🎭 Holography

A hologram records the complete wavefront — the direction and phase of light from every visible point on the object. When reconstructed, your eyes receive different rays depending on viewing angle, just as with a real object, creating genuine parallax and depth perception rather than a 2D optical illusion.

Reflection holograms (like those on credit cards) can be viewed in white light. Transmission holograms typically need laser or monochromatic light to reconstruct clearly. The white-light rainbow hologram uses a cylindrical geometry to work under ordinary illumination.

Stereoscopy presents two slightly different flat images to each eye to create a depth illusion. Holography reconstructs an actual 3D wavefront, so the viewer can move their head and see around objects, there is no screen between them and the image, and accommodation (focus) changes naturally with depth.

Digital holography allows microscopic 3D imaging without lenses, provides quantitative phase maps of transparent objects (like living cells), enables vibration and deformation measurements of mechanical parts (holographic interferometry), and is being developed for lensless endoscopy and AR displays.

Holographic data storage encodes data as 3D interference patterns throughout the volume of a crystal or polymer disc, potentially storing terabytes per disc. Multiple patterns can overlap using different reference beam angles, but commercialisation has been limited by cost and material stability challenges.