用FDTD分析KDP晶体微纳表层对内部光强分布的影响
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摘要
KDP晶体是一种性能优良的非线性光学晶体材料,因其具有较大的非线性光学系数、较高的激光损伤阈值、较宽的透光波段、优良的光学均匀性、易于实现相位匹配、易于生长等特点,而被广泛地用作光学频率转换器件以及光电开关元件。但是,KDP晶体生长以及后续的超精密加工过程中,会形成各种缺陷和表面特征,严重地影响着晶体的激光损伤阈值等光学性能。例如,生长过程中形成的各类包裹体缺陷以及单点金刚石铣削后表面形成的小尺度波纹等。因此,研究这些缺陷对其激光损伤阈值的影响规律和程度大小,不仅可以进一步解释KDP晶体的激光损伤机理,还可为提高光学性能提供理论基础和参数依据,进一步指导快速生长工艺的改进以及加工参数的合理选取,以满足目前激光核聚变装置对KDP晶体光学元件所提出的苛刻要求,对惯性约束核聚变(Inertial Confinement Fusion,ICF)工程至关重要。
本文首先对采用时域有限差分方法(Finite Difference Time Domain,FDTD)建模过程中所涉及到的空间和时间步长选择、吸收边界条件和周期性边界条件设置等相关内容进行分析,并建立平面电磁波垂直投射到光滑的和镀膜的KDP晶体表面的分析模型,采用FDTD方法求解晶体内部的光强,与公式计算结果以及薄膜增透理论进行对比验证,为后续的分析工作做了铺垫。
然后阐述小尺度波纹的产生和提取,分析小尺度波纹、凹坑和包裹体对KDP晶体内部光强分布的影响规律和程度大小。结果表明:小尺度波纹、凹坑和包裹体会使晶体内部的衍射场发生畸变,导致晶体内部光强呈现强弱分布;且畸变程度与不同特征参数(小尺度波纹幅值和周期、凹坑大小、包裹体大小和折射率)有关。
最后对KDP晶体激光损伤阈值实验进行分析,结果表明:晶体的前、后表面损伤和体损伤多以炸裂为主,且后表面炸裂的程度明显比前表面严重;粗糙度不能作为评价表面形貌对KDP激光损伤阈值影响的唯一标准;小尺度波纹对激光的小尺度扰动是激光发生小尺度自聚焦的重要原因。
crystal is widely used as frequency converter and photoectric switch in optical project. Howerever, the defects on the surface or inside KDP crystal as a result from the process of growth and cutting will greatly affect the optical quality of KDP crystal such as laser damage threshold. For example, the different inclusions inside KDP crystal formed in the process of rapid growth and the micro-waviness on the surface of KDP crystal left by single point diamond turning. Therefore, making an in-depth study on the laser damage mechanism and degree affected by those defects not only can explain the causes of damage and provide the theoretical basis for increasing laser damage threshold, but also can guide technics of rapid growth improving and working parameters choosing. Thus, it is significant to reach the rigorous standard for devices of Inertial Confinement Fusion.
In this paper, firstly presented the fundamental theory of Finite Difference Time Domain method that we used to analyze the subsequent problems; built the model of uniform plane electromagnetic wave irradiating on the surface of smooth and film-coated KDP crystal by 2-D FDTD method and campared the results with theoretical results; made preparatory work for subsequent analysis.
Then, presented the formation and extraction of micro-waviness and built the physical model of defects such as micro-waviness, concave pit and inclusion. analyzed the law of how the defects impacting on near-filed light intensity distribution inside and on the surface of KDP crystal by FDTD. Results indicate: defects will distort the incident wave and lead to distribution of strength and weakness of light intensity inside KDP crystal; the degree of distortion has relation with feature parameters of micro-waviness, concave pits and inclusions.
At last, carried out experiments of variable parameter processing using single point diamond turning (SPDT) and laser damage threshold detection of KDP crystal. Results indicate: major damage of KDP crystal is break and the degree of break on back surface is worse than front surface; roughness can not used to be the only criterion of assessment for effect of surface topography on laser damage threshold of KDP crystal; micro-waviness is a crucial influence factor of self-focusing damage.
本文首先对采用时域有限差分方法(Finite Difference Time Domain,FDTD)建模过程中所涉及到的空间和时间步长选择、吸收边界条件和周期性边界条件设置等相关内容进行分析,并建立平面电磁波垂直投射到光滑的和镀膜的KDP晶体表面的分析模型,采用FDTD方法求解晶体内部的光强,与公式计算结果以及薄膜增透理论进行对比验证,为后续的分析工作做了铺垫。
然后阐述小尺度波纹的产生和提取,分析小尺度波纹、凹坑和包裹体对KDP晶体内部光强分布的影响规律和程度大小。结果表明:小尺度波纹、凹坑和包裹体会使晶体内部的衍射场发生畸变,导致晶体内部光强呈现强弱分布;且畸变程度与不同特征参数(小尺度波纹幅值和周期、凹坑大小、包裹体大小和折射率)有关。
最后对KDP晶体激光损伤阈值实验进行分析,结果表明:晶体的前、后表面损伤和体损伤多以炸裂为主,且后表面炸裂的程度明显比前表面严重;粗糙度不能作为评价表面形貌对KDP激光损伤阈值影响的唯一标准;小尺度波纹对激光的小尺度扰动是激光发生小尺度自聚焦的重要原因。
crystal is widely used as frequency converter and photoectric switch in optical project. Howerever, the defects on the surface or inside KDP crystal as a result from the process of growth and cutting will greatly affect the optical quality of KDP crystal such as laser damage threshold. For example, the different inclusions inside KDP crystal formed in the process of rapid growth and the micro-waviness on the surface of KDP crystal left by single point diamond turning. Therefore, making an in-depth study on the laser damage mechanism and degree affected by those defects not only can explain the causes of damage and provide the theoretical basis for increasing laser damage threshold, but also can guide technics of rapid growth improving and working parameters choosing. Thus, it is significant to reach the rigorous standard for devices of Inertial Confinement Fusion.
In this paper, firstly presented the fundamental theory of Finite Difference Time Domain method that we used to analyze the subsequent problems; built the model of uniform plane electromagnetic wave irradiating on the surface of smooth and film-coated KDP crystal by 2-D FDTD method and campared the results with theoretical results; made preparatory work for subsequent analysis.
Then, presented the formation and extraction of micro-waviness and built the physical model of defects such as micro-waviness, concave pit and inclusion. analyzed the law of how the defects impacting on near-filed light intensity distribution inside and on the surface of KDP crystal by FDTD. Results indicate: defects will distort the incident wave and lead to distribution of strength and weakness of light intensity inside KDP crystal; the degree of distortion has relation with feature parameters of micro-waviness, concave pits and inclusions.
At last, carried out experiments of variable parameter processing using single point diamond turning (SPDT) and laser damage threshold detection of KDP crystal. Results indicate: major damage of KDP crystal is break and the degree of break on back surface is worse than front surface; roughness can not used to be the only criterion of assessment for effect of surface topography on laser damage threshold of KDP crystal; micro-waviness is a crucial influence factor of self-focusing damage.
引文
1杨力.现代光学制造工程.北京:科学出版社. 2009: 218-219
2刘红.惯性约束核聚变.现代物理知识. 2002, 14(1): 13-15
3英国《新科学家》杂志网, http://www.newscientist.com, 2010
4 E. I. Moses and W. R. Meier. Preparing for ignition experiments on the National Ignition Facility. Fusion Engineering and Design. 2008, (83): 997-1000
5杨力.先进光学制造技术.北京:科学出版社. 2001: 272-279
6罗山.“国家点火装置”开始运转.激光与光电子学进展. 2004, 41(3): 4-9
7王洪祥,王景贺,孙涛,等.磷酸二氢钾晶体超精密加工存在的若干问题分析.兵工学报. 2006, 27(5): 911-915
8杨福兴.激光核聚变光学元件超精密加工技术的研究.光学技术. 2003, 29(6): 649-651
9张全中,高航,王强国,等.磷酸二氢钾晶体精密磨削的试验研究.兵工学报. 2007, 28(12): 1528-1532
10马彦东,李圣怡,彭小强,等. KDP晶体的磁流变抛光研究.航空精密制造技术. 2007, 43(4): 9-12
11吴东江,曹先锁,高航,等. KDP晶体磨削表面缺陷及损伤分析.中国机械工程. 2008, 19(6): 709-712
12 Demos SG, Staggs M, Kozlowski MR. Investigation of process leading to damage growth in optical materials for large-aperture lasers. APPLIED OPTICS. 2002, 41: 3628-3633
13 Sun X, Xu X G, Gao Z S, et al. Study on the liquid inclusion induced light scatter in KDP crystals. Crystal Growth. 2001, 226: 529-533
14 Runkel M, Jennings R, et al. An Overview of Recent KDP Damage Experiments and Implications for NIF Tripler Performance. SPIE. 1999, 84(2): 247-250
15 Atherton L J, Rainer F, et al. Thermal and Laser Conditioning of Production and Rapid-growth KDP and DKDP Crystal. SPIE. 1994, 36(2): 63-66
16 Mike Runkel, Jim De Yoreo, et al. Laser Conditioning Study of on the Optical Science Laser Using Large Area Beams. SPIE. 1998, 75(2): 113-117
17孙洵,程秀凤,顾庆天,等.杂质对KDP晶体光学质量的影响.强激光与离子束. 2004, 16(7): 830-834
18 T. A. Ereminaa, V. A. Kuznetsova, N. N. Ereminb, et al. On the mechanism of impurity influence on growth kinetics and surface morphology of KDP crystal-II experimental study of influence of bivalent and trivalent impurity ions on growth kinetics and surface morphology of KDP crystals. Journal of Crystal Growth. 2005, 31(2): 586-593
19 R. A. Negres, S. O. Kucheyev, P. DeMange, et al. Decomposition of KH2PO4 Crystals During Laser-induced Breakdown. APPLIED PHYSICS LETTERS. 2005, (86):171107
20孙洵,张艳珍,徐明霞,等. Fe3+对KDP晶体光学质量的影响.人工晶体学报. 2007, 36(6): 1240-1244
21张建芹,王圣来,房昌水,等.阴离子掺杂对KDP晶体光散射的影响.无机材料学报. 2007, 22(2): 268-272.
22陈明君,庞启龙,刘新艳. KDP晶体微纳加工表层杂质对其激光损伤阈值影响的有限元分析.强激光与粒子束. 2008, 20(7): 1182-1186
23牟晓明,王圣来,王波,等. Ca2+对KDP晶体的光损伤阈值的影响.人工晶体学报. 2008, 37(5): 1097-1116
24翟仲军,李晓兵,滕冰,等.快速生长KDP晶体中的包裹体.功能材料. 2008, 1(39): 23-25
25 Woods B, Mike Runkel, et al. Optical Scatter as a Diagnostic Tool for Studying Bulk Defects Which Cause Damage in Conventional and Rapid Growth KDP and DKDP. SPIE. 1995, 2541: 123-130
26 Woods B, Runkel M, et al. Investigation of Damage in KDP Using Ligth Scattering Techniques. SPIE. 1997, 2966: 20-31
27 Woods B, Yan M, et al. Photothermal Mapping of Defects in the Study of Bulk Damage in KDP. SPIE. 1998, 3244: 242-248
28 Garces N Y, Stevens K T, et al. Optical Absorption and Electron Paramagnetic Resonance of Fe Ions in KDP Crystals. Journal of Crystal Growth. 2001, 225: 435-439
29刁立臣,张克从,常新安,等. KDP晶体激光损伤阈值研究的新进展.人工晶体学报. 2002, 31: 99-103
30 Miroslawa Rak, et al. On the Mechanism of Impurity Influence on the Growth Kinetics and Surface Morphology of KDP Crystals-I: Defect Centers Formed by Bivalent and Trivalent Impurity Ions Incorporated in KDP Structure-theoretical
Study. Journal of Crystal Growth. 2005, 273: 577
31 Eremina T A, et al. On the Mechanism of Impurity Influence on the Growth Kinetics and Surface Morphology of KDP Crystals-II: Experimental Study of Influence of Bivalent and Trivalent Impurity Ions on Growth Kinetics and Surface Morphology of KDP Crystals. Journal of Crystal Growth. 2005, 273: 586
32 Tiffany N. Thomas, Terry A. Land, Michael Johnson, et al. Molecular Properties of adsorbates that affect the growth kinetics of archerite (KDP). Journal of Colloid and Interface Science. 2004, 280: 18-26
33孙洵,张艳珍,高顺清,等.包裹体对KDP晶体光损伤阈值的影响.压电与声光. 2004, 26(6): 485-487
34陈明君,姜伟,庞启龙,等. KDP晶体微纳米加工表层缺陷对其激光损伤阈值的影响.强激光与粒子束. 2010, 22(1): 159-164
35王景贺,陈明君,董申,等. KDP晶体单点金刚石切削脆塑转变机理的研究.光电工程. 2005, 32(7): 67-70
36姜伟,陈明君,李明全. KDP晶体飞刀铣削加工参数对表面质量影响的实验研究.航空精密制造技术. 2009, 45(5): 4-7
37叶玉堂,饶建珍,肖峻,等.光学教程.北京:清华大学出版社. 2005: 139-140 208-209
38 Oristaglio M L, Hohmann G W. Diffusion of electromagnetic fields into a two-dimension earth: a finite-difference approach. Geophysics. 1984, 49(7): 870-894
39高本庆.时域有限差分方法.北京:国防工业出版社. 1995: 4-7
40葛德彪,闫玉波.电磁波时域有限差分方法.西安:西安电子科技大学出版社. 2005: 11-13 35-39
41方运,张健,吴丽莹.基于时域有限差分法的液晶光学特性模拟.光学学报. 2010, 30(2): 562-564
42付勇.纳米尺度周期性金属结构异常光传输现象的FDTD数值分析.山东大学博士学位论文. 2008: 24-25
43杨显清,赵家升,王园.电磁场与电磁波.北京:国防工业出版社. 2006: 44-46
44于翔. KDP晶体单点金刚石切削表面微观形貌的二维小波分析.哈尔滨工业大学硕士学位论文. 2007: 19-28
45孙大鹏.基于PSD方法的KDP晶体超光滑表面表征技术研究.哈尔滨工业大学硕士学位论文. 2008: 20-32
46严济慈.晶体生长科学与技术.北京:科学出版社. 1997: 460-462
47 Smolsky I L, Zaitseva N P, et al. Formation of“Hair”Inclusions in Rapidly Potassium Dihydrogen Phosphate Crystals. Journal of Growth. 1996, 166: 228-233
48 Smolski I, De Yoreo J J, et al. Oriented Liquid Inclusions in KDP Crystals. Journal of Crystal Growth. 1996, 169: 741-746
49孙洵,许心光,王正平,等. KDP晶体中散射的研究.无机材料学报. 2002, 17(1): 40-44
50张艳珍,孙洵,蒋晓东,等. KDP晶体体缺陷和损伤的观测方法研究.人工晶体学报. 2006, 35(3): 543-549
51孙洵,孙大亮,许心光,等. KDP(DKDP)晶体中液相包裹体散射的形成.中国科学. 2002, 32(4): 447-451
52王圣来,高樟寿,孔勇发,等. KDP晶体包裹体的拉曼光谱研究.无机材料科学报. 2003, 18(2): 289-294
53朱耀南.光学薄膜激光损伤阈值测试方法的介绍和讨论.激光技术. 2006, 30(5): 532-535
54刘强,林理彬,甘荣兵,等.光学膜层激光损伤阈值均匀性的实验研究.强激光与粒子束. 2003, 15(11): 1061-1064
55孙承伟.激光辐照效应.北京:国防工业出版社. 2002: 264-267 281-282
56林晓东. ICF固体驱动器中的小尺度自聚焦效应研究.四川大学硕士学位论文. 2002: 16-18
2刘红.惯性约束核聚变.现代物理知识. 2002, 14(1): 13-15
3英国《新科学家》杂志网, http://www.newscientist.com, 2010
4 E. I. Moses and W. R. Meier. Preparing for ignition experiments on the National Ignition Facility. Fusion Engineering and Design. 2008, (83): 997-1000
5杨力.先进光学制造技术.北京:科学出版社. 2001: 272-279
6罗山.“国家点火装置”开始运转.激光与光电子学进展. 2004, 41(3): 4-9
7王洪祥,王景贺,孙涛,等.磷酸二氢钾晶体超精密加工存在的若干问题分析.兵工学报. 2006, 27(5): 911-915
8杨福兴.激光核聚变光学元件超精密加工技术的研究.光学技术. 2003, 29(6): 649-651
9张全中,高航,王强国,等.磷酸二氢钾晶体精密磨削的试验研究.兵工学报. 2007, 28(12): 1528-1532
10马彦东,李圣怡,彭小强,等. KDP晶体的磁流变抛光研究.航空精密制造技术. 2007, 43(4): 9-12
11吴东江,曹先锁,高航,等. KDP晶体磨削表面缺陷及损伤分析.中国机械工程. 2008, 19(6): 709-712
12 Demos SG, Staggs M, Kozlowski MR. Investigation of process leading to damage growth in optical materials for large-aperture lasers. APPLIED OPTICS. 2002, 41: 3628-3633
13 Sun X, Xu X G, Gao Z S, et al. Study on the liquid inclusion induced light scatter in KDP crystals. Crystal Growth. 2001, 226: 529-533
14 Runkel M, Jennings R, et al. An Overview of Recent KDP Damage Experiments and Implications for NIF Tripler Performance. SPIE. 1999, 84(2): 247-250
15 Atherton L J, Rainer F, et al. Thermal and Laser Conditioning of Production and Rapid-growth KDP and DKDP Crystal. SPIE. 1994, 36(2): 63-66
16 Mike Runkel, Jim De Yoreo, et al. Laser Conditioning Study of on the Optical Science Laser Using Large Area Beams. SPIE. 1998, 75(2): 113-117
17孙洵,程秀凤,顾庆天,等.杂质对KDP晶体光学质量的影响.强激光与离子束. 2004, 16(7): 830-834
18 T. A. Ereminaa, V. A. Kuznetsova, N. N. Ereminb, et al. On the mechanism of impurity influence on growth kinetics and surface morphology of KDP crystal-II experimental study of influence of bivalent and trivalent impurity ions on growth kinetics and surface morphology of KDP crystals. Journal of Crystal Growth. 2005, 31(2): 586-593
19 R. A. Negres, S. O. Kucheyev, P. DeMange, et al. Decomposition of KH2PO4 Crystals During Laser-induced Breakdown. APPLIED PHYSICS LETTERS. 2005, (86):171107
20孙洵,张艳珍,徐明霞,等. Fe3+对KDP晶体光学质量的影响.人工晶体学报. 2007, 36(6): 1240-1244
21张建芹,王圣来,房昌水,等.阴离子掺杂对KDP晶体光散射的影响.无机材料学报. 2007, 22(2): 268-272.
22陈明君,庞启龙,刘新艳. KDP晶体微纳加工表层杂质对其激光损伤阈值影响的有限元分析.强激光与粒子束. 2008, 20(7): 1182-1186
23牟晓明,王圣来,王波,等. Ca2+对KDP晶体的光损伤阈值的影响.人工晶体学报. 2008, 37(5): 1097-1116
24翟仲军,李晓兵,滕冰,等.快速生长KDP晶体中的包裹体.功能材料. 2008, 1(39): 23-25
25 Woods B, Mike Runkel, et al. Optical Scatter as a Diagnostic Tool for Studying Bulk Defects Which Cause Damage in Conventional and Rapid Growth KDP and DKDP. SPIE. 1995, 2541: 123-130
26 Woods B, Runkel M, et al. Investigation of Damage in KDP Using Ligth Scattering Techniques. SPIE. 1997, 2966: 20-31
27 Woods B, Yan M, et al. Photothermal Mapping of Defects in the Study of Bulk Damage in KDP. SPIE. 1998, 3244: 242-248
28 Garces N Y, Stevens K T, et al. Optical Absorption and Electron Paramagnetic Resonance of Fe Ions in KDP Crystals. Journal of Crystal Growth. 2001, 225: 435-439
29刁立臣,张克从,常新安,等. KDP晶体激光损伤阈值研究的新进展.人工晶体学报. 2002, 31: 99-103
30 Miroslawa Rak, et al. On the Mechanism of Impurity Influence on the Growth Kinetics and Surface Morphology of KDP Crystals-I: Defect Centers Formed by Bivalent and Trivalent Impurity Ions Incorporated in KDP Structure-theoretical
Study. Journal of Crystal Growth. 2005, 273: 577
31 Eremina T A, et al. On the Mechanism of Impurity Influence on the Growth Kinetics and Surface Morphology of KDP Crystals-II: Experimental Study of Influence of Bivalent and Trivalent Impurity Ions on Growth Kinetics and Surface Morphology of KDP Crystals. Journal of Crystal Growth. 2005, 273: 586
32 Tiffany N. Thomas, Terry A. Land, Michael Johnson, et al. Molecular Properties of adsorbates that affect the growth kinetics of archerite (KDP). Journal of Colloid and Interface Science. 2004, 280: 18-26
33孙洵,张艳珍,高顺清,等.包裹体对KDP晶体光损伤阈值的影响.压电与声光. 2004, 26(6): 485-487
34陈明君,姜伟,庞启龙,等. KDP晶体微纳米加工表层缺陷对其激光损伤阈值的影响.强激光与粒子束. 2010, 22(1): 159-164
35王景贺,陈明君,董申,等. KDP晶体单点金刚石切削脆塑转变机理的研究.光电工程. 2005, 32(7): 67-70
36姜伟,陈明君,李明全. KDP晶体飞刀铣削加工参数对表面质量影响的实验研究.航空精密制造技术. 2009, 45(5): 4-7
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