The RoC test setup has been built on the optical table at ATF.
The cavity formed by actual OMC mirrors have been locked.
The modulation frequency of the BB EOM was swept by the network analyzer.
A peak at ~30MHz was found in the transfer function when the input beam was misaligned and clipping was introduced at the transmission PD.
Without either the misalignment or the clipping, the peak disappears. Also the peak requires these imperfections to be directed in the same way
(like pitch and picth, or yaw and yaw). This strongly suggests that the peak is associated with the transverse mode.
The peak location was f_HOM = 29.79MHz. If we consider the length of the cavity is L=1.20m, the RoC is estimated as
RoC = L / (1 - Cos[f_HOM/(c/2/L) * PI]^2)
This formula gives us the RoC of 2.587 m.
I should have been able to find another peak at f_FSR-f_TMS. In deed, there was the structure found at 95MHz as expected.
However, the peak was really weak and the location was difficult to determine as it was coupled with the signal from residual RFAM.
The particle level in the clean booth was occasionally measured. Every measurement showed "zero".
To be improved: