飞秒脉冲激光入射光学薄膜形成瞬态光场分布是一个非稳态过程，该过程不同于纳秒脉冲或连续波入射的情形，不能直接采用求解薄膜特征矩阵的方法进行处理。采用多光束叠加的方法建立了超短脉冲入射单层膜的反射率和内部光强分布的理论模型，并根据ZnS薄膜材料的参数和单层增反膜的特点进行了数值计算。结果表明，对单层增反膜，薄膜反射率与脉宽成正比，并随脉宽增加逐渐趋近于连续波入射时的情形。在同一脉宽下，膜层厚度增加，反射率下降，且反射脉冲形状也发生改变。膜层中的光强分布计算结果也明显不同于连续波辐照情形，且薄膜厚度越大，差异越显著，表现为连续波入射时，膜层内的光强分布呈等振幅的波动，而超短脉冲入射时，波动的振幅逐渐增大，在膜层和玻璃分界处达到最大值。

Different from the light distribution along the propagation direction in optical thin-film induced by nanosecond pulse or continuous wave, the one irradiated by femtosecond laser pulse is an unsteady process, and can not be solved directly by characteristic matrix of coatings. The model is setup by means of multiple-beam interferometry in time domain, and simulated with the parameters of ZnS material after that. The result reveals that, to single layer reflecting film, the reflectance is proportional to the pulse width, and equals ultimately to what illuminated by continuous wave. Furthermore, under the same pulse width, the reflectance decreases with the increase of the film thickness. The distinction of light intensity distribution induced by ultrashort laser pulse and continuous wave is obviously, as well as the increase of the film thickness. In detail, the curve of intensity distribution in the film irradiated by continuous wave flunctuates with the fixed amplitude. However, it grows up gradually under the ultrashort laser pulse.