Investigation of KLN single crystals grown by micro-pulling-down method for blue SHG applications

研究微下拉法生长的 KLN 单晶用于蓝色倍频光的应用

基本信息

批准号：
07555096
负责人：
FUKUDA Tsuguo
金额：
$ 6.08万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

In order to develop for high quality potassium lithium niobate (KLN) single crystals fibers grown by micro-pulling-down (mu-PD) method, the quality of grown crystals and second-harmonic-generation (SHG) were investigated.Although there are several reports concerning growth of KLN by means of Cz or TSSG methods, bulk crystals with sufficient size and good compositional homogeneity for a practical use have not been obtained yet. High quality KLN single crystals were grown via a mu-PD method. Crystal diameter was well controlled, and the maximum pulling-down rate without cracks was attained to be 120 mm/h. The KLN single crystals were obtained as colorless rectangular-fibers with well developed [100] and [001] facet planes. The transmitted light to an a-plane extinguished uniformly under the crossed polarizers indicting high optical uniformity of the crystal.Distribution of phase-matching wavelength along the pulling-down axis was measured. A KLN crystal had a good compositional homogeneity along the pulling-down axis. On the other hand, relatively large variation of phase-matching wavelength is found along the radial direction. The phase-matching wavelength shows its minimum around the center of the section of the fiber and increase toward the periphery. Polarized transmittance analysis reveals that the SHG wavelength variation is due to the change of refractive index for an extraordinary ray. X-ray topographic images showed that the internal strain was diagonally remained, //[101]. This phenomena was more obviously obsered in a faster-grown crystal. Compositional inhomogeneity and/or internal strain is considered to be the possible cause of refractive-index change. They should be avoided by optimizing growth conditions such as growth velocity, temperature gradient and meniscus shape.

为了开发采用微下拉（mu-PD）法生长的高质量铌酸钾锂（KLN）单晶光纤，对生长晶体的质量和二次谐波产生（SHG）进行了研究。关于通过 Cz 或 TSSG 方法生长 KLN 的一些报道，尚未获得具有足够尺寸和良好成分均匀性以供实际使用的块状晶体。通过 mu-PD 方法生长出高质量的 KLN 单晶。晶体直径控制良好，无裂纹最大下拉速率达到120mm/h。 KLN 单晶是无色矩形纤维，具有发达的 [100] 和 [001] 面。到a面的透射光在交叉偏振器下均匀消失，表明晶体具有高光学均匀性。测量了相位匹配波长沿下拉轴的分布。 KLN 晶体沿下拉轴具有良好的成分均匀性。另一方面，沿径向发现相位匹配波长的变化相对较大。相位匹配波长在光纤截面中心附近显示出最小值，并向外围增加。偏振透射率分析表明，SHG 波长变化是由于异常射线的折射率变化造成的。 X射线形貌图像显示内应变呈对角保留，//[101]。在生长较快的晶体中可以更明显地观察到这种现象。成分不均匀性和/或内部应变被认为是折射率变化的可能原因。应通过优化生长条件（例如生长速度、温度梯度和弯月面形状）来避免它们。