What is Holography

By: Dr. James D. Trolinger

Performing a Google search for the definition of “holography” reveals a serious problem in the language of holography and partially explains why the public, in general, is so confused about holography. The average person has no idea about what holography is and isn’t and has never seen a good hologram. Almost all definitions yielded by a Google “Hologram Definition” search are all grossly wrong and define hologram as an image. Others are equally incomplete or outright wrong. Such definitions appear in legitimate dictionaries. See “Incorrect definitions of holography below.  There is little wonder that the general public now thinks all 3D images are holograms. It is the duty of the holography community to create good, correct, general definitions of holography in such a way that, at least part of it, is understandable by the man on the street.

I call upon the Holoknights to endorse one or more definitions of holography and offer them to legitimate information sources to replace incorrect definitions. I have been discussing this problem with a few friends. It is not simple to arrive at a universal definition since each of us has his favorite. I have attempted to compile some of the best features of different inputs. I ask you to look at these and consider endorsing one or more or if you find them unendorsable, produce your own variation for consideration by the Holoknights. I would like to produce at least two or three definitions that all holoknights are willing to endorse.

It appears that we may need at least two definitions, one non-comprehensive, using language that non-technical people can understand and a comprehensive one that requires an understanding of some technical language.

Keep in mind that some of the definitions here attempt accommodate all types of holography and holograms, including those used for 3D imaging, embossed, data storage, and real-time holography such as four-wave mixing, phase conjugate mirrors, and wavefront correcting HOES.

A general definition should also cover all types of holography, not just optical holography, i.e. acoustical and radar.

I include here some of my latest attempts at refining a definition of hologram in a correct, inclusive, understandable way.

 

1. Hologram - A recording of information defining a wave; it can exist in many forms and materials and for many different uses. A common manifestation of a hologram is a photograph of the interference pattern that results from overlaying two laser light beams, known as object and reference beams, originating from the same laser. The object beam comprises light reflected from an illuminated object, and the reference beam comes from the laser unperturbed. When such a photograph is later illuminated with a similar reference beam of light, a 3D image of the object is visible in the space that was originally occupied by that object.

Described in this fashion, the hologram can be thought of as a window in which is frozen the intricate waves that came from the object and which can be turned on at a later time.

Holography is the process of recording and using holograms.

2. Hologram (In science General and comprehensive): a recording of a sufficient amount of the information in an arbitrary wavefront (amplitude and phase) to enable reconstructing and projecting the wavefront or an approximate replica thereof at a later time with exactness limited by sensitivity, resolution, dynamic range, and noise of recording materials. The information can be recorded on a material surface or throughout the volume of a material.

Holograms can comprise any material and mechanism that is capable of storing the necessary information for a sufficient time to enable reconstructing the original wavefront from which the information was obtained.

Holograms are used for:

• 3D imaging

• Security-i.e. Mastercard, visa, and currency

• Advertising and display

• Portraiture

• Art

• Measurement

• Information storage, archival, retrieval and processing

• Optical elements

• Visualization of radar, sonar, ultrasound, lidar, MRI, CAT scans in 3D

3. Hologram (In science General and comprehensive): - a recording of a sufficient amount of the information in an arbitrary wavefront (amplitude and phase) from which the wavefront, or a replica thereof, can be reconstructed and projected at a later time, closely approximating its original form. The information can be recorded on a material surface or throughout the volume of a material. Holograms can comprise any material and mechanism that is capable of storing the necessary information for a sufficient time to enable reconstructing the original wavefront from which the information was obtained.

(The approximation limitation exists because of physical limitations in sensitivity, resolution, dynamic range, and noise or recording materials.)

Holograms are used for:

• 3D imaging

• Security-i.e. Mastercard, visa, and currency

• Advertising and display

• Portraiture

• Art

• Measurement

• Information storage, archival, retrieval and processing

• Optical elements

• Visualization of radar, sonar, ultrasound, lidar, MRI, CAT scans in 3D

4. Hologram- A common manifestation of a hologram is a photograph of the interference pattern that results from the overlaying of two laser light beams, one of which illuminates and is reflected from an object, and the other which comes from the same laser but is completely unperturbed. When such a photograph is later illuminated with an appropriate beam of light, a 3D image of the object is visible in the space which was originally occupied by that object.

Described in this fashion, the hologram can be thought of as a window in which is frozen the intricate waves which came from the object and which can be turned on at a later time

Can we come up with a qualified, simple, understandable, more specific definition for what a layman is likely to see that is still correct? For example:

Hologram-(Optical Hologram) A recording of a light field that contains sufficient information to enable producing an exact replica of the light field later and, for example, can enable producing and viewing 3D images of objects that are indistinguishable from the actual object.

 

Discussion

A discussion on the Facebook/holography page showed that 20 % of the holographers in the poll believed (insisted) that “Holography is photography” . This is an indication that even many holographers, don’t understand what holography or a hologram really is.

 

Incorrect Definitions of holography resulting from a Google search.

1. hol·o·gram

a three-dimensional image formed by the interference of light beams from a laser or other coherent light source.

a photograph of an interference pattern that, when suitably illuminated, produces a three-dimensional image.

Hologram | Definition of Hologram by Merriam-Webster

https://www.merriam-webster.com/dictionary/hologram

2. interference produced by a split coherent beam of radiation (such as a laser); also: the pattern of interference itself.

 

3. hologram meaning: an image made with a laser beam, in which the objects shown look like they have depth rather than appearing flat and can seem to move.

 

4. m? - Definition from WhatIs.com

whatis.techtarget.com/definition/hologram A hologram (pronounced HOL-o-gram ) is a three-dimensional image, created with photographic projection. The term is taken from the Greek words holos (whole) and gramma (message). ... The development of laser technology made holography possible.

 

5. hologram | Definition of hologram in English by Oxford Dictionaries

https://en.oxforddictionaries.com/definition/hologram Definition of hologram - a three-dimensional image formed by the interference of light beams from a laser or other coherent light source.

6. What is a Hologram? | Hologram Definition - Live Science

https://www.livescience.com › Tech

May 23, 2013 - Holography is a photographic technique that records the light scattered from an object, and then presents it in a way that appears three-dimensional. Holograms pop up in movies such as "Star Wars" and "Iron Man," but the technology has not quite caught up to movie magic — yet.

7. Hologram | Define Hologram at Dictionary.com

www.dictionary.com/browse/hologram

Hologram definition, a negative produced by exposing a high-resolution photographic plate, without camera or lens, near a subject illuminated by ...

8. hologram - Dictionary Definition : Vocabulary.com

https://www.vocabulary.com/dictionary/hologram

If you've ever looked through a View-Master, you've seen a hologram — an image or photograph that appears to be three-dimensional.

9. What is a Hologram? - Definition from Techopedia

https://www.techopedia.com/definition/15888/hologram

Hologram Definition - A hologram is an image created by a photographic projection of a recording of a light field rather than an image formed by some...

10. Hologram definition and meaning | Collins English Dictionary

https://www.collinsdictionary.com/us/dictionary/english/hologram

Hologram definition: A hologram is a three-dimensional photographic image created by laser beams. | Meaning, pronunciation, translations and examples.

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