近年来，在光散射颗粒测试技术中越来越多地采用了高斯光束作为入射光，高斯光束的传播及其物理参数对测量结果至关重要。傍轴近似条件下通过菲涅耳基尔霍夫衍射公式推导出高斯光束垂直入射到不同折射率介质中的传播表达式，并通过数值计算进行验证。结果表明，对于非强聚焦高斯光束，当传播方向与界面垂直时，在不同折射率介质中光束的传播仍然满足高斯分布规律，并且其束腰半径参数不变、束腰位置参数取决于相邻介质的折射率比值。

Gaussian beam has been widely employed in optical particle measurements recently, in which the light propagation and the beam′s parameters are very important to measurement results. An analytical expression of diffracted field of a Gaussian beam through a planar interface is derived based on Fresnel-Kirchhoff diffraction integral and under paraxial approximation, which is checked with numerical calculation. Result shows that, while a Gaussian beam, which is weakly focused, propagates normally through a planar interface between materials of mismatched refractive indices, parameters of beam waist radius keep unchanged and location of the beam waist depends on the ratio of refractive indices of neighboring materials.