理论计算了诊断系统空间分辨对辐射热波烧穿图像平整度的影响，发现它会显著降低图像平整度。优化了三色谱仪诊断系统空间分辨并在神光Ⅱ装置上开展了验证性实验，结果表明420 eV能区29 μm空间分辨设置下测量到的热波图像平整区域有了明显改进，热波前沿涨落不超过4.7 ps，远小于X光条纹相机约20 ps的测量不确定度。在此改进下，热波烧穿图像平整度已经不是影响数据分析可靠性的主要因素。

In the field of laser fusion, the ablation rate of target material is mainly measured by the diagnostic of thermal wave burn-through images. The planarity of such images could make great influences on the uncertainty of ablation rate. The improvement of the image planarity has been made based on the theoretical and experimental study of the influence of diagnostical spatial resolution. After optimizing the spatial resolution to 29 μm on the 420 eV channel of the diagnostic, we proved with SG-II experiment that the planarity area of thermal wave burn-through image has been increased largely and the fluctuation of thermal wave front is only 4.7 ps which is much less than the temporal measurement uncertainty (about 20 ps) of X-ray streak camera.