nanotechnology, PHotonics and ultrafast processES laboratory

The laser as technological development is an invention of the sixties, but it has its conceptual origins at the beginnings of the last century when Albert Einstein imagined a two-level atomic system, where the initial state, m, which is the lowest energy level is occupied by electrons and the most energetic level, n, is empty. The interaction between electromagnetic radiation with a collection of these atoms can be summarized in the absorption processes, spontaneous emission, and stimulated emission.

For a laser to work, a material medium is required , for example, a solid, liquid, or a gas (there're a great variety of materials that are used in laser equipment), that has more than two energy levels (usually the laser systems are model as three or four energy levels).

If we constantly radiate with light or through an electric discharge we excite a material, is possible to achieve a population invert, that is to say, that exists a greater population in the superior energy states in respect to the lowest energy level.