I modeled how the Gouy phase of the SRC and mode-matching of the H1-IFO to OMC might change if we change the position of SR2 (to increase or decrease the SR2-SR3 length and SR2-SRM length). The results are summarized in the attached two PDFs (the same nominal parameters are used in both but in one of them I've turned off the uncertainties in the SRC and ARM elements).

The bottom line is, to increase the SRC Gouy Phase from 18 degrees to 23 degrees, we need to either:

• Displace SR2 by +7mm (such that the SR2-SR3 and SR2-SRM distances both increase by 7mm), or
• Add 5W to the SR3 heater, decreasing the SR3 ROC by = -15mm.

Note: these PDFs are auto-generated.