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Holographic interferometry

V.B. Yasinsky (, S.M. Zharkiy (


Holograms have been coming to every home for last years. Colorful labels on audio and video cassettes, holographic trade and protective marks, holograms on credit cards and labels for different products. Many popular magazines have released with the holograms. The large progress in representational holography has achieved. The exhibitions of holographic copies of museum rarities are already arranged. Manufacturing of holographic portraits also grows. Holography have already ceased to be an exotic. However, some holographic applications are not widely known in modern life. It is a problem of image recognition, interferometry of measurement, holographic optical elements, questions of image processing and many others.

This publication about the special holographic application - holographic interferometry.

Of course, holographic interferometry has appeared not on an empty place. The classical interferometry was before. Therefore we shall begin from it.

Classical interferometry

The classical interferometry always have deals only with transparent and a smooth surfaces. It seemed, that's forever. And destiny of interferometry - studying of gases and liquids, mirrors and lenses. Certainly, the field of work was wide there. There were also big practical results.

For example, the mine interferometers for definition of dangerous methane concentration. How many lives they have rescued! Due to those small and very reliable devices the word "interferometer" is well-known in each miner's family. Besides, control at manufacture of optical products. And the measurement of thickness of very thin coverings and super exact control (with accuracy of half of wave length) of movement distances. And express estimation of quality of a surface processing using a special glass plate. What is another possible way to define (at first sight!) a rough surface deviation of some microns from the necessary sizes in several seconds?

Certainly, there is and will be many other applications of interferometry and discoveries, that will made, using this technique. But, I repeat, we talk only about transparent or smooth objects, which deform radiation a very little. There is even a concept - "interferometric accuracy". It means, that the surfaces of optical elements should be processed so that height of roughnesses did not exceed 0,1 wave length of light.

The invention of a holography has enabled to carry out interferometric research not only transparent objects, but also objects which reflected diffused beam. The way of interaction between radiation and object defines separation of objects: phase (transparent) and diffuse (that is reflecting, but not mirror).

Holographic interferometry

What is exactly the new that holography has brought in usual interferometry? At the beginning let's say:

Holography is the method of recording and reconstruction of the total optical information from the object.

If so, and the wave, restored from the hologram, completely corresponds to the object at recording, hence, this wave can be investigated by the same optical methods, as the object. It is possible to carry out shadow, shliren and interferometric measurement. If we also record polarizing characteristics (such ways exist), the opportunities of reception of the information will increase.

In practice it means: if we have the hologram it is possible to investigate the object with short life in details, subsequently by any optical methods, as though the object was static.

There is also used interferometry, but not holographic. The object could be investigated by interferometric (or another optical) methods through its holographic copy, like in holography.

Concept "holographic interferometry" means something absolutely another, using features of holographic principles of information recording. Let's look, what's this...-->