The Influence Of Growth Environment And Post-Treatment To The Quality Of DKDP Crystal

The crystal of potassium di-deuterium phosphate (KD₂PO₄,abbreviated as DKDP)is a crystal material with fine nonlinear optical property. DKDP crystals have the merit of biggish nonlinear optical coefficient, lower half voltage , wider through the wave band , better optical uniformity, easy implementation phase matching, easy to grow large size and high quality crystals etc, so the crystal is widely applied in high-technology areas of the laser frequency conversion, electro-optic modulation, parametric oscillator and Q switch and so on. With the development of these technical fields,the requirement to the quality and the dimensional of DKDP crystals is more and more high, meanwhile the demand is also on the increase.So the crystal growth rate and quality are the current research hotspot. The crystal growth experts of every country strive for growing big size, high quality DKDP crystals.In this paper, the temperature lowing method is used to grow DKDP crystal. The synthesis of DKDP crystal growth raw material mainly react by the high purity reagents of phosphorus pentoxide(P₂O₅) and heavy water (D₂O) into synthesis of deuterate phosphoric acid (D₃PO₄) ,then drip into potassium carbonate(K₂CO₃) in the deuterate phosphoric acid heavy water solution with double decomposition reaction which makes the preparation KD₂PO₄. Due to the existing hydrolyzation- polymerization balance in the synthesis process of DKDP crystal growth solution,easy to have the polyphosphate ion which influence the quality of DKDP crystal in the solution, the crystal growth solution should be regularly acidized and regurgitated under the heat treatment which can make the balance to the hydrolysis direction and reduce concentration of the polyphosphate ion in the solution. In addition, pD value have larger effects on the DKDP crystals growth, so alter the dosage of K2CO3 to regulate the pD value in the solution.This paper adopted orthogonal experiment to explore the deuterium content of solution, the pD value of solution, the aperture of solution filter membrane and the solution overheating time to the influence of DKDP crystals properties. The solution deuterium content including 100%, 92%, 86% three levels, the pD value of solution includes 3.5, 4.0, 4.5 three levels, the microfiltration membrane aperture of solution including 0.4μm,0.22μm,0.15μm three levels, the overheating time including 12 hours,24 hours,36 hours three levels. Using the four factors and three levels designed the orthogonal test table L₉(3⁴) arranging 9 times test to the growth of crystal.The crystal growth process mainly include the preparation of crystal growth equipment , the mensuration of saturation point, the solution processing, the seeds choice , preparation and fixed, and the determination of the cooling speed in the process of crystal growth and so on. In the growth process, the monocline phase crystal have greater influence to the DKDP crystal growth. In this paper, according to the specific circumstances in the process of crystal growth discussed the interference of the monocline phase to the crystal growth and put forward the measures to reduce its appearance. Because of the instability of growing conditions, the growth crystal can exist various defects, such as crystal faces patter, liquor parcel, wedge and add crystal, etc. This paper according to appeared various defects of the actual growth crystal analyses the specific reasons .After growth, tests the growth crystal for the various performance ,including extinction ratio, half wave voltage,deuterium content and the through curve, etc. Using the orthogonal experiment table, analysis and processes of the experimental results of crystal half wave voltage. The experimental results obtained the optimum scheme of DKDP crystal growth, namely, the deuterium content of DKDP crystal growth solution is 92% , the aperture microfiltration membrane is 0.15μm , the pD value of solution is 4.0 , the overheating time is 36h.At the same time, this paper also studied the effect of annealing treatment to improve the optical quality of DKDP crystal. The research results is that the crystal extinction ratio has relatively substantially improve ,half wave voltage is relatively decreases,and the crystal electo-optic properties get a better improve after the crystal annealing treatment. The annealing crystals compared with before, the transmittance and permeation range are slightly lower,which explains the effect of annealing to improve the crystal light permeation performance is not obvious .In short, this paper using the orthogonal test methods make relatively system research to the DKDP crystal growth conditions which affect stability of solution. And using the orthogonal experiment table processes the various test results, obtaining the growth DKDP crystal optimal scheme and other many significant conclusions. Annealing heat treatment can improve the optical quality, which is significant to the crystal applications ,but some problems still needs further research.