【作者】 刘新艳；

【导师】 陈明君；

【作者基本信息】 哈尔滨工业大学 ， 机械制造及其自动化， 2007， 硕士

【摘要】 KDP晶体作为一种性能优良的无机非线性光学材料,广泛应用于激光惯性约束核聚变、激光通信等技术领域。惯性约束核聚变光学制造中的一个关键技术问题是KDP晶体零件的抗激光损伤问题,KDP晶体激光损伤阈值的大小直接影响到惯性约束核聚变系统激光输出的能流密度与其自身的使用寿命。现阶段,KDP晶体激光损伤阈值的实际值远低于理论值,而其研究的重点多集中在晶体内部的稳态及瞬态缺陷,有关于晶体微纳加工表层缺陷对其激光损伤阈值的影响研究的较少。因此,深入研究KDP晶体微纳表层缺陷对其激光损伤阈值的影响,将进一步揭示晶体材料的激光损伤机制,为其激光损伤阈值的提高提供相应的理论基础,并为KDP晶体超光滑表面的获取提供理论基础和参数依据。本文基于有限元分析软件ANSYS,首先根据激光辐照下KDP晶体表面的温度场及热应力场理论,建立了三维晶体模型,研究了在激光照射下,表面未镀膜的、理想的KDP晶体表面的温度场及热应力场的分布情况。其次,针对KDP晶体质软、易潮解、脆性高、对温度敏感和易开裂等不利于光学加工的特点,分别分析了KDP晶体已加工表面存在的残余内应力、微裂纹、微孔及陷穴等多种微纳加工表层缺陷对晶体激光损伤阈值的影响。通过分析发现KDP晶体微纳加工表层缺陷的存在,会影响晶体表面的温度场及热应力场的分布,使入射激光能量积聚在缺陷附近的很小范围内,造成晶体缺陷处产生局部熔融现象,使KDP晶体产生损伤,降低KDP晶体的激光损伤阈值。最后,根据KDP晶体杂质附近的温度场及热应力场理论,分析了微纳加工表层杂质影响下晶体温度场及热应力场的分布情况,发现杂质离子对激光的强吸收作用是造成KDP晶体损伤的主要原因之一,也是影响KDP晶体激光损伤阈值的最主要因素。通过分析还发现杂质半径对晶体的激光损伤阈值也有影响,并得到一个有害的杂质半径,使得杂质吸收能量最多,温度最高。另外杂质种类及杂质含量的不同也会对晶体的激光损伤阈值产生影响。更多还原

【Abstract】 As a kind of inorganic nonlinear optical materials with good properties, KDP crystals has widespread applications in technological areas such as laser inertial confinement fusion and laser communication. The damage of KDP crystal is the key technique of the ICF optical manufacturing. The number of KDP crystal laser damage threshold has the direct influence on the laser output energy-flux density and the life of KDP crystal itself. At the moment, the actual laser damage threshold of KDP crystals is far below the theory laser damage threshold, researches on laser damage threshold are mainly centralized on stationary-state and transient-state deficiency inside the crystals, while researches on influences of machined micro-nano superficial layer are less. So, deep research on influences of micro-nano superficial layer deficiency on laser damage threshold will disclosure laser damage mechanisms of crystal materials further, provide the correlative theoretical foundation of increasing laser damage threshold, also provide theoretical foundation and parameter basis to obtain ultra-smooth surfaces.Firstly, based on finite element analysis software ANSYS, applied with temperature field and thermal stress field theory of KDP crystals surface irradiated by laser, the distribution of temperature field and thermal stress field of surface-uncoated, ideal KDP crystals surfaces is researched in laser irradiation.Secondly, in terms of such characters disadvantageous for optical machining as soft, easily deliquescent, very brittle, sensible to temperature and easy to crack, influences of various micro-nano superficial layer deficiency of KDP crystals are analyzed individually, which includes residual internal stress, micro-crack, micro-pore and concave etc. It is discovered through analysis that the deficiency of crystal micro-nano machined superficial layer all affects the distribution of temperature field and thermal stress field of crystal surfaces, which makes injected laser centralize inside a small area around deficiency resulting in temperature lifting intensively around the deficiency, cause partial melting phenomena, damage of KDP crystals and lowering of KDP crystals laser damage threshold.Finally, based on the temperature field and thermal stress field theory around inclusions of KDP crystals, the distribution of crystal temperature field and thermal stress field is analyzed under the influence of micro-nano machined superficial layer inclusions. It is found that ions of inclusions make great absorbing of injected laser leading to crystal damages. Inclusions’great absorbing of laser is the main factors causing crystal damages, as well as the main factor influencing KDP crystals laser damage threshold. Also the radius of adverse inclusion is obtained, which makes the energy inclusions absorb highest as well as the temperature. In addition, different kinds and different contents of inclusions also affect the crystal laser damage threshold.更多还原