Nutsinee, Stefan
As suggested by alog 31304, we set up a 26:74 mixed input matrix element for PRCL in the next lock:
POP_A_RF9_I to PRCL = 0.0091
REFL_A_RF45_I to PRCL = -849 (yes, a minus sign)
This gave us the expected additionbal slight improvement in PRCL sensing, see the attached plot.
Indeed, this auxiliary noise reduction seems to have given us a range increase of about 5% to 75Mpc.
More importantly though, suddenly the range seemed to be rock-sold, without any up- and down drifts - see the last hour in the attached range plot.
Still to do: PRCL FF & possible modulation depth increase.
After this first step the return will not be as big in terms of range, but the improvement in range stability by itself makes it worth the effort.
We put all this into Guardian (NOISE_TUNINGS), but we didn't test the Guardian yet (the interferometer was too steady).
This is a follow up comparing the ADC noise, the dark noise and measured spectra. ADC noise is about 0.005 cts/√Hz at the input of the filter module. The following table gives the ratio of dark to ADC noise and the ratio of measured noise to dark noise above ~20 Hz.
|
Photodiode Channel |
Whitening Stages |
Ratio dark/ADC |
Ratio |
|---|---|---|---|
| REFL_A_RF9 | 2 | ~10 | ~4/3 |
| REFL_A_RF45 | 1 | ~4 | >3 |
| POP_A_RF9 | 1 | ~2 | >3 |
| POP_A_RF45 | 1 | ~30 | >2 |
The strange gain ratio for the POP9/REFL45 combination is partially explained by a cts2V filter bank that is enabled in REFL45.
