In the real-time monitoring of variations of concentration and temperature of solution by means of contacless interferometry, real-time measurement of changes of refractive index of the solution is prerequisite and essential for post calculation processes. A novel real-time polarized light phase shifting interferometry is proposed in this paper, which was applied to Michaelson type interferometer. Although phase-shifting interferometry provides high spatial resolution, the conventional phase shifting technique by the mechanical movement has not been applied to real-time measurement during crystal growth, due to its physical limitations. We developed a method, using polarized light, and made the real-time measurement possible. The 17% undersaturation aqueous solution of KDP at 20°C was selected as specimen to measure its refractive index during crystal growth. It is found that the present method is a few ten times more sensitive than traditional two-beam interferometry, and more accessible to applications of real-time measurements.
Optical Computed Tomography (OCT) is available for 3-D distribution of solution’s refractive index. The 3-D distribution can be fitted up with divers 2-D slices. Thus, the discrete mathematical model of 3-D refractive index data reconstruction can be framed in a linear ill-posed problem. We proposed a practical reconstruction algorithm, Modified SART with Changing Relaxation Factor based on Simulated Annealing algorithm (CRF-MART), which is a modification of Simultaneous Algebraic Reconstruction Technique (SART). Furthermore, a computer simulation of the reconstruction algorithm was taken in the case of incomplete data. It is shown that reconstructed results have better smoothness and smaller residual, which are a good approximation to the true value.