In this paper, we use Fresnel diffraction from a phase step in transmission to measure the diffusion coefficient in a transparent liquid. A transparent glass plate immersed vertically in a cell containing two diffusing liquids makes a phase step in transmission. When it is illuminated by a parallel beam of light, the diffraction pattern is formed on a screen perpendicular to the direction of the light beam. The diffusion of liquids inside the cell leads to the variation of the diffraction pattern along the edge of the glass plate. The refractive index gradient in the liquids is then obtained by analyzing the diffraction patterns at different times after the beginning of the diffusion process. We then get the diffusion coefficient from the measured gradient. Using this method, we study the diffusion process of the sucrose-water solution and report the diffusion coefficient with a reliable accuracy.

在本文中，我们使用来自透射阶段的菲涅耳衍射来测量透明液体中的扩散系数。垂直浸入含有两种扩散液体的池中的透明玻璃板在透射中产生相位阶跃。当它被平行光束照射时，在垂直于光束方向的屏幕上形成衍射图案。细胞内液体的扩散导致沿玻璃板边缘的衍射图案发生变化。然后通过分析扩散过程开始后不同时间的衍射图案来获得液体中的折射率梯度。然后我们从测量的梯度中得到扩散系数。使用这种方法，