A hologram records the interference pattern between a reference beam and light scattered off an object (the object beam) onto a photosensitive plate. Replaying the plate with only the reference beam diffracts light to reconstruct the full 3D wavefront of the original object.
d = λ / (2 sinθ) (fringe spacing on the plate)
I(x) = |E_ref + E_obj|^2 (recorded interference)
- Laser wavelength — colour of coherent light used; shorter wavelengths give finer fringe spacing and sharper reconstructions.
- Reference beam angle — angle between the reference beam and the plate normal; wider angles compress the fringe spacing.
- Record / Replay — switch between recording the interference pattern (object + reference beams both lit) and replaying it (reference beam only, reconstructing the object).
In Record mode you see both beams converge on the plate, etching fringes. In Replay mode only the reference beam is present, diffracting off the recorded fringes to reconstruct a glowing 3D image of the object.