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Visible Light Spectrum

How does a laser make light?

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February 01, 2009 7:03PM

Laser is short for Light Amplification by Stimulated Eimission of Radiation. Lasers is basicly made of an active medium that is emitting light when it's so called pumped with energy. This pumping can be electricity, or external light. When a medium is active, such as when a HeNe gas is pumped with electric charge, it radiates light. This light is then placed between two parallell mirrors which makes a virually infinite number of copies of this light between those two mirrors. In the directions angular to these mirror, the light from the HeNe gas is amplified by allowing the photons go back and forth between the mirrors. However, when the HeNe gas is pumped with a seretain amount of energy, there is more active gas-molecules than those inactive which is absorbing the light. This is called the lease threshold, from which point allows the light to be amplified instead of absorbed by its own HeNe gas. So from this point the laser starts to radiate laser light. Some of this light must exit one of the mirrors, so one mirror is not fully reflective, but maybe 90% or so. These lasers is called gas-lasers. Also low efficient lasers. Typically 5 - 10% efficiency. Light pumped solid state laser: A chrystal is pumped with external light. This can be a ruby-chrystal. The ruby, especially synthetic ruby, is a very florucent chrystal that emitts light in all directions when exposed to external high energy light. A flashlamp where most possible of the emitting light is focused into the chrystal, the chrystal will absorb high energy photons, and "convert" these shorter wavelegths into the longer red spectrum wavelenth. The ruby is also placed between two parallell mirrors. See first section for explanation. Diode pumped laser (lets take the green 532nm laser): Also called Yag laser. A laser diode is focused into a chrystal that converts the 808nm laser diode light into 1064nm light (Not visible). This 1064nm light is then radiating another chrystal which is a non linear chrystal. When exposed to this 1064nm light, this chrystal will distort the wavelength by emitting a 2.nd harmonic distortion of the 1064nm light. A 2.nd harmonic distortion is a frequency which is the doubble of the main frequency. Therfor this chrystal will emit 532nm light. Polished ends of this chrystal will reflect the 532nm light to amplify it. Infrared radiation such as 808nm and 1064nm light is filtered to allow only the green 532nm light to pass through the laser apperture. These lasers is very efficient. Typically more than 50% of input energy is radiated as laser light.