Holography is considered as one of the most remarkable discoveries in modern times. Nevertheless for its first decades it seems to be getting forgotten.

Originally stepped up back at the end of the 1940s to improve electron microscopy, it can not fulfill this function and the wish of its discoverer hungarian-british physicist Dennis Gábor. Due to sources of pure coherent light, which are indispensable for optical holography, being not yet available, not even Gábor himself can locate a field of application for this phenomenon. He can neither recognize at that point of time the meaning and the potential of his discovery and with it the influence this new medium would have on our daily lives one day. Nor can he imagine the plenty of phantasms emerging from this phenomenen. Phantasms, which seem to be mostly one step ahead of applied holography.

With the discovery of laser light at the beginning of the 1960s, for the first time ever it becomes possible to record and reconstruct a real three-dimensional image of an object. What once simply starts as a little rainbow coloured picture of a toy train, today finds its applications in a vast variety of different optical and acoustical fields.

It is as remarkable as the phenomenon of holography itself, that it could never prevail as a popular medium like movie, TV, radio, the internet, print media, etc. Especially when keeping in mind all the phantasmatic stories which emerge from this medium. A lot of dreams, hopes and promises that holography never made by itself, but some of them is trying to keep.

blog.holographie.eu accompanies my scientific work on holography, which would like to give holography an attention, that elsewhere is mostly refused to it. It is of course initially interested in based techniques and technologies of holography and how it works. Moreover it is also interested in these upcoming phantasms and their stories arising from possible abilities of holography. Especially against the backdrop of holography seems to be reaching a point, where its possibilities and abilities catch phantasms.

This blog would like to serve as a sketch book for unprotected ideas, of which some maybe become expanded, while others are not haunted any further, but wants to be told and should not be unmentioned forgotten.


please visit also www.holographie.eu

2010-06-02

Interference

Interference describes the phenomenon of two waves superimposing (both light, sound and water). It is one of two properties featuring the wave nature of light.

To illustrate and for better understanding, the example of a stone hitting the surface of water should be used again (see Fig. Propagation of water waves outgoing from a point source). With one difference. Two stones now hit the surface of the water - simultaneously and with exact regularity - and cause oscillations. From each point source, where the stone hits the water, wave fronts propagate, which meet and join to a new wave front, that is different from the original two wave fronts. At this point the following phenomenon of behaviour of the two wave fronts can be observed:

When two wave crests meet, they intensify each other and the new wave front is an addition of the two original ones. The same happens when to wave valleys meet. This phenomenon is called constructive interference.

Fig. constructive interference

Both shown waves move parallel to each other. They are in phase. "Auf Lichtwellen bezogen bedeitet das: Licht + Licht = starkes Licht (das ist kein besonders überraschendes Ergebnis)."
[Related to lightwaves this means: light + light = bright light (not a very surprising result)]

But if now a wave crest meet a wave valley, they delete each other - destructive interference.

Fig. destructive interference

Both waves are out of phase. This leads to a strange curiosity: "Licht + Licht = Dunkelheit (das ist auf den ersten Blick sicher überraschend."
[Light + light = darkness (very surprising result)]

Between these above shown extremes, there are of course all possible intermediate stages, depending on the rate of phase difference.

Thomas Young succeeds in about 1800 to proof phenomenon of interference by his double slit experiment.


Fig. Double slit experiment

In a darkened room Young lets light rays pass first a single slit and than a double slit positioned behind. On a projection surface installed behind the double slit appears an interference pattern of superimposing wave fronts as bright and dark stripes.



Fig. Interference pattern

The bright and dark stripes can be explained by phenomena of constructive and destructive interference.

Holography avails itself among others of this phenomenon of interference and works by the same principle. As to be shown in coming entries, holography records the pattern of superimposing lightwaves.

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