While seeming to be three-dimensional, holograms are actually flat films that create the illusion of depth and movement, offering motion parallax and a stereoscopic view unlike 3D movies or simple photographs. Their special properties stem from how they are created using coherent laser beams. When two coherent laser beams—an object beam reflecting off the subject and a reference beam—intersect, they produce a unique interference pattern on the film that encodes the three-dimensional information, and when a laser is shone through this pattern, it reconstructs a perfect copy of the original object beam, making the image appear real and complete.
**Key Themes and Ideas:**This source provides an accessible explanation of how holograms work, highlighting their unique properties that create the illusion of a 3D image. The core themes revolve around the distinction between holograms and other 2D imaging techniques, the crucial role of laser light and interference patterns in their creation, and the resulting visual effects that differentiate them from photographs and even some 3D visual technologies.
Holograms are 2D films that appear 3D: Despite appearing as three-dimensional ghost images, the holographic film itself is completely flat and two-dimensional. This is a fundamental point of confusion addressed at the outset.
Key 3D Properties: Holograms possess two key properties that contribute to their perceived 3D nature:
Motion Parallax: "As you move your gaze, things in the foreground seem to shift faster than things in the background." This is a crucial difference from 3D movies, which lack this effect.
Stereoscopic View: "You see two different images with each eye, which together create the perception of depth." This provides the binocular disparity needed for depth perception. Holograms show different images from different viewpoints: Unlike regular photographs which "looks the same no matter which way you look at it," a hologram changes the image presented depending on the viewer's position. This is essential for the motion parallax effect.
Laser light is essential for creating holograms. The creation of holograms relies on the unique properties of laser light:
Directional: "It's all going in the same direction."
Monochromatic: "It all has the same wavelength." (referred to as having the "same footstep length" in the analogy).
Coherent: "All the light waves are in phase, or in unison." This coherence is "so key to making holograms."
Holograms are created using interference patterns: The core mechanism involves splitting a laser beam into two: an "object beam" that bounces off the subject and a "reference beam" that goes directly to the film. When these beams meet, they create "interference patterns." In the case of holograms, this is a "special one that encodes the specific 3D information about the object onto the holographic film."
Reconstruction of the object beam creates the image: To view the hologram, a laser beam (similar to the reference beam) is shone through the interference pattern on the film. This process, analogous to "C minus A equals B," reconstructs the original "object beam." "Since this reproduced beam is a perfect copy of the object beam, you can't tell whether you're looking at the light from the hologram or from the original scene, complete with motion parallax and stereoscopic views."
Holograms contain information about the entire object in every part: "All parts of the hologram carry information about the object." Cutting a small square of a hologram will still allow you to see the entire object, unlike a photograph.