Yutaro, Kiwamu,

related log: 4770

As a preparation for the hierarchical control on the BS for the longitudinal degree of freedom, we measured a set of transfer functions even though the lock was really solid.

See the attached for the measured responses of the IM and TM stages. Their transfer functions seem to cross at around 3 Hz. Based on this plot, we have made a filter to compensate for the IM stage and it is ready to test.