本文選題：熱光系數(shù) + 吸收邊��； 參考：《武漢理工大學(xué)》2015年碩士論文

【摘要】：折射率和熱光系數(shù)是表征材料光學(xué)性質(zhì)重要的參量。作為常用的紅外光學(xué)材料,鍺在透明區(qū)光學(xué)性質(zhì)研究很成熟,但在吸收邊附近(1550nm附近,屬于近紅外區(qū)),它的折射率和熱光系數(shù)相關(guān)研究較少,論文仔細(xì)分析了鍺材料在吸收邊附近區(qū)域的光學(xué)吸收過(guò)程,指出本征吸收與激子吸收對(duì)吸收邊熱光效應(yīng)存在較大的影響;利用吸收系數(shù)和折射率的內(nèi)在聯(lián)系,建立鍺材料在吸收邊附近的熱光系數(shù)模型;并搭建實(shí)驗(yàn)平臺(tái)實(shí)際測(cè)量了吸收邊附近區(qū)域鍺的熱光系數(shù)。理論建模的具體思路為:在吸收邊附近主要的吸收過(guò)程有本征吸收與激子吸收。本征吸收是由電子帶間躍遷引起的,包括帶間間接躍遷和帶間直接躍遷,建模時(shí)忽略帶間間接躍遷影響,只考慮躍遷概率較高的帶間直接躍遷,這一部分借助經(jīng)典的諧振子模型來(lái)描述。其中,按照對(duì)熱光系數(shù)貢獻(xiàn)的大小,帶間直接躍遷又分為E0直接躍遷和其余直接躍遷。用簡(jiǎn)單的拋物線能帶結(jié)構(gòu)來(lái)描述E0直接躍遷;其余直接躍遷對(duì)熱光系數(shù)的貢獻(xiàn)則用透明區(qū)的折射率模型來(lái)計(jì)算。鑒于所討論為吸收邊附近區(qū)域,論文重點(diǎn)討論激子吸收對(duì)吸收邊附近熱光效應(yīng)的影響,采用wannier激子模型描述。嘗試建立wannier模型中變量與溫度函數(shù)關(guān)系,即可推導(dǎo)出介電常數(shù)與溫度的關(guān)系,進(jìn)而得到折射率—溫度關(guān)系。最后,將諧振子模型與wannier激子模型結(jié)合,實(shí)現(xiàn)對(duì)吸收邊光學(xué)現(xiàn)象的描述。根據(jù)所建模型進(jìn)行理論計(jì)算發(fā)現(xiàn),吸收邊附近熱光效應(yīng)出現(xiàn)反�，F(xiàn)象,即隨溫度升高呈遞增趨勢(shì)的鍺的熱光系數(shù)曲線在吸收邊附近出現(xiàn)一個(gè)突變,即熱光系數(shù)由正值變?yōu)樨?fù)值之后,再趨于某一正值。論文搭建了基于光纖傳感器的實(shí)驗(yàn)平臺(tái)對(duì)鍺膜的熱光系數(shù)進(jìn)行準(zhǔn)確測(cè)量。利用蒸鍍工藝在光纖端面鍍上鍺膜作為傳感單元,利用高低溫實(shí)驗(yàn)箱產(chǎn)生可調(diào)溫度場(chǎng),實(shí)驗(yàn)測(cè)量置于溫箱中的鍺膜反射率隨溫度的變化曲線,進(jìn)而根據(jù)反射率—折射率關(guān)系得到折射率—溫度系數(shù),即熱光系數(shù)。實(shí)驗(yàn)結(jié)果表明:如理論模型所預(yù)測(cè),在吸收邊附近,鍺的熱光系數(shù)隨溫度升高出現(xiàn)由正到負(fù)的變化。實(shí)驗(yàn)結(jié)果與理論模型基本相符,但實(shí)驗(yàn)結(jié)果中熱光系數(shù)的減小趨勢(shì)比理論預(yù)測(cè)要小。論文最后分析了理論模型與實(shí)驗(yàn)結(jié)果存在誤差的原因,并指出之后工作的重點(diǎn)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.
【學(xué)位授予單位】：武漢理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TN213

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中國(guó)期刊全文數(shù)據(jù)庫(kù) 前1條

1 葉帆;顧兵;黃曉琴;;薄膜材料折射率色散的進(jìn)展與展望[J];光學(xué)儀器;2010年04期

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本文編號(hào)：1842687