Mode locking in cw solid-state lasers by linear and nonlinear frequency shifts

A new mechanism of the formation of ultrashort pulses in solid-state lasers, characterised by a shift of the carrier frequency of the lasing field relative to the central frequency of the gain band, is investigated. The interaction between a linear frequency shift and self-phase modulation of the lasing field is capable of ensuring mode locking. An analysis of self-consistent solutions of the equations describing evolution of ultrashort pulses in a laser system yields the parameters of these pulses, which are in good agreement with the experimental results. A study of the stability of the pulses makes it possible to describe a cascade of oscillation effects which accompanies an increase in the ultrashort pulse energy.