Investigations on positively chirped pulses in a thulium-doped fiber laser

Ultrashort pulse fiber lasers with monotonically positively chirped pulse operation schemes have been intensively investigated in the past decade, since this propagation scheme allows for generation of very high pulse energies without limitation by optical wave-breaking or similar nonlinear effects. Pulse energies of several 10 nJ could be generated directly from the oscillator while maintaining fs pulse duration with relatively simple setups [1]. In contrast to other pulse propagation schemes, the pulse energy was found not to be generally limited by the stability of the propagation scheme itself in spite of large nonlinear phase accumulation, but typically by technical issues like the maximum available pump power or overdriving of the saturable absorber mechanism [1,2].