Far-infrared (FIR) molecular lasers have a restricted domain of application because their technology in the 100 μm to 1 mm spectral range is not yet mature. This wavelength range is, however, unavoidable in radioastronomy because of the transparency windows of the Earth's atmosphere, and in semiconductor physics because of the energy domain of some lattice excitations. So far, applications of FIR lasers are limited. They have been used for checking high-voltage cable insulation and, more recently, for security-screening systems. On the other hand, FIR lasers are highly interesting for their instabilities and they have been studied in several laboratories.

The analogy found by Haken between the Lorenz equations and the laser (Maxwell–Bloch) equations for the homogeneously broadened laser triggered the search for an experimental laser system that could be well described by these equations. Haken's model of the laser is based on a semiclassical approach in which the electric polarization is explicitly considered, contrary to the standard rate equations where this variable is absent. By contrast to the laser rate equations, Haken–Lorenz equations admit sustained pulsating intensities and could be relevant for lasers that exhibit spontaneous pulsating instabilities. We have already discussed the complicated case of the ruby laser spiking. The 3.51 μm Xe laser self-pulsations were also known and investigated in detail but the mechanism responsible for this particular instability was partly masked by the difficulty in accounting for the inhomogeneous broadening, which is a dominant process in this laser.