Stimulated emission - what is it?
If you take a closer look at a laser source and the laser beam, sooner or later you will inevitably encounter the term “stimulated emission.” This physical process plays the crucial role -because it ensures that light is amplified in the laser!
Stimulated emission is the emission of a photon, which is triggered by another photon. To explain this process, you have to get into quantum physics. Let’s first consider a quantum mechanical system, for example an atom. Energy is supplied to this system, either by absorption of a photon or collision with another atom. Through this process, the atom goes into an excited state. Now if a photon whose energy exactly matches the energy difference between the current state and a low-density energy level, hits the excited atom, an interesting process begins. The atom is now able to go into a state of low energy - and to deliver the energy difference as another photon in addition to the absorbed photon.
The new photon has the same energy as the absorbed photon, and therefore the same wavelength and frequency. The polarization direction and phasing are identical - it is, so to speak, a copy of the output photon that is emitted.