what they are and how they work
The word "hologram" is a term that derives from the name of the technology that generates it, which is "holography".
From ancient Greek, ὅλος, holos, "all", and γραφή, grafè, "writing", which literally means "I describe everything".
3D hologram technology was theorized in the 1940s by scientist Dennis Gabor. Obviously, it was still in its most rudimentary phase and although it had immediately appeared as an interesting invention, it had not yet been so successful.
In recent years, this technology has gained more popularity, thanks to both digital development and the emergence of new needs and a question that finds its answer in the benefits that 3D holograms offer.
What is a hologram?
When we talk about holograms we generally mean three-dimensional or stereoscopic images - that is something that change perspective when viewed from a different point of observation.
Or, thinking of Star Wars, when Princess Leia appears in the form of a small blue 3D hologram or, again, the three-dimensional touch screens seen in Iron Man.
Some experts define holograms as two-dimensional surfaces capable of manifesting information in three dimensions. What we see in movies is an illusion created with special effects and animations, while in reality holograms are generated through a technique called holography.
Types of holograms
To understand how holograms work, you must first understand how a camera captures a photograph. The shutter opens and light bouncing off the surface of the object passes through the lens and strikes the photographic emulsion on the film or, for digital cameras, the Charge Coupled Device (CCD), a chip that converts light into electrical signals and transforms the falling light into a digital image. Therefore, the image you see is actually the recorded light intensity.
In the case of a hologram, the principle of operation is almost the same, but the setting is different.
How do holograms work?
How to create the hologram
A laser beam is aimed at a plate which divides the laser into two beams, the reference beam and the illumination beam. A shutter opens or moves out of the way of the laser. The light from the reference beam is sent directly to the photographic plate and the illumination beam is reflected from the surface of the object before it strikes the photographic plate.
Subsequently, to recreate the image, the photographic plate is illuminated by a light source, similar to the one used previously. The hologram records a pattern of tiny bands of light called interference fringes. These, through a complex process, are converted by the light source into a reflection identical to the original object.