From birth to present of hologram.

Transcription

1 Revised version: From birth to present of hologram. Ji-Hwan Jeong From ancient age, Mankind tried to deliver information far. There are many methods to do this, language, picture, sculpture, videos so on. But they are almost 2 dimensional, no 3 dimensional. Only sculptures are 3 dimensional, but they are too hard to make and deliver, containing too little information because they don t move. Hologram is our mankind s first attempt to deliver more massive 3D information in more easy and fast way. Though people cannot see hologram many times in our real life, hologram is expected to be improved in future. This paper will explain about background of invention, principle, types, and application at each field. This paper is made to help readers to understand get historical flow of hologram. 1. Introduction In many SF movies, people can see a moving, artificial 3D image. Mankind dreamed about that thing from long ago. But it s first invention was brought in coincidence, not was intended. Farther of hologram is Dennis Gabor who was english inventor and engineer. First time he came up to think about hologram is 1947 but hologram is interesting one to world after over than 10 years. He got nobel prize in physics in First how Dennis Gabor invented it, why hologram cannot be interested so long time, how it get interested again will be discussed. There are several types of hologram but, of course, they have common basic principle. It will be discussed followed by types of hologram. In types of hologram, basic difference, strong point and weak point of each type will be discussed. Finally, hologram is invented quite a long ago but because technology have much limit in present most people cannot see much hologram in life. Although hologram is not commercialized enough to see much in our real life, hologram influenced much in each field, for example, 3D image in architecture. 2. Background In 1947, Dennis Gabor was interested in electron microscope. His main interest was to decrease error and aberration. Theoretical limit was much smaller but experimental one met in limit because of technical limit. The problem was diffraction error and spherical aberration error which are inverse proportion to each other. Electron diffracts at lens and this makes image blur. This is called diffraction error. Diffraction becomes relatively strong at small lens so, to decrease diffraction error, lens must become larger. Meanwhile,, lens must have dot pointed focus in theory, but light far from axis at center don t proceed as theory so focus become small circle, not a dot. This is spherical aberration error. To decrease spherical aberration error lens must

2 become smaller so no more light go far from axis. But this means halving one error means doubling another. While Dennis Gabor was struggling about it, he came up with brilliant idea. It was getting bad electron picture but contains whole information and modify it with optical means. He named that Hologram, in greeks, holo means perfect and gram means information. This idea was start of hologram so it came from electron microscope not the directional effort to get 3D image. Dennis Gabor used electron to this method to get good image but it was disappointing because electron wave don t have same wavelength and intensity. So satisfying image was not given until 1960 when T.Maiman invented laser which is constant intensity and frequency. With help of laser hologram can get image good enough to be considered important. Dennis Gabor get nobel prize in physics in 1971, 24 years later he suggested his idea first. 3. Principle As discussed before, basic of hologram is to getting a bad but full information containing image and fixing it by optical mean. Fig 1 [1] shows overall process of first hologram which used electron. Upper one shows using electron gun to getting bad but full information image. Lower one shows fixing to get clear image. Fig 1. The first hologram s process in [1] It was failed by unequal intensity and wavelength. Moreover, it is hard to understand principle. To understand hologram, there must be understanding of grid interference and diffraction. So, let s see more general one. When light proceed into narrow grids, light diffract and comes out from each grid and those diffract and interfere each other. They will reinforce each other where phase difference is even multiple of π. They will offset each other where phase difference is odd multiple of π In fig 2, right upper led lines represents phase difference is 2 π and right lower one is -2 π. If human look at this grid, it looks like as there is point source of light at other side in grid so this is

3 a kind of simple hologram. Fig 2. Grid diffraction and interference. Hologram is made by two processes, recording and reconstructing. Fig 3. Shows how to record.[2] More exactly, recording lights intensity and direction at the same time. That is different from photography which records only intensity. This is main reason why people can get 3D image by hologram not like in photograph. Let s back to Fig 3. Light which have equal wavelength and intensity called Coherent light. In most case laser is that one. Light comes to beam splitter, and divided. One just goes to photographic plate where 3D information will be recorded. It called reference beam. And another go and scatter from object. This called illumination beam. Scattered light also meets at photographic plate so two lights are interfere each other and makes interference grid pattern. Photographic plate records this grid pattern and there will be both intensity and phase. The photographic plate is sensitive to light and transparent at the beginning but gradually turn black when it meets light. If there is reinforce interference so light have high intensity, the photographic plate will turn black so light cannot pass through it. Otherwise, if there is offset interference, photographic plate will not change and remain transparent. Fig 4 shows process of reconstruction. After recording, irradiate coherent light with same intensity, wavelength, and same direction as reference beam did in recording process. Then, the light will pass through where the offset interference was but blocked in reinforce interference one. Each light diffracts out and interfere each other again. So there will be reinforce interference where that was before in recording process. This is illustrated in fig 5 in more close detail.

4 Fig 3 and 4. Process of recording(left) and reconstruction(right). Fig 5. In left one, photographic plate show light and dark pattern. Light one is where offset interference was and dark one is where reinforce interference was. Right picture shows reconstructing process, original coherent light penetrate where offset interference was and diffract, interfere to make reinforce interference pattern again. 4. Types of hologram Hologram type can be categorized by how to irradiate to photographic plate and thickness of it. Way to irradiate to plate distinguishes transmission and reflection hologram. Transmission means reference beam and illumination beam come from same side of photographic plate and reflection means they come from opposite side of plate. Transmission has brighter and clear color while reflection one have better 3D image.

5 Fig 6. Left side shows transmission and right side shows reflection one. Thickness of photographic plate distinguishes thin hologram and thick hologram. Thin one is recording material is thinner than spacing of interference pattern so light can com out from both side. It can look image from various directions. On the other hand, thick hologram means recording material is thicker than spacing of interference pattern so light can comes out only one side. It better at brighter color and containing various wavelength so it is essential to color hologram. Finally there is somewhat special type of hologram, rainbow hologram. It uses white light instead of laser, so it must have much more error than others. To decrease error it use slit, recording only one dimension information. Rainbow hologram was designed not to get 3D image but to use in security. Rainbow hologram is one of a few examples people can see in real life. It can be seen in credit card and money. There is colorful line which changes color by angle. To counterfeit rainbow hologram, someone must know original object and light s angle and this is very hard to know it by just watching rainbow hologram. 5. Influence of hologram in each feild. As it was discussed before, although commercialization of hologram met limit by not enough technology, it quite have much influence in several field. In medical art, by pointing X-ray can transmit in our body, there are many research tries to use X-ray hologram to look into our body in 3D image. In building, constructing a full holographic image of building to see it before start to build is very useful. In recording historical, cultural asset, it is very important to keep asset s information. It can help people to appreciating and, most of all, restoring it when disappeared or destroyed. Also hologram is used in security to defend counterfeit as rainbow hologram discussed. Finally, many people think hologram in entertainment, like in movie, public performance, so on. But they are not hologram. They are stereography, pepper s ghost so on which seems to similar but principle is different.

6 6. Summary Hologram is a part of human s dream to 3D. It has been invented decades ago, and undergone history of the uninterested because of technical limitation. But at the same time with invention of laser, it became very interesting one to mankind. Although it has not been commercialized yet, it is interesting to human now, having influence to many aspects. As it was, hologram is developing whenever technical opportunity is given. This means hologram is a kind of human s dream, people are very eager to achieve it. According to this historical aspects, it is expected to flourish continue to future. 7. Reference [1] D. Gabor, Microscopy of reconstructed wave front, Research laboratory. British Tompson-Huston company (1947) [2] D. Gabor, A new microscopic principle, Nature 161, (1948)

7 First version: From birth to present of hologram. Ji-Hwan Jeong Mankind tried to deliver information to somewhere from very ancient to now. There are many methods to do this, language, picture, sculpture, video, so on. But there is almost no 3 dimensional way. Only sculptures, but they are too limited. Hologram is our mankind s first attempt to deliver 3D information more generally. Though we cannot see hologram many times in our real life, hologram is expected to be improved in future. This paper will explain about background of invention, principle, types, and application at each field. This paper is made to help readers to understand get historical flow of hologram. 1. Introduction In many SF movies, we can see a moving, artificial 3D image. We mankind dreamed about that thing. But it s first invention was brought in coincidence, not was intended. Farther of hologram is Dennis Gabor who was english inventor and engineer. First time he came up to think about hologram is 1947 but hologram is interesting one to world after over than 10 years. He got nobel prize in physics in First we will see about how Dennis Gabor invented it, why hologram cannot be interested so long time, how it get interested again. There are several types of hologram but, of course, they have common basic principle. It will be discussed followed by types of hologram. In types of hologram, basic difference, strong point and weak point of each type will be discussed. Finally, hologram is invented quite a long ago but because technology have much limt in present we cannot see much hologram we thought in our life. Athough hologram is not commercialized enough to see much in our real life, hologram influenced much in each field, for example, 3D image in architecture. 2. Background In 1947, Dennis Gabor was interested in electron microscope. His main interest is to decrease error and aberration. Theoretical limit was much smaller but experimental one met in limit because of technical limit. The problem was diffraction error and spherical aberration error which are inverse proportion to each other. Halving one means doubling another. While Dennis Gabor was struggling about it, he came up with brilliant idea. It was getting bad electron picture but contains whole information and modify it with optical means. He named that Hologram, in greeks, holo means perfect and gram means information. This idea was start of hologram so it was came from electron microscope not the directional effort to get 3D image. Dennis Gabor used electron to this method to get good image but it was disappointing

8 because electron wave don t have same wavelength and intensity. So satisfying image was not given until 1960 when T.Maiman invented laser which is constant intensity and frequency. With help of laser hologram can get image good enough to be considered important. Dennis Gabor get nobel prize in physics in 1971, 24 years later he suggested his idea first. 3. Principle As we discussed before, basic of hologram is to getting a bad but full information containing image and fixing it by optical mean. Fig 1 [1] shows overall process of first hologram which used electron. Upper one shows using electron gun to getting bad but full information image. Lower one shows fixing to get clear image. Fig 1. The first hologram s process in [1] It was failed by unequal intensity and wavelength. Moreover, it is hard to understand principle. So, let s see more general one. Hologram is made by two process, recording and reconstructing. Fig 2. Shows how to record.[2] More exactly, recording lights intensity and direction at the same time. That is different from photography which records only intensity. This is main reason why we can get 3D image by hologram not like in photograph. Let s back to Fig 2. Light which have equal wavelength and intensity called Coherent light. In most case laser is that one. Light comes to beam splitter, and divided. One just go to photographic plate where we want to record information. It called reference beam. And another go and scatter from object we want to see. This called illumination beam. Scattered light also meets at photographic plate so two lights are interfere each other. In photographic plate, there will be interference pattern. The photographic plate is composed of something special, reacting to light to save intensity and direction. Fig 3 shows process of reconstruction. After recording, irradiate coherent light with same intensity, wavelength, and same direction we used in recording to photographic plate. Then, the light will scattered out as if there is real object. At humans eye we can 3D image.

9 Fig 2. Process of recording Fig 3. Process of reconstruction 4. Types of hologram Hologram type can be categorized by how to irradiate to photographic plate and

10 thickness of it. Way to irradiate to plate distinguishes transmission and reflection hologram. Transmission means reference beam and illumination beam come from same side of photographic plate and reflection means they come from opposite side of plate. Transmission has brighter and clear color while reflection one have better 3D image. Fig 4. Left side shows transmission and right side shows reflection one. Thickness of photographic plate distinguishes thin hologram and thick hologram. Thin one is recording material is thinner than spacing of interference pattern so light can com out from both side. It can look image from various directions. On the other hand, thick hologram means recording material is thicker than spacing of interference pattern so light can comes out only one side. It better at brighter color and containing various wavelength so it is essential to color hologram. Finally there is somewhat special type of hologram, rainbow hologram. It uses white light instead of laser, so it must have much more error than others. To decrease error it use slit, recording only one dimension information. Rainbow hologram was designed not to get 3D image but to use in security. Rainbow hologram is one of a few examples we can see in real life. We can see it in credit card and money. There is colorful line which changes color by angle. To counterfeit rainbow hologram, we must know original object and light s angle and this is very hard to knowing it by just watching rainbow hologram. 5. Influence of hologram in each filed. As we discussed before, although commercialization of hologram met limit by not enough technology, it quite have much influence in several field. In medical art, by pointing X-ray can transmit in our body, there are many research tries to use X-ray hologram to look into our body in 3D image. In building, constructing a full holographic image of building to see it before start

11 to build is very useful. In recording historical, cultural asset, it is very important to keep asset s information. It can help people to appreciating and, most of all, restoring it when disappeared or destroyed. Also, as we discussed before, hologram is used in security to defend counterfeit. Finally, many people think hologram in entertainment, like in movie, public performance, so on. But they are not hologram. They are stereography, pepper s ghost so on which seems to similar but principle is different. 6. Summary Hologram is a part of human s dream to 3D. It has been invented decades ago, having influence in our life, and expected to flourish in future. 7. Reference [1] D. Gabor, Microscopy of reconstructed wave front, Research laboratory. British Tompson-Huston company (1947) [2] D. Gabor, A new microscopic principle, Nature 161, (1948)