Zhu Baoqiang

Algorithm of far-field centre estimation based on phase-only matched filter

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 different 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.

Far-Field Detection System of Laser Beams Alignment Based on Gratings Sampling and On-Axial Illumination

利用高功率激光装置空间滤波器小孔成像和取样光栅的衍射,结合插入的负透镜发散激光来同轴照明小孔,设计出一套新型光路远场监测方案.该方案利用光栅衍射可以灵活取样激光远场,并且在实验平台上进行了实验验证.实验结果表明,其远场监测系统的准直精度达到小孔直径的1.42%,能够满足准直系统远场调整精度(小于小孔直径5%)的要求.

Precision Analysis of New Far-Field Alignment System Using Grating Sampling

光束自动准直系统是高功率激光惯性约束聚变装置的重要子系统,激光远场监测技术是光束自动准直系统的关键技术,基于光栅取样的新型远场监测系统可以利用光栅衍射灵活取样激光远场.对影响光栅取样系统远场监测精度的主要因素进行了分析,结果表明,系统误差为小孔直径的7.49%,包括投影误差和斜成像误差;随机误差小于小孔直径的1%,包括物像关系误差和衍射光耦合误差.

Precise diagnostics for SG-II facility

Diagnostics is important for large laser facilities to monitoring laser status and to analyzing physics phenomena on target. SG-II facility in Shanghai is setup in 2001 with eight beams. Each beams energy is 300J at 351nm, and its pulse width is 1ns. SG-II ninth beam is setup in 2005, its energy is 2700J at 351nm, and its pulse width is 1ns too. In recent years, it is an important international user facility for laser research with precise diagnostics system. With the development of SG-II, a new calorimeter is designed to 400 × 400mm2 in order to measure absolute energy up to 6400J at 351nm. Fast photodiode and 12GHz oscilloscope is used to analyze nanosecond pulse shape. In order to analyze petawatt laser pulse, a single shot auto-correlator is designed to measure pulse width between 0.5~18ps. And pulse contrast is obtained by a cross-correlation with fiber-array, which dynamic range is ~106 when pulse is 1mJ and 10ps. Quality of far-field measurement is 1.1DL for nanosecond pulse,and that is 1.5DL for picosecond pulse.

High Power Laser Multi-Parameter Measurement Technique Based on Integrating Sphere

Aiming at the disadvantage that the traditional measurement technique is sensitive to the incident direction of incident light, a beam-split technique of high power laser multi-parameter measurement based on integrating sphere is proposed. Numerical analysis and simulation about attenuation rate, time waveform of emergent light, and time waveform recovery of incident light are carried out by Monte-Carlo method, which validate the feasibility that the integrating sphere can be used as beam-splitter in laser measurement system. The energy and time waveform of nanosecond laser is measured based on integrating sphere. The theoretical analysis matches well with the experiment result. Experiment and simulation results show that spectrum parameter, energy parameter and time parameter of incident light can be recovered by measuring the parameters of the emergent light, when the light-split technique is used in laser parameters measurement. The proposed technique can conquer the disadvantage that the incident direction of incident light has great influence on the parameters of the emergent light in traditional technique. The proposed technical proposal possesses small volume and is easy to integrate, which can be used in modular design of multiple beam high power laser parameters measurement system.