Research On Growth Of High Quality KTP Crystal And Its Properties

Potassium titanyl phosphate (KTiOPO₄; KTP) is an excellent crystal for second-harmonic conversion of all-solid-state laser.Currently, the main problem of KTP crystal growth is that the polyphosphate flux has high viscosity. The high viscosity usually results in instable growth process and spontaneous crystallization usually occurs. In this dissertation, we focus on the search for new flux system that is more suitable for KTP crystal growth, the exploration of stable growth conditions, and the study of the crystal defects. We successfully reduced the defects and improved the optical quality of crystals by optimising the growth conditions. The main results are as follows:1. A new flux system K₈-BaF₂ was found. The suitable composition of raw materials for crystal growth was also obtained. Compared with the K6P4O13 flux, the new system reduces the viscosity and fastens the solute transport and thus effectively avoids the formation of inclusions during crystal growth. Besides, the new system has a wide crystallization range for KTP and crystal growth temperature is lower than that of the original polyphosphate flux. As a result, the volatility of the solution is effectively reduced.2. The growth conditions of large KTP crystals by TSSG method with the use of the K₈-BaF₂ flux were optimised. The parameters of crystal growth are as follows: the large temperature gradient is 0.8-2.1℃/cm; rotation rate 30-60rpm, cooling rate 0.5-2℃/day, growth period 20-90days, annealing rate 20℃/hour. Good-quality crystals thicker than 20mm in the a direction were obtained. The optical homogeneity of KTP crystal achievesΔn-1.5×10^-6/cm. The damage threshold of KTP was measured with a value of 7.3 GW/cm² @ 1064nm, 7.5ns.3. The raw materials were also synthesized by liquid phase method. The liquid phase method can avoid the problem that TiO2 could not completely react in solid state reactions. High purity starting materials for crystal growth were obtained with the careful control of the reaction conditions. KTP crystals grown using this kind of raw material are of good quality and they exhibit better properties than those grown using raw material synthesized by the solid-state method and even those grown by the hydrothermal method. .4. The defects in KTiOPO₄ crystals grown by both hydrothermal and flux methods were investigated using synchrotron radiation X-ray topography and chemical etching method. According to the experimental results, KTP crystals have growth sector boundaries, growth stripes and dislocations defects.