peter.king@LIGO.ORG - posted 15:04, Tuesday 02 August 2016 - last comment - 15:48, Tuesday 02 August 2016(28813)
ISS changes
Measured 167.3W at the output of the high power oscillator. 162.5W at the input to the pre-modecleaner
with the ISS off.
The diffracted power versus offset slider position was measured. Combined with the power out of the
laser, this gave the percentage diffracted power. The free-running peak-to-peak power fluctuations
measured by the ISS photodiodes as reported by a trend of the PDB EPICS was 0.2Vpp with a mean value of
8.3V. So the 0.1Vp fluctuations represent ~1.2%.
Allowing for some margin, we wish to diffract 2%. 2% of 162.5W is 3.25W. With the digital support
loop on, this corresponds to an offset slider of ~2.5.
The polynomial fit calculating the percentage diffraction was: 220.159x**2 - 97.169x + 11.293.
This was changed to match the measurements done earlier to day to: 97.6751x**2 - 63.548x + 11.458. The
MEDM screen now correctly reports the amount of light diffracted by the ISS AOM.
Jason/Peter
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Recently the datasheet for the RF amplifier inside the AOM driver was looked at. It suggested a continuous maximum RF input of 5dBm for absolutely no damage to one of the chips used. Thus a 5dB attenuator was added, bringing the total attenuation to 6dB.
Attached are plots of the ISS transfer function and the relative power noise for the corresponding gain settings. The spectra is of the out-of-loop photodiode.
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