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    which scientist first came up with the idea of stimulated emission

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    LaserFest

    Laserfest is a yearlong celebration of the 50th anniversary of the laser, which was first demonstrated in 1960

    Early History

    Theory

    In 1917, Einstein laid the foundation for the laser when he introduced the concept of stimulated emission; where a photon interacts with an excited molecule or atom and causes the emission of a second photon having the same frequency, phase, polarization and direction. The acronym LASER stands for "Light Amplification by Stimulated Emission of Radiation".

    The First Laser

    Dr. Theodore Maiman of Hughes Research Laboratories, with the first working laser.

    Photo Credit: HRL Laboratories, LLC

    Theodore Maiman developed the first working laser at Hughes Research Lab in 1960, and his paper describing the operation of the first laser was published in Nature three months later. Since then, more than 55,000 patents involving the laser have been granted in the United States. Today's laser and all of its applications are the result of not one individual's efforts, but the work of a number of prestigious scientists and engineers who were leaders in optics and photonics over the course of history. These include such great minds as Charles Townes at Columbia University, who developed the maser, the precursor to the laser, and Arthur Schawlow at Bell Laboratories, who along with Townes published a key theoretical paper in 1958 that helped lead to the lasers development and who jointly were awarded the first laser patent in 1960.

    Maiman's early laser used a powerful energy source to excite atoms in a synthetic ruby to higher energy levels. At a specific energy level, some atoms emitted particles of light called photons. These newly created photons struck other atoms, rapidly stimulating the emission of more identical photons and amplifying the light intensity. Maiman was able to continue this process of stimulated emission and amplification by placing a completely reflecting silver mirror on one end of the model and a partially reflecting silver mirror on the other. This setup enabled photons to bounce back and forth between the mirrors until they gained enough intensity to burst through the partially silvered end as a powerful, coherent, beam of light--what you can today find on the end of a laser pointer.

    The 1950's

    The Maser

    A predecessor of the laser, called the MASER, for "Microwave Amplification by Stimulated Emission of Radiation", was independently developed in 1954 at Columbia University by Charles Townes and Jim Gordon and in Russia by Nicolay Basov and Alexsandr Prokhorov. These ammonia masers were two-energy-level gaseous systems that could continuously sustain a population inversion and oscillation. In 1956 Nicolaas Bloembergen proposed a three-level solid state maser at Harvard, demonstrated by researchers at Bell Labs that same year.

    Charles Townes and Arthur Schawlow

    Laser Beginnings

    Soon after the maser, Arthur Schawlow and Charles Townes began thinking about ways to make infrared or visible light masers. In 1957 Schawlow and Townes constructed an optical cavity by placing two highly reflecting mirrors parallel to each other, and positioning the amplifying medium in between. In 1958, they published a seminal Physical Review paper on their findings and submitted a patent application for the so-called optical maser.

    The lengthy Physical Review article was widely read in the United States, and generated considerable interest among other researchers, especially experimentalists who attempted to build the first laser. Although the paper rightfully gave Schawlow and Townes recognition as having invented the laser, several others independently came up with the same "open cavity" concept, including Gordon Gould, a graduate student at Columbia University. Gould was also the first to publically use the term laser, for "Light Amplification by Stimulated Emission of Radiation" at the June 1959 Ann Arbor Optical Pumping Conference.

    Laser Patent War

    Gould filed a laser patent in April 1959 but this was denied by the US Patent Office in favor of the Schawlow and Townes optical maser patent (awarded 1960). This led to what is often called the "Thirty Year Patent War", with Gould eventually winning 48 patents many years later for commercially valuable aspects of lasers including optical pumping and specific applications.

    More Laser History

    The first laser Charles H. Townes

    from A Century of Nature: Twenty-One Discoveries that Changed Science and the World Laura Garwin and Tim Lincoln, editors

    Bright Idea: The First Lasers - A history of discoveries leading to the 1960 invention

    The 1960's

    Race to Build the Laser

    After the Schawlow-Townes Physical Review paper was published in 1958, a furious competition ensued to build the first working laser involving institutions such as Bell Labs, Hughes Research Labs, RCA Labs, Lincoln Labs, IBM, Westinghouse, and Siemens. Theodore Maiman at Hughes Research Labs realized that high gain pulsed oscillation could be achieved in ruby by optically pumping with commercial flash lamps, and in May 1960 demonstrated the first working laser. This laser was so easy to build that within weeks several other groups duplicated the achievement.

    Nobel Prize

    स्रोत : laserfest.org

    This Month in Physics History: Einstein predicts stimulated emission

    Einstein predicts stimulated emission

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    August/September 2005 (Volume 14, Number 8)

    This Month in Physics History

    August/September 2005 (Volume 14, Number 8) This Month in Physics History Einstein Predicts Stimulated Emission

    The laser’s invention launched a multi-billion dollar industry. Lasers are used to remove unwanted tattoos; to correct vision defects in laser eye surgery; to cut through steel and other materials in industrial assembly lines; to scan prices in supermarkets and department stores; for optical communications and optical data storage; and in electronic devices like CD and DVD players. The root of all this technological innovation lies in fundamental physics research, specifically, a 1917 paper by Albert Einstein on the quantum theory of radiation.

    “Laser” is an acronym for Light Amplification by Stimulated Emission of Radiation. It describes any device that creates and amplifies a narrow, focused beam of light whose photons are coherent. In a laser, the atoms or molecules of the lasing medium–either a crystal like ruby or garnet, or a gas or liquid–are “pumped,” so that more of them are at higher energy levels than at the ground state.

    Einstein with his second wife, Elsa.

    The end result is a sudden burst of coherent light as the atoms discharge in a rapid chain reaction. This process is called “stimulated emission.” Albert Einstein first broached the possibility of stimulated emission in a 1917 paper, having turned his attention the year before from general relativity to the interplay of matter and radiation, and how the two could achieve thermal equilibrium. Einstein devised an improved fundamental statistical theory of heat, embracing the quantum of energy.

    First, Einstein proposed that an excited atom in isolation can return to a lower energy state by emitting photons, a process he dubbed spontaneous emission. Spontaneous emission sets the scale for all radiative interactions, such as absorption and stimulated emission. Atoms will only absorb photons of the correct wavelength: the photon disappears and the atom goes to a higher energy state, setting the stage for spontaneous emission. Second, his theory predicted that as light passes through a substance, it could stimulate the emission of more light.

    Einstein postulated that photons prefer to travel together in the same state. If one has a large collection of atoms containing a great deal of excess energy, they will be ready to emit a photon randomly. However, if a stray photon of the correct wavelength passes by (or, in the case of a laser, is fired at an atom already in an excited state), its presence will stimulate the atoms to release their photons early–and those photons will travel in the same direction with the identical frequency and phase as the original stray photon. A cascading effect ensues: as the crowd of identical photons moves through the rest of the atoms, ever more photons will be emitted from their atoms to join them.

    It wasn’t until the 1940s and 1950s that physicists found a use for the concept, even though all that was required to invent a laser was finding the right kind of atom, and adding reflecting mirrors to fortify the stimulated emission process by producing a chain reaction. Charles Townes had worked on radar systems during World War II. After the war ended, he turned his attention to molecular spectroscopy, a technique that studies the absorption of light by molecules. Just like radar, molecular spectroscopy bombards the surface of molecules with light and analyzes the scattered radiation to determine the molecule’s structure.

    But the technique was limited by the wavelength of the light produced: in this case, the microwave regime of the electromagnetic spectrum. Townes noticed that as the wavelength of the microwaves shortened, the more strongly the light interacted with the molecules, and the more one could learn about them. He thought it might be possible to develop a device that produced light at much shorter wavelengths. The best way to do this, he thought, would be to use molecules to generate the desired frequencies through stimulated emission.

    स्रोत : www.aps.org

    stimulated emission

    stimulated emission, in laser action, the release of energy from an excited atom by artificial means. According to Albert Einstein, when more atoms occupy a higher energy state than a lower one under normal temperature equilibrium (see population inversion), it is possible to force atoms to return to an unexcited state by stimulating them with the same energy as would be emitted naturally. In stimulated emission the emitted light wave will be coherent (i.e., in phase; see coherence) with the incoming wave. In laser action the stimulating emission triggers a chain reaction in which the radiation from one atom stimulates

    stimulated emission

    physics

    Alternate titles: induced emission

    By The Editors of Encyclopaedia Britannica • Edit History

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    stimulated emission, in laser action, the release of energy from an excited atom by artificial means. According to Albert Einstein, when more atoms occupy a higher energy state than a lower one under normal temperature equilibrium (see population inversion), it is possible to force atoms to return to an unexcited state by stimulating them with the same energy as would be emitted naturally.

    In stimulated emission the emitted light wave will be coherent (i.e., in phase; see coherence) with the incoming wave. In laser action the stimulating emission triggers a chain reaction in which the radiation from one atom stimulates another in succession until all the excited atoms in the system have returned to normalcy. In doing so, coherent monochromatic light (light of a single wavelength) is emitted.

    BRITANNICA QUIZ

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    electrical and electronics engineering

    By Donald G. Fink See All • Edit History

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    Key People: Vannevar Bush Nikola Tesla Charles Proteus Steinmetz Reginald Aubrey Fessenden Edwin H. Armstrong

    Related Topics: electronics engineering avionics electronic system

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    Top Questions

    What is electrical and electronics engineering?

    When did electrical engineering emerge as a discipline?

    What was the first practical application of electrical engineering?

    What kind of research is done in electrical and electronics engineering?

    Summary

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    electrical and electronics engineering, the branch of engineering concerned with the practical applications of electricity in all its forms, including those of the field of electronics. Electronics engineering is that branch of electrical engineering concerned with the uses of the electromagnetic spectrum and with the application of such electronic devices as integrated circuits and transistors.

    In engineering practice, the distinction between electrical engineering and electronics is usually based on the comparative strength of the electric currents used. In this sense, electrical engineering is the branch dealing with “heavy current”—that is, electric light and power systems and apparatuses—whereas electronics engineering deals with such “light current” applications as telephone and radio communication, computers, radar, and automatic control systems.

    The distinction between the fields has become less sharp with technical progress. For example, in the high-voltage transmission of electric power, large arrays of electronic devices are used to convert transmission-line current at power levels in the tens of megawatts. Moreover, in the regulation and control of interconnected power systems, electronic computers are used to compute requirements much more rapidly and accurately than is possible by manual methods.

    Donald G. Fink

    History

    Electrical phenomena attracted the attention of European thinkers as early as the 17th century. The most noteworthy pioneers include Ludwig Wilhelm Gilbert and Georg Simon Ohm of Germany, Hans Christian Ørsted of Denmark, André-Marie Ampère of France, Alessandro Volta of Italy, Joseph Henry of the United States, and Michael Faraday of England. Electrical engineering may be said to have emerged as a discipline in 1864 when the Scottish physicist James Clerk Maxwell summarized the basic laws of electricity in mathematical form and showed that radiation of electromagnetic energy travels through space at the speed of light. Thus, light itself was shown to be an electromagnetic wave, and Maxwell predicted that such waves could be artificially produced. In 1887 the German physicist Heinrich Hertz fulfilled Maxwell’s prediction by experimentally producing radio waves.

    The first practical application of electricity was the telegraph, invented by Samuel F.B. Morse in 1837. The need for electrical engineers was not felt until some 40 years later, upon the invention of the telephone (1876) by Alexander Graham Bell and of the incandescent lamp (1878) by Thomas A. Edison. These devices and Edison’s first central generating plant, in New York City (1882), created a large demand for people trained to work with electricity.

    Alexander Graham Bell

    Alexander Graham Bell, inventor who patented the telephone in 1876, lecturing at Salem, Massachusetts (top), while friends in his study at Boston listen to his lecture via telephone, February 12, 1877.

    © Photos.com/Jupiterimages

    स्रोत : www.britannica.com

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