锗在吸收边附近热光系数的理论建模与测量

发布时间：2018-05-04 10:27

  本文选题：热光系数 + 吸收边　； 参考：《武汉理工大学》2015年硕士论文

【摘要】：折射率和热光系数是表征材料光学性质重要的参量。作为常用的红外光学材料,锗在透明区光学性质研究很成熟,但在吸收边附近(1550nm附近,属于近红外区),它的折射率和热光系数相关研究较少,论文仔细分析了锗材料在吸收边附近区域的光学吸收过程,指出本征吸收与激子吸收对吸收边热光效应存在较大的影响;利用吸收系数和折射率的内在联系,建立锗材料在吸收边附近的热光系数模型;并搭建实验平台实际测量了吸收边附近区域锗的热光系数。理论建模的具体思路为:在吸收边附近主要的吸收过程有本征吸收与激子吸收。本征吸收是由电子带间跃迁引起的,包括带间间接跃迁和带间直接跃迁,建模时忽略带间间接跃迁影响,只考虑跃迁概率较高的带间直接跃迁,这一部分借助经典的谐振子模型来描述。其中,按照对热光系数贡献的大小,带间直接跃迁又分为E0直接跃迁和其余直接跃迁。用简单的抛物线能带结构来描述E0直接跃迁;其余直接跃迁对热光系数的贡献则用透明区的折射率模型来计算。鉴于所讨论为吸收边附近区域,论文重点讨论激子吸收对吸收边附近热光效应的影响,采用wannier激子模型描述。尝试建立wannier模型中变量与温度函数关系,即可推导出介电常数与温度的关系,进而得到折射率—温度关系。最后,将谐振子模型与wannier激子模型结合,实现对吸收边光学现象的描述。根据所建模型进行理论计算发现,吸收边附近热光效应出现反常现象,即随温度升高呈递增趋势的锗的热光系数曲线在吸收边附近出现一个突变,即热光系数由正值变为负值之后,再趋于某一正值。论文搭建了基于光纤传感器的实验平台对锗膜的热光系数进行准确测量。利用蒸镀工艺在光纤端面镀上锗膜作为传感单元,利用高低温实验箱产生可调温度场,实验测量置于温箱中的锗膜反射率随温度的变化曲线,进而根据反射率—折射率关系得到折射率—温度系数,即热光系数。实验结果表明:如理论模型所预测,在吸收边附近,锗的热光系数随温度升高出现由正到负的变化。实验结果与理论模型基本相符,但实验结果中热光系数的减小趋势比理论预测要小。论文最后分析了理论模型与实验结果存在误差的原因,并指出之后工作的重点和努力方向。
[Abstract]:Refractive index and thermo-optical coefficient are important parameters to characterize the optical properties of materials. As a common infrared optical material, germanium has very mature optical properties in transparent region, but it belongs to near infrared region near the absorption edge of 1550nm, and the correlation between refractive index and thermo-optical coefficient of germanium is less. In this paper, the optical absorption process of germanium near the absorption edge is carefully analyzed, and it is pointed out that intrinsic absorption and exciton absorption have a great influence on the absorption of enthalpy light effect, and the intrinsic relation between absorption coefficient and refractive index is used. The thermo-optical coefficient model of germanium near the absorption edge was established, and the experimental platform was set up to measure the thermo-optical coefficient of germanium near the absorption edge. The concrete idea of theoretical modeling is that there are intrinsic absorption and exciton absorption in the main absorption process near the absorption edge. The intrinsic absorption is caused by the electron interband transition, including the indirect and direct interband transitions. The indirect transition between bands is ignored in the modeling, and only the direct transition between the bands with high transition probability is considered. This part is described by the classical harmonic oscillator model. According to the contribution to the thermo-optical coefficient, the direct transition between bands is divided into E0 direct transition and other direct transition. A simple parabolic band structure is used to describe the direct transition of E0, and the contribution of the other direct transitions to the thermo-optical coefficients is calculated by the refractive index model of the transparent region. In view of the discussion of the region near the absorption edge, the influence of exciton absorption on the thermo-optical effect near the absorption edge is discussed in this paper. The wannier exciton model is used to describe it. This paper attempts to establish the relationship between the variables and the temperature function in the wannier model. The relationship between the dielectric constant and the temperature can be deduced, and the relationship between the refractive index and the temperature can be obtained. Finally, the harmonic oscillator model and the wannier exciton model are combined to describe the optical phenomenon of absorption edge. According to the theoretical calculation of the model, it is found that the thermo-optical effect near the absorption edge is anomalous, that is, the thermo-optical coefficient curve of germanium, which is increasing with the increase of temperature, has a sudden change near the absorption edge. That is, the thermo-optical coefficient changes from positive to negative, and then tends to a positive value. In this paper, an experimental platform based on optical fiber sensor is built to measure the thermal optical coefficient of germanium film accurately. Germanium film was deposited on the fiber end surface as sensing unit by evaporation plating process. The adjustable temperature field was produced by using the high and low temperature experimental box. The reflectance curve of germanium film placed in the temperature box was measured experimentally. According to the reflectivity-refractive index relation, the refractive index-temperature coefficient, that is, the thermo-optical coefficient, is obtained. The experimental results show that the thermo-optical coefficient of germanium varies from positive to negative with the increase of temperature near the absorption edge as predicted by the theoretical model. The experimental results are in good agreement with the theoretical model, but the decreasing trend of the thermo-optical coefficient in the experimental results is smaller than that predicted by the theory. Finally, the paper analyzes the reason of the error between the theoretical model and the experimental results, and points out the emphasis and direction of the later work.
【学位授予单位】：武汉理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN213

【参考文献】

中国期刊全文数据库 前1条

1 叶帆;顾兵;黄晓琴;;薄膜材料折射率色散的进展与展望[J];光学仪器;2010年04期

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