Laser
Principle of Laser
The material that generates the laser light is called a laser medium.
Let's assume that the atom in the laser medium caused the stimulated emission.
Other atoms (state of excitation) are necessary for surroundings to cause the stimulated emission in addition following this.
In a word, the excited a large amount of atom is necessary to amplify the photon enough.
The density of the excited atom should be higher than the density of the atom of the ground state so that enough amplification may happen.
In a word, useful a lot of atoms (excited atom) for the stimulated emission are indispensable.
It is called a population inversion that the density of the atom excited from the ground state is high.
Such distribution doesn't exist in the natural world.
In the natural world, a lot of atoms of the ground state are distributed.
The excitation source (electrical discharge, electron beam, and ray, etc.) causes the population inversion in the whole area of the laser medium in the device of the laser oscillation.
The light of the stimulated emission amplifies in the population inversion.
Light is amplified more while light shuttles between the resonance mirrors on both sides of the laser medium.
The laser oscillates when the amount of amplification of the stimulated emission light exceeds the amount of the loss in the laser medium.
It is called a pumping to lead to the population inversion by the energy supply from the excitation source.
In an industrial laser device, the laser medium, the excitation source, and the resonance mirror have combined.
This is called a laser cavity.
A variety of kinds of materials are used for the laser medium.
The wavelength of the generated laser light is different depending on the kind of the material.