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.

Aiming at getting the general requirements of the beam combine for ignition scale laser facilities, the analytical expressions including the factors affecting the combine results are derived. The physical meanings of every part are illustrated. Based on these expressions, the effects of the factors, including the beam configuration, piston error, and tip/tilt error, are studied analytically and numerically. The results show that the beam configuration cannot affect the Strehl ratio (SR) of the combined beam, but it influences the FWHM of the main peak and the ratio of the main peak and the side peak. The beam separation should be no more than 1.24 times the individual beam width for the multibeam combine, and be close to the individual beam width for the two-beam combine as much as possible. The piston error can change the characteristics of the combine beam focus, including the peak intensity, the focal spot morphology, the fractional energy contained within a certain area, and the center of mass. For the two-beam combine, a piston error less than 2π∕5 rad is suitable, and for the multibeam combine, the standard deviation of the piston error should be no more than 2π∕10 rad. The tip/tilt error has a great influence on the combined results. It affects the superposition degree of the focal spots of the combined elements directly. A requirement of 0.5 ～ 1 μrad for the standard deviation of the tip/tilt error is adequate.

The fractional Fourier transform (FRFT) of the flat-topped multi-Gaussian beam (FMGB) is investigated based on the three kinds of FRFT optical systems: Lohmann I, Lohmann II, and quadratic graded-index systems. The analytical expressions for the FRFT of the FMGB are derived based on the propagation of the FMGB through the three systems. By introducing a hard-edge aperture function, the analytical expressions for the FRFT of the FMGB carried out by the apertured FRFT optical systems are presented. The FRFT characteristics of the FMGB for the three kinds of FRFT optical systems with and without apertures are discussed in detail. Results show that the three types of FRFT optical systems have the same function when the apertures are ignored but that significantly different characteristics are exhibited when the apertures appear.

The characteristics of the alignment and misalignment multistage spatial filters are presented in this paper based on their effects on the beam quality. First, the approximate analytical expressions of the modulations of a square beam, which are induced by scatterers and an alignment spatial filter pinhole, are derived. Then, the far field analytical expression of the modulated square beam after its propagation through a nonlinear medium is presented. Subsequently, using a square super Gaussian beam, the modulations induced by an alignment and misalignment spatial filter pinhole are illustrated. The suppressing functions of the alignment and misalignment spatial filters on the hot image are investigated. The effects of the misalignment of the multistage spatial filter pinholes on the output beam quality are studied based on two evaluation factors: fluence beam contrast and fill factor. It is shown that the spatial filter pinhole misalignment has significant influences on both the far field and near field of the downstream beam, especially when nonlinear media exist. The results presented in this paper give important references and guidance for the spatial filter design, installation and alignment.

The generalized analytical expression for the propagation of flat-topped multi-Gaussian beams through a misaligned apertured ABCD optical system is derived. Using this analytical expression, the propagation characteristics of flat-topped multi-Gaussian beams through a spatial filter are investigated. The analytical formula of the electric field distribution in the focal plane is also derived for revealing the effects of the misalignment parameters clearly. It is found that different misalignment parameters have different influences on the electric field distributions of the beam focus spot and the output beam characteristics. The intensity distribution of the beam is mainly determined by the misalignment matrix element E, and the phase distribution is affected by the misalignment matrix elements G and E.

Estimation of the far-field centre is carried out in beam auto-alignment. In this paper, the features of the far-field of a square beam are presented. Based on these features, a phase-only matched filter is designed, and the algorithm of centre estimation is developed. Using the simulated images with di?erent kinds of noise and the 40 test images that are taken in sequence, the accuracy of this algorithm is estimated. Results show that the error is no more than one pixel for simulated noise images with a 99% probability, and the stability is restricted within one pixel for test images. Using the improved algorithm, the consumed time is reduced to 0.049 s.

Beam alignment is used to control the pointing, rotation, and position of a beam automatically. We give an overview of the beam alignment system for a four-pass amplifier system. The coupling relationships between dependent quantities and deviations thereof for parameters of key optical elements are analyzed using matrix optics techniques. The rotation characteristics of a near field are discussed. The characteristics of the four-pass adjustment in the cavity spatial filter are shown and the output characteristics are provided. Finally, we develop an adjustment procedure.参考文献原文>R. A. Zacharias, N. R. Beer, E. S. Bliss, S. C. Burkhart, S. J. Cohen, S. B. Sutton, R. L. Van Atta, S. E. Winters, J. T. Salmon, M. R. Latta, C. J. Stolz, D. C. Pigg, and T. J. Arnold, “Alignment and wavefront control systems of the national ignition facility,” Opt. Eng. 43, 2873–2884 (2004).