An experimental verification of a double torsion pendulum as a technique for the measurement of cross coupling in gravitational reference sensors for space-based gravitational wave detectors.

The double torsion pendulum, which can provide quasi-free fall motion modes with two degrees of freedom simultaneously, can be used to evaluate the crosstalk effect of gravitational reference sensors (GRSs) in space-based gravitational wave detection on the ground. Before the ground test of the crosstalk of a GRS, the cross coupling between the two motion modes of the double torsion pendulum itself should be thoroughly investigated. In this paper, we estimate the cross coupling effect of a double torsion pendulum by calculating the dynamic equations of the pendulum in the presence of fiber thermal noise. The results of the calculation are compared with a subsequent experiment and show good agreement. Thus, it is concluded that the cross coupling of the double torsion pendulum can be accurately removed from GRS crosstalk measurement results.