Sending a correction to the BS mirror affects both the MICH and PRCL degrees of freedom. To avoid the spurious coupling of MICH to PRCL, in Virgo the MICH correction is sent to both BS and PR: In this way the change of PRC length induced by the BS correction is compensated on the PR. The exact coefficient has been obtained from measurements and computations.

In Finesse simulation the actuators are ideal, and therefore the correct coupling coefficients are the geometrical one. A simple simulation has been set up to cross check the correct behavior of powers: the long arms are kept on resonance and the MICH and PRCL degrees of freedom changed indipendently. The results are shown in the following plots.


























































































































Finesse input file can be downloaded here.