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https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/32531
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| 題名: | 孤立電子對在氧化物、氮化物、鹵化物晶體之光學非線性所扮演的角色 |
| 其他題名: | The role of electron lone-pair in the optical nonlinearity of oxide, nitride and halide crystals |
| 作者: | 駱俊宏;Lo, Chun-hung |
| 貢獻者: | 淡江大學物理學系碩士班
李明憲;Lee, Ming-hsien |
| 關鍵詞: | 孤立電子對;硼酸鹽晶體;三鹵鍺化物;碳矽氮化物;非線性光學;能帶解析;lone-pair;borate;BBO;LBO;CBO;CLBO;SiO2;SrBe3O4;CsGeCl3;CsGeBr3;CsGeI3;Si3N4;Si2CN4;SiC2N4;C3N4;MgGeN2;wurtzite;BN;GaN;nonlinear;optical;SHG |
| 日期: | 2005 |
| 上傳時間: | 2010-01-11 02:17:25 (UTC+8) |
| 摘要: | 在許多科學應用上，不同波段的雷射都有其重要的應用，但雷射光波長由於產生機制的特性，其頻率特定。利用倍頻晶體可以將可用雷射光頻率增多，但由於不同晶體適用的雷射源不同，為了能讓各種波段的雷射源都能倍頻，就需要各式各樣的非線性光學晶體。所以對於這些晶體影響非線性光學現象之發生機制等等的徹底瞭解，可以幫助我們找尋或是合成更多的非線性光學晶體。其中氧化物非線性光學晶體由於其損傷門檻高，所以成為一類重要的非線性光學晶體。
對於影響氧化物晶體其非線性光學發生機制的相關研究，之前的研究工作已指出一些明顯的方向，例如像是硼酸鹽晶體中，陰離子基團對於倍頻效應機制具有重大的影響。在本工作中，我們利用新的分析技術，從電荷密度的角度來分析氧化物非線性光學晶體，使我們得知影響氧化物非線性光學晶體的主要因素為何。
利用我們之前研究工作的另一項技術『能帶解析χ(2)』，能使我們得知分子中，對於對倍頻係數最重要的分子軌域為何。本工作的重點則是將此技術應用在固體中，並將晶體中對倍頻係數最重要的軌域以權重方式去加總各個電荷密度。透過此技術『SHG-Density 分析方法』，將空間中對倍頻現象有貢獻的電子雲密度呈現出來，可使我們清楚知道產生倍頻的機制。並且發現了對於氧化物非線性光學晶體其孤立電子對效應為影響非線性光學機制的主因。
為了進一步證實我們看到的是孤立電子對，於是發展了『孤立電子對判定方法』這項技術，並以具有孤立電子對的簡單分子結構來做各項測試，確定程式的可用性及正確性後再將其應用至我們想進行分析的結構之上。結果果真證實了先前的預測即---孤立電子對在非線性光學氧化物中是一個對其倍頻效應機制的重要來源。而這也使我們對非線性光學材料有了更深一層的認識。
最後，對於幾種鄰近於 VIA 族的非線性光學氮化物及鹵化物，我們以相同的技術去分析，並就結果作初步的探討，以期能更加深入和廣泛的理解各種非線性光學材料的性質。
Laser sources of different wavelengths have their own important use in industrial applications as well as fundamental researches, but since light is emitted as a result of transition between electronic states, the available wavelengths is limited in the entire EM wave spectrum. Frequency conversion techniques using Non-linear optical crystals allow the production of laser beam at different wavelengths, and are therefore very desirable. For example, harmonic generation can be used to produce laser beam at shorter wavelength which is essential for the next generation lithography, optical storage and fiber communication. Since each NLO crystal works at certain frequency range and has their own characteristics, it is also desirable to search for wider variety of them. A systematic study of the mechanism of NLO properties of these crystals will be beneficial.
In UV/Visible range, oxide crystals are one of the most important types, which usually have high damage threshold, making them durable under high laser power operation. There has already some progress in the past on understanding the mechanism of NLO properties of oxides. Borate, for example, was found to have largely due to their anion group. In this work, we have proposed a new analysis scheme, which reveals the main factor of optical non-linearity from the picture of electron density.
Using one of our analyzing tools "band-resolved of second order susceptibility", one can identify which several orbitals or bands contribute most in a molecule. This work extends the idea further and makes it
applied on solids even more easily. This is achieved by summing each orbital density based on the SHG weight. Through this "SHG-density plots" we can visualize the electron densities that have with significant contribution to the optical nonlinearity and reveal the SHG mechanism. Using this method that we found that lone-pair electrons play the major role in non-linear optics mechanism of oxide family NLO crystals.
In order to identify lone-pair electrons, the technique of “Lone-pair identification scheme” is developed. After testing this scheme on a few simple molecules known to have lone-pair, the reliability of the scheme is confirmed. This method is then applied to the structures which we are interested in, and it dose prove our claim — lone-pair is one of the significant source leads to the non-linear optical properties of oxide. This leads to a further understanding on the mechanism of non-linear optical materials.
Further more, non-linear optical Nitride and Halide crystals which are next to VIA group are also analyzed by this technique. Some preliminary results were obtained which might be useful toward a general understanding on the properties of various non-linear optical materials. |
| 顯示於類別: | [物理學系暨研究所] 學位論文
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