KDP晶体超精密飞切微纳形貌对激光损伤阈值的影响研究

发布时间：2018-03-05 08:44

本文选题：KDP晶体　切入点：超精密飞切　出处：《哈尔滨工业大学》2013年博士论文　论文类型：学位论文

【摘要】：KH_2PO_4（KDP）晶体较低的激光损伤阈值是限制惯性约束核聚变（InertialConfinement Fusion，ICF）高功率激光器输出能力提升的瓶颈环节。光学元件超精密加工表面中高频形貌信息及各类瑕疵对其光学性能具有重要影响。但是，目前在KDP晶体超精密飞切微纳形貌对其损伤阈值影响机制方面的研究工作尚未见相关报道。本课题首先研究了KDP飞切微纳表面主要形貌要素的表征方法，并提取能够反映晶体光学质量的主要表征参数；然后建立了表面主要微纳形貌特征与晶体损伤阈值之间的映射关系；最后以对晶体损伤阈值影响较大的形貌参数为优化目标，建立了飞切主轴振动模型，并结合实验来指导飞切参数的选择，为KDP晶体超精密加工提供了重要的参考意见。为了对晶体飞切表面波纹度及粗糙度进行分析，本文利用Motif方法、功率谱密度、小波及分形来对表面形貌进行表征。分析发现：Motif方法所获得的波纹度平均幅值能避免对单一成分求权重而直接对表面波纹进行幅值评价；一维、二维PSD曲线以及角谱和半径谱能够对飞切表面进行全波段以及纹理方向性评价；小波变换可以通过多尺度分解与重构实现KDP晶体三维形貌的提取与分析；分形维数可以克服测量仪器的误差而对表面粗糙度进行最真实的评价。上述方法的结合使用对KDP晶体飞切表面微纳形貌的全面表征具有重要意义。为了研究中频波纹对晶体损伤阈值的影响，本文综合利用PSD与傅里叶模方法来分析波纹参数对入射波的调制特性，发现KDP飞切表面频率构成具有多样性特征。对晶体损伤阈值影响较大的危险波纹周期基本集中在80μm-180μm范围内，而该范围内波纹幅值是较周期更敏感的致伤参量。因此，提出使用波纹度Motif平均深度作为衡量飞切表面损伤阈值大小的一个近似度量参数。同时，基于谐波产生的耦合波方程，提出降低飞切波纹幅值是提高晶体倍频效率并改善输出波形的有效措施。为了研究表面粗糙度与亚表层裂纹对光伤阈值的影响，本文利用傅里叶模法来对上述特征的调制属性进行分析，并引入分形理论来表征表面的抗热损伤能力。分析发现：粗糙度增强了晶体表面对激光的热吸收，，而圆周轮廓分形维数分布能够很好地表征飞切表面抗激光热破坏的能力；亚表层裂纹的调制增强是损伤晶体的又一重要机制，亚表层裂纹深度与损伤阈值呈相反的映射关系，而与波纹幅值具有同样的变化规律；即抑制波纹的同时，亚表层裂纹将同时得到改善。综合分析发现：波纹幅值是飞切表面必须抑制的制造误差。为了对引致飞切波纹特征的机床主轴振动特性进行分析，本文提出利用二自由度陀螺的技术方程来建立飞切机床空气主轴的振动模型，定性分析加工过程中切削参数对波纹频率与幅值的影响规律。研究发现，频率成分间存在明显的倍频与差频关系。因此，提出通过对主轴转速及转动惯量比的合理设定，实现频率预测。波纹幅值基本随进给量与切深的增加而增大，进给量的影响较切深稍大。极低转速下虽然有利于小幅降低幅值但却以增加表面破损从而增加热损伤为代价。理论及实验结果显示：转速400r/min左右，进给量10μm/r左右，切深10μm左右，刀具前角-45能够得到较好的飞切表面。
[Abstract]:KH_2PO_4 (KDP) crystal laser damage threshold of lower limit of inertial confinement fusion (InertialConfinement Fusion ICF) to enhance the output capacity of the bottleneck of high power laser. The surface morphology of high frequency information and all kinds of defects of optical components in ultra precision machining has important effects on the optical properties. However, currently in the KDP crystal ultra precision fly micro nano cutting research of morphology and its influence mechanism of damage threshold has been reported. This paper studied the characterization methods of KDP micro nano fly cutting surface morphology of main elements, and extract the main parameters can reflect the crystal optical quality; and the establishment of the main surface micro nano mapping relationship between morphology and crystal damage threshold; finally to threshold on the crystal damage morphology parameters greatly as the optimization goal, established the fly cutting spindle vibration model, and combined with the experiment The selection of flying cutting parameters provides an important reference for the ultra precision machining of KDP crystal.
In order to fly cutting crystal surface waviness and roughness were analyzed by using Motif method, the power spectral density, wavelet and fractal to characterize the surface morphology. Analysis shows that the Motif method which can avoid waviness of the average amplitude of single component weights obtained directly on the surface ripple amplitude of one-dimensional, two-dimensional evaluation; the PSD curve and the angular spectrum and the spectral radius can be full band and texture direction of evaluation on the fly cutting surface; wavelet transform can realize extraction and reconstruction and analysis of KDP crystal morphology of 3D multiscale decomposition; fractal dimension can overcome the error of measuring instrument of surface roughness evaluation has important significance to the most real. According to the above method using the comprehensive characterization of the KDP crystal surface micro nano fly cutting.
In order to study the effect of frequency ripple on the laser damage threshold, this paper analyzes the modulation characteristics of wave parameters of incident wave by using PSD and Fourier modal method, KDP fly cutting surface has the characteristics of diversity. The frequency composition of crystal damage threshold risk larger ripple period is concentrated in the 80 m-180 m range, and this range is more sensitive than the ripple amplitude cycle of the injury parameters. Therefore, the average depth of the ripple of the Motif as an approximate measure parameter to measure the fly cutting surface damage threshold size. At the same time, the coupled wave equation based on the harmonic generation, put forward to reduce the fly cutting ripple amplitude is to improve the efficiency and effective measures to improve the frequency doubling crystal the output waveform.
In order to study the surface roughness and subsurface cracks on the laser damage threshold effects, the modulation property of the characteristics were analyzed by using Fourier modal method and fractal theory is introduced to characterize the surface thermal damage. Analysis shows that the roughness of the crystal surface enhanced laser heat absorption, and the fractal dimension of circular distribution to characterize well fly cutting surface anti laser damage; modulation of subsurface crack is an important mechanism to enhance the damage of crystal, subsurface crack depth is contrary to the mapping relationship between the damage threshold, and has the same change with the ripple amplitude; i.e. suppressing ripples and subsurface crack at improved. Comprehensive analysis shows that the ripple amplitude is the fly cutting manufacturing error surface must be suppressed.
In order to cause the spindle vibration characteristics of corrugated fly cutting are analyzed. The vibration model is proposed in this paper to establish air utilization technology of fly cutting machine tool spindle equation of two degree of freedom gyroscope, a qualitative analysis of the effects of cutting parameters in the process of wave frequency and amplitude. The study found that there is obvious relationship between frequency doubling and frequency difference between components. Therefore, put forward by the spindle speed and inertia setting ratio, frequency prediction. Increase the ripple amplitude with the feed rate and cutting depth increases, the influence of feeding amount is slightly larger. The cutting depth at very low speed is helpful to reduce the amplitude slightly but to increase the surface damage to increase the cost of heating damage. Theoretical and experimental results show that the speed of about 400r/min, the amount of feed about 10 m/r, cutting depth of about 10 m, the rake angle of -45 can get good fly cutting surface.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TN241;TH161

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