光学表面沾染是导致光学成像系统成像质量降低的重要因素之一。对光学表面被直径d=0.3 mm而颗粒间距不同的颗粒沾染的成像系统进行了测试,相应的分辨率值由奥林巴斯公司编写的软件HYRes 3.1给出。然后采用时域有限差分方法(FDTD)计算了相应的前向散射光强分布。结果表明,随着沾染颗粒间距的减小,前向散射光强的最大值在数值上变化不大,但位置更加远离成像面中心,而且光能更加集中于某些点上,分辨率随之减小;当颗粒间距达到一定值时,分辨率严重降低以致无法由软件读出,而前向散射光的最大值也迅速下降,且几乎位于成像面边缘。因此,在光学表面沾染量较小、不足以造成光能传输率明显改变的情况下,沾染颗粒衍射引起的光能分布的改变可以导致光学成像系统成像质量的降低。

Contaminants on the optical surface is one of the key factors that reduce imaging quality of optical imaging system. The imaging system,which is contaminated by particles with the diameter d=0.3 mm and different distances between particles,is examined firstly. The relevant resolution power is obtained by software HYRes 3.1,which is written by Olympus Corporation. Then FDTD (finite-difference time domain) method is used for calculating the distribution of forward scattering intensity. The results show that the maximum intensity changes a little,but location is away from center of image plane,and light energy concentrates on some point as distance between particles falls. At same time,resolution declines. When distance between particles reaches a fixed value,resolution reduces so badly that it cannot be read out by software,and maximum light intensity,which is situated at edge of image plane,drops rapidly. Therefore,the change of the light-energy distribution brought by scattering of particles can reduce the imaging quality of optical imaging system when contaminants quantity on optical surface is too small to change transmissibility.