A hologram is a recording of the complete light field scattered by an object — both amplitude and phase — encoded as an interference pattern on a photosensitive medium. Unlike ordinary photography which captures only intensity, holography (invented by Dennis Gabor in 1948) uses coherent laser light to record phase information, enabling true three-dimensional image reconstruction.
To record a hologram, a laser beam is split into a reference beam and an object beam. The object beam illuminates the subject; the scattered light interferes with the reference beam at the recording medium, creating microscopic fringes that encode depth. On reconstruction, illuminating the hologram with the reference beam diffracts light to recreate the original wavefront, producing a realistic 3D image with parallax.
Holography has evolved far beyond art displays. Digital holography uses CCD cameras and computer algorithms instead of film, enabling applications in microscopy, non-destructive testing of components, data storage (holographic optical discs), and augmented reality waveguide displays. Computer-generated holograms (CGHs) create arbitrary 3D scenes calculated numerically.
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.