Study On Growth And Properties Of KDP Crystal By “2-dimensional Translational Method”

The potassium dihydrogen thiophosphate(KH2PO4, KDP) crystal, as a non-linear optical material with good non-linear optical coefficient and high damage threshold, has been widely used in some special fields, such as inertial confinement fusion(ICF), laser frequency conversion and electro optics modulated. Therefore how to improve growth technology, shorten growth period, achieve large and good-quality KDP crystals have become a research hotspot in recent years.Growth of KDP crystal on point seed is the main method to grow KDP crystal in recent years. As so far, the research is mainly focused on how to improve the quality and growth rate of crystal, including amelioration of experimental facility, improvement of the stability and purification of the solution. Moreover, a lot of researches have indicated that, the flow of solution have a great influence on the quality of KDP crystal. In order to perfect the convection of solution near the crystal, the motion of crystal was changed into "translation" instead of "rotation", and eventually crystals with good quality were achieved in the crystal rapid growth experiments. Through comparing the quality of crystals grown by "rotary movement method” and " 2-dimensional translation method”, the relations between the quality of crystal and convection of solution were analyzed in this article. The main contents of this paper are as follows:1. The solubility curves and the width of metastable of KDP solution at different temperatures were measured by experiments, which laid the foundation for solution preparation and keeping solution stability in crystal growth experiments.2. Based on the “thermodynamics” and “boundary layer” theory, it is obvious that "2-dimensional translation method” is better at keeping the stability of the boundary layer and surface topography. The size of crystal achieved by "2-dimensional translation method" was 55?55?48mm3 in this experiment. As a contrast, the size of crystal achieved by "rotary movement method" was 60?60?45mm3.3. By detecting and comparing the crystals grown in two motion methods, it is indicated that the transmittance of the crystals grown in two different crystal motion methods doesn’t make much difference. However, the crystal grown in "2-dimensional translation method” has better optical homogeneity and lower density of scattering particles.4. By etching the crystals grown in different growth conditions and analyzing the characters of dislocation, it is shown that the number of defects is proportional to the density of dislocation. Secondly, the worse stability of solution get, the more dislocation. Lastly, by comparing the figures of etching pit, it is observed that the crystal grown in "2-dimensional translation method” has less dislocation in cylindrical and pyramidal face.