在冲击波过程中，利用成像型速度干涉仪探测样品自由面的速度时，散斑的叠加使得干涉曲线被严重干扰，影响了速度信息的精密提取。在理论上从光路的角度分析了系统中可能造成散斑的两种因素: 靶面粗糙度和多模光纤。在实验上设计了三种照明方式分别对这两种因素进行验证。离线实验的结果表明，多模光纤的引入对散斑的产生起了主要的作用，这对抑制乃至遏制散斑的产生具有很好的指导性意义。

When we detect the velocity of free surface using imaging velocity interferometer system for any reflector (VISAR) in the shock wave propagation, speckles severely disturb the interference fringe so that it is hard to get the velocity accurately. In this paper, we theoretically analyze two possible factors in terms of optical path that may introduce speckles: roughness of the plat of target and multimode fiber. Then we design three illumination ways to verify these two factors separately in experiment. The result of offline experiment shows that multimode fiber is the main reason for the emergence of speckles and this has instructive value for depressing speckles.