ABSTRACT
In an inhomogeneously broadened laser system (see section A1.8), optical frequencies within the emission bandwidth of the material can experience gain simultaneously at discrete frequencies corresponding to the longitudinal modes of the laser resonator. In the absence of any mechanism to coherently couple energy between these modes, the laser will operate with a continuous-wave (cw) output containing a narrow band of frequencies whose roundtrip cavity gain is highest. An alternative operating regime exists in which each mode is related to its neighbour by a fixed phase relationship and it is this modelocked condition that is used to generate a periodic sequence of ultrashort optical pulses.
