Supersaturation And Deuterium Level Of Kdp / Of Dkdp Crystal Optical Properties Of The Study

KDP/DKDP crystals are non-lineal optical crystal materials with good optical qualities and have been widely applied to the high technology fields such as laser frequency conversion, electrooptical modulation, optic switch and so on. Big-sized KDP/DKDP crystals are the preferred materials for ICF (Inertial Confinement Fusion) and there are no other materials with better optical performance which can be used to substitute for KDP/DKDP crystals at present time. Investigations on KDP/DKDP crystals have been lasting for more than 60 years, but with the help of new methods and advanced instruments, further investigations are still carried out nowadays. The requirements of optical qualities of KDP/DKDP crystals by ICF include their good qualities (high laser damage threshold, high optical uniformity) and big size, but also quantity, for example, the National Ignition Facility (NIF) under construction at Lawrence Livermore National laboratory will require about 600 crystal plates , the sectional area of which is 41cm x 41cm, for Pockels cell, doubler or tripler, and Shenguang Project of China also needs a lot of optical apparatus made of KDP/DKDP crystals. To meet the requirements of NIF, rapid growth of KDP/DKDP crystals is developed based on the improvement of optical qualities.With the development of NIF, USA prohibits the export of relative technology or materials and in the international markets the supply of big-sized and high-quality KDP/DKDP crystals fall short of demand. To supply enough optical apparatus made of KDP/DKDP crystals with required qualities to Shenguang Project, the growth of big-sized and high-quality KDP/DKDP crystals is an arduous task and needs to be solved as soon as possible.The stability of solution is the basis of the growth of KDP/DKDP crystals. The stability of solution decides not only the normal growth of the crystals, but also the optical quality. The analysis of the state of solution during the growth is helpful for the designing of the process of crystal growth and deducing the influence of accidental factors on the growth and quality of crystals then the study on the influence of designed growth conditions on the growth and qualities of KDP/DKDP crystals.This thesis analyzes the state of KDP solution and the main factors which influence the stability of KDP solution during the process of crystal growth. The stability of solution includes both the stable state of the solution and the stable driving force for the crystal growth. To ideal supersaturated KDP solution, the main factors influencing the stability of solution are the supersaturation and the growth temperature. In the real process of crystal growth, the stability of solution is decided by the common- effect of kinds of factors and the common-effect is demonstrated by growth conditions. The stability of solution can be improved by adding some organic or inorganic additives, but the additives will influence the optical quality of the crystals. In order to get high-quality crystals, the methods of improving the stability of solution are the using of ultra-pure raw material, the fine-filtering of solution, the ample-superheating of solution, the continuous filtration and the proper stir during the process of crystal growth.The triplers of ICF are mainly made of big-sized deuterated DKDP crystals. The deuteration of solution influences the optical performance of DKDP crystals greatly. To decide the deuteration of solution to grow DKDP crystals for ICF it is necessary to make systemic researches on analyzing the influence of different degrees of deuteration on the growth and the optical performance of DKDP crystals.Compared with KDP crystal, high- deuterated DKDP crystals ownbetter electrooptical function, lower effect of Raman Scattering, broader band of transmittance, but the higher the degree of deuteration, the bigger the structure and the bi-refraction induced by stress is and the lower the growth rate is.The transmittance of DKDP crystal grown in 50%-deuterated solution deduces rapidly at the band of ultraviolet. X-ray diffraction spectrum of KDP and DKDP crystals shows that the lattice of DKDP crystal grown in 50%-deuterated solution distorts greatest among the crystals grown in other deuterated solutions.It is believed that DKDP crystals grown in 70%~80%-deuterated solutions are ideal for triplers of ICF by synthetically analyzing all the functions of KDP crystal and a series of DKDP crystals.In recent years the technology of oriented rapid growth of big-sized KDP/DKDP crystals has been developing actively, but that technology requires ultra-pure raw material and specially-designed growth tanks, at the same time that technology costs much more than the traditional growth methods, so KDP/DKDP crystals are still grown by traditional temperature deduction method or solution circulation method. To meet the great need of KDP/DKDP crystals, the growth rate of KDP/DKDP crystals can be accelerated by increasing the supersaturation of solution based on the traditional growth methods. The influence and its mechanics of supersaturation on the crystal growth and optical performance are analyzed in the thesis.The increase of solution supersaturation will accelerate the growth rate, but will cause broadening of prisms at the same time. The testing results show that the transmittance of the broadening parts is evidently lower than that of the inner parts. The cone-interference patterns show the stress in the broadening parts is bigger and the homogeneity of these parts is lower. It is considered that the supersaturation influences differently thegrowth rate of different parts and the increasing defects in the broadening parts cause the quality low.