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takafumi.ushiba - 20:14 Monday 20 November 2023 (27676) Print this report
Initial alignment is necessary even when PRFPMI alignment seems good.


PRFPMI lock acquisition is not stable today even though PRFPMI alignment seems good.
The reason is PR3 alignment, which reduces fringes of POP PNC and makes it unstable.
After initial alignment of GRX and IRX, the fringes were recovered and PNC became stable, so it seems necessary to perform initial alignment when POP PNC becomes unstable.


In this aternoon, PRFPMI lock acquisition was not stable.
I thought it was due to just large seismic motion but it was not true: the reason is that the fringe of POP PNC was too small (fig1: peak2peak value is about 100 cnts) even though X/Y transmission with PRFPMI is large (about 130).
So, I performed initial alignment of GRX and IRX.

After the initial alignment, POP PNC fringes recovered (fig2: peak2peak value is about 300 cnts) and PNC can be locked stably.
Then, PRFPMI lock acquisition becomes much stable (it is still failed sometimes maybe due to large seismic motion, though)

So, it seems better to perform initial alignment if POP PNC fringes become small and the PNC lock becomes unstable.

Images attached to this report
Comments to this report:
shinji.miyoki - 22:34 Monday 20 November 2023 (27682) Print this report

I have already bought some lenses (f~400, 500) to try to obtain a better fringe by reducing the beam size from the X-arm to match its beam size with the beam size from the fiber output side on the POP table. If this lens installation can work, will we install it?

Or is it better to enlarge the beam size of the beam from the fiber output side?

In any case, is it better to try to take the MI part alignment again just after the initial alignment?

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