The process of producing a holographic reconstruction involves the phenomenon of diffraction of light. When the photographic plate is developed, the fringe pattern acts as a diffraction grating and when the reference beam is incident upon the photographic plate, it is partly diffracted into the same angle θ at which the original object beam was incident. Thus, diffraction grating created by the two waves interfering has reconstructed the object beam and when we look into the hologram, we sees the object even though it may no longer be present.