A topic that continuously grates on some within the holography community is the corruption of the term ‘hologram’ to apply to any display or image that heightens the sense of solidity or depth. For that group of holographers, there is some guidance and perhaps reassurance from a new research paper from the Changchun Institute of Optics, Fine Mechanics and Physics, China 1.
The paper looks to some of the early pioneers in holography for guidance in how to explain what a hologram is. Yuri Denisyuk, one of the founders of optical holography and inventor of his namesake technique for recording reflection holograms, described a hologram as the ‘optical equivalent’ of an object itself. Illuminating a hologram of an object produces the same light wave for viewing that would be produced by the object itself.
Using these concepts, a hologram can be described to a layman as a window on which information is recorded that enables it to transform light coming from a point source of light into a different light wave, ie., one that would have come from a 3D object sitting behind the hologram.
The researchers recognise that a general definition covering all holograms is unlikely to be understandable or even useful to many people who will see and enjoy optical holograms. However, broad definitions and language are needed to cover the newest forms and applications of holograms, especially non-optical holograms.
An optimal approach might be to adopt at least two consistent definitions: one that is comprehensible to the general public and a second to be understood and used more by the technical community.
In technical language, the researchers argue, a hologram is a recording of any type of complex wave, such as a light, sound, x-ray, radio, or synthetic wave, that employs the principles of diffraction and interference phenomena to store information sufficient to enable reconstruction of a nearly perfect replica of the original wave. This technical definition is consistent with the layman’s definition, and it also rules out other forms of 3D image recording.
More recently, the paper goes on to say, holograms have been described as windows that allow a viewer to look into a different place and time. With holographic movies and with real time holography, the viewer can see action in true 3D, taking place in a different place and time.
The research team points to digital holography (which became viable only after the recent improvements in high-resolution digital technology) as possibly the fastest growing technical holography topic, opening the way for many exciting new applications.
Techniques developed by this industry have enabled faster and lower-cost hologram production than could have been imagined. In science and medicine, digital holography is revolutionising microscopy and imaging. Unlike analogue holography, which relies mostly on fixed recording materials, digital holography employs electronic recording, computers, and software which can be reused and updated.
In summary, the paper examines the language of holography and its origins, problems, and possible solutions to the dilution of the term ‘hologram’, but recognises that ultimately some of the ‘errors’ in the language are so embedded in society that simple and ideal fixes may not be possible.
1 - https://www.eurekalert.org/news-releases/938495
