为满足高功率激光装置光路自动准直系统的高精度要求, 提出一种光束非垂直过孔状态下椭圆光斑的光斑差值快速调节法, 并引入局部自适应阈值二值化算法提高准直图像的定位精度.当椭圆光斑长短轴差值较大时, 利用基于最小二乘法的椭圆拟合改进算法, 求出椭圆光斑长短轴的轴长, 通过远场反射镜调节长短轴轴长差值以调节光斑形状, 直到获得规则的圆形光斑.分析了圆光斑中心与基准位置的偏差值, 将差值转为闭环控制的步进电机调整步数, 实现了高功率激光装置光束的快速自准直.该算法应用在某高功率激光装置光路自动准直系统中, 结果表明, 远场指向精度优于0.033″, 优于目前高功率激光准直系统准直效果, 提高了激光光束的指向性精度.

为提高自动准直效率, 结合以太网, 设计出一套新型光路自动准直控制和检测方案.该方案采用基于耦合矩阵的前馈补偿及图像Jacobian矩阵的近远场串并行准直方式, 并引入局部自适应阈值和二值化算法, 同时将模糊控制算法运用到步进电机的调整过程中, 提高光束近远场图像的处理精度, 降低系统的准直时间.实验结果表明, 该准直系统远场的平均调整误差为空间滤波器小孔直径0.44%, 能够满足准直系统远场调整精度(小于小孔直径5%)的要求, 准直时间由原有的30 mins缩短至12 mins左右.

基于印压断裂力学理论分析了磷酸二氢钾晶体表面缺陷面积与中位裂纹深度的关系.在刀具参量和主轴转数一定的情况下, 采用不同切削深度和进给速率对磷酸二氢钾晶体进行单点金刚石飞切加工实验, 并计算晶体表面单位面积缺陷的占比系数.实验结果表明, 晶体表面缺陷深度与面积占比系数成正相关, 与理论分析结果相符, 进而提出了利用计算晶体表面缺陷占比系数估测缺陷深度的方法.最后基于该方法得到高效率切削步骤, 并加工获得了表面粗糙度算术平均值优于5 nm的超光滑晶体表面.

In order to monitor the volatilization and deposition of organic contaminants on optics surfaces in high power laser facility, online detection of airborne molecular contaminant was investigated based on quartz crystal microbalance and optical microfiber. First, the response performance of quartz crystal microbalance for different densities of airborne molecular contamination was tested. Then the comparison of quartz crystal microbalance and optical microfiber in detecting the surface mass density of airborne molecular contamination was implemented with the view factor method. The characteristics of airborne molecular contamination deposited on optical surface were also studied. The experiment results show that quartz crystal microbalance and optical microfiber have the similar response performance, and thus they can be applied in online airborne molecular contamination detection. When the surface mass density of airborne molecular contamination is larger than 0.5×10－5g/cm2, optical microfiber is preferred due to the higher precision and larger response speed. The more the density of airborne molecular contamination is, the more it deposits on the optics.

In order to monitor the volatilization and deposition of organic contaminants on optics surfaces in high power laser facility, online detection of airborne molecular contaminant was investigated based on quartz crystal microbalance and optical microfiber. First, the response performance of quartz crystal microbalance for different densities of airborne molecular contamination was tested. Then the comparison of quartz crystal microbalance and optical microfiber in detecting the surface mass density of airborne molecular contamination was implemented with the view factor method. The characteristics of airborne molecular contamination deposited on optical surface were also studied. The experiment results show that quartz crystal microbalance and optical microfiber have the similar response performance, and thus they can be applied in online airborne molecular contamination detection. When the surface mass density of airborne molecular contamination is larger than 0.5×10－5g/cm2, optical microfiber is preferred due to the higher precision and larger response speed. The more the density of airborne molecular contamination is, the more it deposits on the optics.

To overcome the problem of cleanliness in the laser′s internal cavity, a glass cavity design for a Nd: glass slab amplifier was proposed, which uses UV-stop quartz glass for its main structure.The design of the main structure of the glass cavity and the sealing are optimized, and metal-coated surfaces are used to prevent light from escaping.The cleanliness of the stainless steel cavity of the slab amplifier of the SG-II-UP laser and the glass cavity of a 100 slab amplifier were compared; the cleanliness of the glass cavity was found to be 70% better than that of the stainless cavity. Further, advanced system analysis program was used to simulate the designed amplifier, with the pumping ratio of the Nd: glass in the glass cavity being increased by 8.84%.Thus, the glass cavity decreases the production of aerosols and enhances the pumping ratio of the Nd∶glass.

To overcome the problem of cleanliness in the laser′s internal cavity, a glass cavity design for a Nd: glass slab amplifier was proposed, which uses UV-stop quartz glass for its main structure.The design of the main structure of the glass cavity and the sealing are optimized, and metal-coated surfaces are used to prevent light from escaping.The cleanliness of the stainless steel cavity of the slab amplifier of the SG-II-UP laser and the glass cavity of a 100 slab amplifier were compared; the cleanliness of the glass cavity was found to be 70% better than that of the stainless cavity. Further, advanced system analysis program was used to simulate the designed amplifier, with the pumping ratio of the Nd: glass in the glass cavity being increased by 8.84%.Thus, the glass cavity decreases the production of aerosols and enhances the pumping ratio of the Nd∶glass.

Magnetic reconnection (MR) is a universal physical process in plasma, in which the stored magnetic energy is converted into high-velocity flows and energetic particles. It is believed that MR plays an important role in many plasma phenomena such as solar fare, gamma-ray burst, fusion plasma instabilities, etc.. The process of MR has been studied in detail by dedicated magnetic-driven experiments. Here, we report the measurements of magnetic reconnection driven by Shenguang II lasers and Gekko XVII lasers. A collimated plasma jet is observed along the direction perpendicular to the reconnection plane with the optical probing. The present jet is very different from traditional magnetic reconnection outflows as known in the two-dimensional reconnection plane. In our experiment, by changing the delay of optical probing beam, we measure the temporal evolution of jet from 0.5 ns to 2.5 ns and its velocity around 400 km/s is deduced. Highcollimated jet is also confirmed by its strong X-ray radiation recorded by an X-ray pinhole camera. With the help of optical interferograms we calculate the jet configuration and its density distribution by using Abel inverting technique. A magnetic spectrometer with an energy range from hundred eV up to one MeV is installed in front of the jet, in the direction perpendicular to the reconnection plane, to measure the accelerated electrons. Two cases are considered for checking the acceleration of electrons. The results show that more accelerated electrons can be found in the reconnection case than in the case without reconnection. We propose that the formation and collimation of the plasma jet, and the electron energy spectrum may be possible directly influenced by the reconnection electric field, which is very important for understanding the energy conversion in the process of MR and establishment of the theoretical model. Finally the electron energy spectra of three different materials Al, Ta and Au are also shown in our work. The results indicate that the higher atomic number material can obtain a better signal-noise ratio, which provides some helpful references for our future work.

Wavefront control is a significant parameter in inertial confinement fusion (ICF). The complex transmittance of large optical elements which are often used in ICF is obtained by computing the phase difference of the illuminating and transmitting fields using Ptychographical Iterative Engine (PIE). This can accurately and effectively measure the transmittance of large optical elements with irregular surface profiles, which are otherwise not measurable using commonly used interferometric techniques due to a lack of standard reference plate. Experiments are done with a Continue Phase Plate (CPP) to illustrate the feasibility of this method.

Reconnection of the self-generated magnetic fields in laser-plasma interaction was first investigated experimentally by Nilson et al. [Phys. Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a solid target layer. An elongated current sheet (CS) was observed in the plasma between the two laser spots. In order to more closely model magnetotail reconnection, here two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated CS a fanlike electron outflow region including three well-collimated electron jets appears. The (> 1 MeV) tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as they are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The ejection also induces a secondary CS.