Introduction to Holography

Introduction to Holography If youre carrying money, a drivers license, or credit cards, youre carrying around holograms. The dove hologram on a Visa card may be the most familiar. The rainbow-colored bird changes colors and appears to move as you tilt the card. Unlike a bird in a traditional photograph, a holographic bird is a three-dimensional image. Holograms are formed by interference of light beams from a laser. How Lasers Make Holograms Holograms are made using lasers because laser light is coherent. What this means is that all of the photons of laser light have exactly the same frequency and phase difference. Splitting a laser beam produces two beams that are the same color as each other (monochromatic). In contrast, regular white light consists of many different frequencies of light. When white light is diffracted, the frequencies split to form a rainbow of colors. In conventional photography, the light reflected off an object strikes a strip of film that contains a chemical (i.e., silver bromide) that reacts to light. This produces a two-dimensional representation of the subject. A hologram forms a three-dimensional image because light interference patterns are recorded, not just reflected light. To make this happen, a laser beam is split into two beams that pass through lenses to expand them. One beam (the reference beam) is directed onto high-contrast film. The other beam is aimed at the object (the object beam). Light from the object beam gets scattered by the holograms subject. Some of this scattered light goes toward the photographic film. The scattered light from the object beam is out of phase with the reference beam, so when the two beams interact they form an interference pattern. The interference pattern recorded by the film encodes a three-dimensional pattern because the distance from any point on the object affects the phase of the scattered light. However, there is a limit to how three-dimensional a hologram can appear. This is because the object beam only hits its target from a single direction. In other words, the hologram only displays the perspective from the object beams point of view. So, while a hologram changes depending on the viewing angle, you cant see behind the object. Viewing a Hologram A hologram image is an interference pattern that looks like random noise unless viewed under the right lighting. The magic happens when a holographic plate is illuminated with the same laser beam light that was used to record it. If a different laser frequency or another type of light is used, the reconstructed image wont exactly match the original. Yet, the most common holograms are visible in white light. These are reflection-type volume holograms and rainbow holograms. Holograms that can be viewed in ordinary light require special processing. In the case of a rainbow hologram, a standard transmission hologram is copied using a horizontal slit. This preserves parallax in one direction (so the perspective can move), but produces a color shift in the other direction. Uses of Holograms The 1971 Nobel Prize in Physics was awarded to the Hungarian-British scientist Dennis Gabor for  his invention and development of the holographic method. Originally, holography was a technique used to improve electron microscopes. Optical holography didnt take off until the invention of the laser in 1960. Although holograms were immediately popular for art, practical applications of optical holography lagged until the 1980s. Today, holograms are used for data storage, optical communications, interferometry in engineering and microscopy, security, and holographic scanning. Interesting Hologram Facts If you cut a hologram in half, each piece still contains an image of the entire object. In contrast, if you cut a photograph in half, half of the information is lost.One way to copy a hologram is to illuminate it with a laser beam and place a new photographic plate such that it receives light from the hologram and from the original beam. Essentially, the hologram acts like the original object.Another way to copy a hologram is to emboss it using the original image. This works much the same way records are made from audio recordings. The embossing process is used for mass production.

William Blake - Visionary Pre-Romantic Poet, Printer and Artist

William Blake - Visionary Pre-Romantic Poet, Printer and Artist William Blake was born in London in 1757, one of six children of a hosiery merchant. He was an imaginative child, â€Å"different† from the beginning, so he was not sent to school, but educated at home. He talked of visionary experiences from a very early age: at 10, he saw a tree filled with angels when he was wandering the countryside just outside town. He later claimed to have read Milton as a child and he began writing â€Å"Poetical Sketches† at 13. He was also interested in painting and drawing in childhood, but his parents could not afford art school, so he was apprenticed to an engraver at the age of 14. Blakes Training as an Artist The engraver to whom Blake was apprenticed was James Basire, who had made engravings of the work of Reynolds and Hogarth and was official engraver to the Society of Antiquaries. He sent Blake to draw the tombs and monuments at Westminster Abbey, a task which brought him to his lifelong love of Gothic art. When his 7-year apprenticeship was complete, Blake entered the Royal Academy, but did not stay long, and continued to support himself making engraved book illustrations. His Academy teachers urged him to adopt a simpler, less extravagant style, but Blake was enamored of grand historical paintings and ancient ballads. Blakes Illuminated Printing In 1782, William Blake married Catherine Boucher, an illiterate farmer’s daughter. He taught her reading and writing and draftsmanship, and she later assisted him in creating his illuminated books. He also taught drawing, painting and engraving to his beloved younger brother Robert. William was present when Robert died in 1787; he said that he saw his soul rise through the ceiling at death, that Robert’s spirit continued to visit him afterwards, and that one of these night visits inspired his illuminated book printing, combining poem text and engraved illustration on a single copper plate and hand-coloring the prints. Blakes Early Poems The first collection of poems William Blake published was Poetical Sketches in 1783 - clearly the work of a young apprentice poet, with its odes to the four seasons, an imitation of Spenser, historical prologues and songs. His most loved collections were next, the paired Songs of Innocence (1789) and Songs of Experience (1794), both published as handmade illuminated books. After the upheaval of the French Revolution his work became more political and allegorical, protesting and satirizing war and tyranny in books like America, a Prophecy (1793), Visions of the Daughters of Albion (1793) and Europe, a Prophecy (1794). Blake as Outsider and Mythmaker Blake was definitely outside the mainstream of art and poetry in his day, and his prophetic illustrated works did not garner much public recognition. He was usually able to make his living illustrating the works of others, but his fortunes declined as he devoted himself to his own ideas and art rather than to what was fashionable in 18th century London. He had a few patrons, whose commissions enabled him to study the classics and develop his personal mythology for his great visionary epics: The First Book of Urizen (1794), Milton (1804-08), Vala, or The Four Zoas (1797; rewritten after 1800), and Jerusalem (1804-20). Blakes Later Life Blake lived the last years of his life in obscure poverty, relieved only a little by the admiration and patronage of a group of younger painters known as â€Å"The Ancients.† William Blake fell ill and died in 1827. His last drawing was a portrait of his wife Catherine, drawn on his deathbed. Books by William Blake Blake: Songs of Innocence and Experience (facsimile edition with introduction by Richard Holmes, Tate Publishing, 2007)Songs of Innocence and of Experience (CD-ROM edition, pages embellished with pop-up commentary and annotations, narrated by Stuart Curran, Octavo, 2003)William Blake: The Complete Illuminated Books (reproductions from the Blake Trust, with introduction by David Bindman, Thames Hudson, W.W. Norton Co., 2001)The Complete Poetry Prose of William Blake (ed. David Erdman, with commentary by Harold Bloom, revised edition, Anchor, 1997)Blake’s Illustrations for the Book of Job (Dover Publications, 1995)The Marriage of Heaven and Hell: A Facsimile in Full Color (Dover Publications reprint, 1994)