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AdV-INJ (Input Mode Cleaner cavity)
gosselin, masserot - 14:41 Friday 16 September 2022 (57073) Print this report
Comment to Fmoderr investigation (56520)

The digital double demodulation done for FModerr is using the signal DAQ_FMOD_Out0 which comes from the photodiode INJ_IMC_TRA.
By looking at the signal, it appears that we can already see some lines at 6 8 and 56 MHz while this a power signal directly coming from the photodiode. Those lines could be associated to amplitude modulation (RAM).
However by taking a look at a GPS time when there was no beam going towards the injection (Chrroc installation) the lines are still present (figure 1). So it seems that the signal gets polluated by the RF frequencies between the photodiode and the demodulation mezzanine.
Figure 2 3 4 are zooms on the 6 8 and 56 MHz lines. One can see a difference of amplitude with and without optical signal for the 6 MHz and the 8 MHz. This can be related to RAM.

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