16 July 2009

Holography

The invention: A lensless system of three-dimensional photography that was one of the most important developments in twentieth century optical science. The people behind the invention: Dennis Gabor (1900-1979), a Hungarian-born inventor and physicist who was awarded the 1971 Nobel Prize in Physics Emmett Leith (1927- ), a radar researcher who, with Juris Upatnieks, produced the first laser holograms Juris Upatnieks (1936- ), a radar researcher who, with Emmett Leith, produced the first laser holograms Easter Inspiration The development of photography in the early 1900’s made possible the recording of events and information in ways unknown before the twentieth century: the photographing of star clusters, the recording of the emission spectra of heated elements, the storing of data in the form of small recorded images (for example, microfilm), and the photographing of microscopic specimens, among other things. Because of its vast importance to the scientist, the science of photography has developed steadily. An understanding of the photographic and holographic processes requires some knowledge of the wave behavior of light. Light is an electromagnetic wave that, like a water wave, has an amplitude and a phase. The amplitude corresponds to the wave height, while the phase indicates which part of the wave is passing a given point at a given time. A cork floating in a pond bobs up and down as waves pass under it. The position of the cork at any time depends on both amplitude and phase: The phase determines on which part of the wave the cork is floating at any given time, and the amplitude determines how high or low the cork can be moved. Waves from more than one source arriving at the cork combine in ways that depend on their relative phases. If the waves meet in the same phase, they add and produce a large amplitude; if they arrive out of phase, they subtract and produce a small amplitude. The total amplitude, or intensity, depends on the phases of the combining waves. Dennis Gabor, the inventor of holography, was intrigued by the way in which the photographic image of an object was stored by a photographic plate but was unable to devote any consistent research effort to the question until the 1940’s. At that time, Gabor was involved in the development of the electron microscope. On Easter morning in 1947, as Gabor was pondering the problem of how to improve the electron microscope, the solution came to him. He would attempt to take a poor electron picture and then correct it optically. The process would require coherent electron beams—that is, electron waves with a definite phase. This two-stage method was inspired by the work of Lawrence Bragg. Bragg had formed the image of a crystal lattice by diffracting the photographic X-ray diffraction pattern of the original lattice. This double diffraction process is the basis of the holographic process. Bragg’s method was limited because of his inability to record the phase information of the X-ray photograph. Therefore, he could study only those crystals for which the phase relationship of the reflected waves could be predicted. Waiting for the Laser Gabor devised a way of capturing the phase information after he realized that adding coherent background to the wave reflected from an object would make it possible to produce an interference pattern on the photographic plate. When the phases of the two waves are identical, a maximum intensity will be recorded; when they are out of phase, a minimum intensity is recorded. Therefore, what is recorded in a hologram is not an image of the object but rather the interference pattern of the two coherent waves. This pattern looks like a collection of swirls and blank spots. The hologram (or photograph) is then illuminated by the reference beam, and part of the transmitted light is a replica of the original object wave. When viewing this object wave, one sees an exact replica of the original object. The major impediment at the time in making holograms using any form of radiation was a lack of coherent sources. For example, the coherence of the mercury lamp used by Gabor and his assistant IvorWilliams was so short that they were able to make holograms of only about a centimeter in diameter. The early results were rather poor in terms of image quality and also had a double image. For this reason, there was little interest in holography, and the subject lay almost untouched for more than ten years. Interest in the field was rekindled after the laser (light amplification by stimulated emission of radiation) was developed in 1962. Emmett Leith and Juris Upatnieks, who were conducting radar research at the University of Michigan, published the first laser holographs in 1963. The laser was an intense light source with a very long coherence length. Its monochromatic nature improved the resolution of the images greatly. Also, there was no longer any restriction on the size of the object to be photographed. The availability of the laser allowed Leith and Upatnieks to propose another improvement in holographic technique. Before 1964, holograms were made of only thin transparent objects. A small region of the hologram bore a one-to-one correspondence to a region of the object. Only a small portion of the image could be viewed at one time without the aid of additional optical components. Illuminating the transparency diffusely allowed the whole image to be seen at one time. This development also made it possible to record holograms of diffusely reflected three-dimensional objects. Gabor had seen from the beginning that this should make it possible to create three-dimensional images. After the early 1960’s, the field of holography developed very quickly. Because holography is different from conventional photography, the two techniques often complement each other. Gabor saw his idea blossom into a very important technique in optical science. Impact The development of the laser and the publication of the first laser holograms in 1963 caused a blossoming of the new technique in many fields. Soon, techniques were developed that allowed holograms to be viewed with white light. It also became possible for holograms to reconstruct multicolored images. Holographic methods have been used to map terrain with radar waves and to conduct surveillance in the fields of forestry, agriculture, and meteorology.By the 1990’s, holography had become a multimillion-dollar industry, finding applications in advertising, as an art form, and in security devices on credit cards, as well as in scientific fields. An alternate form of holography, also suggested by Gabor, uses sound waves. Acoustical imaging is useful whenever the medium around the object to be viewed is opaque to light rays—for example, in medical diagnosis. Holography has affected many areas of science, technology, and culture.

13 July 2009

Heat pump


The invention:

A device that warms and cools buildings efficiently
and cheaply by moving heat from one area to another.

The people behind the invention:

T. G. N. Haldane, a British engineer
Lord Kelvin (William Thomson, 1824-1907), a British
mathematician, scientist, and engineer
Sadi Carnot (1796-1832), a French physicist and
thermodynamicist


Heart-lung machine

The invention: The first artificial device to oxygenate and circulate blood during surgery, the heart-lung machine began the era of open-heart surgery. The people behind the invention: John H. Gibbon, Jr. (1903-1974), a cardiovascular surgeon Mary Hopkinson Gibbon (1905- ), a research technician Thomas J. Watson (1874-1956), chairman of the board of IBM T. L. Stokes and J. B. Flick, researchers in Gibbon’s laboratory Bernard J. Miller (1918- ), a cardiovascular surgeon and research associate Cecelia Bavolek, the first human to undergo open-heart surgery successfully using the heart-lung machine A Young Woman’s Death In the first half of the twentieth century, cardiovascular medicine had many triumphs. Effective anesthesia, antiseptic conditions, and antibiotics made surgery safer. Blood-typing, anti-clotting agents, and blood preservatives made blood transfusion practical. Cardiac catheterization (feeding a tube into the heart), electrocardiography, and fluoroscopy (visualizing living tissues with an X-ray machine) made the nonsurgical diagnosis of cardiovascular problems possible. As of 1950, however, there was no safe way to treat damage or defects within the heart. To make such a correction, this vital organ’s function had to be interrupted. The problem was to keep the body’s tissues alive while working on the heart. While some surgeons practiced so-called blind surgery, in which they inserted a finger into the heart through a small incision without observing what they were attempting to correct, others tried to reduce the body’s need for circulation by slowly chilling the patient until the heart stopped. Still other surgeons used “cross-circulation,” in which the patient’s circulation was connected to a donor’s circulation. All these approaches carried profound risks of hemorrhage, tissue damage, and death. In February of 1931, Gibbon witnessed the death of a young woman whose lung circulation was blocked by a blood clot. Because her blood could not pass through her lungs, she slowly lost consciousness from lack of oxygen. As he monitored her pulse and breathing, Gibbon thought about ways to circumvent the obstructed lungs and straining heart and provide the oxygen required. Because surgery to remove such a blood clot was often fatal, the woman’s surgeons operated only as a last resort. Though the surgery took only six and one-half minutes, she never regained consciousness. This experience prompted Gibbon to pursue what few people then considered a practical line of research: a way to circulate and oxygenate blood outside the body. A Woman’s Life Restored Gibbon began the project in earnest in 1934, when he returned to the laboratory of Edward D. Churchill at Massachusetts General Hospital for his second surgical research fellowship. He was assisted by Mary Hopkinson Gibbon. Together, they developed, using cats, a surgical technique for removing blood froma vein, supplying the blood with oxygen, and returning it to an artery using tubes inserted into the blood vessels. Their objective was to create a device that would keep the blood moving, spread it over a very thin layer to pick up oxygen efficiently and remove carbon dioxide, and avoid both clotting and damaging blood cells. In 1939, they reported that prolonged survival after heart-lung bypass was possible in experimental animals. WorldWar II (1939-1945) interrupted the progress of this work; it was resumed by Gibbon at Jefferson Medical College in 1944. Shortly thereafter, he attracted the interest of Thomas J.Watson, chairman of the board of the International Business Machines (IBM) Corporation, who provided the services of IBM’s experimental physics laboratory and model machine shop as well as the assistance of staff engineers. IBM constructed and modified two experimental machines over the next seven years, and IBM engineers contributed significantly to the evolution of a machine that would be practical in humans. Gibbon’s first attempt to use the pump-oxygenator in a human being was in a fifteen-month-old baby. This attempt failed, not because of a malfunction or a surgical mistake but because of a misdiagnosis. The child died following surgery because the real problem had not been corrected by the surgery. On May 6, 1953, the heart-lung machine was first used successfully on Cecelia Bavolek. In the six months before surgery, Bavolek had been hospitalized three times for symptoms of heart failure when she tried to engage in normal activity. While her circulation was connected to the heart-lung machine for forty-five minutes, the surgical team headed by Gibbon was able to close an opening between her atria and establish normal heart function. Two months later, an examination of the defect revealed that it was fully closed; Bavolek resumed a normal life. The age of open-heart surgery had begun. Consequences The heart-lung bypass technique alone could not make openheart surgery truly practical. When it was possible to keep tissues alive by diverting blood around the heart and oxygenating it, other questions already under investigation became even more critical: how to prolong the survival of bloodless organs, how to measure oxygen and carbon dioxide levels in the blood, and how to prolong anesthesia during complicated surgery. Thus, following the first successful use of the heart-lung machine, surgeons continued to refine the methods of open-heart surgery. The heart-lung apparatus set the stage for the advent of “replacement parts” for many types of cardiovascular problems. Cardiac valve replacement was first successfully accomplished in 1960 by placing an artificial ball valve between the left atrium and ventricle. In 1957, doctors performed the first coronary bypass surgery, grafting sections of a leg vein into the heart’s circulation system to divert blood around clogged coronary arteries. Likewise, the first successful heart transplant (1967) and the controversial Jarvik-7 artificial heart implantation (1982) required the ability to stop the heart and keep the body’s tissues alive during time-consuming and delicate surgical procedures. Gibbon’s heart-lung machine paved the way for all these developments.