Monday, July 22, 2013

Laser – Light Amplification by Stimulated Emission of Radiation

by akshiv, This post originally appeared at Future Science Leaders.

Lasers are awesome! We use them all the time to do neat things like burn cds/dvds, correct vision, point things out, in printers and even to cut and weld things. These devices just generate beams of light, so how are they so powerful?
There are few reasons this is true. The first lies in the kind of light they produce. Instead of emitting light at all energies and frequencies like a light bulb, a laser only emits on kind of light. This emission is called Monochromatic. This means that the intensity of a single kind (wavelength) of light is extremely high and the rest is really low. The second important factor is the size of the beam, light bulbs radiate light in all directions, leading to diffraction and negative interference, this means that the light is spreads out and starts to interact with it self. Where as in laser a very thin beam of light is produced focusing the energy of the light. Lastly, efficiency plays a large role. Most light bulbs (excluding LEDs) are not nearly as efficient with power as lasers. The reason for this has a lot do with how lasers work so lets get into that.
Flashes of light are bounced around an evacuated tube at first. There is a semi reflective mirror on one side and a reflective mirror on the other side. This allows light to bounce around, while also letting the laser light out. As the flashes of light occur they promote electrons to higher energy levels.
The incident photon (particle of light) adds energy to all of the electrons in the material inside the laser. This is getting a little bit complex but basically electrons normally exist in a “ground state” but they can be promoted to higher energy levels, which are unstable. When there are more atoms in the excited state than in the ground state there is a “population inversion”. Due to quantum effects, one of the electrons will come back to the ground state emitting a photon equal to the energy difference. This is a photon of exactly one energy, instead of all of them. This photon then knocks down all of the other electrons, causing them to emit photon of the same energy also. The reason the light is so intense and efficient is because of this exploitation of quantum effects.
About this contributor: I just finished my final year of high school. I love playing ultimate frisbee, skiing and playing the clarinet/guitar. I am happiest when learning random trivia or stargazing. Learning for me is its own reward, whether it is about the quantumly tiny or the cosmologically large.

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