Real-time measurement of refractive index of solution during Crystal Growth by Michaelson interferometry

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.