Instrumentation for Torsion Balance Experiment

The detection and precision measurement of very small forces, especially of gravitational nature, has always been a challenging task. Gravitational forces have to be detected by mechanical means. The torsion balance is a far more sensitive detector of mechanical forces. In our experiment, we have a home-made sensitive torsion balance suspended inside an ultra-high vacuum chamber and the motion of balance is monitored by an optical lever.

During the initial integration phase, very large amplitudes of oscillation are excited in torsion balance and the fact that natural damping for a good torsion balance system is very low. So there was a need to actively reduce the amplitude of several radians in a sensitive torsion balance oscillator to a level far below micro radian. This serves to prepare the system for the measurement of extremely small forces.

In this talk, I will present the instrumentation developed for damping the amplitude of torsion balance oscillator and our scheme related to regular in-situ “Auto-Calibration” of optical lever instrument. We have developed our own sub-micron resolution drivers/controllers for Encoder Micrometers, which are used for moving optical components in optical lever setup. These controllers are minimalistic, stand-alone units and therefore ideal for rugged field use.