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The 50th Anniversary of the Laser

June 13, 2010

No invention in the post-WWII era has so thoroughly altered our way of life than the laser which this year celebrates its 50th anniversary as part of events commemorated by Laser Fest. Pause for a moment and consider its astonishing implications: the world’s entire telecommunications is sent via optical pulses generated by lasers via long-distance fibers that now envelope the Earth’s surface, the information encoded onto compact and digital-video discs is read-out by lasers, ubiquitous bar codes found in retail outlets are scanned by lasers, laser printers are found in homes and offices the world over, laser pointers are used in everyday presentations, digital displays including LCDs and plasmas are illuminated by lasers, optical scalpels powered by lasers are used in surgery as precision instruments; these are but a mere sampling of the all-encompassing presence of lasers in today’s society. Not to mention the pervasiveness of lasers in research laboratories: to probe physical and biological phenomena at ultrashort timescales, to generate intense bursts of energy for interrogating new forms of matter, to one day provide clean forms of energy, and to measure with extreme precision the force of gravity. The 1964 Nobel Prize in Physics awarded to American Charles Townes (then at MIT) and Russians Nikolai Basov and Aleksandr Prokhorov was arguably the most important from a purely technological point of view. Laser is an acronym for light amplification by stimulated emission of radiation and describes a quantum-mechanical phenomena whereby atomic media produce monochromatic (single wavelength), unipolarized, coherent (all light waves are in phase with one another) electromagnetic radiation. These three properties, taken together, are crucial for enabling intense light sources that have found such broad scientific and technological application. The underlying physics governing the operation of the laser is based on the phenomena of stimulated emission. Electrons bound to atoms (made up of a nucleus containing protons and neutrons) reside in one of its discrete quantum states, usually the ground state having the lowest energy (unless excited by an external source of energy). When an electron in an excited state transitions to a state at lower energy, it typically emits a photon (a particle of light) to conserve energy. The salient point about stimulated emission, that Albert Einstein first pointed out, is that in the presence of a photon having an energy equal to the transition energy, electrons can be induced to de-excite and emit another photon remarkably having the same properties as the source photon (i.e., wavelength, polarization, coherence). Charles Townes key insight in 1960 was to somehow create conditions of population inversion whereby a large number of electrons were collectively excited to a higher energy state and thus when de-excited would amplify the emitted light signal via a cascade of further de-excitations in nearby electrons (this picture is somewhat oversimplified but conveys the essence of lasers). Townes fist demonstrated his principals in the microwave regime (a MASER) and was issued the first patent on his invention which has revolutionized the world. This incredibly important invention is certainly worthy of a yearlong celebration.

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From → science, technology

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