wavelength: wavelength of the light source in nanometers
slit width: width of each slit in the grating in nanometers
space between slits: spacing between adjacent slits in each dimension in nanometers
number of slits: total number of slits in each dimension
Snapshot 1: This pattern mainly results from the diffraction effect of each slit in the grating—similar to what would be seen with a single slit of the width specified.
Snapshot 2: The fringes here mainly come from interference of different slits in the grating. Each slit is very narrow so the light is spread out well across the viewing area, with the intensity only slightly reducing towards the edges.
Snapshot 3: The interference pattern from each slit is an obvious envelope multiplying the pattern from interference of different slits in the grating.