It is well known that light can be amplified by stimulated emission e.g. in laser crystals. In a laser crystal, additional effects such as gain saturation, gain guidingand diffraction also come into play. But how do all these effects combine in detail? A clear quantitative understanding of such processes is indispensable for the efficient development of laser devices.
A model for the amplification of a laser beam in a bulk laser may contain the following:
A suitable software such as RP Fiber Power can numerically simulate the beam propagation through the laser crystal (or in many round trips through a laser resonator), taking into account stimulated emission, diffraction, gain guiding, saturable absorption, etc. (Of course, the user of such software does not need to deal with the details of how such things are calculated.) As an example, see a case study on an actively Q-switched laser.
Simpler models assume a fixed transverse profile of the laser beam and effectively propagate only optical powers rather than full beam profiles. They can be processed much faster, but only if one knows that beam profiles are not significantly affected e.g. by gain guiding effects.
Light can also be amplified in rare-earth-doped fibers. The essential physical foundations are the same as for laser crystals, but nevertheless some aspects can be quite different: