Laser

A LASER (Light Amplification by Stimulated Emission of Radiation) is an optical source composed of a resonant optical cavity and a gain medium.

History

The laser was preceded by the maser, a device that operates on similar pricinciples

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to the laser, but produces microwave rather than optical radiation.

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The first maser was built by Charles H. Townes and graduate students J. P. Gordon, and H. J. Zeiger in 1953.

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This maser was incapable of continous output.

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Nikolai Basov and Alexander Prokhorov of the USSR worked independently on the quantum oscillator and solved the problem of continuous output systems by using more than two energy levels. These systems could release stimulated emission without falling to the ground state, thus maintaining a population inversion. In 1964, Charles Townes, Nikolai Basov and Alexandr Prokhorov shared a Nobel Prize in Physics "for fundamental work in the field of quantum electronics, which has led to the construction of oscillators and amplifiers based on the maser-laser principle."

Related Topics:
Nikolai Basov - Alexander Prokhorov

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The first working laser was made by Theodore H. Maiman in 1960 at Hughes Research Laboratories in Malibu, California, beating several research teams including those of Townes at Columbia University, and Arthur L. Schawlow at Bell laboratories. Maiman used a solid-state flashlamp-pumped synthetic ruby crystal to produce red laser light at 694-nanometres wavelength. In the same year the Iranian physicist Ali Javan invented the gas laser. He later received the Albert Einstein Award.

Related Topics:
Theodore H. Maiman - Hughes Research Laboratories - Malibu, California - Townes - Columbia University - Arthur L. Schawlow - Bell laboratories - Flashlamp - Ruby - Crystal - Iran - Ali Javan - Gas laser - Albert Einstein Award

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Townes and Schawlow later described the theory of the laser, or optical maser as it was known. The word laser was coined in 1957 by Gordon Gould. Gould also coined the word iraser, intending "aser" as the suffix and the spectra of light emitted at as the prefix (examples: X-ray laser = xaser, UltraViolet laser = uvaser) but these terms never became popular. Gould was also credited with lucrative patent rights for a gas-discharge laser in 1987, following a protracted 30 year legal battle.

Related Topics:
Townes - Schawlow - Gordon Gould - Patent

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Robert N. Hall developed the first semiconductor

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laser, or laser diode, in 1962.

Related Topics:
Laser diode - 1962

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Hall's device was built in the GaAs material system and produced emission at 850 nm, in the

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near-infrared region of the spectrum.

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The first semiconductor laser with visible emission was demonstrated

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later the same year.

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In 1970, Zhores Alferov in the Soviet Union and Hayashi and Panish of

Related Topics:
1970 - Zhores Alferov - Soviet Union

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Bell Telephone Laboratories independently developed

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continously operating laser diodes at room temperature,

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using the heterojunction structure.

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Since that time, laser research has

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produced a variety of improved and specialized laser types,

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optimized for different performance goals, including

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• new wavelength bands
• maximum average output power
• maximum peak output power
• minimum output pulse duration
• maximum power efficiency

and this research continues to this day.

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Recent innovations

An unforeseen discovery in 1992, lasing without maintaining the medium excited into a population inversion, was discovered in sodium gas in and again in 1995 each in sodium and rubidium gas by various international teams. Normally, electrons in the ground state absorb the pumping and emitted radiation, thwarting the laser gain by heating up the medium. So media with electron levels and transitions amenable to the driving current are desired, and generally those which involve three or four energy levels rather than two make better lasers because the electrons are kept above the ground state, excited, and optically-transparent so as not to heat up, but such media are prone to noisy beams. By using an external maser to induce "optical transparency" in the media by introducing and destructively interfering the ground electron transitions between two paths, the likelihood for the ground electrons to absorb any energy has been cancelled. Though there were initial hopes that this discovery would allow an increase in efficiency (higher than the .01 to .3 for typical media and wavelengths), the idea never panned out commercially or otherwise and remains little more than a backwater in laser research. http://www.aip.org/pnu/1992/physnews.100.htm http://www.aip.org/pnu/1995/physnews.240.htm

Related Topics:
1992 - 1995

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In 1985 at the University of Rochester's Laboratory for Laser Energetics a breakthrough in creating ultrashort-pulse, very high-intensity (terawatts) laser pulses became available using a technique called chirped pulse amplification, or CPA, discovered by Gérard Mourou. Later, in 1994, it was discovered by Mourou and his team at University of Michigan that the balance between the self-focusing refraction (see Kerr effect) and self-attenuating diffraction by ionization and rarefaction of a laser beam of terawatt intensities in the atmosphere creates "filaments" which act as waveguides for the beam thus preventing divergence. If a light filament drops below the intensity needed for this dynamic balance, called modulation instability, it can merge with another filament and continue propagating without broadening as with all earlier means of sending light. The filaments, having made a plasma, though turn the narrowband laser pulse into a broadband pulse having a wholly new set of applications. http://www.aip.org/pt/vol-54/iss-8/p17.html http://www.nrl.navy.mil/content.php?P=03REVIEW59

Related Topics:
1985 - University of Rochester - Laboratory for Laser Energetics - Terawatt - Chirped pulse amplification - Gérard Mourou - 1994 - University of Michigan - Kerr effect - Diffraction - Ionization - Rarefaction - Light filament

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