Figure 7. Photographs of diffraction patterns from a point light source after interactions with circular barriers of different sizes and  configurations.

A. The Poisson spot in the shadow of a disc.  Although very faint at the exposure utilized for this photograph a series of interference fringes surrounds the Poisson spot within the shadow cast by the disc.  These patterns are functions of interactions of the secondary pulson signals indicated in zone d of Fig. 6.  In contrast, the interference patterns surrounding the shadow of the disc are derived from the interactions of the secondary edge signals with the primary signals (zones c and e) as a function of distance of the disc from the detection screen.

B.The Poisson spot in the shadow of a circular slit.  The pattern (Bessel beam) is analogous to that for the twin slit experiment.

C.A central dark spot exhibited by a circular aperture under specific conditions of the Fresnel zone.  The dark spot results from destructive interference between secondary edge pulsons and the primary signal in Zone A of Fig. 9.

D.Diffraction patterns of circular apertures varying in size at a fixed distance in the Fresnel zone.  Increasing the size of the aperture increases the width of the primary pulson signal.  This increases the ratio of the primary signal to the secondary signal while also changing the phase relationships between it and the secondary edge pulsons.  This procedure creates cyclic patterns between constructive and destructive interference at the centerline and increases the number of fringes at the detection screen.

E.The Airy diffraction pattern for a circular aperture under Fraunhofer conditions.  At the appropriate large distances between the aperture and screen, the secondary edge signals constructively interfere with the primary signal at the centerline to create a single, bright central disc in zone A of Fig. 9.  See also Fig. 10.  The interference patterns surrounding the bright central disc are derived from the mutual interference of the secondary signals in zone B of Fig. 9.  As distance is further increased the Airy disc expands slowly and intensity decreases.  At large distances the pulson fronts of the secondary and primary fronts become essentially parallel and the ray paths for points at the detection screen of the secondary and activating pulsons also become essentially parallel.  Under such conditions changes in intensity modulated by interference effects are very gradual.