KAGRA Logbook

Reports 1-1 of 1

VIS (BS)

takafumi.ushiba - 13:53 Thursday 04 June 2020 (14473)

Circuit noise of BS Tilt OpLev

[Yokozawa, Fabian, Oshino, Ushiba]

We did same measurement as klog14464 for BS.
Setup for whitening filter ON is 45dB + 1-stage whiteing.
Analysis result will be posted later.

Since it is difficut to access the light source or QPDs, we coverred the viewport of reciever side (Cover with plastic cap and rap Al foils over it in order not damage viewport itself).
Also, we moved accelerometers from ITMX to BS to measure the common mode reduction ratio of ground motion.
Assigned channels for accelerometers were not changed: ch1 and ch2 are for transmitter and reciver side, respectively.

Note: BS nominal whitening setup is 3dB + 1-stage whitening

Comments to this report:

takafumi.ushiba - 14:45 Tuesday 09 June 2020 (14492)

I calculated the BS circuit noise by using measured ADC and QPD dark noise.
I also compaired the result with mcross signal (see klog14464 for detail).

As you can see, ADC noise level is higher than QPD dark noise level.
So, whitening can reduce the ADC noise.

However, there are some discrepancy between mcross and ADC noise level, even though they are consistent each other in the case of PRM and ITMX.
There are several possibility like coupling from light source, ground motion, and so on, but I'm not sure the reason at this moment.

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