Here are spectra of the ETMX and ITMX oplevs. All blends are on Tbetter, sensor correction was on for ETMX and off for ITMX.
We are bothered right now by large amplitude motion (around 1urad pp) in yaw at very low frequencies.
We've seen this on ITMY before and changing out the laser seemed to fix the problem. I've attached some graphs indicating more clearly what might be occurring. The time series indicates that the power is dropping on all quadrants in with 20 second intervals; although this is very difficult to see by looking at the normalized pit and yaw signals,you can see it very clearly when looking at the individual segments. Similarly, in the spectra, there is only a small indication at 1.0-2.0 Hz that something weird may be going on but when we look at an individual segment, you can see weird spikes starting at 0.056 Hz and then the harmonics following through to higher frequencies. For comparison, I included the ETMX Segment1 spectra and you can see that we shouldn't see those spikes. I'll be investigating this today but my first guess would be either the laser or laser power that's causing a dip in power every 20 seconds, which is pretty odd because we got this laser new "off the shelf" from microlasers.
Some improvement but still oscillatiing a bit.
I've attached new spectra comparing the WIT sensors and the optical lever to show that we can see real motion of the optic for the coil balancing procedure that the SUS team is trying to perform. Also attached is the comparison between ETMX and ETMY, although the ISIs are in a different state, we can see that they are comparable. The last image attached is a trend showing that we still see this power oscillation with a peak to peak of about 240 counts with a period of ~3 seconds. This is much better than the p-to-p of 2500 counts every 19-20 seconds in the previous laser configuration.
Trying to hunt down the exact noise source proved to take longer than I thought it would. I ended up switching between three variables and chooising the best configuration: The laser, the power supply, and the outlet. We have not switched this laser to run with the power board yet but once we implment this change, it'd be interesting to see if this oscillation goes away or gets worse. Richard thinks that the noise comes from the thermo-electric coolers in the laser itself, in which case switching to the power board probably will probably not change this artifact.
