From the intensity profile above, if d ≪ ≪ λ λ , the intensity will have little dependency on θ θ , hence the wavefront emerging from the slit would resemble a cylindrical wave with azimuthal symmetry; If d ≫ ≫ λ λ , only θ θ ≈ ≈ 0 would have appreciable intensity, hence the wavefront emerging from the slit would resemble that of geometrical optics.