Thank for your help
and sry for my late respond

Please take a look at the picture of this document:

d    , d'   , a(1)   ,  a(2){  ,    , wavelength of the light  must be adjust able

and if is possible the simulate must show  i: The fringe width  and  a: ( distance betwen s(1) and s(2) )

By the way it must show the diffraction

Best Regards