For experiments employing interferometry, a double-walled compensation chamber is placed in the path of the reference beam. In order to ensure identical conditions in terms of the undisturbed optical path length, the volumetric capacities of the compensation chamber and growth chamber are kept equal. The inner cell of the compensation chamber contains the KDP solution that has a salt concentration corresponding to saturation conditions at the ambient temperature of . In the growth process, the temperature range utilized is and no deposition was seen in the experiments anywhere in the cell. The solution in the test section and the compensation chamber are at practically identical temperatures throughout the duration of the experiment. This is accomplished by splitting the outlet of the water-circulating pump into two parts, one leading to the growth chamber and the other to the compensation chamber. In the absence of a crystal, the optical path lengths in the test and the compensation chamber could be balanced during the cooling of the solution. Consequently, there was no fringe formation (in the infinite fringe setting mode) and fringe deformation (in the wedge fringe setting mode) from either thermal disturbances or those related to small differences in concentration. Fringe formation in the presence of the crystal occurred due to salt concentration differences in the solution with respect to the average value in the compensation chamber.

In the present set of experiments, the growth of the seed crystal is initiated by slow cooling of the supersaturated solution. Two values of ramp rates have been employed: . The rate at which the solution is cooled plays an important role in controlling the strength of convection currents, and hence the growth rates and crystal quality. Low rates keep the degree of supersaturation to a small value. The growth process is then diffusion-dominated and is inefficient in terms of the size of the crystal grown. On the other hand, very high values of the ramp rate give rise to vigorous convection currents resulting into deterioration of the crystal quality. At intermediate cooling rates, high crystal quality is to be expected.

Stirring the solution reduces the natural convection-induced temperature oscillations by homogenizing the bulk solution. Hence the importance of optimum rates of rotation in crystal growth processes has gained recognition. The two most widely used stirring mechanisms are the rotation of the seed and/or the rotation of the crucible. In the present work, experiments have been conducted by continuously rotating the growing crystal at 15 rpm.