已體積布拉格光柵為可調反射率輸出雷射鏡研究

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研究生：	陳昭介 Zhao-jie Chen
論文名稱：	已體積布拉格光柵為可調反射率輸出雷射鏡研究 Variable reflectivity laser mirror study based on chirped volume Bragg grating
指導教授：	鍾德元 Te -Yuan Chung
口試委員:
學位類別：	碩士 Master
系所名稱：	理學院 - 光電科學與工程學系 Department of Optics and Photonics
畢業學年度：	97
語文別：	中文
論文頁數：	63
中文關鍵詞：	布拉格光柵
外文關鍵詞：	VBG Variable reflectivity
相關次數：	點閱：9 下載：0
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固態雷射操作在在高瓦數時其增益介質會因各種熱效應(thermal effects)之故造成雷射輸出效率比預期為小。本篇論文討論因溫度造成激發放射截面改變而影響其雷射系統輸出效率。本實驗以Nd:YAG雷射系統假設反射率可調整，而做了四種不同種類的Nd:YAG雷射系統1連續波雷射(CW laser)、2主動Q開關雷射(actively Q-switch laser)、3主動Q-switch laser在有放大自發射 (Amplified spontaneous emission)限制條件、4被動式Q開關雷射(Passively Q-switched laser)。而此方法最主要建立在可調式反射率鏡子，在此提出溫差控制VBG內部周期而改變反射率，經由模擬計算可以求出當反射為多少能把增益介質受激輻射熱效應彌補回來，使雷射輸出跟溫度為非相依。
本論文提出以VBG兩側施加溫差會使原本裡面週期性結構變為非週期性結構因此反射率會因此下降，故可以由VBG改變溫差來調控其反射率。而當要施加多少溫差反射率才能達到需求值，先由Comsol multiphysics求出當有溫差時其內部膨脹量分布建立非週期性結構資料，再用T-matrix 求每一不同折射率的反射、折射、傳播光程差求其反射率。最後藉由實驗以改變VBG溫差為雷射輸出鏡，由它的輸出和閥值效率求反射率，證實可以由此架構的VBG可以藉由溫差調整反射率。

The laser’s output efficiency is smaller than before when laser opperated high power because thermal lens did. The thesis disscused the laser’s output efficiency unstable because emission cross section was changed with temperature. The experiment used the Nd:YAG laser system and supposed the reflectivity was adjustable. Then simmulated four different types control system 1 CW laser、2 actively Q-switch laser、3 Amplified spontaneous emission、4 Passively Q-switched laser.
This method based on variable reflectivity mirror so we suggest used the temperature difference to control VBG’s incide period and reflectivity. Thus by simulation we can get how the reflectivity changed to recover gainmedium stimulated emission thermal effection and make output energy was temperature independent.
We used the difference temperature on the VBG to let the period structure becomed unperiod streucure, thus the reflectivity was decreased.
Then the reflectivity was variable by controling temperature difference on VBG. How much temperature difference value that we were need. First the expansion distribution be gotten by used Comsol multiphysics when VBG was temperature difference,thus we can get unperiod structure. And then used the T-matrix to measure refletion、transition、propagation optical difference to get the reflectivity. Finally, we uesd difference temperature VBG to be output laser mirror and got the reflectivity by threshold power and slope efficiency. The result can change reflectivity by temperature difference.

目錄
摘要...............................................................................................................................V
Abstract.......................................................................................................................VI
致謝............................................................................................................................ VII
目錄...........................................................................................................................VIII
表目錄....................................................................................................................... XII
第一章 緒論.................................................................................................................1
1.1 實驗動機........................................................................................................1
1.2 固態雷射熱效應............................................................................................2
1.3 雷射輸出與溫度非相依模擬........................................................................7
1.4 可調式反射鏡................................................................................................8
第二章 實驗原理.........................................................................................................9
2.1 雷射基本原理................................................................................................9
2.1.1 雷射rate equation..............................................................................9
2.1.2 閥值、增益飽和...............................................................................10
2.1.3 circulating power ..............................................................................13
2.1.4 laser output ........................................................................................13
2.2 Nd: GdVO4 特性.........................................................................................16
2.3 可調反射率VBG 原理................................................................................19
2.3.1VBG 簡介............................................................................................19
2.3.2VBG T-matrix ....................................................................................21
第三章 實驗模擬.......................................................................................................24
3.1VBG 溫差內部週期膨脹量模擬...................................................................25
3.1.1 物質參數和邊界設定.......................................................................26
3.1.2 熱膨脹模擬結果...............................................................................27
3.2 VBG 溫度差反射率光譜模擬......................................................................29
3.2.1 matlab 程式碼流程圖和初始值.......................................................29
3.2.2 反射率光譜模擬................................................................................30
3.3 調變反射率使雷射輸出穩定模擬...............................................................34
第四章 實驗架構.......................................................................................................44
4.1VBG 溫控.......................................................................................................44
4.2 線型共振腔(以平面鏡為輸出鏡).................................................................45
4.3 線型共振腔(以VBG 為輸出鏡) ..................................................................46
第五章 數據分析.......................................................................................................47
5.1 VBG 光譜量測與溫控..................................................................................47
5.2 平面鏡為輸出..............................................................................................50
5.3 Beam size 量測..............................................................................................51
5.4 VBG 為輸出耦合鏡......................................................................................53
5.5. 雷射光形M2 及細部光譜分析...................................................................57
第六章 未來展望.......................................................................................................62
6.1.雷射輸出鏡...................................................................................................62
6.2 改進方向和其他應用..................................................................................63
參考文獻.....................................................................................................................64
附件..............................................................................................................................66

                                

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