I’d like to make a reflective diffuser surface (basically engineered diffuser). Behavior would be:

The diffusiveness is defined by grain size (p), 

and the incoming ray would be randomly diffused according to diffraction equation:

sin(theta_out) = sin(theta_in) ± lambda/p * randomness

randomness varies between w0-1]

I couldn’t find it in the scattering option. How could I model this? 
If given instruction, I think I could use user defined surface.. but I’m not sure if there is easier way. 

Thank you for your attention!