Résumé
The quantum cascade laser is a semiconductor light source based on resonant tunnelling and optical transitions between quantised conduction band states. In these devices the principles of operation are not based on the physical properties of the constituent materials, but arise from the layer sequence forming the heterostructure. The quantum design and the control of the layer thickness, down to an atomic mono-layer, allows one to ascribe into a semiconductor crystal, artificial potentials with the desired electronic energy levels and wavefunctions. In recent years the performance of quantum cascade lasers has improved markedly and this semiconductor technology is now an attractive choice for the fabrication of mid-far infrared lasers in a very wide spectral range (3.5-160 m). At present, the best performances are reached at wavelength between 5-10 m, but recent results on new material systems with deeper quantum wells are indicating that this technology will be soon available also in the 3-5 m spectral region.