菲涅耳衍射区超快激光脉冲散斑场特性的研究

Properties of Ultrafast Speckle Fields in Fresnel Diffraction Region

将散斑场的研究拓展到超快激光领域,进而引入了超快散斑的概念。首先在理论上研究了超快脉冲照明随机粗糙表面在菲涅耳衍射区域形成的超快散斑光场及其自相关函数,然后利用光场的自相关、强度系综平均和强度自相关等统计函数导出散斑强度自相关函数。发现超快散斑的强度相关随着时间的推迟逐渐呈现出周期性振荡的特征,且振荡频率依次增大。利用对菲涅耳衍射区超快散斑场的计算模拟,发现了诸如散斑颗粒随时间逐渐增大、颗粒中出现频率越来越大的干涉条纹以及干涉条纹由观察面两侧向中心方向依次消失等一系列全新的动态演化规律。

The studies of the speckle field are extended to the area of ultrafast laser, and the concept of ultrafast speckles is introduced. In the theoretical research, the ultrafast speckle fields in the Fresnel diffraction region and the general expressions of their autocorrelation functions are discussed, and then the speckle intensity autocorrelation function is solved using the optical field autocorrelation and the intensity ensemble average. As time delays, ultrafast speckle intensity space autocorrelation curves present a characteristic of periodic oscillation and the frequency gradually increases. Combined with the computer simulation, the formation and the never-before understood dynamic behaviors of the ultrafast speckles in the Fresnel diffraction region are found and explained. Such dynamic behaviors include the increased speckle grains, the structures of the interference fringes in the speckle grains and the decrease of the spatial period, and the interference fringes gradually disappearing from two sides to the center of the observation plane, etc.