ABSTRACT
This chapter presents the principles of operation of a far-infrared laser and discusses the long-time transient associated with the vibrational bottleneck effect. It considers the situations in which no stable steady state corresponds to the operating conditions and consider the transient regime in which the pumping power of the far-infrared (FIR) laser is suddenly switched on. The chapter analyzes the transients and instabilities of the FIR laser and the slow transients that appear on the output power of a FIR laser with on-off switched pumping. Stability analysis of the laser equations was carried out in a wide variety of situations, including cavity detuning, inhomogeneous broadening, unidirectional or bidirectional operation, and transversal inhomogeneity. The low initial value is usually taken as zero since there is almost no population in the lasing states in absence of pumping. The two modes of instability will be considered successively: Lorenztype instability and two-velocity-group instability, and third, two-photon Raman-type laser instability.
