Local foci of a parabolic binary diffraction lens

The intensity distribution on the optical axis of a parabolic binary diffraction lens is theoretically and experimentally studied. The binary diffraction lens is shown to form an array of focal spots of near-equal intensity on the optical axis. In each local focus, the focal-spot size decreases as the square of the focus number until the paraxiality condition is broken. Theory and experiment are shown to be in good agreement.