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Laser Holography And Hologram Application
Abstract: With the advent of laser, laser holographic gets a quick development and application in the world. This papper maily present the development, principle and application about laser holography. Last I also look into the future of the laser holographic application in the article. Laser holography; holography; transient holographic interferometry; holographic storage
Introduction
Holography is the use of optical interference and diffraction theory, the form of a specific object emitted light waves to interference fringes recorded diffraction reproduction, under certain conditions, to form a three-dimensional image of the original. Is a record of all of the information of the object (amplitude and phase), so called holography or hologram. Development of holography
In 1948, British physicist Gabor (Gabor) first proposed the holographic principles, which laid a theoretical foundation for the birth of holography.
1.1 holographic theory proposed
Development of holography has experienced three stages: the first stage is the initial stage of holography, this stage is mainly theoretical research and a small amount of experiments.
Optical holography invented by D.Gabor,. His early work is committed to improve the resolution of electron microscopy, when scientists think that the new display era has come. 1947 the D. Gabor engaged improve the resolving power of the electron microscope work by WL Bragg in the X-ray Metallography and F. Zernike phase of work inspired display about the introduction of a coherent background [2], gamma The Baiti the idea of holography to improve the resolving power of the electron microscope. In 1948 he used mercury lamp first hologram again phenomenon, in turn, created a holography. But was not strong enough coherent radiation source, the development of holography into a dormant state. Faces enormous obstacles, and the only point results, its early researchers had to abandon this optical display technology.
GL Rogers et al's work in the 1950s greatly expanded wavefront reproduction theory. However, due to the restrictions twins like "and coherent light source, holography into the doldrums after the 1955 stage.
1.3 laser recording laser reproduction period
The second stage is in the emergence of the laser, the laser recording laser reproducing period.
Holography bleak future until the early 1960s due to the work carried out by the radar laboratory of the University of Michigan in the United States before it replay glory. The laboratory engaged the integrated aperture antenna ENLeith J.Upatnieks almost Javen and others made of helium-neon laser, [3], Gabor technology epoch-making improvements, while successfully carrying out the three-dimensional diffuse the matter recording and reproducing experiment.
The emergence of the laser, the development of holography has opened up broad prospects, from 1961 to 1962, EN Leith et al Gabor hologram improved twin like "problem solved in one fell swoop, the introduction of the" the oblique reference beam method ", with a helium-neon laser successfully shot the first practical laser hologram. This makes holography in 1963 to become one of the most active branch in the field of optics. Leith et al in 1964 proposed the concept of the diffusion hologram, and the reproduction of the three-dimensional object. At the same time, the Soviet physicist Lippmann color photographic method and Gabor holography method proposed the concept of a reflection hologram.
1.4 Laser the record white reproduction period
Has the third stage of the development of holography in the 1980s, this stage is the laser recording white reproduction, such as reflection hologram, like holographic rainbow hologram embossed hologram and synthetic holography.
In 1962, former Soviet scientists YNDenisyuk based on G.Lippmann standing wave natural color xerography white light reflection hologram. From this continuous development of applied research, many scientists began their research to explore the potential applications of holography and its applications, such as holographic interferometry, holographic memory, holographic optical elements, holographic microscopy, display holographic calculation holographic and so on. During this period, SABenton rainbow holography invention opened a display hologram applications prelude. Their success, Gabor holographic idea who won the Nobel Prize in Physics in 1971.
2 laser holography principle
2.1 holographic and ordinary photographic
Holographic and ordinary photographic principles and methods essential difference
The ordinary camera based on geometrical optics based on the use of lens imaging to record each point of light intensity distribution, is imaged as a two-dimensional planar image, the relationship between images is little corresponding, can not reproduce an image as long as the backsheet breakage. Ordinary camera can meet the external environment is less demanding, the general conditions.
The hologram is different, it is based on the laws of the physical optics of light interference, diffraction, and the introduction of appropriate coherent reference wave, not only recorded in the amplitude information of the object beam, but also the loss of phase information in the ordinary photographic process recorded. Photosensitive backplane not the image of an object, but the object light and the interference fringes of the reference light, the contrast of these fringes, the shape and density of the stripes reflects the amplitude and phase distribution of the object wave. After developing and fixing processing, it becomes to a hologram. It is equivalent to a complex grating, only in the proper illumination of the light waves in order to reconstruct the original object wave. The hologram is a three-dimensional real image obtained. The relationship between the images is the point of the face should, at every point on the hologram are recorded in the information of all of the object light, regardless of wear or broken, as long as the obtained a small pieces hologram, you can put the original objects in real reproduced.
Of course, the laser holographic shooting requirements much more stringent than the ordinary photographic. First, the light source must be a coherent light source, the hologram is based on the principle of the interference of light, thus requiring the light source must have good coherence [5]. The emergence of the laser light for the hologram provides an ideal light source. Secondly, the holographic system is stable, thin, dense, the interference fringes recorded on the hologram is minimal interference will cause the blurring of interference fringes in the photographic process, and even the interference fringes can not be recorded for this holographic laboratory bench shockproof, all optics of the holographic table with magnetic material fixedly suction in the work table on a steel plate, in addition, the airflow through the optical path, the acoustic interference and temperature changes will cause a change in density of the ambient air, therefore, should be banned in the exposure to loud noises, and can not move around freely, the entire lab absolute quiet. Again, the optical path difference between the object and reference beams should be as small as possible, and can not exceed a maximum of 2cm. There is must use the high-resolution hologram, because the thin dense interference fringes recorded on the hologram backsheet, requires high-resolution photosensitive material. The ordinary photographic photosensitive backsheet due to coarse particles of silver compounds, per millimeter can record only 50 ~ 100 stripes, laser hologram dry plate resolution of up to 3000, can satisfy the requirements of the holographic per millimeter. Finally, the flushing process of the hologram photo flushing process is also very critical. Overall, laser holographic conditions are very harsh.
2.2 Fresnel hologram
The hologram is divided into two steps: wavefront interferometer records and diffraction wavefront reconstruction. The Fresnel hologram, for example, the first wave front interference records, Figure 1 is a Fresnel hologram recording light path.
The laser beam passed through the shutter after the beam splitting plate is divided into two beams: Transmissive bunch by the plane mirror M2 reflection beam expander the L2 beam expander as reference light projected onto the hologram dry plate E; bunch of reflection by the plane mirror M1 reflection the beam expander L1 beam expander shines on the subject, and then through the diffuse reflectance of an object as the object beam projected onto E. Throughout the optical axis of the light path through each element in the same horizontal plane, the beam center. The object light and the reference light angle of about 45o.
Dark in the hologram dry plate is sandwiched between the dry plate holder, so that the photosensitive emulsion surface facing the object light and reference light, and allowed to stand for one minute after the start timing of the exposure device. Remove the dry plate, developing in the darkroom of fixing a period of time after washing water rinse, and finally dry holograms produced good.
Below that the reproduction of the hologram, [8], Fresnel laser holographic is laser reproduction.
Will produce a good the hologram back when shooting the original position of the object is irradiated with the reference light, the hologram in the hologram behind the original location on the virtual image of the object can be observed.
To observe a real image of the original object, it is necessary to modify conjugate light of the reference light to irradiate the hologram can be used Guangping behind the hologram receives a real image of the object,
2.3 rainbow hologram
The rainbow holography initially S.A. Benton. It is the hologram is recorded with a laser, with a white light transmittance reproducing. The basic features one slit is added in the appropriate position in the recording system, limiting the reproducing lightwave to reduce the color of the image blur. According to the characteristics of the human eye is arranged horizontally, the imaging only in the horizontal direction a parallax effect. The rainbow hologram retains the object information in the horizontal direction, and the expense of the vertical direction of the object information, which can reduce the requirements of the coherence time of the illumination light source. It will spread to different wavelengths of light along the vertical direction of color, to false color perspective view of the different colors can be seen at different heights reconstructed image.
At different positions due to the role of the slit, the eyes will see a different color image, especially when the position of the observation point is continuously changing, and will see the color of the image changes continuously showered acquired air rainbow thus become a rainbow hologram. The rainbow hologram diffracted light converging performance, high brightness of the reconstructed image. White light illumination source, coherent scattered markings effects caused by the effects of noise can be avoided.
The rainbow hologram recorded near the real image of the object. According to the real image can be divided into one-step rainbow holography and two-step rainbow holography. Two-step real rainbow holography such as general master hologram, one-step rainbow holography real like generated by the imaging lens.
3 laser holography applications
Since the advent of the laser, the laser holographic rapid development and wide application, embossed rainbow hologram achieve, leading to the rise of the holographic printing industry, to promote the realization of the microscopic holographic microscopy progress, holographic interferometry automatic measurement technology as well as real-time optical image processing etc., has opened up a broad space for holography applications in many fields and far-reaching impact.
3.1 holographic interferometry
Holographic Interferometry is an area of holography since the birth of the most extensive practical application. The early work pioneered the theory and method of holography as the basic means of static and dynamic change detection of non-transparent diffuse surface. That is the reproducing principle of the spatial wavefront using holography, the non-contact three-dimensional measurement of the object surface and to obtain information. Holographic Interferometry micro-stress analysis, surface micro displacement measurement, shape and contour detection, vibration analysis, non-destructive testing and other fields has been widely used. Interferometry in general, as well as other means, it can solve difficult problems, the technology quickly penetrate into the mechanics, fluid mechanics, fracture mechanics, aerodynamics, acoustics, aerospace, chemical, polymer chemistry, medicine, in the field of biology and other disciplines.
Specific methods, it has developed a real-time holographic interferometry, double-exposure holographic interferometry, time-average holographic interferometry, dual-wavelength interferometry, and double pulse stroboscopic holographic interferometry. With the rapid development of photovoltaic technology, computer technology, CCD devices and fiber optic technology, the holographic interferometry cytometry acquisition and processing of information is more convenient, fast and reliable, and can be in harsh environmental conditions, timing measurements of certain physical quantities .
Holographic Interferometry in the 1980s, the United States and other advanced countries in the West have been industrialized. American business turnover in 1985 amounted to only $ 92 million. Since the late 1980s, the rapid development of computer software and hardware technology. Electronic speckle pattern interferometry makes the 1970s was born in the laboratory more mature and practical [9]. Is called electronic speckle pattern interferometry that is based on the principle of markings interferometry close combination with modern electronics and mathematical techniques, the advantage of a high degree of automation, control the acquisition and processing of information by the computer, in real time to carry out the static and dynamic testing. Holographic Interferometry Applied Research, the research project of several universities and research institutes in the early 1980s through the identification, including the study and application of double pulsed ruby laser holographic interferometry, some have reached advanced at the time level [10]. But subsequently Holographic Interferometry research has to remain in the laboratory stage, in some engineering field is used as online real-time detection of desire has yet to perfect implementation.
3.2 holographic storage
Holographic storage has a huge advantage in terms of storage capacity, together with its high redundancy, and unique advantages such as parallel read data read rate is considered to be the most potential competition with traditional magnetic storage technology. Holographic storage, the date of birth from holography full attention. Information creation of high density and large capacity of the holographic storage using holography will be stored into the hologram of the Fourier transform points, these points stored hologram page mode can be arranged in two or three-dimensional array stored in the recording medium, can also be arranged as is stored on the disc like a CD album rotating locus. A recording material for holographic storage more, there is a silver salt can be permanently stored dry version, photopolymers, and the photoresist, there are also the repeated use of the light can be erased thermally conductive plastic, an organic or inorganic light-induced discoloration and light photorefractive materials.
The late 1960s found that the photorefractive effect in photorefractive crystal holographic storage once become a hot and compact design storage solutions. Into the 1980s, optical computing boom again aroused interest in the study of the optical holographic storage. Holographic storage technology in the field of optical computing, such as optical neural networks, optical interconnects, and has broad application prospects in the field of pattern recognition and automatic control. This period of research work is mainly focused on storage and storage materials, holographic memory (system) to forward to the practical.
For nearly 10 years, the photonics technology and devices has also undergone a lot of changes. Made significant progress in photonics technology for holographic memory required for high-performance semiconductor laser, the core components of the liquid crystal spatial light modulator, CCD array detector. The theory of holographic storage, the development of methods and materials to make this technology matures. Contemporary computer technology and optical computing technology is developing rapidly, unquestionably greater than the disk and CD-ROM capacity, higher read speed, better memory devices, thus once again on the agenda of the holographic memory requirements. Currently, digital data, developed holographic memory, as well as three-dimensional holographic storage disk image process continues to accelerate, its applications are increasingly broadening.
In the foreign academia and industry, has many memorable experiment demonstrates that as the commercialization of competitive products must have a storage capacity of holographic memory readout speed and fidelity. Several university laboratories and research institutes in China have also invested in this boom has yet to solve a problem is to find a suitable recording material. No doubt, the next few years will be a good opportunity for planning production of holographic memory that can compete with other storage technologies.
3.3 molded holography
The industrialization has molded holography in the early literature and light holographic monograph does not appear, but holographic experts spent a long time in the lab one by one making slightly hologram unsatisfied, so consider the need to study the hologram replication technology. Similar to the early copy the ordinary printing method, developed a coherent light or non-coherent light mechanical copy and holography copy machines [13]. However, the product is low, high cost, to industrialization.
An embossed hologram anti-counterfeit labels produced in the United States in 1980, the Bank's VISA card with a holographic anti-counterfeiting U.S. banknotes manufactured in 1983. As Peter Lower, vice-chairman of the Intelligence Bureau of the International Chamber of Commerce, said: "laser hologram novelty, strong visual effect, making more difficult and easy application on the packaging of banknotes, can not remove the sexual inexpensive, easy to verify features, make it soon occupied the field of security. "So widely used in the ID card, passport, credit cards, famous, designer clothes label, as well as various types of documents. Realistic three-dimensional display, is constantly changing and colorful image, so that it be fully applied in the packaging, product promotion and decoration.
Embossed holography faster than printing methods, easier way to copy hologram on a polyester film or treated paper. Holography and chemical plating, molding replication technique is a combination of integrated projects. Therefore, this technology into production soon formed industrialization. According to the analysis of the current situation of the domestic and foreign markets, of embossed holograms industry in China's future in three development direction must pay attention: First, how Gui Billiton holographic hot stamping material. Followed holographic packaging material. A sophisticated packaging, the most important thing is to have distinctive and unique appearance. This directly affects the perception from the outside to the inside of the consumer goods, to determine the desire of consumers to buy. Transparent or aluminized rainbow holographic material in full compliance with the requirements of this packaging. If special edition dedicated embossed hologram will enter a wide range of areas - three-dimensional anti-counterfeiting packaging. The third direction is embossed holography combined with modern printing. Leaving consumers to accept samples in the overall packaging of the product or standard paste. Because the combination of the two technologies not only to retain the traditional art effects, and enhance the artistic charm of modern technology [14]. Publications, such as books, magazines, notebook covers and illustrations, calendar, calendars, greeting cards, art pictures, postcards, etc., which will be applied, the market can not be ignored.
It can be said that the most attractive in the packaging industry in the 21st century, anti-counterfeiting efforts strongest material in the case of the embossed hologram.
4 Prospects
Optical holography has come out of the course of half a century, especially after the birth of the world's first laser, the development of optical holography is very compelling, its wide range of applications and other modern technology ought to be written the list of high-tech achievements of the 20th century. In addition to the above areas, such as: substituted ancient holographic grating of the grating element, its volume is thin, light weight, important in modern military and aerospace applications; holographic HUD have also been equipped with modern military equipment [15] ; holographic microscopy and X-ray holography, the combination can be used to study the microscopic structure of the material and the phenomenon of life subtle process, and so on. In another example, the three-dimensional object image of computer hologram can be reproduced does not actually exist, for the three-dimensional image display, making differential filter, detection of a non-spherical lens, to achieve a variety of wavefront shearing interference, and so on. Again, holographic optical elements, holographic space filter, optical fiber holographic optical neural networks, scanners, CD-ROM read-write head and modern communication systems can be used in many fields of research and application in recent years there had been substantial progress . Since the early 1970s, China's laser holographic workers in various fields of optical holography and its application start-up and tracking. Through unremitting efforts, the work done a lot of research and teaching, made a lot of achievements, and has contributed to the development of laser holographic disciplines and their industry. In the development of the science and technology of the human and deposition in the atmosphere in the rapid development of digital technology, the future of optical holography and its industry there will be a more brilliant future.
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