KDP晶体激光分离切割机理及关键技术研究

发布时间：2018-07-15 08:41

【摘要】：KH2PO4(KDP)晶体是目前惯性约束核聚变(ICF)装置中变频器和光开关唯一可使用的大尺寸晶体。然而质软、脆性高、对温度和应力变化敏感、易开裂和潮解等特性,使KDP被公认为是一种极难加工的材料。目前,国内外的研究大量集中在KDP晶体的超精密抛光方面,而关于KDP晶体的切割却鲜有报道。目前KDP晶体的切割仍采用传统带锯或金刚石线锯机械切割方式,不但效率低下,加工安全性也很差,经常发生毁灭性的碎裂。本文针对目前存在的技术难点和挑战,从激光诱导拉应力分离入手,在国内外首次提出了KDP晶体激光分离切割创新技术,为晶体器件的制造提供了一条全新的技术途径。本论文利用KDP晶体抗压强度高(113Mpa)而抗拉强度极低(仅为5～8Mpa)这一特性以及透明材料对激光呈体吸收效应,将超快激光“冷”加工技术和传统激光的“热”加工技术有机结合,提出了KDP晶体双激光束分离切割技术和KDP晶体镜面无损激光分离技术。该技术的基本原理是利用超快激光对KDP晶体进行预处理,实现晶体光吸收率和分子结合力的人工调控,再使用连续激光束在晶体内诱导拉应力或微区拉应力实现晶体沿预处理线分离切割。因此本论文研究工作及成果主要包括以下几个方面： (1)通过光线追迹和波动光学理论,建立了聚焦激光在KDP晶体内的传输模型。模拟分析了不同参数的激光聚焦进不同取向的KDP晶体后的传输、聚焦、双折射离焦和光斑畸变特性。结果表明晶体双折射效应会严重影响E光的传输特性,并推导出了晶体内部产生的三维动态光强分布函数。 (2)研究了超快激光与KDP晶体的相互作用过程,结果表明峰值功率较低时可实现晶体内吸收率和分子结合力的三维调控；而峰值功率较高时可实现微裂纹的预制。研究了传统连续／长脉冲激光与晶体的相互作用,确定了可用于KDP晶体激光分离(或无损镜面分离)的相互作用机理、机制和加工光学系统原型。 (3)基于加工光学系统和光强分布函数,建立了晶体内激光诱导动态温度场和热应力场分布数学模型,揭示了KDP晶体激光分离切割机理和过程。表明分离机理为激光诱导的Y方向拉应力或微区拉应力。同时进行了数值模拟研究,确定了关键激光分离切割参数和最优工艺区间,探明了分离切割过程中的潜在不利因素,以进一步提高分离切割过程的可靠性和稳定性。 (4)基于数值模拟和理论分析研究结果,建立了KDP晶体激光分离和无损镜面分离系统。采用双激光束分离技术实现了KDP晶体相对粗糙度仅为2.684μm,局部粗糙度低于500nm的分离切割,其分离速度为机械切割的20余倍。采用激光无损镜面分离技术实现了KDP晶体表面粗糙度为4.7nm(p-v)和2.1nm(RMS),平面度为5.433μm,角向精度低于0.06°的无损镜面分离,其分离速度更是高达机械切割技术的200倍以上。同时分析了各分离参数的影响规律,并开展了相关激光分离切割技术实验研究和加工工艺优化,获得了一套完整的KDP晶体激光分离切割技术理论。
[Abstract]:KH2PO4 (KDP) crystal is the only large size crystal that can be used in the current inertial confinement fusion (ICF) device. However, it is very soft, high brittle, sensitive to temperature and stress changes, easy to crack and deliquescence, so that KDP is considered to be a very difficult to be machined. At present, a lot of research at home and abroad is concentrated in the KDP crystal. However, there are few reports on ultra precision polishing, while the cutting of KDP crystals is rarely reported. At present, the cutting of KDP crystals is still used by traditional band saw or diamond wire saw. Not only the efficiency is low, but also the processing safety is poor, and it often occurs destructive fragmentation. In this paper, the present technical difficulties and challenges are induced by laser induced tensile stress points. In the first place, the innovative technology of laser separation and cutting of KDP crystals was first proposed at home and abroad, which provided a brand new technical approach for the manufacture of crystal devices.
In this paper, the properties of KDP crystal with high compressive strength (113Mpa) and very low tensile strength (only 5 to 8Mpa), and the absorption effect of transparent materials on laser, are combined to combine the ultra fast laser "cold" technology with the traditional laser "hot" processing technology, and the double laser beam separation and cutting technology of KDP crystal and the mirror surface of the KDP crystal are put forward. The basic principle of this technology is to preprocess the KDP crystal with ultra fast laser to realize the artificial regulation of crystal light absorption and molecular binding force, and then use continuous laser beam to induce tensile stress or micro zone tensile stress in the crystal to separate and cut the crystal along the preprocessing line. Therefore, the work and results of this paper are studied and studied in this paper. It mainly includes the following aspects:
(1) through the ray tracing and the wave optics theory, the transmission model of the focused laser in the KDP crystal is established. The transmission, the focusing, the birefringence and the spot distortion of the KDP crystals with different orientation are simulated and analyzed. The results show that the double refraction effect of the crystal will seriously affect the transmission characteristics of the E light, and the derivation is derived. The three-dimensional dynamic intensity distribution function is generated inside the crystal.
(2) the interaction between the ultrafast laser and the KDP crystal is studied. The results show that the internal absorption rate and the molecular binding force can be controlled in three dimensions when the peak power is low, while the micro crack can be prefabricated when the peak power is high. The interaction between the traditional continuous / long pulse laser and the crystal is studied, and it is determined that the KDP crystal can be used in the crystal. The interaction mechanism, mechanism and prototype of processing optical system for laser separation (or lossless mirror separation).
(3) based on the processing optical system and the light intensity distribution function, a mathematical model of laser induced dynamic temperature field and thermal stress field distribution in the crystal is established. The mechanism and process of laser separation and cutting of KDP crystal are revealed. It is shown that the separation mechanism is the tensile stress or the tensile stress in the Y direction induced by the laser. In order to further improve the reliability and stability of the separation and cutting process, the potential disadvantageous factors in the separation and cutting process are explored by separating the cutting parameters and the optimal process interval by the bond laser.
(4) based on the results of numerical simulation and theoretical analysis, a laser separation and non destructive mirror separation system for KDP crystals is established. The relative roughness of the KDP crystal is only 2.684 u m and the local roughness is lower than that of 500nm by double laser beam separation technology. The separation speed is more than 20 times that of the mechanical cutting. The surface roughness of KDP crystal is 4.7nm (P-V) and 2.1nm (RMS), the plane degree is 5.433 u m and the angle precision is less than 0.06 degrees. The separation speed is more than 200 times as high as that of the mechanical cutting technology. Meanwhile, the influence law of the separation parameters is analyzed, and the experimental research on the related laser separation and cutting technology is carried out and the experimental research on the related laser separation and cutting technology is carried out. A complete set of theory of laser separation and cutting technology for KDP crystal has been obtained through optimization of processing technology.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ131.13;O786

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