and JAC refl/trans.
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