【作者】 李长青；

【导师】 韩杰才；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 博士

【摘要】 本文采用传统的提拉法制备了YAG晶体以及采用固相反应法制备了YAG透明陶瓷,并对YAG晶体和陶瓷的性能进行了表征,为了研究YAG晶体材料的激光损伤性能,采用毫秒、纳秒、飞秒三种特征脉宽的激光对YAG材料进行损伤试验,分析了三种情况的激光损伤YAG材料的形貌及其损伤机理。在YAG单晶制备方面,研究结果表明:采用传统晶体生长的方法-提拉法制备了YAG晶体,能够保证晶体的质量,经加工制备的YAG单晶试样,在空气和真空热处理条件下进行性能对比,采用XPS、透过率、XRD半峰高宽表征手段进行表征,确定影响YAG单晶试样光学质量的影响因素。在YAG透明陶瓷制备方面,研究结果表明:采用高纯的Y₂O₃、Al₂O₃粉或Y₂O₃粉、Al粉固相反应两种途径制备了YAG粉体,研究表明采用Y₂O₃粉、Al粉在固相反应制备出YAG粉体比Y₂O₃、Al₂O₃粉制备生成温度低,能够在1200℃煅烧制备出YAG粉体,而高纯Y₂O₃、Al₂O₃粉体能够烧结合成YAG透明陶瓷,Y₂O₃粉体、Al粉体烧结的YAG陶瓷性能不理想。本文采用毫秒激光损伤YAG单晶,详细研究了毫秒级脉宽单脉冲激光损伤过程及其机理。研究结果表明:YAG晶体或透明陶瓷在毫秒激光损伤条件下是以熔融为主的破坏机理,表面形成锥形熔坑,其深度与激光能量的线性度较好。以激光对YAG单晶的热传导、熔融、汽化、电离四个过程为基础建立数学模型模拟激光损伤,并与实验值对比,具有较好的吻合度。同时还分析了毫秒激光切割YAG晶体的断口形貌,并从理论上加以解释。通过使用纳秒激光对YAG单晶和透明陶瓷损伤形貌及机理进行了详细的研究。研究表明:纳秒激光对YAG产生面损伤时,是以表面蒸发和体蒸发为主要损伤机理;纳秒激光对YAG产生体损伤时,是以热爆炸为主要损伤机理,晶体内部被激光融化,产生膨胀,表面产生了隆起,当激光脉冲能量足够大时,晶体开裂;YAG陶瓷损伤与YAG单晶损伤机理基本相似。本文还研究了飞秒级超短脉宽激光损伤形貌及其机理。研究表明:YAG晶体的飞秒激光面损伤是强电场剥离表面原子机理损伤为主,实验采用的极大值法确定的不同热处理后的YAG烧蚀阈值,采用Robert Eason的介电材料烧蚀阈值计算法计算YAG晶体的烧蚀阈值,两者较接近。采用Betis的电场临界阈值计算法和Bulgakova的库仑爆炸理论的计算法对YAG材料的临界电场进行分析比较,计算结果相近,从机理上解释了表面强电场剥离表面原子。基于飞秒激光对YAG单晶和透明陶瓷产生的原子发射光谱进行了对比,分析出飞秒激光损伤YAG材料产生了Y、Al、Y离子、Al离子、YO分子、AlO分子的发射谱线。更多还原

【Abstract】 YAG crystal was prepared by traditional Czochrolski Method and YAG transparent ceramics was prepared by solid-state reaction method, and the performances of YAG crystal and ceramics were characterized. In order to investigate laser-induced damage of YAG material, millisecond, nanosecond and femtosecond pulsewidth laser were used to induce damage of YAG, three kinds of damage mechanism for YAG by laser were analyzed.For preparation of YAG crystal, the experimental results show that: YAG crystal was prepared by Czochrolski Method-a kind of traditional crystal methods, which guarantee the quality of YAG crystal. To compare the characterization of YAG crystal specimen by heat treatment under vacuum or air with as prepared, XPS, transimittance, FWHM of XRD were used, trying to determine the effect factors of optical quality for YAG crystal.For preparation of YAG transparent ceramic, study results show that:YAG powder could be synthesized by high-purity Y₂O₃, Al₂O₃ powder or Y₂O₃,Al powder by solid-state reaction method. The temperature of YAG powder synthesized by latter method is lower than former one, and YAG powder could be synthesized at 1200℃, YAG transparent ceramics could be prepared by Y₂O₃ ,Al₂O₃ powder and could not by Y₂O₃, Al powder.In this paper, ms laser was used to induce damage for YAG crystal, and the single pulse ms laser induced damage and its mechanism was studied in detail. The results show that: the main mechanism of ms laser damage for YAG crystals or transparent ceramic is melting, cone-shaped keyhole is formed on the surface, and its depth is near linear to laser energy. Laser induced damage to YAG based on heat conduction, melting, vaporization, ionization four processes, a mathematical model is established and results agree well with experimental data. At the same time cutting kerf of YAG crystal by ms laser is analyzed and explained by theory.YAG crystal and transparent ceramics damaged morphology and mechanism by laser is of a detailed study. Research result shows that: For surface damaged YAG by ns laser, surface evaporation and bulk evaporation are the main damage mechanism; For bulk damaged YAG by ns laser, thermal explosion is the main damaged mechanism, crystal is melt by laser inside, then expanded, surface uplift, crystal will be crack while the laser pulse energy sufficiently large; The damage mechanism of YAG ceramic is similar to that of YAG crystal.Ultrashort pulse fs laser induced damage morphology and its mechanism is also studied in detail. Result shows that: main mechanism of crystal damage by laser is strong electric field strip the surface atom. Ablation threshold of different treatment of YAG is determined by maximum value method and it is very near to the value computed by dielectric abalation threshold by Robert Eason, the result is similar between Betis’critical electric field threshold with Bulgakova’Coulomb explosion theory, Strong electric field stripping the atom on the surface is analyzed from theory, Y atom, Al atom, Atom emission spectra of Y ion, Al ion, YO molecule, AlO molecule appear for YAG by fs laser induced damage.更多还原