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How does a Laser Work?

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  • Written By: Michael Anissimov
  • Edited By: Niki Foster
  • Last Modified Date: 09 December 2016
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The LASER (Light Amplification by Stimulated Emission of Radiation) is a triumph of modern optics. By exploiting a quantum mechanical effect called stimulated emission, lasers generate a coherent, nearly monochromatic beam of photons. Non-laser light sources typically generate incoherent, unfocused beams of light at a variety of wavelengths, prohibiting certain applications.

To create a laser, two components are necessary — a gain medium and a resonant optical cavity. For a gain medium, certain crystals, glasses, gasses, semiconductors and even dyed liquids may be used. The gain medium is stimulated by an energy pump source such as an electrical current or another laser. The medium absorbs the energy, exciting the states of the particles in the medium. After a certain threshold, called population inversion, is achieved, shining light through the medium causes more stimulated emission, or release of energy, than absorption.

A resonant optical cavity is a specially sized chamber with a mirror at one end and a semi-silvered mirror at the other. The two reflective surfaces cause light trapped inside to reflect back and forth through the gain medium, acquiring greater energy with each pass. When this effect levels off, the gain is said to be saturated and the light becomes true laser light. Different gain mediums give rise to lasers of different wavelengths.

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Two varieties of laser are continuous and pulse. The continuous laser is more useful for most applications, but the energy in a pulse laser can be very large. The degree to which the beam diverges over time varies inversely with proportion to its diameter. Small beams diverge rapidly, while larger ones remain coherent.

When the laser was patented by Bell Labs in 1960, it could not immediately be given any applications, although spectrometry, interferometry, radar and nuclear fusion were discussed as potential areas of interest. Today, the laser is among the most versatile of technological wonders, with applications in data storage and retrieval, laser cutting, vision correction, surveying, measurements, holography and displays, and even nuclear fusion. Maximum achievable laser pulse intensity has increased exponentially since the mid-1980s. One day, lasers may be used to generate net energy-producing fusion reactions, providing energy for the entire human race. They also might be used to push solar sails into the depths of outer space.

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anon326391
Post 10

Ordinary light scatters due to its varying wavelengths and frequencies, whereas laser beams are highly organized light with all photons traveling in the same frequency and wavelength.

afterall
Post 5

Lasers have also become a fascination of many television shows and movies. One of my favorite movies is the 80s Val Kilmer movie Real Genius, where they help to build an enormous laser, supposedly strong enough to shoot at things from outer space, unknowingly helping a professor create a dangerous weapon.

There was also a plot about lasers in the television show The Big Bang Theory, where the main characters, a group of guys who work in physics at a university in California, make a machine to shoot a laser and reflect it off the moon.

watson42
Post 4

Lasers have really taken over the imaginations of people, even those who are not that interested in science. And I admit that, especially when less was known about them, the concept of figuring out fantastical ideas for how to make a laser were even interesting to me as a kid, and I was much more of a castles and unicorns type when it came to fantasies and imagination.

anon84953
Post 2

this does not really explain how waves travel through a laser.

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