Is a hologram technically possible?

Holograms: The dream of a deceptively real image

In 1962, other researchers made a usable three-dimensional picture of a model railway. The scientists now had lasers available that delivered coherent light in which the phase between two wave trains remains constant. This fact made it much easier to store the necessary phase information. It should ultimately bring holography back to life. Regardless of his previous surrender, Gábor therefore received the Nobel Prize in Physics in 1971 for the invention of holography. Since then, holograms have been considered to be the ultimate advancement in photography.

What the phase of the light waves reveals

In order to actually store the phase information, a so-called object wave and a reference wave are used. The latter is mostly nothing more than a separated partial beam of the object wave; the properties of the two rays are therefore initially the same. The object beam then hits the object to be imaged while the reference beam passes it. Then the two beams are superimposed again - they interfere, as it is called in technical jargon - and the holographic plate is exposed together. In principle, this procedure creates a comparison between "deformed" and "not deformed". It is only through the superposition that it is possible to determine how exactly the object has changed the appearance of one wave. This information is ultimately hidden in a complicated line pattern - experts speak of an interference pattern - that is created on the holographic photo plate.

The appearance of the pattern is not remotely similar to the object - any more than one can recognize the music encoded on it from the shape of the soundtrack on a record. In order for the depicted object to become visible again, light from the reference wave must fall back onto the holographic, partially transparent plate. As a rule, you can then see a three-dimensional image of the object behind it - the wave field is, as it were, restored. As if through a small window, the viewer sees the depicted object behind it. This type of display is called transmission or backlight holograms. There are also many further developments; In some cases, the holograms arise in front of the image plane (reflection holograms) or in it (image plane holograms). The certificates of authenticity on admission tickets, bank notes, passports or credit cards, on the other hand, are so-called rainbow holograms, which do not require a special light source to be viewed.

Several companies and research institutes are working on the development of holographic displays

Some large shipping companies use holographic scanners to measure the dimensions of packages. And archaeologists use more sophisticated versions of such recording devices to create holograms of ancient finds. On the computer, they can then process the images further, for example join fragments together and thus reconstruct the original appearance. With the help of holographic interferometry, engineers also investigate minimal movements or deformations of technical components that are under load in laboratory tests.

In addition to taking pictures, holography can also be used to save data. The advantage over conventional storage methods is that the information can be recorded in the entire volume of the object and not just on its surface. But there is no commercial product here yet.

Calculate holograms on the computer

Holographic technology got a big boost from the development of high-performance computers. Nowadays, holograms can not only be photographed with lasers, but also generated with the help of algorithms. To a certain extent, they calculate the respective interference patterns that are stored in individual holograms - basically the way in which light is refracted so that three-dimensional images are ultimately created. The time-consuming and costly recording process is no longer necessary and moving images in particular have become tangible with this approach. Several companies such as SeeReal or Zebra Imaging as well as various research institutes, including MIT and the University of Arizona, are trying to develop holographic displays.