How Holograms Store Depth Information

A photograph records how bright light was at each point on a flat sensor. A hologram records something a photograph throws away entirely: the phase of the light wave, meaning exactly where each wave crest was at the moment of exposure. That extra piece of information is what lets a hologram reconstruct a full three-dimensional light field, allowing a viewer to shift their head and see around objects in the image, something no ordinary photo permits. The mechanism behind that trick, interference between two laser beams, is one of the more elegant pieces of applied physics in everyday use, showing up on credit cards, currency, and inside optics labs studying next-generation data storage.

Gabor's original insight

Hungarian-British physicist Dennis Gabor invented holography in 1947 while trying to improve the resolution of electron microscopes, and he carried out the first working experiments in 1948, a technique he originally called "wavefront reconstruction" (SPIE, 2023). Gabor later coined the term "hologram" from the Greek "holos," meaning whole, because the technique recorded the entire wave, both its brightness and its phase, rather than just brightness. Between 1948 and 1951 he published three papers giving a full mathematical treatment of the method, equations detailed enough that they still underpin modern holography (SPIE, 2023).

The Nobel Prize in Physics 1971 went to Gabor "for his invention and development of the holographic method," awarded by the Royal Swedish Academy of Sciences more than two decades after his original insight (Nobel Prize, 1971). That gap between invention and recognition is telling. Gabor's original electron-microscopy application never really worked as intended, and for over a decade holography was a mathematically elegant idea without a practical light source capable of making it useful, since none of the light sources available to Gabor in the late 1940s could hold a stable phase relationship long enough to record a usable interference pattern.

Why ordinary photography discards depth information

A camera sensor or piece of film can only register intensity, essentially how much light energy hits each point, and intensity alone can't distinguish between two light waves that differ only in phase (that is, in exactly when their peaks and troughs arrive). Depth information about a three-dimensional scene is encoded in subtle phase differences between light waves reflecting off objects at different distances from the observer. A standard photograph physically cannot capture that information, no matter how high its resolution or how many megapixels the sensor packs in.

This is a genuinely different kind of limitation than resolution or dynamic range. Doubling a camera's pixel count doesn't get it any closer to recording phase, because a photodiode's basic physical response is to integrate incoming light energy over time and space, discarding the wave's timing information as a byproduct of how the sensor works. Phase has to be converted into something intensity-sensitive detectors can register, which is exactly what an interference pattern does.

The laser problem: why 1960 mattered as much as 1947

Holography requires the object beam and reference beam to interfere in a stable, predictable pattern, which depends on the light being coherent, meaning its waves maintain a fixed phase relationship over the distances and exposure times involved. Ordinary light sources, including the mercury-arc lamps Gabor used in his original experiments, emit waves with phase relationships that shift rapidly and randomly, which washes out any interference pattern before it can be recorded onto film. Gabor's early holograms were consequently faint, low-quality, and plagued by a ghostly duplicate image, an artifact of the specific optical setup he used rather than a fundamental flaw in the idea itself.

That changed in 1960, when American physicist Theodore Maiman at Hughes Research Laboratories built the first working laser, a pulsed ruby laser that produced the first practical source of highly coherent light (search summary drawing on Britannica's laser history). A laser's light waves march in lockstep, staying in a fixed phase relationship over distances far longer than anything achievable with a filtered arc lamp, which is precisely the property holography needs. Coherent light is the raw material holography is built from; without it, an interference pattern simply never forms cleanly enough to record.

Gabor's holography sat unused as a laboratory curiosity for roughly thirteen years, from 1947 until the 1960 invention of the laser, because no available light source before then could hold a stable enough phase relationship to record a usable interference pattern.

Two years after Maiman's laser, in 1962, physicists Emmett Leith and Juris Upatnieks at the University of Michigan built the first laser-based transmission holograms, adapting techniques from side-scanning radar research to produce dramatically sharper, ghost-free images compared to Gabor's originals. That same year, Soviet physicist Yuri Denisyuk independently developed volume, or reflection, holography, a technique that could be viewed under ordinary white light rather than requiring a laser for playback, a leap that made holograms far more practical to display outside a physics lab.

Interference: the trick that makes phase visible

Holography solves the phase-recording problem by never trying to record phase directly. Instead, it records an interference pattern, created by splitting a coherent laser beam into two parts: an object beam, which reflects off the subject and carries its phase information, and a reference beam, which travels a known, unaltered path directly to the recording medium. Where the two beams meet at the film or plate, they interfere, reinforcing each other at some points and canceling at others, based on the relative phase between them at each location.

This interference pattern looks like a chaotic scramble of fine light and dark fringes to the naked eye, nothing recognizable as an image. But it encodes both the intensity and the phase of the original object beam indirectly, through the spacing and contrast of those fringes, which is exactly the extra information a plain photograph loses. Under a microscope, the fringes in a typical hologram can be spaced only a fraction of a micrometer apart, fine enough that the recording medium (originally photographic emulsion, and now increasingly a digital sensor or photopolymer) has to resolve detail far beyond what ordinary photography demands.

Why do holograms need laser light to work?

Recording a usable interference pattern requires the object and reference beams to stay in a stable, predictable phase relationship throughout the exposure, a property called coherence. Ordinary light sources emit waves with rapidly, randomly shifting phase relationships, which washes out any interference pattern before it forms. A laser's highly coherent output is what makes the fringe pattern stable and recordable in the first place.

Reconstruction: replaying the wave itself

To view a hologram, the developed plate is illuminated again with a beam matching the original reference beam's angle and wavelength. The microscopic fringe pattern etched into the plate acts as a diffraction grating, a surface with fine, repeating structure that bends light at specific angles depending on wavelength and spacing. That grating bends the reconstruction beam in exactly the pattern needed to recreate the original object beam's wavefront, phase and all, so the light leaving the plate behaves as though it were still bouncing off the original object.

Think of it like a mold used to cast a statue. The mold itself looks nothing like the final statue; it's an inverted, encoded version of the shape. But feed the right material (in this case, light) through that mold in the right way, and out comes a faithful reproduction of the original three-dimensional form, viewable from multiple angles exactly as the real object would be. A second useful analogy is a phonograph record: the grooves cut into vinyl look nothing like music, they're a physical encoding that only produces sound when read back correctly, at the right speed, with the right stylus. A hologram's fringe pattern is similarly meaningless until "read back" with light of the correct angle and wavelength.

What actually happens at the microscopic fringe level?

Each fringe acts as a tiny mirror-like element that redirects part of the illuminating beam. Because the fringes vary continuously in spacing and depth across the plate, the sum of all these tiny redirections reconstructs a full three-dimensional wavefront rather than a single flat image, which is why the reconstructed scene has real depth rather than looking like a projected photograph.

Why holograms show parallax and photographs don't

Because the fringe pattern encodes the entire wavefront rather than a single flat projection, different parts of the hologram plate contain slightly different perspective information, the same way different points on a window would show a slightly different view of a scene behind it. This is why a viewer moving their head in front of a hologram sees the image shift and reveal different angles, an effect called parallax, exactly as they would looking at the real object. A flat photograph cannot reproduce that effect regardless of resolution, because a photograph only ever encodes one fixed viewpoint, frozen at the moment of exposure.

Property	Standard photograph	Hologram
Information recorded	Light intensity only	Light intensity and phase
Recording method	Direct image focusing onto film or sensor	Interference pattern between object and reference beams
Depth perception when viewed	None (flat image)	Full parallax; viewer can see around objects
Requires coherent light source	No	Yes (laser)
Viewing under white light	Yes, always	Only reflection/Denisyuk holograms; transmission types need laser or filtered light
Fragment still shows full scene	No, cropped area is lost permanently	Yes, from a narrower range of angles

Photographs and holograms diverge because one records intensity at fixed points and the other records an interference pattern spread across the whole surface.

Hologram types: transmission, reflection, and computer-generated

Not every hologram is viewed the same way, and the differences trace directly back to how the recording geometry captures the interference pattern.

Transmission holograms, the type Leith and Upatnieks pioneered in 1962, are recorded with the object and reference beams arriving from the same side of the plate. They must be viewed by shining a laser (or laser-like collimated light source) through the plate from behind, with the viewer looking at the light that passes through and reconstructs on the far side. This makes them impractical for casual display but useful in laboratory and scientific contexts where controlled lighting is available.

Reflection holograms, sometimes called Denisyuk holograms after their 1962 Soviet inventor, are recorded with the reference beam and object beam arriving from opposite sides of the plate, which builds fringe layers through the depth of the recording medium rather than across its surface. That layered structure lets the hologram act as its own wavelength filter, so it can be viewed under an ordinary white light bulb or sunlight, reflecting back only the wavelength (and thus color) it was recorded with. This is the technology behind most decorative and fine-art holograms sold today, since it requires no laser for viewing.

Computer-generated holograms (CGH) skip the physical object entirely. Instead of recording light bounced off a real subject, software calculates what an interference pattern would look like for a mathematically defined 3D scene and then either prints or etches that calculated pattern directly onto a surface, or displays it dynamically on a spatial light modulator. This is the approach behind most security holograms on modern currency and identification cards, since it allows precise, difficult-to-forge microstructures without needing a physical laser setup for every print run, and it is also the technology being explored for holographic displays that could someday update in real time like a video screen.

Type	Recording geometry	Viewing light needed	Typical use
Transmission	Object and reference beams, same side	Laser or collimated coherent source	Laboratory optics, scientific demonstration
Reflection (Denisyuk)	Object and reference beams, opposite sides	Ordinary white light	Fine-art holograms, display pieces
Computer-generated (CGH)	Calculated, not physically recorded	Varies (often white light or laser, depending on print)	Security features on currency and ID cards, research displays

The three hologram families differ mainly in how light needs to be delivered at viewing time, a direct consequence of how the interference pattern was recorded or calculated.

Where holography does real technical work

Beyond novelty art, the most visible everyday application of holography is security. Many national currencies and credit cards carry embossed, computer-generated holograms specifically because their microscopic diffraction structures are difficult and expensive to replicate outside specialized equipment, making them a practical anti-counterfeiting layer.

The same phase-recording principle also underlies active research into holographic data storage, an approach that records data as interference patterns throughout the volume of a photosensitive medium rather than only on its surface, in principle allowing many data layers to be stored in the same physical space by varying the reference beam's angle for each layer (Wikipedia, summarizing IEEE and industry sources on holographic data storage). InPhase Technologies, a company spun out of Bell Labs research in December 2000, was among the most prominent efforts to commercialize page-based holographic storage, aiming to record and read entire "pages" of encoded data as single holograms rather than bit by bit (EBU Technical Review on InPhase's holographic storage approach). Related research into bit-wise "micro-holographic" storage, where each individual bit is written as a tiny Bragg reflection grating, continues in academic optics labs as researchers look for ways to push optical storage density well beyond what conventional discs can achieve (ResearchGate summary of InPhase Technologies' demonstration platform).

A third, less flashy but genuinely useful application is holographic interferometry, an engineering technique that detects microscopic deformations in materials by comparing interference patterns recorded before and after a mechanical or thermal stress is applied to an object. Because holography preserves phase information with such precision, even nanometer-scale shifts in a surface's shape show up as visible fringe changes when the two holograms are compared, which makes it valuable for nondestructive testing of aircraft components, pressure vessels, and other structures where invisible microcracking would otherwise go undetected until failure.

What people get wrong about holograms

A common misconception, reinforced by pop culture depictions of "holographic" projections floating in mid-air with no physical recording medium, is that holography is primarily about projecting a 3D image into empty space. Actual optical holography always requires a physical recording medium, whether a photographic plate, photopolymer film, or digital sensor, plus specific illumination conditions to reconstruct the image. Free-floating volumetric displays and stage effects use entirely different technologies and don't rely on interference-pattern recording at all.

Most floating projection effects seen in concerts and stage shows, for instance, use a centuries-old illusion technique called Pepper's Ghost, which reflects a projected image off an angled sheet of glass or transparent film to create the appearance of a figure floating on stage. It shares no underlying physics with Gabor's wavefront reconstruction and cannot show real parallax the way an actual hologram does, since it is fundamentally a two-dimensional projection viewed from a fixed angle.

A second misconception is that cutting a hologram in half destroys half the image. Because the interference pattern is distributed across the entire plate rather than mapped point-to-point like a photograph, a smaller fragment of a hologram can still reconstruct the complete scene, just from a narrower range of viewing angles and often at reduced resolution and brightness. This is a direct consequence of how the recording works: every point on the plate receives light from the entire object during exposure, so every point retains at least some information about the whole scene, unlike a photograph where each point on the film corresponds to one specific point on the subject.

A third, more subtle confusion is treating "hologram" as synonymous with any glossy, shifting, rainbow-colored sticker. Many of those cheap decorative stickers are not true holograms at all but diffraction gratings or simpler embossed patterns designed to scatter light attractively without encoding a genuine three-dimensional wavefront. Real holograms, by contrast, reconstruct actual depth and parallax that shift consistently and predictably as a viewer moves, which is a useful test for distinguishing a genuine hologram from a decorative imitation.

The takeaway

Holograms work by recording an interference pattern between two laser beams rather than a direct image, capturing both the intensity and the phase of light reflected from an object. That extra phase information, thrown away by every ordinary photograph, is precisely what allows a reconstructed hologram to show real parallax, letting a viewer look around an object exactly as they would if it were physically present. Dennis Gabor's 1947 insight had to wait for Maiman's 1960 laser before it became a practical technology, and the same physical principle now shows up in far more places than novelty art, from the security features protecting currency to ongoing research into packing data into three physical dimensions rather than two.

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FAQ

Q: Who invented holography?

Dennis Gabor invented holography in 1947 while researching improvements to electron microscopy, running the first working experiments in 1948 and coining the term "hologram" from the Greek "holos" (whole) because the technique recorded the complete light wave rather than just its intensity. He received the 1971 Nobel Prize in Physics for the invention (Nobel Prize, 1971).

Q: Why can't an ordinary photograph capture depth the way a hologram can?

A photograph only records light intensity at each point on the film or sensor. Depth information is encoded in the phase of light waves, subtle differences in wave timing caused by objects at different distances, which intensity-only recording cannot capture no matter how high the resolution.

Q: Why do holograms require laser light?

Recording an interference pattern requires the light waves to maintain a stable, predictable phase relationship, a property called coherence. Ordinary light sources have rapidly shifting phase relationships that wash out interference patterns, while lasers, first built in 1960, produce the highly coherent light holography needs.

Q: What's the difference between a transmission hologram and a reflection hologram?

A transmission hologram is recorded with both beams on the same side of the plate and must be viewed with a laser shining through it. A reflection, or Denisyuk, hologram is recorded with the beams on opposite sides, which lets it be viewed under ordinary white light, making it the more common format for decorative and fine-art holograms.

Q: Does cutting a hologram in half destroy half the recorded image?

No. Because the interference pattern is distributed across the entire recording medium rather than mapped point-to-point, a fragment of a hologram can still reconstruct the full scene, though from a narrower range of viewing angles and typically at lower resolution and brightness.

Q: Are the floating "holograms" seen in movies and concerts real holography?

No. Most floating projection effects seen in entertainment use a technique called Pepper's Ghost, which reflects a projected image off angled glass or transparent film, not the interference-based recording and reconstruction process that defines true optical holography.

Q: Are holograms used for anything besides art and novelty displays?

Yes. Computer-generated holograms are widely used as security features on currency and credit cards because their microstructures are difficult to counterfeit, and the same interference-recording principle underlies research into holographic data storage and holographic interferometry, an engineering technique for detecting microscopic material deformation.