【作者】 朱胜军；

【导师】 王圣来；

【作者基本信息】 山东大学 ， 材料学， 2014， 博士

【摘要】 磷酸二氢钾(KH2PO4,简称KDP)晶体和磷酸二氘钾((K(H1-xDx)2PO4,简称DKDP)晶体,其生长研究已有80多年的历史,是一种长盛不衰、性能优良的多功能水溶性晶体材料。它具有优良的压电、电光、铁电以及非线性效应,早已被广泛应用于激光变频、参量振荡、电光调制、高速Q开关和压电换能器等高技术领域。近年来,惯性约束核聚变(ICF)工程蓬勃发展,吸引了世界各国的普遍关注,就我国而言,目前“神光III”点火工程已经被列入国家中长期重大工程。大尺寸的KDP(DKDP)晶体是迄今为止唯一可用于ICF工程的非线性光学材料,因而关于该晶体的研究被推上了一个新台阶。目前,对KDP类晶体的研究主要集中在如何更加快速的生长出高质量的KDP晶体,以满足ICF工程的需要。利用传统方式包括传统降温法、循环流动法等生长KDP晶体,晶体生长速度很慢(0.5-1mm/day)、生长周期长、风险大、成本高；并且生长时需要大截面籽晶,制备困难；生长后的晶体还存在大块的非晶帽区,晶体的利用率低。20世纪末,国外发展的“点籽晶“全方位生长技术,利用点状籽晶生长大尺寸KDP晶体,使晶体的生长速度提高了一个数量级,大大缩短了晶体的生长周期和生长成本；并且点状籽晶制备容易；生长的晶体恢复区很小,晶体的利用率大大提高。因而快速生长成为现在KDP晶体生长的关键技术和研究热点,也是我们国内急需突破的技术瓶颈。目前KDP晶体快速生长技术主要存在两个问题：一是快速生长溶液的稳定性低,溶液在生长过程中容易发生二次成核现象,晶体快速生长是在高过饱和度溶液中进行,生长溶液需要保持较高的稳定性,溶液中一旦发生二次成核,晶体生长将被迫中止；二是相比传统慢速生长的KDP晶体,快速生长晶体的光学质量明显下降,比如紫外区吸收增加、光学均匀性降低、内部光散射加重以及激光损伤阈值降低等。这两个问题大大限制了KDP晶体快速生长技术在实际中的应用。另外,随着晶体尺寸的放大,晶体光学参数如折射率、非线性系数、线性吸收系数的均一性变得越来越重要。非线性光学材料光学参数不均一可能导致光束波前畸变和光束去极化,从而影响器件设计的精确性和安全性,限制其光学应用。对于大尺寸的KDP/DKDP晶体,生长时间长(1-2年),晶体的生长环境如溶液温度、杂质离子含量、溶液动力学条件等都随时间发生变化,晶体不同部位样品的光学参数能否保持均匀一致尚存疑问且缺乏研究。针对上述问题,本文系统研究了过饱和度、动力学条件、添加剂等因素对晶体快速生长溶液的稳定性、生长动力学、生长形态、生长缺陷以及快速生长晶体的光学透过率、光学均匀性、光散射和激光损伤阈值等光学性能的影响,以期解决快速生长中存在的问题,为实现高质量KDP晶体的快速稳定生长提供更丰富的理论和实验依据。另外,对大尺寸KDP/DKDP晶体的光学参数均一性问题进行了一些探讨研究。本论文的主要内容如下：1.采用激光偏振干涉技术确定了过饱和度与KDP晶体(100)面生长速度的关系,利用“点籽晶”快速生长法在不同过饱和度的溶液中生长了KDP晶体并对晶体的光学性能进行了表征,从而系统地研究了过饱和度对KDP晶体快速生长溶液稳定性、生长动力学、生长形态、生长缺陷以及晶体的透过光谱、光学均匀性、光散射和激光损伤阈值的影响。实验表明：溶液过饱和度越大,KDP晶体的生长速度越快,而且相比晶体的Z向,晶体X向的生长速度增加的幅度更大；溶液过饱和度越大,溶液的稳定性越差,晶体越容易产生包藏、开裂、添晶等宏观缺陷；溶液过饱和度越大,生长的晶体在紫外区的透过率越低,光学均匀性越差,晶体内部光散射越严重,激光损伤阈值越低；传统法生长的KDP晶体的光学质量比快速生长晶体的好,快速生长的晶体锥面生长区的光学质量比柱面生长区的好。溶液中存在的杂质金属离子是导致高过饱和度溶液中KDP晶体快速生长困难和光学性能下降的重要因素。2.通过测量不同饱和温度、搅拌方式、过滤、过热、以及添加剂条件下,KDP晶体快速生长溶液的亚稳区宽度,研究了这些因素对KDP晶体快速生长溶液稳定性的影响并分析了其各自的影响机理,继而提出了一系列提高溶液稳定性的措施。结果表明：溶液的亚稳区宽度随溶液饱和温度的降低而增加；对溶液进行搅拌有助于提高溶液的亚稳区宽度；快速生长架的引入并未对溶液的亚稳区宽度产生显著影响,而籽晶的引入使溶液的亚稳区宽度明显降低；对溶液进行过滤和过热处理均能显著提高溶液的亚稳区宽度；添加剂对KDP溶液的亚稳区宽度影响复杂,溶液中的无机阴/阳离子会降低溶液的亚稳区宽度,而添加一些典型的金属有机螯合剂则能提高溶液的的亚稳区宽度。最终,在优化处理过的溶液中,实现了KDP晶体的快速稳定生长,生长速度达到20mm/day。3.选取了几种有机物作为添加剂,包括乙二胺四乙酸(EDTA).二乙烯三胺五乙酸(DTPA)、环己二胺四乙酸(CDTA)和柠檬酸(CA),利用“点籽晶”快速生长技术从添加这些有机物的溶液中生长了一系列KDP晶体并表征了晶体的光学性能,以此研究了有机添加剂对KDP晶体快速生长和光学性能的影响。实验发现：在溶液中添加适量浓度的EDTA、DTPA、CDTA或CA均会对KDP晶体的快速生长和光学性能产生有利的影响,比如生长溶液的稳定性提高、晶体(100)面的死区“缩小”、生长速度提高、晶体在紫外区的吸收大大减少、光学均匀性提高、光散射减弱、激光损伤阈值提高,其中DTPA和CDTA对KDP晶体快速生长和光学性能的改善效应更显著；然而过高浓度的添加则会产生相反的影响。我们认为适量浓度的EDTA、DTPA和CDTA对KDP晶体的正面影响主要是由于三者对溶液中杂质金属离子的螯合作用引起的,而CA的正面影响是由于CA能够降低晶面对生长基元的表面能引起的；高浓度添加剂对KDP晶体的负面影响是由于它们的水解产物吸附于KDP晶体表面而对晶体生长产生阻碍作用引起的。在本论文实际应用中,以100ppm DTPA或CDTA作为添加剂对改善晶体快速生长习性和光学性能是最佳方案。4.在本单位生长出大尺寸KDP和70%-DKDP晶体的基础上,通过精确测量两种晶体不同生长部位样品的折射率、二阶非线性光学系数和线性光学吸收系数,表征了大尺寸晶体光学参数的均一性情况,结合晶体的生长和测试条件分析了影响大尺寸晶体光学参数均一性的因素。结果如下：(a)我们测得的KDP晶体的三个光学参数与文献数据基本一致,但DKDP晶体的光学参数与文献数据偏差较大,其中DKDP晶体的折射率比文献数据偏大10-3量级,线性吸收系数比文献数据大一个数量级,数据差异的原因可能是与测试样品氘含量的不同有关。(b)氘化对晶体的三个光学参数有明显影响。DKDP晶体的折射率、二阶非线性光学系数和近红外区的线性吸收系数均比KDP的小,其中折射率的偏差约为104量级,二阶非线性系数的差值约为0.02,线性吸收系数的偏差约为10-2量级。(c)大尺寸晶体不同生长部位样品的光学参数存在偏差。离恢复区越远的样品其折射率越大,不同部位样品折射率差值的波动范围介于104-10。量级之间；离恢复区越远的样品其二阶非线性系数越大,不同部位样品二阶非线性系数的最大偏差约为5%。上述两种光学数据的偏差可能与晶体不同生长部位的结晶质量优劣存在某种关联。大尺寸晶体中间部位样品的线性吸收系数最低,靠近恢复区样品的最大,靠近锥头区样品的居于中间位置,线性吸收系数的不均一性可能与晶体不同生长部位的杂质含量存在差异有关。(d)综合晶体三种光学参数的实验结果,我们认为大尺寸KDP/DKDP晶体靠近恢复区样品的光学质量最差,而远离晶体恢复区样品的光学质量相对较好。更多还原

【Abstract】 Potassium dihydrogen phosphate (KH2PO4, or KDP) and its analogs deuterated potassium dihydrogen phosphate ((K(H1-xDx)2PO4, or DKDP), which is an unfailing soluble crystal because of its multifunction properties, has been researched for about80years. It has been widely used in laser frequency conversion, parametric oscillation, electro-optical modulation, high speed Q-switch and piezoelectric transducers and other fields, because of its excellent piezoelectric, electro-optic, ferroelectric and non-linear effects. In recent years, inertial confinement fusion (ICF) project is to flourish. Large size KDP (DKDP) crystal is so far the only non-linear optical crystal materials can be used in ICF project, so the research about this crystal is brought to a new level.Currently, the study about KDP crystal is focused on the following two aspects: one is to accelerate the growth rate of crystals; another is to improve the optical properties of crystals. Very slow growth rate, a few mm a day, of conventional techniques resulting in high cost of final crystals is particularly annoying. For this reason,"point seed" rapid growth technique, by which the growth rate can be one order of magnitude or more large than that of conventional techniques, has been developed during recent years.However, there are two major problems for such rapid growth technique limiting its use. Firstly, this process of rapid growth can be very unstable because of spontaneous nucleation from solutions at the high supersaturation needed to obtain high growth rate. Another, optical properties especially of prismatic sector of rapidly grown crystals, such as UV transmittance, resistance to damage by laser radiation, are deteriorated greatly. Therefore how to enhance the solution stability and improve the optical quality of rapidly grown KDP crystals are both extremely important.Therefore, in this paper we studied the effects of various parameters involving supersaturation, hydrodynamic conditions, impurity metal ions, organic additives and other factors on rapid crystal growth habit and optical quality of KDP crystal. Moreover, we also explored the issue about "optical heterogeneity of larger KDP crystal". The main contents of this paper are as follows:1. The dependence of growth rate of (100) face of KDP crystal on supersaturation was measured by using laser polarization interference technique. KDP crystals were grown from different supersaturation solutions by conventional cooling method and the "point seed" rapid growth method, and optical properties of grown crystals were characterized. The effects of different supersaturation on the growth habit and optical properties of KDP crystals were systematic studied. Experimental results showed that:the greater the degree of supersaturation, the faster the growth rate of the crystal, and the growth rate of X direction is growth faster than that of Z direction, which also led to the decrease of crystal aspect ratio with the increase of the saturation. With the increase of the solution saturation, the solution stability becomes worse, and crystals prone to appear inclusions, cracking, and other macro defects. Moreover, the ultraviolet transmittance of the grown crystal decrease, the optical uniformity become worse, light scattering becomes serious and the laser damage threshold decrease. Additionally, optical quality of pyramidal sector of crystals is superior than that of prismatic sector. Impurity of metal ions is an important factor to cause growth difficulties and performance degradation of crystals grown in high supersaturation solutions.2. The metastable zone widths of growth solutions in different treatment conditions were measured. The effects of stirring, seed crystal, filtering, overheating, and different additives on the solution stability were investigated and the impact mechanisms were analyzed respectively. KDP crystal was grown successfully by "point seed" rapid growth method at growth rate of about10mm/day. Experimental results showed that:The metastable zone width of growth solutions increase with the decrease of solution saturation temperature. The metastable zone width decreases without stirring, and30rpm/min stirring make the solution maintain uniform. The introduction of the rapid growth shelf has little effects on metastable zone width of growth solutions. In the presence of seed crystal, the metastable zone width of growth solutions decreases. The metastable zone width of growth solutions increases with filtration and overheating of solutions. Effect of additives on the metastable zone width is complex, the metastable zone width of growth solutions increases in the presence of100ppm EDTA or DCTA, while it decrease in the presence of100ppm Fe3+orSO42-.3. Some organic compounds, including ethylene diamine tetraacetic acid (EDTA), diethylene triamine pentaacetic acid (DTPA), cyclohexane diamine tetraacetic acid (CDTA) and citric acid (CA) were selected as new additives and were added into the growth solution. A series of KDP crystals were obtained by the "point seed" rapid growth technique from these solutions. The effects of these organic additives on growth habit and optical properties of KDP crystals were described and compared with each other. The impact reason was also analyzed combined with the structure of KDP crystals and the chemical characteristics of these compounds. The results showed that, the addition of an appropriate amount of EDTA, DTPA, CDTA or CA has positive effects on growth habit and optical quality of KDP crystals. It can enhance the solution stability, reduce the "dead zone" and promote the growth rate of (100) faces of the crystal. Furthermore, it can increase the UV transmittance and laser damage threshold, improve the optical homogeneity and mitigated the light scattering of these as grown KDP crystals. However, excess addition had adverse effects. The appropriate addition concentration of EDTA, DTPA and CDTA is all about100ppm. The beneficial influence of EDTA, DTPA and CDTA is due to the chelating action of these organic additives with metal ion impurities in growth solutions. The appropriate addition concentration of CA is about1000ppm. The beneficial influence of CA is considered to be connected with the synergistic bactericidal effect and reducing effect of surface energy.4. Several key optical parameters of large scale KDP and70%DKDP crystal self-grown by our laboratory including the refractive index, the nonlinear coefficient and the linear absorption coefficient were measured. These dates were compared with those of foreign reports. These dates of different sector of large scale crystals were also compared and the reasons for the differences between these dates were analyzed combined with the crystal growth conditions and test conditions. The measured results showed that the optical parameters of KDP crystal has litter difference with those of foreign reports, but the dates of DKDP crystal has large difference with those of foreign reports. The different deuterium contents of DKDP samples is lead to the larger differences dates. Furthermore, there is inhomogeneity in different parts of the large scale crystal. For example, the refractive indices of sample selected from part close to the recovery area of crystal are less than that of selected from part away from the recovery area. These deviations are in the order of10-5-10-4. The inhomogeneity of refractive indices and the nonlinear coefficient is related to the different crystalline quality of different parts in large scale crystal, while the inhomogeneity of linear absorption coefficient is related to the different impurity metal ions contents of different parts in large scale crystal.更多还原