| The butterfly and drumhead mechanical modes for the aLIGO BS were calculated in COMSOL. The resonant frequencies for the two acoustic modes are 2.45 kHz and 3.61 kHz, matching the results in reference for instance.
For a quick projection for the resonant frequencies going from aLIGO to CE, the height and width of the BS are increased assuming the mass is increased from 14 kg to 70 kg, while keeping the aspect ratio fixed. The resonant frequencies for the two mechanical modes as a result becomes smaller, to 1.43 kHz and 2.11 kHz respectively, risking getting in the detection band.
Next step is to implement a mechanical ring with high stiffness outside the BS barrel to combat the decrement of the resonant frequencies of the relevant mechanical modes. |