= Holography
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<Holography> records the <wave interference> between a <holographic object wave> and a known <holographic reference wave>, then uses that record to reconstruct a <wavefront>. The record is a <hologram>. A <photographic plate> or <photodetector> measures <light intensity>; the relative <wave phase> is encoded in the positions and contrast of <interference fringes>, rather than measured directly as an optical oscillation. Reillumination makes the recorded pattern act as a <diffraction grating> that produces an image-bearing field.
The useful change of viewpoint is to preserve a field that can propagate again, instead of only a focused brightness picture. Recovered <complex amplitude> permits refocusing with the <Fresnel propagator>; a spatially extended <hologram> can also supply different viewing directions. The recoverable information is limited by the collected <aperture>, recorded <spatial frequencies>, <optical coherence> and separation of unwanted <diffraction orders>.
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