Schematic illustration of the adjacent path interference. (a) The one-to-one imaging from near-field x to far-field x′ due to the spatial frequency chirp Δf(x) = − ∂Φ (x)/∂x, and (b) the corresponding far-field intensity distribution of the adjacent discrete harmonics ((q₁,q₂) and ). The shaded area indicates the interference region. The interference components from two paths are from opposite sides of the near-field separated by Δx. The far-field fringe interval is denoted by Δx′.