Optical techniques applied to crystal growth

A direct comparison of interferometry, schlieren and shadowgraph in the context of growth of optical crystals from an aqueous solution has been conducted. The three techniques reveal similar trends in terms of the spatial distribution of concentration gradients in the vicinity of the growing crystal. The initial dissolution and unsteadiness, a stable and symmetric growth regime and the final stratification of the solution are brought out. The free convection crystal growth experiment is thus limited in the long run by the localization of high concentration gradients around the growing crystal. The stratification here is stable and suppresses fluid motion. This limits the size of the crystal that can be grown. Based on the ease of instrumentation, image clarity and simplicity of data analysis, the laser schlieren technique emerges as better suited for process control, as compared to interferometry and shadowgraph.