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Temporal solitons in free-space femtosecond enhancement cavities


Temporal dissipative solitons in nonlinear optical resonators are self-compressed, self-stabilizing and indefinitely circulating wave packets. Owing to these properties, they have been harnessed for the generation of ultrashort pulses and frequency combs in active and passive laser architectures, including mode-locked lasers1,2,3,4, passive fibre resonators5 and microresonators6,7,8,9,10,11. Here, we demonstrate the formation of temporal dissipative solitons in a free-space enhancement cavity with a Kerr nonlinearity and a spectrally tailored finesse. By locking a 100-MHz-repetition-rate train of 350-fs, 1,035-nm pulses to this cavity-soliton state, we generate a 37-fs sech²-shaped pulse with a peak-power enhancement of 3,200, which exhibits low-frequency intensity-noise suppression. The power scalability unique to free-space cavities, the unprecedented combination of peak-power enhancement and temporal compression, and the cavity-soliton-specific noise filtering attest to the vast potential of this platform of optical solitons for applications including spatiotemporal filtering and compression of ultrashort pulses and cavity-enhanced nonlinear frequency conversion.

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Fig. 1: Concept for efficient CS generation.
Fig. 2: Set-up, locking scheme and f0-dependence of the soliton regime.
Fig. 3: Soliton evolution.
Fig. 4: Soliton characterization.
Fig. 5: Phase and intensity stability.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.


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The authors gratefully acknowledge helpful suggestions from T. Herr and A. Apolonskiy. The authors thank S. Breitkopf and T. Buberl for assistance with the laser system, J. Gessner for phase measurements of cavity mirrors and M. Fischer for support concerning the offset-frequency stabilization. The authors thank the European Research Council (ERC) (617173), Deutsche Forschungsgemeinschaft (DFG) Excellence cluster ‘Munich Centre of Advanced Photonics’ (MAP) for funding.

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Authors and Affiliations



N.L., C.H. and I.P. planned and coordinated the experiments. N.L. designed and performed the experiments, and analysed the data. C.H., T.S., M.H. and I.P. assisted with experiments and data analysis. M.H. and N.L. developed the model and performed the simulations. V.P. and M.T. designed and produced the cavity optics. E.F. contributed to the experimental concept. C.R. and A.L. conceived and implemented the spectral shift of the erbium oscillator for seeding the ytterbium amplifier system. J.L. designed and provided the amplifier system. N.L., M.H. and I.P. wrote the manuscript with input from all other authors. I.P. and F.K. supervised the project.

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Correspondence to N. Lilienfein or I. Pupeza.

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The authors declare no competing interests.

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Supplementary information

Supplementary Information

This file contains more information on the simulation methods and results, and Supplementary Figures 1–8.

Supplementary Video 1

Locking procedure.

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Lilienfein, N., Hofer, C., Högner, M. et al. Temporal solitons in free-space femtosecond enhancement cavities. Nature Photon 13, 214–218 (2019).

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