laser holography and its uses

Holograms are used in various fields such as security for packages or credit cards, Medical to receive a more accurate view, and detail-oriented mapping. Due to the highly accurate nature of the holographic image, they have also been used to record and show precious items that cannot normally be on display to the public, such as the collections from the Faberge museum in St Petersburg by the Hellenic Institute for holography.

Holography is more than a technique for secure or unusual image recording, many other applications exist, such as surface metrology, microscopy and data storage. Holography is the key to future developments such as virtual or augmented reality.

There are different methods for creating the holographic recording, but the laser is often the principle source of coherent light. Since the “image” creation is based on the phase difference between the two light paths caused by the object of the study, any phase difference (non-coherence) caused by the laser through operation, will either destroy the resolution or severely reduce the available depth of field of the final image. The coherence length (narrow linewidth) of the laser is a key characteristic that needs to be considered in the setup. This is not as critical during the reproduction of holographic plates, so the coherence can be much shorter.
Like standard photography, the creation of an image needs exposure time. This exposure time is dependent on the sensitivity of the recording media and the amount of light that is available. As the source of light for holography is the laser, higher power outputs offer shorter exposure times and/or larger fields of view. 

The final consideration when looking at lasers for holography is the actual wavelength needed for the best results. Security patches and labels would be useless if they were recorded in the IR region outside the range of the human eye. The eye has different sensitivity to different wavelengths through the visible region. Many modern holographic images make use of multiple wavelengths, red green and blue to produce the colored final image.

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