Growth imperfections in oriented grown KDP crystals by X‐ray topographic analysis

Potassium dihydrogen phosphate (KDP) crystals were restrained to grow in two dimensions only, using a specially designed platform. This enables us to grow the blanks of frequency conversion elements that satisfy type‐II phase matching direction out of a type‐II phase‐matched seed crystal. Synchrotron radiation topography was used to study the growth mechanism of these profiling grown KDP crystals. It is found that both dislocation growth mechanism and layer growth mechanism were involved in the growing process. Inclusions, growth striations and dislocations were the main defects that influenced the crystalline quality of these crystals. High‐resolution X‐ray diffraction was employed to study the lattice integrality of the crystal.     

Improvement of growth habit and optical properties of rapidly grown KDP crystal by adding diethylene triamine pentacetate acid in growth solution

By altering the concentration of a new additive ‐ diethylene triamine pentacetate acid (DTPA) in the growth solution, a series of KDP crystals were obtained by the “point seed” rapid growth method. The growth rates up to about 20 mm/day. Effects of DTPA on the growth habit and optical properties of these as‐grown KDP crystals were investigated. The results reveal that, with the increase of DTPA concentration in growth solution, the contents of impurity metal ions incorporated into crystal and aspect ratio of crystal morphology were both decreased gradually, while the UV transmittance of crystal was enhanced continually. In the presence of moderate concentration of DTPA (100–200 ppm), the solution stability was increased and optical properties of crystal (including optical homogeneity, light scattering and laser damage threshold) were all improved. However excessive doping (>500 ppm) has opposite effects. The impact mechanism was also analyzed combining with the structure of KDP crystal and chemical characteristics of DTPA molecular.     

点籽晶法快速生长中等口径KDP单晶及其性能表征

本文使用德国MERCK公司生产的KDP原料和自行研制的晶体快速生长装置,采用"点籽晶"快速生长法成功生长出了150 mm级中等口径的KDP单晶,晶体生长速度达到20 mm/d.晶体生长过程中,生长溶液稳定,没有杂晶出现,生长的晶体完好且透明.X射线粉末衍射和摇摆曲线分析表明晶体有着较好的结构完整性;同时,测试了晶体的透过光谱和光损伤阈值,发现快速生长的晶体有着较好的光学性能.     

点状籽晶法生长KDP晶体中散射颗粒分布

在不同的溶液pH值条件下进行了点状籽晶法慢速和快速生长KDP晶体实验,发展了观察晶体中散射颗粒分布的激光层析技术,通过图像处理得到了KDP晶体内部(100)面完整的散射颗粒分部图,对不同生长速度、不同pH值条件下点状籽晶法生长的KDP晶体的散射颗粒分部做了对比.利用表面光学投影技术观察了晶体表面宏观形貌,并由此分析了不同生长条件下生长机制对散射颗粒分布的影响.测定了散射颗粒密度不同部位的晶体透过率.     

Study on rapid growth of KH2PO4 and its characterization

Large size crystals of KH₂PO₄ (KDP) were grown by adopting rapid growth technique from point seeds in a 1500‐liter crystallizer which is used to grow KDP crystals by conventional method. The grown KDP crystal size can reach to 310 × 310 × 320 mm³ and the average growth rate was 8mm/day. The optic properties of the rapidly grown KDP crystals were characterized comparing with the KDP crystals grown by the traditional temperature reduction method. We found it that the optical quality of the KDP crystals we grown rapidly are not significantly different from those of KDP crystals grown by traditional method. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Na+对KDP晶体生长的影响

本文利用传统的降温法和"点籽晶"快速生长法在不同Na+掺杂浓度的溶液中生长KDP晶体,定量研究了Na+对KDP晶体生长的影响.实验发现:Na+的存在降低了溶液的稳定性,致使KDP晶体柱面容易扩展.Na+的存在对KDP晶体的光学性能基本没有影响.     

超大尺寸KDP/DKDP晶体研究进展

KDP/DKDP晶体具有生长方法简单、成本较低、光学性能良好等优点,而可生长出的超大尺寸KDP/DKDP晶体是目前唯一可用于高功率激光工程的单晶材料。但是在晶体的生长过程中存在很多影响因素,同时对晶体进行后处理也会影响晶体的性能,这都直接关系到超大尺寸KDP/DKDP晶体的实际应用。鉴于此,本文综述了近些年超大尺寸KDP/DKDP晶体的重要研究进展, 特别是针对传统生长和快速生长中存在的问题和相应的解决对策以及晶体性能相关的研究,并重点对晶体的透过率、氘化率、激光诱导损伤等进行了分析和讨论。     

KDP/DKDP晶体生长的研究进展

采用传统降温法,KDP晶体的生长速度一般在1～2 mm/d,DKDP晶体的生长速度甚至更慢,并且晶体的恢复区域较大,利用率低;而采用快速生长法,晶体的生长速度可以提高到20～50 mm/d,并且晶体的恢复区域小,利用率高.本文回顾了KDP/DKDP晶体生长的研究进展.并重点评述了KDP/DKDP晶体快速生长的研究进展,报道了近年来大尺寸、高质量KDP晶体的研究动态.     

pH值对KDP晶体位错结构的影响

在一定的过饱和度下,分别用点状和片状籽晶在不同pH值溶液中生长出了KDP晶体.利用化学腐蚀法对KDP晶体的不同晶面进行了腐蚀,得到了清晰的位错蚀坑.应用光学显微镜对位错蚀坑的分布特点和密度做了观察分析,发现很多位错蚀坑成线状排布.pH值对KDP晶体位错密度有较大影响,低pH值条件下生长出的晶体位错密度较大.测试了KDP晶体样本的透过率,结果表明位错密度对KDP晶体的透过率没有明显的影响.     

KDP single crystal growth via three‐dimensional motion growth method

A novel system for rapid crystal growth, namely three‐dimensional motion growth method (“3D MGM”) was proposed. Using this system, a potassium dihydrogen phosphate (KDP) seed was grown to a single crystal with a final size of 50×55×85 mm³. The KDP crystal was characterized by Raman spectroscopy, UV‐vis‐NIR spectroscopy, extinction ratio, laser damage threshold, and etching studies. Raman spectrum shows KDP crystal grown by “3D MGM” maintains good crystallinity as that grown by rotating‐crystal method (“RCM”). The “3D MGM” grown KDP crystal has much better transmittance, higher extinction ratio, higher damage threshold and less dislocation density, compared to “RCM” grown crystal.     

Influence of SiO32‐ impurity on growth habit of potassium dihydrogen phosphate crystal

By altering the concentration of silicate (SiO₃^2‐) impurity in the solution, a series of potassium dihydrogen phosphate (KDP) crystals was obtained by the conventional temperature cooling and the rapid growth methods, respectively. It was observed that the presence of SiO₃^2‐ made KDP crystals tapering in conventional cooling method, while more SiO₃^2‐ induced inclusions at prismatic sectors in the rapid growth method. Laser‐polarization‐interference results showed that SiO₃^2‐ extended the dead zone and reduced the growth rate of (100) face of KDP crystals. The negative influence of SiO₃^2‐on the growth was considered absolutely similar to the effect of cations. It was also suggested that the stability of solution doped with SiO₃^2‐ was improved without seed crystals, while it was destructed with seed crystals. The inhibition mechanism was analyzed in terms of SiO₃^2‐ absorption on (100) face. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rapid Z-plate seed regeneration of large size KDP crystal from solution

Regeneration process of a 330×330×20 mm³ Z-plate seed is carried out in a 1.5 metric tonnage volume crystallizer that placed in a water bath of temperature fluctuation less than ±0.02 °C within 10 days. The surface of the whole crystal was restored by the formation of a box-like structure filled with growth solution, and then the transparent layer of perfect tetragonal KDP crystal without inclusions, crack and milky regions just like those produced by traditional slow cooling technique can be grown from solution. After the regeneration, the height of KDP crystal is merely 0.5 times the side of plate seed. We found it that the optical transmission and laser damage threshold of the KDP crystals we grown are not significantly different from those of KDP crystals grown by traditional method.     

Improvement of Initial Conditions of the Crystal Growth by Dissolution and Refaceting

The influence of significant dissolution and refaceting of KDP and Rochelle salt crystals on their further growth is studied. It is shown that the crystal growth rate ‐ initial crystal size dependence is better defined for growth after refaceting. Initial conditions for growth of individual crystals after refaceting are better defined, than in the case of classical seed nucleation. By dissolution and refaceting, it is easy to provide the same initial conditions for crystal growth in each of several experiments, preformed under the same macroscopic external conditions.     

Synergy of organic dyes for KDP crystal growth

Single potassium dihydrogen phosphate (KDP) crystals were grown in a supersaturated solution containing an organic dye (sunset yellow FCF, brilliant blue FCF, and sky blue). The growth rate, morphology, and impurity dye distribution of faces, (100) and (101) in a KDP crystal were measured as dye concentration and the supersatutation of KDP were changed. Complete expressions for the effect of dye on all aspects of the growth of KDP crystals were discussed. The growth rates of (100) and (101) faces were well correlated by the empirical equation, and resulted in good estimation of the morphology. The distribution of dye in a KDP crystal was represented by the distribution model containing the minimum growth rate for coloring. The growth rate equation and distribution equation were expressed by functions of the supersaturation and dye concentration, and they could effectively provide the operational conditions with coloring the KDP crystal. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

KDP晶体中散射颗粒形成机理的研究

本文在不同掺杂条件下,采用传统降温法生长了KDP晶体,利用超显微和透射电镜对KDP晶体中的散射颗粒进行了观察,在此基础上对其进行了分类.实验结果表明,不同种类散射颗粒的形成源于溶液中杂质与晶体化学键作用力的不同,造成这一结果的根本原因与KDP晶体的结构特性密切相关.     

KDP晶体生长过程中溶液稳定性的研究

在KDP晶体生长过程中,溶液的稳定性对KDP晶体的光学质量影响较大.溶液的稳定性是多种因素共同作用的结果.本文主要研究了过饱和KDP溶液中晶胚的分布情况、降温过程中晶体生长驱动力与降温速度之间的关系,并分析了KDP晶体实际生长过程中影响溶液稳定性的主要因素.我们认为,通过改善KDP晶体生长过程中溶液的稳定性,并与其它措施和技术相结合,是提高KDP晶体光学质量的有效途径.     

Influence of La3+ ions on growth and NLO properties of KDP single crystals

Single crystals of pure and Lanthanum added KDP crystals were grown from aqueous solution. The influence of La³⁺ ions in KDP crystals is studied. Isolated centers are formed by La³⁺ ions in KDP structure along (100) plane. La³⁺ ions incorporated into superficial crystal growth layer and slightly affect the growth process as they generate weak lattice stresses. The creation of these weak lattice stress is confirmed by Vickers's micro hardness test. The HRXRD analysis showed reduced structural defects in the La added KDP in the (100) plane than pure KDP. The incorporation of La in the crystal was confirmed by EDAX analysis. The Kurtz's powder SHG efficiency was found to be 1.5 times that of pure KDP. The UV‐Vis transmission spectra of La added KDP showed excellent transmittance from 1100 nm to 340 nm and did not show any change in lower cutoff wavelength with respect to pure KDP. Laser damage threshold value has been determined using Q‐switched Nd:YAG laser operating at 1064 nm and with 65 ns pulses in single shot mode. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and high frequency dielectric study of pure and thiourea doped KDP crystals

Non linear optical (NLO) materials have acquired new significance with the advent of a large number of devices utilizing solid‐state laser sources. Several NLO materials have been used for this kind of technological applications. The Potassium di‐hydrogen phosphate (KDP) one of NLO material having superior non linear optical properties has been exploited for variety of applications. In the present investigation we have grown KDP crystals from aqous solution with thiourea, an organic non linear optical material. We could enhance the SHG efficiency of thiourea doped KDP crystal. It was 1.99 times more that of pure KDP. We observed more enhancements in nonlinearity for low concentration of thiourea.The crystal structure and cell parameters of grown crystal were determined from Powder XRD.The incorporation of thiourea in the grown crystals was qualitatively analyzed from FT‐IR study. The absorption spectra of pure and thiourea doped KDP crystal reveal that thiourea doped KDP crystals would be a better nonlinear optical (NLO) material for second harmonic generation (SHG) than pure KDP. The thermal decomposition and weight loss of pure and thiourea doped KDP crystal was observed by thermogravimetric (TGA) analysis and Differential Scanning Calorimetry (DSC). The high frequency dielectric study of pure KDP crystal, thiourea doped KDP crystals and organic additive thiourea was carried out using X‐band at frequency 8GHZ and 12GHZ by transmission line wave guide method. We observed low dielectric constant of thiourea doped KDP crystal when it is doped with 2mole% of thiourea. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

KDP晶体激光损伤机理研究

大口径KDP晶体是唯一可用作激光约束核聚变(ICF)中Pockels盒和倍频器件的晶体材料,但是低的抗激光损伤阈值使其应用受到了限制.本文从电子-空穴对的产生及稳定机制、光伤实体的本质等方面总结了多年来人们对KDP晶体激光损伤机理的研究进展,尤其从多光子电离、碰撞电离、激光加热三个方面定性阐述了电子-空穴对的产生机制, 而电子-空位对的稳定机制是探讨光损伤的关键步骤.另外从晶体生长过程及后处理两个方面初步讨论了提高光伤阈值和光学均匀性的途径.     

生长温度对KDP晶体光学性质影响的研究

用降温法在不同的温度下快速生长KDP晶体,并测量其透过光谱、光学均匀性、金属杂质含量和光散射性能.结果表明随着生长温度的提高,KDP晶体的紫外光吸收和光散射点密度明显降低,但均匀性和杂质金属离子含量并无明显变化.