A 10 mW helium-neon laser was used as the light source. The beam that was generated wasthen split using a spatial filtering assembly. The light was then passed through the diffusioncell. The light then proceeded to meet the multiple beam interferometer. After multiple reflections from the interferometer, it was observed that the beam interfered at the screen S to produce interferograms. Every five minutes, an interferogram picture was captured by a CCD camera aimed at the screen and saved in the PC for processing . Since the refractive index is different for different planes in the cell, the light passing through them will have different path lengths. The extremum points will reflect as humps on the fringe pattern. As diffusion proceeds, we will see that the extremum points will shift outwards. Here,to calculate the diffusion coefficient, we need to measure the distance d (between the two extreme points in the interferogram at times t1 and t2.