Very nice work!

From the fitting of the measured Gouy phase for each higher order modes, the round-trip Gouy phase of IMC is 64.6 +/- 0.2 deg (see attached figure).
This means that the cavity g-factor (rooted) is -0.428 +/- 0.004.
Using the measured round-trip length 53.30253(5) m (klog #616) and assuming MCi and MCo to be flat, the measured MCe RoC is 37.33 +/- 0.09 m.
This agree with the designed value 37.3 m, Hirose-san's measurement 37.3(1) m and Nakano-kun's previous measurement (see klog #637).