Consider a series of N narrow slits separated by distances d. In the far-field approximation, the phase difference as a function of distance d from the slits and angle from the normal is given by
where k is the wavenumber. The intensity due to multiple interference is then
This function has a extrema when
which holds when
giving
The absolute maximum occurs at
Principal maxima occur at
and principal minima at
where is not an integer. There are zeros between principal maxima, and secondary maxima between principle maxima.
Double Slit Interference, Interference
