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AdV-PSL (Commissioning of SS)
mwas - 15:04 Tuesday 01 June 2021 (52004) Print this report
Spectra of PSTAB photodiode

To have a status of the 50Hz in the PSTAB photodiodes I have made some plots using the time when the master laser was swapped. This provided a time without a beam at 12:00 UTC on May 11, and time with the PSTAB loop closed on May 12 at 00:00 UTC.

Figure 1 is an amplitude spectral density (V/rtHz) and Figure an amplitude spectrum (V) with a 10s duration FFT. Figure 3 and 4 are the same data using 1s duration FFT. For the ASD the broadband noise level doesn't depend on the resolution, while for the AS the 50Hz line height does not depend on the resolution, as should be the case.

Note that the dark noise spectra are higher than when the loop is closed. As the photodiode is in loop, and the high gain of the loop suppress the noise below the PD sensing noise. I couldn't find the out-of-loop photodiode PSTAB_PD1_AC channel in the data, it was present during O3.


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mwas - 11:29 Wednesday 16 June 2021 (52165) Print this report

I made a factor 2 mistake in the sampling frequency of the channels, this made the 50Hz harmonics appear as 25 Hz harmonics in the figures.

Figure 1 and 2 show respectively the amplitude spectrum density (in V/rtHz) and the amplitude spectrum (in V) for a FFT length of 10s (so a 0.1Hz frequency resolution) once this factor 2 error is corrected.

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