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R&D (FilterCavity)
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MichaelPage - 16:23, Thursday 09 May 2024 (3556)Get code to link to this report
OPO replacement ATC beam setup

Logan, Michael

We once again found that the beam profile is showing some strange behavior with the asymmetry of the beam divergence. By using the profiler camera we see that it is probably due to misalignment of the Faraday isolator.

Comments related to this report
MichaelPage - 18:45, Thursday 09 May 2024 (3557)

We took a Thorlabs IO-5-1064-HP from a box of miscalleneous optics for KAGRA filter cavity testing (next to Mitsuhashi Roberts linkage experiment, purchased end of FY23).

We put it on a micro tilt adjustment stage and made sure it could be adjusted to the beam height from the Mephisto (72-73 mm). Actually the Faraday isolator that was already there was just put on a pedestal post instead of an adjustment stage, so it is likely that the vertical alignment through the FI was not good, generating a visible higher order mode and causing the improper beam profile.

LoganGarans - 22:09, Tuesday 14 May 2024 (3558)
Yesterday I prepared a new beam path to measure the beam profile directly from the laser. Today I measured the beam profile and at first it looks normal. So as we thought, the problem seems to be with the Faraday Isolator. I need to finish making the beam profile with all measurements to be sure of that but for now, it looks normal (at least with the W profile values).
LoganGarans - 14:51, Wednesday 22 May 2024 (3559)
Because the beam profile was normal, I put back the QWP and the HWP and verified if it was s-polarized yesterday. Today, I put the new Faraday Isolator and adjusted it. I measured the intensity without the FI at around 30mW and with at around 27mW. That gives a transmission about 90% and the manufacturer gives 91% of transmission. But because I had trouble adjusting it, I'll do a beam profile tomorrow to check the new FI and the setup.