Figure 4
From: A high-resolution polarimeter formed from inexpensive optical parts
(a,c) Time series showing the experimentally determined phase-difference between the object and reference signals for a typical “blank” measurement, before (a) and after (c) exponential filtering. The measurements were obtained with ultra-pure water using a 5-cm optical cell, with a 0.6-ms sample time, an sDFT window size of 1024 data points, and a motor speed of eight revolutions per minute. Exponential filtering was carried out using λ = 0.0128, equivalent to a 2.9-s time constant, see Eq. (11). (b,d) Time series showing the experimentally determined phase-difference between the object and reference signals for a typical “active” measurement, before (b) and after (d) exponential filtering. The data were obtained with 202 mg/ml sucrose in the optical cell, using the same settings as for the blank measurement. (e) Time series showing the optical rotation angle calculated from the data in (c,d), using Eq. (6). (f) Down-sampled time series for the optical rotation angle, obtained by averaging the data in (e) in 6-s blocks. The dotted line represents the mean optical rotation angle of 5.3798°. The standard deviation is \(0.00044\), implying a \(3\sigma \) accuracy of ±0.0013 (g) Results of ten successive measurements of the phase difference between the object and reference signals for a typical blank measurement, obtained with ultra-pure water in the 5-cm optical cell. The measurements were recorded at 1-minute intervals, using a 6-s time average of the exponentially filtered phase and identical settings to those used in (e). The measurements are distributed about a mean value of −1.4604° with a standard deviation of 0.00093°, implying a \(3\sigma \) precision of ±0.0028°. The straight lines between points are a guide to the eye.
