Hologram Technology A challenge and future

A hologram is a physical structure that diffracts light into an image. The term 'hologram' can refer to both the encoded material and the resulting image. A holographic image can be seen by looking into an illuminated holographic print or by shining a laser through a hologram and projecting the image onto a screen.

Holography is the science and practice of making holograms. Typically, a hologram is a photographic recording of a light field, rather than of an image formed by a lens, and it is used to display a fully three-dimensional image of the holographed subject, which is seen without the aid of special glasses or other intermediate optics. The hologram itself is not an image and it is usually unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of seemingly random variations in the opacity, density, or surface profile of the photographic medium. When suitably lit, the interference pattern diffracts the light into a reproduction of the original light field and the objects that were in it appear to still be there, exhibiting visual depth cues such as parallax and perspective that change realistically with any change in the relative position of the observer.

In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram. In a side-by-side comparison under optimal conditions, a holographic image is visually indistinguishable from the actual subject, if the hologram and the subject are lit just as they were at the time of recording. A microscopic level of detail throughout the recorded volume of space can be reproduced. In common practice, however, major image quality compromises are made to eliminate the need for laser illumination when viewing the hologram, and sometimes, to the extent possible, also when making it. Holographic portraiture often resorts to a non-holographic intermediate imaging procedure, to avoid the hazardous high-powered pulsed lasers otherwise needed to optically "freeze" living subjects as perfectly as the extremely motion-intolerant holographic recording process requires. Holograms can now also be entirely computer-generated to show objects or scenes that never existed.
Holography is distinct from lenticular and other earlier autostereoscopic 3D display technologies, which can produce superficially similar results but are based on conventional lens imaging. Stage illusions such as Pepper's Ghost and other unusual, baffling, or seemingly magical images are also often incorrectly called holograms.

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In its early days, holography required high-power expensive lasers, but nowadays, mass-produced low-cost semi-conductor or diode lasers, such as those found in millions of DVD recorders and used in other common applications, can be used to make holograms and have made holography much more accessible to low-budget researchers, artists and dedicated hobbyists.

It was thought that it would be possible to use X-rays to make holograms of very small objects and view them using visible light.Today, holograms with x-rays are generated by using synchrotrons or x-ray free-electron lasers as radiation sources and pixelated detectors such as CCDs as recording medium.The reconstruction is then retrieved via computation. Due to the shorter wavelength of x-rays compared to visible light, this approach allows to image objects with higher spatial resolution.As free-electron lasers can provide ultrashort and x-ray pulses in the range of femtoseconds which are intense and coherent, x-ray holography has been used to capture ultrafast dynamic processes

How it works

Recording a hologram

Reconstructing a hologram

Close-up photograph of a hologram's surface. The object in the hologram is a toy van. It is no more possible to discern the subject of a hologram from this pattern than it is to identify what music has been recorded by looking at a CD surface. Note that the hologram is described by the speckle pattern, rather than the "wavy" line pattern.

Holography is a technique that enables a light field, which is generally the product of a light source scattered off objects, to be recorded and later reconstructed when the original light field is no longer present, due to the absence of the original objects.Holography can be thought of as somewhat similar to sound recording, whereby a sound field created by vibrating matter like musical instruments or vocal cords, is encoded in such a way that it can be reproduced later, without the presence of the original vibrating matter.