New measuring method of fiber alignment in precision torsion pendulum experiments*

Testing the extreme weak gravitational forces between torsion pendulum and surrounding objects will indicate new physics which attracts many interests. In these measurements, the fiber alignment plays a crucial role in fulfilling high precision placement measurement, especially in measuring the deviation between the fiber and source mass or other objects. The traditional way of the fiber alignment requires to measure the component of the pendulum body and then transfer to the torsion fiber by some complicated calculations. A new method is reported here by using a CCD camera to get the projection image of the torsion fiber, which is a direct and no-contact measurement. Furthermore, the relative position change of the torsion fiber can also be monitored during the experiment. In our experiment, the alignment between the fiber and the center of the turntable has been operated as an example. Our result reaches the accuracy of several micrometers which is higher than the previous method.