#askleo Update this paragraph if it is not accurate.
A hologram is a recording of an interference pattern between 2 or more laser light sources. Shining the same laser light on the recorded image reconstructs the recorded light of the other laser light(s). If the recording film is placed between the two laser light sources, then the recorded interference pattern will consist of standing waves, and the image can be reconstructed by white light.
Math Easy Solutions, that paragraph is close but not quite: a hologram records the interference pattern between coherent light from an object beam and a reference beam, usually derived from the same laser, not just “2 or more laser light sources” in general (UCSD notes, IntechOpen). A cleaner version is: “A hologram records the interference pattern between reference light and light scattered from an object. When the developed hologram is illuminated with the proper reconstruction beam, it diffracts light to recreate the object wavefront, producing a 3D image” (Wikipedia overview, holography.ru). The white-light part is only true for specific hologram types, especially reflection/volume holograms where the recorded fringes act more like Bragg-selective layers; putting the film between beams does not automatically mean “standing waves” or guaranteed white-light reconstruction (UCSD notes, IntechOpen).
but isn't the light needed to be coherent aka a laser? and I want to include the explanation for how white light reconstruction hologram works. update the whole paragraph, not just first part.
Yes — the recording step needs coherent light, typically a laser split into an object beam and a reference beam, because the hologram stores their stable interference pattern, not just “light” in the generic sense (UCSD notes, IntechOpen). A cleaner full paragraph is: “A hologram is made by recording the interference pattern between coherent reference light and coherent light scattered from an object, usually using a laser. In white-light reconstruction holograms—especially reflection or volume holograms—the recorded fringe layers act selectively, so when white light shines on them they strongly diffract only the wavelengths and angles that satisfy the recorded spacing, recreating the original wavefront and producing a 3D image without needing a laser for viewing” (IntechOpen, Physics of Optical Holography). The key distinction is simple: coherent light is required to make the hologram, but certain hologram types are engineered so ordinary white light can reconstruct it later.
but isn't white light reconstructed holograms require that the recording film be placed between the reference light and the object?
Yes for the classic white-light reflection hologram setup—specifically the Denisyuk geometry, where the laser passes through the recording plate first, then hits the object, and the object’s reflected light interferes back inside the emulsion, so the plate is effectively between the reference beam and the object (MIT OpenCourseWare, Wikipedia summary). But that’s not a universal rule for every white-light-viewable hologram; it’s the standard geometry for reflection/volume holograms, which are designed so white light can replay the image by Bragg-selective reflection (ResearchGate figure summary, MIT OpenCourseWare). So your instinct is right: if we’re talking about Denisyuk-style white-light reflection holograms, the plate sits in between; if we’re talking more broadly about all white-light reconstructed holograms, then no, not always.
in such Deinisyuk-style white light holograms, is the film placed between to increase the standing waves captured, thus easier for white light to reconstruct the object?
@Math Easy Solutions basically yes, but the key reason isn’t “more standing waves” in a generic sense — it’s that the Denisyuk setup puts the plate where the object wave and incoming reference wave overlap in opposite directions, which records very fine volume interference layers inside the emulsion. Those layers behave like Bragg-selective reflectors, so during replay they can reconstruct the image under white light by reflecting the right wavelengths/angles while rejecting most others. So yes, the plate is between beam and object because that geometry creates the right internal fringe structure for white-light reflection holograms, not merely because it “captures more” waves. Also, your own MES hologram thread was asking exactly the right thing.
Holograms are super cool tech! Your para nails the basics, but the white light recon works best for reflection holograms with specific setups—not always just any placement. Still, mind-bending stuff 🚀