The purpose of this paper is to examine the holography technology. The paper is segmented into several sections. The first section focuses on the history of holography from the time it was first invented throughout the various technological advancements that have taken place to make better holograms. The paper further explores the basic principles behind the work of holograms and the main methods used in the development of different types of holograms that exist today. The third section mainly focuses on the laboratory experiments and how they are setup in examining different types of holograms. The final section summarizes the paper by looking at the areas where holography is applied. This section also focuses on the challenges in the holography technology and the future of this technology (Schmidt Group of Companies, 1978).
History of Holography
Holography is the process of developing the hologram of an object. A hologram can be described as a flat surface which appears to contain a three dimensional image of an object. The British-Hungarian scientist Dennis Gabor first discovered holography back in the year 1947. He came up with the holography theory as he was working in order to improve the electron microscope resolution. In his experiments, he coined the term hologram, which comes from two Greek words: holos, which means whole and gramma meaning, message (Francon, 1974).
The first paper that Gabor wrote on holography attracted immediate attention from scientists all over the world. Most of them were willing to advance the newly discovered work. G.L Rogers, A.B Baez, P. Kirkpatrick and M.E Haine were among those who contributed greatly. In the initial years of the holography discovery, a mercury arc lamp was the only appropriate source of light for making holograms. This source of light produced holograms that lacked depth. Holograms also contained distortions and an extraneous twin image. These limitations in one way or the other restricted research.
As research continued in the decade that followed, more sources of light to be used in holography were discovered. Still, the sources were not coherent in that they were monochromatic, had a single wavelength and were from a single point. This big challenge was finally overcome in 1960 after the Laser’s invention. The laser as a source of lights was pure meaning that in contained no noise and its intensity and was perfect for making holograms. In the decade that followed, many holography applications and techniques were developed.
In the year 1962, Emmett Lieth and Juris Upatnieks received recognition from the University of Michigan for discovering the possibility of holography to be used as a three-dimensional visual medium. In the same year, the two scientists duplicated Gabor’s original technique, but this time using a laser technology. As a result, they developed the first laser transmission hologram of 3-D objects. Although the transmission holograms required the laser light to view, the images were clear and had realistic depth. The work done by the two scientists gave rise to the standardization of the equipment currently used to make holograms (Anderson, 1980).
Currently, many laboratories in the world are equipped with the equipment required to make holograms: a laser wave, optical devices (mirrors, lens, and beam splitters) needed for directing light, an isolation table, and a film holder. The off-axis method that Lieth and Upatnieks come up with is still the staple of holographic methodology.
In 1968, Dr. Stephen A. Benton invented the white-light transmission holography during his research on holographic television. This was a very big step in holographic display and holography in general. Holograms are produced using white-light transmission that can be viewed in normal white light creating a ‘rainbow’ image. The brilliance and depth of the image soon drew the attention of many artists. They adapted this methodology to their artistic work. This further brought holography to public awareness. Dr. Benton’s invention is very important since it make it possible for the mass production of holograms by the use of embossing technique. Holograms are then printed by stamping the pattern obtained onto plastic. The produced hologram can be duplicated many times at a very cheap price each. Currently, the advertising, banking and even the publishing industries use embossed holograms (Schmidt Group of Companies, 1978).
In the year 1970, Lloyd Cross came up with an integrated hologram from the combination of conventional cinematography and the white-light transmission. This produced moving 3-D images. The 1970’s witnessed the development of a prototype that was projected on a holographic movie. This came as a collaboration of Victor Komar with his colleagues at the All-Union Cinema in Russia. Holographic artists have improved their understanding of holograms and currently contribute to the technology through the creative process. The artistic work has gained international recognition, and many exhibitions are being held all arround the world.
The principles of Holography
The principle behind the physical phenomenon of the hologram lies on the interference and diffraction of light waves (Schmidt Group of Companies, 1978). Holograms are photographs of 3-Dimensional impressions on the surface of light waves. Thus in order to make a holograph, one is required to take a photograph of light waves. There stands out a big challenge in trying to take a photograph of a moving wave. The picture taken will be blurring. It is more challenging trying to photograph an object moving at a very high speed. For example, imagine that it is required to photograph a photon that moves at the speed of 300 kilometers per second. This becomes impossible.
The only solution to curb this problem is to find a way of stopping the moving object. Thus, the most appropriate technique to use is interference. Interference of waves occurs when waves from different sources meet and cross each other. The pattern produced when two waves interfere in termed as ‘standing still wave’. The standing still effects solve the initial problem of taking a photograph of a moving object. Different sources of light to photograph the interference pattern are available. Among those sources, laser light is the best. The light produced by a laser is coherent meaning that the light waves are of the same wavelength and are in phase (Hariharan, 2002).
When two waves with similar characteristics cross each other, they may perform addition or subtraction. The addition occurs when two waves of the same size meets at their high points, which are referred to as the crests. As a result, waves adds up together to produce a wave that is a twice high as the original waves. On the other hand, when two waves with similar characteristics meet at their low points, which are referred to as the troughs of the waves, they add up together to produce a wave that is as twice low as the original wave (Schmidt Group of Companies, 1978).
A last example of interference occurrence arises when one wave at its low point crosses another wave at its high point. In this case, the two waves subtract each other and cancel out. The cancelling out does mean that the light wave is destroyed. It implies that there is no light at the spot of subtraction. Constructive interference is used to refer to the situation when two light waves add up to produce either a higher wave or a lower wave than the original wave. On the other hand, destructive interference is used to refer to the situation that arises when two waves subtract or even cancel.
The interference phenomenon is the backbone of the holography technology. Every object of a holography that one makes develops a unique interference pattern that uniquely identifies the object.
For the purpose of this paper, I will use the diagram below to illustrate the working of a holograph.
In holography, there are two waves that are involved in creating the interference pattern of the object whose hologram is to be developed.
To begin with, there is the wave that bounces off the object whose hologram is to be developed. Thus, it is termed as the object wave, which is labeled 6 in the above diagram. We need a second wave that will cross the object wave to perform the interference function. As indicated in the diagram, this wave is called the reference wave, labeled 5. When the object wave crosses the reference wave, a standing wave of the interference is created, and a photograph is taken at this point. This produces the hologram of the object.
The semi-transparent mirror is used to split the beam produced by the laser into two: the signal beam and the reference beam. The signal beam is then directed by a mirror to a lens. The lens expands the beam and illuminates the object. The second beam termed as the reference beam is directed by a mirror too. It is later expanded by a lens and falls onto a photoplate. The photoplate records the interference pattern that is produced when the object beam meets the reference beam. This process develops a transmission hologram. Ordinary photochemical treatment is done for the hologram to appear. The 3-d image of the object is seen by exposing the hologram to a beam of the laser light. For the image to be seen in ordinary white light, the hologram has to be copied to the reflection hologram. This circumstance is the basis of creating three-dimensional holograms.
To add time (motion) to the holograph, one will be required to move the object or turn it around and then shoot again. One can also move the mirrors and the lenses and then shoot again. The waves that were originally recorded will intercept with the waves of the new perspective.
The Bragg’s diffraction effect is used to explain how the three-dimensional (volumetric) holograms operate. Layers of blackening are formed after the processing of the hologram. Consequently, the ‘Bragg planes’ are created, which exhibits the property to the reflect light. This means that a three-dimensional figure is created on an emulsion. The thick-layer hologram presents an affective reconstruction of an object wave. This is possible if the angle of incidence of the reference light wave at the time of recording and reconstruction is maintained. The wavelength of the reference beam is not supposed to be changed during the reconstruction of the object from the hologram (Schmidt Group of Companies, 1978).
There also exists a different procedure of recording a reflective hologram. This principle was developed by Jurii N. Denesyuk. In the creation of reflective volumetric holograms, he used the object and the reference beams formed with the assistance of a semi-transparent mirror. The beams are directed by the mirror on a plate from opposite directions. The object beam illuminates the photographic plate on the emulsion layer. The reference beam, on the other hand, illuminates on the part of the glass substrate. During the recording process, the object wave is formed from the transmission hologram. The main advantage of the reflective holograms is that they can be reconstructed to view the object using other sources of light apart from the laser light, which is the case with the transmission holograms. Such sources of light may include the sun and the incandescent bulbs (Ackermann et al., 2007).
Another important advantage offered by the reflective holograms is that the color of light from the laser will be restored during the reconstruction process. This is equally important since the holograms developed using this method will be of the same color as the object (Ackermann et al., 2007).
A mathematical model can be used to illustrate the idea behind holography. The complex number U can be used to model the wave of a single-frequency light wave. This represents the magnetic or the electric field of the light wave. The reference and the object waves at any given point of a holographic system can be given byURand U0 respectively. The interference beams is given by; UR+ U0, and the energy of the interference beam is proportional to the square of the magnitude of the combined waves. This is given as
| UR+ U0 |2 = UR U0* + k|UR|2 + | U0|2 + U0* UR
If the photographic plate is then exposed to the two beam s of light and then developed, its transmittance, T, is proportional to the light energy that was incident on the plate, which is given by;
T=k U0UR*+ k|UR|2 + k | U0|2 +k U0*UR, where k is a constant.
When the plate developed is lighted using the reference beam, the light transmitted through the photographic plate, UH is equal to the transmittance T multiplied by the reference beam amplitude UR. This gives;
UH = TUR = k U0 |UR|2 + k|UR|2 UR + k| U0|2 UR+ k U0* |UR|2
As it can be seen in the above equation, UH has four terms. Each of these represents a beam of light emerging from the hologram. The terms that we are concerned with are the first and the fourth terms. The first term is proportional to U0, which is the reconstructed object beam. This beam enables the viewer to see the initial object even after the object has been removed from the present point of view (Ackermann et al., 2007).
The fourth term (k U0* |UR|2) is referred to as the conjugate object beam. The beam has the reverse curvature to the object beam. It forms the object’s real image in the space beyond the holographic plate.
In both the transmission and reflection holograms, a common hologram plate can be used. The diagram below shows such hologram plate that can be used.
The process of making a Hologram
As Albert Einstein said once, “Everything should be made as simple as possible but not simpler”. The steps described below will ensure that the process of making holograms is understandable, safe, and less expensive. To be able to make a hologram, a number of equipments are needed. The laser is by far the most important component of the holographic set-up. The laser is a source of light to illuminate the object for which the hologram is being developed. The laser produces the light of a specific wavelength, as opposed to the sun light, which consists of many wavelengths. To make the process precise and the image to be clearer, any other source of light must be kept out. This is achieved by setting up the process in the dark. Holography also requires specific exposure time. This can be achieved by the use of a shutter or electronically. Electronic control involves timing the laser so that it produces the light for a specific duration. After the light has been produced by the laser, it passes through a beam splitter. The beam from the laser is divided into two beams. Each of the beams goes through a lens. From the lens, it falls onto a mirror and is reflected onto the imaging medium. After splitting one of the beams, the object beam goes to the object where it is scattered into different directions. The other beam is the reference beam and falls onto the imaging medium directly. On the imaging medium, the object beam and the reference beams cause interference that makes the original image (Hariharan, 2002).
The formation of the image on the hologram is dependent on the stability of the various components needed to make the hologram. Light is made up of very tiny wavelength rays. Any interference to the beam of light use can damage the image formed greatly. It is, therefore, important that any form of interference such as that from noise or vibration is eliminated. As such, the holographic laboratory is set in a relatively dark environment and in a vibration free environment.
The time required for exposure in order to obtain an image of required quality depends on the quality of the laser being used. The size of the object being illuminated is also a determining factor. In addition to these, the quality of the recording image is also a determining factor. When using very powerful lasers, exposure time is just some few minutes. For very accurate imaging such as that of live people, a very high level of stability is needed in the components of the holographic setup. In such a case, a pulsed laser is necessary. This can be able to produce a large amount of energy within a short duration of time such that the exposure can last for microseconds. This short time minimizes the chances of any movement within the various components of the setup. Large objects generally need larger components. They are also much difficult to image as compared to small objects.
The object to be illuminated needs to be rough so that the light that falls onto it can be spread over to many directions. A smooth surface reflects light onto one point on the recording medium, which makes most of the light fall onto locations other than the recording medium. When setting up the equipments, many types of lasers can be used. As noted earlier, the laser is meant to give a monochromatic light. An example of the lasers is the red lasers. These are lasers that produce light of characteristic red light. This is light with almost similar wavelength character. Other sources of light should be put out. If possible, the room should be absolutely dark.
The following steps can be followed to align the equipment needed to make a hologram.
- Clip a red laser tightly on a holder and adjust its position so that red light beam is projected horizontally.
- Position the object a distance of 35 to 40 cm away from the laser.
- Ensure that the object in completely illuminated. To achieve this, place a white board behind the object and observe the shadow formed while adjusting the laser position.
After obtaining optimum illumination, remove the white board.
- Block the light from the laser by placing an opaque screen between the laser and the object. This screen acts as a shutter.
- Get a holographic plate ensuring it is not exposed to light. This can be achieved by removing it from its container in a dark room.
- Place the plate against the object with the sticky side leaning on the object. Ensure that it is intact. You can give it about 10 seconds to completely settle. From now onwards, ensure that the room is calm.
- Remove the shutter slowly while still preventing the laser light from reaching the object. This gives time for the vibrations to calm.
- After about 2 seconds, expose the object and the plate completely for not less than 5 seconds. This time can be as long as 40 seconds. Then, shut the laser light.
- Finally, process the holographic plate. (Jeong, T.H. 2009).
The process of developing the hologram involves several steps. The powder that contains the photo chemicals is mixed with water to form a solution. The plate is dipped into the solution for approximately 20 seconds. It is then rinsed using distilled water for variable amounts of time. This is usually 30 seconds. The plate is then dipped into the bleach for about 20 seconds followed by drying. The plate should be dried vertically. This can be achieved by leaning the plate onto a paper towel and placing them against a wall. After the hologram is completely dry, you can view it using a point source. A good example of a point source is a projector or a spotlight.
Not all lasers can be used in making a hologram. The laser needs to meet the required specifications and it should be pre tried. The laser should be of a specific coherence, power, and polarization. To be able to determine whether the room is not vibrating, a bottle of water can be placed at a specific location and then direct light on it. The reflected light from the bottle can show clearly whether the room is vibrating or not.
The developer solution may differ from one manufacturer to the other. The typical composition of holography developing solution includes catechol, ascorbic acid, sodium sulphite, urea, and water. The bleach is made up of water, potassium dichromate, and sodium bisulfate. The holographic plate that is used is made up of a side emulsion that is able to record the image. The plate is made such that it can only record light of a specific wavelength. However, some of the plates used are able to record all the wavelengths of the spectrum.
The beam spreader is the equipment that separates the light from the laser into two. It is placed between the laser and the lenses. A narrow beam laser is also useful where its light is reflected away from the first mirror resulting in a uniform beam. There are many types of holograms namely; reflection hologram, transmission hologram, and rainbow hologram. Classification is based on the arrangement of the parts of the holographic process, particularly, on the position of the recording medium, the object and the beam of light.
Types of holograms
Rainbow hologram was invented in 1968 by a scientist Stephen Benton. White light is used in viewing the rainbow hologram unlike the other types of holograms. Rainbow holography retains three dimensional property of the image as much as possible. This is because spectral blur is much reduced by using horizontal slit. This process eliminates the vertical parallax. Vertical parallax is the main cause of blur in the image. When viewed from a front position, a rainbow hologram produces varying colors of the spectrum. A good example of such a hologram is like the one used in credit cards or identification cards (Schmidt Group of Companies, 1978).
The process of making a rainbow hologram is as identified below. Light from the laser is directed onto an object. Preceded to this, the beam from the laser is split into two. One of the beams is called the reference beam and the other – the object beam. The object beam is directed onto the object while the reference beam is passed through a lens onto the recording medium. A major distinguishing feature in the rainbow holography is that a slit is placed between the illuminated object and the lens. The slit is horizontal in position.
The resulting recording medium, therefore, receives both the reference beam and the object beam. The recording medium experiences some interference between the reference and the object beam. To be able to view the hologram developed or the image, the medium is illuminated by a beam of equivalent wavelength to the reference beam. To be able to view this image, an observer will need to position himself to the right of the hologram (Hariharan, 2002). Because the object beam passes through a slit of specified dimension, the image on the hologram appears as if an observer is looking at the object through a slit. Therefore, at any given position an observer can only see a small horizontal portion of the image. With a change in the position of observation, one can be able to see the different portions of the image but not all the parts at a time. Does it, therefore, mean that one will need to keep on changing positions always to be able to see the entire image? If the wavelength used to illuminate the image is changed, the position of the image changes (Schmidt Group of Companies, 1978). This implies that from the same position, an observer can observe different portions of the image. The solution to the question of viewing the whole image is attained by illuminating the hologram using light of many different wavelengths. This is achieved by illuminating the hologram using white light directed from the left side. Because of the many different wavelengths present in the white light, each of them reconstructs a different portion of the image making the whole image visible. Because of the different colors from the white light, the color of the image changes as one changes the position of viewing vertically. This type of hologram is mostly applicable in security seals such as in the banking sector (Hariharan, 2002).
The other type of holograms is the reflection hologram. Just as the name suggests, a reflection hologram is viewed by a principle of reflection. Different from the earlier rainbow hologram, a reflection hologram is viewed from the same side as the source of light. During the formation of a reflection hologram, the object and the reference beam strike the plate on different and opposite sides. This means that one of the beams must strike a reflecting medium so that another one strikes the film from the backward side. A very common application of this type of holography is in sun glasses or in labeling DVD’s and CD’s. Principles of image formation are generally similar, but the viewing of the resultant image is slightly different. The image that is perceived by the viewer is a reflection of the light from the hologram. Mirror is s good example to illustrate this clearly. The image that the viewer sees in the mirror is a reflection of the light from the object. In this case, white light is directed from the object, and, therefore, the image is visible in all its colors. The process involved in recording the holograph leads to subdivision of reflection holography into two main parts namely: one step reflection hologram and two step reflection hologram. The single step reflection hologram is simple in nature. However, it is not very practical. During the formation of the hologram, the object and the reference beams strike the film from different positions. This results in high interference. As such, a high resolution in the emulsion of the film is perceived. A major characteristic in this type of a hologram is that only light of a specific wavelength is selected in making the image. The other wavelengths are absorbed into the matrix of the film (Hariharan, 2002).
In a two step reflection hologram, two holograms are made. The first is the normal hologram called the master hologram. Many copies are then made from the master hologram. The copy holograms are made such that the image from the hologram is made to appear half in front and half behind the recording medium. This way the image on the hologram is easily perceived (Ackermann et al., 2007).
One major characteristic of a reflection hologram is that it can be viewed in the white light such as sunlight or other light with many wavelengths. The requirement for viewing is that the light must be on a straight line. A good example of such a source is the slide projector light. By proper construction, the reflection hologram gives a well defined three dimensional image of the object. The fringes on the hologram are the one that enable the hologram to absorb a portion of light and reflect the other. This is because the fringes are arranged close to one another in the matrix of the hologram. The spacing of the fringes remains constant so that layers of the fringes are placed at equal distances. The light with the wavelength equivalent to the fringe spacing is reflected in preference. All the others are absorbed instead. This makes the image that is viewed to be monochromatic. As indicated earlier, the light directed to the hologram must be at the same angle as the viewer. This is practically impossible, because either the source of light will block the viewer if the source is placed in front of the viewer or the viewer can also block the source if he or she is positioned before the light source. To eliminate this difficulty, the playback light is usually directed at an angle of about 160 degrees so as to enable the viewer to see the image (Schmidt Group of Companies, 1978).
The image seen from a reflection hologram is a three dimensional image. It can be seen either in front or behind the plate. When the image is seen behind the plate, it is called a virtual image while if it appears in front of the plate, it is called a real image. It is better to view a virtual image because, despite the size of the plate, you can see the unchanged image. This is different from the real image where the size of the plate is an important determinant. In case of viewing the virtual image, the plates act as a guide to where you are to look and focus. This can be explained by a window example (Hariharan, 2002). To be able to see something through a window, you just need to look through within the limits of the window’s perimeter. However, when viewing something between you and the window, it will be a less useful tool to guide you on where to focus. It is, therefore, advantageous to view the virtual image. The real image is disadvantageous in that the object must be smaller than the plate onto which the image is to be formed. It is difficult and almost impossible to view the whole image if the object is larger than the plate. Imagine looking at a tree in front of you but behind a window.
Reflection holograms are important because they need relatively shorter exposure time to make as compared to transmission holograms. Unlike other holograms, we can view the reflection hologram using point source white light such as sunlight during a clear day. Various sources of light that can be used to illuminate reflection holograms are; silver halides, dichromate gelatin, or the photopolymer light. The choice of a particular source depends on the application to which the hologram is to be used (Ackermann et al., 2007).
The other type of hologram is a transmission hologram. This is one among the earliest holograms. It is also among the most widely used holograms. A major feature of this type of a hologram is that it is made when light from the object and the reference beam strike the image plate at the same side. This implies that different from the reflection hologram where the reference and object beams strike the plate from opposite sides, in this case both the beams strike the hologram plate from the same direction. Rainbow holography can, therefore, be classified as transmission type. In the formation of a holographic image, the hologram is illuminated from the rear side. This is similar to the photographic image. A photographic negative is illuminated from the rear side, and the viewer observes the image from the other side. The illuminating light is scattered as it passes through the plate and is perceived as an image to the viewer.
The process of imaging involves the reference and the object beam interfering on the film. The object beam carries information about the object. Two types of transmission holograms have been identified as laser transmission holograms and white light transmission holograms (Ackermann et al., 2007).
Application of holography
It is evident from the above discussion that the new and attracting technology of holography has numerous advantages. These advantages have led to the development of countless number of applications worldwide that aim at exploiting the advantages presented by this technology. Some of the applications are highlighted below.
Over the years, many sellers including retailers, whole sellers, and supermarkets have employed this technology to advertise goods and services. They have placed these advertisements outside their premises to attract potential customers. This is seen a better form of advertisement since this method is relatively cheaper as compared to other modes of advertisements. Holograms are also placed on packaging of products, which acts as a different form of advertisement. Big companies to push their products and services to customers in trade shows mostly use projection holograms. Holograms have also been used in the publishing industry. They are used on the book/magazine covers.
The bars code technology is widely used in supermarkets and other trade shops. They are used to identify the products being sold to a customer to determine their prices. Holographic lens are used to read the bars codes placed at the products.
Holograms are used in making Holographic Optical elements (HOEs), which are used by pilots in navigating aircrafts. While looking through the windscreens of the aircrafts, pilots can read their parameters and instruments using holographic display projected in front of their eyes. This technology has also been incorporated in newer automotive models (Hariharan, 2002).
Many companies and government in providing security on most important documents such as credit cards, identification cards, debit cards, driving license among others, use holography. This ensures that such documents are not reproduced to facilitate fraud. This in turn ensures security.
Many researchers and designers have employed the holographic interferometry in testing and designing many products. Producers of engines, car tires, artificial bones, and joints among other use this technology to test their products for any faults. This ensures that products will satisfy their customers with the highest quality. Further, holograms have been applied by artists in their work such as the creation holographic portrait among other artistic work.
Future of holography
Although there are many applications that employ the holography technology, the field is not fully exploited. There are more areas of applications that are currently under study. Examples of such applications are highlighted below (Ackermann et al., 2007).
There are many researchers worldwide who are working hard to make holographic televisions a reality in the nearest future (Schmidt Group of Companies, 1978).
The capability of a very small piece of hologram to store large volumes of data has a great potential in the world of computers. A small piece of a hologram of the sugar cube size can contain data up to the tune of 1000 GB or more. This is more advantageous compared to the data storage methods such as DVD’s and CD’s, which can only hold data to the capacity of 4.7 GB and 700MB respectively. If this line of research is taken, the hard drives in computers will no longer be needed in the future. This will bring a great revolution in the storage capabilities. Holograms can also be used to manufacture optic or holographic computers. Such computers will be capable of delivering billions if not trillion bits of data faster than today’s fastest computers.
In museums, holograms can be used to animate content of the artifacts stored there. This will enable exhibitors to display their artifacts more effectively to the viewers. This method is more effective and economical compared to the texts labels used today in nearly all museums in the world (Schmidt Group of Companies, 1978).
In the above discussion, I have focused on the history and the developments that followed the invention of holography back in the year 1947. The paper explored the major contributions that were made in the holography technology by various scientists in the world. As see, their contribution took holography a notch higher than it was anticipated by its inventor. The paper went on to explain the basic methodologies and principles that lie behind the working of holograms. It explained the recoding and processing of the two types of holograms; i.e. the transmission holograms and the reflective holograms. The paper also highlighted some of the advantages of the reflective holograms over the transmission holograms.
The paper continued to outline the experiments used in the development of holograms. It gives the systematic procedure required to effectively develop a hologram. In the third section, the paper discusses the various types of holograms that exist in the current world. It explained in details the working of the various types of holograms. In the final part of the paper, I have outlined the various areas where holograms are currently used. This part also introduces some potential areas that require attention to take holography to greater heights in the future (Schmidt Group of Companies, 1978).
The discussion in this paper is of great importance to a wide range of audience. It ranges from scientists and students to manufacturers, traders, and many others. It can be useful to students since it highlights various fields they can decide to explore to further their studies (Ackermann et al., 2007).