Laser Hologram Applications

Holography

In 1948, British physicist Gabor (Gabor) first proposed the holographic principles, which laid a theoretical foundation for the birth of holography.

Fresnel Hologram

The holographic into interference records in two steps: wavefront 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.

The laser holography Fresnel reproduced with a laser.

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, the optical path as shown in Figure 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.

The application of laser holography

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.

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.

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 from the date of the birth of holography has been sufficient 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.

Molded Hologram

The industrialization has molded holography in the early literature and light holographic monograph does not appear, but holographic experts spend long hours 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.

Outlook

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.

Calculation hologram : the use of computer simulation of propagation of light , through the computer to form a hologram formed print hologram Microform Motherboard. Also available laser direct write system forming a computer hologram CGH or using a liquid crystal light valve or spatial light modulator display holograms, using the illumination optical reproducing such a holographic method is referred to as a computer generated hologram ; one of the important characteristics of a hologram is that it scale small recording interference fringes reached nanoscale , which resulted in too much information for the computer generated hologram , a hologram contains coded reproduced is a calculation amount is too large , so that the Fourier spectrum , and therefore early CGH able to handle the images are simple symbols a

Digital hologram : digital holography is a new holographic imaging method proposed by the of Gu Dexin door in 1967 , CCD optocoupler devices instead of traditional dry version recorded holograms by computer in digital form on the holographic Figure reproduced , constrained by a variety of conditions but then , there has been no significant progress , with the advent of the development of computer technology and high resolution CCD , charge-coupled device , digital holographic technology before they get rapid development .

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