Abstract
In the previous chapter, we presented the foundations of the interaction between radiation and material. In the end, the necessary criterion to produce laser radiation was derived: population inversion. Population inversion is the prerequisite for the predominance of stimulated emission, the basic process of the laser.
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Notes
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Entropy can be seen as a measurement for the degree of order or the quality of energy. Lower entropy means a high amount of order and high quality. Irreversible processes always lead to an increase of entropy.
- 2.
Exothermic reaction: reaction during energy excess, i.e., the reaction releases energy.
- 3.
Adiabatic process: the process runs so slowly that the gas is always found in a momentary equilibrium.
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cw = continuous wave, not pulsed.
- 5.
Phase transition of the first kind: energy or entropy of the system as a function of the order parameters change discontinuously, i.e., they make a jump. Phase transition of the second kind: energy or entropy change continuously. The first derivation is, however, discontinuous, i.e., the function has a “bend.” In the case of the laser, the pump output is the order parameter.
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The concepts power and intensity are used here synonymously, since––in these calculations––the intensity can be converted into output simply by multiplying it with the cross-sectional area of the laser medium; effects dependent upon transversal coordinates are neglected.
- 7.
In the quantum theory of the solid body, such lattice vibrations are called phonons and are treated similar to photons as particles. The interaction of the atoms with the phonons is then seen as a collision between atom and phonon.
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Poprawe, R., Boucke, K., Hoffman, D. (2018). The Production of Laser Radiation. In: Tailored Light 1. RWTHedition. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-01234-1_8
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DOI: https://doi.org/10.1007/978-3-642-01234-1_8
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