L. Bellon, L. Buisson, S. Ciliberto, F. Vittoz, Review of Scientific Instruments 73 3286-3290 (2002)
doi: 10.1063/1.1499210
In order to test the fluctuation-dissipation relation on rheological properties of soft materials, we built an experiment to measure thermally excited strain in a sample and compare it to the classical response to an external stress. The rheometer is based on a cylindrical Couette geometry. We use differential interferometry to achieve better than 1E-10 rad/root(Hz) sensitivity in angular position above 0.5 Hz. The forcing method, based on electrostatic interaction in a capacitor, generates torques comparable to that of thermal noise. Experiments on a calibrated silicon oil show good agreement between response and fluctuation measurements.