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Holographic displays: then and now



Run the software for modeling and display a full-size model for editing in space. Turn on the communicator and talk not with the flat image of the interlocutor on the video call, but with its volume projection through which the favorite carpet shines through. Move the curtain back and see the weather forecast on the window pane, the situation with traffic jams, and in general - how it is there. Start the car engine and receive additional alerts on the road markings, possible hazards and other important information at the windshield site.

If before all this was the lot of science fiction, now this has moved from the category “Fantastic” to the category “Near Future”. We will try to tell about how modern scientists are bringing the age of holography closer, how it all began, and what difficulties holographic technologies are experiencing at the moment.

How holographic images are created


The human eye sees physical objects, as light is reflected from them. The construction of a holographic image is based precisely on this principle - a beam of reflected light is created that is completely identical to that which would be reflected from a physical object. A person, looking at this beam, sees the same object (even if he looks at it from different angles).
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Higher resolution holograms are static drawings, the “canvas” of which is a photopolymer, and the “brush” is a laser beam that changes the structure of photopolymer materials once. As a result, the photopolymer processed in this way creates a holographic image (light falls on the plane of the hologram, the photopolymer creates its fine interference pattern).

By the way, about the interference itself. It occurs if a certain range of electromagnetic waves is formed in a certain space, and their frequencies coincide with a rather high degree. Already in the process of recording a hologram in a specific area, two waves are added — the first, the reference, comes directly from the source, the second, the object, is reflected from the object. A photographic plate with a sensitive material is placed in the same area, and a picture of darkening bands appears on it, corresponding to the distribution of electromagnetic energy (interference pattern). Then the plate is illuminated by a wave, which is close in characteristics to the reference one, and the plate converts this wave into close to objective one.

The result is that the observer sees about the same light that would be reflected from the original recording object.

Brief historical background


It was 1947 year. India gained independence from Britain, Argentina granted women electoral rights, Mikhail Timofeevich Kalashnikov created his famous machine gun, John Bardeen and Walter Bratteynomiz are conducting an experiment that allowed creating the world's first active bipolar transistor, the production of Polaroid cameras begins.

And Dennis Gabor gets the world's first hologram.



In general, Dennis tried to increase the resolution of electron microscopes of that era, but in the course of an experiment aimed at this, he obtained a hologram.

Alas, Gabor, like many minds, was a little ahead of his time, and he simply didn’t have the necessary technology to get good quality holograms (this cannot be done without a coherent light source, and Theodore Meiman will demonstrate the first laser on an artificial ruby ​​crystal only 13 years later).

But after 1960 (ruby red laser with a wavelength of 694 nm, pulsed, and helium-neon, 633 nm, continuous) it went much more vigorously.




1962 . Emmet Leith and Juris Upatnieks, Michigan Technological Institute. Creating a classic hologram recording scheme. Transmission holograms were recorded - in the process of restoring the hologram, light was passed through a photoplate, but some of the light is reflected from the plate and also creates an image that can be seen from the opposite side.




1967 . The first holographic portrait is recorded using a ruby ​​laser.


1968 . The photographic materials themselves are also being improved, thanks to which Yuriy Nikolaevich Denisyuk develops his own recording scheme and receives high-quality holograms (they restored the image by reflecting white light). Everything is going quite well, so much so that the recording scheme gets the name “Denisyuk Scheme”, and the holograms - “Denisyuk Holograms”.




1977 . Multiplex hologram of Lloyd Cross, consisting of several dozen angles, each of which can be seen only at one angle.

Pluses - the size of the object to be recorded is not limited to the laser wavelength or the size of the photoplate. You can create a hologram of an object that does not exist (that is, simply by drawing the invented object from several angles at once).

Cons - the lack of vertical parallax, to consider such a hologram can only be on the horizontal axis, but not above or below.




1986 Abraham Seke realizes that there is no limit to perfection, and proposes to create a source of coherent radiation in the near-surface region with the help of x-rays. The spatial resolution in holography always depends on the size of the radiation source and its distance from the object - this made it possible to restore the atoms that surrounded the emitter in real space.

Now


Today, some prototypes of holographic video displays work in much the same way as modern LCD monitors: they scatter light in a special way, forming pseudo-3D, rather than creating an interference pattern. What is connected with the main disadvantage of this approach is that only one person sitting at the right angle to the monitor can properly assess such a picture. All other viewers will not be so impressed.

Of course, fans of science fiction and new technologies are sleeping and seeing how holographic displays will become as familiar as wifi at home or the camera in a smartphone, comparable to a soapbox that is not the worst. And although the ideal hologram, as understood by the majority, is in fact not today and not tomorrow, developments on this topic are already underway.


Institute of Science and Advanced Studies, Korea. A working prototype of a new 3D holographic display, the performance characteristics of which is about a couple of thousand times better than that of existing analogues.

The weak link of such displays is the matrix. While the matrix consists of two-dimensional pixels. The Koreans used the usual (but good) display together with a special modulator for the front of the optical pulse. The result was a high-quality hologram, however, a small one - 1 cubic centimeter.



There was a time when it was believed that the scattering of light is a serious obstacle to the normal recognition of projected objects. But as our practice shows, modern 3D-displays can be significantly improved by learning to control this dispersion. Proper scattering has increased both the viewing angle and the overall resolution,
- says Professor Yonken Park .


Griffith University, Swinburne University of Technology, Australia. Graphene based holographic display.

Scientists armed with the method of Gabor, mentioned at the very beginning of this post, and made a high-resolution 3D-holographic display based on a digital holographic screen, consisting of small dots that reflect light.

Pros - a viewing angle of 52 degrees. For the normal perception of the picture, no additional pribludy in the form of 3D-glasses and other things are needed.

By the way, about 52 degrees. The viewing angle is greater, the less pixels will be used. Graphene oxide is processed by photoreduction, which creates a pixel that is able to bend the color for the holo image.

Developers believe that this approach in its time will be able to initiate a revolution in the development of displays, especially on mobile devices.


University of Bristol, UK. Ultrasound holography.

The object is created in the air using a variety of ultrasound emitters aimed at a cloud of water vapor, which is also created by the system. Implementation, of course, more difficult than in the case of the usual screen, but still.




The result is a projection of the object, which can not only be viewed from all sides, but also touched.



The oscillation frequency of such an interference pattern is from 0.4 to 500 Hz.

One of the main activities in which developers assume the useful use of technology is medicine. The doctor will be able to “feel” it on the basis of the data of the medical card and the modeled organ. You can also create volumetric projections of any products on presentations. A positive effect is also predicted when replacing touchscreens in places of mass use with similar technology (electronic menus, terminals, ATMs). How difficult and expensive it will be to implement - by itself, is the second question.

And so far what entertainment services of a certain direction can reach is scary (but interesting) to think.


Vancouver, Canada. Interactive holographic display.



What do you need:



As you can see, the interest in holography, once launched by science fiction, does not even stop to think - on the contrary, it is only gaining momentum.

It is quite possible that in the very near future almost in every apartment there will be holographic screens created using one of the methods described above. Or based on some new, because scientists continue to invent more and more new materials that are an excellent tool for the development of technology.

Now it is difficult to imagine a modern person without a smartphone in his pocket, perhaps soon a wrist watch with a holographic projector will become an integral part. Or a new round of development of smart houses and smart cars will show how else you can use the possibilities of holography.

The latter, by the way, is no longer just a fantasy - for example, we are creating the first holographic navigator for cars that provides a display of augmented reality on the windshield in the driver’s focus area. And we will tell something about him in one of the following posts.

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Source: https://habr.com/ru/post/323752/

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