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It is 50 years since lasers were developed from an Einstein theory.


This year marks the 50th anniversary of the laser, an acronym for Light Amplification by Stimulated Emission of Radiation. As a basic principle, lasers take the light emitted from a source in all directions and concentrate it into a beam in a single direction.

Einstein established the theoretical possibility of lasers in a 1916 paper, "On the quantum theory of radiation." He showed that light exists as photons, bundles of wave energy, and that the energy of the photon corresponds to the frequency of the waves in the bundle.

In his paper he conceived of the idea of stimulated emission: that if an electron is in an excited state when a photon with the right level of energy collides with it, the electron will drop to a lower energy state and emit another photon of the same energy, moving in the same direction. That results in two identical photons travelling together. When this process is amplified by the physical structure of the laser it results in a high-intensity beam of light.

The principle was first applied practically in 1953 when Charles Hard Townes, working with two graduate students, James Gordon and Herbert Zeiger, created the maser (Microwave Amplification by Stimulated Emission of Radiation). Independently, AM Prokhorov and NG Basov developed a maser in 1955 but theirs was capable of continuous output. Townes, Prokhorov and Basov were jointly awarded the Nobel Prize for Physics in 1964.

In 1958, Townes and Arthur Schawlow published a paper in which they discussed the possibility of extending the maser concept to optical frequencies. Initially referred to as optical masers, these were soon renamed lasers.

The principle was first demonstrated in practice by Theodore Maiman, who was working at the Hughes Research Laboratory. He used a rod-shaped ruby crystal surrounded by a spiralling high-intensity flashlamp. The two ends of the ruby rod were coated with silver, with one end less reflective to allow some of the radiation to escape as a beam. When the flashlamp was fired, an intense red beam emerged.

Once Maiman's ruby laser was announced at a press conference in July 1960, teams working on lasers across the country started making progress quickly and by the end of the year, three different types of laser had been demonstrated. The technology developed rapidly and was soon in use across industry, in medicine, and eventually in consumer products such as CD players.

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Title Annotation:THE ARCHIVE
Author:Philpot, Fenella
Publication:Professional Engineering Magazine
Date:Jun 2, 2010
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