石英旋光性及其偏光干涉谱的测试分析

【作者】 孔德福；

【导师】 宋连科；

【作者基本信息】 曲阜师范大学 ， 光学， 2010， 硕士

【摘要】 石英晶体是一种重要的光学材料,旋光性是石英晶体的重要性质之一。利用石英晶体的旋光性制成的器件在色散滤波、光通讯、退偏等领域有重要应用。查阅相关资料发现,对于石英晶体材料双折射性的研究很多,而对于其旋光性研究大多是应用方面的,对石英晶体旋光性的本质研究报道很少。在本论文中,比较系统研究了石英晶体晶系类别、微观结构及原子排列方式、石英旋光率、旋光色散的有关知识以及磁致旋光、菲涅耳假设等知识。借鉴有机螺旋模型理论,分析了石英晶体旋光性与微观螺旋结构的内在联系,采用微螺旋结构螺距变化,解释了石英旋光率的方向性、热效应以及与有机液体旋光率的差异性。石英微观螺旋结构特性决定了其螺旋长度ι在一定温度下是一定的,并且沿光轴方向有最大螺距,这正好体现了旋光现象最明显、旋光率最大的特点；当传播方向偏离光轴时,螺距向光传播方向投影后会变小,从而旋光率也变小,直至垂直光轴方向旋光性为零。当温度变化升高时,石英晶体发生热膨胀,内部原子距离增大从而导致螺距s变大,旋光率随之增大,这个解释与温度升高时石英旋光率测试结果吻合。本文也从微观电磁理论的角度对晶体旋光性的根本原因进行解释,进一步验证了石英体旋光性的原因。研究认为反对称旋性张量εαβ是物质旋光的根本原因,当矩阵εαβ或相应回转矢量gαβ的元素不全为0时的物质具有旋光性。石英晶体所属的六方晶系的gαβ的独立元素有3个,晶体的对称性会使gαβ中的独立元素减少。在石英旋光晶体透射比进行了理论分析的基础上,对300-1500nm波段范围内常温状态下利用双光路对比测量方法对偏光干涉谱线进行了实验测量。实验结果显示,在紫外区由于石英吸收明显,峰值透射率偏低,这与理论分析结果有一定区别,而且谱线周期很小,原因是紫外区石英旋光率随波长变化率很大；红外光区由于旋光率随波长变化率趋近于零而导致谱线周期很大；在可见光区峰值透射比在60%左右,由于旋光率随波长变化率不大,晶体厚度对谱线周期影响明显。在温度变化的环境下对300-1500nm进行了测试,通过分析所得谱线及对应极值波长表明：随着温度升高,透射谱线向长波方向漂移,进一步分析得出漂移的主要原因是由于温度升高导致石英晶体旋光率变大而引起的,其中旋光率变大可以利用螺旋理论解释为：由于石英晶体热膨胀导致微观结构中螺距变大造成的。文章的第三章和第四章是本文的主要部分,也是本文的主要创新点：1、探索性利用螺旋理论的知识解释石英晶体旋光性的有关特点,采用微螺旋结构螺距变化的解释,较好解释石英旋光率的方向性、热效应以及与有机液体旋光率的差异性。2、用双光路对比法对石英旋光晶体在可见光区进行偏光透射谱线测试,并对测试所得的透射谱线进行分析测量。实验结果显示,常温下可见光区,由于旋光率随波长变化率不大,晶体厚度对谱线周期影响明显；在温度变化的环境下,随着温度升高,透射谱线向长波方向平移,进一步分析得出平移的主要原因是由于温度升高导致石英晶体旋光率变大,热膨胀导致了微观结构的螺距变大,从而验证了螺旋理论的正确性。本文理论分析与实验测试相结合,对石英晶体旋光性本质研究和相关应用提供了一定参考。更多还原

【Abstract】 Quartz crystal is an important kind of optical material. Optical activity is one of its important properties. Devices made with optical activity of quartz crystal have important applications in the field of dispersion filtering, optical communication, depolarization and so on.. Referring to related literatures, study of quartz crystal is mainly concerned with birefringence of the material and the application of its optical activity, while work on the nature of optical activity has little been done.In the paper, the following knowledge is systematically studied. It includes category of quartz crystal system, specific rotation of quartz crystal, relevant knowledge of rotatory dispersion, magneto-optical rotation, Fresnel assumption etc.Reference to spiral model of organic liquid theory, the internal relation between the optical activity of quartz crystal and micro-spiral structure is analyzed. With pitch changing, directivity and thermal effect of specific rotation of quartz as well as its difference from specific rotation of the organic liquid are explained. Helical length l is definite at a certain temperature and the largest pitch goes along the optical axis, which is independent on spiral structure characteristic of quartz crystal. This just reflects the characteristics that optical rotation is the most obvious and specific rotation is the largest. As propagation direction deviates from the optical axis, projection of pitch along the light propagation direction and specific rotation get smaller, till optical rotation of vertical optical axis decreases to zero. When the temperature increases, thermal expansion arises and internal atomic distance increase. As a result, the pitch s gets larger and specific rotation increases relevantly. This interpretation is well consistent with test results about specific rotation. An explanation about the cause of optical activity has been given with micro-electromagnetic theory. The cause of optical activity of quartz crystal is further verified. It is supposed that antisymmetry rotation tensor (?) is the basic reason for optical rotation of the material and when all elements of matrix (?) or the corresponding rotation vector gαβare not zero, the material performs optical activity. Quartz crystal belongs to hexagonal crystal system, whose gαβhas three independent elements. Symmetry of crystal can make independent elements of gαβdecrease.On the basis of theoretical analysis of transmittance of quartz crystal, polarization interference spectrum range from 300nm to 1500nm is measured with double beam path measuring method. Experimental results show that the peak transmission ratio is low due to obvious absorption of quartz in the ultraviolet region. This is different from theoretical results to some extent. And period of spectral line is small because specific rotation of quartz crystal changes greatly with wavelength in this region, while period of spectral line is large in infrared light district because the change rate of specific rotation with wavelength is almost zero. In visible region, the peak transmission ratio is 60% or so. Because of specific rotation changing little with wavelength, thickness of crystal has a apparently impact on period of spectral line. A test is done at different temperature within 300-1500nm. According to the analysis of spectral line, as the temperature increases, there is a shift of the spectral line towards long wave. Further analysis shows that the main cause is that specific rotation of quartz crystal gets large with temperature increasing. The increase of specific rotation may be explained by spiral theory here, i.e. it is because thermal expansion results in pitch increasing in microstructure.The third chapter and the fourth chapter are main part of the paper, and they are also main innovation points:1. Characteristics of quartz crystal optical activity is explained by means of spiral theory. Pitch change in micro-spiral structure better interpret directivity and thermal effect of specific rotation of quartz as well as its difference from specific rotation of the organic liquid.2. Polarization interference spectrum of quartz crystal in visible region is measured with double beam path measuring method and analysis of the experimental spectral line is presented. According to the results, thickness of crystal has a significantly impact on period of spectral line in visible region at room temperature because specific rotation changes little with wavelength. While there is a shift of the spectral line towards long wave as the temperature increases. Further analysis shows that the main cause is that specific rotation of quartz crystal gets large with temperature increasing. And thermal expansion results in pitch increasing in microstructure. The spiral theory is verified.Study of both theoretical analysis and experimental tests is made in the paper. It provide a reference to studying the nature of the optical activity of quartz crystal and relevant applications.更多还原