Hologrammi

Hologrammi (hologram) is a recording of the light field of an object that stores both the intensity and the phase of light. When illuminated by a suitable reference beam, the hologram diffracts light to reproduce a three-dimensional image that changes as the observer moves, providing parallax and depth cues without a physical object present.

Principle: In holography, light from a coherent source is split into an object beam that illuminates the scene and a reference beam aimed at the recording medium. The interference between these beams creates a pattern that encodes the wavefront of the light. Upon reconstruction, the recorded interference acts as a diffractive optical element that recreates the original wavefront.

History: The concept was introduced by Dennis Gabor in 1948 as an extension of holography for electron microscopy. Practical holograms became possible after the invention of the laser, with the first working holograms demonstrated in the early 1960s by Emmett Leith and Juris Upatnieks.

Formats and techniques: Holograms can be transmission (viewed with coherent light) or reflection (viewed with white light). Off-axis and in-line geometries describe the arrangement of beams. Digital holography uses electronic sensors to record holograms and numerical reconstruction rather than optical replication.

Applications: Holography is used for data storage research, security features on banknotes and ID cards, art, medical imaging, and holographic displays for visualization and augmented reality. In metrology, holographic interferometry measures small deformations and vibrations.