KAGRA Logbook

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IOO (Laser Bench)

kohei.yamamoto - 20:45 Wednesday 14 November 2018 (6984)

Measurement of modulation index with frequency swept

Fujii, Kohei Yamamoto

Related Link :6830, 6933, 6971

Today, again we measured the modulation index with frequency swept as we did in 6830.
What changed from the measurement is the configuration of PM monitor(see 6933), i.e. we have HWP and PBS for the power tuning.
It also means that the polarization axes of AOM 1st diffraction beam and main beam are matched at the order of the polarization extinction ratio of the PBS.

(Other Conditions)
- We didn't have HWPs before EOMs.
- dB : SG(10dB)+Distribution amp + RF amp + attenuator (for the RF amp & attenuator combination, see 6971).

(Result)
See plots.
Unfortunately, we still have the weird oscillation & asymmetry b/w upper and lower sideband, however we will move on to the next measurements.

Images attached to this report

Comments to this report:

kohei.yamamoto - 12:19 Tuesday 20 November 2018 (7047)

We found what caused this problem, i.e. just RBW setting...
The value I used is too small, and here I updates the data and attaches the fine plots.
The set-up for the experiment is exactly same as the original one.
WIth this modification, we will do the measurements regarding modulation index which seems related to this mistake.

Anyway, we still have the asymmetry b/w upper and lower sideband which is not negligible.
We need to consider this in the data analysis of subsequent measurements.

Images attached to this comment