How does a point object form a zone lens in a hologram?

In holography, a point object forms a zone lens—specifically a sine-wave zone plate—through the interference of two coherent optical fields.1

When a point object is illuminated, it scatters light that acts as one of these fields. This light interacts with a coherent background or reference wave on a recording medium, such as high-resolution film. The resulting interference pattern, which consists of alternate light and dark areas, is recorded as a hologram. This recorded pattern functions as a zone lens because it captures the phase and amplitude information of the light field.12

When this hologram is later illuminated with a collimated beam of light, the zone lens structure diffracts the light to produce two beams: one that converges to form a real image and another that diverges as if originating from a virtual focus. For more complex objects, the resulting hologram is effectively a summation of individual zone lenses, with each point on the object contributing its own specific zone lens pattern.1