Hologram Creation: Interference & Diffraction

Waves propagate by following a helical and spindle-like trajectory, while also pulsating all along! The article looks at the various phenomena associated with the propagation of waves and the interaction between them.

Interference occurs as a result of the overlay of two or more waves within a shared area of space. As a result, there appears an increase in the amplitude of the resulting wave at some points and a decrease in others (interference minima and maxima values). The result is the so-called interference pattern. The interference pattern remains steady and unchangeable over time, because it has been generated by a source that vibrates at a constant rate. An example of such a pattern is the phenomenon, which is observed when throwing two pebbles on a smooth water surface. After the pebbles touch the water, one can observe how a pair of waves (ripples) is being formed, which gradually expand and intersect with one another. The crests of the waves will be forming bigger waves at places, while lower at others. Interference also occurs when a thin light beam penetrates a thin solid layer. When the layer is of certain thickness, the beam is being reflected two times – one time on each side of the layer, as the reflected beams are able to interfere. 

In order to facilitate the further understanding to the process of interference, it is necessary to examine its accompanying process – diffraction. Diffraction is the process by which a wave is diverting from its straightforward propagation (this process occurs when a wave encounters an obstacle – e.g. when passing through a barrier’s slit). As a result of the combination between both phenomena (interference and diffraction), there appears an illusory holographic image. In most simple terms, the hologram is the result of a wave interaction creating an interference pattern upon a photo-sensitive film surface. As mentioned above, the resultant pattern resembles concentric circles that are being formed when throwing pebbles onto a water surface. When the photo-sensitive emulsion is being illuminated with a laser beam, there appears a diffraction and there appears a three-dimensional image of the captured object.

The obtained illusion of a three-dimensional object existing in the real world is a particularly convincing and believable one. However, there is no such thing as a material object actually. The image is visible but an illusory one. If we put our hand through it, we will be able to see that this is merely an illusion.

HOLOGRAPHY - THE SCIENCE OF 3D IMAGES CREATION

Holography – (from Greek όλος (holos) – whole + γραφή (grafe) – to write) is the science concerned with the creation of holograms: A method of visualization that allows for the recording and projection of illusory three-dimensional images through using a laser beam. In addition, holographic equipment can also be used for storing and processing data.

The Hungarian-British physicist Dennis Gabor was awarded the Nobel Prize in Physics in 1971 “for his invention and development of the holographic method”. The discovery was an unexpected result of research into improving electron microscopes. The technique as originally invented is still used in electron microscopy, where it is known as electron holography, but optical holography did not really advance until the development of the laser in 1960, which are powerful sources of coherence light. Coherence light was efficient in the process of obtaining and recreation of holographic images. The laser was invented by Theodore Maiman. The concentrated and intense of coherence light has a wide application in multiple areas. It can substitute the scalpel, it can record and read sound and image from optical media, it can ‘fuel’ the nucleus merging during nuclear reactions, it can visualize embossed images and so on. The sunlight that we refer to as ‘’white light’’, is actually a combination of few single-colored (monochromatic) lights ranging from the red to blue color, and they are complementing among one another. The light of the laser beam is a single-colored one. The waves differ from another in terms of length. Each color has a different corresponding wavelength. The white light is comprised of multitude of wavelengths, whereas the laser one – solely by one. This light is coherent – i.e. all the waves composing it are monophasic ones. The white light is non-coherent – it resembles something of a crowded boulevard. The laser beam light is concentrated, directed and therefore, more intense than the light of other sources.

When an atom receives energy from an external source (for example, heat), its electrons absorb that energy by changing their orbits: they now turn into the so-called “excited” electrons. They have changed their energy and are being in an unstable (unbalanced) state. When returning to a balanced state, they emit (and thereby transform) the energy absorbed from the external source as light (also energy). Depending on the material that is used, there is a different color for the laser’s light. Usually the holograms are the same color as the light of the laser itself. Its real colors can hardly be seen. The first practically usable holograms of modern type (“thick plaque”) were created by Yuri Denisuk (Soviet physicist). They project are able to project the real color of the object.

The principle way for hologram projection is the following: the laser light is being split into two beams of light. The first beam is directed towards the object (that we wish to be holographized, which is also the reflective beam. The second light beam is pointing to a reflective mirror (“reference beam”). The reference beam interacts with the light reflected by the object, and the resultant interference pattern is being recorded onto the light-sensitive medium – the holographic plaque (equivalent to photographic film). The hologram is the recorded memory of the interaction between the electromagnetic waves of the main beam and the one reflected by the object.

A HUGE QUANTITY OF INFORMATION STORED ON A TINY SPACE

There are more aspects of importance characterizing the holograms in addition to their three-dimensionality. If the holographic plaque containing the image is made of glass, and if this glass is being shattered, each shattered piece of glass will be still containing the entire image of the object. Even in the tiny glass pieces are then being continuously broken down into tiny pieces, one will still be able to reconstruct the entire image upon such tiny amount of space. Unlike photographic images, each little fragment of the holographic image contains the complete information that has been stored on the plaque. When we speak of holographic principle, what we mean is that the part contains the all, while the all is being contained inside the part.

Another important feature of the hologram is its ability to store huge volumes of information on a particularly small area. A simple adjustment of angle allows for multitude of various images to be recorded all on the same surface. Images created in such way might be reconstructed by illuminating the holographic plaque with a laser beam under the same angle as the one that the image has been recorded. Researchers have identified that by applying this method, an amount of information equivalent to the information contained inside fifty Bibles might be recorded on a photographic film with the size of a single square inch!

Prof. Karl Pribram explains the capacity of our brains to record such massive amount of memories (information) on such a tiny space through the holographic principle. The way in which holograms work also provides quite a convenient and elegant of an explanation on why the brain does not lose any memories when some parts of it has been removed (the part contains the all, while the all is being contained inside the part). John von Neumann (American-Hungarian mathematician) calculates that during an average life span, the brain is able to record information approximately amounting to 280×1018 bits. This is a shockingly massive amount of information and there are researchers are queuing to explain the mechanism behind such storage capacities. The holographic principle is able to provide an explanation for the occurrence of such a mechanism.

Summary: The holographic image is a three-dimensional object. We can’t tell by simply looking at it whether if it is really a real object or an image. We can identify that it is an illusory image only by putting our hand through it. But what if this holographic image is surrounded by an energy field, which does not allow our hand to penetrate it? Our hand would stop right where the field begins. The field would cause the according impulses (pressure, contact, temperature) that would indicate to the brain receptors that there is a barrier at that place. The impulses are different depending on the field that is being ‘touched’. However, they are all being interpreted as dense ‘matter’, which has the according characteristics – softness, hardness, elasticity, warmth etc. What we actually touch is the blocking field interpreted as matter by the brain. Similarly, the eyes are also transmitting an impulse that they ‘see’ an image that has be interpreted as a color. The hologram turns into an existing “matter” having its own characteristics, parameters and properties…

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