De La Rue
De La Rue plc is a British banknote manufacturing, security printing of passports and tax stamps, brand authentication and paper-making company with headquarters in Basingstoke, England. It has a factory on the Team Valley Trading Estate in Gateshead, other facilities in Loughton and Bathford. There are overseas offices in Sri Lanka and Malta, it is listed on the London Stock Exchange. The company was founded by Thomas de la Rue, who moved from Guernsey to London in 1821 and set up in business as a'Leghorn' straw hat maker as a stationer and printer. In 1831 he secured his business a Royal Warrant to produce playing cards. In 1855 it started printing postage stamps and in 1860 banknotes. In 1896, the family partnership was converted into a private company. In 1921, the de la Rue family sold their interests; the company was first listed on the London Stock Exchange in 1947. Called Thomas De La Rue & Company, Limited, it changed its name in 1958 to The De La Rue Company Limited. A takeover bid for De La Rue was made by the Rank Organisation in 1968, but this was rejected by the Monopolies commission as being against the public interest.
In 1991 the company's name was changed again – this time to De La Rue plc. In 1965 De La Rue established a joint venture with the Italian printer and inventor Gualtiero Giori called De La Rue Giori. Based in Switzerland, the company specialized in building banknote printing equipment; the company printed banknotes for the Central Bank of Iran during the 1960s. In 1995, the company acquired Portals Limited, listed on the London stock market since 1904. For 300 years Portals had been regarded as the leading banknote paper manufacturer in the world, having manufactured banknote paper for the Bank of England since 1724. In 1997, De La Rue acquired Harrison and Sons, the stamp and banknote printers based in High Wycombe; the factory closed permanently in 2003. In early 2002, De La Rue purchased Smurfit Diamond Packaging Corporation of Sequoia Voting Systems, a California based company, a large provider of electronic voting systems in the United States, for $23 million. After losing money for three years in a business way out of the company's traditional lines, on March 2005 Sequoia was sold to Smartmatic, a multi-national technology company which had developed advanced election systems, voting machines included.
In 2003, the company acquired the Debden based banknote printing operations of the Bank of England. In 2003 and 2004 the company supplied banknotes to Iraq; the company was recognised by Hermann Simon as a role model for other small- to medium-sized businesses in his book Hidden Champions. The Highest Perfection, a history of De La Rue was published in 2011. Written by Peter Pugh for De La Rue, it covered the years 1712–2003. In August 2014, the company announced the appointment of Martin Sutherland as chief executive officer. In 2016, the Cash Handling division was sold to Privet Capital. In September 2016, the Bank of England issued its polymer five pound note, the first note from the bank to be printed on polymer. In December 2016, the company announced. In March 2018, the company sold the paper business. De La Rue retained a 10 % share in Portals. In April 2018, the company decided to appeal against the decision of the British government to manufacture passports in France, it subsequently decided against appealing.
De La Rue sells high-security printing technology for over 150 national currencies. De La Rue produces a wide range of other secure documents, including: Bank cheques Driving licences Passports Postage stamps Tax stamps Traveller's cheques Vouchers In 1843 De La Rue established its first overseas trade, as de la Rue's brother Paul travelled to Russia to advise on the making of playing cards. Thomas de la Rue's designs for playing cards are the basis for the modern standard design; the playing card business was sold to John Waddington in 1969. The company has printed postage stamps for the United Kingdom and some of its colonies, for Italy and for the Confederate States of America; some famous stamps such as the Cape of Good Hope triangulars were printed by De La Rue & Co. after Perkins Bacon fell out of favour with the postal authorities of the time. The first 50 years of postage stamp production were chronicled in John Easton's The De La Rue History of British and Foreign Postage Stamps 1855–1901.
De La Rue claims to have developed the first practical fountain pen in 1881 and was a leading manufacturer of fountain pens in Britain. Products were marketed under the "Onoto" brand. Production of fountain pens by De La Rue ceased in Britain in 1958 but continued for a few more years in Australia. During the 1930s De La Rue created a number of board games; these included a cricket game, produced in a number of different editions, Round The Horn, a game which re-created the annual race of grain-laden, square-rigged sailing cargo ships from Australia to London. The games used playing cards as part of the component set. List of mints Banknotes of the pound sterling Commonwealth banknote-issuing institutions Gemalto - a competitor Giesecke & Devrient – a competitor based in Munich Hong Kong Note Printing – founded in 1984 by Thomas De La Rue Official website History of De La Rue’s playing cards A research website with more detail of De La Rue company history Article and images of 1930s De La Rue Board Game, Stumpz
Elizabeth II
Elizabeth II is Queen of the United Kingdom and the other Commonwealth realms. Elizabeth was born in London as the first child of the Duke and Duchess of York King George VI and Queen Elizabeth, she was educated at home, her father acceded to the throne on the abdication of his brother King Edward VIII in 1936, from which time she was the heir presumptive. She began to undertake public duties during the Second World War, serving in the Auxiliary Territorial Service. In 1947, she married Prince Philip, Duke of Edinburgh, a former prince of Greece and Denmark, with whom she has four children: Charles, Prince of Wales; when her father died in February 1952, she became head of the Commonwealth and queen regnant of seven independent Commonwealth countries: the United Kingdom, Australia, New Zealand, South Africa and Ceylon. She has reigned as a constitutional monarch through major political changes, such as devolution in the United Kingdom, Canadian patriation, the decolonisation of Africa. Between 1956 and 1992, the number of her realms varied as territories gained independence and realms, including South Africa and Ceylon, became republics.
Her many historic visits and meetings include a state visit to the Republic of Ireland and visits to or from five popes. Significant events have included her coronation in 1953 and the celebrations of her Silver and Diamond Jubilees in 1977, 2002, 2012 respectively. In 2017, she became the first British monarch to reach a Sapphire Jubilee, she is the longest-lived and longest-reigning British monarch as well as the world's longest-reigning queen regnant and female head of state, the oldest and longest-reigning current monarch and the longest-serving current head of state. Elizabeth has faced republican sentiments and press criticism of the royal family, in particular after the breakdown of her children's marriages, her annus horribilis in 1992 and the death in 1997 of her former daughter-in-law Diana, Princess of Wales. However, support for the monarchy has been and remains high, as does her personal popularity. Elizabeth was born at 02:40 on 21 April 1926, during the reign of her paternal grandfather, King George V.
Her father, the Duke of York, was the second son of the King. Her mother, the Duchess of York, was the youngest daughter of Scottish aristocrat the Earl of Strathmore and Kinghorne, she was delivered by Caesarean section at her maternal grandfather's London house: 17 Bruton Street, Mayfair. She was baptised by the Anglican Archbishop of York, Cosmo Gordon Lang, in the private chapel of Buckingham Palace on 29 May, named Elizabeth after her mother, Alexandra after George V's mother, who had died six months earlier, Mary after her paternal grandmother. Called "Lilibet" by her close family, based on what she called herself at first, she was cherished by her grandfather George V, during his serious illness in 1929 her regular visits were credited in the popular press and by biographers with raising his spirits and aiding his recovery. Elizabeth's only sibling, Princess Margaret, was born in 1930; the two princesses were educated at home under the supervision of their mother and their governess, Marion Crawford.
Lessons concentrated on history, language and music. Crawford published a biography of Elizabeth and Margaret's childhood years entitled The Little Princesses in 1950, much to the dismay of the royal family; the book describes Elizabeth's love of horses and dogs, her orderliness, her attitude of responsibility. Others echoed such observations: Winston Churchill described Elizabeth when she was two as "a character, she has an air of authority and reflectiveness astonishing in an infant." Her cousin Margaret Rhodes described her as "a jolly little girl, but fundamentally sensible and well-behaved". During her grandfather's reign, Elizabeth was third in the line of succession to the throne, behind her uncle Edward and her father. Although her birth generated public interest, she was not expected to become queen, as Edward was still young. Many people believed he would have children of his own; when her grandfather died in 1936 and her uncle succeeded as Edward VIII, she became second-in-line to the throne, after her father.
That year, Edward abdicated, after his proposed marriage to divorced socialite Wallis Simpson provoked a constitutional crisis. Elizabeth's father became king, she became heir presumptive. If her parents had had a son, she would have lost her position as first-in-line, as her brother would have been heir apparent and above her in the line of succession. Elizabeth received private tuition in constitutional history from Henry Marten, Vice-Provost of Eton College, learned French from a succession of native-speaking governesses. A Girl Guides company, the 1st Buckingham Palace Company, was formed so she could socialise with girls her own age, she was enrolled as a Sea Ranger. In 1939, Elizabeth's parents toured the United States; as in 1927, when her parents had toured Australia and New Zealand, Elizabeth remained in Britain, since her father thought her too young to undertake public tours. Elizabeth "looked tearful", they corresponded and she and her parents made the first royal transatlantic telephone call on 18 May.
In September 1939, Britain entered the Second World War. Lord Hailsham suggested that the two princesses should be evacuated to Canada to avoid the frequent aerial bombing; this was rejected by Elizabeth's mother. I won't leave wit
Nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is hard and ductile. Pure nickel, powdered to maximize the reactive surface area, shows a significant chemical activity, but larger pieces are slow to react with air under standard conditions because an oxide layer forms on the surface and prevents further corrosion. So, pure native nickel is found in Earth's crust only in tiny amounts in ultramafic rocks, in the interiors of larger nickel–iron meteorites that were not exposed to oxygen when outside Earth's atmosphere. Meteoric nickel is found in combination with iron, a reflection of the origin of those elements as major end products of supernova nucleosynthesis. An iron–nickel mixture is thought to compose Earth's outer and inner cores. Use of nickel has been traced as far back as 3500 BCE. Nickel was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who mistook the ore for a copper mineral, in the cobalt mines of Los, Hälsingland, Sweden.
The element's name comes from a mischievous sprite of German miner mythology, who personified the fact that copper-nickel ores resisted refinement into copper. An economically important source of nickel is the iron ore limonite, which contains 1–2% nickel. Nickel's other important ore minerals include pentlandite and a mixture of Ni-rich natural silicates known as garnierite. Major production sites include the Sudbury region in Canada, New Caledonia in the Pacific, Norilsk in Russia. Nickel is oxidized by air at room temperature and is considered corrosion-resistant, it has been used for plating iron and brass, coating chemistry equipment, manufacturing certain alloys that retain a high silvery polish, such as German silver. About 9% of world nickel production is still used for corrosion-resistant nickel plating. Nickel-plated objects sometimes provoke nickel allergy. Nickel has been used in coins, though its rising price has led to some replacement with cheaper metals in recent years. Nickel is one of four elements that are ferromagnetic at room temperature.
Alnico permanent magnets based on nickel are of intermediate strength between iron-based permanent magnets and rare-earth magnets. The metal is valuable in modern times chiefly in alloys. A further 10% is used for nickel-based and copper-based alloys, 7% for alloy steels, 3% in foundries, 9% in plating and 4% in other applications, including the fast-growing battery sector; as a compound, nickel has a number of niche chemical manufacturing uses, such as a catalyst for hydrogenation, cathodes for batteries and metal surface treatments. Nickel is an essential nutrient for some microorganisms and plants that have enzymes with nickel as an active site. Nickel is a silvery-white metal with a slight golden tinge, it is one of only four elements that are magnetic at or near room temperature, the others being iron and gadolinium. Its Curie temperature is 355 °C; the unit cell of nickel is a face-centered cube with the lattice parameter of 0.352 nm, giving an atomic radius of 0.124 nm. This crystal structure is stable to pressures of at least 70 GPa.
Nickel belongs to the transition metals. It is hard and ductile, has a high for transition metals electrical and thermal conductivity; the high compressive strength of 34 GPa, predicted for ideal crystals, is never obtained in the real bulk material due to the formation and movement of dislocations. The nickel atom has two electron configurations, 3d8 4s2 and 3d9 4s1, which are close in energy – the symbol refers to the argon-like core structure. There is some disagreement. Chemistry textbooks quote the electron configuration of nickel as 4s2 3d8, which can be written 3d8 4s2; this configuration agrees with the Madelung energy ordering rule, which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 3d8 4s2 energy level the 3d8 4s2 3F, J = 4 level. However, each of these two configurations splits into several energy levels due to fine structure, the two sets of energy levels overlap; the average energy of states with configuration 3d9 4s1 is lower than the average energy of states with configuration 3d8 4s2.
For this reason, the research literature on atomic calculations quotes the ground state configuration of nickel as 3d9 4s1. The isotopes of nickel range in atomic weight from 48 u to 78 u. Occurring nickel is composed of five stable isotopes. Isotopes heavier than 62Ni cannot be formed by nuclear fusion without losing energy. Nickel-62 has the highest mean nuclear binding energy per nucleon of any nuclide, at 8.7946 MeV/nucleon. Its binding energy is greater than both 56Fe and 58Fe, more abundant elements incorrectly cited as having the most tightly-bound nuclides. Although this would seem to predict nickel-62 as the most abundant heavy element in the universe, the high rate of photodisintegration of nickel in stellar interiors causes iron to be by far the most abundant. Stable isotope nickel-60 is the daughter product of the extinct radionuclide 60Fe, whi
Bank of Mauritius
The Bank of Mauritius is the central bank of the Republic of Mauritius. It was established in September 1967 as the central bank of Mauritius, it was modelled on the Bank of England and was, in effect, set up with the assistance of senior officers of the Bank of England. Amongst its responsibilities is the issuance of the Mauritian currency, the Mauritian rupee. In the 19th Century three separate commercial banks, now all defunct, operated under the Bank of Mauritius name; the first Bank of Mauritius started operations in 1813 or so, but survived only until 1825. The second Bank of Mauritius was a British overseas bank with two boards of directors, one in London and the other in Port Louis, it favored the interests of the planter class. In 1838 traders established Mauritius Commercial Bank to give themselves an alternative source of credit as until its establishment the Bank of Mauritius had a monopoly on the island; the financial crisis of 1847 in London resulted in the collapse of the sugar market, severe losses to both of Mauritius's banks.
Bank of Mauritius ceased business in 1848, though the Mauritius Commercial Bank has survived to the present. Local interests established the third Bank of Mauritius in 1894 to take over the local business of the failed New Oriental Bank Corporation. In 1911 the bank opened a branch in the Seychelles. However, in 1916 the Mercantile Bank of India acquired the bank. HSBC in turn acquired the Mercantile Bank in 1959; because of this history, HSBC refers to itself as the oldest foreign bank in Mauritius. The next foreign bank to arrive, to survive to the present, was National Bank of South Africa, an ancestor of Barclays Bank Mauritius. In addition to the above three banks, a bank by the name of the Colonial Bank of Mauritius and Dependencies, operated between 1812 and 1813. Before the establishment of the Bank, the currency issue was managed by a Board of Commissioners of Currency; the duties of the Board were restricted to those of an issuing authority. The setting up of the Bank of Mauritius marked the beginning of a new phase in the monetary history of Mauritius, with the monetary system moving forward from the stage of'Sterling Exchange Standard', under which currency was issued in exchange for sterling at a fixed rate of exchange, to that of a'managed currency' in which the discretionary role of the monetary authority becomes important.
The Bank of Mauritius Act 1966 lays down the purposes of the Bank which are to'safeguard the internal and external value of the currency of Mauritius and its internal convertibility' and to'direct its policy towards achieving monetary conditions conducive to strengthening the economic activity and prosperity of Mauritius.' The Bank has been set up as the authority, responsible for the formulation and execution of monetary policy consistent with stable price conditions. It has responsibility for safeguarding the stability and strengthening of the financial system of Mauritius. On 12 March 2008, the Bank of Mauritius launched the online sales of commemorative coins and Dodo Gold Coins to international buyers. Central banks and currencies of Africa Economy of Mauritius List of banks in Mauritius List of central banks Mauritian rupee Mauritius Commercial Bank. 1963. The Mauritius Commercial Bank Limited, 1838-1963. Port Louis
Bi-metallic coin
Bi-metallic coins are coins consisting of two metals or alloys arranged with an outer ring around a contrasting center. Common circulating examples include the ₹10, €1, €2, 2 and 5 PLN, 50 CZK, 100 and 200 HUF, 1 and 2 BGN, British £1 and £2, Canadian $2, South African R5, Turkish 1 lira, IDR 1K, Hong Kong $10, Argentine $1, Brazilian R$1, Chilean $100 and $500, Colombian $500 and $1000, all Mexican coins of $1 or higher denomination. Bi-metallic coins have been issued for a long time, with known examples dating from the 17th century, while the Roman Empire issued special-occasion, large medallions with a center of bronze or copper and an outer ring of orichalcum, starting with the reign of Hadrian; the silver-center cent pattern produced by the United States in 1792 is another example. In the 1830s and 1840s, British medalist Joseph Moore produced large numbers of bi-metallic "penny model" and less common "halfpenny model" tokens, as a proposal to replace the large penny and halfpenny coins.
Though not legal tender, Moore's tokens were circulated and accepted at face value by many merchants. Despite their popularity, the Royal Mint rejected the proposal, did not reduce the size of the penny and halfpenny until decimalization. In recent times, the first circulating bi-metallic coin was the Italian 500 lire, first issued in 1982. Morocco, with its 5-dirhams coin in 1987. India introduced 10-rupee bi-metallic coins in 2009 that are dated 2006. Since 1996, Canada has produced bi-metallic $2 coins. Great Britain has issued a bi-metallic 2-pound coin since 1997; the first tri-metallic circulating coins were 20-francs coins introduced in France and Monaco in 1992. These were similar to the corresponding bi-metallic 10-francs coins, but had two rings instead of one; as well as circulating coins, where they are restricted to high-denomination coins, bi-metallic coins are used in commemorative issues made of precious metals. For example, the only bi-metallic coin of the United States is the $10 Library of Congress commemorative, made of a gold ring around a platinum center.
They are used as a way of securing against coin counterfeiting. The manufacturing process is similar to that of ordinary coins, except that two blanks are struck at the same time, deforming the separate blanks sufficiently to hold them together. Worldwide Bi-Metallic Collectors Club - website World bimetallic coin news - WBCN - website: new issues, country index and reference prices
Dodo
The dodo is an extinct flightless bird, endemic to the island of Mauritius, east of Madagascar in the Indian Ocean. The dodo's closest genetic relative was the also-extinct Rodrigues solitaire, the two forming the subfamily Raphinae of the family of pigeons and doves; the closest living relative of the dodo is the Nicobar pigeon. A white dodo was once thought to have existed on the nearby island of Réunion, but this is now thought to have been confusion based on the Réunion ibis and paintings of white dodos. Subfossil remains show the dodo was about 1 metre tall and may have weighed 10.6–17.5 kg in the wild. The dodo's appearance in life is evidenced only by drawings and written accounts from the 17th century; as these vary and only some of the illustrations are known to have been drawn from live specimens, its exact appearance in life remains unresolved, little is known about its behaviour. Though the dodo has been considered fat and clumsy, it is now thought to have been well-adapted for its ecosystem.
It has been depicted with brownish-grey plumage, yellow feet, a tuft of tail feathers, a grey, naked head, a black and green beak. It used gizzard stones to help digest its food, thought to have included fruits, its main habitat is believed to have been the woods in the drier coastal areas of Mauritius. One account states, it is presumed that the dodo became flightless because of the ready availability of abundant food sources and a relative absence of predators on Mauritius. The first recorded mention of the dodo was by Dutch sailors in 1598. In the following years, the bird was hunted by sailors and invasive species, while its habitat was being destroyed; the last accepted sighting of a dodo was in 1662. Its extinction was not noticed, some considered it to be a mythical creature. In the 19th century, research was conducted on a small quantity of remains of four specimens, brought to Europe in the early 17th century. Among these is a dried head, the only soft tissue of the dodo that remains today.
Since a large amount of subfossil material has been collected on Mauritius from the Mare aux Songes swamp. The extinction of the dodo within less than a century of its discovery called attention to the unrecognised problem of human involvement in the disappearance of entire species; the dodo achieved widespread recognition from its role in the story of Alice's Adventures in Wonderland, it has since become a fixture in popular culture as a symbol of extinction and obsolescence. The dodo was variously declared a small ostrich, a rail, an albatross, or a vulture, by early scientists. In 1842, Danish zoologist Johannes Theodor Reinhardt proposed that dodos were ground pigeons, based on studies of a dodo skull he had discovered in the collection of the Natural History Museum of Denmark; this view was met with ridicule, but was supported by English naturalists Hugh Edwin Strickland and Alexander Gordon Melville in their 1848 monograph The Dodo and Its Kindred, which attempted to separate myth from reality.
After dissecting the preserved head and foot of the specimen at the Oxford University Museum and comparing it with the few remains available of the extinct Rodrigues solitaire they concluded that the two were related. Strickland stated that although not identical, these birds shared many distinguishing features of the leg bones, otherwise known only in pigeons. Strickland and Melville established that the dodo was anatomically similar to pigeons in many features, they pointed to the short keratinous portion of the beak, with its long, naked basal part. Other pigeons have bare skin around their eyes reaching their beak, as in dodos; the forehead was high in relation to the beak, the nostril was located low on the middle of the beak and surrounded by skin, a combination of features shared only with pigeons. The legs of the dodo were more similar to those of terrestrial pigeons than of other birds, both in their scales and in their skeletal features. Depictions of the large crop hinted at a relationship with pigeons, in which this feature is more developed than in other birds.
Pigeons have small clutches, the dodo is said to have laid a single egg. Like pigeons, the dodo lacked the vomer and septum of the nostrils, it shared details in the mandible, the zygomatic bone, the palate, the hallux; the dodo differed from other pigeons in the small size of the wings and the large size of the beak in proportion to the rest of the cranium. Throughout the 19th century, several species were classified as congeneric with the dodo, including the Rodrigues solitaire and the Réunion solitaire, as Didus solitarius and Raphus solitarius, respectively. An atypical 17th-century description of a dodo and bones found on Rodrigues, now known to have belonged to the Rodrigues solitaire, led Abraham Dee Bartlett to name a new species, Didus nazarenus, in 1852. Based on solitaire remains, it is now a synonym of that species. Crude drawings of the red rail of Mauritius were misinterpreted as dodo species. For many years the dodo and the Rodrigues solitaire were placed in a family of their own, the Raphidae, because their exact relationships with other pigeons were unresolved.
Each was placed in its own monotypic family, as it was thought that they had evolved their similarities independently. Osteological and DNA analysis has since led to the dissolution of the family Raphidae, the dodo and sol
Holography
A hologram is an image that appears to be three dimensional and which can be seen with the naked eye. Holography is the practice of making holograms. A hologram is a photographic recording of a light field, rather than an image formed by a lens; the holographic medium, i.e. the object produced by a holographic process is unintelligible when viewed under diffuse ambient light. It is an encoding of the light field as an interference pattern of variations in the opacity, density, or surface profile of the photographic medium; when suitably lit, the interference pattern diffracts the light into an accurate reproduction of the original light field, the objects that were in it exhibit visual depth cues such as parallax and perspective that change realistically with the relative position of the observer. That is, the view of the image from different angles represents the subject viewed from similar angles. In its pure form, holography requires the use of laser light for illuminating the subject and for viewing the finished hologram.
A microscopic level of detail throughout the recorded scene can be reproduced. In common practice, major image quality compromises are made to eliminate the need for laser illumination to view the hologram, in some cases, to make it. Holographic portraiture resorts to a non-holographic intermediate imaging procedure, to avoid the hazardous high-powered pulsed lasers otherwise needed to optically "freeze" moving subjects as as the motion-intolerant holographic recording process requires. Holograms can now be computer-generated to show objects or scenes that never existed. Holography is distinct from lenticular and other earlier autostereoscopic 3D display technologies, which can produce superficially similar results but are based on conventional lens imaging. Images requiring the aid of special glasses or other intermediate optics, stage illusions such as Pepper's Ghost and other unusual, baffling, or magical images are incorrectly called holograms; the Hungarian-British physicist Dennis Gabor was awarded the Nobel Prize in Physics in 1971 "for his invention and development of the holographic method".
His work, done in the late 1940s, was built on pioneering work in the field of X-ray microscopy by other scientists including Mieczysław Wolfke in 1920 and William Lawrence Bragg in 1939. The discovery was an unexpected result of research into improving electron microscopes at the British Thomson-Houston Company in Rugby and the company filed a patent in December 1947; the technique as invented is still used in electron microscopy, where it is known as electron holography, but optical holography did not advance until the development of the laser in 1960. The word holography comes from the Greek words ὅλος and γραφή; the development of the laser enabled the first practical optical holograms that recorded 3D objects to be made in 1962 by Yuri Denisyuk in the Soviet Union and by Emmett Leith and Juris Upatnieks at the University of Michigan, USA. Early holograms used silver halide photographic emulsions as the recording medium, they were not efficient as the produced grating absorbed much of the incident light.
Various methods of converting the variation in transmission to a variation in refractive index were developed which enabled much more efficient holograms to be produced. 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 refinement, the "rainbow transmission" hologram, allows more convenient illumination by white light rather than by lasers. Rainbow holograms are used for security and authentication, for example, on credit cards and product packaging. Another kind of common hologram, the reflection or Denisyuk hologram, can be viewed using a white-light illumination source on the same side of the hologram as the viewer and is the type of hologram seen in holographic displays, they are capable of multicolour-image reproduction. Specular holography is a related technique for making three-dimensional images 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. Most holograms produced are of static objects but systems for displaying changing scenes on a holographic volumetric display are now being developed. Holograms can be used to store and process information optically. In its early days, holography required high-power expensive lasers, but nowadays, mass-produced low-cost semi-conductor or diode lasers, such as those found in millions of DVD recorders and used in other common applications, can be used to make holograms and have made holography much more accessible to low-budget researchers and dedicated hobbyists, it was thought that it would be possible to use X-rays to make holograms of small objects and view them using visible light. Today, holograms with x-rays are generated by using synchrotrons or x-ray free-electron lasers as radiation sources and pixelated detectors such as CCDs as recording medium.
The reconstruction is retrieved via computation. Due to the shorter wavelength of x-rays compared to visible light, this approach allows imaging objects with higher spatial resolution; as free-electron lasers can provide ultrashort and x-ray pulses in the range of femtoseconds which are intense and coherent, x-ray holography
Mauritius
