Holograph

Holograph, in manuscript contexts, is a document written entirely by the author in their own handwriting. Such holographs can be drafts, letters, or entire works and are often signed and dated. They are valued as primary sources for dating, provenance, and authenticity because the handwriting directly attests to the creator. Holographic documents may be fragile or altered, and their acceptability as evidence or as literary sources often depends on jurisdictional rules governing authentication and preservation. A holographic will is a related concept: a will handwritten by the deceased that is recognized in some legal systems if it meets local requirements.

In optics, holograph refers to a hologram, the three-dimensional image produced by holography. Holography records the light field by creating an interference pattern between a reference beam and light from an object. The concept arose with Dennis Gabor in 1947 and was realized with lasers in the 1960s. A hologram reconstructs a 3D image when illuminated by coherent light; it often requires a laser and a photosensitive medium. Variants include transmission and reflection holograms, as well as digital holography.

Applications span security features, data storage, art, archival imaging, and scientific visualization.

Despite close spelling, holograph and hologram are not fully interchangeable: holograph usually means the handwritten document, while hologram denotes the optical image; holography is the field.