Quote: 
Quote: 
 modulation depth = 0.390 +/ 0.062

There are two modulation frequencies that make it to the arm cavities, at ~11MHz and ~55MHz. Each of these will have their own modulation depth indepedent of each other. Bundling them together into one number doesn't tell us what's really going on.

I'm sorry. I misunderstood two things when writing elog 11741: the number of modulation frequencies, and how to distinguish modulation peaks and HOM peaks.
Now, I report about interpretation of the peaks marked in grey in Attachment #1 in elog 11745.
Summary:
The peaks marked in grey are interpreted as 3rd and 4th HOM resonance, if we assume that the radius of curvature of ETMY is slightly different from measured value. (measured: 57.6 m > assumed: 59.3 m)
What I have done:
I plotted the differences in frequency between HOM peaks and 00 mode peaks (see Attachment #1) vs. expected orders of modes. The plot is shown in Attachement #2.
By fitting these data points, I calculated most likely value of gradient of this plot. This value corresponds: g_ITMYg_ETMY=0.3781. However, measured data of the radii of curvature suggests that g_ITMYg_ETMY=0.358. Assuming that this disagreement comes from the difference between measured and real values of ROC of ETMY (ITM is almost flat so that change of ROC of ITM doesn't have significant effect on g_ITMg_ETM), ROC of ETMY should be 59.3 m, different from measured value 57.6 m.
What I'd like to know:
 Is such disagreement of ROC usual? Could it happen?
 Are there any other possible explanations for this disagreement (or interpretations of the peaks marked in grey)? 