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强激光复杂光机组件光学元件激光损伤在线检测技术研究
【作者】 彭志涛；
【导师】 魏晓峰；
【作者基本信息】 中国工程物理研究院 ， 光学工程， 2011， 博士
【摘要】 为实现聚变反应所需的物理条件,要求辐照到靶面的激光脉冲能量大于1MJ量级,因此激光驱动器必须具备足够的输出能力和负载能力。研究和实践都表明,3ω波段光学元件的激光损伤阈值较低。终端集成光机组件做为ICF激光驱动器的关键单元组件之一,集成了多种大口径光学元件,处于驱动器的末端,三倍频激光通量高达3.0J/cm2,这种复杂的光机组件的光学元件在接近其损伤阈值的情况下运行,昂贵的频率转换晶体、光栅和透镜等元件在如此高的激光通量辐照下,极易损伤,从而限制了装置的输出能力。光学元件的安全使用策略要求激光设计和运行人员不仅重视光学元件的品质,还要对光学元件进行全流的管理。通过在线检测光学元件的损伤状态,在光学元件损伤增长加速之前将光学元件换下,离线对光学元件损伤进行修复使光学元件可以循环利用,就能延长光学元件的使用寿命。光学元件损伤在线检测是光学元件安全使用策略的重要支撑。随着ICF激光驱动器通量水平的进一步提高,终端集成光机组件负载能力提升迫切需要对终端集成光机组件光学元件损伤状态进行检测。本论文对终端集成光机组件光学损伤在线检测系统和关键技术进行了深入的研究,主要研究内容包含以下几个方面：1.开展了背光照明损伤成像和全内反射照明损伤成像技术研究,提出了基于全内反射分时照明的终端集成光机组件光学元件损伤在线检测(Final Optics Damage Inspection, FODI)总体技术路线,建立了光学元件分时全内反射照明损伤成像信噪比模型；2.研究了高分辨多维空间扫描大口径光学元件损伤成像技术,提出了适合终端集成光机组件光学元件损伤在线检测的成像模块光学方案和结构方案；3.研究了终端集成光机组件光学元件照明技术。提出了基于全内反射大口径元件损伤均匀照明的技术方案,开展了阵列LED和光纤边缘照明技术研究,对比了两种技术方案的优劣,优化了照明参数,研制了可用于终端集成光机组件光学元件全口径照明的光源；4.开展了损伤图像分析技术研究,提出了一种改进的基于局部信噪比增强的(Local Area Signal -to-Noise Ratio, LASNR)特征提取算法并建立一种新颖的信息表示方法,有效的实现了FODI损伤图像的特征提取和信息表示,为后续信息挖掘和光学元件状态评价与决策奠定了基础；提出了通过像素灰度等级辐射标定估算成像后尺寸小于CCD像素尺寸的损伤点大小的检测思想,解决了成像分辨率受限条件下极其微小的损伤点的跟踪检测难题。将亚像素分析技术应用于光学元件损伤点的尺寸检测,利用该技术对损伤点的尺寸进行了计算。5.研制了损伤检测成像模块和照明光源等关键模块,开展了终端集成光机组件光学元件损伤检测综合实验,验证了FODI技术路线,考核了关键技术,实现了对大口径光学元件损伤在线检测,支撑了大口径元件损伤在线检测技术方案的确定。
【Abstract】 Experiment in inertial confinement fusion(ICF) required very strict condition on output ability,beam quality,load capacity and controll ability.In order to achieve the condition in fusion,the energy on target must exceed 1MJ.At the 351nm wavelengh,it was believed that the laser-induced damage threshold of optics is lowed,putting the optics in 351nm of the laser at higher risker to laser-induced damage.With the laser fluence up to 3J/cm2,after few high fluence shots,as a key component,Located at the target chamber,the integrated optics module(IOM) is easy to be damaged.Laser-induced damage of large aperture optics would decrease the optics lifetime,such as KDP cristial,fused cilica lens and sampling grating.et.al,and has been the main limter of imprived the load capacity of laser facility.The management stratege of optics requires the worked to put more attention on optics quality,as well as the management of each process. High-powerlaser-induced material damage is a self-accelerating process. With the subsequent laser shots, the initial damage on the optics will gradually growth. In order to aviod the disaste damage in follow-up shots, the surface damage of optics was be inspected by the online optics damage inspection,when the flaw has grown to the maxmum allowed size,the optics will be replaced and sent to the damage mitigation and repaired. FODI is the base of the safe management stategy of optics. As the construction of the SG-III facity, the demand for final optics damage inspection is increasingly urgent. On-line damage inspection system and key technology research are also urgent, which are the problems need to sovle that research faced now. Based on the above requirement this paper research the final optical damage inspection and key technologies in-depth and the following technological advances have made:Firstly, Proper illumination of the optic to be imaged is critical for the successful performance of the FODI system, Two imaging methods will be employed to illuminate the optics, bright-field back illumination and edge illumination. The first time systematically studied the online damage inspection problem in large, high-power final optics, a roadmap of total internal reflection illumination dark-field imaging technology is presented to achieve online high-resolution damage image of final optics. In order to solve the problem that it is difficult to distinguish the damage from two adjacents optics due to the shallow depth of imaging field, the method of time- sharing illumination of large aperture optics was developed for damage imaging, and the model of signal noise ratio was developed for dark field imgeing mode.Second, the study of techniques for damage imaging to the integrated optics module(IOM),high resolution and many dimensions scanning.The engineering proposal of optics and was develped for IOM damage inspection.Third, proper illumination of the optic is critical for the successful performance of the IOM optics damage inspection, based on total internal reflection, the two edge illumination method was proposed to illuminate the optics, linear array LED light source and fiber laser,and studied to verify the implementation of large aperture optics uniform illumination.Final the parameter of illumination was optimized. It was demonstrated the method of optical components illumination from the corners with the fiber laser to achieve total internal reflection uniform illumination within the full-aperture.Fourth, studed on the image analysis of damage.A modified Local Area Signal-to-Noise Ratio (LASNR) segmentation algorithm was developed to capture signal in the image at every pixel within an object versus the noise in its local neighborhood.With a character method of information, the character extraction and characterization is efficency achieved for data minning.Based on classify and machine learning, the method of data analysis and damage evaluation is proposed. a radiation calibration method is proposed. By increasing the exposure time, a slight damage point can be detected online. Calibration of radiation can solve the problem of point tracking and inspection of very small damage when the CCD pixel object resolution is more than the size of flaw.Fifth, the first time in the country designed and developed a high resolution IOM1 optics damage inspection system (FODI). The integaration experimental was carried out to test the technical proposal and key techniques for FODI. The results show that this technique is feasible for lare aperture optics online damage inspection.