摘要：从理论和实验两方面出发,讨论了颗粒的折射率对光能分布及粒径分布反演结果的影响,同时给出了衍射理论的完整适用条件及基于衍射理论的粒度仪的最佳光靶尺寸。

关键词： 颗粒测量;衍射理论;Mie理论

Abstract： T he Fraunhofer diffraction theory （FDT ） is widely applied in particle sizing．T hrough theoretical and experimental comparison the effects of refractive index on energy distribution falled in photo-detector are discussed．And combined with some conclusions drawn out by other researchers the confining factors of FDT are presented．As a result we draw out its whole application range for particle measuring and the best light-collectionangle for particle sizer based on FDT． 

Keywords：particle measurement；Fraunhofer diffraction theory；Mie′s theor