中文摘要：

聚焦特性是一项非常重要的技术指标，它直接决定着激光装置的峰值功率密度。提出了一种大口径、高能量激光的聚焦特性诊断方法，可用于实现皮秒拍瓦激光系统的聚焦特性在线诊断功能。该方法设计了基于长焦距透镜法的高精度、低误差的远场测量单元，然后通过焦斑测量单元的测试数据来校验远场测量单元，最后提供皮秒拍瓦激光聚焦特性的实时诊断功能。实验结果表明，远场测量单元和焦斑测量单元的测试数据之间的相似度接近于1。因此，可以通过远场测量单元的测试数据，结合皮秒拍瓦激光的能量、脉宽数据，实现物理实验过程中的峰值功率密度实时监测功能。

英文摘要：

Focusing performance is an important parameter to improve peak power intensity of a laser facility. This paper provides a diagnostic method of focusing performance in order to realize a function of online diagnosing for focusing performance in petawatt laser. A high preciseness and low tolerance far-field diagnostics unit is designed in this method. Then measurement data is testified by a focal spot measurement unit in target room. At last the far-field diagnostics unit can be used to prove online diagnosing for focusing performance in petawatt laser. Experimental result shows that similarity between the far-field diagnostics unit and the focal spot measurement unit is about 1. So measurement data of far-field diagnostics unit can be used to diagnose peak power intensity with energy data and pulse width data when online diagnosing of peak power intensity in physics experiments is realized.