Fig. shows typical normalised output signals for the reference and object channels using ultra-pure water in the 5-cm optical cell. The signals were obtained with a sample time Δt of 1 ms and 12-bit digitisation. Non-linear least-squares fitting indicates that both signals are well described by pure mono-sinusoids of frequency 6.22 ± 0.01 Hz (mean ± one standard deviation), with a small phase-difference 𝜙 -of 2.08 ± 0.28° between the two signals. The low 𝜙 -value reflects the fact that the polarisation axes of P1 and P2 are approximately aligned and water is optically inactive. Fig. shows equivalent data for an active measurement, using an enantiomerically pure 200 mg/ml solution of D-sucrose molecules in water. The signals are again well described by pure mono-sinusoids of frequency 6.22 ± 0.01 Hz. The effect of the optically active sucrose molecules, however, is to induce a positive optical rotation in the polarisation axis of the object beam, which manifests itself as a large positive phase-difference 𝜙 ) of 12.75 ± 0.27° between the object and reference signals. Hence, applying Eq. ( ), we obtain an optical rotation angle of 𝜃 $%& = 0.5 × (12.75-2.08) = 5.34 ± 0.28°.