Generation of ultrashort light pulses in a dye laser with injection of a stimulated seed signal

An analysis is made of the conditions for the self-excitation of a dye laser subjected to extremely unsteady pumping when after each pump pulse the initial gain changes greatly during a round trip of a wave across the laser cavity. An analytic expression is obtained for the criterion of unsteady self-excitation which reduces in the limit to the familiar steady-state condition. Recurrence relationships are derived for the kinetics of the rise of the subthreshold gain when the pumping is provided by a train of ultrashort light pulses. These relationships can be used to calculate the number of pulses needed to attain the self-excitation conditions. The results of the analysis are used to study the realisation and characteristics of two new scenarios of the excitation of synchronously pumped lasers with injection of a seed signal which can be either superfluorescence or radiation from an auxiliary low-Q, but 'rapidly switched', laser. Important advantages of these scenarios are a large reduction in the lasing threshold and a widening of the range of active media which can be used in synchronously pumped lasers.