1. Principles

1.1 Excitation and ionization

According to the principle of energy conservation, for an atom to emit energy, it must first have received it. To achieve this, external energy is supplied to the atom in the form of heat, electricity or optics (in the case of lasers). If the energy is sufficient, the electrons move to a higher level in around 10 ^–8 s. The return to the stable state is accompanied by the emission of spectral radiation characteristic of the transition....