Substraight Thermo-Elastic: what does it all mean?
in substratethermal.py, is the thermo-elastic noise for the reflection off of the HR surface only? Or does it include the transmission through the ITM?
Because, if we need to consider the thermo-refractive noise of the ITM (which we do do), then it seems like there should be some thermo-optic quantity for that, that coherently combines the TR+TE to get TO.
In the case where the arm cavity finesse is very high, the ITM bulk effects would be small for DARM, but would be significant for SRCL, but gwinc doesn't care about SRCL yet.