Holography (from the Greek ὅλος hólos, "whole" + γραφή grafē, "writing, drawing") is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system (a camera or an eye) is placed in the reconstructed beam, an image of the object will be seen even when the object is no longer present. The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the image appear three-dimensional. The holographic recording itself is not an image - it consists of an apparently random structure of either varying intensity, density or profile - an example can be seen below.

The technique of holography can also be used to store, retrieve, and process information optically. While it has been possible to create a 3-D holographic picture of a static object since the 1960s, it is only in the last few years that arbitrary scenes or videos can be shown on a holographic volumetric display.

Overview and history

Holography was invented in 1947 by the Hungarian-British physicist Dennis Gabor (Hungarian name: Gábor Dénes), work for which he received the Nobel Prize in Physics in 1971. Pioneering work in the field of physics by other scientists including Mieczysław Wolfke resolved technical issues that previously had prevented advancement. The discovery was an unexpected result of research into improving electron microscopes at the British Thomson-Houston Company in Rugby, England, and the company filed a patent in December 1947 (patent GB685286). The technique as originally invented is still used in electron microscopy, where it is known as electron holography, but holography as a light-optical technique did not really advance until the development of the laser in 1960.

The first practical optical holograms that recorded 3D objects were made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks at University of Michigan, USA. Advances in photochemical processing techniques to produce high-quality display holograms were achieved by Nicholas J. Phillips.

Several types of holograms can be made. Transmission holograms, such as those produced by Leith and Upatnieks, are viewed by shining laser light through them and looking at the reconstructed image from the side of the hologram opposite the source. A later refinement, the "rainbow transmission" hologram, allows more convenient illumination by white light rather than by lasers. Rainbow holograms are commonly seen today on credit cards as a security feature and on product packaging. These versions of the rainbow transmission hologram are commonly formed as surface relief patterns in a plastic film, and they incorporate a reflective aluminum coating that provides the light from "behind" to reconstruct their imagery.

Another kind of common hologram, the reflection or Denisyuk hologram, is capable of multicolour-image reproduction, using a white-light illumination source on the same side of the hologram as the viewer.

Specular holography is a related technique for making three-dimensional imagery by controlling the motion of specularities on a two-dimensional surface. It works by reflectively or refractively manipulating bundles of light rays, whereas Gabor-style holography works by diffractively reconstructing wavefronts.

One of the most promising recent advances in the short history of holography has been the mass production of low-cost solid-state lasers, such as those found in millions of DVD recorders and used in other common applications, which are sometimes also useful for holography. These cheap, compact, solid-state lasers can, under some circumstances, compete well with the large, expensive gas lasers previously required to make holograms and are already helping to make holography much more accessible to low-budget researchers, artists and dedicated hobbyists.

It was thought that it would be possible to use X-rays to make holograms of molecules and view them using visible light. However, X-ray holograms have not been created to date.

How holography works

A detailed theoretical account of how holography works is provided by Hariharan.

The basics

Holography is a technique which enables a light field to be recorded, and reconstructed later when the original light field is no longer present. It is analogous to sound recording where the sound field is encoded in such a way that it can later be reproduced.

Though holography is often referred to as 3D photography, this is a misconception. A photograph represents a single fixed image of a scene, whereas a hologram, when illuminated appropriately, re-creates the light which came from the original scene; this can be viewed from different distances and at different orientations just as if the original scene were present. The hologram itself consists of a very fine random pattern, which appears to bear no relationship to the scene which it has recorded.

To record a hologram, some of the light scattered from an object or a set of objects falls on the recording medium. A second light beam, known as the reference beam, also illuminates the recording medium, so that interference occurs between the two beams. The resulting light field generates a seemingly random pattern of varying intensity, which is recorded in the hologram. The figure below is a photograph of part of a hologram - the object was a toy van. The photograph was taken by backlighting the hologram with diffuse light, and focusing on the surface of the plate.

It is important to note that the holographic recording is contained in the random intensity structure (which is a speckle pattern), and not in the more regular structure, which is due to interference arising from multiple reflections in the glass plate on which the photographic emulsion is mounted. It is no more possible to discern the subject of the hologram from this random pattern than it is to identify what music has been recorded by looking at the hills and valleys on a gramophone record surface or the pits on a CD.

When the original reference beam illuminates the hologram, it is diffracted by the recorded hologram to produce a light field which is identical to the light field which was originally scattered by the object or objects onto the hologram. When the object is removed, an observer who looks into the hologram "sees" the same image on his retina as he would have seen when looking at the original scene. This image is often called a virtual image, as it can be seen even though the object is no longer present. The figure shown at the top of this article is an image produced by a camera which is located in front of the developed hologram which is being illuminated with the original reference beam. The camera is focused on the original scene, not on the hologram itself.

Holography explained in terms of interference and diffraction

For a better understanding of the process, it is necessary to understand interference and diffraction. Interference occurs when one or more wavefronts are superimposed. Diffraction occurs whenever a wavefront encounters an object. The process of producing a holographic reconstruction is explained below purely in terms of interference and diffraction. It is somewhat simplified but is accurate enough to provide an understanding of how the holographic process works.

For those unfamiliar with these concepts, it is worthwhile to read the respective articles before reading further in this article.

Plane wavefronts

A diffraction grating is a structure with a repeating pattern. A simple example is a metal plate with slits cut at regular intervals. A light wave incident on a grating is split into several waves; the direction of these diffracted waves is determined by the grating spacing and the wavelength of the light.

A simple hologram can be made by superimposing two plane waves from the same light source on a holographic recording medium. The two waves interfere giving a fringe pattern whose intensity varies sinusoidally across the medium. The spacing of the fringe pattern is determined by the angle between the two waves, and on the wavelength of the light.

The recorded light pattern is a diffraction grating. When it is illuminated by only one of the waves used to create it, it can be shown that one of the diffracted waves emerges at the same angle as that at which the second wave was originally incident so that the second wave has been 'reconstructed'. Thus, the recorded light pattern is a holographic recording as defined above.

Point sources

If the recording medium is illuminated with a point source and a normally incident plane wave, the resulting pattern is a sinusoidal zone plate which acts as a negative Fresnel lens whose focal length is equal to the separation of the point source and the recording plane.

When a plane wavefront illuminates a negative lens, it is expanded into a wave which appears to diverge from the focal point of the lens. Thus, when the recorded pattern is illuminated with the original plane wave, some of the light is diffracted into a diverging beam equivalent to the original plane wave; a holographic recording of the point source has been created.

When the plane wave is incident at a non-normal angle, the pattern formed is more complex but still acts as a negative lens provided it is illuminated at the original angle.

Complex objects

To record a hologram of a complex object, a laser beam is first split into two separate beams of light. One beam illuminates the object, which then scatters light onto the recording medium. According to diffraction theory, each point in the object acts as a point source of light so the recording medium can be considered to be illuminated by a set of point sources located at varying distances from the medium.

The second (reference) beam illuminates the recording medium directly. Each point source wave interferes with the reference beam, giving rise to its own sinusoidal zone plate in the recording medium. The resulting pattern is the sum of all these 'zone plates' which combine to produce a random (speckle) pattern as in the photograph above.

When the hologram is illuminated by the original reference beam, each of the individual zone plates reconstructs the object wave which produced it, and these individual wavefronts add together to reconstruct the whole of the object beam. The viewer perceives a wavefront that is identical to the wavefront scattered from the object onto the recording medium, so that it appears to him or her that the object is still in place even if it has been removed. This image is known as a "virtual" image, as it is generated even though the object is no longer there.

A simplified mathematical model of the recording and reconstruction process

A light wave can be modelled by a complex number U, which represents the electric or magnetic field of the light wave. The amplitude and phase of the light are represented by the absolute value and angle of the complex number. The object and reference waves at any point in the holographic system are given by U_O and U_R. The combined beam is given by U_O + U_R. The energy of the combined beams is proportional to the square of magnitude of the combined waves as:

$|U\_O\; +\; U\_R|^2=U\_O\; U\_R^*+|U\_R|^2+|U\_O|^2+\; U\_O^*U\_R$

If a photographic plate is exposed to the two beams and then developed, its transmittance, T, is proportional to the light energy that was incident on the plate and is given by

$T=kU\_O\; U\_R^*+k|U\_R|^2+k|U\_O|^2+\; kU\_O^*U\_R$

where k is a constant.

When the developed plate is illuminated by the reference beam, the light transmitted through the plate, U_H is equal to the transmittance T multiplied by the reference beam amplitude U_R, giving

$U\_H=TU\_R=kU\_O|U\_R|^2+k|U\_R|^2U\_R+k|U\_O|^2U\_R+\; kU\_O^*U\_R^2$

It can be seen that U_H has four terms, each representing a light beam emerging from the hologram. The first of these is proportional to U_O. This is the reconstructed object beam which enables a viewer to 'see' the original object even when it is no longer present in the field of view.

The second and third beams are modified versions of the reference beam. The fourth term is known as the "conjugate object beam". It has the reverse curvature to the object beam itself and forms a real image of the object in the space beyond the holographic plate.

When the reference and object beams are incident on the holographic recording medium at significantly different angles, the virtual, real and reference wavefronts all emerge at different angles, enabling the reconstructed object to be seen clearly.

The efficiency of a hologram

The efficiency of a hologram is a measure of the fraction of the reference beam energy which is converted into reconstructed beam energy. There are several recording medium and set-up parameters which affect holographic efficiency:

the recording medium may be thin or thick (the latter is known as a volume hologram)

the holographic recording may involve phase or amplitude modulation

the reconstruction may be made by transmission or by reflection

A thin hologram is one where the thickness of the recording material is significantly smaller than the spacing of the interference pattern which makes up the hologram. In a volume, or thick, hologram, the depth of the recording material is equal to or significantly greater than the fringe spacing.

An amplitude modulated hologram is one where the optical transmittance of the recording medium varies with the intensity of the fringe pattern. A phase hologram is one where the phase of the re-constructing reference beam varies according to the intensity of the recorded fringe pattern.

A transmission hologram is one where the object and reference beams are incident on the recording medium from the same side, whereas a reflection hologram has the object and reference beams incident from opposite sides; the reconstructing beam is then incident on the hologram from the same side as that where the viewer of the reconstruction is located.

Thin holograms

The discussion above of how holography works, relates to a thin amplitude transmission hologram. The transmittance of the recorded hologram varies with the intensity of the interference pattern produced by the combined object and reference beams. A straightforward example of this is the use of photographic emulsion on a transparent substrate. The emulsion is exposed to the interference pattern, and is subsequently developed giving a transmittance which varies with the intensity of the pattern.

In a phase transmission hologram, the transmittance of the recording is proportional to the phase of the recorded fringe pattern. It can be shown that when such a plate is illuminated by the original reference beam, it is diffracted into several different beams, one of which is equivalent to the original object wavefront.

A phase hologram is made by changing either the thickness or the refractive index of the material in proportion to the intensity of the holographic interference pattern. Many of the recording media listed below act as phase recording media. Photographic emulsion recordings, which give amplitude recordings when developed under normal conditions, can be converted to phase modulation recordings by a process known as bleaching.

It should be noted that if a thin hologram is illuminated with a broad spectrum light beam (for example a white light source), each wavelength will reconstruct an object beam of slightly differing shape and size, and the net effect will be that the original object will not be discernible.

Volume holograms

It might appear at first sight that a hologram could not be made using a recording medium whose thickness is much greater than the wavelength of the light used to make the hologram, because the interference pattern recorded will now be three dimensional and its structure will vary significantly with hologram depth so that it cannot give rise to a single reconstructed object beam. This is not the case, however.

Consider a simple hologram made from two plane waves which intersect in the recording medium, one being incident normally, and the other incident at an angle θ as above. An interference pattern is formed consisting of planes of constant phase, whose spacing is given by d = λ/sin θ. If the hologram is illuminated with one of the original plane waves, Bragg's law shows that diffracted waves occur at angles given by sin θ = nλ/d, where n is an integer. The first of these beams. which is also the most powerful, can be shown to correspond to the second of the original beams, and is therefore effectively a reconstructed object beam.

The arguments used above to show how a hologram can be made using a point source, and then a complex object which can be considered to be a set of point sources, can be applied again here to show that a volume hologram can reconstruct the object beam when illuminated by the original reference beam.

A significant advantage of a volume hologram compared with a thin hologram is that the reconstructed beam only occurs at the Bragg angle, which means that if it is illuminated with a light source which has a broad spectrum of wavelengths, reconstruction occurs only at the wavelength of the original laser used. This allows the holographic reconstruction to be done using a white light source, as is the case with most display and security holograms.

Reflection holograms can only be made using volume holograms. The main advantage of a reflection hologram is that the reference beam is incident on the same side of the hologram as where the viewer is located, making viewing more convenient. Volume reflection holograms can have either amplitude or phase modulation. A volume reflection hologram is often referred to as a Denisyuk hologram.

Theoretical maximum efficiencies

The maximum theoretical efficiencies of the various types of holographic recordings, as quoted by Hariharan, It should be noted that standard photographic film has a very low, or even zero, response at the frequencies involved and cannot be used to make a hologram.

Since each point in the object illuminates all of the hologram, the whole object can be reconstructed from a small part of the hologram. Thus, a hologram can be broken up into small pieces and each one will enable the whole of the original object to be imaged. One does, however, lose information and the spatial resolution gets worse as the size of the hologram is decreased — the image becomes "fuzzier".

Holographic recording media

The recording medium must be able to resolve the interference fringes as discussed above. It must also be sufficiently sensitive to record the fringe pattern in a time period short enough for the system to remain optically stable, i.e., any relative movement of the two beams must be significantly less than λ/2. It is possible to record holograms in certain materials using a high-power pulsed laser technique that uses only a couple of nanoseconds to record the holographic pattern.

The recording medium has to convert the interference pattern into an optical element that modifies either the amplitude or the phase of the holographic interference pattern to produce either an amplitude or a phase hologram.

Most materials used for phase holograms reach the theoretical diffraction efficiency for holograms, which is 100% for thick holograms (Bragg diffraction regime) and 33.9% for thin holograms (Raman-Nath diffraction regime, holographic films typically some micrometers thick). Amplitude holograms have a lower efficiency than phase holograms and are therefore used more rarely.

The table below shows the principal materials for holographic recording. Note that these do not include the materials used in the mass replication of an existing hologram. The resolution limit given in the table indicates the maximal number of interference lines per millimeter of the gratings. The required exposure is for a long exposure. Short exposure times (less than 1/1000 of a second, such as with a pulsed laser) require a higher exposure due to reciprocity failure.

Embossing and mass production

An existing hologram can be replicated, either in an optical way similar to holographic recording or, in the case of surface relief holograms, by embossing. Surface relief holograms are recorded in photoresists or photothermoplastics and allow cheap mass reproduction. Such embossed holograms are now widely used, for instance, as security features on credit cards or quality merchandise. The Royal Canadian Mint even produces holographic gold and silver coinage through a complex stamping process. The first book to feature a hologram on the front cover was The Skook (Warner Books, 1984) by JP Miller, featuring an illustration by Miller. That same year, "Telstar" by Ad Infinitum became the first record with a hologram cover and National Geographic published the first magazine with a hologram cover.

The first step in the embossing process is to make a stamper by electrodeposition of nickel on the relief image recorded on the photoresist or photothermoplastic. When the nickel layer is thick enough, it is separated from the master hologram and mounted on a metal backing plate. The material used to make embossed copies consists of a polyester base film, a resin separation layer and a thermoplastic film constituting the holographic layer.

The embossing process can be carried out with a simple heated press. The bottom layer of the duplicating film (the thermoplastic layer) is heated above its softening point and pressed against the stamper, so that it takes up its shape. This shape is retained when the film is cooled and removed from the press. In order to permit the viewing of embossed holograms in reflection, an additional reflecting layer of aluminum is usually added on the hologram recording layer.

It is possible to print holograms directly into steel using a sheet explosive charge to create the required surface relief.

Applications

Art

Early on, artists saw the potential of holography as a medium and gained access to science laboratories to create their work. Holographic art is often the result of collaborations between scientists and artists, although some holographers would regard themselves as both an artist and a scientist.

Salvador Dalí claimed to have been the first to employ holography artistically. He was certainly the first and best-known surrealist to do so, but the 1972 New York exhibit of Dalí holograms had been preceded by the holographic art exhibition that was held at the Cranbrook Academy of Art in Michigan in 1968 and by the one at the Finch College gallery in New York in 1970, which attracted national media attention.

During the 1970s, a number of art studios and schools were established, each with their particular approach to holography. Notably, there was the San Francisco School of Holography established by Lloyd Cross, The Museum of Holography in New York founded by Rosemary (Possie) H. Jackson, the Royal College of Art in London and the Lake Forest College Symposiums organised by Tung Jeong (T.J.). None of these studios still exist; however, there is the Center for the Holographic Arts in New York and the HOLOcenter in Seoul, which offers artists a place to create and exhibit work.

During the 1980s, many artists who worked with holography helped the diffusion of this so-called "new medium" in the art world, such as Harriet Casdin-Silver of the USA, Dieter Jung of Germany, and Moysés Baumstein of Brazil, each one searching for a proper "language" to use with the three-dimensional work, avoiding the simple holographic reproduction of a sculpture or object. For instance, in Brazil, many concrete poets (Augusto de Campos, Décio Pignatari, Julio Plaza and José Wagner Garcia, associated with Moysés Baumstein) found in holography a way to express themselves and to renew the Concrete Poetry (or Shape Poetry).

A small but active group of artists still use holography as their main medium, and many more artists integrate holographic elements into their work. Some are associated with novel holographic techniques; for example, artist Matt Brand employed computational mirror design to eliminate image distortion from specular holography.

The MIT Museum and Jonathan Ross both have extensive collections of holography and on-line catalogues of art holograms.

Data storage

Holography can be put to a variety of uses other than recording images. Holographic data storage is a technique that can store information at high density inside crystals or photopolymers. The ability to store large amounts of information in some kind of media is of great importance, as many electronic products incorporate storage devices. As current storage techniques such as Blu-ray Disc reach the limit of possible data density (due to the diffraction-limited size of the writing beams), holographic storage has the potential to become the next generation of popular storage media. The advantage of this type of data storage is that the volume of the recording media is used instead of just the surface. Currently available SLMs can produce about 1000 different images a second at 1024×1024-bit resolution. With the right type of media (probably polymers rather than something like LiNbO₃), this would result in about one-gigabit-per-second writing speed. Read speeds can surpass this, and experts believe one-terabit-per-second readout is possible. In 2005, companies such as Optware and Maxell produced a 120 mm disc that uses a holographic layer to store data to a potential 3.9 TB, which they plan to market under the name Holographic Versatile Disc. Another company, InPhase Technologies, is developing a competing format. While many holographic data storage models have used "page-based" storage, where each recorded hologram holds a large amount of data, more recent research into using submicrometre-sized "microholograms" has resulted in several potential 3D optical data storage solutions. While this approach to data storage can not attain the high data rates of page-based storage, the tolerances, technological hurdles, and cost of producing a commercial product are significantly lower.

Dynamic holography

In static holography, recording, developing and reconstructing occur sequentially, and a permanent hologram is produced.

There also exist holographic materials that do not need the developing process and can record a hologram in a very short time. This allows one to use holography to perform some simple operations in an all-optical way. Examples of applications of such real-time holograms include phase-conjugate mirrors ("time-reversal" of light), optical cache memories, image processing (pattern recognition of time-varying images), and optical computing.

The amount of processed information can be very high (terabits/s), since the operation is performed in parallel on a whole image. This compensates for the fact that the recording time, which is in the order of a microsecond, is still very long compared to the processing time of an electronic computer. The optical processing performed by a dynamic hologram is also much less flexible than electronic processing. On one side, one has to perform the operation always on the whole image, and on the other side, the operation a hologram can perform is basically either a multiplication or a phase conjugation. In optics, addition and Fourier transform are already easily performed in linear materials, the latter simply by a lens. This enables some applications, such as a device that compares images in an optical way.

The search for novel nonlinear optical materials for dynamic holography is an active area of research. The most common materials are photorefractive crystals, but in semiconductors or semiconductor heterostructures (such as quantum wells), atomic vapors and gases, plasmas and even liquids, it was possible to generate holograms.

A particularly promising application is optical phase conjugation. It allows the removal of the wavefront distortions a light beam receives when passing through an aberrating medium, by sending it back through the same aberrating medium with a conjugated phase. This is useful, for example, in free-space optical communications to compensate for atmospheric turbulence (the phenomenon that gives rise to the twinkling of starlight).

Hobbyist use

Since the beginning of holography, experimenters have explored its uses. Starting in 1971, Lloyd Cross started the San Francisco School of Holography and started to teach amateurs the methods of making holograms with inexpensive equipment. This method relied on the use of a large table of deep sand to hold the optics rigid and damp vibrations that would destroy the image.

Many of these holographers would go on to produce art holograms. In 1983, Fred Unterseher published the Holography Handbook, a remarkably easy-to-read description of making holograms at home. This brought in a new wave of holographers and gave simple methods to use the then-available AGFA silver halide recording materials.

In 2000, Frank DeFreitas published the Shoebox Holography Book and introduced using inexpensive laser pointers to countless hobbyists. This was a very important development for amateurs, as the cost for a 5 mW laser dropped from $1200 to $5 as semiconductor laser diodes reached mass market. Now, there are hundreds to thousands of amateur holographers worldwide.

In 2006, a large number of surplus Holography Quality Green Lasers (Coherent C315) became available and put Dichromated Gelatin (DCG) within the reach of the amateur holographer. The holography community was surprised at the amazing sensitivity of DCG to green light. It had been assumed that the sensitivity would be non-existent. Jeff Blyth responded with the G307 formulation of DCG to increase the speed and sensitivity to these new lasers.

Many film suppliers have come and gone from the silver-halide market. While more film manufactures have filled in the voids, many amateurs are now making their own film. The favorite formulations are Dichromated Gelatin, Methylene Blue Sensitised Dichromated Gelatin and Diffusion Method Silver Halide preparations. Jeff Blyth has published very accurate methods for making film in a small lab or garage.

A small group of amateurs are even constructing their own pulsed lasers to make holograms of moving objects.

Holographic interferometry

Holographic interferometry (HI) is a technique that enables static and dynamic displacements of objects with optically rough surfaces to be measured to optical interferometric precision (i.e. to fractions of a wavelength of light). It can also be used to detect optical-path-length variations in transparent media, which enables, for example, fluid flow to be visualized and analyzed. It can also be used to generate contours representing the form of the surface.

It has been widely used to measure stress, strain, and vibration in engineering structures.

Holoprinters

A holoprinter is a holographic printing device that can print out full-colour digital holograms from a rendered 3D model or a video series. The machine can cost up to half a million dollars and is about the size of a small room. It uses red, green and blue lasers to write a series of dots, or holopixels, across a holographic medium. The holopixel contains information about the whole image from its own unique perspective. The information for each holopixel is computed from a series of rendered images generated via computer graphics. The holographic medium is typically a polymer film. The film may require development after exposure. It is then laminated on to a hard plastic backing. Printing a digital hologram can take several hours, as each holopixel dot has to be written individually in three colours, where the colours overlap within the medium. The size of a holopixel is typically around a square millimeter.

There are only a few digital holoprinter manufacturers in the world, including Geola (Lithuania), View Holographics (UK) and Zebra Imaging (US).

Interferometric microscopy

The hologram keeps the information on the amplitude and phase of the field. Several holograms may keep information about the same distribution of light, emitted to various directions. The numerical analysis of such holograms allows one to emulate large numerical aperture, which, in turn, enables enhancement of the resolution of optical microscopy. The corresponding technique is called interferometric microscopy. Recent achievements of interferometric microscopy allow one to approach the quarter-wavelength limit of resolution.

Sensors or biosensors

The hologram is made with a modified material that interacts with certain molecules generating a change in the fringe periodicity or refractive index, therefore, the color of the holographic reflection.

Security

gold bars use kinegrams as a security measure.]] Security holograms are very difficult to forge, because they are replicated from a master hologram that requires expensive, specialized and technologically advanced equipment. They are used widely in many currencies, such as the Brazilian real 20 note, British pound 5/10/20 notes, Estonian kroon 25/50/100/500 notes, Canadian dollar 5/10/20/50/100 notes, Euro 5/10/20/50/100/200/500 notes, South Korean won 5000/10000/50000 notes, and Japanese yen 5000/10000 notes. They are also used in credit and bank cards as well as passports, ID cards, books, DVDs, and sports equipment.

Holography allows for different levels of security, depending on budget and intensity of security. The highest level of security in fully custom holography, this involves the design and creation of unique images in three dimensions, cost can range from $5,000 to $15,000. For a tightly budgeted project, there are two choices of hologram: overprint holographic diffraction foil or custom etched diffraction material, which are not dimensional but diffract light into patterns of bright rainbow light.

Other applications

Holographic scanners are in use in post offices, larger shipping firms, and automated conveyor systems to determine the three-dimensional size of a package. They are often used in tandem with checkweighers to allow automated pre-packing of given volumes, such as a truck or pallet for bulk shipment of goods. Holograms produced in elastomers can be used as stress-strain reporters due to its elasticity and compressibility, the pressure and force applied are correlated to the reflected wavelength, therefore its color.

Non-optical holography

In principle, it is possible to make a hologram for any wave.

Electron holography is the application of holography techniques to electron waves rather than light waves. Electron holography was invented by Dennis Gabor to improve the resolution and avoid the aberrations of the transmission electron microscope. Today it is commonly used to study electric and magnetic fields in thin films, as magnetic and electric fields can shift the phase of the interfering wave passing through the sample. The principle of electron holography can also be applied to interference lithography.

Acoustic holography is a method used to estimate the sound field near a source by measuring acoustic parameters away from the source via an array of pressure and/or particle velocity transducers. Measuring techniques included within acoustic holography are becoming increasingly popular in various fields, most notably those of transportation, vehicle and aircraft design, and NVH. The general idea of acoustic holography has led to different versions such as near-field acoustic holography (NAH) and statistically optimal near-field acoustic holography (SONAH). For audio rendition, the wave field synthesis is the most related procedure.

Atomic holography has evolved out of the development of the basic elements of atom optics. With the Fresnel diffraction lens and atomic mirrors atomic holography follows a natural step in the development of the physics (and applications) of atomic beams. Recent developments including atomic mirrors and especially ridged mirrors have provided the tools necessary for the creation of atomic holograms, although such holograms have not yet been commercialized.

Things often confused with holograms

Effects produced by Lenticular printing and Video projection, and Pepper's Ghost are often confused with holograms.

In 2010, there was a series of concerts organized by Crypton Future Media which included Hatsune Miku, a singing synthesizer application and its female character, performing on stage as a "holographic" character. This effect was actually achieved through a special method of rear projection against a semi-transparent screen.

In 2011, in Beijing, apparel company Burberry produced the "Burberry Prorsum Autumn/Winter 2011 Hologram Runway Show", which included life size 2-D projections of models. The company's own video shows several centered and off-center shots of the main 2-dimensional projection screen, and all the 3-D effects stem from 2-D perspective. The claim that holography was used was reported as fact in the trade media.

Holography in fiction

Holograms are often used as plot devices in science fiction.

The Carpathian Castle (1893 novel by Jules Verne) the plot revolves around prima donna La Stilla, represented at the times of the events as a hologram

The Jetsons (1962-3 television series) uses holograms as entertainment devices, replacing the television in many episodes

Star Trek: The Animated Series (1974 television series) episode "The Practical Joker", the holodeck is introduced

Star Wars (1977 film), use of the hologram in the movies and video games of the series to display people remotely communicating with each another

Hello America (1981 book by J.G. Ballard), holographic technology is used by president Charles Manson to scare nomad peoples along the United States of America, showing images of American pop culture icons such as Gary Cooper, Mickey Mouse, or the Enterprise space ship.

(1987 television series), uses the holodeck extensively; beginning with this series, various episodes and films throughout the Star Trek series feature holographic characters and ships

Red Dwarf (1988 television series), after a catastrophic radiation leak inside the Jupiter mining vessel called 'Red Dwarf', crew member Second Technician Arnold Rimmer is resurrected as a hologram and walks about the ship and planets they encounter. Because he is a "soft-light hologram," he cannot touch anything as objects just pass right through him. However, later in the series he meets 'Legion,' a gestalt entity with advanced technology, who upgrades Rimmer's light bee - the object that projects his hologram by hovering around - changing his projection to what is called in the show "hard-light," thus allowing him to once again touch objects other than computer-generated.

Back to the Future Part II (1989 film), a giant projection hologram is used as an advertisement for the (fictional) 2015 film Jaws 19

Total Recall (1990 film), the main character uses a device, similar to a wristwatch, to produce a hologram of himself and deceive his foes

Star Trek: Voyager (1995-2001 television series) introduced the Emergency Medical Hologram (EMH) doctor

Yu-Gi-Oh! (1996–present manga,film,television series,video games), use of holographic technology used in order to make a game called Duel Monsters appear to be more life like, Duel Monsters is a game where players using a wrist mounted Duel Disk summon monsters and cast spells and traps in order to bring a players life points to 0 or diminish all the cards in a players deck. Used throughout the entire series

Stargate: SG-1 (1997-2007 television series), various characters appear as holograms in various episodes: The Asgard masquerade themselves holographically as Norse gods to the primitive peoples under their protection, Morgan le Fay in "The Pegasus Project" and Myrddin as a Merlin in "Avalon" and "Camelot" as a holographic sentry; Heliopolis "Book"; the puddle jumper starship has a holographic HUD

Lost in Space (1998 film), June Lockhart (Maureen Robinson) appeared as Will's school principal "Cartwright" in a hologram

Power Rangers Time Force (2001 series), their chrono morphers use holographic communication.

Halo (series) (2001 video game) uses "holotanks" to display the avatar of an artificial intelligence construct. In Halo: Reach, an Armor Ability called the hologram allows the user to create an identical decoy.

The First $20 Million Is Always the Hardest (2002 film) Computer geeks develop a $99 computer using a holographic projector as both the display and user interface.

Stargate: Atlantis (2004-2009 television series), the Atlantis city-starship features a hologram room that allows access to the Ancient database in the form of holograms; an Ancient Control Chair contains holographic projectors; in the episode "Rising", Melia (a member of the Atlantean High Council during the first siege of Atlantis some ten millennia ago) is first seen as a hologram describing the history of the Ancients in the Pegasus Galaxy; Aurora-class battleship can project holograms remotely for communication purposes

The Island (2005 film), a holographic projector surrounded the military compound where clones were kept to give the illusion of a tropical environment; holographic displays are present on various terminals, including the MSN information terminal in Los Angeles

Dead Space (2008 video game), to replace the player's HUD, a holographic display shows up in front of the player's character

Avatar (2009 film), holographic displays are used extensively on terminals and HUDs

Iron Man and Iron Man 2, the 2008 and 2010 films.

Enthiran (2010 film), Chitti, the robot, can be telecommunicated with using a "virtual calling" where each caller can be seen as a holographic projection in front of the robot during the call

See also

Specular holography

Volume hologram

Digital holography

Digital planar holography

Holographic Sensor

Holonomic brain theory

Integral imaging

Holographic principle

Tomography

List of emerging technologies

Phase-coherent holography

Australian Holographics

Holographic data storage

Computer generated holography

References

Further reading

Lasers and holography: an introduction to coherent optics W. E. Kock, Dover Publications (1981), ISBN 978-0-486-24041-1

Principles of holography H. M. Smith, Wiley (1976), ISBN 978-0-471-80341-6

G. Berger et al., Digital Data Storage in a phase-encoded holograhic memory system: data quality and security, Proceedings of SPIE, Vol. 4988, p. 104-111 (2003)

Holographic Visions: A History of New Science Sean F. Johnston, Oxford University Press (2006), ISBN 0-19-857122-4

Three-Dimensional Imaging Techniques Takanori Okoshi, Atara Press (2011), ISBN 978-0-9822251-4-1

External links

International Hologram Manufacturers Association

— "Wavefront reconstruction using a coherent reference beam" — E. N. Leith et al.

The nobel prize lecture of Denis Gabor

MIT's Spatial Imaging Group with papers about holographic theory and Holographic video

Medical Applications of Holograms

How Stuff Works - holograms

Center for the Holographic Arts, New York - a non-profit organisation promoting holography

Specular holography art site

Faster way to produce holographic tiles

Abrasion, hand-drawn holograms

Category:British inventions Category:Photographic techniques Category:3D imaging Category:Hungarian inventions Category:Laser image generation Category:Emerging technology

Coordinates	38°53′51.61″N77°2′11.58″N
Name	Beijing
Official name	Municipality of Beijing • 北京市
Native name
Settlement type	Municipality
Total type	Municipality
Map caption	Location of Beijing Municipality within China
Coordinates display	inline,title
Coordinates region	CN
Subdivision type	Country
Subdivision name	China
Parts type	Divisions - County-level - Township-level
Parts	16 districts, 2 counties289 towns and villages
Government type	Municipality
Leader title	CPC Ctte Secretary
Leader name	Liu Qi
Leader title1	Mayor
Leader name1	Guo Jinlong
Area total km2	16801.25
Elevation m	43.5
Population total	19612368
Population as of	2010
Population density km2	auto
Population blank1 title	Ranks in China
Population blank1	Population: 26th; Density: 4th
Population demonym	Beijinger
Demographics type1	Major ethnic groups
Demographics1 title1	Han
Demographics1 info1	96%
Demographics1 title2	Manchu
Demographics1 info2	2%
Demographics1 title3	Hui
Demographics1 info3	2%
Demographics1 title4	Mongol
Demographics1 info4	0.3%
Timezone	China standard time
Utc offset	+8
Postal code type	Postal code
Postal code	100000 - 102629
Area code	10
Blank name sec1	GDP
Blank info sec1	2009 estimate
Blank1 name sec1	- Total
Blank1 info sec1	US$173.7 billion (nominal) US$283.92 billion (PPP) (13th)
Blank2 name sec1	- Per capita
Blank2 info sec1	US$10,070 (nominal) US$17,063 (PPP) (2nd)
Blank3 name sec1	HDI (2008)
Blank3 info sec1	0.891 (2nd) — high
Blank4 name sec1	License plate prefixes
Blank4 info sec1	京A, C, E, F, H, J, K, L, M, N, P 京B (taxis)京G, Y (outside urban area)京O (police and authorities)京V (in red color) (military headquarters,central government)
Blank name sec2	City trees
Blank info sec2	Chinese arborvitae (Platycladus orientalis)
Blank1 name sec2
Blank1 info sec2	Pagoda tree (Sophora japonica)
Blank2 name sec2	City flowers
Blank2 info sec2	China rose (Rosa chinensis)
Blank3 name sec2
Blank3 info sec2	Chrysanthemum (Chrysanthemum morifolium)
Website	www.beijing.gov.cn
Footnotes	}}

Beijing (, , ), also known as Peking ( or ), is a metropolis in Northern China, and the capital of the People's Republic of China. Governed as a municipality under direct administration of the central government, Beijing borders Hebei Province to the north, west, south, and for a small section in the east, and Tianjin Municipality to the southeast. Beijing is one of the Four Great Ancient Capitals of China.

Beijing is divided into 14 urban and suburban districts and two rural counties. Beijing is a major transportation hub, with dozens of railways, roads and motorways passing through the city. It is also the destination of many international flights arriving in China. Beijing is recognized as the political, educational, and cultural center of the People's Republic of China, while Hong Kong and Shanghai predominate in economic fields. The city hosted the 2008 Olympic Games.

Few cities in the world besides Beijing have served as the political and cultural centre of an area as immense as China for so long. The Encyclopædia Britannica describes it as "one of the world's great cities," and declares that the city has been an integral part of China’s history for centuries; there is scarcely a major building of any age in Beijing that does not have at least some national historical significance. Its art treasures and universities have long made the city a centre of culture and art in China. ( is represented in pinyin as j, as in Beijing. The latter is best approximated in English as "bay-DJING", rather than the hyperforeign pronunciation "bay-ZHING".)

The pronunciation "Peking" is also closer to the Fujianese dialect of Amoy or Min Nan spoken in the city of Xiamen, a port where European traders first landed in the 16th century, while "Beijing" more closely approximates the Mandarin pronunciation of the city's name.

The city has been renamed several times. During the Jin Dynasty, the city was known as Zhongdu (), and then later, under the Mongol Yuan Dynasty, as Dadu () to the Chinese and Daidu to Mongols (also recorded as Cambuluc There were cities in the vicinities of Beijing by the 1st millennium BC, and the capital of the State of Yan, one of the powers of the Warring States Period (473-221 BC), Ji (薊/蓟), was established in present-day Beijing.

After the fall of the Yan, the subsequent Qin, Han, and Jin dynasties set up local prefectures in the area. Later in 1264, in preparation for the conquest of all of China to establish the Yuan Dynasty, Kublai Khan decided to rebuild it slightly north to the center of the Jin capital, and in 1272, he made this city his capital as Dadu (大都, Chinese for "great capital"),

Ming and Qing period

In 1368, Zhu Yuanzhang, soon after declaring himself the first emperor of the Ming Dynasty, sent an army toward Dadu, still held by the Yuan. The last Yuan emperor fled north to Shangdu, and Zhu razed the Yuan palaces in Dadu to the ground. The city was renamed Beiping (北平) in the same year, and Shuntian (順天) prefecture was established in the area around the city. In 1403, the new (and third) Ming emperor - the Yongle Emperor - renamed this city 'Beijing', It is believed that Beijing was the largest city in the world from 1425 to 1650 and from 1710 to 1825. Other notable buildings constructed during the Ming period include the Temple of Heaven (built by 1420). Tiananmen, now a state symbol of the People's Republic of China and featured on its emblem, was first built in 1420, and rebuilt several times later. Tiananmen Square was built in 1651 and enlarged in 1958. Jesuits finished building the first Beijing-area Roman Catholic church in 1652 at the Xuanwu Gate, where Italian Jesuit Matteo Ricci (1552–1610) had lived; the modern Nantang (南堂, Southern Cathedral) has been built over the original cathedral.

The end of the Ming came in 1644 when, for 40 days, Li Zicheng's peasant army captured Beijing and overthrew the Ming government. When the powerful Manchu army arrived at the outskirts of the city, Li and his followers abandoned the city and as a result the Manchu forces, under Prince Dorgon, captured Beijing without a fight.

Prince Dorgon established the Qing Dynasty as a direct successor to the Ming, and Beijing remained China's capital. The Qing Emperors made some modifications to the Imperial residence, but in large part, the Ming buildings and the general layout remained unchanged. Beijing at this time was also known as Jingshi, which corresponded to the Manchu Gemun Hecen with the same meaning. The classic Chinese novel Dream of the Red Chamber is set in Beijing during the early years of Qing rule (the end of the 17th century). as photographed in the early 20th century]]

During the Second Opium War, Anglo-French forces captured the city, looted and burned the Summer Palace and Old Summer Palace in 1860. Under the Convention of Peking that ended the war, Western powers secured the right to establish permanent diplomatic presence in the Beijing Legation Quarter. In 1900, Beijing was again invaded by foreign powers to quell the Boxer Rebellion. Some important Imperial structures in the city were destroyed during the fighting, including the Hanlin Academy and Summer Palace.

Republican era

The Xinhai Revolution of 1911, aimed at replacing Qing rule with a republic, originally intended to establish its capital at Nanjing. After high-ranking Qing official Yuan Shikai forced the abdication of the Qing emperor in Beijing and ensured the success of the revolution, the revolutionaries in Nanjing accepted that Yuan should be the president of the new Republic of China and the capital remains at Beijing. Yuan gradually consolidated power and became by 1915 the new emperor of China, but died less than a year into his reign. China then fell under the control of regional warlords, and the most powerful factions fought frequent wars (the Zhili-Anhui War, the First Zhili-Fengtian War, and the Second Zhili-Fengtian War) to take control of the capital at Beijing. Following the success of the Kuomintang (KMT)'s Northern Expedition, which pacified the warlords of the north, Nanjing was officially made the capital of the Republic of China in 1928, and Beijing was renamed Beiping (Peip'ing) (北平) on 28 June that year, in English meaning "northern peace" or "north pacified". and was made the seat of the Provisional Government of the Republic of China, a puppet state that ruled the ethnic Chinese portions of Japanese-occupied northern China; the government was later merged into the larger Wang Jingwei Government based in Nanjing.

People's Republic

proclaiming the establishment of the People's Republic of China in 1949]]

On 31 January 1949, during the Chinese Civil War, Communist forces entered Beijing without opposition. On 1 October of the same year, the Communist Party of China, under the leadership of Mao Zedong, announced in Tiananmen the creation of the People's Republic of China and renamed the city back to Beijing. Just a few days earlier, the Chinese People's Political Consultative Conference had decided that Beijing would be the capital of the new government.

At the time of the founding of the People's Republic, Beijing Municipality consisted of just its urban area and immediate suburbs. The urban area was divided into many small districts inside what is now the 2nd Ring Road. The Beijing city wall was torn down to make way for the construction of the 2nd Ring Road, which was finished by 1981 in accord with the 1982 city plan. That road was the first of a series of new ring roads intended for motor vehicles rather than for bicycles.

Following the economic reforms of Deng Xiaoping, the urban area of Beijing has expanded greatly. Formerly within the confines of the 2nd Ring Road and the 3rd Ring Road, the urban area of Beijing is now pushing at the limits of the recently constructed 5th Ring Road and 6th Ring Road, with many areas that were formerly farmland now developed residential or commercial districts. According to a 2005 newspaper report, the size of the newly developed Beijing land was one and a half times larger than the land of old Beijing within the 2nd Ring Road. Wangfujing and Xidan have developed into flourishing shopping districts, while Zhongguancun has become a major centre of electronics in China. In recent years, the expansion of Beijing has also brought to the forefront some problems of urbanization, such as heavy traffic, poor air quality, the loss of historic neighbourhoods, and significant influx of migrants from various regions of the country, especially rural areas.

On 13 July 2001, the International Olympic Committee selected Beijing as the host for the 2008 Summer Olympics.

Geography

2010-08-08]] , an extensive imperial garden in the center of Beijing]]

Beijing is situated at the northern tip of the roughly triangular North China Plain, which opens to the south and east of the city. Mountains to the north, northwest and west shield the city and northern China's agricultural heartland from the encroaching desert steppes. The northwestern part of the municipality, especially Yanqing County and Huairou District, are dominated by the Jundu Mountains, while the western part of the municipality is framed by the Xishan Mountains. The Great Wall of China, which stretches across the northern part of Beijing Municipality, made use of this rugged topography to defend against nomadic incursions from the steppes. Mount Dongling in the Xishan ranges and on the border with Hebei is the municipality's highest point, with an altitude of 2303 m. Major rivers flowing through the municipality include the Yongding River and the Chaobai River, part of the Hai River system, and flow in a southerly direction. Beijing is also the northern terminus of the Grand Canal of China which was built across the North China Plain to Hangzhou. Miyun Reservoir, built on the upper reaches of the Chaobai River, is Beijing's largest reservoir, and crucial to its water supply. The urban area of Beijing is situated in the south-central part of the municipality and occupies a small but expanding part of the municipality's area. It spreads out in bands of concentric ring roads, of which the fifth and outermost, the Sixth Ring Road (the numbering starts at 2), passes through several satellite towns. Tian'anmen (Gate of Heavenly Peace) and Tian'anmen Square are at the centre of Beijing, and are directly to the south of the Forbidden City, former residence of the emperors of China. To the west of Tian'anmen is Zhongnanhai, residence of the paramount leaders of the People's Republic of China. Running through central Beijing from east to west is Chang'an Avenue, one of Beijing's main thoroughfares.

Climate

The city's climate is a rather dry, monsoon-influenced humid continental climate (Köppen climate classification Dwa), characterised by hot, humid summers due to the East Asian monsoon, and generally cold, windy, dry winters that reflect the influence of the vast Siberian anticyclone.

Air quality

Joint research between United States and Chinese researchers in 2006 concluded that much of the city's pollution comes from surrounding cities and provinces. According to the research, 34% of PM_2.5 and on average 35-60% of ozone can be traced to sources outside the city. Shandong Province and Tianjin Municipality have a "significant influence on Beijing's air quality", partly due to the prevailing south/southeasterly flow during summer and the mountains to the north and northwest.

In preparation for the 2008 Summer Olympics and after promising to clean up the city's air, nearly US$17 billion was spent. Beijing implemented a number of air improvement schemes for the duration of the games. This included stopping work on all construction sites, closing many factories both in and around Beijing, closing some gas stations, and cutting motor traffic by half. Two new subway lines were opened and thousands of old taxis and buses were replaced to encourage residents to use public transport. The Beijing government encouraged a discussion to keep the odd-even scheme in place after the Olympics, and although the scheme was eventually lifted on 21 September 2008, it was replaced by new restrictions on government vehicles and a new restriction that does not allow the use of a car once a week based on the last number of the license plate. In addition to the vehicle restrictions, staggered office hours and retail opening times have been encouraged to avoid the rush hour, and parking fees were increased.

Beijing was the first city in China to require the Chinese equivalent to the Euro 4 emission standard. Some 357,000 "yellow label" vehicles — those that have too high emission levels — have been banned from Beijing altogether.

The government regularly uses cloud-seeding measures to increase the likelihood of rain showers in the region to clear the air prior to large events as well as to combat drought conditions in the area.

According to the United Nations Environmental Program (UNEP), China has spent 17 billion over the last three years on a large-scale green drive. Beijing has added 3,800 natural gas buses, the largest fleet in the world. Twenty percent of the Olympic venues' electricity comes from renewable energy sources. The city has also planted hundreds of thousands of trees and increased green space in an effort to make the city more livable.

One year after the 2008 Olympics, Beijing's officials reported that the city was enjoying the best air quality this decade because of the measures taken during the Olympic Games. Nonetheless Beijing still faces air pollution problems.

Dust storms

Dust from erosion of deserts in northern and northwestern China results in seasonal dust storms that plague the city; the Beijing Weather Modification Office sometimes artificially induces rainfall to fight such storms and mitigate their effects. In the first four months of 2006 alone, there were no fewer than eight such storms. In April 2002, one dust storm alone dumped nearly 50,000 tons of dust onto the city before moving on to Japan and Korea.

Cityscape

Administrative divisions

, in northwestern Beijing at night]] area]] in Beijing's Chaoyang District]] , located in the Xicheng District, is traditionally considered one of Beijing's most beautiful and charming scenic areas.]] Major neighbourhoods in urban Beijing include the following. Neighbourhoods may overlap across multiple districts (see below):

Neighborhoods Qianmen Tian'anmen Di'anmen Chongwenmen Xuanwumen Fuchengmen Xizhimen Deshengmen Andingmen Sanlitun Dongzhimen Chaoyangmen Yongdingmen Zuo'anmen You'anmen Guangqumen Guang'anmen Dongbianmen Xibianmen Hepingmen Fuxingmen Jianguomen Gongzhufen Fangzhuang Guomao Hepingli Ping'anli Beixinqiao Jiaodaokou Kuanjie Wangjing Wangfujing Dengshikou Wudaokou Xidan Dongdan Zhongguancun Panjiayuan Beijing CBD Yayuncun

Subdivisions Beijing Municipality comprises 16 administrative sub-divisions, county-level units governed directly by the municipality (second-level divisions). Of these, 14 are districts and 2 are counties. On July 1, 2010 Chongwen District () and Xuanwu District () were merged into Dongcheng District and Xicheng District respectively. The urban and suburban areas of the city are divided into six (6) districts: Miyun County Yanqing County

Towns Towns within Beijing Municipality but outside the urban area include (but are not limited to): Changping Huairou Miyun Liangxiang Liulimiao Tongzhou Yizhuang Tiantongyuan Beiyuan Xiaotangshan

Several place names in Beijing end with mén (), meaning "gate", as they were the locations of gates in the former Beijing city wall. Other place names end in cūn (), meaning "village", as they were originally villages outside the city wall.

Beijing's 18 districts and counties are further subdivided into 273 lower (third)-level administrative units at the township level: 119 towns, 24 townships, 5 ethnic townships and 125 subdistricts.

Architecture

Three styles of architecture predominate in urban Beijing. First, the traditional architecture of imperial China, perhaps best exemplified by the massive Tian'anmen (Gate of Heavenly Peace), which remains the People's Republic of China's trademark edifice, the Forbidden City, the Imperial Ancestral Temple and the Temple of Heaven. Next there is what is sometimes referred to as the "Sino-Sov" style, built between the 1950s and the 1970s, with structures tending to be boxy and sometimes poorly constructed. Finally, there are much more modern architectural forms — most noticeably in the area of the Beijing CBD and Beijing Financial Street.

Beijing of the early 21st century has witnessed tremendous growth of new building constructions, showing various modern styles from international designers. A mixture of both old and new styles of architecture can be seen at the 798 Art Zone, which mixes 1950s design with a blend of the new.

Politics and government

Municipal government is regulated by the local Communist Party of China (CPC) in issuing administrative orders, collecting taxes, and operating the economy. The local party authority is headed by the Beijing CPC Secretary (北京市委书记). The local CPC also directs a standing committee of the Municipal People's Congress in making policy decisions and overseeing local government. Local government figures include a mayor, vice-mayor, and numerous bureaus focusing on law, public security, and other affairs. Additionally, as the capital of China, Beijing houses all the important national governmental and political institutions, including the National People's Congress.

Economy

, Park Hyatt, Yintai, CCTV Headquarters, Jingguang]] , the economic centre of Beijing]] is one of the busiest streets in Beijing, with nearly 100,000 visitors daily (August 2008).]] is a technology hub in Haidian District]]

Beijing is amongst the most developed cities in China with tertiary industry accounting for 73.2% of its GDP; it was the first post industrial city in mainland China. Finance is one of the most important industries of Beijing. By the end of 2007, there were 751 financial organizations in Beijing that generated 128.6 billion RMB revenue accounting for 11.6% of the total financial industry revenue of the entire country. It also accounts for 13.8% of Beijing's GDP, the highest percentage of that of all Chinese cities. Beijing is home to 26 Fortune Global 500 companies, the third most in the world behind Tokyo and Paris.

In 2010, Beijing's nominal GDP reached 1.37 trillion RMB. Its per capita GDP was 78,194 RMB. In 2009, Beijing's nominal GDP was 1.19 trillion RMB (US$174 billion), a year-on-year growth of 10.1% from the previous year. Its GDP per capita was 68,788 RMB (US$10,070), an increase of 6.2% from the previous year. In 2009, Beijing's primary, secondary, and tertiary industries were worth 11.83 billion RMB, 274.31 billion RMB, and 900.45 billion RMB. Urban disposable income per capita was 26,738 yuan, a real increase of 8.1% from the previous year. Per capita pure income of rural residents was 11,986 RMB, a real increase of 11.5%. Per capita disposable income of the 20% low-income residents increased 16.7%, 11.4 percentage points higher than the growth rate of the 20% high-income residents. The Engel's coefficient of Beijing's urban residents reached 31.8% in 2005 and that of the rural residents was 32.8%, declining 4.5 percentage points and 3.9 percentage points, respectively, compared with 2000.

Beijing's real estate and automobile sectors have continued to boom in recent years. In 2005, a total of 28.032 million square metres of housing real estate was sold, for a total of 175.88 billion RMB. The total number of cars registered in Beijing in 2004 was 2,146,000, of which 1,540,000 were privately owned (a year-on-year increase of 18.7%).

The Beijing CBD, centred at the Guomao area, has been identified as the city's new central business district, and is home to a variety of corporate regional headquarters, shopping precincts, and high-end housing. The Beijing Financial Street, in the Fuxingmen and Fuchengmen area, is a traditional financial centre. The Wangfujing and Xidan areas are major shopping districts. Zhongguancun, dubbed "China's Silicon Valley", continues to be a major centre in electronics and computer-related industries, as well as pharmaceuticals-related research. Meanwhile, Yizhuang, located to the southeast of the urban area, is becoming a new centre in pharmaceuticals, IT, and materials engineering. Urban Beijing is also known for being a centre of pirated goods and anything from the latest designer clothing to the latest DVDs can be found in markets all over the city, often marketed to expatriates and international visitors.

Major industrial areas include Shijingshan, located on the western outskirts of the city. Agriculture is carried out outside the urban area of Beijing, with wheat and maize (corn) being the main crops.

Specially designated industrial parks in Beijing include: Zhongguancun Science Park, Yongle Economic Development Zone, Beijing Economic-technological Development Area, and Tianzhu Airport Industrial Zone.

Demographics

The registered population of Beijing municipality consists of people holding either Beijing hukou permits (permanent residence), or temporary residence permits. The 2010 census revealed that the total population in Beijing reached 19.6 million.

After Chongqing and Shanghai,

Most of Beijing's residents belong to the Han Chinese majority. Other ethnic minorities include the Manchu, Hui, and Mongol. A Tibetan-language high school exists for youth of Tibetan ancestry, nearly all of whom have come to Beijing from Tibet expressly for their studies. A sizable international community exists in Beijing, many attracted by the highly growing foreign business and trade sector, others by the traditional and modern culture of the city. Much of this international community lives in the areas around the Beijing CBD, Sanlitun, and Wudaokou. In recent years there has also been an influx of South Koreans (estimate 200,000 in 2009) who live in Beijing predominantly for business and study purposes. Many of them live in the Wangjing and Wudaokou areas.

Excludes members of the People's Liberation Army in active service.

Culture

dish from the Qing dynasty]]

People native to urban Beijing speak the Beijing dialect, which belongs to the Mandarin subdivision of spoken Chinese. This speech is the basis for putonghua, the standard spoken language used in mainland China and Taiwan, and one of the four official languages of Singapore. Rural areas of Beijing Municipality have their own dialects akin to those of Hebei province, which surrounds Beijing Municipality.

Beijing opera, or Peking opera (Jīngjù, 京剧), is well-known throughout the nation. Commonly lauded as one of the highest achievements of Chinese culture, Beijing opera is performed through a combination of song, spoken dialogue, and codified action sequences, such as gestures, movement, fighting and acrobatics. Much of Beijing opera is carried out in an archaic stage dialect quite different from Modern Standard Chinese and from modern Beijing dialect.

Siheyuans line hutongs (), or alleys, which connect the interior of Beijing's old city. They are usually straight and run east to west so that doorways can face north and south for Feng Shui reasons. They vary in width — some are very narrow, enough for only a few pedestrians to pass through at a time.

Once ubiquitous in Beijing, siheyuans and hutongs are now rapidly disappearing, as entire city blocks of hutongs are leveled and replaced with high-rise buildings. Residents of the hutongs are entitled to live in the new buildings, in apartments of at least the same size as their former residences. Many complain, however, that the traditional sense of community and street life of the hutongs cannot be replaced. Residents, however, have limited control over their own property, as the government usually owns it. Some particularly historic or picturesque neighbourhoods of hutongs are being preserved and restored by the government, especially for the 2008 Olympics.

Beijing cuisine is the local style of cooking in Beijing. Peking Duck is perhaps the most well-known dish. The Manhan Quanxi is a rare traditional banquet originally intended for the ethnic-Manchu emperors of the Qing Dynasty; it remains very prestigious and expensive. The Fuling Jiabing is a traditional Beijing snack food, a pancake (bing) resembling a flat disk with filling, made from fu ling (Poria cocos (Schw.) Wolf, or "tuckahoe"), an ingredient common in traditional Chinese medicine. Teahouses are also common in Beijing. Chinese tea comes in many varieties and some rather expensive types of Chinese tea are said to cure an ailing body extraordinarily well.

The cloisonné (or Jingtailan, literally "Blue of Jingtai") metalworking technique and tradition is a specialty of Beijing's cultural art, and is one of the most revered traditional crafts in China. Cloisonné making requires elaborate and complicated processes which includes: base-hammering, copper-strip inlay, soldering, enamel-filling, enamel-firing, surface polishing and gilding. Beijing's lacquerware is also well known for its sophisticated and intrinsic patterns and images carved into its surface, and the various decoration techniques of lacquer includes "carved lacquer" and "engraved gold".

Younger residents of Beijing have become more attracted to the nightlife, which has flourished in recent decade, breaking prior cultural traditions that practically restricted it to the upper class.

Places of interest

At the heart of Beijing's historical centre lies the Forbidden City, the enormous palace compound that was the home of the emperors of the Ming and Qing dynasties; the Forbidden City hosts the Palace Museum, which contains imperial collections of Chinese art. Surrounding the Forbidden City are several former imperial gardens, parks and scenic areas, notably the Beihai, Shichahai, Zhongnanhai, Jingshan and Zhongshan. These places, like the Beihai Park are described to be masterpieces of Chinese gardening art, and are popular tourist destinations with tremendous historical importance; Zhongnanhai during the modern era has also been the political heart of various Chinese governments and regimes and is now the headquarters of the Communist Party of China. From Tiananmen Square, which is located right across the Forbidden City, there are several notable sites, such as the Tiananmen, Qianmen, the Great Hall of the People, National Museum of China, Monument to the People's Heroes, and Mausoleum of Mao Zedong. The Summer Palace and the Old Summer Palace both lie at the western part of the urban city of Beijing; the Summer Palace, a UNESCO World Heritage Site, displays a comprehensive collection of imperial gardens and palaces that functioned as the summer retreat for the Qing Dynasty emperors.

Among the best known religious sites in the city is the Temple of Heaven (Tiantan), located in southeastern Beijing, also a UNESCO World Heritage Site, where emperors of the Ming and Qing dynasties made visits for annual ceremonies of prayer to Heaven for good harvest; located in the opposite direction of the Temple of Heaven at the northern part of the city are the Temple of Earth (Ditan), and the Temple of the Sun (Ritan) and Temple of the Moon (Yuetan), both respectively located in the eastern and western parts of the urban area. Other well-known temple sites located in Beijing include the Dongyue Temple, Tanzhe Temple, Miaoying Temple, White Cloud Temple, Yonghe Temple, Fayuan Temple, Wanshou Temple and the Big Bell Temple. The city also has its own Confucius Temple, and a Guozijian. The Cathedral of the Immaculate Conception was built in 1605, and is the oldest Catholic church in Beijing. The Niujie Mosque is also the oldest mosque in Beijing, with a history over a thousand years old.

Beijing contains several well-preserved pagodas and stone pagodas, such as the towering Pagoda of Tianning Temple, which was built during the Liao Dynasty from 1100–1120, and the Pagoda of Cishou Temple, which was built in 1576 during the Ming Dynasty. Several historically important stone bridges are also located in Beijing, including the 12th century Lugou Bridge, the 17th century Baliqiao bridge and the 18th century Jade Belt Bridge. The Beijing Ancient Observatory displays pretelescopic spheres dating back to the Ming and Qing dynasties. The Fragrant Hills (Xiangshan) is a popular scenic public park that consists of natural landscape areas as well as traditional and cultural relics. The Beijing Botanical Garden exhibits over 6,000 species of plants, including a variety of trees, bushes and flowers, and an extensive peony garden. The Taoranting Park, Chaoyang Park, Haidian Park and Zizhu Yuan are all popular recreational parks that consist of a variety of natural landscapes. The Beijing Zoo is a center of zoological research that also contains rare animals from various continents, including the giant panda of China.

Beijing is also known for its siheyuan (courtyard houses) and hutong (alleys), although they are increasingly disappearing due to the growth of city constructions and are giving way to high-rises. The city has several well-preserved neighborhoods of siheyuan, including some of the more grand courtyard houses, such as the Prince Gong Mansion. There are over one hundred museums in Beijing, and aside from the Palace Museum in the Forbidden City and the National Museum of China, other major museums include the National Art Museum of China, the Capital Museum, the Beijing Art Museum, the Military Museum of the Chinese People's Revolution, the Geological Museum of China, the Beijing Museum of Natural History and the Paleozoological Museum of China. The archaeological Peking Man site at Zhoukoudian is another World Heritage Site within the Beijing municipality, and it contains a wealth of discoveries, including one of the first specimens of Homo erectus, and an assemblage of bones of the gigantic hyena Pachycrocuta brevirostris. There are several sections of the UNESCO World Heritage Site Great Wall of China located in the municipality, most notably Badaling, Jinshanling, Simatai and Mutianyu.

Media

Television and radio

Beijing Television (BTV) broadcasts on numbered channels 1 through 10. Three radio stations feature programmes in English: Hit FM on FM 88.7, Easy FM by China Radio International (CRI) on FM 91.5, and the newly launched Radio 774 on AM 774. Beijing Radio Stations is the family of radio stations serving the city audience; its stations include the music station on 97.4 FM as well as a series of other stations focused on news, sports, educational programming, and others.

Press

The well-known Beijing Evening News (Beijing Wanbao, 北京晚报), covering news about Beijing in Chinese, is distributed every afternoon. Other newspapers include The Beijing News (Xin Jing Bao, 新京报), the Beijing Star Daily, the Beijing Morning News, and the Beijing Youth Daily (Beijing Qingnian Bao), as well as English-language weeklies Beijing Weekend and Beijing Today (the English-language edition of Youth Daily). People's Daily and China Daily (English) are published in Beijing as well. Nationally circulated Chinese newspapers are also available in Beijing.

Publications primarily aimed at international visitors and the expatriate community include the English-language periodicals Time Out Beijing, City Weekend, Beijing This Month, Beijing Talk, That's Beijing.

The international press, including English and other languages' newspapers and magazines, are available in major international hotels and friendship stores, and content often appears complete.

Sports

Beijing hosted the 2008 Summer Olympics and the 2008 Summer Paralympics. City officials relocated 350,000 people for the construction of the Beijing National Stadium, which was completed on 28 June 2008. Professional sports teams based in Beijing include:

Chinese Super League

* Beijing Guoan

Chinese Football Association Jia League

* Beijing Baxy

* Beijing Institute of Technology FC

Chinese Basketball Association

* Beijing Ducks

Women's Chinese Basketball Association

* Beijing Shougang

Asia League Ice Hockey

* China Sharks

China Baseball League

* Beijing Tigers

The Beijing Olympians of the ABA, formerly a CBA team, kept their name and maintained a roster of primarily Chinese players after moving to Maywood, California in 2005.

Transport

With the growth of the city following economic reforms, Beijing has evolved as the most important transport hub in the People's Republic of China, and within the larger East Asian region. Encircling the city are five ring roads, nine expressways and city express routes, eleven China National Highways, several railway routes, and an international airport.

Railways

Beijing has long been the largest railway hub in China. There are railway lines from Beijing to Shanghai, Guangzhou, Kowloon, Harbin, Qinhuangdao, Baotou, Yuanping, Chengde, and Tianjin. As of 2010 July 1, Beijing Railway Station has 173 trains stopping daily, while Beijing West Railway Station has 232 trains, Beijing South has 163 trains, Beijing North has 22. The state-of-the-art Beijing South Railway Station re-opened in August 2008, and serves as the Beijing terminus for the Beijing-Tianjin high-speed train, one of the fastest regular passenger train service in the world, as well as all other high-speed CRH trains. International trains to cities in Mongolia, Russia, Vietnam and North Korea, all run through Beijing.

Several other railway stations in urban Beijing handle regular passenger traffic: Beijing East and Qinghuayuan. Fengtai stations had been closed for renovation. There are also a number of other stations serving suburban areas. Passenger trains in China are numbered according to their direction in relation to Beijing.

Roads and expressways

:See: Ring Roads of Beijing, Expressways of Beijing and China National Highways of Beijing for more related information.

Beijing is connected via road links from all parts of China as part of the National Trunk Road Network. Nine expressways of China connect with Beijing, as do eleven China National Highways. Due partly to its design as an ancient capital, roads in Beijing often are in one of the four compass directions.

Beijing's urban transport is dependent upon the five "ring roads" that successively surround the city, with the Forbidden City area marked as the geographical center for the ring roads. The ring roads appear more rectangular than ring-shaped. The 1st Ring road is not officially defined. The 2nd Ring Road is fully located in Beijing's inner city areas. Ring roads tend to resemble expressways progressively as they extend outwards, with the 5th Ring Road and 6th Ring Road being full-standard National expressways - linked to other roads only with interchanges. Expressways to other regions of China are generally accessible from the 3rd Ring Road outward.

One of the biggest concerns with traffic in Beijing involves its traffic jams. Even outside of rush hour, several roads still remain clogged up with traffic. Urban area ring roads and major thoroughfares, especially near Chang'an Avenue, are normally cited as high-congestion areas.

Exacerbating Beijing's traffic problems is its relatively underdeveloped mass transit system. Beijing's urban design layout further complicates the situation of the transport system. The authorities have introduced several bus lanes where, during rush hour, all vehicles except for public buses must keep clear. In the beginning of 2010, Beijing had 4 million registered automobiles. For the end of 2010, the government expects 5 million cars in Beijing. In 2010, new car registrations in Beijing averaged 15,500 per week.

Towards the end of 2010, the city government of Beijing announced a series of drastic measures to tackle traffic jam, including limiting the number of new plates issued to passenger cars to 20,000 a month and barring cars of non-Beijing plates from entering areas within the Fifth Ring Road during rush hours.

Air

's new Terminal 3]]

Beijing's primary airport is the Beijing Capital International Airport (IATA: PEK; near Shunyi), which is about 20 km northeast of city centre. Beijing Capital International Airport is the 2nd busiest airport in the world (after Hartsfield-Jackson Atlanta International Airport) and the busiest in Asia in 2009. With renovations for the 2008 Olympics, the airport now boasts three terminals, with Terminal 3 being one of the largest in the world. Most domestic and nearly all international flights arrive at and depart from Capital Airport. Capital Airport is the main hub for Air China and a hub for China Southern and Hainan Airlines. The capital links Beijing with almost every other Chinese city with regular air passenger service. It is linked to central Beijing by the Airport Expressway and is a roughly 40-minute drive from the city centre during good traffic hours. Prior to the 2008 Olympics, another expressway, the 2nd Airport Expressway, was built to the Airport, as well as a light rail system, which is now connected to the Beijing Subway.

Other airports in the city include Liangxiang, Nanyuan, Xijiao, Shahe and Badaling. Nanyuan serves as the hub for only one passenger airline, and these airports are primarily for military use and less well-known to the public.

Public transit

The Beijing Subway opened in 1971, and had only two lines until the opening of Line 13 in 2002. Since then, the subway has expanded to fourteen lines. Line 1 and Batong Line, its eastern extension, crosses almost all of urban Beijing from east to west. Lines 4 and 5 serve as two north-south axial lines. Fare is 2 yuan flat with unlimited transfers except for the Airport Express line, which costs 25 yuan per trip. There are nearly 700 bus and trolleybus routes in Beijing, including three bus rapid transit routes. All public transport can be accessed with the Yikatong card, which uses radio frequencies to be scanned at subway stations and on public transit buses. In May 2010, Beijing's municipal government announced plans to add 21 new subway lines by the year 2020. The plan calls for 30 subway lines and 450 stations in Beijing, reaching 1,050 kilometers in distance. When implemented, residents within the Fourth Ring Road will be able walk to a station in 10 to 15 minutes. The suburbs will be connected by new radial lines.

Registered taxis can be found throughout Beijing, a large number of unregistered taxis also exist. As of 30 June 2008, all fares on legal taxis start at 10 Renminbi for the first 3 km and 2.00 Renminbi per additional kilometer, not counting idling fees. Most taxis are Hyundai Elantras, Hyundai Sonatas, Peugeot Citroëns and Volkswagen Jettas. After 15 km, the base fare is increased by 50% (but only applied to the portion of the distance over 15 km, so that the passenger is not retroactively charged extra for the first 15 km). Between 11 pm and 5 am, the fee is increased by 20%, starting at 11 RMB and increasing at a rate of 2.4 RMB per km. Rides over 15 km and between 11 pm and 6 am apply both charges, for a total increase of 80% (120%*150%=180%).

Bicycles

Beijing has long been well-known for the number of bicycles on its streets. Although the rise of motor traffic has created a great deal of congestion and bicycle use has declined bicycles are still an important form of local transport. Large numbers of cyclists can be seen on most roads in the city, most of the main roads have dedicated bicycle lanes. Beijing is a relatively flat city which makes cycling possible for people of normal fitness. The rise of electric bicycles and electric scooters, which have similar speeds and use the same cycle lanes, may have brought about a revival in bicycle-speed two-wheeled transport. It is possible to cycle to most parts of the city and, compared to many western cities, conditions are relatively safe. Because of the growing traffic congestion the authorities have indicated more than once that they wish to stimulate cycling in Beijing but it is not clear whether there is sufficient will to translate that into action on a significant scale.

Education

is a top university in mainland China]] Beijing is home to a great number of colleges and universities, including several well-regarded universities of international stature, such as Peking University and Tsinghua University (two of the National Key Universities).

Partner cities

Beijing has two partner cities, both in Europe:

See also

Large Cities Climate Leadership Group

List of hospitals in Beijing

List of mayors of Beijing

Tourist attractions of Beijing

2045 Peking - the name of an asteroid

Notes and references

Further reading

Cammelli, Stefano Storia di Pechino e di come divenne capitale della Cina, Bologna, Il Mulino, 2004. ISBN 9788815099105

Harper, Damian, Beijing: City Guide, 7th Edition, Oakland, California: Lonely Planet Publications, 2007.

Harper, Damian, Beijing: City Guide, 6th Edition, Oakland, California : Lonely Planet Publications, 2005. ISBN 1740597826.

External links

Beijing Government website and

Economic profile for Beijing at HKTDC

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Category:Capitals in Asia Category:Host cities of the Summer Olympic Games Category:Independent cities Category:Metropolitan areas of China Category:Municipalities of the People's Republic of China Category:North China Plain Category:Articles including recorded pronunciations