Mode-locked, rare earth-doped fiber oscillators are ideal sources for numerous ultrafast applications, as they possess a large spectral bandwidth and allow for a robust and compact implementation.

Due to the tight confinement of intense laser light in the small fiber core and the long interaction length, the light field of an ultrashort pulse experiences a strong nonlinear response during propagation, which, together with the high single-pass gain, leads to a rich nonlinear dynamic inside a fiber-laser resonator. The pulse dynamics can strongly differ from other mode-locked solid-state lasers since the gain and the nonlinearity as well as the intra-cavity dispersion in mode-locked fiber oscillators can be orders of magnitude higher than in their bulk-laser counterparts. Hence, besides being driven by application demands, passively mode-locked fiber lasers themselves are an interesting research area and a variety of different operation regimes have been explored. Recent research focuses on cavities using only elements with positive group velocity dispersion, where highest performance levels are obtained. In such lasers, despite the unbalanced net-group delay-dispersion and large nonlinear phase shift the pulse experiences each round trip, self-sustaining mode-locked operation can be obtained using strong dissipation for pulse shaping.

In our group we investigate pulse formation, evolution and shaping in mode-locked fiber oscillators both in experiment and numerical simulations. Our research addresses the tailoring of the pulse dynamics for the generation of ultrashort pulses to suit specific applications. A particular focus is set on the performance scaling of femtosecond fiber oscillators in terms of average and peak power. Novel micro-structured very-large-mode-area fibers allow for outstanding performance levels towards sub-100fs pulses with >10MW peak power at >100W of average power.

Selected publications:

[1] M. Baumgartl, F. Jansen, F. Stutzki, C. Jauregui, B. Ortaç, J. Limpert, and A. Tünnermann, "High average and peak power femtosecond large-pitch photonic-crystal-fiber laser," Opt. Lett.  36(2), 244-246 (2011).

[2] M. Baumgartl, B. Ortaç, T. Schreiber, J. Limpert, and A. Tünnermann, "Ultrashort pulse formation and evolution in mode-locked fiber lasers," Appl. Phys. B 104(3), 523-536 (2011).


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