Math model for bead

It cold be a Gaussion mulitply a Cosin. If the bandwidth of the bright part is the same as that of the dark part, it coud just be a Cosin function. Need to check the cross intensity function again.
[new]: From the intensity of the cross line, we can see the bandwidth of the bright part is not even close to that of the dark part. So it is not a standard Cosin function. A Gaussian function multiply a Cosin function will also not work because it can only change the magnitude but can not change the bandwidth. I think this model is similar with the diffraction of circular aperture except for the magnitude of the central bright part.