8/11/26
[Huyen, Jim, Michael, Shoshana]
CRS Commissioning (from list in G2601523):
- Looked at the IMC pitch and length measurements with and without CRS in loop (picture 1, reference w/o CRS in loop)
- Configuration: used 30mHz blend in RY, 250mHz blend in X
- See pitch improvement (as expected), don't see much improvement in length
- Next Steps: Will try again but next time pushing the X blend down from 250mHz to 100mHz to see if that reduces the length noise.
Noise Hunting:
- Switched CRS laser for NRS laser
- Didn't see improvement, the NRS laser is about half the power of the CRS one, so we didn't expect a huge improvement, but we saw none at all and worse noise
- Insulated NRS laser with a large thermal mass (copper blocks) and wrapped in bubble wrap
- Tried wiggle test, turns out it was very sensitive to motion near the laser
- The fiber makes a sharp-ish turn near the laser output due to the cover, we taped down the fiber in a way that will hopefully lessen the strain on it and take more data
Continued Noise Hunting
- Changing temperature value on temporary TEC
- Did math, to get a laser temp of 20 degree C, need to set R to 12.53kΩ
- R=R0*eβ*(1/T - 1/T0) with R=set resistance (in Ω), R0= 10kΩ, T=desired temperature in K, T0 = 25oC = -248.15 K, β = 3950 K (information from E2600086 & TEC data sheet)
- We have switched this back to 10.72, (i.e. 25 C), as that is where the laser is meant to operate
- Reducing Fiber Bend
- in order to get rid of the bend in the fiber, we are just leaving the cover open, which we are allowed to do because there is a clasp on the connection point which cannot be opened by hand (picture 1)
Results:
- Neither adjusting the TEC or straightening out the fiber improved the noise (picutre 2)
- It is unlikely that the excess noise is coming from the laser
- Both HoQIs give around the same noise spectrum, so it's unlikely it's from the CRS drifting or being un-centered.
- There is very little coherence between the SUM and the HOQI_DIST which indicates that the SUM is working as a good estimate of the incoherent noise (i.e. the instrument noise)
Next Steps:
- There is the possibility that the CRS is too rung up (i.e. not damped down enough) to get a good noise floor measurement
- The constant low frequency drift/oscillation that we see in all the readouts from the ISI motion could also be a source of the excess noise, which we can test via putting the SUM data through a high pass filter and taking the spectra of that data.
Put the HoQI signals through a high pass in the front end, but this didn't fix the noise issue. (picture 1)
We grounded the damping pins to see if that would reduce some of the noise.
Additionally, the TEC should be set to 10.72, and stay there as that is ideal for the laser
Damped down the CRS as much as it could go and took a spectra and left the damping on. When the damping is left on and soon after it is turned off, it looks like there is some slight improvement at the 1-3Hz range in the SUM measurement (picture 1).
Additionally, we want to look at the drift that CRS sees, it's probably the CRS still settling, but it's something to keep an eye on
